 throughput this kind of implicit link rate-compatible convolutional codes. adaptation can be superior to explicit link adaptation as In the discussion SO far, it has been assumed that the additional redundancy is only added when needed, that is receiver has received all the previously transmitted re- when previous higher-rate transmissions were not pos- dundancy versions. If all redundancy versions provide the sible to decode correctly. Furthermore, as it does not try same amount of information about the data packet, the to predict any channel variations, it works equally well, order of the redundancy versions is not critical. However, regardless of the speed of which the terminal is moving. for some code structures, not all redundancy versions are Since implicit link adaptation can provide a gain in of equal importance. One example hereof is Turbo codes, system throughput, a valid question is why explicit link where the systematic bits are of higher importance than adaptation at all is necessary. One major reason for having the parity bits. Hence, the initial transmission should at explicit link adaptation is the reduced delay. Although least include all the systematic bits and some parity bits. relying on implicit link adaptation alone is sufficient from In the retransmission(s), parity bits not part of the initial a system throughput perspective, the end-user service transmission can be included. However, if the initial quality may not be acceptable from a delay perspective. Chapter 4.6 WCDMA evolution: HSPA and MBMS Erik Dahlman, Stefan Parkvall, Johan Skold and Per Beming The first step in the evolution of WCDMA radio access is parameters cannot be used and diversity as a mean to the introduction of High-Speed Downlink Packet Access maintain good coverage is important. For MBMS, macro- (HSDPA) in Release 5 of the 3GPP/WCDMA specifi- diversity through multi-cell reception is employed for cations. Although packet-data communication is this purpose. supported already in the first release of the WCDMA The evolu