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Rate and diversity impose a fundamental tradeoff in wireless communication. We propose a novel distributed space-time coding (DSTC) scheme based on constellation rotation (DSTC-CR) for Amplify-and-Forward relay networks. The proposed code can achieve full-diversity or full-rate, and also offers a flexibility for a desired rate-diversity tradeoff. This code can work well with arbitrary signal constellation and any number of relays and achieve minimal-delay. Through analysis of pairwise error probability, coding design criteria, Chernoff bound, decoding strategies and optimal power allocation are provided. Simulation results show that DSTC-CR scheme outperforms diagonal DSTC (DDSTC) and distributed linear dispersion (DLD) code at high power. From the comparison with DDSTC, the DSTC-CR scheme can achieve the same information rate using a lower modulation order. [ABSTRACT FROM AUTHOR]

This paper focuses on conditional optimization as a decoding primitive for high rate space-time codes that are obtained by multiplexing in the spatial and code domains. The approach is a crystallization of the work of Hottinen et al. which applies to space-time codes that are assisted by quasi-orthogonality. It is independent of implementation and is more general in that it can be applied to space-time codes such as the Golden Code and perfect space-time block codes, that are not assisted by quasi-orthogonality, to derive fast decoders with essentially maximum likelihood (ML) performance. The conditions under which conditional optimization leads to reduced complexity ML decoding are captured in terms of the induced channel at the receiver. These conditions are then translated back to the transmission domain leading to codes that are constructed by multiplexing orthogonal designs. The methods are applied to several block space-time codes obtained by multiplexing Alamouti blocks where it leads to ML decoding with complexity O (N²) where N is the size of the underlying QAM signal constellation. A new code is presented that tests commonly accepted design principles and for which decoding by conditional optimization is both fast and ML. The two design principles for perfect space-time codes are nonvanishing determinant of pairwise differences and cubic shaping, and it is cubic shaping that restricts the possible multiplexing structures. The new code shows that it is possible to give up on cubic shaping without compromising code performance or decoding complexity. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the pairwise error probability (PEP) of distributed space–time codes, in which the source and the relay generate Alamouti space–time code in a distributed fashion. We restrict our attention to the space–time code construction for Protocol III in Nabar et al. (IEEE Journal on Selected Areas Communications 22(6): 1099–1109, 2004). In particular, we derive two closed-form approximations for PEP when the relay is either close to the destination or source and an upper bound for any position of the relay. Using the alternative definition of Q-function, we can express these PEPs in terms of finite integral whose integrand is composed of trigonometric functions. We further show that with only one relay assisted source-destination link, system still achieves diversity order of two, assuming single-antenna terminals. We also perform Monte-Carlo simulations to verify the analysis. [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]

This paper introduces a new rate-2, full-diversity space-time code for four transmit antennas and one receive antenna. The 4 x 4 codeword matrix consists of four 2 x 2 Alamouti blocks with entries from Q (i, √5), and these blocks can be viewed as quaternions which in turn represent rotations in R3. The Alamouti blocks that appear in a codeword are drawn from the icosian ring consisting of all linear combinations of 120 basic rotations corresponding to symmetries of the icosahedron. This algebraic structure is different from the Golden code, but the complex entries are taken from a common underlying field. The minimum determinant is bounded below by a constant that is independent of the signal constellation, and the new code admits a simple decoding scheme that makes use of a geometric correspondence between the icosian ring and the E8 lattice. [ABSTRACT FROM AUTHOR]

We consider the "one-shot frame synchronization problem," where a decoder wants to locate a sync pattern at the output of a memoryless channel on the basis of sequential observations. The sync pattern of length N starts being emitted at a random time within some interval of size A, where A characterizes the asynchronism level. We show that a sequential decoder can optimally locate the sync pattern, i.e., exactly, without delay, and with probability approaching one as N → ∞, if the asynchronism level grows as O(eN α), with a below the synchronization threshold, a constant that admits a simple expression depending on the channel. If α exceeds the synchronization threshold, any decoder, sequential or nonsequential, locates the sync pattern with an error that tends to one as N → ∞. Hence, a sequential decoder can locate a sync pattern as well as the (nonsequential) maximum-likelihood decoder that operates on the basis of output sequences of maximum length A + N - 1, but with far fewer observations. [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]

1/ f β noise has been revealed in both self-paced and synchronized tapping sequences, without being consistently taken into consideration for the modeling of underlying timing mechanisms. In this study we characterize variability, short-range, and long-range correlation properties of asynchronies and inter-tap intervals collected in a synchronization tapping experiment, attesting statistically the presence of 1/ f β noise in asynchronies. We verify that the linear phase correction model of synchronization tapping in its original formulation cannot account for the empirical long-range correlation properties. On the basis of previous accounts of 1/ f β noise in the literature on self-paced tapping, we propose an extension of the original synchronization model by modeling the timekeeping process as a source of 1/ f β fluctuations. Simulations show that this ‘1/ f-AR synchronization model’ accounts for the statistical properties of empirical series, including long-range correlations, and provides an unifying mechanistic account of 1/ f β noise in self-paced and synchronization tapping. This account opens the original synchronization framework to further investigations of timing mechanisms with regard to the serial correlation properties in performed time intervals. [ABSTRACT FROM AUTHOR]

In this paper, a method is proposed to construct spectrally efficient unitary space-time codes for high-rate differential communications over multiple-antenna channels. Unlike most of the known methods which are designed to maximize the diversity product (the minimum determinant distance), our objective is to increase the spectral efficiency. The simulation results indicate that for high spectral efficiency and for more than one receive antenna, the new method significantly outperforms the existing alternatives. In the special case of two transmit antennas, which is the main focus of this paper, the relation between the proposed code and the Alamouti scheme helps us to provide an efficient maximum-likelihood (ML) decoding algorithm. Also, we demonstrate that similar ideas can be applied to designing codes for more than two transmit antennas. As an example, we present a construction for 4-by-4 unitary constellations which has a good performance, compared with the other known codes. [ABSTRACT FROM AUTHOR]

Proofs to the conjectures made by Jing and Hassibi on having fully diverse (3 × 3 ) SU(3) and AB unitary space-time codes art, presented in this correspondence. We first prove that the SU(3) codes are fully diverse if and only if the design parameters P, Q, R, and S are all odd integers, and in addition, are relatively prime. For the type I AB codes, it is shown that full diversity can be achieved if and only if the integers P Q, R, and S are relatively prime. Finally, we show that such condition is also sufficient for having fully diverse type II AB codes. [ABSTRACT FROM AUTHOR]

A high-resolution time-to-digital converter (TDC) implemented in a general purpose field-programmable-gate-array (FPGA) is presented. Dedicated carry lines of an FPGA are used as delay cells to perform time interpolation within the system clock period and to realize the fine time measurement. Two Gray-code counters, working on in-phase and out-of-phase system clocks respectively, are designed to get the stable value of the coarse time measurement. The fine time code and the coarse time counter value, along with the channel identifier, are then written into a first-in first-out (FIFO) buffer. Tests have been done to verify the performance of the TDC. The resolution after calibration can reach 50 Ps. [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]

The potential promised by multiple transmit antennas has raised considerable interest in space-time coding for wireless communications. In this paper, we propose a systematic approach for designing space-time trellis codes over flat fading channels with full antenna diversity and good coding advantage. It is suitable for an arbitrary number of transmit antennas with arbitrary signal constellations. The key to this approach is to separate the traditional space-time trellis code design into two parts. It first encodes the information symbols using a one-dimensional (M, 1) nonbinary block code, with M being the number of transmit antennas, and then transmits the coded symbols diagonally across the space-time grid. We show that regardless of channel time-selectivity, this new class of space-time codes always achieves a transmit diversity of order M with a minimum number of trellis states and a coding advantage equal to the minimum product distance of the employed block code. Traditional delay diversity codes can be viewed as a special case of this coding scheme in which the repetition block code is employed. To maximize the coding advantage, we introduce an optimal construction of the nonbinary block code for a given modulation scheme. In particular, an efficient suboptimal solution for multilevel phase-shift-keying (PSK) modulation is proposed. Some code examples with 2-6 bits/s/Hz and two to six transmit antennas are provided, and they demonstrate excellent performance via computer simulations. Although it is proposed for flat fading channels, this coding scheme can be easily extended to frequency-selective fading channels. [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]

This paper presents a moment matching approach for constructing an equivalent model of an ATM cell arrival process based on inter-cell arrival time measurement. As compared to a renowned parameter-matching technique proposed by Heffes and Lucatoni, the advantage of this approach is that the matching parameters are more easily obtained in real traffic situation. This approach has been tested on an MMBP[Poisson] process, and results show that only the first four moments are required to capture the key characteristics in this process. [ABSTRACT FROM AUTHOR]

The article provides historicals briefs from the journal's past articles. Some of the articles published include an article on misunderstanding of the SMPTE time code published in the January 1983 issue and the practical problems in recording and reproduction of music for motion pictures by David Mendoza published in the January 1933 issue.

The article presents abstracts of papers related to radio transmissions that will be appearing in the forthcoming issues of the journal "IEEE Transactions on Communications." The paper "Performance of Filterbank and Wavelet Transceivers in the Presence of Carrier Frequency Offset," by Tiziano Bianchi, Fabrizio Argenti and Enrico Del Re investigates the performance of a generic filterbank transceiver in the presence of a carrier frequency offset. The paper "Reduced-Complexity Decoding of LDPC Codes," by I. Chen, A. Dholakia, E. Eleftheriou, M. Fossorier and X.-Y. Hu presents information on various log-likelihood-radio-based belief-propagation decoding algorithms and their reduced-complexity derivatives for low-density parity-check codes. The paper "Multistage Iterative Decoding With Complexity Reduction for Concatenated Space-Time Codes," by Andres Reial and Stephen G. Wilson presents a multistage iterative decoding structure that takes full advantage of the concatenated nature of the transmission path, treating the modulator and channel stages as an additional encoder in serial concatenation.