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

This paper presents field experimental results on throughput performance employing adaptive modulation and channel coding (AMC) coupled with hybrid automatic repeat request (HARQ) with packet combining based on the high-speed downlink packet access (HSDPA) air interface in the forward link under multipath fading channel. In the implemented equipment, optimum modulation and coding scheme (MCS) is selected among four candidates such as 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) according to the measured signal-to-interference power ratio (SIR) over one transmission time interval (TTI) (=2 msec) in AMC and both Type-I HARQ with packet combining, (hereafter Chase combining) and Type-II HARQ (incremental redundancy) are implemented in the preliminary evaluation on AMC by the laboratory experiments employing multipath fading simulators, we elucidate that the average throughput above 5 Mbps was achieved at the average received signal energy per chip-to-background noise power spectrum density ratio (E_c/N₀) of approximately 17 dB in a 1-path fading channel with the fading maximum Doppler frequency of f_D=5 Hz and nevertheless that the achievable average peak throughput becomes approximate 2.6 Mbps due to the multipath interference in a 2-path fading channel when the average signal power of the second path was lower by 3 dB than that of the first path. We compare the superiority of incremental redundancy and Chase combining in a slow-to-fast multipath fading channel along with the use of the AMC. Furthermore, we present the achievable throughput performance employing AMC coupled with HARQ with packet combining in a real multipath fading channel by field experiments conducted near Tokyo, in order to clarify the potential of HSDPA for actual system application.