Notes for Antenna Installation:
A. Installation environment
-->The installation environment includes the surroundings near the antenna and near the base station. The surroundings near the antenna mainly consider the isolation between antennas, and the influence of iron towers and buildings on antennas; the surroundings near the base station mainly consider the influence of high buildings lower than 500 meters along the radio signal transmission.
- During the installation of base station antennas, it is required to notice whether they may lead to big shadow in the coverage area, and to kept away from obstacle, for example, in the installation of antennas on the top of a building, you should make sure no obstacle against radio signal on the top, and try to install the antennas near the edge.
B. Antenna Isolation
--> The receiver and transmitter of the base station shall be isolated in a certain degree;
--> Isolation between antennas: The attenuation of signals from one port of an antenna to that of the other one in actual installation of antenna;
--> GSM system: The isolation between two transmitting antennas and between the transmitting and receiving antennas shall be 30dB at least;
- Antenna vertical layout: Lv=28+40log(k/λ)(dB) about 50cm (900Mhz)
- Antenna horizontal layout: Lv=22+20log(d/λ)-(G1+G2)-(S1+S2)(dB)
About 10 * wavelength (900Mhz)
C. Meet the distance requirements for space diversity gain
--> For space diversity, the distance between two receiving antennas is required to be 12～18λ;
--> The higher the antenna is installed, the bigger the horizontal distance between diversity antennas is; normally, the diversity horizontal distance shall be equal 0.11 time of the effective height of the antenna;
--> To reduce the inter influence of two antennas, the diversity antenna horizontal distance at any effective height of antenna shall be over 3m.
X.Cell layer design
Umbrella Cell :
1)BTS stationed at height that is generally higher than the average building height. Within coverage area, the umbrella cell include several macro-cells.
2)The frequency utilization at the umbrella cell is lesser.
3)Usually, umbrella cell is provided at urban area where there are uplifted bridges and light rails. Along this uplifted bridges and light rails, the mobile can travel at high speed.
4)In a middle sized city where there are many high buildings, umbrella cells are also utilized.
5)Umbrella cells can provide coverage solution for high-rised building and frequency interference.
Macro cell :
The antenna is mounted slightly above the average height of the buildings. Coverage area of the antenna is usually several streets consisting of several BTSs.
2)Carry the network’s core traffic intensity.
3)The suggested distance between the BTSs should not be smaller than 0.4 km.
Micro cell :
1)The antenna is mounted at the level lower than the average building height.
2)Antenna is usually mounted at the ground floor of the building wall or in the interior of the building.
3)Coverage area is usually : one street long OR part of the street OR in the interior of the building.
4)The utilization of the frequencies is rather high.
5)Micro cell is used to cover the blind spot area among the macro cells and carry the traffic at the hot spot area.
XI.Capability planning
- Traffic model
-> Grade of service GOS、average traffic per subscriber during busy hour( erlang )、subscriber density
- BTS total amount
-> Total coverage area、coverage area/ BTS
- Channel configuration
- Proportion of cortrol and traffic channels /cell
Prediction of mobile capacity can be done through the following criterion :
Base on the analysis of the traffic of fixed network.
2)Base on the speed of the increase of mobile subscribers.
Analysis of subscriber density can be done through the following criterion :
Business area.
2)Important governmental department.
3)Airport, bus – stop.
4)Office area and residential area.
Note :
1)Base on the amount of traffic intensity, the configuration of the BTS ‘s TCH and SDCCH can be derived.
2)Coverage planning and capacity planning can be analyzed together.
3)A change in the coverage area will effect the load of the cell.
4)Hot spot area ‘s traffic should be considered and capacity planned carefully.
5) Frequency reuse can be utilized for capacity planning.
XII.Site survey
- Determining an ideal position of Base Station site
- Survey for determined station site.
- Decision of parameter design.
Steps involved in the BTS site survey :
1)Firstly, we considered the ideal position of the BTS.
2)As according to the position of the BTS, we do a drive test.
3)Either through rental or purchase, confirm whether we can have the designated position for the BTS’s location.
4)Confirm whether the basic requirements ( power supply, transmission lines and wireless propagation ) can be met.
5)Draw up the BTS engineering drawings ( BTS floor plan, and antenna position ).
When the BTS’s site survey has been completed, the basic cell planning is completed.
1.Base site survey preparation
Gathering information from site survey
- Population distribution
- Traffic Distribution
- Major Streets
- City Structure
- Local Customs
- Mountains , Coastline
2.Base station survey——site selection(1)
Principle for Selection of Base Station
Criterions of BTS site selection:
The distance difference between the final location and the ideal location of the BTS should not be more than one quarter of the BTS coverage area’s radius.
2)Under no effect of the designated location of the BTS, try to reuse the existing resources ( antenna tower, transmission line and power supply ). In this way, the capital investment and construction time can be cut down.
3)It is recommended not to install BTSs at the border of the urban area, sub-urban area and high hill ( 200 to 300 m above sea level ). This is done for ease of controlling the coverage area and cut down the difficulty of engineering work. In addition, maintenance work is more easier.
4)The location of new BTS should be chosen at places where good transport accessibility, good power line accessibility and good environmental safety and good space saving are achieved.
5)Avoid choosing locations where there are others high power transmitters, high power radars and others interference sources.
6)Avoid locating the BTS near to the bushes of tree where it will cause fast fading.
7)Take note of the reflections and diffractions when the location of the BTS is located near to the lake and metallic building material.
8)When BTS location is situated within the urban area, locations of BTS can be located at the different levels of the building so as to materialize the multi-layer cell structure.
9)At the initial network construction, it is important that the coverage area include important areas.
3. Base station survey——site selection(2)
How to choose Base Station Site.
a. Condition
Try to locate the base station at an ideal position as according to the propagation model.
b.contain
Strong inference equipment 、tower、floor distribution、sharing site equipment,etc.
c.record
Longitude and dimensionality、equipment scales、equipment power supply、transmission、waterproof、lightning grounding、floor load，etc.
Criterion of the location of antenna :
Whether any blockage in the first fresno zone of the antenna’s propagation path.
2)Do the location of the antennas satisfy the inter-modulation criterions?
3)Is the antenna suitable?
Equipment room engineering drawings consist of :
Position of the BTS.
2)Locations of the transmission line and power supply.
Considerations in antenna system :
1) Type of antenna.
2) Type of feeder cable.
3) Antenna height.
4) Directional angle of the antenna.
5) Degree of the antenna’s down-tilt.
XIII.Network Planning Tool-ASSET
- Coverage Planning
- Traffic Analysis
- Neighbour Cell Planning
- Frequency Planning
- Interference Analysis
ASSET software is a common software for doing nominal cell planning. With the usage of a 3-D digital map, and accurate coefficient constants, the coverage areas of the network can be accurately being simulated and predicted.
The analysis of the ASSET is output in a graphic and data format. Base on the output, the system designer can make an evaluation and do adjustments.
The coverage prediction is largely effected by whether accurate propagation model that is being used. ASSET support correction of CW model.
Coverage prediction
The initial planning and survey is the basis for the coverage prediction.
Digital Map Database
- DEM(Digital Elevation Model,Digital Terrain Height Data)
- DOM(Digital Overlay Model,Clutter)
- LDM(lines Digital Model,Line Vector Data)
- BDM(Digital vector Model.Building)
a. The BDM ( Building Distribution Model )map depict the location and height of the building on the each square unit of the digital map. BDM map is used on micro cell where there is relatively large traffic load.
Digital map use the data recorded to output the digital map.
The recorded database have two types. The first database type output the grid map. The second database type output the grid data.
The recorded data has the following types : high resolution database, digital terrain model’s database, digital elevation model’s database and clutter’s database.
The resolution can be divided into the following types : 5 meter resolution, 20 meter resolution and 100 meter resolution. Resolution of the map depict the size of the grid of the digital map.
b. DEM(Digital Elevation Model,Digital Terrain Height Data)
c. LDM(lines Digital Model,Line Vector Data)
XIV.GSM Bandwidth
GSM900：
BTS receive frequency：f1（n）＝890.2＋（n－1）×0.2 MHz
BTS transmit frequency：f2（n）＝f1（n）＋45 MHz
Totally 124 pairs of frequencies。
GSM1800：
BTS receive frequency ：f1（n）＝1710.2＋（n－512）×0.2 MHz
BTS transmit frequency ：f2（n）＝f1（n）＋95 MHz
Totally 375 pairs of frequencies 。
Frequency reuse is being adopted in GSM network for a larger capacity purpose.
Due to the usage of frequency reuse and the good GSM technology, GSM has been adopted in many countries around the world.
1.Frequency planning
- Traditional re-use approach
-> 4*3 re-use
- Tight Frequency Re-use
-> Multiple tight re-use
-> 1*3
-> Over layer/Under layer
The most common frequency reuse pattern is 4 X 3. It represent the 12 cells being the basic frequency reuse clutter. 4 represent 4 base stations and 3 represent there are 3 sector cell for each base station.
A frequency reuse pattern that is smaller than 4X3 ( example 1 X 3 ) will be consider as tight frequency reuse.
Multi-layer frequency reuse pattern ( MRP ) – the cells at different layers adopt different frequency pattern. At the lower cell layer, a more tighter frequency reuse pattern is being adopted as compared to the frequency reuse adopted at the higher cell layer. Thus, at the lower cell layer, there are more channels available. When a tight frequency reuse pattern is being used, frequency hopping should be used.
Underlay and Overlaid cell :
Divide the available frequencies into 2 groups. The first group of frequencies cater for the underlay cell. The second group of frequencies cater for the overlay cell. The underlay cell has a larger overage area and a less tight frequency reuse pattern ( 4 X 3 ). The overlay cell absorb higher traffic and have a tighter frequency reuse pattern ( for example 3 X 3 ).
2.ASSET is used for Frequency Planning.
The principle of frequency planning :
1). Within the same base station, it is not allowed to have 2 same frequencies.
2). Within the same base station and assume that frequency hopping is not adopted, the frequencies adopted should have a difference of a minimum of 2.
3). If the frequency reuse pattern is not 1 X 3, then try to avoid having the same frequency usage in the neighbouring cel ( co-channel interference ).
4). At normal situations, when frequency reuse pattern (1 X 3 ) is adopted, the number of frequencies involved in the frequency hopping is 2 times the frequencies allocated to the cell.
5). Emphasis is put on co-channel interference. Avoid neighbouring cell having the same frequencies used for the BCCH carrier.
3.Neighbour cell allocation
- According to coverage prediction result run from the ASSET software， neighbour relation between neighbour cell is produced。
Through the calculation of the ASSET software, we derive the best coverage and capacity prediction.
The neighboring BCCH carrier and neighboring BSIC cannot be the same as the target cell.
4.Interference analysis
- DTX
. Uplink DTX will save the MS power.
. Downlink DTX will save the BTS power .
- Frequency hopping
- Power control
-> Power is controlled in the forward and reverse link.
Discontinuous Transmission (DTX) makes it possible to switch off the radio transmitter during speech pauses. The purposes of this function is to reduce overall radio interference level in the air interface and to decrease MS power consumption.
DTX Uplink
The silent periods are detected by the mobile. During the silent periods the transmitter in the MS is switched off. The MS is providing the characteristic information about the background noise. This should create a feeling of ongoing connection to the other end of the conversation.
DTX Downlink
In downlink DTX, the received speech information from the MSC is analyzed and the background acoustics noise is evaluated.
The result of this analysis which includes characteristic parameters of background noise and control information is transmitted to the BTS.
The BTS makes the final decision to transmit the information and cut the radio transmitter. The background noise are transmitted at regular intervals during speech pauses.
DTX downlink should be used together with DTX uplink and frequency hopping to achieve the lowest interference.
There are two types of frequency hopping : baseband hopping and synthesizer hopping.
The frequency hopping sequence can be cyclic or random.
5.Parameter design
- Plan of Location area
- Channel Configuration
- Cell Design Data
6.Location area planning
- Related parameter
->Paging capacity
->Period location update
In Telecom system, the maximum capacity of one LAI is 300 TRXs.
Try to avoid the border of the LAI be located near shopping mall, and hignway. This is to avoid heavy load of location updating.
7.Distribution of logical channels
Channel Concept
LOGICAL CHANNELS
There are 12 logical channels in the system. Two are used for traffic, nine for control signaling and one for message distribution.
Traffic CHannels (TCH)
There are two types of TCHs:
· Full rate channel : used for full rate speech at 13kbps, or data up to 14.4kbps
· Half-rate channel : used for half rate speech at 6.5kbps, or data up to 4.8kbps
CONTROL CHANNELS
There are three different groups of control channels with each group containing three different logical channels.
Broadcast CHannels (BCH) (Down-link Only)
· Frequency Correction CHannel (FCCH) - used for frequency correction of MS
· Synchronization CHannel (SCH) - carries information on the TDMA frame number and the Base Station Identity Code (BSIC) of the BTS.
· Broadcast Control CHannel (BCCH) - Broadcasts cell specific information to the MS
Common Control CHannels (CCCH)
· Paging CHannel (PCH) - used on the down-link to page the MS
· Random Access CHannel (RACH) - used on the up-link by the MS to request allocation of an SDCCH, either as a page response or an access at MS call origination/registration.
· Access Grant CHannel (AGCH) - used on the down-link to allocate an SDCCH or a TCH to an MS.
Dedicated Control CHannels (DCCH) (Up-link and Down-link)
· Stand alone Dedicated Control CHannel (SDCCH) – used for system signaling during call setup or registration, up-link and down-link, as well as the transmission of short text messages in idle mode.
· Slow Associated Control CHannel (SACCH) : Measurement Reports from the MS to the BTS are sent on the up-link. On the downlink the MS receives information from the BTS what transmitting power to use and also instructions on Timing Advance (TA). In addition, the SACCH is used for the transmission of short text messages in call connected (busy) mode.
· Fast Associated Control CHannel (FACCH) – Control channel associated with a TCH. Also referred to as Fast Associated Signaling (FAS), the FACCH works in stealing mode. That is, 20 ms of speech is replaced by a control message. It is used during handover, as SACCH signaling is not fast enough. Used on up-link and down-link.
Cell Broadcast CHannel (CBCH)
This is used only on the down-link to carry Short Message
8.Channels configuration
There are two types of Channels Configuration :
-Traffic Channels Configuration
-Signalling Channels Configuration
The allocation for traffic channels is derived from the total traffic intensity, and target of GoS ( Grade of service ).
For example :
Assuming there are 2000 MS in one cell’s coverage area and 0.025 Erlang/subscriber, thus the total traffic intensity is 50 Erlang. Assume the probability of call congestion is 2%. From the Erlang B table, we can derived that 25 TCH channels are required.
The same concept of channel configuration go for the control channels. It is recommended that for every 2 TRX, we allocate one SDCCH/8.
For less traffic intensity area ( rural area ), we can use SDCCH/4.
9.Cell design data document
Radio parameter for network planning
- Network identity parameter
- System control parameter
- Cell select parameter
- Network function parameter
Network Identity:
LOCATION AREA IDENTITY (LAI)
The LAI is used for paging, and tells the MSC which Location Area (LA) the MS is located in. It is also used for location updating of mobile subscribers.
The LAI comprises the following:
LAI= MCC + MNC + LAC
MCC Mobile Country Code, the same as the IMSI MCC
MNC Mobile Network Code, the same as the IMSI MNC
LAC Location Area Code - the maximum length of the LAC is 16 bits, enabling 65,536 different location areas to be defined in one PLMN
CELL GLOBAL IDENTITY (CGI)
The CGI is used for cell identification within a location area.
This is done by adding a Cell Identity (CI) to the components of an LAI. The CI has a maximum length of 16 bits.
The CGI consists of:
CGI= MCC + MNC + LAC + CI
BSIC: Base Station Identity Code. It is transmitted on the SCH and is expressed as:
NCC = National Color Code of PLMN. Numeric 0 - 7.
BCC = Base Station Color code. Numeric 0 - 7.
Each operator in various countries is assigned one NCC value n to ensure that the same NCC is not used in adjacent PLMNs.
The purpose of the BSIC is to distinguish between cells with the same carrier frequency but from different clusters. It can also be
used to distinguish between cells from different operators on two country borders. It is essential for the locating algorithm that the correct neighbouring cells are evaluated.
10.Engineering document
- Network planning report
- Total-list of engineering parameter
- Network design document
Good documentation is the corner stone to the success in cell planning.
Thank you very much
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