GSM/EDGE: A mobile communications system determined to stay

The Global System for Mobile Communications (GSM) is still the most successful mobile communications system worldwide. During the last decade, major steps have been taken towards an improvement of GSM with respect to performance and spectral efficiency. To serve the increasing demands of more and more users for higher data rates, significant efforts are made towards a further evolution of GSM. The standard extension Voice Services over Adaptive Multi-User Channels (VAMOS) has been specified in 3GPP Release 9. In VAMOS mode, two overlaid Gaussian minimum-shift keying (GMSK) signals are transmitted in the same time slot and frequency channel, potentially doubling the capacity of existing GSM networks in many cases. In this paper, we address channel estimation and detection techniques for the VAMOS downlink. In a new 3GPP work item called TIGHTER, it is also foreseen to tighten all downlink receiver performance requirements for all data and voice services by at least 2 dB through the application of more sophisticated processing techniques at the receiver. Furthermore, a 3GPP study on Signal Precoding Enhancements for EGPRS2 (SPEED) to further modify the modulation and coding for data services by introducing OFDM has been started recently. We present ideas for improved receivers to enable tighter performance requirements and for SPEED transmission concepts, which might merit further investigation. (C) 2011 Elsevier GmbH. All rights reserved.