Trellis-coded Unitary Space-time Modulation Research Articles

A Systematic Set Partitioning for Unitary Space-Time Signal Sets

Proper partitioning of a unitary space-time (UST) signal set is essential for the optimal design of trellis coded unitary space-time modulation (TC-USTM). The unique properties of these UST signals have necessitated a different partitioning methodology from that of the conventional two dimensional constellations. In this letter, we propose a systematic set partitioning through a novel subset-pairing strategy, for an arbitrary UST signal set. This approach leads to a geometrically congruent partitioning, i.e., subsets of the same size (order) have identical intra-distance profiles. Based on this partitioning, the resulting TC-USTM can achieve a minimum bit error probability.

On Trellis Coded Noncoherent Space-Time Modulation

Unitary space-time modulation (USTM) is well-tailored for noncoherent space-time modulation. Trellis coded USTM (TC-USTM) can obtain significant coding gains over uncoded USTM for the noncoherent block fading channel. Conventional TC-USTM schemes expand the signal set of uncoded USTM by a factor of two. In this letter, we propose a new TC-USTM scheme in which the size of USTM set is not limited to be just double for uncoded USTM. However, in TC-USTM schemes, because signals of the same trellis branch are transmitted over the same fading coefficients, one trellis branch can only obtain one temporal diversity. In this letter, we also propose a new trellis coded noncoherent space-time modulation scheme by interleaving space-time signals. The proposed scheme can enlarge temporal diversity at the price of increased complexity and delay. Simulation results demonstrate the excellent error performances of codes found by computer searches for both schemes.

Constellation Design for Trellis-Coded Unitary Space Time Modulation Systems

We consider the problem of creating signal constellations for trellis-coded unitary space-time communication links, where neither the transmitter nor the receiver knows the fading gains of the channel. Our study includes constellation-design techniques for trellis-coded schemes with and without parallel paths, which allows us to find a tradeoff between low complexity and high performance. We present a new formulation of the constellation design problem for trellis-coded unitary space-time modulation (TCUSTM) schemes. The two key differences in our approach against those of other authors are that we not only combine the constellation design and mapping by set partitioning into one step, but we also use directly the Chernoff bound of the pairwise error probability as a design metric. By novelly employing a theorem for the Clarke subdifferential of the sum of the k largest singular values of the unitary matrix, we also present a numerical optimization procedure for finding signal constellations resulting in high-performance communications systems. To demonstrate the advantages of our new design method, we report the best constellations found for TCUSTM systems. Simulation results show that these constellations achieve a 1-dB coding gain at a bit-error rate of 10-4 against usually used constellations

Trellis-Coded Unitary Space-Time Modulation

Space-time coding is well established for high data rate communications over wireless channels with perfect channel state information. On the other hand, the case where the channel state information is unknown has received limited attention. Recently, a new signaling scheme called unitary space-time modulation that is suitable for the latter case has been proposed. We describe the use and design of trellis-coded space-time modulation schemes that use unitary space-time constellations. We construct these codes using a novel suboptimal code design criteria and study the performance of trellis-coded unitary space-time modulation for block fading channels under the assumption of no channel state information. Simulation results show that the proposed schemes improve the performance compared to uncoded transmission with the same spectral efficiency. The results are also compared with the turbo-coded modulation scheme Bahceci (2002) and the differential detection scheme described Jafarkhani (2001) under the same assumptions.

On performance analysis and design criteria for trellis coded unitary space-time modulation

In this letter, we present formulas for the pairwise error-event probability (PEP) and bit error probability (BEP) of trellis-coded unitary space-time modulation (TC-USTM) operated in a piecewise constant Rayleigh fading channel. From these analyses we discovered design criteria for the TC-USTM encoder to achieve an optimal BEP performance. We conduct simulations and verify that our analyzes are accurate, especially at high signal-to-noise ratio (SNR).