cess (TDMA) (Layer 1) In the GSM network the digital information is arranged in blocks As can be seen from the OSI model Layer 1 contains the channel and transmitted in precisely defined timeslots. An eight timeslot coding, error protection and interleaving. These processes are de- structure is used. Users are allocated a timeslot by the system during signed to ensure that data is transmitted correctly. If minor errors which data transfer takes place. The radio network, and hence the occur the decoder may be able to correct them. The interleaving radio test equipment, must be capable of being synchronised process ensures that, if a signal is degraded for a short period of together. time, sequential data is not lost. In order to measure timing parameters the test equipment must use The following sections describe the testing of the radio link, the sampling rates which are much faster than the data rate. The r.f. lowest part of Layer 1. The fundamental tools for receiver testing carrier power may be turned off between timeslots in a controlled are described and the equipment required for transmitter testing is manner. The test equipment must, therefore, be able to measure the identified. power output over a wide dynamic range. 61.10.1 Receiver measurements 61.8.1.2 Frequency hopping 61.10.1.1 Signal generator requirements Frequency hopping is used within the GSM system. Each timeslot Signal generators for GSM applications convert a given bit se- of information may be transmitted at a different radio frequency. quence into the corresponding modulated r.f. carrier signal. Con- Table 61.12 Comparison of conventional and digital mobile radio measurements Conventional mobile-radio measurements GSM measurements Measurement modes Continuous parameter settings Time-limited settings Continuous measurements Time referenced measurements Test tones Data telegrams Frequency division multiple access Time division multiple access/frequency division multiple access Bandwidth R.F. 10-25kHz R.F. 200kHz plus frequency hopping A.F. 3k