 and as- (transmit, receive, channel, power) can be controlled directly signed to time slots. Continuous analogue signals that were and all the measurements required such as sensitivity, fre- employed for testing in the past would obviously be out of place quency response, distortion, transmitter power, modulation, in digital environments. signal to noise ratio, power consumption can be performed with Modern digital modulation techniques affect the phase and the tester. amplitude of the r.f. carrier continuously over time. Generating Of much greater interest is the complete system test in which digital signals of this kind, or analysing them, is beyond the the mobile radio operates as if it were in the cellular network. capabilities of conventional test equipment such as signal gen- The test set in this case forms a test system which simulates the erators, modulation analysers and power meters. base station, permitting calls to be sent from and received at the mobile station in real time via the r.f. connector. Once again the In 1992 CEPT established a special working committee called the r.f. and a.f. measurements will also be handled by the test set, Groupe Speciale Mobile (GSM) to formulate a new digital cellular operated either in the manual mode or under programme con- standard. This was achieved and in 1992 the GSM (now renamed trol. The test set can also send the telegrams necessary for Global System Mobile) was launched. initiating channel handover or power level switching. An extensive range of signalling and r.f./a.f. tests must be made as 61.8.1 Analogue and GSM test methods illustrated by the test menus taken from a modern test set, as in Table 61.11. The GSM system is one of a range of radio communication systems The table summarises the signalling procedures and measure- which use fully digital techniques. ments required for the three most common analogue cellular stand- Other examples are: Table 61.11 Test menus TACSIETACS Call mobile-base Call mobile-base Call mobile-base Call base-mobile Call bas