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Dual ARQ

Dual ARQ. Description ARQ sub-channels Call Flow Summary. Dual ARQ. Dual ARQ is a strategy which exploits ACKs, NAKs and retransmissions at the physical-layer and the RLP-layer. Number of retransmissions are configurable for both layers.

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Dual ARQ

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  1. Dual ARQ • Description • ARQ sub-channels • Call Flow • Summary

  2. Dual ARQ • Dual ARQ is a strategy which exploits ACKs, NAKs and retransmissions at the physical-layer and the RLP-layer. • Number of retransmissions are configurable for both layers. • RLP timer is introduced for layer 2 NAK.Covers delay associated with physical layer retransmissions. • Physical layer ACK/NAKs are generated for one or more slots. • Objectives • Reduces layer 2 frame error w/o excessive layer 2 packet delay • Impact on end-to-end TCP performance. • Dual layer ARQ scheme optimizes the following: • supports fast error recovery per cell-site through physical layer ARQ • supports robust error recovery and fast cell switching through layer 2 (RLP)

  3. Symbol Repetition (Factor=128) Signal Point Mapping 0->+1 1-> -1 2048 chips / Slot F-ARQ 128 Symbols / Slot max 1 symbol / slot Walsh Cover ( + + - - - - + + + + - - - - + +) Dual ARQ sub-channels RL physical layer fast ARQ sub-channel for ACK/NAK • Part of 1XRTT RL proposal for 1XEV • transmitted as required to acknowledge Forward Link data packets • Only the serving BTS for the forward link decodes the ACK/NAK sub-channel. Reverse RLP NAK • Reverse RLP NAK frame is sent on R-DCCH or R-FCH.

  4. Dual ARQ Procedures and Call Flow(Physical layer ARQ) Transmit side: Twindow Twindow Twindow Twindow ACK/ NAK ACK/ NAK ACK/ NAK ACK/ NAK Receive side: • The transmit side expects an ACK/NAK from the receive side within a timing window, Twindow. The timing window is defined with respect to the time when the physical layer frame is transmitted • The receive side is expected to send out an ACK/NAK within a timing window, after the physical layer frame is received. This timing window is configured/negotiated with the BTS during call setup. • The BTS identifies which physical layer frame the ACK/NAK corresponds to by the relative time the ACK/NAK is received. No sequence number is required for the physical layer frame.

  5. Dual ARQ Procedures and Call Flow(Dual layer interaction: Scenario 1 – no layer 2 retransmission triggered) RLP receive Physical layer receive RLP transmit Physical layer transmit ACK NAK Frame erasure detected, NAK timer started ACK Frame received Before NAK timer Expires, no RLP NAK is sent ACK

  6. Dual ARQ Procedures and Call Flow(Dual layer interaction: Scenario 2 –layer 2 retransmission triggered) In this example,up to 1 retransmission attempt is allowed at physical layer RLP receive Physical layer receive RLP transmit Physical layer transmit ACK NAK Frame erasure detected, NAK timer started ACK NAK NAK timer Expires, RLP NAK is sent

  7. Dual ARQ Procedures and Call Flow(Dual layer interaction: Scenario 3 – physical layer NAK is decoded as ACK) In this example,up to 1 retransmission attempt is allowed at physical layer RLP receive Physical layer receive RLP transmit Physical layer transmit ACK NAK-> ACK Frame erasure detected, NAK timer started ACK ACK NAK timer Expires, RLP NAK is sent

  8. Dual ARQ Procedures and Call Flow(Dual layer interaction: Scenario 3 – physical layer ACK is decoded as NAK) In this example,up to 1 retransmission attempt is allowed at physical layer RLP receive Physical layer receive RLP transmit Physical layer transmit ACK ACK->NAK ACK Duplicates detected, discard ACK

  9. Dual ARQ Summary • Combined physical layer/RLP ARQ scheme will reduce delays compared to RLP-only ARQ strategies. • Favorable impact on end-to-end TCP performance. • The number of retransmissions at both layers is configurable. • Settable timers should allow robust recovery from messaging errors.

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