Terms of Use as given at the website. Future Enhancements and Services Future Enhancements and Services Mobile Receive Figure 11-4 The two time slots 0123456701234567 used in HSCSD. Measure Neighbor Mobile Transmit 0123456701234567 Data Rate-28.8 Kbps Enhanced General Packet Radio Service (E-GPRS) It is proposed that EGPRS will offer eight additional coding schemes. The lower layers of the user data plane, which has been specifically designed for GPRS operation, is reflected in the protocol stack, comprising the physical, Radio Link Control/Medium Access Control (RLC/MAC), and Logical Link Control (LLC) layers. Although the LLC layer can be used without modifi- cations when EDGE functionality is introduced, it is necessary to modify the RLC/MAC layer to support features such as efficient multiplexing and link adaptation. The basic modifications needed for EDGE consider the form of the data blocks that are being transferred across the radio interface. For EGPRS, several combinations of interleaving and coding have been pro- posed, whereas in the current GPRS proposals, the interleaving depth is set to four bursts. Link adaptation offers mechanisms for choosing the best modulation and coding alternative for the current radio link. In GPRS, only the coding scheme can be altered between two consecutive LLC frames; however, with EGPRS, a refined link adaptation concept can be utilized that enables both coding and modulation schemes to be changed to suit the given radio link. In addition, link adaptation should enable seamless switching between the two modulation schemes to such an extent that in EGPRS, the uplink state flag (USF) information can be modulated using Binary Offset Quad- rature Amplitude Modulation (B-O-QAM) and the user data by Quaternary Offset Quadrature Amplitude Modulation (Q-O-QAM). B-O-QAM is used in this case for the broadcast purposes and facilitates the characteristics of being robust and therefore available in the entire GSM coverage area. Downloaded from Digital Engineering Library @ McGraw-Hi