Unitary Space-time Modulation Scheme Research Articles

High rate trellis coded differential unitary space-time modulation via super unitarity

We introduce a new trellis coded differential unitary space-time modulation scheme for multiple-antenna wireless systems. In the new scheme, the constellation expansion is executed using a super unitarity technique so that the number of available unitary matrices is increased but the transmitted symbol alphabet is kept the same. A novel set partitioning strategy is then applied to the expanded matrix set. This scheme avoids the rate-loss problem suffered by traditional code design. We provide some examples using the proposed code construction method. Compared with existing ones, the new codes can not only achieve lower transmitter and receiver complexity, but also provide higher coding gains

Differential Super-Orthogonal Space-Time Trellis Codes

In this paper, we present two differential trellis coded space-time modulation schemes when the channel state information is not available at the transmitter and at the receiver. First, we extend the design of super-orthogonal space-time trellis codes to improve their performance. Then, based on these extended super-orthogonal codes, we propose the first differential scheme. Compared with the trellis coded differential unitary space-time modulation scheme, not only does the proposed differential scheme achieve full diversity, but also it provides identical or higher coding gain and much lower decoding complexity. In order to achieve further improved coding gain in addition to full diversity for more than two transmit antennas, we propose a second differential scheme which is based on super-quasi-orthogonal codes. Such a differential scheme outperforms the differential modulation scheme based on super-orthogonal codes with simpler decoding. Simulation results demonstrate the good performance of our schemes

A Unitary Space-Time Modulation Scheme with Multistage Decoding

The complexity of maximum-likelihood (ML) decoding for unitary space-time modulation (USTM) is exponential in the code rate times symbol periods. In this letter, we propose a new USTM scheme which consists of USTMs with noncoherent multistage decoding. The decoding of the proposed scheme is less complex than ML decoding. We also find some good codes of the proposed scheme according to the design criterion. Simulation results indicate that our codes perform better than seamless USTMs over the quasistatic fading channels.

Estimating statistical properties of MIMO fading channels

We propose maximum likelihood (ML) and restricted maximum likelihood (REML) methods for estimating the mean and covariance parameters of multi-input multi-output (MIMO) Ricean and Rayleigh block-fading channels using measurements from multiple coherent intervals containing both amplitudes and phases of the received signal. Correlated and independent fading scenarios with structured and unstructured line-of-sight (LOS) array response models are considered. Computationally efficient ML and approximate ML (AML) estimators are proposed for unitary space-time modulation schemes and orthogonal designs in correlated fading. We also derive Crame/spl acute/r-Rao bounds (CRBs) for the unknown parameters, discuss initialization of the proposed algorithms, and evaluate their performance via numerical simulations under the block- and continuous-fading scenarios.

Fast differential unitary space-time demodulation via square orthogonal designs

This paper presents a natural concatenation between the real or complex square orthogonal designs and the differential unitary space-time modulation scheme for multiple transmit antennas. This concatenation renders the differential unitary space-time demodulator to detect in a decoupled way the information symbols and hence to have a very low decoding complexity. This fast differential demodulation method for multiple transmit antennas can be regarded as a generalization of the existing differential detection method proposed by Tarokh and Jafarkhani for two and four transmit antennas based on orthogonal designs. By using a systematic matrix-vector representation, a unified and simplified form of differential unitary demodulation via square orthogonal designs for any number of transmit antennas and any transmission rate in bits per channel use is provided.

Unitary space-time modulation via cayley transform

A prevoiusly proposed method for communicating with multiple antennas over block fading channels is unitary space-time modulation (USTM). In this method, the signals transmitted from the antennas, viewed as a matrix with spatial and temporal dimensions, form a unitary matrix, i.e., one with orthonormal columns. Since channel knowledge is not required at the receiver, USTM schemes are suitable for use on wireless links where channel tracking is undesirable or infeasible, either because of rapid changes in the channel characteristics or because of limited system resources. Previous results have shown that if suitably designed, USTM schemes can achieve full channel capacity at high SNR and, moreover, that all this can be done over a single coherence interval, provided the coherence interval and number of transmit antennas are sufficiently large, which is a phenomenon referred to as autocoding. While all this is well recognized, what is not clear is how to generate good performing constellations of (nonsquare) unitary matrices that lend themselves to efficient encoding/decoding. The schemes proposed so far either exhibit poor performance, especially at high rates, or have no efficient decoding algorithms. We propose to use the Cayley transform to design USTM constellations. This work can be viewed as a generalization, to the nonsquare case, of the Cayley codes that have been proposed for differential USTM. The codes are designed based on an information-theoretic criterion and lend themselves to polynomial-time (often cubic) near-maximum-likelihood decoding using a sphere decoding algorithm. Simulations suggest that the resulting codes allow for effective high-rate data transmission in multiantenna communication systems without knowing the channel. However, our preliminary results do not show a substantial advantage over training-based schemes.