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 :

1)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.

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 control and traffic channels /cell

Prediction of  mobile capacity can be done through the following criterion :

1)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 :

1)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. 

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. 

Base site survey preparation

Gathering information from site survey

•Population distribution

•Traffic Distribution

• Major Streets

• City Structure

• Local Customs

• Mountains 、Coastlines.etc

Base station survey——site selection(1)

Principle for Selection of Base Station

Criterions of BTS site selection:

1)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 diffraction 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 multilayer cell structure.

9)At the initial network construction, it is important that the coverage area include important areas.

Base station survey——site selection(2)

 

How to choose Base Station Site.

Condition Contain Record Try to locate the base station at an ideal position as according to the propagation model. Strong inference equipment 、tower、floor distribution、sharing site equipment,etc. Longitude and dimensionality、equipment scales、equipment power supply、transmission、waterproof、lightning grounding、floor load，etc.

Criterions of the location of antenna :

1)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 criterion?

3)Is the antenna suitable?

Equipment room engineering drawings consist of :

1)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.

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)

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 thedigital map.                                                                                                                                                                                

 

LDM(lines Digital Model,Line Vector Data)

 The next post we will describe about the GSM Bandwidth, For more details,Please Click here