- "Question 1 : Since mobile stations need to abide my international laws, can there be a mobile station that uses not GMSK but any other?"
You don't need to worry about this. The system determines this (GPRS protocol). On a radiocomtester (see below) you can set this manually but a public network doesn't allow that.
- Question 2 : "what type of a receiver is used to measure these dBm measurements?"
This is not a receiver but a radiocommtester like this one or this one. This instrument has all the functionality of a BTS and also includes a fading and noise generator capable of generating real-life conditions. This comtester can answer a call from, or initiate a call from the MS in the exact same way as a normal cellular network except that data is generally not speech/SMS but usually bit patterns (PBRS). To perform a receiver sensitivity test the MS is generally put in loopback mode via an AT command (sent via a PC through the serial port of the device). The MS sends the bit pattern generated by the radiocomtester back via the uplink. The radiocomtester compares the original bits with the received bits a calculates the BER, FER, etc. By reducing the output level of the comtester you can determine the level where the communication breaks down.
RF engineers who are still in the phase of developing a frontend also use what is called a Vector Signal Generator, Vector Signal Generator. This instrument can generate a GSMK (or other) signal modulated with a fixed data pattern or PRBS. They usually have their own way of determining the BER or FER since only a downlink path exists.
- "Question 2 : "Because at a particular point, amount of GSM radiation in dBm is also highly dependent on my antenna characteristics too. Am I correct?"
Yes, but such tests are typically done in what is called 'conducted mode' where the antenna of the MS is replaced by a small connector connected to the comtester via a short stretch of coax cable.
Radiated versions of such tests exist, but generally take place in a anechoic chamber, usually by a full conformance/performance test system way beyond the capabilities of an average application developer.
- "Question 2 :"Does that mean I will have slightly better performance than depicted from this map?"
No, the figures you see in the document are receiver input levels. An antenna is a passive device and can never amplify the signal. Antenna gain is not real gain but the relative gain with respect to an omnidirectional antenna. A better antenna factor can increase the level at the receiver input with respect to the prevailing field strength at that location, but never the field strength itself, of course.
- "Question 3: Could you please post a direct link to the GSM specification".
Finding a doc in there is indeed looking for a needle in a haystack. Here.