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.

Different types of Voice quality measurement systems and score evaluation (GSM and WCDMA)

There are different types of quality measurement system exist in telecommunication. For voice and video quality,  we use different types of measurement policy. But few standards are common and ratified by the different regulatory body such as ITU, ETSI, AT & T etc. During the measurement or testing procedure, we use different types of algorithm for different measurement system or different testing purpose. But among them few standards are very popular and vastly used for assessing the voice and video quality. Generally we can classify the measurement system into two parts one is subjective evaluation and another is objective evaluation.

Different types of voice quality measurement systems are given bellow:

ITU-T recommendation for voice quality testing

• MUSHRA (Multiple stimulated with hidden reference and anchor) , In MUSHRA we use "lossy audio compression algorithm". MUSHRA ratified by ITU-R BS 1534- 2 and ITU- R BS 1534-3. It's a subjective evaluation system.

• PSQM (Perceptual speech quality measurement) is such a measurement system  which allows automated and simulation based methodologies for rating both voice clarity and  transmitted voice quality. This system ratified by ITU-T P 861. In PSQM, we use a psychoacoustical mathematical modeling algorithm to analyze the pre and post transmitted voice signals. ITU-T already replaced PSQM(ITU-T P861) by PESQ (ITU-T P862).

•  PESQ (Perceptual evaluation of speech quality) was developed as a model of subjective tests as per industry standard which will be widely used in Telecommunication system. It was standardized as ITU-T recommendation P.862 (02/01). Latter PESQ scores mapped into MOS score which was standardized as ITU-T P862.1. The scoring values of  PESQ SQI MOS(speech quality index mean opinion score)  ranges from 1 to 5 inwhich 1 means worse and 5 means best. The final score of PESQ SQI MOS is the arithmetic mean of all the tested scored.  

                    The thematic presentation of PESQ SQI MOS is given bellow:

Geographical distribution of PESQ SQI MOS Score from DT log 

• POLQA (Perceptual Objective Listening  Quality Assessment) is the most recent ratified voice quality assessment system and best suited for wide band audio signal measurement. POLQA covers a model to predict a speech quality or alternatively we can treat it as digital speech signal analysis and rating procedure. POLQA was developed as per ITU- T 863 recommendation. It's the most widely implemented voice assessment system and excellent successor of PESQ (P8621). As like PESQ values POLQA scores ranges from 1 to 4.5. POLQA score evolution almost like PESQ. 1 means worse and the value equivalent to 4 or above 4 is excellent.

POLQA Reference vs Degraded audio signal