Field experiments on adaptive modulation and channel coding coupled with hybrid ARQ with packet combining based on HSDPA air interface

摘要

This paper presents field experimental results on the throughput performance employing adaptive modulation and channel coding (AMC) coupled with hybrid automatic repeat request (ARQ) with packet combining based on the High-Speed Downlink Packet Access (HSDPA) air interface in the forward link in a multipath fading channel. In the implemented equipment, the optimum modulation and coding scheme (MCS) is selected among four candidates: MCSI (QPSK data modulation with the channel coding rate R = 1/2, hereafter simply referred to as QPSK with R = 1/2); MCS2 (QPSK with R = 3/4); MCS3 (16QAM with R = 1/2); and MCS4 (16QAM with R = 3/4). It is selected according to the measured signal-to-interference power ratio (SIR) over one transmission time interval (TTI) (=2 msec) in AMC, and both Type-I hybrid ARQ with packet combining, (hereafter Chase combining) and Type-II hybrid ARQ (Incremental redundancy) are implemented. Field experimental results verify that the AMC loop satisfactorily works so that almost the maximum throughput is achieved at each instantaneous received SIR over one TTI by accurately selecting the optimum MCS, and clarify that the peak throughput of approximately 6.4 Mbps is achieved when the instantaneous received SIR is greater than 21.5 dB, at the average moving speed of approximately 5 km/h in an actual multipath fading channel (note that the achieved peak throughput of approximately 6.4 Mbps at nine-code multiplexing suggest the possibility of a peak throughput above 10 Mbps when 15-c ode multiplexing is applied). Furthermore, the field experiments elucidate that Incremental redundancy exhibits superior throughput performance to that of Chase combining in the lower received SIR environments, thereby in the low throughput channel below approximately 2.3 Mbps, where retransmissions of data packets frequently occur caused by the selection errors of the optimum MCS in the AMC.