gure 2.74 Time mask for normal GMSK burst Burst Structure (GMSK Versus 8-PSK) 3GPP TS 05.05, Annex B identifies the following GSM/EGPRS burst structures for the transmitted power level versus time. Figure 2.74 shows the time mask for normal duration bursts (NB, FB (frequency connection burst), dB and SB (synchronisation burst)) at GMSK modulation. Figure 2.75 shows the time mask for normal duration bursts (NBs) at 8-PSK modulation. The grey 'envelope' shows a conceptual example of the appearance of a normal burst. Average Power Levels over the Burst Period Figure 2.76 shows an example of an existing GSM/GPRS BCCH TRX with eight normal bursts in GMSK (note that the average power is constant and the power down interval is exaggerated to illustrate timeslot separation). Figure 2.77 shows an example of a GSM/EGPRS BCCH TRX with a 3TSL EGPRS mobile active on the downlink with five normal bursts in GMSK (APD = 0 dB) and three normal bursts in 8-PSK (APD = 2 dB). In this example, the average power decreases by 2 dB during the last three bursts due to 8-PSK. This has the following key impacts: slightly lower throughput near the cell edge or in a poor C/I environment; 2 dB lower signal level to neighbouring cells or GSM phones evaluating neighbours. Figure 2.78 shows an example of GSM/EGPRS BCCH TRX with a 2 dB backoff and a 3TSL EGPRS mobile active on the downlink with five normal bursts in the GMSK (APD = 0 dB) and three normal bursts in 8-PSK (APD = 0 dB). Note that the average power remains constant since both GMSK and 8-PSK are operating in the linear range of the PA. Radio Network Optimisation (***) (147 symbols) 7056/13 (542,8)Us t (us) Figure 2.75 Time mask for EGPRS 8-PSK burst PDTCH PDTCH PDTCH P(dB) t(us) Figure 2.76 Average BCCH power with GMSK PDTCH PDTCH PDTCH 8-PSK/ 8-PSK/ 8-PSK/ P(dB) t(us) Figure 2.77 Average BCCH power with GMSK / 8-PSK mix Radio Network Planning and Optimisation P(dB) t(us) Figure 2.78 Average BCCH power with a 2 dB backoff 52 Multiframe Structure of the PDTCH Figure 2.79 shows the 52 m