carrier telegram, bit 58 acting as the BFI flag. This gives rise to three new test parameters which, depending on application, can be used as a measure of transmission quality (Fig- ure 61.29). bit 58 Transmitter Figure 61.30 I-Q (vector) demodulator Modulator Channel coder units for analysing digitally modulated signals (constellation analy- sers) have a limited use. Demodulator Channel decoder A precise analysis of dynamic behaviour can only be obtained by Receiver fast sampling of the r.f. signal or the corresponding I/Q signals (Figure 61.30). If the samples are stored in a memory of sufficient size, they can be post processed for comprehensive and flexible Figure 61.29 Recognising frame errors in the GSM mobile analysis of the transmitter, as shown in the GSM transmitter meas- urement flowchart of Figure 61.31. Frequency hopping receiver 1. BER; bit error rate, number of bad bits found in the trans- mission as a whole. Analogue I/Q recovery 2. FER; frame erasure rate, number of bad frames. 3. RBER; residual bit error rate, BER for 'good' frames. As these measurements are carried out on the logical GSM chan- High-resolution, high speed nels (e.g. traffic channel, control channel), very long measurement A/D conversion times may result under certain circumstances because of the various data rates and the required BER values. Mass storage of samples 61.10.1.4 Additional receiver measurements The quality criteria (BER, FER, RBER) described earlier replace the parameters S/N and SINAD in analogue radio systems. With Frequency-hopping regard to the reception quality, other well known receiver measure- behaviour ments are also carried out, such as co-channel rejection, adjacent channel rejection, blocking and spurious responses to 12.75GHz. In most cases, the interfering signal generator has to meet stringent Modulation analysis spectral purity requirements. Depending on the test method, un- modulated or GSM modulated, static or frequency hopping inter- ference generators are required. With adjacent channel measurem