HSDPA

Physical Layer

• Hybrid ARQ with Soft Combining (incremental redundancy)
• 24-bit CRC attached to each transport block
• Allows 16QAM data modulation for Rel.5/6 & 64QAM for Rel.7 (Note: Higher order modulation increases EVM at cell edge)

DOWNLINK CHANNELS

• HS-PDSCH (Data)
• HS-SCCH (HS-RNTI, TFRI (Channelisation code list, modulation scheme, TB size), HARQ process number)
• F-DPCH (TPC-only R99 legacy channel used for Rel.6 HDSPA)

UPLINK CHANNELS

• HS-DPCCH (HARQ ACKs/NACKs for downlink & CQI reports)

CQI Reports

CQI value sent by UE is a request to the NodeB for a corresponding:

• Transport block size
• Modulation scheme
• Number of HS-DSCH codes

MAC Layer

• MAC-hs layer defined for Rel.5
• MAC-ehs layer defined for Rel.6 (allows variable-size MAC-d payloads)
• Allowed MAC layer to be moved out to the NodeB for faster HARQ operation
• Uses reordering queues