An efficient symbol-level combining scheme for MIMO systems with hybrid ARQ

Low‐complexity symbol‐level combining for hybrid automatic repeat request in multiple‐input multiple‐output systems with linear detection

“…o(r, j, n) = n regardless of r, j, and n, is also considered for the proposed SLC scheme. In addition, the optimal row vector selection criterion (denoted as the optimal (OPT) criterion in the sequel) based on the highest SINR with the exact SINR computation according to a given detection criterion is considered for the proposed SLC scheme as well, where the OPT criterion finds a combination of the row vectors that achieves the highest SINR for a given MMSE or ZF detection among all possible Brute-force combining [11] O (r + 1)N R N 2 T + N 3 T Pre-combining [10] O N R N 2 T + N 3 T Post-combining [10] O N R N 2 T + N 3 T CASLC-IQ [12] O…”

“…In [12], two QRD-SLC schemes were proposed, which consist of the concatenation-assisted SLC with the direct QRD (CASLC-DQ) and that with the incremental QRD (CASLC-IQ). Since the CASLC-IQ achieves the identical performance to the CASLC-DQ with a reduced computational complexity, only the CASLC-IQ is considered in this paper.…”

“…Owing to sending the same transmit symbols over transmissions, Chase combining-based HARQ (CC-HARQ) [2] can be jointly used with other techniques in a much easier way [7][8][9][10][11][12][13][14], e.g. precoding scheme at the transmitter [7][8][9] and the symbol-level combining (SLC) scheme at the receiver [10][11][12][13][14]. Specifically, a number of SLC schemes [10][11][12][13] have been developed for CC-HARQ in multiple-input multiple-output (MIMO) systems to provide additional space diversity as well as time diversity.…”

“…precoding scheme at the transmitter [7][8][9] and the symbol-level combining (SLC) scheme at the receiver [10][11][12][13][14]. Specifically, a number of SLC schemes [10][11][12][13] have been developed for CC-HARQ in multiple-input multiple-output (MIMO) systems to provide additional space diversity as well as time diversity.…”

“…The work in [11] has shown that the pre-combining scheme achieves the identical performance to the brute-force combining scheme with a reduced computational complexity. To further reduce the computational complexity, the QR decomposition-based SLC (QRD-SLC) schemes were proposed, which have the same performance as the pre-combining scheme with a reduced computational complexity in case of the maximum-likelihood (ML) detection [12]. However, if linear detection such as the minimum mean-square-error (MMSE) or zero-forcing (ZF) is considered instead of ML detection at the receiver, the QRD-SLC schemes require a higher computational complexity than the pre-combining scheme by performing the QRD on the aggregated channel matrix in every retransmission.…”