Experiments on real-time 1-Gbps packet transmission using antenna-independent AMC in MIMO-OFDM broadband packet radio access (2006)

This paper presents experimental results on real-time 1-Gbps packet transmission using antenna-independent adaptive modulation and channel coding (AMC) in 4-by-4 MIMO multiplexing using Maximum Likelihood Detection employing QR decomposition and the M-algorithm (QRM-MLD) with adaptive selection of surviving symbol replica candidates based on the maximum reliability (ASESS) in OFDM radio access. In the implemented MIMO transceiver, the optimum data modulation and Turbo coding rate are selected independently at each transmission stream based on the received signal-to- interference plus noise power ratio (SINR) of each packet frame over a 100-MHz bandwidth. The experimental results show that antenna-independent AMC is effective in improving the throughput when the difference in the average path-loss among transmission branches appears such as a difference of greater than 6 dB due to e.g., shadowing variations. It is further shown that the extremely high-speed real-time packet transmission of greater than 1 Gbps in a 100-MHz channel bandwidth (i.e., 10 bits/second/Hz) is achieved at the average received signal energy per symbol-to-noise power spectrum density ratio (Es/N0) per receiver branch of approximately 18 dB using antenna- independent AMC in 4-by-4 MIMO multiplexing. I. INTRODUCTION For future mobile communication systems beyond the 3G system, an all packet-based highly-efficient radio access scheme is necessary with a short delay (i.e., low latency) and with high affinity to IP-based core networks. Among the requirements for radio access, the supportable data rate is the most directly related to providing customer services. In Recommendation ITU-R M.1645, the maximum data rate supported in the new mobile access scheme is defined as 100 Mbps and that in the new nomadic/local area wireless access scheme is greater than 1 Gbps (1). Although two different target data rates in the respective radio environments are defined in the recommendation, our concept is to support these two data rate requirements using the same radio access, i.e., the same air interface by only changing the radio parameters for realizing deployment of one radio access at low cost (2). We presented field experimental results on the measured throughput of greater than 100 Mbps using Variable Spreading Factor (VSF)-Orthogonal Frequency and Code Division Multiplexing (OFCDM) transceivers employing a 100- MHz channel bandwidth in real propagation environments (3). Furthermore, the effectiveness of key techniques relevant to packet access such as adaptive modulation and channel coding (AMC) and hybrid ARQ with packet combining for broadband radio access with a 100- MHz channel bandwidth was clarified, and the achievable radio throughput and TCP throughput as a function of the cell distance in cellular environments were reported. In this paper, we present experimental results on real-time packet transmission of greater than 1 Gbps using antenna-independent AMC associated with frequency diversity in 4-by-4 multiple-input multiple-output (MIMO) multiplexing (4), (5) in Orthogonal Frequency Division Multiplexing (OFDM) radio access. Assuming the main application of MIMO multiplexing to such local areas where there is a high traffic demand in a small area, we employ a high coding rate together with a spreading factor of one based on the proposed VSF concept. The radio parameters such as the carrier frequency, channel bandwidth, and sub- carrier spacing of the implemented MIMO transceivers are identical to those of the transceivers with which we previously attained the throughput of greater than 100 Mbps in field experiments according to our proposed radio access concept (3). In the implemented MIMO multiplexing transceiver, we applied adaptive selection of surviving symbol replica candidates based on the maximum reliability (hereafter ASESS) (6) in MLD employing QR decomposition and the M-algorithm (hereafter QRM-MLD) (7) to reduce the extremely high level of computational complexity in the conventional MLD (hereafter Full MLD). By employing the QRM-MLD with ASESS, the required average received signal energy per bit-to-noise power spectrum density ratio (Eb/N0) using MLD, which satisfies the same packet error rate (or throughput), is much smaller than that using Minimum Mean Squared Error (MMSE) type co-channel interference suppression or Vertical-Bell Laboratories layered Space Time (V-BLAST) method (8), with only a few times computational complexity that of MMSE receiver. The current paper focuses on real-time 1-Gbps high-speed packet transmission using antenna-independent AMC using the QRM- MLD with ASESS. In the OFDM based broadband radio access, the AMC in the frequency domain exploiting frequency-selectivity is very beneficial in improving the sector or user throughput in SISO (i.e., independent AMC at each frequency block unit called a chunk). In the case of MIMO multiplexing with 4-by-4 antennas, however, our view is that the AMC in the frequency domain is not always effective for the following reasons. If there are four receiver antenna branches, the averaging of all received signals after orthogonalization by QR decomposition is necessary over four received antenna branches to achieve accurate signal detection. Accordingly, the difference in the received signal level among the chunks becomes small due to the large receiver diversity effect by four antenna branches. In addition, when AMC in the frequency domain is not employed, a mobile station (MS) only has to report one channel quality indicator (CQI) set at every one- packet duration. This brings about a reduction in the number of control signaling bits. Therefore, in the paper, we employ frequency diversity over the entire channel bandwidth instead of AMC in the frequency domain. Thus, we implemented antenna-independent AMC, in which the optimum data modulation and Turbo coding rate are selected independently at each transmission stream according to the feedback received signal-to-interference plus noise power ratio (SINR) (note that the interference power is the inter-symbol interference caused by the delayed multipath, which exceeds the guard interval duration) of each packet frame for all transmitter antenna branches over a 100-MHz bandwidth. The rest of the paper is organized as follows. We first present the configuration of the implemented transceiver in Section II. Next, Section III describes the experiment setup for the subsequent experiments in Section IV.