【正文】 ownlink and dualbinary phase shift keying (BPSK) in the uplink. Dualchannel BPSK modulation is similar to QPSK. The release 7 introduces 64 QAM transmission for the downlink and 16 QAM for the uplink. 16 QAM can double the bit rate pared to QPSK by transmitting four bits instead of two bits per symbol. 64 QAM can increase the peak bit rate by 50 percent pared to 16 QAM because 64 QAM transmits six bits with a single symbol. On the other hand, the constellation points are closer to each other for the higher order modulation, and the required signaltonoise ratio for correct reception is higher. The difference in the required signaltonoise ratio is approximately 6 dB between 16 QAM and QPSK and also between 64 QAM and 16 QAM. Therefore, downlink 64 QAM and uplink 16 QAM can be utilized only when the channel conditions are favorable. The system simulation results with 64 QAM in macro cells are illustrated in Fig. 3. The 64 QAM modulation improves the user data rate with 15–25 percent probability depending on the scheduling (RR = round robin, PR = proportional fair). The rest of the time the channel conditions are not good enough to enable the reception of 64 QAM modulation. New HSDPA and HSUPA terminal categories were added in release 7. The HSDPA categories 13 and 14 include 64 QAM, and categories 15 and 16, MIMO. The peak bit rate with 64 QAM is Mbps and with MIMO, Mbps. The bination of 2x2 MIMO and 64 QAM modulation would push the theoretical peak data rate beyond 40 Mbps。 however, that bination is not included in release 7but will be discussed for release 8. The HSUPA category 7 is added in release 7 with 16 QAM capability, doubling the uplink peak rate to Mbps. CELL CAPACITY AND DATA RATE ENHANCEMENT WITH ADVANCED MOBILE RECEIVERS The introduction of HSDPA to release 5 included performance requirements with Rake receiver using single antenna. Release 6 brought two types of enhanced receivers: enhanced type 1,corresponding to a twoantenna Rake receiver and enhanced type 2, corresponding to a oneantenna chip equalizer. Release 7 brought further enhanced type 3, corresponding to a twoantenna chip equalizer. The antenna diversity improves the signal to interference ratio because the interference is partly uncorrelated in the different antennas. The chip equalizer removes intracell interference caused by the multipath propagation leading to higher signaltointerference ratio. When the signaltointerference ratio increases, user equipment (UE) will report higher channel quality information (CQI) values back to the basestation. The CQI refers to the particular datarate the terminal expects to receive with the current signal strength and multipath environment. The advanced receiver with the chip equalizer improves the capability of the mobile terminal to pensate difficult channel conditions, which results in a higher CQI value reported by the advanced mobile terminal than by a mobile terminal without any equalizer. Higher CQI enables the base station to transmit with larger transport block sizes, corresponding to a higher data rate and thus, a mobile terminal with a chip equalizer receiver is able to receive high data rates in more difficult channel conditions. The advantage of such a relation between the advanced receivers and reported CQI values is that no modifications are required to the base station algorithms to benefit from the advanced receivers in mobile terminals. Note that 3GPP will not define the type of advanced receiver one must use。 only a reference receiver is used to set the performance requirements that a mobile terminal must meet to declare it as enhanced Type 1, 2, or 3pliant. The advanced receivers in mobile terminals improve the single user data rates and cell capacities due to increased average CQI reporting as discussed previously. The capacity improvements are shown in Fig. 4, assuming finite transmission buffers. The simulation results are shown with different number of codes in the work and with round robin and a proportional fairpacket scheduler. More details about the HSDPA packet schedulers can be found in [2]. The gain of the twoantenna equalizer receiver is 100–150 percent pared to the oneantenna Rake and 50–80 percent pared to the oneantenna equalizer. The achievable macro cell capacity is 4 Mbps with a twoantenna equalizer with a dedicated HSDPA carrier and proportional fair scheduler. That capacity corresponds to the spectral efficiency of nearly 1 bps/Hz/cell. The downlink MIMO transmission further improves the cell throughput. The more detailed capacity evaluations can be found in[5]. Additional downlink capacity enhancements can be achieved with intercell interference cancellation in the receiver of the mobile terminal. Such enhanced receivers also are being studied in 3GPP to improve the capacity and especially the celledge data rates. Those receivers are called enhanced Type 3i. LAYER 2 OPTIMIZATION WITH FLEXIBLE RLC AND MAC SEGMENTATION The WCDMA release 99 specification was based on the packet retransmissions running from the radio work controller (RNC) to the mobile terminal on the layer 2. The layer 2 radio link control (RLC) packets were required to be relatively small to avoid the retransmission of very large packets in case of transmission errors. Another reason for the relatively small RLC packet size was the requirement to provide sufficiently small step sizes for adjusting the data rates for the release 99 channels. The RLC packet size in release 99 is not only small, but it is also fixed for acknowledged mode data, and there are only a limited number of block sizes in unacknowledged mode data. This limitation is due to transport channel limitations. The RLC payload size is fixed to 40 bytes in release 99 for acknowledged mode data. The same RLC so