Wireless communication involves transmitting information such as voice and data through electromagnetic waves without wires. It allows for flexible and mobile connectivity between devices. The document discusses various topics related to wireless communication including point-to-point communication, multiuser systems, modulation techniques, channel models and capacity. It provides an overview of the evolution of wireless technologies and applications.

1. WIRELESS
COMMUNICATIONS
Presenter :- Melkamu Deressa
(B.Sc, M.Sc, PhD Candidate)
March , 2015
Xidian University
Xi’an ,P.R of China

2. OUTLINE
Introduction
Point-to-Point Communication
Multiuser Systems
Conclusion

3. Decoding
Sender
AWGN
Receiver
Feedback
Channel
Encoding
Message
Noise
Process of communication
30-03-2015 02:08:20
Introduction
 A group of connected devices that communicate voice and
data through the air by means of electromagnetic waves,
such as Radio, television, mobile telephone, and satellite
communications in open space.
What is a Wireless Communication?

4. Types of Wireless Communication
Cellular
Wireless computer network
Radio service

5. Wireless Applications (services)
• In vehicles and traffic lights.
• In aircrafts and underwater.
• In Military and security needs
• Hospitals
• Street lamps
• Petroleum and Chemical industries

6. 2015/3/30 6
Advantages:
• Wireless
• Speed
• Cost
• Durability
• Flexibility
• Place of device
Disadvantages:
• security vulnerabilities
• Power consumption
• Compatibility issues
• high costs for setting the
infrastructure
• Influenced by physical
obstructions, climatic conditions,
interference from other
wireless devices
Advantages and Disadvantages
of Wireless Communication

7. 2015/3/30
7
Evolution of Current Systems
• Wireless Systems today
2G Cellular: ~30-70 Kbps.
3G running 300Kbps and Cellular in testing: 384Kbps
WLANs: ~10 Mbps and planned to up grad ~70 -100Mbps
 4G Cellular: 100Mbps-1Gbps
• Next Generation Expected as
5 G : 1 Gbit/s to be offered, simultaneously
Coverage should be improved
Signaling efficiency enhanced.
• Technology Enhancements
Hardware: Better batteries. Better circuits/processors.
Link: Antennas, modulation, coding, adaptively, DSP,
Network: Dynamic resource allocation. Mobility support.
Application: Soft and adaptive QoS.

8. Wireless Data Vision
• Geographically to expand to all needed application areas
TAXI
Region
Campus
City
In-Building
laptops, PDAs
• Technically to make it:-
 Faster and More Persistent
 More Secure
 More Deployable and Manageable
 Ease At Home

9. 2015/3/30 9
Wireless Applications Devices
• Laptops
• Cellular phones
• Headphones
• Keyboards
• Printers
• Speakers
• Global Positioning
Systems (GPS)
• Laser Bridges
• Emergency Services
• Robotics
• Biotechnology
• Nanotechnology
• Radio Frequency
Identification (RFID)
transponders
The possibilities are endless!

10. OUTLINE
Introduction
Point-to-Point Communication
Multiuser Systems
Conclusion

11. Point-to-Point Communication
• Point-to-point communication is a networking technique
for linking or connecting to physical networking devices
with the help of wireless technology.

12. Cont.…..
• Many devices such as bridges, routers, connectors and
transmitters work collectively in point to point wireless
networks.
• It is platform independent and works efficiently and
effectively for receiving and transmitting data from one
place to another.

13. Supplementary Chapter 3
Communication Channel Technology
S3-13
Communication Channel
• Communication channel is a connection between
transmitter and receiver through which data can be
transmitted.
• Communication channel also called as communication
media or transmission media
General Communication Model
Transmitter
Communication
channel
Receiver

14. Shannon’s Wireless Communication System
Source
Source
Encoder
Channel
Encoder
Mod-
ulator
User
Source
Decoder
Channel
Decoder
Demod-
ulator
Message
Signal
Channel code
word
Estimate of
Message signal
Estimate of
channel code word
Received
Signal
Modulated
Transmitted
Signal
Wireless
Channel

15. AWGN Channel
• Additive white Gaussian noise (AWGN) is a basic noise
model used in information theory to mimic the effect of
many random processes that occur in nature.
• This channel is assumed to corrupt the signal that n(t),
which denotes a sample function of the additive white
Gaussian noise process with zero-mean and two-sided
power spectral density.
 Thus the channel capacity for the AWGN channel is
given by:
1
log(1 )
2
P
c
N
 

16. 2)
• In this channel, the transfer function assumed for
the m’th user can be represented as:
• The random magnitude is assumed to be Rayleigh
random variables for all users and sub-carriers, where
Rayleigh distribution is:
Rayleigh Fading Channel
𝝆 𝒎,𝒊
𝐻 𝑚[𝑓𝑐 + 𝑖
𝐹
𝑇𝑏
] = 𝜌 𝑚,𝑖 𝑒 𝑗𝜃 𝑚,𝑖
2
,
2
,
,
2,
, 2
,
( )
m i
m i
m i
m i
p m i
m i
f e







17. Rician Fading Channel
• If we consider line-of-sight (LOS) with magnitude
b0=const, the transfer function assumed for the m’th user
can be represented as:
• The NLOS magnitude factors are assumed to have
the following Rician distribution:
𝝆 𝒎,𝒊
,
,
[ ] m ije
m c
m ib
F
H f i
T
 
2 2
, ,
2 2
, ,
,
(
2,
, 2
,
( )
m i o o m i
o
m i m i
m i
b b
I
m i
m i
m i
f
 
 







18. • Channel capacity(C): It is the maximum capacity at which data
can be transmitted at a given communication Path, or cannel under a
given conditions.
• Data Rate (BPs): The rate at which data can be communicated,
impairments ,such as noise ,limit data rate that can be achieved.
• Band width (B): the band width of transmitted signal as constrained
by the transmitter and the nature of the transmission medium (herzth).
• Noise (N): Impairments on communication path.
• Error rate - Rate at which errors occurs (BER)
 error = transmit 1 and receive 0; transmit 0 and receive 1
Channel Capacity

19. Cont.….
• Shannon during WWII, defines the notion of channel capacity and
provides a mathematical model.
• The key result states that the capacity of the channel, as defined
by mutual information between the input and output of the channel,
where the maximization is with respect to the input distribution.
Shannon–Hartley theorem states the channel capacity C, meaning the
theoretical tightest upper bound on the information rate.
where
C is the channel capacity in bits per second.
B is the Bandwidth of the channel in hertz (passband bandwidth in case of a modulated signal);
S is the average received signal power over the bandwidth (in case of a modulated signal, often denoted C, i.e. modulated
carrier), measured in watts (or volts squared);
N is the average noise or interference power over the bandwidth, measured in watts (or volts squared); and
S/N is the signal-to-noise ratio(SNR) or the carrier-to-noise ratio (CNR) of the communication signal to the Gaussian
noise interference expressed as a linear power ratio (not as logarithmic decibels).
2log (1 )
S
C B
N
 

20. • The block diagram on the top shows the blocks common to all communication
systems
• Communication System: Components/subsystems act together to accomplish
information transfer/exchange.
Communication systems
Digital
Analog
Communication is the transfer of information from one place to
another.

21. Modulation and Demodulation
BDG(xx) 21
• Modulation is the process of changing one or more
properties ( Amplitude, frequency or phase) of the analog
carrier in proportion with the information signal.
• Reverse process of modulation and converting the
modulated carrier back to the original information is
known as demodulation.
Modulation
Analog
Modulation
Digital
modulation

22. • Modulation :- Converting digital to analog information to
wave form suitable for transmission over a given medium.
• It involves varying ome parameter of carrier wave
(sinusoidal waveform) at agiven frequency as a function of
the message signal.
• General sinusoid:-
Modulation
𝐴cos(2𝛱𝑓𝑐 𝑡 + 𝜑
Amplitude Frequency
Phase
• If the information is digital changing parameters is called
“keying “(e.g. ASK, PSK,FSK)

23. Why Modulation is necessary?
1. It is difficult to radiate Low Frequency (LF) signal
from antenna in the form of Electro Magnetic (EM)
energy.
2. Information signal often occupy the same frequency
band that would interfere with each other.
23

24. Types of Analog Modulation
 Amplitude Modulation (AM)
• Amplitude modulation is the process of varying the amplitude of a carrier
wave in proportion to the amplitude of a baseband signal. The frequency of
the carrier remains constant
 Frequency Modulation (FM)
• Frequency modulation is the process of varying the frequency of a carrier
wave in proportion to the amplitude of a baseband signal. The amplitude of
the carrier remains constant
 Phase Modulation (PM)
• Another form of analog modulation technique which we will not discuss
The total bandwidth required for AM can be
determined from the bandwidth of the audio signal:
BAM = 2B.
Frequency modulation
Amplitude modulation
The total bandwidth required for FM can be
determined from the bandwidth of the audio signal:
BFM = 2(1 + β)B. Where  is usually 4.
Phase modulation
The total bandwidth required for PM can be
determined from the bandwidth and maximum
amplitude of the modulating signal: BPM = 2(1 + β)B.
Where  = 2 most often.

25. • In digital wireless communication systems, the modulating
signal may be represented as a time sequence of symbols or
pulses, where each symbol has m finite states. Each symbol
represents n bits of information where n = log2m bits/symbol.
Digital Modulation
Types of Digital modulation Techniques
(a) If the information signal is digital and amplitude of carrier is varied
proportional to information signal, a digitally modulated signal
known as Amplitude Shift Keying (ASK) is produced.
(b) If frequency of the carrier is varied, Frequency shift Keying (FSK)
is produced.
(c) If phase of the carrier is varied , Phase Shift Keying (PSK) is
produced.

26. Digital Modulation and
Demodulation
signal x(t) = A cos(2πft + Φ)
• A – amplitude
• f – frequency
• Φ – phase (initial angle of the sinusoidal function at its origin

27. Digital Modulation Techniques
Amplitude Shift Keying (ASK)
Frequency Shift Keying (FSK)
Phase Shift Keying (PSK)

28. Amplitude Shift Keying (ASK)
• In ASK, the two binary values are represented by to different
amplitudes of the carrier frequency.
• The resulting modulated signal for one bit time is




0,0
1),2cos(
)(
binary
binarytfA
ts c
• Susceptible to noise
• Inefficient modulation technique
• used for
 up to 1200bps on voice grade lines
 very high speeds over optical fiber

29. Frequency Shift Keying (FSK)
• The most common form of FSK is Binary FSK (BFSK)
• Two binary values represented by two different frequencies
( f1 and f2 )




0),2cos(
1),2cos(
)(
2
1
binarytfA
binarytfA
ts


• less susceptible to noise than ASK
• used for
 up to 1200bps on voice grade lines
 high frequency radio (3 to 30MHz)
 even higher frequency on LANs using coaxial cable

30. Phase Shift Keying (PSK)
• Phase of carrier signal is shifted to represent data
• Binary PSK (BPSK): two phases represent two binary digits
1)(),2cos()(
0),2cos(
1),2cos(
0),2cos(
1),2cos(
)(











tdtftAd
binarytfA
binarytfA
binarytfA
binarytfA
ts
c
c
c
c
c





(C)PSK

31. Quadrature Amplitude
Modulation (QAM)
• QAM is described by a constellation consisting of
combination of phase and amplitudes
• The rule governing bits-to-symbols are the same, i.e. n bits
are mapped to M=2n symbols
• QAM used on asymmetric digital subscriber line (ADSL)
and some wireless standards
• logical extension of QPSK
• send two different signals simultaneously on same carrier
frequency
 use two copies of carrier, one shifted by 90°
 each carrier is ASK modulated

32. 32
16-QAM Constellation Using
Gray Coding
• 16-QAM has the following constellation
• Note gray coding where adjacent symbols differ by only 1
bit
0010001100010000
1010
1110
0110
1011
1111
0111
1001
1101
0101
1000
1100
0100

33. Advantages digital modulation
technique
• High data rate
• High spectral efficiency (minimum bandwidth occupancy)
• High power efficiency (minimum required transmit power)
• Robustness to channel impairments (minimum probability
of bit error)
• Low power/cost implementation
• Amplitude/Phase modulation and Frequency modulation.
Spectral properties
• Techniques, more efficient multiple access strategies, and
better security and privacy.

34. OUTLINE
Introduction
Point-to-Point Communication
Multiuser Systems
Conclusion

35. Multiuser Systems
• In this system resources (power, bandwidth, etc.) must
be divided among the multiple users.
• It is a system that jointly estimate the channel response
and detect all the user’s bits.
• Shown to have better performance as well as reduced
computational complexity.

36. Multiuser channel
• A multiuser channel refers to any channel which
must be shared among multiple users.
• There are two different types of multiuser channels:
the broadcast channel and the multiple access channel.
Multiuser
Channel

37. A Broadcast Channel
• It is a channel which has one transmitter sending to many
receivers, and thus the bandwidth and power of the
transmitter must be divided accordingly. Examples of broadcast
channels include all radio and television transmissions, the downlink (satellite-
to-earth station) of a satellite system, and the base station-to-mobile
transmission of a cellular system.

38. 38
Multiple Access
• Allow multiple users to share same medium.
• A multiple access channel has many transmitters sending
signals to one receiver.
 Share a finite amount of radio spectrum(limited bandwidth).
 High performance
 Duplexing generally required
• 3 Main access techniques:
 Frequency Division MA (FDMA).
 Time Division MA (TDMA).
 Code Division MA (CDMA).
Police station
Public school
City Hall
Public Library
Fire station
Medical Center
Inter
net

39. Frequency Division
• Two bands of frequencies for every user
• Forward band
• Reverse band
• Duplexer needed
• Frequency separation between forward band and reverse
band is constant
frequency separation
reverse channel forward channel
f

40. Time Division
• Uses time for forward and reverse link
• Multiple users share a single radio channel
• Forward time slot
• Reverse time slot
• Noncontiguous transmission
• Digital data
• No duplexer is required
time separation
t
forward channelreverse channel

41. • Unique code to differentiate all users
• Sequence used for spreading have low cross-correlations
• Allow many users to occupy all the frequency/bandwidth
allocations at that same time
• Receivers detect only the desired codeword. All others
appear as noise.
• Receivers must know transmitter’s codeword.
• Processing gain is the system capacity
How many users the system can support
Code-Division

42. Random Access
• Assumes dedicated channels wasteful - no dedicated
channel assigned to each user
• Users contend for channel when they have data to send
• Very efficient when users rarely active; very inefficient
when users have continuous data to send
• Scheduling and hybrid scheduling used to combine
benefits of multiple and random access
• Random Access Techniques
Aloha (Pure and Slotted)
Carrier sensing
Typically include collision detection or avoidance
Poor performance in heavy loading

43. Random Access protocols
Random access MAC protocol specifies
• How to detect collisions
• How to recover from collisions (e.g., via delayed
retransmissions)
Random access MAC protocols:-
Slotted ALOHA
ALOHA
CSMA and CSMA/CD

44. • Time is divided into equal size slots (= sending one
frame)
• a newly arriving station transmits at the beginning of
the next slot
• Highly decentralized: only slots in nodes need to be
in sync and simple.
• It has difficulties with collisions, wasting slots, idle
slots and nodes may be able to detect collision in
less than time to transmit packet
Slotted Aloha

45. Pure (unslotted) ALOHA
• Slotted ALOHA requires slot synchronization
• A simpler version, and no slot synchronization
• A node transmits without awaiting for the beginning of a
slot (when frame first arrives transmit immediately)

46. CSMA (Carrier Sense Multiple
Access)
• CSMA: listen before transmit. If channel is sensed busy,
defer transmission
• Persistent CSMA: retry immediately when channel
becomes idle (this may cause instability)
• Non persistent CSMA: retry after random interval of time
• Note: collisions may still exist, since two stations may
sense the channel idle at the same time ( or better, within a
“vulnerable” window = round trip delay)

47. CSMA/CD (Collision Detection)
• CSMA/CD: like in CSMA
collisions are detected within a few bit times
Transmission is then aborted, reducing the channel
wastage considerably
persistent retransmission is implemented
• Collision detection is easy in wired LANs:
can measure signal strength on the line
• Collision detection cannot be done in wireless LANs :
• CSMA/CD can approach channel utilization =1 in LANs:
low ratio of propagation over frame transmission time

48. Conclusions
• Communication is the process of meaningful interaction
among human beings and also currently among various
networked devices.
• The wireless vision encompasses many exciting systems
and applications with technical challenges transcend across
all layers of the system design.
• During Point-to-point communication one process sends a
message and another process receives through effective
communication channel according to the capacity of the
information whether analog or digital data.
• A multiuser systems can be accessed randomly (ALOHA ,
CSMA,..) or deterministically (TDMA, FDMA, CDMA) which many
transmitters sending signals on dedicated channels.

49. The END
Thank you for attention!