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Cooperative communications are effective in improving the performance and extend the coverage of wireless networks. One issue is to find proper methods to allocate cooperative nodes. In this paper we investigate the effects of relay position and power allocation strategy in cooperative communications employing space-time codes (STCs). We consider non-ideal links between source, relay, and destination enabling the analysis of relay allocation problem based on the performance of each link in realistic scenarios. The frame error rate for various channel conditions, available diversity, relay positions, and transmitted power levels is obtained. Both the situation of balanced and unbalanced transmit power levels for source, relay, and destination are compared. Cooperative pragmatic STCs in block fading channel (BFC) are considered for our analysis. The results provide insight on how to allocate relay nodes based on geometry, link quality, and transmitted power considerations. [ABSTRACT FROM AUTHOR]

The goal of combining beamforming and space-time coding is to obtain full-diversity order and to provide additional received power (array gain) compared to conventional space-time codes. In this work, a class of code constellations is proposed, called generalized partly orthogonal designs (PODs) and both high-rate and low-rate feedback information is incorporated with possible feedback errors. A binary symmetric channel (BSC) model characterizes feedback errors. Two cases are studied: first, when the BSC bit error probability is known a priori to the transmission ends, and second, when it is not known exactly. Based on a minimum pairwise error probability (PEP) design criterion, we design a channel optimized vector quantizer (COVQ) for feedback information and a precoder matrix codebook to adjust the transmission codewords. The attractive property of our combining scheme is that it converges to conventional space-time coding with low-rate and erroneous feedback and to directional beamforming with high-rate and error-free feedback. This scheme also shows desirable robustness against feedback channel modeling mismatch. [ABSTRACT FROM AUTHOR]

In this paper, we consider distributed space-time coding for two-way wireless relay networks, where communication between two terminals is assisted by relay nodes. Relaying protocols using two, three, and four time slots are proposed. The protocols using four time slots are the traditional amplify-and-forward (AF) and decode-and-forward (DF) protocols, which do not consider the property of the two-way traffic. A new class of relaying protocols, termed as partial decode-and-forward (PDF), is developed for the two time slots transmission, where each relay first removes part of the noise before sending the signal to the two terminals. Protocols using three time slots are proposed to compensate the fact that the two time slots protocols cannot make use of direct transmission between the two terminals. For all protocols, after processing their received signals, the relays encode the resulting signals using a distributed linear dispersion (LD) code. The proposed AF protocols are shown to achieve the diversity order of min{N, K} (1 - (log log P/log F)), where N is the number of relays, P is the total power of the network, and K is the number of symbols transmitted during each time slot. When random unitary matrix is used for LD code, the proposed PDF protocols resemble random linear network coding, where the former operates on the unitary group and the latter works on the finite field. Moreover, PDF achieves the diversity order of min{N, K} but the conventional DF can only achieve the diversity order of 1. Finally, we find that two time slots protocols also have advantages over four-time-slot protocols in media access control (MAC) layer. [ABSTRACT FROM AUTHOR]

Since the standard union bound for space-time codes may diverge in quasi-static fading channels, the limit-before-average (LBA) technique has been exploited to derive tight performance bounds. However, it suffers from the computational burden arising from a multidimensional integral. In this paper, efficient bounding techniques for space-time codes are developed in the framework of Gallager bounds. Two closed-form upper bounds, the ellipsoidal bound and the spherical bound, are proposed that come close to simulation results within a few tenths of a decibel. In addition, two novel methods of weight enumeration operating on a further reduced state diagram are presented, which, in conjunction with the bounding techniques, give a thorough treatment of performance bounds for space-time codes. [ABSTRACT FROM AUTHOR]

Super-orthogonal space–time trellis codes (SOSTTC) are full rate, full diversity space–time codes with high coding gains for quasi-static fading channels. In this paper, this design approach is extended to fast fading channels and new SOSTTC are proposed for BPSK and QPSK modulations based on the design criteria valid for this type of channels. The new full rate codes have 4- and 16-state trellises for BPSK and QPSK cases, respectively, to avoid parallel transitions which restrict the error performance. The frame error performances are evaluated through computer simulations and it is shown that the proposed codes have superior performance in the fast fading case compared to their counterparts previously given in the literature for fast and quasi-static fading channels. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The diversity product and the diversity slim are two very important parameters for a good-performing unitary space-time constellation. A basic question is what the maximal diversity product (or sum) is. In this correspondence, we are going to derive general upper bounds on the diversity sum and the diversity product for unitary constellations of any dimension n and any size m using packing techniques on the compact Lie group U(n). [ABSTRACT FROM AUTHOR]

There exist two important design criteria for unitary space time codes. In the situation where the signal-to-noise ratio (SNR) is large the diversity product (DP) of a constellation should be as large as possible. It is less known that the diversity sum (DS) is a very important design criterion for codes working in a low SNR environment. So far, no general method to design good-performing constellations with large diversity for any number of transmit antennas and any transmission rate exists. In this correspondence, we propose constellations with suitable structures, which allow one to construct codes with excellent diversity using geometrical symmetry and numerical methods. The presented design methods work for any dimensional constellation and for any transmission rate. [ABSTRACT FROM AUTHOR]

In this paper, we study the performance of a bandwidth efficient space-frequency turbo encoding scheme over wideband channels. Results are presented for simulated wideband MIMO channels consisting of two transmit antennas and up to two receive antennas. In addition, wideband channel measurements undertaken with practical multi-element antenna structures at both the access point (AP) and mobile terminal (MT) are presented. Analysis is in terms of channel capacity, 10% channel outage capacity and space frequency iterative decoding for an IEEE802.11a physical layer complaint modem. It is shown when operating with a spectral efficiency of 1.2 hits/s/Hz. the iterative decoded space time codes comes within approximately 4.7 dB of 10 outage capacity over Rayleigh fading wideband channels with two transmit and two receive antennas. Over measured channels the iterative decoding scheme performs within 7.7 dB 10% of outage capacity. Losses due to channel state information estimation are also investigated. [ABSTRACT FROM AUTHOR]

In a wireless system with multipath multiple-input multiple-output (MIMO) channels using antenna arrays, the delay spread of multipaths results in intersymbol interference (IS!) and channel frequency selectivity. In contrast with the channel frequency selectivity, spatial gains at the multipath angles also naturally result in channel angle selectivity. Based on the channel selectivity structures characterized by the path delays and the path directions-of-departure/arrival, in this letter, we seek new insights into the matching of space-time codes and multipath MIMO channels in their angle-frequency (AF) structures. [ABSTRACT FROM AUTHOR]

A multiple input, multiple output (MIMO) diffuse optical communications link is implemented and evaluated using a 2 × 2 Alamouti-type space-time coding scheme to increase link performance beyond that of single input, single output (SISO) and multiple input, single output (MISO) systems. We present a representative profile of received power versus distance, and comparative bit-error probability performance. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1108–1110, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21558 [ABSTRACT FROM AUTHOR]