Abstract
Enhanced Data Rates for GSM Evolution (EDGE) is currently being standardized as the evolution path for GSM. EDGE improves the spectral efficiency by employing an 8PSK modulation scheme with 3pi/8 rotation between symbols, which triples the GSM data rate. A Linearized-GMSK pulse shaping filter is employed to remain within the 200kHz bandwidth of GSM. In order to facilitate the ease of transition from GSM to EDGE, system parameters such as symbol rate and time slot structure remain unchanged. As a result, a network capable of EDGE can be deployed with limited investment and within a short time frame, with just an upgrade in the transceiver and the system software. The introduction of EDGE modulation has a significant effect in the receiver. The LGMSK filter introduces Inter-symbol interference whose effect becomes severe due to multi-path fading and Doppler Spreading. In addition, 8-PSK has a smaller Euclidean distance between symbols than GMSK, which makes EDGE more prone to errors. Therefore a robust equalizer is required. The research objective is to mitigate the effects of fast time-varying frequency selective fading channels in the presence of noise and interference, by optimizing the trade-off between complexity and performance. This leads to four main areas of study: Reduced-state Equalization, Pre-filtering, Reduced-state Soft Output Equalization and Joint Pre-filter, Channel and Reduced State Soft Output Data Estimation. The optimum scheme. Maximum Likelihood Sequence Estimation, based on the Viterbi Algorithm, for a 6-tap channel requires 32768 (85) trellis states. Using the techniques developed in this thesis, an implementation margin of 5.9 dB over the EDGE standard requirement is achieved with only a 2 trellis state equalizer. Subsequently, based on this low complexity structure, a new method is developed involving two stages of equalizers in cascade. With reduced decision errors and improved noise variance estimation, the two stage scheme leads to a performance surpassing the single stage, with good resistance to interference. Finally, a joint scheme of moderate complexity is developed to support the scenario of a high speed train.