【文章內容簡介】 lution is applied to HSDPA release 5 and HSUPA release 6, as well: the 40byte packets are transmitted from RNC to the base station in the case of HSDPA. An additional configuration option to use an 80byte RLC packet size already was introduced in release 5 to avoid extensive RLC protocol overhead, layer 2 processing, and RLC transmission window stalling. With the 2ms transmission time interval(TTI) used with HSDPA, this leads to possible data rates being multiples of 160 kbps and 320kbps, respectively. As the data rates are further increased in release 7, increasing the RLC packet size even more would have a significant impact on the granularity of the data rates available for HSDPA scheduling and the possible minimum data rates. 3GPP HSDPA and HSUPA allow the optimization of the layer 2 operation because layer 1retransmissions are used, and the probability of layer 2 retransmissions is very low. Also, the release 99 transport channel limitation does not apply to HSDPA/HSUPA because the layer 2block sizes are independent of the transport formats. Therefore, it is possible to use flexible and considerably larger RLC sizes and introduce segmentation to the Medium Access protocol(MAC) layer in the base station. This optimization is included in the release 7 downlink operation and is called the flexible RLC and MAC segmentation solution. The RLC block size in a flexible RLC solution can be as large as an Inter Protocol (IP) packet, which is typically 1500 bytes for download. There is no requirement for packet segmentation in RNC. By introducing the segmentation to the MAC, the MAC can perform the segmentation of the large RLC packet data unit (PDU), based on physical layer requirements when required. The flexible RLC and MAC segmentation offers a number of benefits in terms of layer 2 efficiency and in terms of peak bit rates. ? The relative layer 2 overhead is reduced. With the RLC header of 2 bytes, the RLC overhead is 5 percent in case of a 40byte RLC packet. When the RLC packet size increases to 1500 bytes, the RLC header over head is reduced to below percent, and the total L2 overhead is reduced to 1 percent. The reduction of the overhead can improve the effective application data throughput. ? The RLC block size can be flexibly selected according to the packet size of each application. That flexibility helps to avoid unnecessary padding that is no longer required in a flexible RLC solution. This is relevant especially for the small IP packet sizes that are typical in VoIP or streaming applications. ? Less packet processing is required in RNC and in the mobile terminal with an octet aligned protocol header. The number of packets to be processed is reduced since the RLC packet size is increased, and octet aligned protocol headers avoid bit sifting in high data rates connections. Both reduce layer 2 processing load and make the high bit rate implementation easier. ? Full flexibility and resolution of available data rates for the HSDPA scheduler. SET UP TIME REDUCTION WITH ENHANCED FORWARD ACCESS CHANNEL The WCDMA work data rate and latency are improved with the introduction of release 5 HSDPA and release 6 HSUPA. The enduser performance can be further improved by minimizing the packet call set up time and the channel allocation time. The expected packet call set up time with release 7 will be less than one second. After the packet call has been established, user data can flow on HSDPA/HSUPA in the Cell_DCH (dedicated channel) state. When the data transmission is inactive for a few seconds, the UE is moved to the Cell_PCH (paging channel) state to minimize the mobile terminal power consumption. When there is more data to be sent or received, the mobile terminal is moved from Cell_PCH to Cell_FACH (forward access channel) and to the Cell_DCH state. Release 99 FACH can be used for signaling and for small amounts of user data. Release 5 and release 6 do not provide any improvements in FACH performance. The idea in release 7 enhanced FACH is to utilize the release 5 HSDPA transport and physical channels also in the Cell_FACH state to improve the enduser performance. The concept is illustrated in Fig. 5. The enhanced FACH concept offers the following performance benefits: ? FACH data rates can be increased from the current 32 kbps beyond 1 Mbps. The end user could get immediate access to relatively high data rates without the latency of channel allocation. ? The state transition from Cell_FACH to Cell_DCH would be practically the work resources for the channel allocation are available, a seamless transition to Cell_DCH can take place, because the physical channel is not changed. ? Discontinuous reception could be used in Cell_FACH to reduce the power consumption. The discontinuous reception can be implemented because enhanced FACH uses a short, 2ms transmission time interval instead of the 10 ms of release 99. The discontinuous reception in Cell_FACH state is not part of 3GPP release 7 specifications. Because the existing physical channels are utilized in enhanced FACH, there are only minor changes in layer 1 specifications, which allow fast implementation of the feature. Enhanced FACH can coexist with release 99 and with HSDPA/HSUPA on the same carrier. No new power allocation is required for enhanced FACH because the same HSDPA power allocation is used as for the existing HSDPA. VOICEOVERIP CAPACITY ENHANCEMENT Circuitswitched voice used to be the only way to provide voice service in cellular works. The introduction of third generation works, including WCDMA release 99, made it possible to run voiceoverIP (VoIP) over cellular works with reasonable quality, but with lower spectral efficiency than circuitswitched voice. 3GPP releases 5 and 6 HSPA was originally designed to carry high bitrate, delaytole