Hybrid ARQ for future WiMAX system
As a mandatory feature of WiMAX system, hybrid ARQ (HARQ) plays a crucial role in ensuring transmission reliability needed on the wireless link. We evaluated the performance of current HARQ protocol in the context of 802.16j multihop relay network and 802.16m next generation WiMAX system. Based upon the insights gained therein, we further designed an adaptive HARQ scheme, which performs intelligent fragmentation to adapt to the channel condition, and provides indispensable support to traffic aggregation/tunneling.
Background & Objective: HARQ is a key technology in next generation wireless systems that spans both MAC and PHY layers, and exploits time/frequency diversity and coding gain. However, the complicated interaction between HARQ, ARQ at MAC layer and the capacity at physical layer has not been completely understood, let alone been optimized. The objective of this work is to establish a full understanding of the cross-layer protocol interaction and address the performance issues identified thereof.
Technical Discussion: We first developed a more profound understanding of the interaction between MAC layer ARQ, HARQ and physical layer capacity, the confirmed that no window lock effect would occur at ARQ or HARQ level, given the current setting of IEEE 802.16e PHY. Nevertheless, the study reveals that HARQ performance can severely deteriorate in IEEE 802.16j relay network or IEEE 802.16m next generation WiMAX system, due to potential mismatch of various operating parameters. As a solution, we designed an adaptive HARQ protocol, which fragments upper layer packet at the MAC layer instead of in HARQ, if the physical channel condition degrades below certain threshold. Moreover, we identified the operating region of the number of parallel channels (i.e., ACID) in HARQ that can optimize the system level performance for the 802.16j and 802.16m network. Last but not least, we proposed a set of new features for HARQ so that it can support the aggregation/tunnel operation on relay links.
Future Direction: The proposed HARQ scheme that provides support to tunneling/aggregation operation has been accepted into IEEE 802.16j draft standard. New contributions based upon the research results of this project will be made to IEEE 802.16m.
Contact: Zhifeng (Jeffrey) Tao
Technology Area: Digital Communications
Modification Date: September 20, 2007
