Monday, September 17, 2012

Power Control Overview

1. During handover, MS will access the target cell with the maximum transmitting power (associated handover command) allowed by the target cell. But if “MS power prediction after HO” is enable, then MS will use the optimized power to access the target cell.
2. During intra-cell handover, the current power will be retained.
3. Power control can be implemented on TCH carriers only, BCCH carrier is not allowed power control. Because MS needs to measure the receiving level of BCCH from the adjacent cell. It will be inaccurate when power control is performed on BCCH.
4. Power control is performed independently for each channel.


When MS accesses the network via RACH channel, its transmitting power is the “MS max. TX power level” get from the system information sent on BCCH. MS send the first message on dedicated channel also uses the “MS max TX power level” ,this is not under the control of the system before the power control command which carried on SACCH of SDCCH or TCH. The implementation procedure is as follows:
1. According to the uplink receiving level and receiving quality reported by BTS, consider the maximum transmitting power of MS, BSC calculates the proper transmitting power for the MS.
2. Power control command and the TA value will be transmitted to MS at layer 1 header carried by each downlink SACCH block.
3. MS receives the power control command carried by SACCH header at the end of each SACCH report period, Then MS will carry out the command in the beginning of next report period. MS can change power 2dB per 13 frames (60ms) maximum.
4. After MS executed the power control command, it will set the current power class at the layer 1 message header of the next uplink SACCH, and transmit it to BTS in the measurement report. Therefore, it will take 3 measurement report periods for the new power class (in each power control command) to be available.
Note: Each integral SACCH message block (measurement report) is composed of 4 burst. A power control implementation process in whole takes the time of 3 measurement reports.
power control algorithm: HW I and HW II power control

Power control judgment and the selection of HWI algorithm or HWII algorithm
Power control algorithm selected in power control data table
Power control judgment is controlled by BTS measurement report pre-processing item which can be selected in handover control data table
MR. Pre-process (measurement report pre-processing): This switch decide where power control be processed. If  measurement report pre-processing is “yes”, power control is processed in BTS, and when setting it “no”, power control is processed in BSC.

Set pre-processing “yes” is to reduce the signaling load in Abis interface.
1.If Abis E1 is in 15:1 mode, it should be set “yes”, otherwise the Abis capacity for speed is not enough;
2.BTS22C 0110 version should be set “No”;
3.Satellite transmission BTS should be set “yes”;
4.We should consider few type of BTS has relationship with HWI algorithm and HWII algorithm, please check the product manual.

Sunday, April 29, 2012

Cell Reselect Penalty Time PT

Value range: 0~31, the corresponding time is 20~620s. 31 is to change the function direction of CRO on C2.
Unit: None
Content: Cell Reselect Penalty Time.
Recommendation: 0
If the communication in a cell is affected due to very heavy traffic or some other reasons, this cell should be the last where MS works in (there is a repulse for this cell). In this case, PT can be set as 31, which causes TO invalid. C2 value is the difference of C1 and CRO, therefore, C2 value of this cell is decreased manually. MS will reselect this cell with little possibility. Besides, the network operator can set CRO according to the repulse degree to this cell. The higher the repulse degree, the larger CRO.
For the cell with very low traffic, MS should prefer to work in this cell. In this case, CRO is recommended to be between 0-20dB. It can be set according to the preference degree to this cell. The higher the preference degree and the larger CRO. Generally TO is recommended to be the same or a little more than CRO. PT is mainly used to prevent MS’s too frequent cell reselections. Generally it is recommended to be 0 (20s) or 1 (40s).
For the cell with medium traffic, generally CRO is recommended to be 0 and PT be 31 as a result of C2=C1, that is, no manual modification on the cell.
Setting of PT can effectively prevent the fast moving MS from accessing the micro-cell. This parameter can be set according to the size of micro-cell. And it is recommended to be 20s for the ordinary micro-cells. When PT is set as 31, it is used to change the direction of action to CRO.