Comparison of GPRS and GSM signals

[techie]

I have noticed that at some place where the GSM signal strength is quite good, but still the GPRS cannot get connected. Does GPRS need exceptionally good signal strenght. Or does it use some other frequency than voice GSM channel. I can call on the phone but cannot connect GPRS. But at some places, I can do both.

 

[pisoiu]

at+csq signal strength

True, not all places where GSM signal is good, are ok for GPRS. For that is more relevant to check the BER, your modem should be able to provide this information. For example, BER is provided by AT+CSQ for GM862 modems.

/pisoiu

 

[techie]

csq gprs

True but I wanted to know if GPRS requires a better signal quality as compared to speech. The speech is also digitized and is using the same medium and frequency as GPRS. So does GPRS require an exceptional singal quality and will not connect if the signal is below that exceptional limit.

 

[pisoiu]

gsm vs gprs

Not necesarily. I've encountered situations when reported signal for voice was very poor, nearly lowest limit, and still being able to make GPRS connection, and also situations in which the signal strength was exceptional, but GPRS was down. My guess is that there is not a strict relation between the signal strength for voice and the required signal strength for GPRS. What I've noticed to be accurate enough as a GPRS signal strength indicator is the BER (bit error rate) reported by the modem.

/pisoiu

 

[artem]

gsm ber

It could be case with channel availability for GPRS - they use virtual alike channels which share the same physical place as voice - sometimes operators can manipulate channle allocation for gprs and give voice connections more priority than for packets . Also, GPRS can be activated per cell basis , so for certain cells you wont get the service . And, of course, it could be result of poor network planning , done by operator .
To be sure - ask operator for trouble and if they care - you will get an answer.

 

[techie]

gprs modem signal quality

But the BER can only be detected when a call is in progress. If I have a GPRS modem, how can I assess the BER. The AT+CSQ gives the value 99 and the documentation says that BER can only be measured during a call.

Added after 9 minutes:

Please correct me if I am wrong:

I take my laptop and GPRS modem on a car and start from a location where GPRS is connecting OK. (*99***1# = CONNECT, start PPP). I drive to the point where there is a problem. The CONNECT is still there. I try again. Still OK. I turn off the modem, power up again, the answer is NO DIALTONE. I drive away, still NO DIALTONE. I drive past the problem point, still NO. I drive well into the good zone. Now CONNECT.

Since the ATD*99***1# only connects the laptop to the phone's GPRS function and does not do any TCP/IP yet till the PPP has fully started, is there some check in the modem that prevents GPRS CONNECT but "IF WE COULD OVERRIDE THIS CHECK, WE MAYBE ABLE TO GET SOME TCP/IP PACKETS, ALTHOUGH WITH HIGH CRC ERRORS"

 

[artem]

+csq: 99,99

It seems you can nto make attach to GPRS network , once power on has been done . But did you try to detach instead of power off ?
Did you change BTS when drive out of good zone ?
You can find it by quering cell id from modem (if such command is implemented )
Are you able to use GPRS via normal phone ? (send MMS connect to internet ...)

 

[techie]

gprs versus gsm

I think that the phone scans for GPRS when you first turn it on. If you lose your regular GSM signal due to weakeness, once you reenter an area where the signal is strong enough for the phone to receive it, the GSM automatically gets picked up again, BUT NOT THE GPRS. You have restart the phone.

also : What is BTS

 

[pisoiu]

at+csq 99 99

But the BER can only be detected when a call is in progress. If I have a GPRS modem, how can I assess the BER. The AT+CSQ gives the value 99 and the documentation says that BER can only be measured during a call.
.....

I guess this is modem dependant. I use telit GM862GPRS and it reports BER all the time. Yes, sometimes is 99 but not always.
BTS is the Base Transceiver System, it is basically the cell which is linked to your mobile.

/pisoiu

 

[artem]

gsm vs gprs vs edge

I think mobile will not be attached to GPRS if there is no request from user. Also GPRS and GSM signals are send on the same freq and same trasceiver - their levels are same if no special power featuers are used . So GPRS must be more reliable in data transfer than voice - which does not have retransmit feature on data loss . This is most probably your operator problem.

Added after 3 minutes:

BER actually calculating , when mobile is active with transmit and receive - the GSM network uses BER from mobile phone to estimate downlink quality and make a handover to another cell if cre=iterias are fulfilled .

pisoiu, i think your phone reports the last stored BER value.

 

[rami.masadeh]

at csq good values

i think that this problem have many reasons
1: the operator may reserve most of the channels for GSM not GPRS.
2: there is no available or free GPRS channels when you are trying to connect.
3: the place where you are try to connect located between 2 BTS.
4: and the quality of the signal very bad,
note that the if you have 2 channels GSM and GPRS one and you have BER the GPRS will affected more than the GSM since the GPRS need higher data rate than GSM [/b]

 

[artem]

where does the signal come from in gsm

rami.masadeh , GPRS achieve higher data transfer rate by using more than 1 timeslot which is same timeslot used to conduct speech .

 

[rami.masadeh]

gsm csq .99 bit error rate

ok i know that the GPRS need higher data rate than GSM and i say that in my reply, but there is important point that u have to know if the operator use GPRS or EDGE technology EDGE technology need higher data rate, but it have an advatge on GPRS it have its own channels , not like GPRS the data and calls share the same bandwidth, as i told you youy have to check the mobile operator in order to insure that the switching engineer reserve channles for GPRS or not in this area

 

[sachinlan]

csq reliable gprs

GSM ad GPRS signals are trasmitted on the same frequecy carrier but in differet time slots. GPRS (data) time slots are shared with GSM(voice) time slots. So whenever there is a heavy( voice ) traffic in a network, voice calls will occupy the Data (GPRS) time slots too since voice calls are given a priority over data calls.
That is why you will not get GPRS time slots and GPRS will be slow or unavailable.

 

[srajput]

Re: at+csq 99 99

Hello sir..,
i am confused about this BER error ..clarify me plz ..,actually i am using SIM5216 GSM modem and i am trying to send the SMS it is always showing ME Failure ,but the SMS receiving is working fine and while making cal using ATD it is ending the cal without begin ..,so plz guys tel me is this ME Eroor becoz of the BER error ? i am getting AT+CSQ? is 31,99 .

Thanks in advance .

I guess this is modem dependant. I use telit GM862GPRS and it reports BER all the time. Yes, sometimes is 99 but not always.
BTS is the Base Transceiver System, it is basically the cell which is linked to your mobile.

/pisoiu

 

[replay]

Bump!
Can anyone clarify this question about Bit Error Rate? I'm using SIM5320 3G module and I'm getting this '99' <ber> value (AT+CSQ) all the time so now I wanna know if it is normal. I haven't tried making or receiving a call yet, so if it's true that BER can only be measured during a call, then I guess it's ok. Right?