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1、<p><b>　　外文資料原</b></p><p>　　High-Speed Packet Access Evolution in</p><p>　　3GPP Release 7</p><p><b>　　ABSTRACT</b></p><p>　　High-speed pack

2、et access (HSPA) was included in Third Generation Partnership Project(3GPP) releases 5 and 6 for downlink and for uplink. The 3GPP release 7 offers a number of HSPA enhancements, providing major improvements to the end-u

3、ser performance and to net-work efficiency. The release 7 features are introduced in this paper. Release 7 also is known as HSPA evolution or HSPA+.</p><p>　　The HSPA+ downlink peak bit rate can be increased

4、 to 28.8 Mbps with a multiple input multiple output (MIMO) antenna solution, and</p><p>　　the uplink rate can be increased to 11.5 Mbps with higher order modulation in release 7. The higher peak rates are fa

5、cilitated by the layer 2 optimization in downlink. In addition, the terminal power consumption can be reduced considerably for packet applications.</p><p>　　The downlink cell capacity will be enhanced with n

6、ew types of terminal requirements for a two-antenna equalizer and with MIMO. Altogether, release 7 features nearly double the cell capacity compared to release 6 with emphasis on the capacity of voice-over-IP (VoIP) serv

7、ice.</p><p>　　3GPP release 7 enables the simplification of the network architecture. The number of net-work elements for the user plane can be reduced</p><p>　　from four in release 6 to two in r

8、elease 7. The HSPA flat architecture in release 7 is similar to the architecture agreed upon for 3GPP long-</p><p>　　term evolution (LTE), thus enabling the later ,smooth evolution from HSPA to LTE.</p>

9、;<p>　　LTE will be specified as part of release 8 and further push the radio capabilities higher with larger bandwidth and lower latency. The LTE</p><p>　　performance target is to provide two-to-four

10、times the performance of the HSPA release 6 reference case [1]. 3GPP release 7 and 8 solutions for the HSPA evolution will be worked in parallel together with the LTE development, and some aspects of the LTE work are exp

11、ected to reflect on the HSPA evolution as well.</p><p>　　3GPP release 7 was completed in June 2007 ,with some work remaining on the performance requirements. Commercial deployment and</p><p>　　d

12、evices are expected by 2009.</p><p>　　INTRODUCTION</p><p>　　The Third Generation Partnership Program(3GPP) specifications included major improvements in downlink data rates and capacity in relea

13、se 5 with the introduction of high-speed downlink packet access (HSDPA) in 2002. Similar technical solutions were applied to the uplink direction as part of the release 6 with high-speed uplink packet access (HSUPA) at t

14、he end of</p><p>　　2004. HSDPA and HSUPA technologies are described in [2]. 3GPP release 7 in June 2007 completed a number of additional and substantial enhancements to the end-user performance, to the cell

15、throughput, and to the network architecture. The detailed 3GPP release 7 solutions and their performance benefits are summarized in this paper.</p><p>　　CONSUMPTION REDUCTION WITH</p><p>　　CONTI

16、NUOUS PACKET CONNECTIVITY</p><p>　　The technology evolution, in general, helps to decrease the mobile terminal power consumption. Also, the fast and accurate power control in</p><p>　　wide-band

17、code division multiple access(WCDMA) helps to minimize the transmitted power levels. The challenge in 3GPP fromrelease 99 to release 6 is still the continuous reception and transmission when the mobile terminal is using

18、HSDPA/HSUPA. 3GPP release 7 introduces a few improvements to HSDPA/HSUPA that help to reduce the power</p><p>　　consumption for packet services like browsing and voice-over-IP (VoIP).</p><p>　　3

19、GPP release 6 mobile terminal keeps transmitting the physical control channel even if there is no data channel transmission. Release 7 mobile terminal cuts off the control channel transmission when there is no data</p

20、><p>　　channel transmission, allowing it to shut down the transmitter completely. This solution is called discontinuous uplink transmission, and it brings clear savings in transmitter power consumption.</p&g

21、t;<p>　　A similar concept also is introduced in the downlink, where the terminal must wake up only occasionally to check if the downlink data</p><p>　　transmission is starting again. The terminal can

22、use the power-saving mode during other parts of the frame if there was no data to be received.</p><p>　　This solution is called downlink discontinuous reception. The discontinuous transmission concept is ill

23、ustrated in Fig. 1 for Web browsing. As soon as the Web page is downloaded, the connection enters discontinuous transmission and reception.</p><p>　　The estimated savings in mobile terminal power consumption

24、 are shown in [3]. The power consumption of the radio modem ideally can be</p><p>　　reduced by more than 50 percent when the user is reading the Web page. The difference in the actual operation times will be

25、 smaller because</p><p>　　there are other components — such as display and application processor — taking some power, but there will still be major benefits in the mobile</p><p>　　terminal opera

26、tion times.</p><p>　　PEAK DATA RATE INCREASE WITH</p><p>　　MIMO AND HIGHER ORDER</p><p>　　MODULATION</p><p>　　The downlink peak data rate with release 6 HSDPA is 10.8 M

27、bps, with 3/4 coding and 14.4 Mbps, without any channel coding. In theory,</p><p>　　there are a number of ways to push the peak data rate higher: larger bandwidth, higher order modulation, or multi-antenna t

28、ransmission with</p><p>　　multiple input multiple output (MIMO). MIMO and higher order modulation are included into HSPA evolution in release 7. 3GPP long term evolution (LTE) also enables larger bandwidth,

29、up to 20 MHz. The 3GPP MIMO concept, for HSDPA operation in release 7, employs two transmit antennas in the base station and two receive antennas in the terminal and uses a closed loop feedback from the terminal for</

30、p><p>　　adjusting the transmit antenna weighting. The diagram of the MIMO transmission is shown in Fig. 2. </p><p>　　Higher order modulation enables higher peak bit rate without increasing the tran

31、smission bandwidth. Release 6 supported quadrature phase shift keying (QPSK) and 16 quadrature amplitude modulation (QAM) transmission in the downlink and dual-binary phase shift keying (BPSK) in the uplink. Dual-channel

32、 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 compared to QPSK by transmitting four bits </p><p>

33、;　　The system simulation results with 64 QAM in macro cells are illustrated in Fig. 3. The 64 QAM modulation improves the user data rate</p><p>　　with 15–25 percent probability depending on the scheduling (R

34、R = 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.</p><p>　　New HSDPA and HSUPA terminal categories were a

35、dded 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 21.1 Mbps and with MIMO, 28.0 Mbps. The combination of 2x2 MIMO and 64 QAM modulation wou

36、ld push the theoretical peak data rate beyond 40 Mbps; however, that combination 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, doublin

37、g the uplink p</p><p>　　CELL CAPACITY AND DATA RATE</p><p>　　ENHANCEMENT WITH</p><p>　　ADVANCED MOBILE RECEIVERS</p><p>　　The introduction of HSDPA to release 5 include

38、d performance requirements with Rake receiver using single antenna. Release 6 brought two types of enhanced receivers: enhanced type 1,corresponding to a two-antenna Rake receiver and enhanced type 2, corresponding to a

39、one-antenna chip equalizer. Release 7 brought further enhanced type 3, corresponding to a two-antenna chip equalizer.</p><p>　　The antenna diversity improves the signal to interference ratio because the inte

40、rference is partly uncorrelated in the different antennas. The chip equalizer removes intra-cell interference caused by the multipath propagation leading to higher signal-to-interference ratio. When the signal-to-interfe

41、rence 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 receiv</p><p>

42、;　　The advanced receiver with the chip equalizer improves the capability of the mobile terminal to compensate difficult channel conditions, which results in a higher CQI value reported by the advanced mobile terminal tha

43、n 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</p><p>　　and thus, a mobile terminal with

44、a chip equalizer receiver is able to receive high data rates in more difficult channel conditions.</p><p>　　The advantage of such a relation between the advanced receivers and reported CQI values is that no

45、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 i

46、s used to set the performance requirements that a mobile terminal must meet to declare it as enhanced Type 1-, 2-, or 3-compliant.</p><p>　　The advanced receivers in mobile terminals improve the single user

47、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</p><p>　　res

48、ults are shown with different number of codes in the network and with round robin and a proportional fair-packet scheduler. More</p><p>　　details about the HSDPA packet schedulers can be found in [2]. The ga

49、in of the two-antenna equalizer receiver is 100–150 percent compared to the one-antenna Rake and 50–80 percent compared to the one-antenna equalizer. The achievable macro cell capacity is 4 Mbps with a two-antenna equali

50、zer with a dedicated HSDPA carrier and proportional fair scheduler. That capacity corresponds to the spectral efficiency of nearly 1 bps/Hz/cell.</p><p>　　The downlink MIMO transmission further improves the

51、cell throughput. The more detailed capacity evaluations can be found in[5].</p><p>　　Additional downlink capacity enhancements can be achieved with inter-cell interference cancellation in the receiver of the

52、 mobile terminal. Such enhanced receivers also are being studied in 3GPP to improve the capacity and especially the cell-edge data rates. Those receivers are called enhanced Type 3i.</p><p>　　LAYER 2 OPTIMIZ

53、ATION WITH</p><p>　　FLEXIBLE RLC AND</p><p>　　MAC SEGMENTATION</p><p>　　The WCDMA release 99 specification was based on the packet retransmissions running from the radio network con

54、troller (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. Ano

55、ther 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.</p><p>　　The RLC payload size is fi

56、xed to 40 bytes in release 99 for acknowledged mode data. The same RLC solution is applied to HSDPA release 5 and HSUPA release 6, as well: the 40-byte packets are transmitted from RNC to the base station in the case of

57、HSDPA. An additional configuration option to use an 80-byte 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

58、 2-ms transmission time interval(T</p><p>　　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

59、 available for HSDPA scheduling and the possible minimum data rates.</p><p>　　3GPP HSDPA and HSUPA allow the optimization of the layer 2 operation because layer 1retransmissions are used, and the probability

60、 of</p><p>　　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. Ther

61、efore, 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.</p><p>　　This optimization is included in the

62、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 Internet Protocol (IP) packet, which is typically 1500 bytes

63、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 requ

64、irements when required.</p><p>　　The flexible RLC and MAC segmentation offers a number of benefits in terms of layer 2 efficiency and in terms of peak bit rates.</p><p>　　? The relative layer 2

65、overhead is reduced. With the RLC header of 2 bytes, the RLC overhead is 5 percent in case of a 40-byte RLC packet. When the RLC packet size increases to 1500 bytes, the RLC header over head is reduced to below 0.2 perce

66、nt, and the total L2 overhead is reduced to 1 percent. The reduction of the overhead can improve the effective application data throughput.</p><p>　　? The RLC block size can be flexibly selected according to

67、 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

68、in VoIP or streaming applications.</p><p>　　? 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 sinc

69、e the RLC packet size is increased, and octet</p><p>　　aligned protocol headers avoid bit sifting in high data rates connections. Both reduce layer 2 processing load and make the high bit rate implementation

70、 easier.</p><p>　　? Full flexibility and resolution of available data rates for the HSDPA scheduler.</p><p>　　SET UP TIME REDUCTION WITH</p><p>　　ENHANCED FORWARD ACCESS</p>

71、<p><b>　　CHANNEL</b></p><p>　　The WCDMA network data rate and latency are improved with the introduction of release 5 HSDPA and release 6 HSUPA. The end-user</p><p>　　performanc

72、e can be further improved by minimizing the packet call set up time and the channel allocation time. The expected packet call set</p><p>　　up time with release 7 will be less than one second. After the packe

73、t 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 t

74、o 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. Releas</p&g

75、t;<p>　　? 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.</p><p&

76、gt;　　? The state transition from Cell_FACH to Cell_DCH would be practically seamless.After the network resources for the channel allocation are available, a seamless transition to Cell_DCH can take place, because the phy

77、sical channel is not changed.</p><p>　　? 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,

78、 2-ms 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.</p><p>　　Because the existing physical channe

79、ls are utilized in enhanced FACH, there are only minor changes in layer 1 specifications, which allow fast</p><p>　　implementation of the feature. Enhanced FACH can co-exist with release 99 and with HSDPA/HS

80、UPA 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.</p><p>　　VOICE-OVER-IP</p><p>　　CAPACITY

81、 ENHANCEMENT</p><p>　　Circuit-switched voice used to be the only way to provide voice service in cellular networks. The introduction of third generation networks, including WCDMA release 99, made it possible

82、 to run voice-over-IP (VoIP) over cellular networks with reasonable quality, but with lower spectral efficiency than circuit-switched voice. 3GPP releases 5 and 6 HSPA was originally designed to carry high bit-rate, dela

83、y-tolerant data. A number of features have been introduced to 3GPP releases 6 and 7 to improve </p><p>　　The discontinuous uplink transmission of Fig. 1 not only reduces the power consumption, but also less

84、interference is caused by the terminal</p><p>　　and consequently, higher capacity can be achieved. The discontinuous uplink transmission can be applied for VoIP calls as well. The terminal can shut down the

85、transmitter between the VoIP packets. The VoIP capacity gain of release 7 discontinuous uplink transmission is approximately 50 percent compared to release 6.</p><p>　　The VoIP capacity simulations are summa

86、rized in Fig. 6 in terms of maximum number of simultaneous users per sector per 5-MHz carrier.</p><p>　　The circuit-switched capacity with release 99 is estimated to be 60–70 users, whereas the VoIP capacity

87、 with HSPA release 7 increased to 120</p><p>　　users. The VoIP capacity assumes that IP header compression is used.</p><p>　　3GPP release 7 also allows high-speed,shared-channel channel (HS-SCCH

88、)-less operation in downlink to minimize the interference</p><p>　　from HS-SCCH. The gains of HS-SCCH-less operation are not included in Fig. 6, but are presented in [10].</p><p>　　The main reas

89、ons for the higher VoIP capacity over HSPA compared to the circuit-switched voice over -dedicated channels are summarized</p><p>　　as follows.</p><p>　　? Minimized L1 control overhead with downl

90、ink, fractional-dedicated physical channel(DPCH) of release 6 and discontinuous uplink transmission of release 7.</p><p>　　? Fast L1 signaling allows the use of L1 retransmissions from node-B also for VoIP,

91、leading to a lower power requirement. The retransmissions cannot be used for voice when using dedicated channels because the</p><p>　　L2 retransmission delay is too long from the RNC.</p><p>　　?

92、 The equalizer terminal for HSDPA can reduce the intra-cell interference and improve the capacity.</p><p>　　? The VoIP optimized base station scheduler improves operation with HSDPA. Voice transmission on a

93、dedicated channel cannot utilize scheduling.. In short, all the latest 3GPP activities are targeted to improve packet data performance. Also VoIP service benefits from those improvements, pushing VoIP efficiency higher.

94、Non-IP multimedia subsystem (IMS) VoIP services still will have challenges with mobile terminal power consumption due to frequent keep-alive messages. Those messages must beexchange</p><p>　　terminal to main

95、tain the IP connectivity. That aspect of the mobile terminal power consumption can be improved with discontinuous recep-</p><p>　　tion in the Cell_FACH state. That feature will be discussed as part of releas

96、e 8.</p><p>　　MULTICAST AND BROADCAST DATA</p><p>　　RATE INCREASE WITH</p><p>　　SINGLE FREQUENCY NETWORK</p><p>　　Multimedia broadcast multicast service (MBMS) was adde

97、d to 3GPP as part of release 6. 3GPP release 6 can use soft combining of the MBMS</p><p>　　transmission from the adjacent cells. The soft combining considerably improves MBMS performance at the cell edge com

98、pared to receiving</p><p>　　the signal from a single cell only. Therefore, release 6 MBMS provides a very good starting point for broadcast services from the performance point of view.</p><p>　　

99、Even if the soft combining can be utilized in release 6, the other cell signals still cause interference to the MBMS reception because the adjacent cells are not orthogonal due to different scrambling codes. If the same

100、scrambling code would be used in all cells, together with a terminal equalizer, the other cells transmitting the same signal in a synchronized network would be seen as a single signal with time dispersion. That solution