GSM Bandwidth

There are 2 kind of GSM Bandwidth :

-GSM 900 :

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。

 

-GSM 1800 :

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.

Channel space： 200kHz

 no allocated

 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.
Mufti-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 ). 

•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 neighboring cel( co-channel interference ).
4)At normal situations,when frequency reuse pattern (1 X 3) is 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 neighboring cell having the same frequencies used for the BCCH carrier.

Neighbor cell allocation

•According to coverage prediction result run from the ASSET software，neighbor relation between neighbor 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.

Next post we will describe about the Interference Analysis , Please click here.