1. All rights reserved to ATSPL
Prepared By:
Neha Sharma
APEKSHA TELECOM SERVICES PVT. LTD.
2. In 19th century long distance communication was simplified: Telegraphy, and
later on telephony. Both techniques were wireline.
Voice was transmitted the first time in 1906, and one of the first radio broadcast
transmission in 1909, New York.
All rights reserved to ATSPL
Telecommunications, also known as telecom, is the
exchange of information (all types of voice, data and
video transmission) over significant distances by
electronic means.
From ancient to modern times, mankind has been
looking for means of long distance communications.
For centuries, letters proofed to be the most reliable
way to transmit information.
3. All rights reserved to ATSPL
The economically most successful wireless application in the first half of the
20th century was radio broadcast.
The first commercial wireless car phone telephony service started in the late
1940 in St. Louise, Missouri (USA). In the 50ies, several vehicle radio
systems were also installed in Europe. These systems are nowadays called
single cell systems.
The user data transmission takes place between the mobile phone and the
base station (BS). The transmission of user data from the base station to the
mobile phone is called downlink (DL), the transmission from the mobile
phone to the base station uplink (UL) direction.
4. Limitation of single cell systems- the mobile communication service was only
available within the cell.
To overcome this limitation, cellular systems were introduced. With the
introduction of cellular mobile communication systems, we refer to
generations.
First generation mobile communication systems like TACS (Total Access
Communications System), NMT (Nordic Mobile Telephony), AMPS
(Advanced Mobile Phone Service), C450 etc. All of them were commercially
launched in the 80s of the last century.
The 1st generation mobile communication systems often offered national wide
coverage but there were limitations like:
a. Most of them did not support roaming.
b. Supported speech transmission, but not data transmission, such as fax.
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5. Radio Frequency- RF is any of the electromagnetic wave frequency that lie
in the range from 3KHz-300GHz.
Frequency- It is defined as the number of occurrences of a repeating event
(cycles or vibration) per unit time. Every Communication needs a medium,
Similarly RF utilizes the Electromagnetic spectrum for Radio to provide
wireless communications.
Mathematically, Frequency is the reciprocal of the time period or time interval.
F=1/T Unit- s-1 or Hz.
7. Frequency band- It is an interval in the frequency domain, delimited by a
lower frequency and an upper frequency.
Carrier- The “useful signals”, like speech, music, etc. are what we call low-
band signals; they have low frequencies from about 50 Hz to 20 kHz. We
have two challenges in communication: we need to use high frequencies (so
the antennae are relatively small) and we prefer sending as many signals as
possible in a frequency band. So, we use carrier signals.
A carrier or a carrier signal(usually sinusoidal) is modulated with an input
signal, have a higher frequency (say 98 MHz), so we have more efficient
antennae and by using multiple carriers we can send multiple signals at the
same time.
Modulation- It is the process of varying one or more properties of a periodic
waveform, called the carrier signal with a modulating signal that contains
information to be transmitted. Most of the system uses FM or AM.
9. A base station in a radio transmitter/receiver, includes an antenna which
is used in a mobile telecommunication network. The base station
maintains the communication between the network and the mobile
users through a radio link.
10. Operator- A Mobile Network Operator (MNO) is a telecommunication
service provider organization that provides voice and data communication
services for its subscribed mobile users.
Vendor- In telecom, a vendor is an organization that sells its equipment to
the operator.
Sub-Vendor- In telecom sub-vendors are the organization that delivers the
project and provides manpower for the project delivery.
11.
12. The term Transmission Mode defines the direction of the flow of information
between two communication devices i.e. it tells the direction of signal flow
between the two devices.
There are three ways or modes of data transmission: Simplex, Half duplex
(HDX), Full duplex (FDX)
13. Simplex- In simplex communication network, communication can
take place only in one direction. Communication is unidirectional.
For e.g.- A television broadcast, loudspeaker system. An announcer
speaks into a microphone and his/her voice is sent through an
amplifier and then to all the speakers.
14. Duplex- A duplex communication system is a point-to-point system
composed of two connected parties or devices that can communicate with
one another in both directions.
It is of two types-
1) Full-Duplex
2) Half-Duplex
15. Half-Duplex- Each Party can communicate with the other but not
simultaneously, the communication is one direction at a time. For eg- A
walkie-talkie operates in half duplex mode. It can only send or receive a
transmission at any given time. It cannot do both at the same time.
16. Full Duplex- In a full duplex system, both the parties can communicate
with each other simultaneously. For eg- Telephone- The parties at both the
ends of a call can speak and be heard by the other party simultaneously.
17. FDMA- The frequency spectrum is divided into a number of narrowband
channels. These channels are assigned to users. Therefore, users transmit in
their assigned frequency range . This is assigned dynamically and be
reassigned once the call is completed. The frequency identifier is served as a
channel identifier. This technology is used in Analog Mobile Phone
Systems(AMPS).
TDMA- The same channel is used by multiple users. The available time is
divided into a number of time slots. These slots are assigned to users sharing
the same channel. Thus, TDMA provides more spectral efficiency than
FDMA. The capacity is increased N times, where N is the number of time
slots within a channel. That is ,N users can be accommodated in a channel.
The frequency assignment along with the assigned time slot serve as a channel
identifier. This technology is used in GSM.
18. Comparison of Multiple Access Technologies
CDMA- The wideband spectrum is shared by all users. Each user is spread
with Pseudo-random binary sequence. The wideband frequency assignment
along with the Pseudo-random sequence serves as the channel identifier.
19. Duplexing: Duplexing is used to differentiate UL & DL, to avoid interference.
Types of Duplexing:
FDD: Frequency Division Duplexing
Frequency is divided to separate UL & DL. UL Bandwidth and DL Bandwidth
will always stay same, so called as Symmetric communication. Also called as
‘Paired Communication’.
TDD: Time Division Duplexing
Same Frequency is utilized for UL and DL, but to avoid interference the
Bandwidth used is divided in asymmetrical time periods to separate and UL &
DL, hence called as ‘Asymmetric communication’ and also as ‘Unpaired
communication’.
2G – Only FDD
3G – FDD/TDD
4G – FDD/TDD
22. In 1920, mobile communication system was first used by military while in
1940’s; it was put in use for civil purpose.
Since 1980's, 1G analog mobile communication system adopts cellular
networking technology. Till 1982 Cellular Systems were exclusively Analog
Radio Technology.
At the end of 1980’s Analog System was unable to meet continuing demands
due to:
Severely confined spectrum allocations
Interference in multipath fading environment
Incompatibility among various analog systems
Inability to substantially reduce the cost of mobile terminals & infrastructure
required
Easy to eavesdrop and misuse the subscriber’s account
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23. Since mobile communication started to become a mass market, so improved
solutions were urgently required. This led to the inauguration of the 2nd
generation mobile communication systems.
2G cellular networks were commercially launched on the GSM standard
in Finland by Radiolinja in 1991.
European Telecommunication Standard Institute (ETSI) developed GSM.
During 1990s, Digital mobile communication system characterized by digital
transmission, Time Division Multiple Access (TDMA), and narrowband Code
Division Multiple Access (CDMA) were developed.
Standards of Second Generation
GSM
CDMA IS95
Personal Digital Cellular (PDC)
24. Compared with 1G mobile communication system, 2G mobile
communication system has the following advantages:
Provides high spectrum utilization and large system capacity.
Provides diversified services (voice services and low-rate circuit-
switched data services).
Enables automatic roaming.
Provides better voice quality.
Provides good security.
Can be interconnected with ISDN and PSTN.
25. GSM 2.5G
GSM system (2.5G) Phase2 and Phase2+ were then developed, adopting high-
rate adaptive coding solution. GPRS provides the data rate up to 171 kbps. Two
high-rate data service options are:
High Speed Circuit Switched Data (HSCSD) based on high-speed data bit rate
and circuit switching
General Packet Radio Service (GPRS) based on packet switched data
GSM 2.75G
Enhanced Data Rates for GSM Evolution (EDGE) developed by the European
Telecommunications Standards Institute (ETSI) adopts 8-PSK (Phase Shift
Keying) modulation. It supports data rate up to 384 kbps theoretically. EDGE is
more advanced than GPRS. However, EDGE cannot provide rate up to 2 Mbps as
3G system does. Therefore EDGE is often called 2.75G.
26. 1) 900 MHz band
◦ Uplink frequency range: 890 MHz ~ 915 MHz
◦ Downlink frequency range: 935 MHz ~ 960MHz
2) 1,800 MHz band
◦ Uplink frequency range: 1,710 MHz ~ 1,785 MHz
◦ Downlink frequency range: 1,805 MHz ~ 1,880 MHz
3) 1,900 MHz band
◦ Uplink frequency range: 1,850 MHz ~ 1,910 MHz
◦ Downlink frequency range: 1,930 MHz ~ 1,990 MHz
Channel interval
The interval between two adjacent channels in any band is 200 kHz.
Channel configuration
All channels are configured with the same interval.
27. 900MHz-
UL=890-915 MHz
DL=935-960 MHz
Bandwidth- F2-F1
915-890Mhz= 25MHz
Duplex Distance- Difference in upper limit of UL and DL or Difference in
lower limit of UL and DL.
935-890MHz=45MHz
960-915MHz=45MHz.
28. No. of carriers- (Total BW)/(BW allocated to 1 carrier)
=(25X106)/(200X103)
=125 Carriers or frequency(1 carrier for guard band ,available 124 for use)
Wavelength- λ=c/f
=(3X108)/(900X106)
=33 cm
ARFCN(Absolute Radio Frequency Channel Number)-
UL=890-915 MHz
DL=935-960 MHz
30. Duplex Distance- Difference in upper limit of UL and DL or Difference in
lower limit of UL and DL.
1805-1710MHz=95MHz
1880-1785MHz=95MHz
No. of carriers- (Total BW)/(BW allocated to 1 carrier)
=(75X106)/(200X103)
= 375Carriers or frequency(1 carrier for guard band ,available 374 for use)
Wavelength- λ=c/f
=(3X108)/(1800X106)
=16cm
32. Duplex Distance- Difference in upper limit of UL and DL or Difference in
lower limit of UL and DL.
1930-1850MHz=80MHz
1990-1910MHz=80MHz.
No. of carriers- (Total BW)/(BW allocated to 1 carrier)
=(65X106)/(200X103)
=300Carriers or frequency(1 carrier for guard band available 299 for use).
Wavelength- λ=c/f
=(3X108)/(1900X106)
=15cm
33. ARFCN(Absolute Radio Frequency Channel Number)-
UL=1850-1910 MHz
DL=1930-1990 MHz
For E.g.- n=12
UL=1850+0.2(12-1)
=1852.2MHz
DL=1852.2+80MHz
=1932.2MHz
34.
35. GSM system consists of:
Network Subsystem (NSS)
Base Station Subsystem (BSS)
Operation and Maintenance Subsystem (OMS)
Mobile Station (MS)
36. Network Switching Subsystem (NSS)
NSS is the core element of network switching which interfaces with subscriber
services for voice and data.
NSS Main components are:
◦ Mobile Switching Centre (MSC)
◦ Home Location Register (HLR)
◦ Visitor Location Register (VLR)
◦ Equipment Identification Register (EIR)
◦ Authentication Centre (AUC)
Home Location Register - HLR is a central database of a system. HLR stores all
the information related to subscribers, including the roaming authority, basic
services, supplementary services, and current location information. It provides
routing information for MSC for call setup. HLR may cover several MSC service
areas or even the whole PLMN.
37. Visitor Location Register - VLR stores all subscriber information in its
coverage area and provides call setup conditions for the registered mobile
subscribers. As a dynamic database, VLR must exchange large volume of
data with HLR to ensure data validity. When an MS leaves the controlling
area of a VLR, it registers in another VLR. The original VLR deletes the
temporary records of that subscriber. VLR integrated within MSC.
Equipment Identification Register - EIR stores the parameters related to
MS. It can identify, monitor, and block the MS. EIR preventing
unauthorized MS from accessing the network.
Authentication Centre - AUC is a strictly protected database that stores
subscriber authentication information and encryption parameters. AUC
integrated with HLR physically.
38. Base Station Subsystem BSS serves as a bridge between NSS and MS. It
performs radio channel management and wireless reception and transmission.
Base Station Controller (BSC) and Base Transceiver Station (BTS) are main
components of BSS.
Base Station Controller - Located between MSC and BTS, it controls and
manages more than one BTS. It performs radio channel assignments. BTS and
MS transmit power control, and inter-cell handover. BSC is also small a switch
that converge and connects local network with the MSC through A interface.
Abis interface connects BTS to BSC.
Base Transceiver Station - BTS is wireless transceiving equipment controlled
by the BSC in BSS. BTS carries radio transmission. It performs wired-related
wireless conversion, radio diversity, radio channel encryption, and hopping.
Um interface connects BTS to MS.
39. The GSM Networks also called GSM Public Land Mobile Network (PLMN)
provide voice and other circuit switched services.
GPRS, also called GPRS PLMN, networks provide internet and other packet
switched services.
Radio Access Network (RAN) known as Base Station System (BSS) is used
by both GSM and GPRS networks.
RAN connects to GSM Networks through A interface and to GPRS Networks
using Gb interface. GSM Networks are based on SS7 and Mobile Application
Part (MAP) protocols.
The MSC provides connectivity between BSS and rest of GSM PLMN.
40. GPRS are based on IP backbone. GPRS connects to the GSM PLMN through
SS7 Protocol to access HLR and other database.
The Serving GPRS Support Node(SGSN) provides connectivity between
BSS and rest of GPRS PLMN.
The Gateway GPRS Support Node (GGSN) provides connectivity to internet
or X.25 or both. It acts as a gateway/router.
The SGSN function is similar to MSC/VLR except that it serves packet.
PCU: Packet Control Unit, PCU, which differentiates whether data is to be
routed to the packet switched or circuit switched networks.
41. Signalling Channels
Broadcast Channels:
1. Frequency Correction Channel(FCCH)
2. Synchronization Channel(SCH)
3. Broadcast Control Channel(BCCH)
Common Control Channels:
1. Paging Channel(PCH)
2. Random Access Channel(RACH)
3. Access Grant Channel(AGCH)
Dedicated Control Channels:
1. Standalone Dedicated Control Channel(SDCCH)
2. Slow Associated Control Channel(SACCH)
3. Fast Associated Control Channel(FACCH)
42. Broadcast Channel
The Broadcast Control Channel (BCCH)
It is a DL channel and is transmitted by the BTS at all times. The RF carrier used
to transmit the BCCH is referred to as the BCCH carrier. The MS monitors the
information carried on the BCCH periodically (at least every 30 secs), when it is
switched on and not in a call.
The BCCH Consists of:
Location Area Identity (LAI).
List of neighboring cells that should be monitored by the MS.
List of frequencies used in the cell.
Cell identity.
43. Power control indicator.
DTX permitted.
Access control (i.e., emergency calls, call barring ... etc.).
CBCH description.
The BCCH is transmitted at constant power at all times, and all MS that may
seek to use it to measure its signal strength. “Dummy” bursts are transmitted
to ensure continuity when there is no BCCH carrier traffic.
44. Frequency Correction Channel (FCCH):
This is transmitted frequently on the BCCH timeslot and allows the mobile to
synchronize its own frequency to that of the transmitting base site. The FCCH
may only be sent during timeslot 0 on the BCCH carrier frequency and therefore
it acts as a flag to the mobile to identify Timeslot 0.
Synchronization Channel (SCH):
The SCH carries the information to enable the MS to synchronize to the TDMA
frame structure and know the timing of the individual timeslots. The following
parameters are sent:
Training Sequence Code(TSC)
Frame number.
Base Station Identity Code (BSIC).
The MS will monitor BCCH information from surrounding cells and store the
information from the best six cells. The SCH information on these cells is also
stored so that the MS may quickly resynchronize when it enters a new cell.
45. Common Control Channel
The Common Control Channel (CCCH) is responsible for transferring control
information between all mobiles and the BTS. This is necessary for the
implementation of “call origination” and “call paging” functions.
PCH- Used by BTS to page MS.
RACH- Used by MS to access the network. This occurs when mobile initiates or
responds to a page.
AGCH- Used by the BTS to assign a dedicated control channel to a MS in response
to an access message received on the Random Access Channel. The MS will move
to the dedicated channel in order to proceed with either a call setup, response to a
paging message, Location Area Update or Short Message Service.
Cell Broadcast Channel (CBCH)-This channel is used to transmit messages to be
broadcast to all MS’s within a cell. The CBCH uses a dedicated control channel to
send its messages, however it is considered a common channel because all mobiles
in the cell can receive the message.
46. Dedicated Control Channel
SDDCH- It carries TCH information. A single MS for call setup,
authentication, location updating and SMS point to point use a SDCCH.
SACCH-Conveys power control and timing information in the downlink
direction (towards the MS) and Receive Signal Strength Indicator (RSSI), and
link quality reports in the uplink direction.
FACCH-The FACCH is transmitted instead of a TCH. The FACCH ‘‘steals”
the TCH burst and inserts its own information. The FACCH is used to carry
out user authentication, handovers, and immediate assignment.
47. Traffic Channels
TCH/F-A GSM full rate channel uses 24 frames out of a 26-multiframe. The
channel bit rate of a full-rate GSM channel is 22.7 kbit/s, although the actual
payload data rate is 9.6-14 kbit/s, depending on the channel coding.
TCH/H-A GSM half rate channel uses 12 frames out of a 26-multiframe. The
channel bit rate of a half-rate GSM channel is 11.4 kbit/s, although the actual
data capacity is 4.8-7 kbit/s, depending on the channel coding.
48. Each BTS radiates tuning frequency to MS in Downlink through
FCCH, MS on receiving Tuning Frequency, checks inside its SIM,
whether mobile has this Tuning Frequency or not. If not it will discard
the info else SIM itself will generate same Tuning frequency and the
frequency correction happens between MS and BTS that we have got
FCCH.
49. SCH has information about Training Sequence Code (TSC) and Base Station
Identity Code (BSIC). TSC is a code given to each MS by BTS. MS has to
give TSC to BTS if it wants to communicate with the BTS, else BTS will not
communicate with MS. On receiving TSC, BTS will send BSIC info to MS.
BSIC is a two digit code made from Base Colour Code (BCC) and Network
Colour Code (NCC).
BCCH has information about Cell Global Identity (CGI), Carrier, power and
neighbour. Information given by BCCH is- Cell Complete Identity, Downlink
Frequency, DL power BTS, UL power, neighbouring cell, Cell selection and
reselection will be provided by BCCH to MS.
50. When MS wants to make a call, it will request by RACH that he is looking
for traffic channel TCH. BTS will search TCH info by SDCCH, Then will
send AGCH depending on network information on SDCCH, else no AGCH if
SDCCH is not found.
SDCH in background will search for TCH if it gets TCH info, it will come up
with TCH info, else network will not be available or network busy.
SACCH provides power information, carrier information, link quality, Time
advance information that how far MS is from BTS and network information
during on call.
Handover process and call termination goes from FACCH to BTS.
51. Mobile-Originating Call (MOC)
This is the transaction for an outgoing call from the MS.
Mobile-Terminating Call (MTC)
This is the transaction for an incoming call to the MS.
52. To Understand a technology more easily, the problems/ issues will give lot of
insight into the characteristics of the technology.
Here are the fundamental problems in RF Transmission (BTS/MS).
Path Loss
Shadowing
Multipath Fading
Timing Advance
53. Path Loss- Loss in the signal strength with the distance increase between
MS and BTS( no obstacle).
Possible Solutions are as follows-
1) To increase the power level of BTS.
2) Change in the orientation of antenna direction.
3) Increase or decrease in the height of antenna.
4) Electrical or Mechanical Downtilt
5) Booster/ Repeaters- Booster for single person, repeaters for more than 50
less than 100 people.
6) Introduction of new site at the cell edge if there are more than 500 affected
people.
54. Shadowing- Loss in signal strength due to obstacle, towards or away from
the cell edge.
Multipath Fading- Loss in signal strength when multiple signals from the
same source are received from multiple paths i.e when one MS receives
more than one signal from the same source from multiple path because of
reflection, refraction, scattering etc.
Possible Solutions-
1) Space Diversity
2) Phase Diversity
3) Cross Polarized Antenna
55. 1) Space Diversity- Another antenna is placed at λ/2 distance which rectifies
multipath fading.
2) Phase Diversity- Another antenna is placed with an angle of either
450,600,900 or 1200 which rectifies multipath fading.
3) Cross Polarized Antenna- Dipole antenna 1 TX/RX and other only RX is
placed which rectifies multipath fading.
Timing Alignment- In order to continue the ongoing call MS has to be
always time aligned with the BTS so that MS does not loses the bits sent by
BTS to MS.
Due to distance, MS sometimes misses to receive the bits by BTS. A MS can
miss maximum of 63 bits, if bits are missed more than 63 call will be
disconnected.
So in order to be time aligned with the BTS, time advance concept is used.
56. When a mobile moves from one cell to another, the call must be retained without the
call being dropped. The process of retaining the connection is known as handover.
In 2G hard handover occurs.
Hard Handover- (Break the connection before make) In hard handover the
connection with the previous cell(serving cell)is first broken before a connection is
established with a new cell.
57. Intra-BTS Handover- In this type of GSM Handover the MS remains attached
with the same Base Station Transceiver, but only changes the channel or slot.
This form of GSM handover occurs if it is required to change the frequency or
slot being used by a mobile because of interference, or other reasons. It is
handover from one sector to another sector of same BTS.
Inter-BTS(Intra-BSC)Handover- This form of GSM handover occurs when the
mobile moves out of the coverage area of one BTS but into another controlled by
the same BSC. It is handover from one BTS to another BTS.
58. Inter-BSC(Intra-MSC) Handover- When the mobile moves out of the
range of cells controlled by one BSC, a more involved form of handover has
to be performed, handing over not only from one BTS to another but one
BSC to another.
59. Ping-Pong Handover
Ping-Pong Handover occurs when the MS is handed over from one cell to
another but is quickly handed back to the original cell.
In simple words, that the MS moves back and forth between the overlapped
area of two adjacent cell.
The solution is to allow MS to continue maintain a radio link with the current
BSi, until the signal strength from BSj, exceeds the signal strength from BSi by
some pre-specified threshold value.
61. It is defined as sequential change of carrier frequency on the radio link
between the MS and BTS.
Frequency Hopping rule is simple, that our conversation must remain on
the same physical channel and time slot for the entire time we are on a
particular site. If the network were able to move us from slot to slot, and
from frequency to frequency, then we could randomize the effects of
interference.
It serves the purpose of frequency reuse and to avoid co-channel
interference.
62. The frequency hopping sequences are orthogonal inside one cell (i.e. no
collisions occur between communications of the same cell), and
independent from one cell to an homologue cell (i.e. using the same set of
RF channels, or cell allocation).
The hopping sequence is derived by the mobile from parameters broadcast
at the channel assignment, namely, The mobile allocation (set of
frequencies on which to hop), MA: Mobile allocation of radio frequency
channels, defines the set of radio frequency channels to be used in the
mobiles hopping sequence.
The index offset (to distinguish the different mobiles of the cell using the
same mobile allocation).
MAIO: Mobile allocation index offset.(0 to N 1, 6 bits).
63. MAIO is applied to same timeslot of different TRX (belonging to a same cell).
For instance, each timeslot will have a different MAIO, because they're using
the same HSN.
The hopping sequence number of the cell (which allows different sequences
on homologue cells)
HSN: Hopping sequence (generator) number (0 to 63, 6 bits).
HSN =0, means cyclic hopping (no hopping, generally BCCH carrier)
64. 1) Rx Level- It is the power level received by MS from BTS. Its range vary
from 0 to -120 dBm.
2) Rx Quality- This is an integer value of which can be between 0 and 7 and
reflects the quality of voice. 0 is the best quality, 7 is the worst. It depends on
BER.
Rx Level Interpretation
0 to -65dBm Very Good
-65 to -85dBm Okay
-85 to -105dBm Bad
-105 to -120dBm Not acceptable
65. 3) BER- Bit Error Rate It defines the number of bits in error and it should not
be more than 25%.
0.0%<BER<=0.2%->0
0.2%<BER<=0.4%->1
0.4%<BER<=0.8%->2
0.8%<BER<=1.6%->3
1.6%<BER<=3.2%->4
3.2%<BER<=6.4%->5
6.4%<BER<=12.8%->6
12.8%<BER<=25%->7
OKAY
VERY GOOD
NOT
ACCEPTABLE
66. 4) C/I Carrier to Interference Ratio or Co Channel Interference-
Interference occurs when nearest sites radiates power at same frequency(n) and
also the power level of one cell should be greater than equal to 6dBm.
5) C/A Adjacent Channel Interference Ratio-Interference occurs when nearest
sites radiates power at adjacent frequency(n-1,n+1)and also the power level of
one cell should be greater than equal to 9dBm.
6) RLT Radio Link Time-Out- RLT is defined as time after which MS will
automatically disconnect the call from BTS, if they are not able to communicate.
67. After every 480ms BTS sends SACCH frames to the MS. A timer is defined
in the network (generally 32), till the SACCH frames are not received by MS,
the counter value of timer goes down by 1 (31,30,29,28….) as soon as
SACCH frames are received, the timer counter goes up to by +2. If the
counter goes beyond 4, there is another timer defined in BTS (generally
2000ms, 4000ms, 8000ms) which starts. If still SACCH frames are not
received and timer goes off, the radio link is terminated and call is
disconnected.
7) Power Control-Power Control refers to the process of controlling the power
from/to UE.
MS and BTS adjusts their power in dedicated mode according to the distance
between them.
When distance increases power level has to be increased, and when distance
decreases power level needs to be decreased.
It helps to avoid interference and saves MS battery.
68. 8) DTx- Discontinuous Transmission- MS sends dummy bits to BTS
while it is not speaking(just listening) to maintain the radio link. It
gives an advantage of MS battery saving and there is no interference
while listening in air interface.
69. Dense Urban Area
Urban Area
Sub-Urban Area
Rural Area
Open Area
Quasi Open Area
Water
Vegetation
Highway
Railways
Hills/Hilly Areas
70. An RF site survey is the process of planning and designing a wireless
network, to provide a wireless solution that will deliver the required
wireless coverage, data rates, network capacity, roaming capability
and Quality of Service.
This requires analysis of building floor plans, inspection of the facility, and
use of site survey tools.
71. Tools for RF Survey-
1) GPS(Garmin 72h)
2) Magnetic Compass
3) Measuring Tape
4) Digital Camera(MS)
5) Data sheet by operator
6) Notebook
7) Pen or Pencil
72. 1. Nominal based RF-Survey
2. Blind RF-Survey
In Nominal based RF-Survey planning team gives exact latitude, longitude and
search ring of the location.
In Blind RF-Survey Planning team does not gives the exact location. Engineer has
to find the exact location for the survey.
74. Antenna Height Calculation
For GBT,
1 Km coverage
Antenna ht. = Average Building Ht. + 15 meters
2 Km coverage
Antenna ht. = Average Building Ht. + 15 meters + 5 meters
For RTT/RTP,
1 Km coverage
Antenna ht. = Average Building Ht. + 8 meters
2 Km coverage
Antenna ht. = Average Building Ht. + 8 meters + 5 meters
75. For GBT-
Given- Average Building Height=G+1
Calculate Tower Height for 10km coverage
Solution-
Antenna Height=7+15+(5X9)
=67m
Tower Height=80m
80. 500m Coverage-
Avg BH=G+5
ActBH=G+1
AvgBH=4+(5X3)
=19m
ActBH= 4+3
=7m
AH=AvgBH+8m
=19+8
=27m
10 Downtilt reduces coverage by 200m
20 Downtilt reduces coverage by another 200m
Therefore total 20 downtilt for 500m coverage.
81. In drive test Key Parameter Indicators(KPI) are monitored to check the
performance of the network.
We measure 5 parameters for the performance of the network-
Accessibility- It is defined as if ‘n’ number of people are trying to access the
network, how many out of n users got actual access to the network.
Retainability- Out of total number of users who got access to the network, how
many calls got disconnected by the users is retainability. Users which were
retained in the network.
Mobility- Out of number of users who retained in the network, how many calls
got proper handover without being disconnected.
Integrity-Belief of a network in terms of its throughput.
Availability-Network should be available all the time, most of the sites must be
on-air all the time.
82. 1) Continuous Wave DT- Using omnidirectional antenna path loss is
calculated and number of sites in the particular area with that radius is
calculated using mathematical Okumura Model.
2) Bench Marking- It is useful to analyse other operators coverage area. One
can put 5 SIM and connect them to the laptop with drive test tool installed, we
can measure the signal strength of the surrounding cell site.
3) New Town DT- Checking the function of BTS (new site) includes signal
strength, handover & call quality.
4) Optimization DT- Parametric level optimization & physical level
optimization. Performance of each site KI value is stored in server. According
to that we can change parameter/physical level optimization.
83. 5) Cluster DT- This is an actual dive test in which cell sites are formed into
a group of 20-25 sites.
6) Routine DT-This test contacts on particular time interval its may be 45
days once. Normal DT need to check everything.
7) Pre-DT- Pre-DT going to conduct before changing BTS. It done both in
idle and dedicated mode.
8) Swap DT- Equipment of the existing vendor is swapped with the
equipment of new vendor.
9) Post-DT- Pre-DT is repeated for the new vendor’s equipment.
84. 10) TRAI DT-According to Telecommunication Regulatory Authority of
India it is mandatory that network performance should meet the desired
standard. For that Drive test is done.
11) SCFT/SCVT- Single Cell Functionality Test/ Single Test Verification
Test. SCFT is for verifying whether individual sector works well or not, by
making a single cell function test of BTS hardware and software.
12) IBS/Walk Test- In Building Solution/Walk Test, engineer has to walk
with the laptop in a mall, building, corporate offices to check network
performance.
13) Customer Complaint- This drive test is done if customer complaints are
registered. For e.g., if you are a big user, a booster can be equipped in your
building.
85. For more information:
Visit www.apekshatelecom.com
Contact Person: Mr. Bikas Singh
Contact No.: +91-9535333550
All rights reserved to ATSPL
