MAC-hs sublayerAs compared with R99, HSDPA adds a MAC sublayer (MAC-hs sublayer) in the system architecture. The MAC-hs sublayer is introduced in Node B for the following reasons: 1. 1. Fast scheduling of multiple users. 1. 2. Reduces the retransmission delay, and thus improve subscriber experience. 1. 3. Improves the link adaptation performance of the AMC technology. The AMC technology adjusts the modulation and coding mode according to the channel quality. Its performance is sensitive to the delay in reporting the channel quality. The longer the delay is, the worse the link adaptation performance is. Physical Channel To implement the function of the HSDPA, new channels are introduced in the physical layer of the 3GPP R5. 1. High-Speed Physical Downlink Shared Channel (HS-PDSCH): the physical channel used for transmitting downlink subscriber data 1. High-Speed Shared Control Channel (HS-SCCH): the signaling channel used for the downlink in the physical layer 1. High-Speed Dedicated Physical Control Channel (HS-DPCCH): the signaling channel used for the uplink in the physical layer HS-PDSCH The HS-PDSCH is a physical downlink channel. It is introduced to carry the actual subscriber data transmission. The spreading factor is fixed to 16, the modulation mode can be QPSK or 16QAM, and 1/3 Turbo codes are used for channel coding.

M refers to the bit number represented by each modulation symbol. For QPSK, M is equal to 2 and the bit number of the physical channel in the 2ms TTI is 960, which means the bit rate is 480 kbps. For 16QAM, M is equal to 4 and the bit number of the physical channel in the 2ms TTI is 1,920, which means the bit rate is 960 kbps.If 15 code channels transmit data concurrently and the modulation mode is 16QAM, the peak rate of the physical layer is 14.4 Mbps [15 (number of HS-PDSCH code channels) * 960kbps] apeak rate of the MAC-hs layer is 13.976 Mbpsthe largest MAC-hs PDU to be transmitted is 27,952 bits in size and the largest bit number of the physical channel is 28,800: 15 (number of HS-PDSCH code channels) * 1,920 (number of physical channel bits per code channel). Therefore, the maximum MAC-hs rate of the HS-PDSCH is 27,952 bits/2 ms =13.976 Mbps, and the maximum physical channel rate is 28,800 bits/2 ms = 14.4 Mbps.

HS-SCCH The HS-SCCH is a physical downlink channel. It is introduced to carry the physical layer signaling required by the coding HS-PDSCH. The spreading factor is 128, the modulation mode is QPSK, channel codes are convolutional codes, and the first-order rate is used for matching. As shown in Figure 3-4, the signaling carried by the HS-SCCH comprises two parts: The first part (Slot #0) includes channelization codes and modulation mode. The UE decodes the information in Slot #1 to enable the HS-PDSCH receiving process at the Slot #2 start time and avoid the chip-level data cache at the UE side. The second part (Slot #1 and Slot #2) includes the size indication of transport block, HARQ process number, RV parameter, and indication of new data. According to the maximum number of users supported by code multiplexing, the UTRAN allocates a corresponding number of HS-SCCH code channels. Each UE can monitor a maximum of four HS-SCCHs. Usually, a maximum of four users are scheduled within one TTI (thus preventing the HS-SCCHs from consuming excessive power and code channel resources). The number of HS-SCCHs can be configured according to the power resource and code channel resource of the HSDPA service. If a UE is scheduled continuously, the HS-SCCHs should use the same code channel within continuous TTIs, so as to reduce UE complexity and enhance the reliability of signaling.

Number of HS-SCCH corresponds to the max number of user that can be scheduled in 1 TTI.E.g HS-SCCH = 3 corresponds that max 3 users can be scheduled in 1 TTIHS-DPCCH The HS-DPCCH is physical uplink channel. It is introduced to carry necessary feedback information, including the HS-PDSCH decoding information (ACK/NACK) and channel quality indicator (CQI). Its spreading factor is 256 and its modulation mode is BPSK.

Part I: The ACK/NACK domain indicates the decoding result of the HS-PDSCH. 10 bits are used to indicate the downlink decoding information, including ACK/NACK/DTX. The ACK domain indicates that the downlink HS-SCCH and HS-PDSCH decoding results are correct. The NACK domain indicates that the downlink HS-SCCH decoding result is correct but the HS-PDSCH decoding result is not correct. The DTX domain indicates that the downlink HS-SCCH decoding result is not correct and the HS-PDSCH is not demodulated. Part II: The CQI domain indicates the channel quality of the UE. The CQI value ranges from 0 to 30. 0 indicates that the channel quality is very bad and thus transmission is not allowed. The CQI values of 1 to 30 indicates that the supported channel quality ranges from single-code-channel QPSK transmission to 15-code-channel 16QAM transmission (including diversified rates