Abstract
In this paper, a multiuser space-time line code (MU-STLC) scheme is newly designed that concurrently delivers multiple STLC signals to multiple users, and a preprocessing matrix for the MU-STLC is derived based on the minimum mean square error criterion. The novel MU-STLC method retains the conventional STLC receiver structure so that each user linearly combines the received signals without using the full channel state information to decode the STLC signals. With more transmit antennas than the number of users having two receive antennas, a transmit antenna selection (TAS) scheme is investigated in combination with the proposed MU-STLC method, and the detection signal-to-interferenceplus-noise ratio (SINR) is derived depending on a specific TAS pattern. The performance improvement obtained from the TAS is significant, yet finding the optimal TAS pattern is a combinatorial problem that requires prohibitively high computational complexity. To resolve this issue, a greedy TAS algorithm is also proposed that iteratively selects the transmit antenna maximizing the detection SINR in each greedy step. The numerical results verify the efficacy of the proposed MU-STLC system with the SINR-based greedy TAS algorithm in terms of the bit error rate performance and computational complexity. For example, comparing with a scheme that selects four antennas from eight antennas randomly to support four users, the proposed TAS scheme can reduce the required signal-to-noise ratio for achieving 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> bit-error-rate by approximately 6 dB when quadrature phase-shift keying is employed. Furthermore, the proposed method can achieve comparable performance to the optimal antenna selection scheme with the reduced computational complexity by O(M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> ) from O(M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">U+3</sup> ), where M and U are the numbers of transmit antennas and selected antennas (or users), respectively.
Highlights
A new full-rate full-spatial diversity achieving scheme, called space–time line code (STLC), was proposed in [1], [2]
Under the symmetric channel state information (CSI) conditions, i.e., full CSI is required at a transmitter for STLC whereas, at a receiver for space–time block code (STBC), the full spatial-diversity gain is achieved at both systems
Whereas an optimal beamforming scheme with CSIT requires a complexity order of O(M 3) for finding the dominant singular vector, the complexity of the STLC linearly increases with the number of transmit antennas, O(M), and the STLC scheme is more robust against the CSI uncertainty [2]
Summary
A new full-rate full-spatial diversity achieving scheme, called space–time line code (STLC), was proposed in [1], [2]. For the proposed MU-STLC transmission, the transmitter uses a preprocessing matrix designed in the minimum mean square error (MMSE) sense based on the CSI, and each user having two receive antennas decodes its STLC signal, utilizing the low-complexity STLC combining structure. RU, rU,2 where ru,t ∈ C2×1 is the received signal vector, whose nth element ru,n,t is the received signal at the nth receive antenna of user u at time t; H = [h1 · · · hm · · · hM ] and hm ∈ C2U×1 is a channel vector between the mth transmit antenna and users, which is static for t = 1 and 2 and E[hmhHm ] = IM ; P = p1 · · · pU and pk is an M -by-1 antenna selection vector for the kth STLC symbols, namely sk, and sk,, whose ith element pk,i = 1 if the ith transmit antenna is selected, and pk,i = 0 otherwise; and Z ∈ C2U×2 is a noise matrix whose elements are independent and identically distributed (i.i.d.) complex Gaussian random variables with zero mean. From (22), the optimal W t is obtained as follows:
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