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 Up-link:
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 Down-link
In down-link 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 down-link should be used together with DTX up-link and frequency hopping to achieve the lowest interference.

There are two types of frequency hopping : base band hopping and synthesizer hopping.
The frequency hopping sequence can be cyclic or random.

Parameter design

The parameter that we should design as below :

  

•   Plan of Location area   

•   Channel Configuration

•   Cell Design Data

Location area planning  

 

• Related parameter

          -Paging capacity
          -Period location update 

All technologies company, the maximum capacity of one LAI is 300 TRXs.
Try to avoid the border of the LAI be located near shopping mall, and highway. This is to avoid heavy load of location updating.

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 

Channels configuration

•        Traffic channels configuration

•        Signaling 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.

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 neighboring cells are evaluated.

 

 

END