Unitary Space-Time Modulation for Single-Carrier Transmission Over Frequency-Selective Channels

In this paper, we have proposed a bandwidth efficient turbo trellis-coded modulation scheme for the non-coherent multiple-antenna Rayleigh fading channel, where the channel state information (CSI) is not necessary both at the transmitter and the receiver. In this scheme, we merge the unitary space-time modulation (USTM) as constellations with the turbo trellis-coded modulation, resulting in the turbo trellis-coded USTM (TTC-USTM), with the trellis-coded USTM encoder as the component encoders. We have also derived the iterative maximum a posteriori (MAP) algorithm. Through computer simulations, we demonstrated that without bandwidth expansion, TTC-USTM produces significant coding gains over its uncoded counterparts.

In this paper, we consider spatial modulation (SM) operating in a frequency-selective single-carrier (SC) communication scenario and propose zero-padding instead of the cyclic-prefix considered in the existing literature. We show that the zero-padded single-carrier (ZP-SC) SM system offers full multipath diversity under maximum-likelihood (ML) detection, unlike the cyclic-prefix based SM system. Furthermore, we show that the order of ML detection complexity in our proposed ZP-SC SM system is independent of the frame length and depends only on the number of multipath links between the transmitter and the receiver. Thus, we show that the zero-padding applied in the SC SM system has two advantages over the cyclic prefix: 1) achieves full multipath diversity, and 2) imposes a relatively low ML detection complexity. Furthermore, we extend the partial interference cancellation receiver (PIC-R) proposed by Guo and Xia for the detection of space-time block codes (STBCs) in order to convert the ZP-SC system into a set of narrowband subsystems experiencing flat-fading. We show that full rank STBC transmissions over these subsystems achieves full transmit, receive as well as multipath diversity for the PIC-R. Furthermore, we show that the ZP-SC SM system achieves receive and multipath diversity for the PIC-R at a detection complexity order which is the same as that of the SM system in flat-fading scenario. Our simulation results demonstrate that the symbol error ratio performance of the proposed linear receiver for the ZP-SC SM system is significantly better than that of the SM in cyclic prefix based orthogonal frequency division multiplexing as well as of the SM in the cyclic-prefixed and zero-padded single carrier systems relying on zero-forcing/minimum mean-squared error equalizer based receivers.

This study presents a framework of the unitary space time modulation (USTM) constellation based on antipodal points over Grassmannian manifold. The antipodal constellation enables an intrinsic simplified ML detecting algorithm. The algebraic orthogonal USTM constellation is also an antipodal constellation which, apart from being adaptive to the antipodal simplified ML detector, also has another simplified ML detector based on its self-indexing features, and the latter is simpler because of getting rid of the matrix operation. A searching orthogonal USTM constellation based on the grid search algorithm is obtained under the presented framework and its minimum Frobenius chordal distance and simulation performance are be superior to those of the algebraic orthogonal USTM constellation.

Cyclic prefixed single carrier (CP-SC) transmission over frequency selective channels is considered. In conventional CP-SC systems, the cyclic prefix is discarded at the receiver side. This suboptimal strategy allows simple frequency domain equalization. In this paper, a new CP-SC receiver exploiting the whole received signal (including the cyclic prefix) for data estimation is proposed. With reasonable additional complexity, the proposed architecture outperforms the conventional CP-SC receiver, in terms of bit error rate. Simulations results show that the proposed scheme also improves the goodput, i.e. error-free rate, of the communication link

In this paper, the formulae for the pairwise error-event probability (PEP) and the bit error probability (BEP) of the trellis coded unitary space-time modulation (TC-USTM) in a piecewise constant Rayleigh fading channel are derived. These analyses demonstrate that a multi-input multi-output (MIMO) system with M transmit and N receive antennas, apart from a diversity gain of MN for the space-time signal design, a coding gain of l/sub min/ can also be obtained for the TC-USTM, where l/sub min/ is the length of the shortest error event. Additional coding gain comes from the product of the dissimilarities along the path of the shortest error event. These analyses suggest the design criteria of the TC-USTM encoder to obtain an optimal BEP performance. Propositions are also presented to satisfy these criteria. We demonstrate through simulations that these analyses are accurate, especially at sufficiently high signal to noise ratio (SNR).

Unitary space-time modulation (USTM) can perform well without channel state information (CSI) in fast fading channels when signal-to-noise ratio (SNR) is large enough. However, it loses its advantages at low SNR or the channel coherence interval is T = 1. In this condition, the information should be carried by multilevel structured constellations with single transmit antenna. In this paper, we propose a simple non-coherent multilevel space-time modulation (MSTM) scheme, combine it with turbo coding, and derive the corresponding decoding algorithm. Simulation results verify that it can greatly improve the system performance. Finally, we propose an indirect method to get the extrinsic information transfer (EXIT) chart and analyze the convergence characteristics.

Recently, a maximum likelihood (ML) detection rule for differential unitary space time modulation (DUSTM) under the existence of unknown carrier frequency offset (CFO) has been derived. However, the ML detection is based on the exhaustive search over all the unitary group codes. In this paper, we design an efficient detection algorithm for newly derived ML rule, by modifying the bound intersection detector (BID). Our proposed algorithm is seen as a generalization of the existing BID that is known to be an optimal detector for the conventional DUSTM. The simulation results show that the proposed algorithm can save a large portion of the computational complexity compared to the naive searching method.

This work addresses the problem of coherently detecting turbo coded orthogonal frequency division multiplexed (OFDM) signals, transmitted through frequency selective Rayleigh fading channels. A single transmit and receive antenna is assumed. The channel output is distorted by a carrier frequency and phase offset, besides additive white Gaussian noise (AWGN). A new frame structure for OFDM, consisting of a known preamble, cyclic prefix and data is proposed. A filter that is matched to the preamble is used for start-of-frame (SoF) detection. A two-step ML detector for frequency-offset estimation is proposed, which has a much lower complexity compared to the single step ML detector. Turbo decoding and data interleaving is used to significantly enhance the bit-error-rate (BER) performance of the coherent receiver. Simulation results show that the BER performance of the practical coherent receiver is close to the ideal coherent receiver, for data length equal to the preamble length, and attains a BER of about 4× 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> at an SNR of just 8 dB. It is also shown that the probability of erasure is less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> for a preamble length of 512 QPSK symbols. The proposed algorithms are well suited for implementation on a DSP-platform.

We develop an adaptive receiver for multiple-input multiple-output (MIMO) frequency selective channels that employ space-time block-coded transmissions with cyclic prefixing. The receiver performs both interference suppression and equalization for multiuser transmissions. The structure of the space-time code is exploited to show that the receiver can be implemented on a per-frequency-bin basis rather than on a block-by-block basis. The adaptation scheme requires solving N independent problems each of complexity O(M/sup 2/) per block iteration, where M is the number of users and N is the block size.

This paper proposes an optimal training sequence framework for general block transmission systems over spatially correlated multiple-input multiple-output (MIMO) frequency selective channels. The pilot design is based on a formulation that minimizes the Bayesian Cramér-Rao bound (BCRB) for the mean squared error (MSE) of channel estimation, and is thus MSE optimal in nature. The novelty of the proposed work lies in development of a generic pilot design scheme applicable to all the four MIMO block transmission systems, namely single carrier cyclic prefix (SC-CP), single carrier zero padded (SC-ZP), multi-carrier zero padded (MC-ZP), and multi-carrier cyclic prefix (MC-CP) systems. Simulation results are presented to illustrate the superior performance of the proposed technique over the conventional pilot sequences, in terms of both MSE as well as bit error rate (BER).

In the equalization of frequency-selective multiple-input-multiple-output (MIMO) channels, it is usually assumed that the length of the channel impulse response (CIR), which is also referred to as the channel order, is known. However, this is not true in most practical situations, and it is a common approach to overestimate the channel order to avoid the serious performance degradation that occurs when the CIR length is underestimated. Unfortunately, the computational complexity of maximum-likelihood sequence detection (MLSD) in frequency-selective channels exponentially grows with the channel order; hence, overestimation can actually be undesirable because it leads to more expensive and inefficient receivers. In this paper, we introduce an algorithm for MLSD that incorporates the full estimation of the MIMO CIR parameters, including its order. The proposed technique is based on the per-survivor processing (PSP) methodology; it admits both blind and semiblind implementations, depending on the availability of pilot data, and is designed to work with time-selective channels. In addition to the analytical derivation of the algorithm, we provide computer simulation results that illustrate the effectiveness of the resulting receiver.

This work develops a general framework for maximum likelihood (ML) demodulation in cooperative wireless systems with a demodulate-and-forward (DF) protocol at the relays. Although this general structure admits both coherent and noncoherent modulation, we analyze the performance of this demodulator mainly for noncoherent demodulation and compare it to existing results for coherent demodulation. The ML demodulator consists of a band of square-law devices followed by a nonlinear combiner. We develop an accurate approximation for this demodulator using a band of square-law devices followed by a piecewise-linear (PL) combiner. This approximation not only has certain implementation advantages, but also leads to a tight closed form approximation for the bit error rate (BER) of the ML demodulator. Based on this closed-form result, we derive a high signal-noise-ratio (SNR) approximation, that provides a simpler but tight approximation of the BER of the ML demodulator.

In this paper, we design an implementation of a kind of reduced-complexity maximum likelihood (ML) detector for spatial modulation (SM) deployed in a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system. Based on National Instruments Universal Software Radio Peripheral (NI USRP) platform, two USRP Reconfigurable Input / Output (USRP-RIO) devices are used as the transmitter and the receiver. Error performance comparisons between the reduced-complexity ML detector and conventional ML detector are made in an indoor environment, as well as the comparison between SM scheme and space-frequency block code (SFBC) scheme. 6 different pictures are exploited as transmitted data, and are reconstructed in the receiver side, so the performance of each scheme is taken on the reconstructed pictures. Both of the calculated bit error ratio (BER) and the reconstruction result of each transmitted pictures, validate the highly consistent error performance of HL_ML detector and conventional ML detector, as well as the error performance superiority of SM over SFBC.

Optical Orthogonal Frequency Division Multiplexing (O‐OFDM) provides major advantages in mitigating Group‐Velocity Dispersion (GVD) in Single Mode Fiber (SMF). Unfortunately, when the uncompensated long‐haul transmission ranges become very large, substantial dispersion is accumulated. Owing to the large accumulated dispersion, the Cyclic Prefix (CP) duration will occupy a substantial fraction of the OFDM frame. This effect sets some limitations on the overall throughput and the spectral efficiency. Moreover, the transmission is inefficient because of the energy wastage contained within the CP. In the case where the CP length is shorter than the Channel Impulse Response (CIR), energy wastage is reduced but the system performance is limited by the Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI). To overcome this problem, a Time Domain Equalizer (TEQ) immediately after the channel is proposed. It can cancel the residual ISI and ICI caused by both the GVD and the CP length being shorter than the CIR. The simulation results show that, using BER of 10−3 as a reference, the system performance improves by 2.69thinspacedB while considering 6‐feedforward/5‐feedback‐weight Decision Feedback TEQ (DF‐TEQ) and 2.03 dB while considering 10‐tap Least Mean Square TEQ (LMS‐TEQ) even though the CP length is shorter than the CIR. This method reduces size of the CP, and consequently the performance of the system will be improved. Copyright © 2011 John Wiley &amp; Sons, Ltd.

This paper investigates the joint maximum likelihood (ML) data detection and channel estimation problem for Alamouti space-time block-coded (STBC) orthogonal frequency-division multiplexing (OFDM) wireless systems. The joint ML estimation and data detection is generally considered a hard combinatorial optimization problem. We propose an efficient low-complexity algorithm based on branch-estimate-bound strategy that renders exact joint ML solution. However, the computational complexity of blind algorithm becomes critical at low signal-to-noise ratio (SNR) as the number of OFDM carriers and constellation size are increased especially in multiple-antenna systems. To overcome this problem, a semi-blind algorithm based on a new framework for reducing the complexity is proposed by relying on subcarrier reordering and decoding the carriers with different levels of confidence using a suitable reliability criterion. In addition, it is shown that by utilizing the inherent structure of Alamouti coding, the estimation performance improvement or the complexity reduction can be achieved. The proposed algorithms can reliably track the wireless Rayleigh fading channel without requiring any channel statistics. Simulation results presented against the perfect coherent detection demonstrate the effectiveness of blind and semi-blind algorithms over frequency-selective channels with different fading characteristics.