MQAM space-time block coding with differential detection

Differential space-time coding (DSTC) has received much interest as it obviates the requirement of the channel state information at the receiver while maintaining the desired properties of space-time coding techniques. In this paper, by introducing star quadrature amplitude modulation (star QAM) method, two kinds of multiple amplitudes DSTC schemes are proposed. One is based on differential unitary space-time coding (DUSTC) scheme, and the other is based on differential orthogonal space-time coding (DOSTC) scheme. Corresponding bit-error-rate (BER) performance and coding-gain analysis are given, respectively. The proposed schemes can avoid the performance loss of conventional DSTC schemes based on phase-shift keying (PSK) modulation in high spectrum efficiency via multiple amplitudes modulation. Compared with conventional PSK-based DSTC schemes, the developed schemes have higher spectrum efficiency via carrying information not only on phases but also on amplitudes, and have higher coding gain. Moreover, the first scheme can implement low-complexity differential modulation and different code rates and be applied to any number of transmit antennas; while the second scheme has simple decoder and high code rate in the case of 3 and 4 antennas. The simulation results show that our schemes have lower BER when compared with conventional DUSTC and DOSTC schemes.

Differential space-time coding was proposed recently in the literature for multi-antenna systems, where neither the transmitter nor the receiver knows the fading coefficients. Among existing schemes, double differential space-time (DDST) coding is of special interest because it is applicable to continuous fast time-varying channels. However, it is less effective in frequency-selective fading channels. This paper’ls authors derived a novel time-frequency double differential space-time (TF-DDST) coding scheme for multi-antenna orthogonal frequency division multiplexing (OFDM) systems in a time-varying frequency-selective fading environment, where double differential space-time coding is introduced into both time domain and frequency domain. Our proposed TF-DDST-OFDM system has a low-complexity non-coherent decoding scheme and is robust for time-and frequency-selective Rayleigh fading. In this paper, we also propose the use of state-of-the-art low-density parity-check (LDPC) code in serial concatenation with our TF-DDST scheme as a channel code. Simulations revealed that the LDPC based TF-DDST OFDM system has low decoding complexity and relatively better performance.

A new space-time coding (STC) scheme for multiple-input multiple-output synthetic aperture radar systems is proposed in this paper. In the new scheme, two successive signal periods are put into one transmit duration to minimize the time-variant channel effect. The even and odd components of the transmitted waveforms are modulated into distinct Doppler frequencies in the azimuth direction and can be separated by bandpass filter in the range-Doppler domain. The presented STC scheme can suppress the interchannel ambiguous energy caused by the time-variant channel responses, which typically occur in conventional STC schemes, and increase the signal-to-noise ratio of the echoes by a decoding matrix. To further suppress the interference, a waveform called time and frequency comb-like chirp (TFCC) is proposed. With the application of the complementary comb-like structure in the time and frequency domains, two TFCC waveforms are short-term shift-orthogonal and constant envelope. Moreover, these corresponding TFCC waveforms can share the same antenna and time gate without sacrificing any TFCC waveforms' peak level. The theoretical analysis and simulation results illustrate the feasibility of the proposed scheme.

A downlink beamforming combined space-time coding and power control scheme for DS-CDMA systems in frequency selective fading channel is presented in this paper, in which the space-time coding is implemented by using two array antennas and the beamforming weights and transmitted power vector are obtained by an iterative algorithm such that the whole radiated power is minimized while the signal-to-interference and noise (SINR) requirements is maintained. Then a simplified algorithm for decreasing the complexity due to the existence of multipaths is suggested using equivalent one-path channel vector (EOCV) to replace multipath vectors. Simulations compare the performance between conventional space-time coding scheme and our method.

In this work, we propose two high-rate quasi-orthogonal space-time coding (STC) schemes which are designed in conjunction with the successive interference cancellation (SIC) based receiver. The symbols of the proposed STC are of judiciously designed diversity order which can be effectively exploited by the SIC based receiver to cancel interference as well as to obtain diversity gain. The proposed STC scheme's amicable quasi-orthogonal structure lends itself to efficient low-complexity linear decoding. Simulation results show that the proposed STC scheme achieves better multiplexing-diversity tradeoffs than the existing conventional schemes in noise-limited single-cell scenarios. In the interference-limited multi-cell scenario, the application of proposed SIC-amiable STC to the coordinated multi-point transmission and reception (CoMP) also achieves higher throughput than the conventional schemes.

In this paper, Beam Pattern Scanning (BPS), a transmit diversity technique, is compared with two well known transmit diversity techniques, space-time block coding (STBC) and space-time trellis coding (STTC). In BPS (also called beam pattern oscillation), controlled time varying weight vectors are applied to the antenna array elements mounted at the base station (BS). This creates a small movement in the antenna array pattern directed toward the desired user. In rich scattering environments, this small beam pattern movement creates an artificial fast fading channel. The receiver is designed to exploit time diversity benefits of the fast fading channel. Via the application of simple combining techniques, BPS improves the probability-of-error performance and network capacity with minimal cost and complexity. In this work, to highlight the potential of the BPS, we compare BPS and Space-Time Coding (i.e., STBC and STTC) schemes. The comparisons are in terms of their complexity, system physical dimension, network capacity, probability-of-error performance, and spectrum efficiency. It is shown that BPS leads to higher network capacity and performance with a smaller antenna dimension and complexity with minimal loss in spectrum efficiency. This identifies BPS as a promising scheme for future wireless communications with smart antennas.

Most existing space-time coding (STC) schemes have been developed for flat fading channels. To obtain antenna diversity gain, they rely on channel state information (CSl) required at the receiver through channel estimation techniques. This paper proposes a new decision feedback decoding scheme for Alamouti-based space-time block coding (STBC) transmission over time-selective fading channels. In wireless channels, time-selective fading effects arise mainly due to Doppler shift and carrier frequency offset. Modelling the time-selective fading channels as the first-order Gauss-Markov processes, we use recursive algorithms such as Kalman filtering, LMS and RLS algorithms for channel tracking. The proposed scheme consists of the symbol decoding stage and channel tracking algorithms. Computer simulations confirm that the proposed scheme shows the better performance and robustness to time-selectivity.

Antenna spacings, the angle spread and the Rice factor significantly affect the correlation of fading coefficients in a multi-antenna system. We study the effect of these parameters on the performance of different types of detection schemes in a BLAST architecture. We show that the detection method based on lattice decoding is more resistant to the correlated fading than other types of detection which are based on successive interference cancellation. We notice that highly correlated fades significantly degrade the performance of detection techniques based on successive interference cancellation whereas they slightly affect the lattice decoding algorithm. We also study the effects of correlated fades on some space-time block codes. We show that space-time block codes from orthogonal design are more resistant to correlation than other high rate linear space-time block codes.

In this paper, the bit error rate (BER) performance of multiuser multiple-input multiple-output (MIMO) systems over Rayleigh fading channels is studied, and corresponding asymptotic performance is analyzed. Based on the asymptotic analysis at high signal to noise ratio (SNR), using the probability density functions (PDF) of the instantaneous channel power gain, the diversity gain and coding gain of the system with transmit antenna selection (TAS) scheme and space-time block coding (STBC) scheme are derived, respectively. As a result, the same full diversity gain is achieved for two transmission schemes, but their coding gains are different. With the obtained diversity gain and coding gain, the asymptotic BER expressions for two transmission schemes are respectively derived, which are in good agreement with the corresponding simulation results. The results show that the multiuser MIMO system with TAS scheme has better BER performance than that with STBC scheme due to higher coding gain.

In this paper we consider a collaborative hybrid ARQ protocol where retransmissions are handled by a number of cooperating nodes employing a distributed orthogonal space time coding scheme. Outage performances are analyzed by assuming a distributed randomized orthogonal space- time coding scheme (DR-OSTC) to be employed by the relaying terminals during the retransmission session. The antenna selection version of the DR-OSTC requires that each cooperating node chooses randomly and independently to serve as one of the space-time virtual antennas. By avoiding any predefined terminal-to-codeword mapping, the random selection of the space-time codewords substantially reduces the needed control overhead with respect to other distributed space-time coding strategies and it simplifies the node coordination task. According to this scheme, we develop a novel analytic model to evaluate the outage probability and tackle the problem of designing the minimum number of cooperating nodes M so as to meet a specific outage probability requirement at the destination node. Finally, according to these results, we develop simple but effective design rules tailored for the collaborative hybrid ARQ protocol in practical environments.

Differential unitary space-time modulation is an attractive space-time technique because it does not require channel estimation. In this paper, we propose a new differential space-time code with rate 2.5 bit/s/Hz for two transmit antennas. In contrast to the original unitary space-time codes with one level of amplitude, the powers of the matrices in this new differential space-time code are different. We design a decoding algorithm based on the Viterbi algorithm to differentially detect the transmitted data. Simulation results show that the new two amplitude level differential space-time code outperforms the original unitary space-time code with rate 2.5 bit/s/Hz.

Cooperative communications can be used to improve communication reliability. However, the transmissions from different relaying nodes result in a great challenge in practice. The use of TDMA for relaying transmissions causes large transmission delay. In contrast, FDMA and CDMA associate with the issue of imperfect frequency and timing synchronization due to the simultaneous transmissions from the relaying nodes. In this work, we propose a space-time network coding (STNC) scheme utilizing transform-based coding to improve communication reliability while maintaining a stable network throughput and overcoming the issue of imperfect frequency and timing synchronization. Based on TDMA, a node in the network forms a linearly-coded signal from the overheard symbols and transmits it to the destination in its dedicated time slot. The pairwise error probability (PEP) is analyzed and design criteria of the STNC are derived to ensure achieving full diversity. Simulations are conducted to verify the performance of the proposed scheme and to reveal its advantage over a distributed space-time block coding scheme under timing synchronization errors.

In this paper, a source-assisting differential distributed space time block coding (SA-DDSTBC) scheme is proposed for cooperative networks. Firstly, in most existing works on distributed space time block coding (DSTBC), the destination node is assumed to have perfect channel state information (CSI), thus, signal recovery is straight forward. In practice however, some scenarios exist whereby the destination node is unable to acquire CSI. Consequently, this work incorporates differential concepts with DSTBC to facilitate signal recovery in cooperative networks operating in environments where CSI acquisition is impractical. Secondly, different from most works on DSTBC which assume that the source-destination link is unavailable, the proposed scheme employs a source-assisting (SA) strategy that exploits the additional diversity path provided by the source-destination link. The numerical and simulation results obtained illustrate that compared to the conventional DSTBC schemes, the proposed SA-DDSTBC scheme achieves non-coherent signal recovery and improved BER and diversity performance with negligible increase in decoding complexity.

In this paper, we propose two distributed linear convolutional space-time coding (DLC-STC) schemes for full-duplex (FD) asynchronous cooperative communications. The DLC-STC Scheme 1 is for the case of the complete loop channel cancellation, which achieves the full asynchronous cooperative diversity. The DLC-STC Scheme 2 is for the case of the partial loop channel cancellation and amplifying, where some loop signals are used as the self-coding instead of treated as interference to be directly cancelled. We show this scheme can achieve full asynchronous cooperative diversity. We then evaluate the performance of the two schemes when loop channel information is not accurate and present an amplifying factor control method for the DLC-STC Scheme 2 to improve its performance with inaccurate loop channel information. Simulation results show that the DLC-STC Scheme 1 outperforms the DLC-STC Scheme 2 and the delay diversity scheme if perfect or high quality loop channel information is available at the relay, while the DLC-STC Scheme 2 achieves better performance if the loop channel information is imperfect.

An adaptive distributed space-time coding (DSTC) scheme is proposed for two-hop cooperative MIMO networks. Linear minimum mean square error (MMSE) receive filters and adjustable code matrices are considered subject to a power constraint with an amplify-and-forward (AF) cooperation strategy. In the proposed adaptive DSTC scheme, an adjustable code matrix obtained by a feedback channel is employed to transform the space-time coded matrix at the relay node. The effects of the limited feedback and the feedback errors are assessed. Linear MMSE expressions are devised to compute the parameters of the adjustable code matrix and the linear receive filters. Stochastic gradient (SG) and least-squares (LS) algorithms are also developed with reduced computational complexity. An upper bound on the pairwise error probability analysis is derived and indicates the advantage of employing the adjustable code matrices at the relay nodes. An alternative optimization algorithm for the adaptive DSTC scheme is also derived in order to eliminate the need for the feedback. The algorithm provides a fully distributed scheme for the adaptive DSTC at the relay node based on the minimization of the error probability. Simulation results show that the proposed algorithms obtain significant performance gains as compared to existing DSTC schemes.