y gradually degrades for a higher MCS due to the decreasing forward error correction. The actual receiver sensitivity must be taken from the receiver Eb/NO versus BLER 'waterfall' curve measurements for the given fading environment. Incremental redundancy recovers 1-2 dB on the highest coding schemes due to a hybrid automatic repeat request (ARQ) Type II, which essentially improves forward error coding though maximum ratio combining. GMSK Versus 8-PSK Backoff The introduction of 8-PSK modulation and coding schemes has introduced an inherent amplifier design constraint which must be made when planning and optimizing EGPRS radio performance. Specifically, the average power of 8-PSK driven timeslots must be decreased in order to meet the GSM specifications for adjacent channel power and spurious emissions. With this in mind, it is clearly easier to minimize this average power decrease when designing base station transmitter power amplifiers (PAs) compared with mobile transmitters. Therefore, mobile transmitters will typically require more backoff than their base station transmitter counterparts for maximum 8-PSK EGPRS transmission. At this point, it is worth mentioning the distinction between backoff and average power decrease as referenced within this text. Backoff refers to the intentional decrease in PA output power while an average power decrease refers to the resulting average measured power of an 8-PSK signal in the time domain. Further explanation is discussed later in this chapter. This section summarises the impact of 8-PSK timeslots requiring an average power decrease (APD) while operating on EGPRS capable transmitters. For reference in this section, it will be assumed that the requirement is 2 dB APD for the BS transmitter and 4 dB APD for the mobile transmitter during 8-PSK transmission. There are three main considerations when one or more timeslots are operating at 8-PSK with 2 dB 1. Impact to the current EGPRS user. The 'link budget' for the current user will be 2 dB lower when in the 8-PSK mode. This 