Radio Frequency Engineering

WCDMA breathing effect and Coverage - Capacity trade off

In WCDMA, the relation between coverage and capacity referred to as “breathing effect”.  The load of WCDMA network has a greater effect on it's coverage. The load of WCDMA network impacts on own system in two ways, depending on which link (uplink and downlink) has been taken into account.  For uplink as more user added to the network, higher interference or noise will be detected at the Node B end.  This effect called rise over thermal. That’s why UE need to transmit at higher power to overcome this effect.

Rise Over Thermal (dB)

When the loading of the system increases the Ec/No degrades, but the RSCP remains constant. Degrading Ec/No is an indication of increased other cell interference which demands the increase of downlink traffic power. Power being a limited resource, the requirement of higher transmit power may not be available, thus the coverage not being met in loaded condition; this scenarios called “coverage and capacity trade-off” for the downlink in a WCDMA systems.

Coverage and Capacity Trade Off

GSM Radio Parameter Details and Score evaluation from Drive Test (DT) end

Radio Parameters :
RxLev: Rxlevel represents received signal strength of GSM network. Rxlevel is an independent drive test (DT ) parameter. Value of Rxlevel generally expressed in dbm. Rxlevel ranges from -10 dBm to -120 dBm. Here , value of Rxlevel "-10dbm"  represents strongest signal and "-120dbm" represents weakest signal. The acceptable values of Rxlevel in a commercial GSM network should be above -95 dbm (-10 dbm to -95dbm).
Geographical presentations of Rxlevel (Received signal level) in Laxmur- Noakhali Highway
RxQual: RxQual means for received signal quality. RxQual measured on the basis of BER. So,RxQual is a dependent parameter. RxQual ranges from 0 to 7. Here "0" represents the best quality signal and 7 represents the worst quality signal. The acceptable values of RxQual in a commercial GSM network is "0 to 5".

Geographical presentations of RxQual (Received Signal Quality) in Laxmur- Noakhali Highway
BER: BER means for bit error rate. Actually BER is a  Ratio of the number of bit errors to the total number of transmitted bits in a certain period of observation. BER is inversely proportional to the Rxlevel and directly proportional to the interference level. The acceptable values of BER in a commercial GSM network should be bellow 6.4. Depending on BER values RxQual is measured. The relationship between BER and RxQual is given bellow:

Relationship between BER and RxQual
FER: FER means for Frame Erasure Rate. FER represents the percentage of a ratio (frames being dropped due to high number of bit errors by total number of transmitted frame) in a certain period of observation. GSM MOS value (Voice Quality indication) largely depends on FER value. FER is also a dependent parameter; the value of FER (Frame Erasure Rate) depends on BER ( Bit Error Rate).

SQI : SQI means for Speech Quality Index .SQI is a dependent parameter, the values of SQI depends on the BER, FER and Speech Codec. There are three types of Speech Codec in GSM, these are EFR ( Enhanced full rate 12.2 kbit/s), FR (Full rate 13.2 kbits/s), HR (Half rate 5.6 kbit/s).  The value of SQI is updated every 0.5s and SQI values ranges from 0 to 30. Here, "0" represents worse quality speech and "30" represents best quality speech. The acceptable values of SQI in a commercial GSM network should be above 15.

C/I : C/I represents  the ratio carrier-over-interference. The ratio between the signal strength of the current serving cell and the signal strength of unwanted (interference) signal components. The acceptable values of C/I in a commercial GSM network should be above 9dbm".

MS Power Control Level: MS power control level indicates the transmit power control  scheduled by the base transceiver station (BTS). This parameter is valid only in dedicated mode. Generally it's ranges from 0 to 31.

DTX: DTX means for Discontinuous transmission.  DTX is a mechanism which allows the radio transmitter to be switched off during speech pauses. This feature saves the power consumption of the Radio transmitter, which is important for User Equipment(UE) or Mobile station(MS) and it's also decreases the overall interference level on the radio channels affecting the capacity of the network.

TA: TA means for timing advance. TA represents the length of time takes to reach a signal from base station to the mobile station (MS). In GSM TA value changes after every 550 meters.TA values ranges from 0 to 63. That is a GSM cell can cover maximum (63 X 550) = 34.6 km

RLT Counter (Cur): RLT Counter(Cur) means Radio link timeout counter (current). This parameter defines the  value of the radio link counter. RLT Counter(Cur) ranges of 0 – 64. When RLT counter (Cur) reaches zero it results in normal DROP Call.

RL Timeout Counter (MAX): This parameter defines the maximum value of the radio link counter. RLT Counter(MAX) range from 4 – 64 in step size of 4.

MS Behavior Modified: This window shows current settings for the mobile station, for example whether handover is disabled or not, multi band reporting enabled or not etc.