My thesis

Misr University for Science & Technology
Faculty of Engineering
Department of Electronics and Communication Engineering
Simulation and Implementation for Several PAPR
Reduction Techniques in OFDM using USRP with
LABVIEW
Authors:
1. Mohamed Rabie Ragab 40115
2. Ahmed Fathi Gouda 40023
3. Amal Hamed Abdelmonem 43034
4. Yasmin Hamdy Baioumy 40424
5. Ahmed Mahmoud Anwar 40121
Associated Professor:
Dr. MAMDOUH GOUDA

II
Acknowledgements
First of all I would like to thank my supervisor Dr.Mamdouh
Gouda who believed in me and was continuously supporting me in
every problem that occurred during the writing of this report. I
especially thank him for his encouragement and his accurate
comments which were of critical importance, during this work. Our
cooperation was truly an inspiring experience, I feel grateful.
Very special thanks to Eng.Mohamed Hussien, doctoral
student of communication engineering, for his eagerness and great
assistance in order to accomplish the writing of this report. I would
also want to thank the members of the examining committee,
assistant professors as well as the audience during this report’s
presentation. Special thanks goes to all my friends for their advice,
their continuous support and their tolerance during the writing of
this report, without your moral support and love I could not have
made it until the end. I would like to dedicate this work to my
beloved parents and families who always believed in us, always were
there and will always be whenever we need them. we owe you
everything.

III
List of Figure
Fig. 2.1 Discrete Fourier Transform ............................................................................................................ 10
Fig. 2.2 ISI Due to channel filtering .............................................................................................................. 12
Fig. 2.3 Overlap of neighboring subcarriers, Inter Carrier Interference (ICI) ............................. 13
Fig. 2.4 Multipath reception leads to location and frequency-selective fading ........................... 13
Fig. 2.5 Echo Delay.............................................................................................................................................. 14
Fig. 2.6 Inter Symbol Interference (ISI)...................................................................................................... 14
Fig. 2.7 Multi Carrier.......................................................................................................................................... 15
Fig. 2.8 Channel Impulse Response.............................................................................................................. 16
Fig. 2.9 Flat Channel........................................................................................................................................... 16
Fig. 2.10 Orthogonal subcarriers.................................................................................................................. 17
Fig. 2.11 Block diagram of Orthogonal subcarriers ............................................................................... 18
Fig 2.12 Subcarrier with Guard Band.......................................................................................................... 19
Fig. 2.13 Difference between spectra of FDM and OFDM ..................................................................... 19
Fig. 2.14 OFDM Implementation.................................................................................................................... 20
Fig. 2.15 Discrete Fourier Transform (DFT)............................................................................................. 21
Fig. 2.16 OFDM transmitter............................................................................................................................. 22
Fig. 2.17 OFDM receiver ................................................................................................................................... 22
Fig. 2.18 Guard Period ...................................................................................................................................... 23
Fig. 3.1 Power samples of one symbol OFDM signal .............................................................................. 28
Fig. 3.2 Block diagram of OFDM system...................................................................................................... 29
Fig. 3.3 Histogram of Real part of OFDM signal amplitude................................................................. 31
Fig. 3.4 Histogram of Imaginary part of OFDM signal amplitude...................................................... 31
Fig. 3.5 OFDM signal magnitude.................................................................................................................... 32

IV
Fig. 3.6 OFDM transmitter basic scheme ..................................................................................................... 32
Fig. 3.7 Linear and Non-Linear Power Amplifier .................................................................................... 33
Fig. 3.8 256-QAM constellations: (a) regular and (b) modified mapping to reduce...................... 35
Fig. 3.9 Types of PAPR Reduction Techniques......................................................................................... 38
Fig. 4.1 SDR Sender and Receiver module diagram ............................................................................... 41
Fig. 4.2 USRP Connection Diagram............................................................................................................... 42
Fig. 4.3 Detailed view of Front Panel of NI USRP-2920 ......................................................................... 46
Fig. 4.4 NI USRP-2920 Front Panel ............................................................................................................... 46
Fig. 4.5 MIMO Expansion cable ...................................................................................................................... 47
Fig. 4.6 USRP Antenna....................................................................................................................................... 47
Fig. 4.7 Gigabit Ethernet Cable....................................................................................................................... 48
Fig. 4.8 Power Supply........................................................................................................................................ 48
Fig. 4.9 The USRP Configuration.................................................................................................................... 49
Fig. 4.10 Detailed block diagram of NI-USRP 2920................................................................................. 50
Fig. 4.11 Power connections to the USRP kit ............................................................................................ 51
Fig. 4.12 Ethernet cable and antenna connections to the USRP......................................................... 52
Fig. 4.13 Connections of the NI-USRP kit to the host PC........................................................................ 52
Fig. 4.14 Verifying the device in NI-USRP-Configuration Utility........................................................ 53
Fig. 4.15 Changing the device IP of the device.......................................................................................... 54
Fig. 5.1 The block diagram of the Communication System.................................................................. 58
Fig. 5.2 The block diagram of OFDM Transceiver................................................................................... 58
Fig. 5.3 The block diagram of OFDM transmitter using Labview ...................................................... 59
Fig. 5.4 The block diagram of OFDM Receiver using Labview............................................................ 59
Fig. 5.5 SLM General Block Diagram............................................................................................................ 60
Fig. 5.6 SLM Block Diagram using Labview ............................................................................................... 61

V
Fig. 5.7 Received 4-QAM Constellation for SLM....................................................................................... 62
Fig. 5.8 Received 16-QAM Constellation for SLM..................................................................................... 62
Fig. 5.9 Received 64-QAM Constellation for SLM..................................................................................... 63
Fig. 5.10 Received 256-QAM Constellation for SLM ............................................................................... 63
Fig. 5.11 CCDF for SLM with different types of Modulation................................................................. 64
Fig. 5.12 PTS General Block Diagram .......................................................................................................... 65
Fig. 5.13 PTS Block Diagram using Labview ............................................................................................. 66
Fig. 5.14 Received 4-QAM Constellation for PTS (V=4 & V=16) respectively................................ 67
Fig. 5.15 Received 4-QAM Constellation for PTS (V=32 & V=64) respectively............................. 67
Fig. 5.16 CCDF for PTS 4-QAM with different number of Sub-blocks (V)........................................ 68
Fig. 5.18 Received 16-QAM Constellation for PTS (V=32 & V=64) respectively .......................... 69
Fig. 5.19 CCDF for PTS 16-QAM with different Sub-blocks (V)........................................................... 70
Fig. 5.21 Received 64-QAM Constellation for PTS (V=32 & V=64) respectively .......................... 71
Fig. 5.23 Active Constellation Extension (a) for QPSK (b) for 16 QAM............................................ 73
Fig. 5.24 ACE Block Diagram using Labview............................................................................................. 73
Fig. 5.25 Received 4-QAM Constellation for ACE..................................................................................... 74
Fig. 5.26 Received 16-QAM Constellation for ACE................................................................................... 74
Fig. 5.27 Received 64-QAM Constellation for ACE................................................................................... 75
Fig. 5.28 Received 256-QAM Constellation for ACE................................................................................ 75
Fig. 5.29 CCDF for ACE with different types of Modulation.................................................................. 76
Fig. 5.30 TI General Block Diagram.............................................................................................................. 77
Fig. 5.31 TI Block Diagram using Labview................................................................................................. 77
Fig. 5.32 Received 4-QAM Constellation for TI......................................................................................... 78
Fig. 5.33 Received 16-QAM Constellation for TI...................................................................................... 78

VI
Fig. 5.34 Received 64-QAM Constellation for TI...................................................................................... 79
Fig. 5.35 Received 256-QAM Constellation for TI ................................................................................... 79
Fig. 5.36 CCDF for TI with different types of Modulation..................................................................... 80
Fig. 5.37 Interleaving General Block Diagram ......................................................................................... 81
Fig. 5.38 Interleaving Block Diagram using Labview ............................................................................ 81
Fig. 5.39 Received 4-QAM Constellation for Interleaving .................................................................... 82
Fig. 5.40 Received 16-QAM Constellation for Interleaving.................................................................. 82
Fig. 5.41 Received 64-QAM Constellation for Interleaving.................................................................. 83
Fig. 5.42 CCDF for Interleaving with different types of Modulation................................................. 83
Fig. 5.43 ACF General Block Diagram.......................................................................................................... 85
Fig. 5.44 ACF Block Diagram using Labview ............................................................................................. 85
Fig. 5.45 Received 4-QAM Constellation for ACF..................................................................................... 86
Fig. 5.46 Received 16-QAM Constellation for ACF................................................................................... 86
Fig. 5.47 CCDF for ACF with different types of Modulation.................................................................. 87
Fig. 5.48 Hardware Component..................................................................................................................... 88
Fig. 5.49 Received signal for various V=4,16,32,64 using 4-QAM ...................................................... 90
Fig. 5.50 Received signal in time domain for various V = 4,16,32,64 using 4-QAM................... 91
Fig. 5.51 CCDF for PTS 4-QAM with different Sub-blocks (V).............................................................. 92
Fig. 5.52 Received signal for various V=4,16,32,64 using 16-QAM................................................... 93
Fig. 5.53 Received signal in time domain for various V=4,16,32,64 using 16-QAM ................... 94
Fig. 5.55 Received signal for various V=4,16,32,64 using 64-QAM...................................................... 96
Fig. 5.56 Received signal in time domain for various V=4,16,32,64 using 64-QAM .................. 97

VII
List of Table
Table 1 Summary of all Generation................................................................................................................................ 7
Table 2 Comparison between FDM and OFDM .......................................................................................................20
Table 3 PAPR for picked modulation formats........................................................................................................35
Table 4 PAPR Reduction Techniques ..........................................................................................................................37
Table 5 The Features of NI-USRP-2920 TX & RX.................................................................................................43
Table 6 Connectors of NI USRP-2920..........................................................................................................................44
Table 7 NI USRP-2920 Module LEDs..........................................................................................................................45
Table 8 The System Parameters used for Simulation............................................................................................57
Table 9 CCDF values for SLM with different types of Modulation................................................................64
Table 10 CCDF values for PTS 4-QAM Modulation with different number of sub-blocks(V)...........68
Table 11 CCDF values for PTS 16-QAM Modulation with different number of sub-blocks(V) ........70
Table 13 CCDF values for ACE with different types of Modulation..............................................................76
Table 14 CCDF values for TI with different types of Modulation...................................................................80
Table 15 CCDF values for Interleaving with different types of Modulation...............................................84
Table 16 CCDF values for ACF with different types of Modulation..............................................................87
Table 17 The System Parameters used for Implementation...............................................................................89
Table 18 CCDF values for PTS 4-QAM Modulation with different number of sub-blocks(V)...........92

VIII
Abbreviations
OFDM : Orthogonal Frequency-Division Multiplexing
OFDMA : Orthogonal Frequency-Division Multiple Access
FDM : Frequency-Division Multiplexing
FDMA : Frequency-Division Multiple Access
TDM : Time-Division Multiplexing
TDMA : Time-Division Multiple Access
CDMA : Code-Division Multiple Access
COFDM : Coded Orthogonal Frequency-Division Multiplexing
PAPR : Peak to Average Power Ratio
ISI : Inter Symbol Interference
ICI : Inter Carrier Interference
1G : First Generation
2G : Second Generation
3G : Third Generation
4G : Fourth Generation
5G : Fifth Generation
DUC : Digital up Converter
HDSL : High-bit-rate Digital Subscriber Line
ADSL : Asymmetric Digital Subscriber Line
VDSL : Very-high-speed Digital Subscriber Line
DAB : Digital Audio Broadcasting
DVB : Digital Video Broadcasting
HDTV : High-Definition Television

IX
IEEE : Institute of Electrical and Electronics Engineers
UMTS : Universal Mobile Telecommunication System
PDS : Pacific Digital Cellular
D-AMPS : Digital-Advanced Mobile Phone Services
NMT : Nordic Mobile Telephony
TACS : Total Access Communication System
AMPS : Advanced Mobile Phone Service
AWGN : Additive White Gaussian Noise
CCDF : Complementary Cumulative Distribution Function
PDF : Probability Density Function
FFT : Fast Fourier Transform
IFFT : Inverse Fast Fourier Transform
S/P : Serial to Parallel
P/S : Parallel to Serial
DFT : Discrete Fourier Transform
DAC : Digital to Analog Converter
ADC : Analog to Digital Converter
Tx : Transmitter
Rx : Receiver
RF : Radio Frequency
HPA : High Power Amplifier
BER : Bit Error Rate
FM : Frequency Modulation
CP : Cyclic Prefix
QAM : Quadrature Amplitude Modulation
QPSK : Quadrature Phase-Shift Keying

X
M-PSK : Multiple Phase-Shift Keying
SDR : Software Defined Radio
MIMO : Multi Input Multi Output
NI : National Instruments
USRP : Universal Software Radio Peripheral
SLM : Selected Level Mapping
PTS : Partial Transmit Sequences
TR : Tone Reservation
TI : Tone Injection
ACE : Active Constellation Extension
AI : Adaptive Interleaving
ACF : Amplitude Clipping and Filtering

XI
Contents
Chapter One: Introduction to wireless Communication
1.1 Aim of this Thesis ....................................................................................................................................................2
1.2 Evolution of wireless communications............................................................................................................3
1.2.1 First generation (1G) cellular systems .............................................................................................3
1.2.2 Second generation (2G) cellular systems.........................................................................................3
1.2.3 Third generation (3G) cellular systems............................................................................................4
1.2.4 Fourth generation (4G) wireless broadband systems .......................................................................5
1.2.5 Next generation technology .............................................................................................................6
1.3 Summary of all generations.................................................................................................................................7
Chapter Two: Orthogonal Frequency Division Multiplexing
2.1 OFDM Historical Overview.............................................................................................................................11
2.2 Important Definitions..........................................................................................................................................11
2.2.1 Inter-Symbol Interference (ISI) ....................................................................................................12
2.2.2 Inter-Carrier Interference (ICI) .....................................................................................................12
2.3 OFDM as a Multicarrier Transmission Technique.................................................................................13
2.4 OFDM Concept.....................................................................................................................................................15
2.4.1 Analysis..........................................................................................................................................16
2.4.1.1 Time Domain Analysis ...........................................................................................................16
2.4.1.2 Frequency Domain Analysis...................................................................................................16
2.4.1.3 Conclusion from both Domains Analysis ...............................................................................17
2.5 Orthogonality of OFDM....................................................................................................................................17
2.6 Comparing FDM to OFDM .............................................................................................................................19
2.6.1Frequency Division Multiplexing (FDM).......................................................................................19
2.6.2 Orthogonal Frequency Division Multiplexing (OFDM)................................................................19

XII
2.7 OFDM Implementation......................................................................................................................................20
2.7.1 Implementation using “FFT/IFFT”................................................................................................21
2.8 OFDM Transmitter..............................................................................................................................................21
2.9 OFDM Receiver....................................................................................................................................................22
2.10 Cyclic Prefix ........................................................................................................................................................23
2.11 Strengths and drawbacks of OFDM ...........................................................................................................24
2.11.1 OFDM advantages .......................................................................................................................24
2.11.2 OFDM disadvantages...................................................................................................................24
Chapter Three: The Peak-to-Average power Ratio
3.1 Introduction to Peak to Average Power Ratio (PAPR) .........................................................................27
3.2 Definitions of PAPR ............................................................................................................................................27
3.2.1 (PAPR) of a continuous time signal...............................................................................................28
3.2.2 (PAPR) of a discrete time signal....................................................................................................29
3.3 PAPR of OFDM signal ......................................................................................................................................29
3.3.1 Calculation of PAPR........................................................................................................................30
3.3.2 Complementary Cumulative Distribution Function.......................................................................30
3.4 Identification of the Problem...........................................................................................................................32
3.5 PAPR Effect...........................................................................................................................................................34
3.6 Factors influencing the PAPR........................................................................................................................34
3.6.1 The number of sub carriers ............................................................................................................34
3.6.2 The order of Modulation................................................................................................................34
3.6.3 Constellation shape ........................................................................................................................35
3.6.4 Pulse Shaping.................................................................................................................................35
3.7 Existing Approaches for PAPR Reduction .................................................................................................36
3.8 PAPR Reduction Techniques ...........................................................................................................................37

XIII
Chapter Four: Getting Start with Software Defined Radio
4.1 Software Defined Radio.....................................................................................................................................41
4.2 The Hardware of USRP and Software of Labview..................................................................................42
4.2.1 Hardware Specifications ................................................................................................................43
4.2.2 Connectors of NI USRP-2920........................................................................................................44
4.2.3 NI USRP-2920 Module LED.........................................................................................................45
4.2.4 NI USRP-2920 Front Panel ...........................................................................................................46
4.3 USRP Parameters configuration....................................................................................................................49
4.4 System Implementation.......................................................................................................................................50
4.4.1 NI-USRP 2920 Block diagram ......................................................................................................50
4.4.2 Interfacing of the Host PC with the Kit .........................................................................................51
Chapter Five: Simulation and Implementation Results
5.1 The overall system design specifications ....................................................................................................57
5.2 OFDM Physical Layer .......................................................................................................................................57
5.3 The Simulation Results.......................................................................................................................................60
5.3.1 Selected Level Mapping (SLM).....................................................................................................60
5.3.1.1 Block Diagram........................................................................................................................60
5.3.1.2 SLM Equations .......................................................................................................................61
5.3.1.3 SLM Results............................................................................................................................62
5.3.2 Partial Transmit Sequences (PTS) .................................................................................................65
5.3.2.1 Block Diagram........................................................................................................................65
5.3.2.2 PTS Equations.........................................................................................................................66
5.3.2.3 PTS Results.............................................................................................................................67
5.3.3 Active Constellation Extension( ACE ).........................................................................................73
5.3.3.1 Block Diagram........................................................................................................................73

XIV
5.3.3.2 ACE Results............................................................................................................................74
5.3.4 Tone Injection (TI).........................................................................................................................77
5.3.4.1 Block Diagram........................................................................................................................77
5.3.4.2 TI Results.................................................................................................................................78
5.3.5 Interleaving ....................................................................................................................................81
5.3.5.1 Block Diagram........................................................................................................................81
5.3.5.2 Interleaving Results.................................................................................................................82
5.3.6 Amplitude Clipping and Filtering (ACF).......................................................................................84
5.3.6.1 Block Diagram........................................................................................................................85
5.3.6.2 ACF Equations........................................................................................................................85
5.3.6.3 ACF Results............................................................................................................................86
5.4 The Implementation Results for PTS technique using USRP ..............................................................88
5.4.1 The System Parameters Used for Implementation........................................................................89
5.4.2 Implementation Results of PTS using USRP.................................................................................90
Conclusion ............................................................................................................................................100
Future Work.........................................................................................................................................101
DISSEMINATION..................................................................................................................................102
Reference..............................................................................................................................................104

XV
PREFACE
Orthogonal frequency-division multiplexing (OFDM) is an orthogonal waveform technique for
encoding digital data on multiple carrier frequencies. OFDM has developed into a popular
scheme for wide band digital communication, used in applications such as wireless networks and
4G mobile communications such as LTE, WIMAX and Wi-Fi. It still exists with some of the
drawbacks, out of which, high peak to average power ratio (PAPR) gives rise to non-
linear distortion, inter-symbol interference and out-of-band radiation. There has been
various ways developed and implemented to reduce PAPR . we will describe all of these
techniques to reduce PAPR such as : Partial Transmit Sequence (PTS) , Selective Level
Mapping ( SLM ) , Interleaving , Tone Injection ( TI ) and Active Constellation Extension(
ACE ) which comes under Signal scrambling techniques . And Amplitude Clipping and
Filter (ACF) which comes under signal distortion technique. In this thesis, we simulate all
these techniques using LABVIEW software then implement Partial Transmit Sequence (PTS)
technique on Universal Software Radio Peripheral (USRP).
Organization of this thesis
 Chapter One: Overview of wireless communication.
 Chapter Two: Fundamentals of OFDM Systems.
 Chapter Three: Peak to Average Power Ratio (PAPR).
 Chapter Four: OFDM System Implementation Using Software Defined Radio.
 Chapter Five: Simulation and Implementation Results.

Chapter One
Introduction to wireless
Communication

Chapter One Introduction of Wireless Communication
2
Chapter 1
Introduction of wireless communication
1.1 Aim of this Thesis
The pervasive use of wireless communications is more and more conditioning lifestyle
and working habits in many developed countries. Examples of this trend are the ever increasing
number of users that demand Internet connection when they are traveling, the use of cellular
phones to check bank accounts and make remote payments, or the possibility of sharing
moments in our lives with distant friends by sending them images and video clips. In the last few
years, the proliferation of laptop computers has led to the development of wireless local area
networks (WLANs), which are rapidly supplanting wired systems in many residential homes and
business offices. More recently, wireless metropolitan area networks (WMANs) have been
standardized to provide rural locations with broadband Internet access without the costly
infrastructure required for deploying cables. A new generation of wireless systems wherein
multimedia services like speech, audio, video and data will converge into a common and
integrated platform is currently under study and is expected to become a reality in the near
future.[1]
The promise of portability is clearly one of the main advantages of the wireless
technology over cabled networks. Nevertheless, the design of a wireless communication system
that may reliably support emerging multimedia applications must deal with several technological
challenges that have motivated an intense research in the field. One of this challenge is the harsh
nature of the communication channel. In wireless applications, the radiated electromagnetic
wave arrives at the receiving antenna after being scattered, reflected and diffracted by
surrounding objects. As a result, the receiver observes the superposition of several differently
attenuated and delayed copies of the transmitted signal.
The constructive or destructive combination of these copies induces large fluctuations in
the received signal strength with a corresponding degradation of the link quality. In addition, the
characteristics of the channel may randomly change in time due to unpredictable variations of the
propagation environment or as a consequence of the relative motion between the transmitter and
receiver. A second challenge is represented by the limited amount of available radio spectrum,
which is a very scarce and expensive resource. It suffices to recall that European
telecommunication companies spent over 100 billion dollars to get licenses for third-generation
cellular services. To obtain a reasonable return from this investment, the purchased spectrum
must be used as efficiently as possible. A further impairment of wireless transmissions is the
relatively high level of interference arising from channel reuse. Although advanced signal
processing techniques based on multiuser detection have recently been devised for interference
mitigation, it is a fact that mobile wireless communications will never be able to approach the
high degree of stability, security and reliability afforded by cabled systems. Nevertheless, it
seems that customers are ready to pay the price of a lower data throughput and worse link quality
in order to get rid of wires.[1]

3
1.2 Evolution of wireless communications
Before proceeding to a systematic study of OFDM and OFDMA, we think it useful to
review some basic applications of such schemes and highlight the historical reasons that led to
their development. The current section is devoted to this purpose, and illustrates the evolution of
wireless communication systems starting from the theoretical works of Maxwell in the
nineteenth century till the most recent studies on broadband wireless networks. Some historical
notes on multicarrier transmissions are next provided in the last section of this introductory
chapter.
1.2.1 First generation (1G) cellular systems
Despite its theoretical relevance, the cellular concept was not widely adopted during the
1960s and 1970s. To make an example, in 1976 the Bell Mobile Phone had only 543 paying
customers in the New York City area, and mobile communications were mainly supported by
heavy terminals mounted on cars. Although the first patent describing a portable mobile
telephone was granted to Motorola in 1975 mobile cellular systems were not introduced for
commercial use until the early 1980s, when the so-called first generation (1G) of cellular
networks were deployed in most developed countries. The common feature of 1G systems was
the adoption of an analog transmission technology. Frequency modulation (FM) was used for
speech transmission over the 800-900 MHz band and frequency division multiple access
(FDMA) was adopted to separate users' signals in the frequency domain. In practice, a fraction of
the available spectrum (sub-channel) was exclusively allocated to a given user during the call
set-up and retained for the entire call.[1]
In the early 1980s, 1G cellular networks experienced a rapid growth in Europe,
particularly in Scandinavia where the Nordic Mobile Telephony(NMT) appeared in 1981, and in
United Kingdom where the Total Access Communication System (TACS) started service in
1985. The Advanced Mobile Phone Service (AMPS) was deployed in Japan in 1979, while in the
United States it appeared later in 1983. These analog systems created a critical mass of
customers. Their main limitations were the large dimensions of cell phones and the reduced
traffic capacity due to a highly inefficient use of the radio spectrum.
At the end of the 1980s, progress in semiconductor technology and device
miniaturization allowed the production of small and light-weight hand held phones with good
speech quality and acceptable battery lifetime. This marked the beginning of the wireless cellular
revolution that took almost everyone by surprise since in the meantime many important
companies had stopped business activities in cellular communications, convinced that mobile
telephony would have been limited to rich people and would have never attracted a significant
number of subscribers.
1.2.2 Second generation (2G) cellular systems
The limitations of analog radio technology in terms of traffic capacity became evident in
the late 1980s, when 1G systems saturated in many big cities due to the rapid growth of the
cellular market. Network operators realized that time was ripe for a second generation (2G) of
cellular systems that would have marked the transition from analog to digital radio technology.

4
This transition was not only motivated by the need for higher network capacity, but also by the
lower cost and improved performance of digital hardware as compared to analog circuitry.
Driven by the success of NMT, in 1982 the Conference of European Posts and
Telecommunications (CEPT) formed the Group Special Mobile (GSM) in order to develop a
pan-European standard for mobile cellular radio services with good speech quality, high spectral
efficiency and the ability for secure communications. The specifications of the new standard
were approved in 1989 while its commercial use began in 1993. Unlike 1G systems, the GSM
was developed as a digital standard where users' analog signals are converted into sequences of
bits and transmitted on a frame-by-frame basis. Within each frame, users transmit their bits only
during specified time intervals (slots) that are exclusively assigned at the call setup according to
a time-division multiple-access (TDMA) approach.[1]
Actually, the GSM is based on a hybrid combination of FDMA and TDMA, where
FDMA is employed to divide the available spectrum into 200 kHz wide sub-channels while
TDMA is used to separate up to a maximum of eight users allocated over the same sub-channel.
In Europe the operating frequency band is 900 MHz, even though in many big cities the 1800
MHz band is also being adopted to accommodate a larger number of users. Many modern
European GSM phones operate in a "dual-band" mode by selecting either of the two
recommended frequencies. In the United States, the 1900 MHz frequency band is reserved to the
GSM service.
In addition to circuit-switched applications like voice, the adoption of a digital
technology enabled 2G cellular systems to offer low-rate data services including email and short
messaging up to 14.4 kbps. The success of GSM was such that by June 2001 there were more
than 500 million GSM subscribers all over the world while in 2004 the market penetration
exceeded 80% in Western Europe. The reasons for this success can be found in the larger
capacity and many more services that the new digital standard offered as compared to previous.
1G analog systems. Unfortunately, the explosive market of digital cell phones led to a
proliferation of incompatible 2G standards that sometimes prevent the possibility of roaming
among different countries. Examples of this proliferation are the Digital Advanced Mobile Phone
Services (D-AMPS) which was introduced in the United States in 1991 and the Japanese Pacific
Digital Cellular (PDS). The Interim Standard 95 (IS-95) became operative in the United States
starting from 1995 and was the first commercial system to employ the code-division multiple-
access (CDMA) technology as an air interface.
1.2.3 Third generation (3G) cellular systems
At the end of the 1990s it became clear that GSM was not sufficient to indefinitely
support the explosive number of users and the ever-increasing data rates requested by emerging
multimedia services. There was the need for a new generation of cellular systems capable of
supporting higher transmission rates with improved quality of service as compared to GSM.
After long deliberations, two prominent standards emerged: the Japanese-European Universal
Mobile Telecommunication System (UMTS) and the American CDMA-2000 [161]. Both
systems operate around the 2 GHz frequency band and adopt a hybrid FDMA/CDMA approach.

5
In practice, groups of users are allocated over disjoint frequency sub-bands, with users sharing a
common sub-band being distinguished by quasi-orthogonal spreading codes. The CDMA
technology has several advantages over TDMA and FDMA, including higher spectral efficiency
and increased flexibility in radio resource management. In practical applications, however,
channel distortions may destroy orthogonality among users' codes, thereby resulting in multiple
access interference (MAI). In the early 1990s, problems related to MAI mitigation spurred an
intense research activity on CDMA and other spread-spectrum techniques. This led to the
development of a large number of multiuser detection (MUD) techniques, where the inherent
structure of interfering signals is exploited to assist the data detection process.
The introduction of 3G systems offered a wide range of new multimedia applications
with the possibility of speech, audio, images and video transmissions at data rates of 144-384
kbps for fast moving users up to 2 Mbps for stationary or slowly moving terminals. In addition to
the increased data rate, other advantages over 2G systems are the improved spectral efficiency,
the ability to multiplex several applications with different quality of service requirements, the use
of variable bit rates to offer bandwidth on demand and the possibility of supporting asymmetric
services in the uplink and downlink directions, which is particularly useful for web browsing and
high-speed downloading operations. Unfortunately, the impressive costs paid by telecom
providers to get 3G cellular licenses slackened the deployment of the 3G infrastructure all over
the world and led to a spectacular crash of the telecom stock market during the years 2000/2001.
As a result, many startup companies went bankrupt while others decreased or stopped at all their
Investments in the wireless communication area. This also produced a significant reduction of
public funding for academic research.[1]
1.2.4 Fourth generation (4G) wireless broadband systems
4G refers to the fourth generation of cellular wireless standards. It is a successor to 3G
and 2Gfamilies of standards. The nomenclature of the generations generally refers to a change in
the fundamental nature of the service, non-backwards compatible transmission technology and
new frequency bands. The first was the move from 1981 analogue (1G) to digital (2G)
transmission in 1992.This was followed, in 2002, by 3G multi-media support, spread spectrum
transmission and at least200 Kbit/s, soon expected to be followed by 4G,which refers to all-IP
packet-switched networks, mobile ultra-broadband (gigabit speed) access and multi-carrier
transmission. Pre-4G technologies such as mobile WiMAX and first-release 3G Long Term
Evolution (LTE) have been available on the market since 2006and 2009 respectively.
It is basically the extension in the 3G technology with more bandwidth and services
offers in the 3G.The expectation for the 4G technology is basically the high quality audio/video
streaming over end to end Internet Protocol. If the Internet Protocol (IP)multimedia sub-system
movement achieves what it going to do, nothing of this possibly will matter. WiMAX or mobile
structural design will become progressively more translucent, and therefore the acceptance of
several architectures by a particular network operator ever more common.[1]

6
1.2.5 Next generation technology
5G (5th generation mobile networks or 5th generation wireless systems) is a name used in
some research papers and projects to denote the next major phase of mobile telecommunications
standards beyond the upcoming 4G standards, which are expected to be finalized between
approximately 2011 and 2016. Currently 5G is not a term officially used for any particular
specification or in any official document yet made public by telecommunication companies or
standardization bodies such as 3GPP, WiMAX Forum or ITU-R. New 3GPP standard releases
beyond 4G and LTE Advanced are in progress, but not considered as new mobile generations.[2]
5G Technology stands for 5th Generation Mobile technology. 5G technology has
changed the means to use cell phones within very high bandwidth. User never experienced ever
before such a high value technology. Nowadays mobile users have much awareness of the cell
phone (mobile) technology. The 5G technologies include all type of advanced features which
makes 5G technology most powerful and in huge demand in near future.[2]
The gigantic array of innovative technology being built into new cell phones is stunning.
5G technology which is on hand held phone offering more power and features than at least 1000
lunar modules. A user can also hook their 5G technology cell phone with their Laptop to get
broadband internet access. 5G technology including camera, MP3 recording, video player, large
phone memory, dialing speed, audio player and much more you never imagine. For children
rocking fun Bluetooth technology and Pico nets has become in market.[2]
5G technology going to be a new mobile revolution in mobile market. Through 5G
technology now you can use worldwide cellular phones and this technology also strike the china
mobile market and a user being proficient to get access to Germany phone as a local phone. With
the coming out of cell phone alike to PDA now your whole office in your finger tips or in your
phone. 5G technology has extraordinary data capabilities and has ability to tie together
unrestricted call volumes and infinite data broadcast within latest mobile operating system. 5G
technology has a bright future because it can handle best technologies and offer priceless handset
to their customers. May be in coming days 5G technology takes over the world market. 5G
Technologies have an extraordinary capability to support Software and Consultancy. The Router
and switch technology used in 5G network providing high connectivity. The 5G technology
distributes internet access to nodes within the building and can be deployed with union of wired
or wireless network connections. The current trend of 5G technology has a glowing future.[2]
A new revolution of 5G technology is about to begin because 5G technology going to
give tough completion to normal computer and laptops whose marketplace value will be
effected. There are lots of improvements from 1G, 2G, 3G, and 4G to 5G in the world of
telecommunications. The new coming 5G technology is available in the market in affordable
rates, high peak future and much reliability than its preceding technologies.[2]

7
1.3 Summary of all generations
Table 1 Summary of all Generation
Generation
Feature
1G 2G 3G 4G 5G
Deployment 1970-1980 1990-2001 2001-2010 2011 2015-20 onwards
Data Rates 2kbps 14.4-64 kbps 2Mbps
200Mbps to
1Gbps
1Gbps and higher
Technology
Analog Cellular
Technology
Digital Cellular
Technology: Digital
narrow band circuit
data, Packet data
Digital Broadband
Packet data:
CDMA 2000
EVDO, UMTS,
EDGE.
Digital
Broadband Packet
data: WiMax LTE
Wi-Fi
wwww Unified IP
seamless
combination of
broadband LAN,
PAN, MAN, WLAN
Service
Analog voice
service
No data service
Digital voice with
higher clarity
SMS,MMS Higher
capacity packetized
data
Enhanced audio
video streaming
video
conferencing
support Web
browsing at
higher speeds
IPTV support
Enhanced audio-
video streaming
IP telephony HD
mobile TV
Dynamic Information
access Wearable
devices AI
Capabilities
Multiplexing
Switching
FDMA TDMA,CDMA CDMA CDMA CDMA
Standards
MTS, AMTS,
IMTS
2G:GSM 2.5:GPRS
2.75:EDGE
IMT-2000 3.5G
HSDPA 3.75G
HSUPA
Single unified
standard LTE,
WiMaX
Single unified
standard
WEB Standard www www (IPv4) www (IPv4) wwww (IPv6)

Chapter Two
Orthogonal Frequency
Division Multiplexing

Chapter Two T Orthogonal Frequency Division Multiplexing
10
Chapter 2
Orthogonal Frequency Division Multiplexing
Due to the high data rate transmission and the ability to against frequency selective
fading, orthogonal frequency division multiplexing (OFDM) is a promising technique in the
current broadband wireless communication system.
Orthogonal frequency division multiplexing (OFDM) technology is to split a high-rate
data stream into a number of lower rate streams that are transmitted simultaneously over a
number of subcarrier. Because the symbol duration increases for the lower rate parallel
subcarrier, the relative amount of dispersion in time causes by multipath delay spread is
decreased.
In a classical parallel data system, the total signal frequency band is divided into “N”
non-overlapping frequency sub-channels, each sub-channel is modulated with a separate symbol
and then the “N” sub-channels are frequency-multiplexed. It seems good to avoid spectral
overlap of channels to eliminate inter-channel interference. However, this leads to inefficient use
of the available spectrum. To cope with the inefficiency, the ideas proposed from the mid- 1960s
were to use parallel data and FDM with overlapping sub-channels, in which, each carrying a
signaling rate b is spaced apart in frequency to avoid the use of high-speed equalization and to
combat impulsive noise and multipath distortion, as well as to fully use the available bandwidth.
The employment of discrete Fourier transform to replace the banks of sinusoidal
generator as shown in “Figure (2.1)”and the demodulation significantly reduces the
implementation complexity of OFDM modems.
Fig. 2.1 Discrete Fourier Transform

11
Inter-symbol interference is eliminated almost completely by introducing a guard interval
with zero padding in every OFDM symbol. In the guard time, the OFDM symbol is cyclically
extended to avoid inter-carrier interference (cyclic prefix).
2.1 OFDM Historical Overview
In 1971, Weinstein and Ebert applied the Discrete Fourier Transform (DFT) to parallel
data transmission systems as part of modulation and demodulation process.
In the 1980s, OFDM was studied for high-speed modems digital mobile communication
and high-density recording and pilot tone is used to stabilize carrier and frequency control in
addition to Trellis code is implemented.
In 1980, Hirosaki suggested an equalization algorithm in order to suppress both inter-
symbol and inter-carrier interference caused by the channel impulse response or timing and
frequency errors.
In the 1990s, OFDM was exploited for wideband data communications Mobile radio FM
channels:
 Fix-wire network
 High-bit-rate digital subscriber line (HDSL)
 Asymmetric digital subscriber line (ADSL)
 Very-high-speed digital subscriber line (VDSL)
 Digital audio broadcasting (DAB)
 Digital video broadcasting (DVB)
 High-definition television (HDTV) terrestrial broadcasting
 There exist three mechanisms about the digital terrestrial television broadcasting system
European (COFDM )
 Wireless LAN HIPERLAN2 (European)
 IEEE 802.11a (U.S.A)
 IEEE 802.11g (U.S.A)
Now, OFDM technique has been adopted as the new European DAB standard, DVB
standard, widely used in all WiMAX implementations, a candidate of 4G mobile
communication, in IEEE 802.16 broadband wireless access system standards, and IEEE 802.20
mobile broadband wireless access and more other advanced communications systems.[16 , 17]
2.2 Important Definitions
Inter-symbol interference (ISI) and inter-carrier interference (ICI) are very important
phenomena that a signal can face so we will focus here on their detailed meaning.

12
2.2.1 Inter-Symbol Interference (ISI)
In telecommunication, inter-symbol interference (ISI) is a form of distortion of a signal
in which one symbol interferes with subsequent symbols as shown below in “Figure (2.2)”. This
is an unwanted phenomenon as the previous symbols have similar effect as noise, thus making
the communication less reliable. ISI is usually caused by multipath propagation or the inherent
non-linear frequency response of a channel causing successive symbols to "blur" together. The
presence of ISI in the system introduces errors in the decision device at the receiver output.
Therefore, in the design of the transmitting and receiving filters, the objective is to minimize the
effects of ISI, and thereby deliver the digital data to its destination with the smallest error rate
possible. Ways to fight inter-symbol interference include adaptive equalization and error
correcting codes.
From the receiver point of view, the channel introduces time dispersion in which the
duration of the received symbol is stretched; extending the symbol duration causes the current
received symbol to overlap previous received symbols and results in inter-symbol interference
(ISI).
Fig. 2.2 ISI Due to channel filtering
2.2.2 Inter-Carrier Interference (ICI)
Interference caused by data symbols on adjacent subcarriers, ICI occurs when the
multipath channel varies over one OFDM symbol time as shown below in “Figure (2.3)”, when
this happens, the Doppler shifts on each multipath component cause a frequency offset on the
subcarriers, resulting in the loss of orthogonality among them. This situation can be viewed from
the time domain perspective, in which the integer number of cycles for each subcarrier within the
FFT interval of the current symbol is no longer maintained due to the phase transition introduced
by the previous symbol, Finally, any offset between the subcarrier frequencies of the transmitter
and receiver also introduces ICI to an OFDM symbol.

13
Fig. 2.3 Overlap of neighboring subcarriers, Inter Carrier Interference (ICI)
2.3 OFDM as a Multicarrier Transmission Technique
OFDM is a special case of multicarrier transmission, where a single data stream is
transmitted over a number of lower rate subcarrier. Multi-carrier methods belong to the most
complicated transmission methods of all and are in no way inferior to the code division multiple
access (CDMA) methods, But why this complexity? The reason is simple: the transmission
medium is an extremely difficult medium to deal with.
The terrestrial transmission medium involves
 Terrestrial transmission paths.
 Difficult line-associated transmission conditions.
The terrestrial transmission paths, in particular, exhibit the following characteristic features:
 Multipath reception via various echo paths caused by reflections from
buildings, mountains, trees, vehicles.
 Additive white Gaussian noise (AWGN).
 Narrow-band or wide-band interference sources caused by internal combustion
engines, streetcars or other radio sources.
 Doppler Effect i.e. frequency shift in mobile reception.
Fig. 2.4 Multipath reception leads to location and frequency-selective fading
An effect known as “red-light effect” in car radios, the car stops at a red stop light and
radio reception ceases. If one were to select another station or move the car slightly forward,
reception would be restored. If information is transmitted by only one discrete carrier precisely at

14
one particular frequency, echoes will cause cancellations of the received signal at particular
locations at exactly this frequency. This effect is a function of the frequency as shown in “Figure
(2.5)”, the intensity of the echo and the echo delay.
Fig. 2.5 Echo Delay
If high data rates of digital signals are transmitted by vector modulated (I/Q modulated)
carriers, they will exhibit a bandwidth which corresponds to the symbol rate.
The available bandwidth is usually specified. The symbol rate is obtained from the type
of modulation and the data rate. However, single carrier methods have a relatively high symbol
rate, often within a range of more than 1 MS/s up to 30 MS/s. This leads to very short symbol
periods of 1 μs and shorter (inverse of the symbol rate). However, echo delays can easily be
within a range of up to 50 μs or more in terrestrial transmission channels. Such echoes would
lead to inter-symbol interference between adjacent symbols or even far distant symbols and
render transmission more or less impossible. An obvious trick would now be to make the symbol
period as long as possible in order to minimize inter-symbol interference as shown in “Figure
(2.6)”and, in addition, pauses could be inserted between the symbols, so-called guard intervals.
Fig. 2.6 Inter Symbol Interference (ISI)
However, there is still the problem of the location- and frequency selective fading
phenomena. If then the information is not transmitted via a single carrier but is distributed over
many, up to thousands of subcarriers and a corresponding overall error protection is built in, the

15
available channel bandwidth remaining constant, individual carriers or carrier bands will be
affected by the fading, but not all of them.
Many thousands of subcarriers are used instead of one carrier, the symbol rate is reduced
by the factor of the number of subcarriers and the symbols are correspondingly lengthened
several thousand times up to a millisecond. The fading problem is solved and, at the same time,
the problem of inter-symbol interference is also solved due to the longer symbols and the
appropriate pauses between them.
A multi-carrier method is born and is called Coded Orthogonal Frequency Division
Multiplex (COFDM). It is now only necessary to see that the many adjacent carriers do not
interfere with one another, i.e. are orthogonal to one another.[18]
2.4 OFDM Concept
An OFDM signal consists of a number of closely spaced modulated carriers. When
modulation of any form - voice, data, etc. is applied to a carrier, then sidebands spread out either
side. It is necessary for a receiver to be able to receive the whole signal to be able to successfully
demodulate the data. As a result when signals are transmitted close to one another they must be
spaced so that the receiver can separate them using a filter and there must be a guard band
between them. This is not the case with OFDM. Although the sidebands from each carrier
overlap, they can still be received without the interference that might be expected because they
are orthogonal to each another. This is achieved by having the carrier spacing equal to the
reciprocal of the symbol period.
Fig. 2.7 Multi Carrier
To see how OFDM works, it is necessary to look at the receiver. This acts as a bank of
demodulators, translating each carrier down to DC. The resulting signal is integrated over the
symbol period to regenerate the data from that carrier. The same demodulator also demodulates
the other carriers. As the carrier spacing equal to the reciprocal of the symbol period means that
they will have a whole number of cycles in the symbol period and their contribution will sum to
zero - in other words there is no interference contribution.

16
2.4.1 Analysis
To completely understanding the concept of OFDM we make analysis in time and
frequency domains.
2.4.1.1 Time Domain Analysis
Assume a channel that has the following impulse response “h (t)”, if we send a pulse
“S(t)” over this channel, the pulse shape would be convolved with the channel impulse response
as shown in “Figure (2.8)”.
Fig. 2.8 Channel Impulse Response
Note that the pulse becomes dispersed or extended in time interfering with surrounding
pulses and causing inter-symbol interference (ISI) and Now compare the two cases of T >> τ and
T < τ:
 T < τ: Pulse completely distorted. ISI is significant in this case.
 T > τ: Pulse extended but the extension is much smaller than “T” the output behaves like
the transmitted rectangular pulse.
2.4.1.2 Frequency Domain Analysis
A wideband signal is completely distorted while a narrow band signal is essentially
seeing a flat channel as shown in “Figure (2.9)”.
Fig. 2.9 Flat Channel

17
A high data rate transmitted signal has a consequent large bandwidth, this means that it
subjected to frequency selective or frequency dependent fading, which can distort the signal
significantly, one solution is to divide the bandwidth available for transmission into many
narrowband sub channels.
Low data rate sub channel‘s frequency component encounter an almost flat channel. (The
band over which the channel is almost constant is called the coherence bandwidth of the channel)
Relative to the narrow sub channel, the channel is basically a frequency-independent complex
number, i.e.; amplitude and a phase shift.
2.4.1.3 Conclusion from both Domains Analysis
Short pulses suffer severely from channel, But we need these short pulses in order to send
a greater number of them at given time period, i.e., to increase data or bit transmission rate, one
solution is to use short pulses (high data rate) and an equalizer at receiver, the equalizer is a filter
that compensates for the distortion induced by channel characteristics.
For very high data rates a sophisticated equalizer is needed and may not be ever feasible,
is there another solution? Yes, stick to long pulses. But how can we then increase the data rate?
We can use many frequency channels (called sub channels), and hence the name FDM
(Frequency Division Multiplexing), over each of these sub channels the data rate is low, but
taken together and since they operate in parallel, a very high data rate can be achieved while
circumventing the dispersive influence of the channel.
2.5 Orthogonality of OFDM
In OFDM, the spectra of subcarriers overlap but remain orthogonal to each other “Figure
(2.10)”, this means that at the maximum of each subcarrier spectrum, all the spectra of other
subcarriers are zero.[19]
Fig. 2.10 Orthogonal subcarriers

18
The receiver samples data symbols on individual subcarriers at the maximum points and
demodulates them free from any interference from the other subcarriers and hence no ICI, the
orthogonality of subcarriers can be viewed in either the time domain or in frequency domain:
 From the time domain perspective, each subcarrier is a sinusoid with an integer
number of cycles within one FFT interval.
 From the frequency domain perspective, this corresponds to each subcarrier
having the maximum value at its own center frequency and zero at the center frequency
of each of the other subcarriers. Two functions, , are orthogonal over an
interval.
[a, b] mathematically this can be written as shown in “Equation(2.1)”:
The output of the integrator can be expressed as follows in “Equation (2.2)”:
This integral satisfies the orthogonality definition, to implement this integral sine wave
carriers are used, Consequently, the harmonic exponential functions (sine wave carriers) with
frequency separation “Δf= 1/TU” are orthogonal as shown below in “Figure (2.11)”.
Fig. 2.11 Block diagram of Orthogonal subcarriers

19
2.6 Comparing FDM to OFDM
2.6.1Frequency Division Multiplexing (FDM)
In Frequency Division Multiplexing system, signals from multiple transmitters are
transmitted simultaneously (at the same time slot) over multiple frequencies. Each frequency
range (sub-carrier) is modulated separately by different data stream and a spacing (guard band) is
placed between sub-carriers to avoid signal overlap as shown “Figure (2.12)”.
Fig 2.12 Subcarrier with Guard Band
2.6.2 Orthogonal Frequency Division Multiplexing (OFDM)
OFDM is a multiplexing technique that divides the bandwidth into multiple frequency
sub carriers. OFDM also uses multiple sub-carriers but the sub-carriers are closely spaced to
each other without causing interference, removing guard bands between adjacent sub-carriers.
Here all the sub carriers are orthogonal to each other. Two periodic signals are orthogonal when
the integral of their product, over one period, is equal to zero. The use of OFDM results in
bandwidth saving as seen in the “Figure (2.13)”. [20]
Fig. 2.13 Difference between spectra of FDM and OFDM

20
Table 2 Comparison between FDM and OFDM
2.7 OFDM Implementation
Keeps a time slot of length TS fixed, considers modulation in frequency direction for
each time slot, starts with a base transmit pulse “g(t)”.then obtains frequency-shifted replicas of
this pulse, that is, if “g(t) = g0(t)” is located at the frequency “f = 0”, then “gk(t)” is located at
“f =f*k”, in contrast to the first scheme, for each time instant l, the set of K (or K + 1)
modulation symbols is transmitted by using different pulse shapes “gk(t)”, the parallel data
stream excites a filter bank of K (or K + 1) different band pass filters. The filter outputs are then
summed up before transmission. This setup is depicted in “Figure (2.14)”.
Fig. 2.14 OFDM Implementation
The transmitted signal in the complex baseband can be represented as shown below in
“Equation (2.3)”.
It is obvious that we come back to the first setup if we replace the modulation symbols
“Skl” by “Skl exp (−j2πfklTs)” in Equation, such a time-frequency-dependent phase rotation does
not change the performance, so both methods can be regarded as equivalent.
Point of
Comparison
Orthogonal Frequency Division
Multiplexing ( OFDM)
Frequency Division Multiplexing
(FDM)
Bandwidth
All sub-channels are dedicated to a
single data source
Bandwidth dedicated to several sources
Carrier Sum of a number of orthogonal carriers No relationship between the carriers
Guard band No guard band between carriers There is a guard band between carriers
Efficiency Better spectral efficiency Low spectral efficiency
ISI Overcomes ISI and delay spread
More subject to ISI and external
interference from other RF sources
(

21
However, the second – the filter bank – point of view is closer to implementation,
especially for the case of OFDM, where the filter bank is just an FFT, as it will be shown later.
2.7.1 Implementation using “FFT/IFFT”
In order to overcome the daunting requirement for L RF radios in both the transmitter and
the receiver, OFDM uses an efficient computational technique, discrete Fourier transform (DFT)
as shown “Figure (2.15)”.
Fig. 2.15 Discrete Fourier Transform (DFT)
Discrete Fourier transform (DFT) leads itself to a highly efficient implementation
commonly known as the Fast Fourier Transforms (FFT), this FFT and its inverse operation
which is called (IFFT) can create a multitude of orthogonal subcarriers using a single radio.
2.8 OFDM Transmitter
The OFDM transmitter shown below in “Figure (2.16)” will be briefly discussed in the
next few words. Initially, the bit sequence is first subjected to channel encoding to reduce the
probability of error at the receiver due to the channel effects, these bits are mapped to symbols of
QPSK, QAM, or any other modulation schematic, the symbol sequence is converted to parallel
format, IFFT (OFDM modulation) is applied to convert the block of frequency data to a block of
time data that modulates the carrier, the sequence is once again converted to the serial format.
Now OFDM symbol already generated, after then, guard time is provided between the
OFDM symbols and the guard time is filled with the cyclic extension of the OFDM symbol, and
windowing is applied to the OFDM symbols to make the fall-off rate of the spectrum steeper,
the resulting sequence is converted to an analog signal using a DAC and passed on to the RF
modulation stage, finally, The resulting RF modulated signal is, then, transmitted to the receiver
using the transmit antennas.

22
Fig. 2.16 OFDM transmitter
2.9 OFDM Receiver
The OFDM receiver shown below in “Figure (2.17)” will be briefly discussed in the next
few words. Initially, At the receiver, first RF demodulation is performed, Then the signal is
digitized using an ADC, Timing and frequency synchronization are performed, then the guard
time is removed from each OFDM symbol, then The sequence is converted to parallel format,
After then FFT (OFDM demodulation) is applied to get back to the frequency domain, The
output is then serialized. Symbol de-mapping is done to get back the coded bit sequence, and
Channel decoding is, then, done to get the user bit sequence.
Fig. 2.17 OFDM receiver

23
2.10 Cyclic Prefix
The key to making OFDM realizable in practice is the use of the FFT algorithm, due to
its low complexity. In telecommunications, the term cyclic prefix refers to the prefixing of a
symbol with a repetition of the end. Although the receiver is typically configured to discard the
cyclic prefix samples, the cyclic prefix serves two purposes.
As a guard interval, it eliminates the inter-symbol interference from the previous symbol,
while as a repetition of the end of the symbol; it allows the linear convolution of a frequency-
selective multipath channel to be modeled as circular convolution, which in turn may be
transformed to the frequency domain using a discrete Fourier transform.
In order for the cyclic prefix to be effective (i.e. to serve its aforementioned objectives),
the length of the cyclic prefix must be at least equal to the length of the multipath channel.
Although the concept of cyclic prefix has been traditionally associated with OFDM systems, the
cyclic prefix is now also used in single carrier systems to improve the robustness to multipath.
In order for the IFFT/FFT to create an ISI-free channel, the channel must appear to
provide a circular convolution, adding cyclic prefix to the transmitted signal, as the following
copy “n” values from the end of the symbols sequence and use them in the guard region as
shown “Figure (2.18)”.
Fig. 2.18 Guard Period
In addition to preventing interference between original signals, signal after adding cyclic
prefix the cyclic prefix above realizes the purpose of the OFDM by making each sub channel see
a flat channel response.
One must take into consideration that the cyclic prefix must be larger than the delay
spread to overcome the inter-symbol interference.[21]

24
2.11 Strengths and drawbacks of OFDM
2.11.1 OFDM advantages
 Immunity to selective fading: One of the main advantages of OFDM is that is more
resistant to frequency selective fading than single carrier systems because it divides the
overall channel into multiple narrowband signals that are affected individually as flat
fading sub-channels.
 Resilience to interference: Interference appearing on a channel may be bandwidth
limited and in this way will not affect all the sub channels. This means that not all the
data is lost.
 Spectrum efficiency: Using close-spaced overlapping sub-carriers, a significant OFDM
advantage is that it makes efficient use of the available spectrum.
 Resilient to ISI: Another advantage of OFDM is that it is very resilient to inter-symbol
and inter-frame interference. This results from the low data rate on each of the sub-
channels.
 Simpler channel equalization: One of the issues with CDMA systems was the
complexity of the channel equalization which had to be applied across the whole channel.
An advantage of OFDM is that using multiple sub-channels, the channel equalization
becomes much simpler.
2.11.2 OFDM disadvantages
 Sensitive to carrier offset and drift: It is very sensitive to phase noise and frequency
synchronization errors, which translates into more stringent specifications for local
oscillators.
 High peak to average power ratio: An OFDM signal has a noise like amplitude
variation and has a relatively large dynamic range, or peak to average power ratio. This
impacts the RF amplifier efficiency as the amplifiers need to be linear and accommodate
the large amplitude variations and these factors mean the amplifier cannot operate with a
high efficiency level.

Chapter Three
The Peak-to-Average
power Ratio

Chapter Three The Peak to Average Power Ratio
27
Chapter 3
The Peak-to-Average power Ratio
3.1 Introduction to Peak to Average Power Ratio (PAPR)
In the orthogonal frequency division multiplexing (OFDM) the peak power might be
much larger than the average power, due to adding up subcarriers coherently which resulting in
large peak-to-average power ratio (PAPR).
PAPR is a very important situation in the communication system because it has big
effects on the transmitted signal. Low PAPR makes the transmit power amplifier works
efficiently, on the other hand, the high PAPR makes the signal peaks move into the non-linear
region of the RF power amplifier which reduces the efficiency of the RF power amplifier.
In addition, high PAPR requires a high-resolution digital- to- analog converter (DAC) at
the transmitter, high-resolution analog -to -digital converter (ADC) at the receiver and a linear
signal. Any non-linearity in the signal will cause distortion such as inter-carrier-interference
(ICI) and inter symbol interference (ISI). [3]
There are a number of techniques to deal with the problem of PAPR. Some of them are
"amplitude clipping", "clipping and filtering", "coding", "partial transmit sequence (PTS)",
"selected mapping (SLM) ‟ and "interleaving‟. These techniques achieve PAPR reduction at the
expense of transmit signal power increase, bit error rate (BER) increase, data rate loss,
computational complexity increase, and so on.
3.2 Definitions of PAPR
Presence of large number of independently modulated sub-carriers in an OFDM system
the peak value of the system can be very high as compared to the average of the whole system.
This ratio of the peak to average power value is termed as Peak-to-Average Power Ratio
Coherent addition of N signals of same phase produces a peak which is N times the
average signal.
The PAPR effect is shown in "Figure. 3.1". And it can be seen that the peak power is
about 17 times the average power.

28
Fig. 3.1 Power samples of one symbol OFDM signal
This figure shows that one of the samples have high peaks, and in order to transmit a
signal with these high peaks, a high signal span is required from the power amplifier. But such
types of power amplifiers are costly. [3]
3.2.1 (PAPR) of a continuous time signal
For a continuous time baseband OFDM signal, the PAPR of any signal is defined as the
proportion of the maximum instantaneous power of the signal and its average power. If
x (t) is a transmitted baseband OFDM signal, then PAPR is defined as:
Where,
is the original signal.
Τ is the interval time.
is the peak signal power.
is the average signal power.

29
3.2.2 (PAPR) of a discrete time signal
For a discrete OFDM signal, the PAPR is computed from 'L' time oversampled
OFDM signal as:
Where, L
is the discrete signal.
N is the total number of subcarriers.
is the expectation.
3.3 PAPR of OFDM signal
"Figure 3.2" shows the end-to-end block diagram of an OFDM system in which the
discrete-time signal after IFFT at the transmitter can be expressed as:
(3.4)
Fig. 3.2 Block diagram of OFDM system.
Let's have a look on the mathematical explanation of the PAPR. The input bit stream
given to OFDM system is first mapped on a selected modulation technique Ex: QAM, QPSK,
BPSK etc. From this, a complex OFDM vector of symbols is obtained. Let’s this complex valued

30
vector is a data block 'X' consisting of complex data , , , .the complex base band
representation of this multicarrier signal can be determined by the above "Equation 3.4".
In the above equation ,'N' tells the number of subcarriers in the OFDM system. is the
modulated data carried by the sub-carrier.
This equation is actually performing the Inverse Fast Fourier Transform (IFFT) through
which, a time domain symbol is obtained .it can be represented as:
x=IFFT(X). Therefore, 'x' represents a vector of N elements (o to N-1) of time domain
signals and x (n) is element. Whereas 'X' is a set of modulated data carried by 'N' different
subcarriers.
3.3.1 Calculation of PAPR
Now the peak to Average power ratio of this transmitted signal can be calculated in dB
from equation (3.5) given below
(3.5)
In order to observe the PAPR performance of a signal, the Cumulative Distributed
Function (CDF) or the Complementary Cumulative Distribution Function (CCDF) is used.
Through the CCDF, it can be observed that the PAPR of the signal exceeded a certain value.
3.3.2 Complementary Cumulative Distribution Function
In the modern communication word, CCDF measurements prove as one of the precious
tool. The CCDF plots offer a comprehensive analysis of signal power peaks. It is a statistical
technique that provides the amount of time, a signal spends any given power level.
However by using these plots, a probability can be seen that a signal data block exceeds a
given threshold. These CCDF plots can be used to analyze the PAPR performance of the signal.
Mathematical Explanation: in order to calculate the CCDF of a given data, the following
steps should be followed:
 Cal. The probability density function (PDF) of the data
 Take the integral of the PDF to get the CDF (Cumulative Distributed Function)
 Subtract the CDF from '1' to get the CCDF (as: CCDF=1-CCDF)
Or equivalently, it can summarize as:
CDF= & CCDF=1-CCDF (3.6)
Mathematically, it can be explained as follows:

31
P (PAPR>z) =1-P (PAPR z) =1- =1- (3.7)
Where, F (z) represent the CDF and z is the given reference level.
The histogram plots for the real part, imaginary part and the absolute value of a time
domain OFDM signal are shown in Figure 3.3, 3.4 and 3.5 respectively. The plots shown in
Figures 3.3(a) and (b) are obtained after performing the computer simulations of an
OFDM system having N=256 QPSK modulated subcarriers as shown in "Figure 3.2". The
signal obtained from IFFT block of “Figure 3.2"is complex OFDM signal. After that real,
imaginary and absolute values of OFDM signal (x[n]) are calculated and their histograms are
plotted. [5]
The power of OFDM signal has chi-square distribution. The distribution of PAPR is
often expressed on the one hand Complementary Cumulative Distribution Function (CCDF). In
probability theory and statistics, the CCDF describes the probability that a real-valued random
variable X with a given probability distribution will be found at a value greater than or equal to
x. [5 and 6]
Fig. 3.3 Histogram of Real part of OFDM signal amplitude
Fig. 3.4 Histogram of Imaginary part of OFDM signal amplitude

32
Fig. 3.5 OFDM signal magnitude
3.4 Identification of the Problem
Multi-carrier phenomena is considered to be one of the major development in wireless
communication and among them OFDM is becoming the important standard. However, high
PAPR is the major drawback of OFDM, which results in lower power efficiency hence impedes
in implementing OFDM. To overcome the low power efficiency requires not only large
back off and large dynamic range DAC but also highly efficient HPA and linear converters.
These demands result in costly hardware and complex systems. Therefore to lessen the difficulty
of complex hardware design it has become imperative to employ efficient PAPR reduction
techniques.
This high RAPR can make a cause of certain drawbacks for Example:
 Increased complexity in the analog to digital and digital to analog converter.
Fig. 3.6 OFDM transmitter basic scheme
In some applications, the drawbacks of high PAPR overcome the benefits of OFDM To
understand how and where the PAPR of the signal becomes a problem, it is necessary to take a
look at the OFDM transmitter," Figure 3.6" shows a basic scheme. The information data is
generated and shaped in the Data block, this takes place in frequency domain, then comes the
IFFT block and the signal is afterwards in digital time domain. To send the signal through the

33
antenna, it must be first converted to analog time domain by means of an D/A converter and then
amplified with an RF power amplifier. After the RF amplifier comes the antenna which sends the
signal to the OFDM receiver over the wireless channel.
 Reduction is efficiency of RF amplifiers
Before transmitting the signal it must path through present high power amplifier (HPA).
We already know that we have two main types of power amplifiers which are:
 Linear Power Amplifiers (Ideal): They are perfect amplifiers from linearity as
shown below in “Figure (3.7)” while its destructive disadvantage operating with
very low efficiency of maximum 25% so if we used it the battery of the mobile
phone will rapidly exhausted.
Fig. 3.7 Linear and Non-Linear Power Amplifier
 Non Linear Power Amplifiers(Actual): They are perfect amplifiers from the
efficiency point of view as they can operate with very high efficiency hence
battery can survive for long time, and on the other side this type main
disadvantage is operating in a nonlinear region of operation as shown above in
“Figure (3.7)” which leads to loss of orthogonality & hence leads to intermarries
interference.
When transmitted through a nonlinear device, a high peak signal generates out-of-band
energy (spectral re-growth) and in-band distortion (constellation tilting and scattering). These
degradations may affect the system performance severely, so, we must operate our system in the
linear region of the nonlinear power amplifier. [4 and 9].

34
3.5 PAPR Effect
 The power amplifiers at the transmitter need to have a large linear range of
operation.
 Non-linear distortions and peak amplitude limiting introduced by the
High Power amplifier (HPA) will produce inter-modulation between the
different carriers and introduce additional interference into the system.
 Additional interference leads to an increase in the Bit Error Rate (BER) of the
system.
 The Analog to Digital converters and Digital to Analog converters need to
have a wide dynamic range and this increases complexity.
A way to avoid non-linear distortion is by forcing the amplifier to work in its linear
region, but unfortunately such solution is not power efficient and thus not suitable for wireless
communication. And at manually clipping the output signal in-band distortion (additional noise)
and out-of-band radiation (ACI) took place.
3.6 Factors influencing the PAPR
3.6.1 The number of sub carriers
In Multi-Carrier Systems the complex base band signal for one symbol in an OFDM
system can be expressed as follows:
t (3.8)
Where N is the modulating symbol and is the number of sub carriers. For moderately
large numbers of m-PSK (multiple phase-shift keying) sub carriers the quadrature
components of x (t) each tends towards a Gaussian distribution (giving the sum of their
power amplitude a Rayleigh distribution). Consequently, whilst the peak value possible is N
times the individual sub carrier peak, the probability of any value close to that peak occurring is
very low. For example, with only 24 sub carriers, the probability of the PAPR exceeding
4dB is and of exceeding 8dB is only .[5]
3.6.2 The order of Modulation
High data bandwidth efficiency (in terms of b/s/Hz) this can be achieved by utilizing
higher order modulations based, for instance, on QAM. When using a higher-order modulation
such as QAM type, the PAPR of the summed OFDM signal is increased by the PAPR of the
QAM constellation utilized. Nevertheless, the probability of these higher peaks happening is
accordingly less. Furthermore, since among benefits of OFDM is one that sub carriers could

35
have their modulation independently varied to adapt to channel conditions, the joined PAPR in
any system utilizing this technique might are hard to predict and control. PAPR for an unfiltered
base band signal is listed in the following Table 3 . [8]
Table 3 PAPR for picked modulation formats
Modulation PAPR[dB]
M-PSK (reference) 0
16-QAM 2.55
64-QAM 3.68
256-QAM 4.23
256-QAM (modified) 2.85
3.6.3 Constellation shape
The last entry in Table 3 is for a constellation obtained by modifying 256- QAM to
reduce PAPR. This modified constellation shape is shown in figure 3.8. However, there is an
additional processor load associated with encoding and decoding this constellation.
Fig. 3.8 256-QAM constellations: (a) regular and (b) modified mapping to reduce
PAPR
3.6.4 Pulse Shaping
In terrestrial communications, it is popular to use pulse shaping to the base band
signal, to decrease the bandwidth of the transmitted spectrum, but this causes overshoot
and can increase the PAPR of the modulating signal by 4-5 dB [8].

36
3.7 Existing Approaches for PAPR Reduction
As in everyday life, we must pay some costs for PAPR reduction. There are many factors
that should be considered before a specific PAPR reduction technique is chosen. These factors
include PAPR reduction capability, power increase in transmit signal, BER increase at the
receiver, loss in data rate, computational complexity increase, and so on. Next we briefly discuss
each of them and corresponding known PAPR reduction methods. You can find more details
about these techniques in "Chapter 5".
 PAPR Reduction Capability Careful attention must be paid to the fact that some
techniques result in other harmful effects. For example, the Amplitude Clipping
technique in Page 80, clearly removes the time domain signal peaks, but results
in in-band distortion and out-of-band radiation.
 Power Increase in Transmit Signal Some techniques require a power increase in
the transmit signal after using PAPR reduction techniques. For example, Tone
Reservation (TR) , requires more signal power because some of its power must be
used for the peak reduction carriers. Tone Injection (TI) in page 73, uses a set of
equivalent constellation points for an original constellation point to reduce PAPR.
Since all the equivalent constellation points require more power than the original
constellation point, the transmit signal will have more power after applying TI.
 BER Increase at the Receiver other techniques may have an increase in BER at
the receiver if the transmit signal power is fixed or equivalently may require
larger transmit signal power to maintain the BER after applying the PAPR
reduction technique. For example, the BER after applying Active Constellation
Extension in Page 69, will be degraded if the transmit signal power is fixed. In
some techniques such as SLM in Page 56, the entire data block may be lost if the
side information is received in error. This may also increase the BER at the
receiver. Loss in Data Rate Some techniques require the data rate to be reduced,
the block coding technique needs a portion of information symbols to be
dedicated to control the PAPR. In SLM and PTS, the data rate is reduced due to
the side information used to inform the receiver of what has been done in the
transmitter. In these techniques the side information may be received in error
unless some form of protection such as channel coding is employed. When
channel coding is used, the loss in data rate due to side information is increased
further.
 Computational Complexity Techniques such as PTS in chapter 5 found a
solution for the PAPR reduced signal by using many iterations and performing
exhaustive search, so it costs a lot to implement it in hardware. This report will
propose a low complexity version of PTS which use more intellectual method to
find optimum phase for PAPR minimization. [10, 11, 12]

37
3.8 PAPR Reduction Techniques
Several PAPR reduction techniques have been proposed in the literature .These
techniques are divided into two groups - signal scrambling techniques and signal distortion
techniques which are given below:
a) Signal Scrambling Techniques:
 Block Coding Techniques
 Block Coding Scheme with Error Correction
 Selected Mapping (SLM)
 Partial Transmit Sequence (PTS)
 Interleaving Technique
 Tone Reservation (TR)
 Tone Injection (TI)
Signal scrambling techniques work with side information which minimized the effective
throughput since they commence redundancy. Signal distortion techniques introduce band
interference and system complexity also. Signal distortion techniques minimize high peak
dramatically by distorting signal before amplification.
b) Signal Distortion Techniques:
 Peak Windowing
 Envelope Scaling
 Peak Reduction Carrier
 Clipping and Filtering
Table 4 PAPR Reduction Techniques

38
Fig. 3.9 Types of PAPR Reduction Techniques

Chapter Four
Getting Start with Software
Defined Radio

Chapter Four Getting Start with Software Defined Radio
41
Chapter 4
Getting Start with Software Defined Radio
4.1 Software Defined Radio
Definition:
SDR is an idea which has been in focus since the early nineties. The main
purpose of Software Defined Radio was to create a device which should be capable of working
with many radios operating at different parameters. Moreover, it can adjust to any range and any
modulation scheme by using a powerful software along with programmable hardware.
An alternative definition for SDR is to merge hardware and software technologies to
make the system flexible for wireless communication [7] [8].
Software Defined Radio provide an effective and inexpensive solution for building
multi-mode, multi-range and multifunctional wireless devices that can be improved by means
of software advancements. By using SDR enabled devices, the same piece of “hardware"
can be modified to perform different functions at different times.
SDR performs noteworthy amount of signal processing in a common PC. In SDR, signal
handled in digital domain instead in analog domain as in the conventional radio. The analog
signal can be converted to the digital domain with the help of Analog to Digital
Converter.
This figure shows that the ADC process is taking place after the Front End (FE) circuit. The A/D
converter will convert the signal to digital form and pass it to the baseband processor for more
processes; detection, channel coding, source coding and etc.
Fig. 4.1 SDR Sender and Receiver module diagram

42
4.2 The Hardware of USRP and Software of Labview
Communication between the USRPs and the computers is handled by LabVIEW drivers.
Initial user input includes the TX/RX frequency, IQ sample rate, IP address of the USRP, and the
TX/RX gain. Thereafter LabVIEW can continuously fetch or transmit samples and then close the
connection. The USRPs also have the ability to share information and communicate with each
other through a MIMO (multiple input multiple output) cable. This was used solely for
debugging parameters like internal vs actual frequency offset. "Figure 4.2" shows the high
level flow of data, from LabVIEW on a computer to a USRP, into the air, received on another
USRP, and recovered in LabVIEW on another computer. All arrows are bidirectional, because
the hardware supports duplex communications.
Fig. 4.2 USRP Connection Diagram

43
4.2.1 Hardware Specifications
The features of NI-USRP-2920 are discussed below:
Table 5 The Features of NI-USRP-2920 TX & RX
Parameter Value in Transmitter Kit Value in Receiver Kit
Frequency Range 50 MHz to 2.2 GHz 50 MHz to 2.2 GHz
Frequency Step < 1 kHz < 1 kHz
Max. Output Power (Pout)
50 MHz to 1.2 GHz 50 mW to
100 mW (17 dBm to 20 dBm)
1.2 GHz to 2.2 GHz 30 mW to
70 mW (15 dBm to 18 dBm)
----------------------
Max. Input Power (Pin) ---------------------- 0 dBm
Gain Range 10 dB to 31 dB 0 dB to 31.5 dB
Gain Step 1.0 dB 0.5 dB
Frequency Accuracy 2.5 ppm 2.5 ppm
Max. Real-Time
instantaneous-bandwidth
16-bit sample-width 20 MHz
8-bit sample width 40 MHz
Max. I/Q Sampling Rate
16-bit sample-width 25 MS/s
DAC 2 Channels 16-bit, 400 MS/s 14 bit, 100 MS/s

44
4.2.2 Connectors of NI USRP-2920
The front end connectors of the USRP-2920 kit are discussed in the following table.
Table 6 Connectors of NI USRP-2920
Connector Use
RX1
TX1
RF signal input and output terminal. RX1/TX1 is an SMA (f) connector with
an impedance of 50 Ω, and is a single-ended input or output channel.
RX2 RF signal input and output terminal. RX2 is an SMA (f) connector with an
impedance of 50 Ω, and is a single-ended input or output channel.
REF IN
Input terminal for an external reference signal for the local oscillator (LO) on
the NI USRP-2921. REF IN is an SMA (f) connector with an impedance of
50 Ω, and is a single-ended reference input. REF IN accepts a 10 MHz signal
with a range of 0 dBm to 15 dBm.
PPS IN
Pulse per second timing reference input terminal. PPS IN is an SMA (f)
connector with an impedance of 50 Ω, and is a single-ended input. PPS IN
accepts 0 V to 3.3 V TTL and 0 V to 5 V TTL signals.
MIMO
EXPANSION
The multiple-input, multiple-output (MIMO) EXPANSION interface port
connects two USRP devices using a compatible MIMO cable.
GB ETHERNET
The gigabit Ethernet port accepts an RJ-45 connector and gigabit Ethernet
compatible cable (Category 5, Category 5e, or Category 6).
POWER The power input accepts a 6 V, 3 A external DC power connector.

45
4.2.3 NI USRP-2920 Module LED
The module LEDs are listed in the following table:
Table 7 NI USRP-2920 Module LEDs
LED Indication
A
Indicates the transmit status of the NI USRP-2921 module:
OFF—The module is not transmitting data.
GREEN—The module is transmitting data.
B
Indicates the status of the physical MIMO cable link:
OFF—The devices are not connected using the MIMO cable.
GREEN—The devices are connected using the MIMO cable.
C
Indicates the receive status of the NI USRP-2921 module:
OFF—The device is not receiving data.
GREEN—The module is receiving data.
D
Indicates the firmware status of the NI USRP-2921 module:
OFF—The firmware is not loaded.
GREEN—The firmware is loaded.
E
Indicates the reference lock status of the LO on the NI USRP-2921 module:
OFF—There is no reference signal or the LO is not locked to a reference signal.
BLINKING—The LO is not locked to a reference signal.
GREEN—The LO is locked to a reference signal.
F
Indicates the power status of the NI USRP-2920 module:
OFF—The device is powered off.
GREEN—The device is powered on.

46
4.2.4 NI USRP-2920 Front Panel
The front panel of the USRP kit for the demonstration is shown in the following figure.
The use of all the ports available is also shown in the diagram itself
Fig. 4.3 Detailed view of Front Panel of NI USRP-2920
Fig. 4.4 NI USRP-2920 Front Panel

47
1) MIMO Expansion:
The MIMO expansion cable is used to link a pair of USRP systems together. Length is 0.5
meters. Only one cable needed for every linked pair of USRP systems.
Fig. 4.5 MIMO Expansion cable
2) Antenna :
This version works with a central frequency in the range from 50 MHz up to 2.2 GHz, covering
the FM radio, GPS, GSM, OFDM and radar bands.
Fig. 4.6 USRP Antenna

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