The project is about networking and planning. In the first phase of project background knowledge of GSM is gained as 2g technology run over GSM. Its major components, architecture and functioning knowledge is gained. As the project consists of radio waves so one must know about their propagation properties like diffraction, reflection, refraction and scattering of waves. All the information is gathered for the city profiling of Lahore which is the major phase of the project. All the details like population of different areas, boundary marking of urban, sub urban, and open areas are done. The city is divided into different areas according to their population in urban, sub urban, and fields.
The next phase which is the third one estimations and assumptions are done. This is assumed that the new service provider needs vendor and is going to launch its setup in the specific city. And the service provider has selected the most suitable vendor for this project. There are number of users which have to be covered and different problems which are the headache of the vendor not the service provider espically related to the network and planning should be solved by vendor. In the next phase which is fourth one calculations are done with the help of raw data gathered in the previous stage. The number of cells and their radius is calculated of different areas so that the total number of BTS are determined.
Now the fifth phase consists of theoretical coverage and capacity planning of the network. It includes the planning of cells and clusters for practical implementation and the direction of BTS will be selected for particular coverage area. The Okumara-Hata model is used for capacity planning as this is the most accurate one. Path losses and the radius of urban, suburban and open areas are calculated from Okumara-Hata model.
Now the sixth phase consists of frequency planning. Different ranges of frequencies is allocated to different cells by the reuse technique. The capacity factors and the signal to interference ratio have decided the cell and the cluster size. This planning is implemented on the map of Lahore.
Contents
Fundamentals of Cellular Communication 1
Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Shape of a Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1.2 Area of a Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Frequency Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.1 Cluster Size(N) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 Interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3.1 Adjacent Channel Interference . . . . . . . . . . . . . . . . . . 6
1.3.2 Co-channel Interference . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4 Improving Coverage And Capacity . . . . . . . . . . . . . . . . . . . . . . . 6
1.4.1 Cell Spliting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.4.2 Sectoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.4.3 Microcell Zone Concept . . . . . . . . . . . . . . . . . . . . . 9
1.5 Radio wave Propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.5.1 Large Scale Propagation . . . . . . . . . . . . . . . . . . . . . 10
1.5.2 Small Scale Propagation . . . . . . . . . . . . . . . . . . . . . . 10
1.5.3 Free Space Propagation Model . . . . . . . . . . . . . . . . . 10
1.6 Propagation Mechanisms 11
1.6.1 Reflection 11
1.6.2 Diffraction 11
1.6.3 Scattering 12
1.7 Small-Scale Fading 13
2 GSM
3 Profile of a City
4 Site Planning
5 Frequency Planning
Fundamentals of Cellular Communication
In this chapter, all the background knowledge which is required for this project has been discussed.
Cell
The area covered by single BTS(base transceiver station) is known as cell.
Shape of the cell
The shape of the cell depends upon the coverage of the base station. The actuall coverage of the base station is known as footprint and it is found with the help of measurements from the field. We can make our calculations easier by using the shape of circle noting that there would not be spaces between them. As the purpose is to provide coverage to each and every subscriber. But if there are spaces between the coverage areas then the person in that specific area will not be able to get any coverage.
To cover the problem of interleaving spaces, the shapes that can be used theoretically are:
Square
Triangle
Hexagon
Chapter 1. Fundamentals of cellular communication 2
But in selection criteria one thing must be kept in mind that every person within a cell get same coverage specially the person at the edges of the cell. So hexagon is the shape among these three choices with largest coverage area. Its coverage area and shape is closest to the circle and it helps tessellate. Omnidirectional antenna is used in the center of it, and if we want to use sectored directional antenna then it must be used at any three corners of it.
Chapter 1. Fundamentals of cellular communication 3
Area of the Cell
The area of a cell with radius R is shown in figure 1.1(a), is given by:
(1.1)
1.2 Frequency planning
In the development of the cellular system, its capacity is limited due to given bandwidth. So, in order to solve this problem Cellular Systems rely on an intelligent and reuse of channels through out the coverage area. Each cellular base station is allocated a group of radio channels to be used with in a cell. Base station in the adjacent cells use completely different frequencies. For this purpose antennas are used such that their power may get limited within the cell. In this way the allocated frequencies maybe reused in different cells again. The design process of selecting and allocating channel groups for all of the cellular base stations within a system is called frequency reuse or frequency planning.
We use two types of antennas:
Omnidirectional antenna
Sectored directional antenna
Omnidirectional antennas are used in the center excited cells and sector directional antennas are used in the edge excited cells.
To understand the concept of frequency reuse, let us say that S are the total no. of duplex channels available for use, k number of channels given to each cell i.e. k<S, N are the no. of cells in which S channels are divided. So the total number of channels can be expressed as:
S=kN (1.2)
Where N is the no. of cell which uses the complete set of available frequencies known as cluster
frequency reuse factor (1.3)
Each cell is in the cluster is assingned of the available channels.
The radio frequency from 3hz to 3000GHz are separated into 12 bands, as shown in the table. Frequency spectrum has different propagation characteristics. As far as concerned to the mobile communication, we only pay attention to the UHF spectrum.
1.2.1 Cluster size(N)
If we use N large (a larger cluster size), the ratio between the cell radius and
the distance between co-channel cell decreases, which causes weaker co-channel interference. But if N is smaller, by keeping the cell size constant then we need more clusters to coveran area. Hence the capacity is increased. So if we use N larger then the quality of voice is good but the capacityis less and vice versa. How to obtain the balance between the capacity and the voice quality? It is the problem that must be settled by frequency plan. So, the good frequency plan may realize the promotion of the network capacity on the basis of maintain a good voice quality.
Interference
Interference is the major limiting factor in the capacity and performance of the cellular network. The interference is due to a call in the neighbouring cell, another mobile in the same cell, another base station operating in the same frequency. Interference causes crosstalk and noise. There are two types of interference.
Adjacent channel interference
Co-channel interference
1.3.1 Adjacent channel interference
Adjacent channel interference results from the signals which are adjacent in frequencies to the desires signal. Adjacent channel interference may be caused by inadequate filtering, such as incomplete filtering of unwanted modulation products in frequency modulation (FM) systems, improper tuning, or poor frequency control, in either the reference channel or the interfering channel, or both. It causes near-far problem.
Adjacent channel interference may be reduced by careful channel assignment, filtering and power control within a cell.
1.3.2 Co-channel interference
Co-channel cells are the cell which use the same set of frequencies. For example in figure 1.2 all the A's are the co-channel cell because they use the same set of frequencies. Interference due to the co-channel cells is called co-channel interference. It can be reduced by using greater value of N(cluster size). If D is the distance between the co-channel cells and R is the radius of the cell, then by using greater value of N the ratio between D to R is increased hence reducing co-channel interference.
The relation can b written as:
(1.4)
Improving coverage and capacity
The number of channels assingned to a cell became insufficiently as the demand of wireless system increases. To provide more channels per unit coverage, some techniques are introduced which improve the coverage and capacity. These techniques are:
Cell splitting
Sectoring
Microcell zone concept
1.4.1 Cell Splitting
Cell splitting is the process of subdividing a congested cell into smaller cells, each with its own base station. In this process we reduce the antenna height and power of the base station. Cell splitting increases the capacity by increasing frequency reuse factor.
In cell splitting
Channel assignment techniques remain the same.
SIR remains the same
Trunking inefficiency do not get suffer.
Trunking efficiency is the measure of the number of users which can be offered a particular GOS with the particular configuration of the fixed channels.
The grade of service (GOS) is the measure of the ability of a user to access a trunked system during the busiest hour.
The radius of the new cell is reduce to half. So power is also reduced.
1.4.2 Sectoring
Sectoring uses directional antennas to control the interference and frequency reuse of channels. The co-channel interference is reduced and thus increasing system performance by using directional antenna. A cell is normally partitioned into three 120 sectors or six 60°sectors.
When sectoring is used, the channels used in a particular cell are broken into sectored groups and are used only within a particular sector. The no. of channels get divided into sectored groups, so the trunking efficiency is reduced. In sectoring SIR is improved by reducing interference and trunking efficiency is reduced. Handoff increased in sectoring. The s/I improvement allows to decrease the cluster size N in order to improve the frequency reuse, and thus the system capacity. Further improvements in s/I is achieved by downtilting the sector antennas.
1.4.3 Microcell Zone Concept
Microcell Zone concept distributes the coverage of a cell and extends the cell boundry to hard to reach places. It maintains the S/I and trunking efficiency, and increases the coverage and capacity of an area.
Radio wave propagation
Radio waves propagate through different channels and by different ways to reach the MS(Mobile Station). It also depends upon the speed of the wave. The propagation of radio waves depends into two types:
Large scale propagation
Small scale propagation(Fading)
1.5.1 Large scale propagation
The model predicts that the average signal strength for all transmitter-receiver (TR) distance on a scale known as large scale propogation model.
1.5.2 Small scale propagation
The models that predicts the rapid fluctuation of the received signal strength over very short travel distance known as small scale propagation model or fading.
1.5.3 Free Space Propagation Model
The free space propagation model is used when the transmitter and receiver have line of sight (LOS) between them to predict the received signal strength.
Where Pr is the received power. Pt is transmitted power, Gt and Gr are transmitter and receiver antenna gain respectively, do is T-R separation, L is the system loss factor and λ is the wavelength.
Propagation Mechanisms
The propagation mechanisms which effect propagation are:
Reflection
Scattering
Diffraction
Reach directly (in case of Line of Sight)
If there is line of sight signal reach the Mobile station directly and signal power is very strong.
Reflection
Reflection occurs when a propagating electromagnetic wave falls upon an object which is very large as compare to the wavelength of the propagating wave. It occurs from buildings, walls, surface of earth etc.
1.6.2 Diffraction
Diffraction occurs when the path between the transmitter and receiver is obstructed by a surface that has sharp edges. It source is any sharp edge object. Knife edge diffraction Model is used for diffraction.
Scattering
Scattering occurs when a propagating electromagnetic wave falls upon an object which has small dimension as compared to the wavelength of the propagating wave. Scattering occurs due to rough surfaces, small objects or any irregularities. Objects such as lamp posts, trees scatter the radio waves. Radar Cross Section Model is used for sectoring.
1.7 Small Scale Fading
Fading is the fluctuation in the received signal strength over very short distance. Fading is due to reception of different versions of same signals. Following are the factors which influence Small-Scale Fading are:
Multipath propagation:
Due to absence of LOS signal follows the multipath due to reflection, diffraction, scattering.
Speed of the mobile:
Fading also accurs due to the movement of the mobile as the signal strength changes.
Speed of the surrounding objects:
Fading also occurs due to the movement of mobile, if the speed of the surrounding object is much faster then the speed of the mobile then it also induces Doppler shift.
The transmission BW (bandwidth) of the signal:
The received signal is distorted if the transmitted signal bandwidth is greater than the bandwidth of the channel.
Chapter 2
2.1 GSM
The first GSM network was launched in 1991. The GSM network was structured hierarchically. It consists of one administrative region, which is assingned to MSC. Each administrative region is consists of atleast one location area (LA). LA is also called the visited area. An LA consists of several cell groups. Each cell group is assingned to a base station controller (BSC). Cells of one BSC may belong to different LAs. GSM distinguishes explicity between users and identifiers. The user identity is associated with a MS by mans of personal chip cards, the subscriber identity module (SIM). The SIM is portable and transferable MSs. The mobile station Roaming number is a temporary location-dependent ISDN number. It is assingned by a locally responsible Visited Location Number (VLR). The GSM technical specifications define the different entities that from the GSM network by defining their functions and interface requirements. The GSM network can be defined into four main parts.
Mobile station (MS).
Base station Subsystem (BSS).
Network and switching Subsystem (NSS).
Operation and support Subsystem (OSS).
2.1.1 Mobile station
A mobile station consists of two main parts.
The mobile equipment and terminal.
The subscriber identity module (SIM).
2.2.1 THE Terminal
There are different types of terminal distinguished principally by their power and application:
The fixed terminals are the ones installed in cars. Their maximum allowed output power is 20 w.
The GSM portable terminals can be installed in vehicles. Their maximum allowed output power is 8 w.
The hand held terminals have experienced a biggest success depending upon their weight and volume, which are continuously decreasing. These terminals can emit upto 2 w. The evolution of technologies allow to decrease the maximum allowed power to 0.8 w.
2.2.2 SIM
Sim is a smart card that identifies the terminal.
By inserting the sim card into the terminal, the user can have access all the subscribed services.
Without the sim card, the terminal is not operational.
The sim card is protected by four digit personal identification number(PIN).
2.3 The Base Station Subsystem
The BSS connects the Mobile station and NSS. It is incharge of the transmission and reception.
The BSS can b divided into two main parts.
The Base transceiver station (BTS) or base station.
The Base Station Controller(BSC).
2.3.1 The Base Transiver Station
The BTS corresponds to the transceivers and antenna used in each cell of the network.
Tha BTS is usually placed in the center of a cell.
Its transmitting power defines the size of the cell.
Each BTS has between one and sixteen transceivers depending upon the density of users in the cell.
2.4 The Base Station Controller
The BCS controllers the group of BTS and manages their radio resources.
The BCS is incharge of handover, frequency hoping and exchange of radio frequency power level of BTSs.
2.5 The Network and Switching Subsystem
It is to manage the communication between mobile users and other users, such as mobile users, ISDN users, telephony users,etc.
It store the information in data bases about the subscriber and manage their mobility.
2.6 The Mobile Services Switching Center (MSC)
It is the central component of the NSS.
The MSC performs the switching functions of the network.
It also provides connection to other networks.
This is the main architecture of the GSM.
Chapter 3
Profile of a City
One of the important phase of the project in which all the detail information is gathered about different areas and their population including city boundary, market analysis and roads are the key features in these details are city profiling. This phase is divided into different tasks.
Lahore City Map
First is to get the detailed map of the Lahore city, which includes all the aspects related to the project. These are following:-
Area division
Commercial area
Residential area
Dense area
Open area
Water area
Boundaries of City
Boundary Marking
The project "Radio Frequency Planning " is basically the frequency planning of the city, not to its belongings areas. The exact boundary of the city is marked in order to concentrate on the marked area.
Population
Population of the city plays an important role in the frequency planning. It helps a lot in the estimations and assumptions. The population of the city is around 10 million.
Estimations and Assumptions
This part is mainly concerned with the frequency planning. When a new telecommunication company comes in the market, it estimates it users. This estimation is done with respect to the total population of the particular area. The estimations are done to estimate the users on urban, suburban and open areas.
2.5 Area Division
The area division depends upon the percentage of populatin in an area and type of area as it is the important factor in the site as wall as frequency planning. The Lahore city is divided into three major areas.
2.5.1 Urban Area
Urban area is an area which is surrounded by increased density of human- created structures in comparison to the areas surrounding it. This term is at one end of the spectrum of suburban and rural areas.
2.5.2 Sub-Urban Area
Suburban area is inhabited districts located either inside a town or city's outer rim or just outside its official limits.
2.5.3 Open Area
Open area is sparsely settled places away from the influence of large cities. Such areas are distinct from more intensively settled urban and suburban areas, and also from unsettled lands such as outback or wilderness. There are less population as compared to urban and sub-urban areas.
Chapter 4
Site Planning
4.1.1 Urban Area
4.1.2 Sub-Urban Area
HATA Model for Urban Area
= Path loss in Urban Areas. Unit: decibel (dB)
= Height of base station Antenna. Unit: meter (m)
= Height of mobile station Antenna. Unit: meter (m)
= Frequency of Transmission. Unit: megahertz (MHz).
= Distance between the base and mobile stations. Unit: kilometer
To calculate radius of a site of Urban Area
For Downlink
=-75 dBm(this power covers both indoor and outdoor coverage range -70 to -90 dBm )
= 35 m(Average height of antenna in city is 30 to 200 m)
= 1.5 m
= 13 dBm
= 46 dBm (Max Power transmitted by Base Station)
= Cable loss = 2.01 dBm
= 945 Mhz (Downlink frequency 935 to 960 MHz)
= Combine Loss= 5.5 dBm
Putting in HATA equation
For Uplink
= -102 dbm(Min Power received by Base Station)
= 29.1 dBm (Max transmitted power mobile)
= 900 MHz (890 to 915 MHz)
Putting in HATA equation
We will be using d=0.90 Km as it covers both Uplink and Downlink.
For Sub-Urban Area
For Downlink
For downlink of Suburban parameters are same as for Urban.
For Uplink
Uplink parameters are also same as Urban Areas
We will be using d=2.32 Km for Suburban Area.
For Open Areas
Downlink
For downlink parameters are same as Urban Areas
For Uplink
We will be using d=8 for Open Areas.
We will be using 65 degree directional Antennas.
Angle between 2 consecutive lobes is 120 degree.
r=Radius of lobes
For Full Lobe
For All 3 Lobes
Area of site in Urban
Area of site in Suburban
Area of site in Fields(Open Area)
Chapter 5
Frequency Planning
One of the major breakthrough solving the problem of spectral congestion and user capacity is the cellular concept. Cellular radio systems rely on reuse of channels throughout a coverage region. A group of radio channels are allocated to each cellular base station to be used within a area known as cell. Different channels are assingned in the adjacent cells of the base station. The same group of channels can be used by limiting the coverage area, within the boundaries of a cell to cover different levels, within tolerable limits. Frequency planning is the design process of selecting, allocating or assinging channel group stations within a system.
The theoretical calculations, and fixed size of a cell is assumed, that can differentiate no of channels in a cell and from that can differentiate cluster size and will differ, the capacity of the cellular system. There is a trade-off between the interference abd capacity in theoretical calculation as if we reduce the cluster size more cells are needed to cover the area and more capacity. But from another perceptive small cluster size causes the ratio between cell radius, and the distance between co-channels cells to increase, leading to stronger co-channels interference.
In practical calculations, a fixed no of channels are allocated to a cell. One channel per lobe 3channels are allocated to a cell. The capacity can be increased by allocating 2 channels per lobe or 6 channels per cell. But after allocating channels once, they will remain fixed for the whole cellular system and frequency planning.
Now as with the fixed no of channels as per cell, the capacity will remain constant of the system and we can achieve weaker co-channel interference, by having a small cluster size(N). A cluster size of 7 is selected in this project, which is also discussed. So in later practical world , there is not a trade-off between capacity and co-channel interference.
5.2.2 How to Locate Co-Channel Cell
Starting with any cell as a reference, we can find the nearest "co-channel" cells, that is, those cells that uses the same channel set, as follows:
Move I cells along any chain of hexagons, turn it counter-clockwise 60 degrees, move j cells along the chain that lies on this new heading. So that the jth cell and the reference cell are co-channel cells. Now return to the reference cell and set forth along a different chain of hexagons using the same procedure.
