This document discusses wireless communication and GSM networks. It provides an overview of multiple access techniques used in wireless networks like TDMA, FDMA, and CDMA. It then describes the development and standards of GSM networks and how they were created to provide a digital cellular standard across Europe to resolve issues with different analog 1G systems. Finally, it summarizes the call setup process in a GSM network for a mobile terminated call, including analyzing the number, interrogating the HLR and MSC/VLR, generating a temporary MSRN, and initiating paging to locate the called subscriber.

1. ABSTRACT
This report is based on the study of wireless communication.
Wireless communication provides mobility. TDMA, FDMA, CDMA are the various multiple access techniques. There are several
network generations which evolved during the years.
The development of GSM started in 1982, when the Conference of European Posts and Telegraphs (CEPT) formed a study group
called Groupe Spécial Mobile (the initial meaning of GSM). The group was to study and develop a pan-European public cellular
system in the 900 MHz range, using spectrum that had been previously allocated.
GSM, the Global System for Mobile communications, is a digital cellular communications system which has rapidly gained
acceptance and market share worldwide, although it was initially developed in a European context. In addition to digital transmission,
GSM incorporates many advanced services and features, including ISDN compatibility and worldwide roaming in other GSM
networks. The advanced services and architecture of GSM have made it a model for future third-generation cellular systems, such as
UMTS.
The objective to develop this 2G standard is to resolve the roaming problem in the six existing different 1G analog cellular systems in
Europe. The global system for mobile communications (GSM) is a set of recommendations and specifications for a digital cellular
telephone network. These recommendations ensure the compatibility of equipment from different GSM manufacturers, and
interconnectivity between different administrations, including operations across international boundaries.In 1982, frequency bands of
890-915 MHz and 935-960 MHz were allocated for Pan European Public land Mobile Network (PLMN), and GSM was formed.
1

2. Chapter 1
INTRODUCTION
Why Wireless Communication?
The popularity of wireless communication is due to the fact that it provides mobility. Mobility can be of two types:-
 User Mobility: In this the user is mobile but not the devices. This means that user is not accessing the same
telecommunication service all the time in motion. Example, a user is accessing the internet using his same account from
different locations.
 Device portability: In this the device moves. This means that user is accessing the telecommunication services all the time in
motion. Example, a mobile phone system.
All the communication devices exhibit one of the following:
Fixed and wired: Device is fixed and communication medium is wired. Example, typical desktop computer.
Fixed and wireless: Device is fixed but communication medium is wireless. Example, desktop computers with wireless
connections.
Mobile and wired: Device is mobile but communication medium is wired. Example, laptops.
Mobile and wireless: Device is mobile and communication medium is wireless. Example, mobile phone systems.
2

3. 1.1 HISTORY OF WIRELESS COMMUNICATION
The origin of mobile communication followed quickly behind the invention of radio in the late 1880s. The first application of mobile
radio was related to the navigation and safety of ships at sea. As radio concepts developed so did its use as a communication tool.
Frequency Division Multiple Access
Each Frequency Division Multiple Access (FDMA) subscriber is using the same medium (air) for communicating but they are assigned a specific
frequency channel. While they are using the frequency channel, no one else in that cell or neighboring cell can use the frequency channel. In
current analog cell systems, each channel is 30 kHz. When a FDMA cell phone establishes a call, it reserves the frequency channel for the entire
duration of the call. The voice data is modulated into this channel’s frequency band (using frequency modulation) and sent over the airwaves. At
the receiver, the information is recovered using a band-pass filter. The phone uses a common digital control channel to acquire channels.
FDMA systems are the least efficient cellular system since each analog channel can only be used by one user at a time. Not only are these channels
larger than necessary given modern digital voice compression, but they are also wasted whenever there is silence during the cell phone
conversation. Analog signals are also especially susceptible to noise – and there is no way to filter it out. Given the nature of the signal, analog cell
phones must use higher power (between 1 and 3 watts) to get acceptable call quality. Given these shortcomings, it is easy to see why FDMA is
being replaced by newer digital techniques.
Time Division Multiple Access
Time Division Multiple Access (TDMA) subscribers share a common frequency channel but use the channel only for a short time.
They are each given a time slot and allowed to transmit only during that time slot. When all the available time slots in a given
frequency are used the next user must be assigned to a time slot on another frequency.
3

4. TDMA builds on FDMA by dividing conversations by frequency and time. Since digital compression allows voice to be sent at well
under 10 kilobits per second (equivalent to 10 kHz), TDMA fits three digital conversations into a FDMA channel (this is 30 kHz).
Code Division Multiple Access
Code Division Multiple Access (CDMA) subscribers share a common frequency channel. All users are on the same frequency at the
same time, they are divided however by codes. CDMA systems have no channels, but instead encode each call as a coded sequence
across the entire frequency spectrum. Each conversation is modulated, in the digital domain, with a unique code (called a pseudo-noise
code) that makes it distinguishable from the other calls in the frequency spectrum. Theoretically CDMA provides many times the
channel capacity of TDMA. Proponents of CDMA also claim that there are fewer dropped calls when crossing cell boundaries.
4

5. Chapter 2
GSM NETWORK CONCEPT
The Global System for Mobile Communications (GSM) is a set of recommendations and specifications for a digital cellular
telephone network (known as a Public Land Mobile Network, or PLMN) GSM networks are digital and can cater for high system
capacities
They are consistent with the world-wide digitization of the telephone network, and are an extension of the Integrated Services
Digital Network (ISDN), using a digital radio interface between the cellular network and the mobile subscriber equipment.
GSM FREQUENCIES
GSM systems use radio frequencies between 890-915 MHz for receiveand between 935-960 MHz for transmit.
RF carriers are spaced every 200 kHz, allowing a total of 124 carriers for use.
An RF carrier is a pair of radio frequencies, one used in each direction.
Transmit and receive frequencies are always separated by 45 MHz.
5

6. Extended GSM (EGSM)
EGSM has 10MHz of bandwidth on both transmit and receive.
Receive bandwidth is from 880 MHz to 890 MHz.
Transmit bandwidth is from 925 MHz to 935 MHz.
Total RF carriers in EGSM is 50.
Figure 2.1 Uplink and downlink
6

7. 2.1 Channel Concept
Figure 2.2 Channel Concept
7

8. 2.1.1 Signaling Channel
These are the main types of signaling Channels:
Broadcast Channels (BCH) - Transmitted by the BTS to the MS. This channel carries system parameters needed to identify the
network, synchronize time and frequency with the network, and gain access to the network.
Common Control Channels (CCH) - Used for signaling between the BTS and the MS and to request and grant access to the
network.
Standalone Dedicated Control Channels (SDCCH) - Used for call setup.
Associated Control Channels (ACCH) - Used for signaling associated with calls and call-setup. An ACCH is always allocated in
conjunction with a TCH or SDCCH.The above categories can be divided into the following logical channels:
Broadcast Channels (BCH)
Broadcast Control Channel (BCCH)
Frequency Correction Channel (FCCH)
Synchronization Channel (SCH)
Cell Broadcast Channel (CBCH)
Common Control Channels (CCCH)
Paging Channel (PCH)
Random Access Channel (RACH)
Access Grant Channel (AGCH)
8

9. Dedicated Control Channel (DCCH)
Standalone Dedicated Control Channel (SDCCH)
Fast Associated Control Channel (FACCH)
Slow Associated Control Channel (SACCH)
Figure 2.3 Downlink
Figure 2.3 Uplink
2.1.2 Traffic Channel
Traffic Channels are used to carry two types of information to and from the user:
Encoded Speech
Data
9

10. There are two basic types of Encoded Speech channel
Encoded Speech - Encoded speech is voice audio that is converted into digital form and compressed.
Full Rate Speech TCH (TCH/FS) - 13 kb/s
Half Rate Speech TCH (TCH/HS) - 5.6 kb/s
Data - Data refers to user data such as text messages, picture messages, internet browsing, etc. It includes pretty much everything
except speech.
Full rate Data TCH (TCH/F14.1) - 14.4 kb/s
Full rate Data TCH (TCH/F9.6) - 9.6 kb/s
Full rate Data TCH (TCH/F4.8) - 4.8 kb/s
Half rate Data TCH (TCH/F4.8) - 4.8 kb/s
Full rate Data TCH (TCH/F2.4) - ≤2.4 kb/s
Half rate Data TCH (TCH/H2.4) - ≤2.4 kb/s
Figure 2.4: Full Rate Traffic Channel (TCH/FS)
10

11. Figure 2.5: Half Rate Traffic Channel (TCH/HS)
2.2 Frequency Hopping
There are two types of frequency hopping method available for the BTS: synthesizer hopping and baseband hopping.
Synthesizer Hopping - This requires the TRX itself to change frequencies according to the hopping sequence. So, one TRX would
hop between multiple frequencies on the same sequence that the MS is required to.
Baseband Hopping - In this method there are several TRX and each one stays on a fixed frequency within the hopping frequency
plan. Each TRX would be assigned a single time slot within a TDMA frame. For example, time slot 1 might be assigned to TRX 2 in
one TDMA frame and in the next TDMA frame it would be assigned to TRX 3, and the next frame would be TRX 3. So, the data on
each time slot would be sent on a different frequency each frame, but the TRXs on the BTS do not need to change frequency. The
BTS simply routes the data to the appropriate TRX, and the MS knows which TRX to be on for any given TDMA frame.
11

12. GSM ARCHITECTURE
2.3 Base Station Subsystem (BSS)
To understand the paging process, we must analyse the functions of the BSS.
The Base Station Subsystem consists of the following elements:
 BSC Base Station Controller
 BTS Base Transceiver Station
 TC Transcoder
The Base Station Controller (BSC) is the central network element of the BSS and it controls the radio network. This means that the
main responsibilities of the BSC are: Connection establishment between MS and NSS, Mobility management, Statistical raw data
collection, Air and A interface signalling support.
12

13. Figure 2.7: GSM Architecture
The Base Transceiver Station (BTS) is a network element maintaining the Air interface. It takes care of Air interface signalling, Air
interface ciphering and speech processing. In this context, speech processing refers to all the functions the BTS performs in order to
guarantee an error-free connection between the MS and the BTS.
The TransCoder (TC) is a BSS element taking care of speech transcoding, i.e. it is capable of converting speech from one digital
coding format to another and vice versa. We will describe more about the transcoder functions later.
13

14. BSC
TC
BTS BSC
TC
BTS
BTS
Figure2.8: The Base Station Subsystem(BSS)
The BTS, BSC and TC together form the Base Station Subsystem (BSS) which is a part of the GSM network taking care of the
following major functions:
Radio Path Control
In the GSM network, the Base Station Subsystem (BSS) is the part of the network taking care of Radio Resources, i.e. radio channel
allocation and quality of the radio connection. For this purpose, the GSM Technical Specifications define about 120 different
parameters for each BTS. These parameters define exactly what kind of BTS is in question and how MSs may "see" the network when
moving in this BTS area. The BTS parameters handle the following major items: what kind of handovers (when and why), paging
organization, radio power level control and BTS identification.
14

15. BTS and TC Control
Inside the BSS, all the BTSs and TCs are connected to the BSC(s). The BSC maintains the BTSs. In other words, the BSC is capable
of separating (barring) a BTS from the network and collecting alarm information. Transcoders are also maintained by the BSC, i.e. the
BSC collects alarms related to the Transcoders.
Synchronization
The BSS uses hierarchical synchronization which means that the MSC synchronizes the BSC and the BSC further synchronizes the
BTSs associated with that particular BSC. Inside the BSS, synchronization is controlled by the BSC. Synchronization is a critical issue
in the GSM network due to the nature of the information transferred. If the synchronization chain is not working correctly, calls may
be cut or the call quality may not be the best possible. Ultimately, it may even be impossible to establish a call.
Connection Establishment between MS and NSS
The BSS is located between two interfaces, the Air and the A interface. From the call establishment point of view, the MS must have
a connection through these two interfaces before a call can be established.
Collection of Statistical Data
The BSS collects a lot of short-term statistical data that is further sent to the NMS for post processing purposes. By using the tools
located in the NMS the operator is able to create statistical "views" and thus observe the network quality.
15

16. A Base Station Subsystem is controlled by an MSC. Typically, one MSC contains several BSSs. A BSS itself may cover a
considerably large geographical area consisting of many cells. (A cell refers to an area covered by one or more frequency resources).
Each cell is identified by an identification number called Cell Global Identity (CGI) which comprises the following elements:
CGI = MCC + MNC + LAC + CI
MCC Mobile Country Code
MNC Mobile Network Code
LAC Location Area Code
CI Cell Identity
There is one 2Mbit/s PCM line reserved for each BTS to provide the connection to NSS. But as you can see, the BTS’s are used at
different times and on different days. Why not use the same line for both of the two BTSs? It can be done, but in this case there has to
be a concentrator between MSC and BTS. The BSC acts as a concentrator (in addition to being the radio network controller). One
BSC is capable of serving several BTSs.
16

17. Chapter 3
Call Setup
3.1 A Mobile Terminated Call and Paging
A- GM SC HLR M S C /V L R
PSTN
S u b s c r ib e r
C A L L S E T U P (M S IS D N )
ANALYSE NUM BER
C A L L S E T U P (M S IS D N )
M S IS D N
IM S I
M SRN
M SRN
C A L L S E T U P (M S R N )
P A G IN G
Figure 3.1 : Simplified steps in setting up a call
17

18. L o ca tio n A re a
P a g in g
P a g in g
BTS BTS
M o b ile re s p o n d s
P a g in g
to p a g in g
BTS
Figure 3.2. The Paging Process
1. A subscriber in a fixed network dials a number of a mobile phone. The dialled number is the MSISDN.
2. The Public Switched Telephone Network (PSTN) exchange analyses the number and contacts the Gateway Mobile Services
Switching Centre (GMSC).
3. The Gateway MSC analyses the MSISDN and sends a message to the Home Location Register (HLR).
4. The HLR checks its database to determine the current location of the called subscriber.
5. The HLR interrogates the MSC/VLR (Visitor Location Register) that is currently serving the called subscriber.
6. The serving MSC/VLR generates a temporary MSRN (Mobile Subscriber Roaming Number).
18

19. 7. MSC/VLR sends MSRN to HLR and the HLR forwards the MSRN to the GMSC.
8. The GMSC identifies the serving MSC/VLR as the destination for routing the call.
9. Destination MSC/VLR receives MSRN. It identifies the number that is called and traces the called subscriber.
The destination MSC/VLR initiates a paging process in the Location Area to locate the called subscriber. The mobile phone of the
called subscriber recognises the paging signal and answers it
EXC GM SC HLR M SC VLR BSS MS
1 . c h a n n e l a s s ig n m e n t
2 . s e c u rity p ro c e d u re s
3 . c a ll s e tu p
4 . c h e c k s e rv ic e s e tc .
5 . a ll o k
6 . c a ll is p ro c e e d in g
7 . tra ffic c h a n n e l a llo c a te d
8 . s e t u p th e c a ll
9 . c a ll s e t u p c o m p le te
1 0 . a le rt
1 1 . B a n s w e rs
Figure 3.3 : Mobile Originated Call Procedure
19

20. 3.2 Location Update
Types of Location Update
In practice, there are three types of location updates:
1. Location Registration (power on)
2. Generic
3. Periodic
Location registration takes place when a mobile station is turned on. This is also known as IMSI Attach because as soon as the
mobile station is switched on it informs the Visitor Location Register (VLR) that it is now back in service and is able to receive calls.
As a result of a successful registration, the network sends the mobile station two numbers that are stored in the SIM (Subscriber
Identity Module) card of the mobile station.
These two numbers are the Location Area Identity (LAI) and the Temporary Mobile Subscriber Identity (TMSI). The network, via
the control channels of the air interface, sends the LAI. The TMSI is used for security purposes, so that the IMSI of a subscriber does
not have to be transmitted over the air interface. The TMSI is a temporary identity, which regularly gets changed.
A Location Area Identity (LAI) is a globally unique number.
A Location Area Code (LAC) is only unique in a particular network.
20

21. MSC
VLR
LA 2
LA 1
Figure 3.4 : Location Update
Every time the mobile receives data through the control channels, it reads the LAI and compares it with the LAI stored in its SIM card.
A generic location update is performed if they are different. The mobile starts a Location Update process by accessing the
MSC/VLR that sent the location data .A channel request message is sent that contains the subscriber identity (i.e. IMSI/TMSI) and
the LAI stored in the SIM card. When the target MSC/VLR receives the request, it reads the old LAI which identifies the MSC/VLR
that has served the mobile phone up to this point. A signalling connection is established between the two MSC/VLRs and the
subscriber’s IMSI is transferred from the old MSC to the new MSC. Using this IMSI, the new MSC requests the subscriber data from
the HLR and then updates the VLR and HLR after successful authentication.
21

22. MS BSS M SC VLR new V L R o ld HLR
1 . c h a n n e l a s s ig n m e n t
2 . lo c a tio n u p d a te re q u e s t
3 . re q u e s t s u b s c rib e r id e n tity
4 . re q u e s t s u b s c rib e r id e n tity
5 . re q u e s t s u b s c rib e r d a ta
6 . re q u e s t s u b s c rib e r d a ta
7 . s e c u rity p ro c e d u re s
8 . u p d a te lo c a tio n
9 . u p d a te H L R
1 0 . u p d a te a c k n o w le d g e m e n t
1 1 . c a n c e l o ld lo c a tio n
1 2 . lo c a tio n c a n c e llin g a c c e p te d
Figure 3.5: location update procedure
3.3 Handover
In a mobile communications network, the subscriber can move around. How can we maintain the connection in such cases? To
understand this, we must study the process of handing over the calls.Maintaining the traffic connection with a moving subscriber is
made possible with the help of the handover function. The basic concept is simple: when the subscriber moves from the coverage area
of one cell to another, a new connection with the target cell has to be set up and the connection with the old cell has to be released.
There are two reasons for performing a handover:
22

23. 1. Handover due to measurements occurs when the quality or the strength of the radio signal falls below certain parameters
specified in the BSC. The deterioration of the signal is detected by the constant signal measurements carried out by both the
mobile station and the BTS. As a consequence, the connection is handed over to a cell with a stronger signal.
2. Handover due to traffic reasons occurs when the traffic capacity of a cell has reached its maximum or is approaching it. In
such a case, the mobile stations near the edges of the cell may be handed over to neighbouring cells with less traffic load.
The decision to perform a handover is always made by the BSC that is currently serving the subscriber, except for the handover for
traffic reasons. In the latter case the MSC makes the decision. There are four different types of handover and the best way to analyze
them is to follow the subscriber as he moves:
Intra cell - Intra BSC handoverThe smallest of the handovers is the intra cell handover where the subscriber is handed over to
another traffic channel (generally in another frequency) within the same cell. In this case the BSC controlling the cell makes the
decision to perform hanover.
23

24. Air A
BSC TC
BTS
el
hann
O ld C
n el
Ch an
N ew
Figure: 3.6 Intra Cell - Intra BSC Handover
Inter cell - Intra BSC handover
The subscriber moves from cell 1 to cell 2. In this case the handover process is controlled by BSC. The traffic connection with cell 1 is
released when the connection with cell 2 is set up successfully.
24

25. A ir A
BTS B SC TC
BTS
O ld C ell / B TS N ew C ell / B TS
Figure 3.7: Inter Cell - Intra BSC handover
Inter cell - Inter BSC handover
The subscriber moves from cell 2 to cell 3, which is served by another BSC. In this case the handover process is carried out by the
MSC, but, the decision to make the handover is still done by the first BSC. The connection with the first BSC (and BTS) is released
when the connection with the new BSC (and BTS) is set up successfully.
25

26. N ew C ell / B T S
A ir A
B SC TC
B TS
M SC VL R
B SC TC
B TS
Old C ell / B TS
Figure3.8: InterCell-InterBSCHandover
Inter MSC handover
The subscriber moves from a cell controlled by one MSC/VLR to a cell in the domain of another MSC/VLR. This case is a bit more
complicated. Considering that the first MSC/VLR is connected to the GMSC via a link that passes through PSTN lines, it is evident
that the second MSC/VLR can not take over the first one just like that.
The MSC/VLR currently serving the subscriber (also known as the anchor MSC), contacts the target MSC/VLR and the traffic
connection is transferred to the target MSC/VLR. As both MSCs are part of the same network, the connection is established smoothly.
26

27. It is important to notice, however, that the target MSC and the source MSC are two telephone exchanges. The call can be transferred
between two exchanges only if there is a telephone number identifying the target MSC.
N ew C ell / B T S
A ir A
B SC TC
B TS
M SC VL R
B SC TC
B TS
M SC VLR
Old C ell / B TS
Fig 3.9: Inter Cell - Inter MSC Handover
Such a situation makes it necessary to generate a new number, the Handover Number (HON). The generation and function of the
HON are explained in the following text.
The anchor MSC/VLR receives the handover information from the BSS. It recognises that the destination is within the domain of
another MSC and sends a Handover Request to the target MSC via the signaling network. The target MSC answers by generating a
HON and sends it to the anchor MSC/VLR, which performs a digit analysis in order to obtain the necessary routing information.
27

28. This information allows the serving MSC/VLR to connect the target MSC/VLR. When the two MSCs are connected, the call is
transferred to a new route.
In practice, the handover number is similar to the roaming number. Moreover, the roaming number and the handover number have a
similar purpose, that is connecting two MSCs. The structure of the handover number is shown below:
HON = CC + NDC + SN
 CC= Country Code
 NDC= National Destination Code (of the serving network)
 SN= Subscriber Number
The call will not last forever and the connection has to be released sooner or later. To understand the process of releasing the
connection, we must consider a few things such as: Who pays for the call, which exchange takes care of the charging operation and
where is the subscriber data stored.
28

29. Chapter 4
RF PLANNING
4.1 Objective
The overall objectives of any RF Design depend on a number of factors that are determined by the needs and expectations of the
operator, the resources made available by the operator, any service levels determined by the contract between operator and Vendor but
only as they affect the RF Design, and the resources that are available at the Technical Centre or Business Unit that is responsible for
the RF Design.
Generally speaking the RF Design should satisfy the following criteria:-
Maximizing coverage
Providing sufficient capacity
Providing an acceptable quality of service
Minimizing cost
29

30. 4.2 RF Design
The RF design engineer for that particular region would then decide the type of antenna to be used, the antenna height above ground
level, Frequency Re Use pattern; the antenna orientation, the antenna mechanical or electrical down tilt if required and the base station
maximum transmit power. RF Design includes the following:
Antenna Selection
LAC Design
Grid Design
Morphology Definition
Link Budget
Frequency Re Use Technique
30

31. The Cell Planning Process
System Growth Traffic Analysis
System Tuning Nominal Cell Plan
System Installation Coverage & Interference
Prediction
31

32. Cell planning begins with traffic and coverage analysis. The analysis should produce information about the geographical area and the
expected capacity (traffic load). The types of data collected are:
Cost
Capacity
Coverage
Grade Of Service (GOS)
Available frequencies
Speech quality
System growth capability
The basis for all cell planning is the traffic demand, i.e. how many subscribers use the network and how much traffic they generate.
The Erlang (E) is a unit of measurement of traffic intensity.
32

33. It can be calculated with the following formula:
A = n x T / 3600 Erlang
Where,
A = offered traffic from one or more users in the system
n = number of calls per hour
T = average call time in seconds
The geographical distribution of traffic demand can be calculated by the use of demographic data such as:
Population distribution
Car usage distribution
Income level distribution
Land usage data
Telephone usage statistics
Other factors, like subscription/call charge and price of MSs
33

34. 4.3 RF Drive Test
Every good RF design, after its implantation should be evaluated. There are few ways to do this, for example through analysis of KPI
(Key Performance Indicator) or through prediction tools and signal interference. Other very common and efficient way to evaluate the
network is conducting a Drive Test. But what is it?
The name is intuitive: take a drive test. The Drive Test is a test performed in cellular networks regardless of technology (GSM,
CDMA, UMTS, LTE, etc. ...). Means collecting data on vehicle movement. Its variation has also intuitive: Walk Test, ie, collect data
by walking areas of interest.
The analysis of drive test is fundamental for the work of any professional in the field of IT and Telecom comprising two phases: data
collection and data analysis.
34

35. Figure 4.1 : Drive Test Setup
Types of Drive Test
The main types of Drive Test are :
Performance Analysis
Integration of New Sites and change parameters of Existing Sites
Marketing
35

36. Benchmarking
36

37. Figure 4.2 : Drive Test Result
37

38. Chapter 5
TRANSMISSION AND PLANNING
5.1 Introduction
The propagation of radio waves is generally affected by several factors, irrespective of the radio communication service or the
specified purpose of telecommunication. These factors are described below.
5.2 Propagation Mechanisms
Depending on topography and meteorological conditions,radio wave can be propagated in different ways,normally,but not
always,causing attenuation.One of the main tasks of radio engineering is to evaluate the attenuation of radio signals between
transmitters and receivers.
In order to do this,it is helpful to categorize propagation mechanisms:
Free Space Propagation
Refraction
Diffraction
Reflection and Scattering
38

39. Absorption
Line Of Sight
The earth atmosphere influences the propagation of radion waves in different ways.The radio waves travel with different
velocities in different parts of the atmosphere,due to the variations in the electrical characteristics,which cause refaction.
Due to the atmospheric refraction the radio waves are usually bent slightly downwards,which allows a somewhat longer path
length than the straight line With the bending effect in mind it is customary to speak about a radio optic line of sight,rather than a
geometricalline of sight.Under normal conditions the radio optic line of sight reaches further than a geometrical line of sight.
The standard atmosphere and the other atmospheric conditions affecting the refraction factor and which occurs at a given site is
described by the earth radius factor k.The k value depending on the climatic conditions is 4/3 when applied to a standard
atmosphere.
Figure:5.1 : Line of Sight
39

40. The First Fresnel Zone
The radio optical Earth radius can be described using the effective Earth radius factor.
Clearance
Even if free line of sight is available on the entire path,close-by obstacles might have an attenuating effect if they ae loacated close
enough to the path .It is customary to define a fresnel zone around the centerline of the path.the first Fresnel zone is defined as azone
sshaped as an eellipsoid with its focal points at the antennas on both ends of the path.The fresnel zone decreases with increasing
frequency.
Provided that there is no obstacle within the first Fresnel zone the obstacle attenuation can be ignored,the clearance requirement is
satisfied .
40

41. Figure:5.2:The first Fresnel zone
5.3 Path Profiles
The purpose of the path profile is to provide information concerning free line of sight between the selected station sites, and to decide
whether there is sufficient clearance to avoid obstacle attenuation.The path profile will also be used when determining the fading of
the received signal.
The path profile is essentially a plot of the elevation of the arth as a function of the distance along the path between the transmitting
and receiving sites.The data is derived by locating the two terminals on an elevation contour map,drawing a straight linebetween the
two points,and reading the elevation contours at suitable distance intervals.
The topographical information used to design a path profile can also be derived from topographical map databases,which include an
altitude databse and a land use database.
41

42. 5.4 Path and Site Survey
During the planning microwave radio link paths it is often necessary to closely survey the intended Hop on the location in order to
evaluate the Obstacles by sight.Also the intended site and antenna carrier site should bechecked concerning space,power availability
and strength.The following checked list covers the important items to be investigated.
The geometrical position of the intended site.
The antenna carrier height above groun level.
The antenna carrier type,strength and torsion strength.
The site altitude above mean sea level.
The possibility of installing antennas required height.
All obstacles in path directions,including their heights and widths.
Potential reflecting surfaces.
The radio environment.other radio installations or interfering signals.
The distance between indoor and outdoor equipment.
The main power availability.
The battery backup possibilities.
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43. The possibilities to install antenna feeders or multi-conductors cables between indoor and outdoor equipment regarding
available space,grounding,wall entrance,bending radii etc.
For new sites,access to roads and to power transformer stations must be considered.
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44. REFERENCE
Study training material at Vodafone,Ranchi
www.google.com
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