Search

Selective mapping (SLM) has been employed to reduce the peak interference-to-carrier ratio (PICR) in OFDM systems. Here, we significantly reduce the computational complexity of SLM using subsets of intermediate signals within the inverse fast Fourier and fast Fourier transforms, while achieving performance close to that previously obtained. Index Terms--Orthogonal frequency-division multiplexing, peak interference-to-carrier ratio (PICR), selective mapping (SLM).

We construct new MDS or near-MDS self-dual codes over large finite fields. In particular, we show that there exists a Euclidean self-dual MDS code of length n = q over GF(q) whenever q = [2.sup.m] (m [greater than or equal to] 2) using a Reed-Solomon (RS) code and its extension. It turns out that this multiple description source (MDS) self-dual code is an extended duadic code. We construct Euclidean self-dual near-MDS codes of length n = q - 1 over GF(q) from RS codes when q [equivalent to] 1 (mod 4) and q [less than or equal to] 113. We also construct many new MDS self-dual codes over GF(p) of length 16 for primes 29 [less than or equal to] p [less than or equal to] 113. Finally, we construct Euclidean/Hermitian serf-dual MDS codes of lengths up to 14 over GF([q.sup.2]) where q = 19, 23, 25, 27, 29. Index Terms--Multiple description source (MDS) codes, Reed-Solomon (RS) codes, self-dual codes.

A low-complexity partial transmit sequence (PTS) technique is described for reducing the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) signal. This new method has reduced the multiplicative complexity, while providing PAPR reduction that is similar to other methods such as original PTS (O-PTS), and has lower additive complexity.

The problem of selecting a code for finite monotone sources with X symbols is considered. The selection criterion is based on minimizing the average redundancy (called Minave criterion) instead of its maximum (i.e., Minimax criterion). The average probability distribution [bar.[P.sup.N]] whose associated Huffman code has the minimum average redundancy, is derived. The entropy of the average distribution (i.e., H ([bar.[P.sup.N]])) and the average entropy of the monotone distributions (i.e., [bar.H([P.sup.N]))] are studied. It is shown that both log N - H([P.sup.N]) and log N - [bar.H([P.sup.N])] are asymptotically equal to a constant ([~.bar] 0.61). Therefore, there is only a negligible penalty (at most 1.61 bits/symbol) in using a simple fixed-length code with respect to the optimal code. An efficient near-optimal encoding technique is also proposed. The consequences of the two approaches, i.e., Minave and Minimax, are compared in terms of their associated distributions and associated codes. In order to evaluate the average performance of the Minimax code, we prove that the informational divergence of the average distribution and Minimax distribution asymptotically grows as -2.275 + log log N. Index Terms--Average redundancy, finite monotone sources, fixed-length code, Huffman code, Minave code, Minimax code, minimum average criterion.

The iterative decoding structure and component maximum a posteriori decoders used for decoding binary concatenated codes can be extended to the nonbinary domain. This paper considers turbo codes over nonbinary rings, specifically ternary, quaternary, penternary, hexernary, and octernary codes. The best rate-l/2 component codes are determined using a practical search algorithm. The performance of the resulting rate-l/3 turbo codes on an additive white Gaussian noise channel using q-ary phase-shift keying modulation is given. Index Terms--Nonbinary turbo codes, ring codes.

In this letter, we propose a new modulation scheme called pulse position amplitude modulation (PPAM) for ultra-wideband (UWB) communication systems. PPAM combines pulse position modulation and pulse amplitude modulation to provide good system performance and low computational complexity. The channel capacity of PPAM is determined for a time-hopping multiple-access UWB communication system. The error probability and performance bounds are derived for a multiuser environment. Index Terms--Code-division multiple access (CDMA), pulse amplitude modulation (PAM), pulse position modulation (PPM), ultra-wideband (UWB) communications.

It is well known that the problem of finding stabilizer quantum-error-correcting codes (QECC) is transformed into the problem of finding additive self-orthogonal codes over the Galois field GF (4) under a trace inner product. Our purpose is to classify the extremal additive circulant self-dual codes of lengths up to 15, and construct good codes for lengths 16 [less than or equal to] n [less than or equal to] 27. We also classify the extremal additive 4-circulant self-dual codes of lengths 4, 6, 8, 12, 14, and 16 and most codes of length 10, and construct good codes of even lengths up to 22. Furthermore, we classify the extremal additive bordered 4-circulant self-dual codes of lengths 3, 5, 7, 9, 11, 13, 15, and 17, and construct good codes for lengths 19, 21, 23, and 25. We give the current status of known extremal (or optimal) additive self-dual codes of lengths 12 to 27. Index Terms--Additive codes, circulant codes, 4-circulant codes, quantum codes.

This correspondence investigates the asymptotic performance of single parity-check (SPC) product codes (PCs) from a decoding point of view. Specifically, the probability of bit error is bounded before and after the decoding of each dimension, similar to the analysis of "iterated codes" by Elias. It is shown that the asymptotic probability of bit error can be driven to zero as the number of dimensions, and hence the block length, increases at signal-to-noise ratios (SNRs) within 2 dB of capacity over the additive white Gaussian noise (AWGN) channel. Index Terms--Asymptotic analysis, iterated codes, single parity-check (SPC) product codes (PCs).

In this correspondence, we classify all optimal linear [n, n/2, d] codes over [F.sub.4] up to length 18. In particular, we show that there is a unique optimal [12, 6, 6] code and three optimal [16, 8, 7] codes, up to equivalence. Index Terms--Codes over [F.sub.4], optimal linear codes.

We present a method for maximum likelihood decoding of the (48, 24, 12) quadratic residue code. This method is based on projecting the code onto a subcode with an acyclic Tanner graph, and representing the set of coset leaders by a trellis diagram. This results in a two level coset decoding which can be considered a systematic generalization of the Wagner rule. We show that unlike the (24, 12, 8) Golay code, the (48, 24, 12) code does not have a Pless-construction which has been an open question in the literature. It is determined that the highest minimum distance of a (48, 24) binary code having a Pless-construction is 10, and up to equivalence there are three such codes. Index Terms--Linear block codes, maximum-likelihood decoding, trellis diagram.

Turbo-codes are decoded using iterative decoding algorithms with somewhat elusive convergence properties. In this paper, the modes of convergence observed in an extensive series of turbo-code simulations are categorized by examining the bit convergence behavior for each frame. Based on these results, a new method for decoder termination based on average log-likelihood ratios is presented and compared with other methods. As an application, a selective repeat automatic repeat request (ARQ) system is considered. Index Terms--Decoder convergence, iterative decoding, log-likelihood decoding, stopping criterion, turbo-codes.

Optimal double circulant self-dual codes over F(sub 4) have been found for each length n < 40. For lengths n < 14. 20, 22. 24, 2S, and 30, these codes are optimal self-dual codes. For length 26, the code attains the highest known minimum weight. For n > 32, the codes presented provide the highest known minimum weights. The [36, 18, 12] self-dual code improves the lower bound on the highest minimum weight for a [36, 18] linear code Index Terms: Double circulant codes, self-dual codes.

In this correspondence, we give a characterization of certain quasi-cyclic self-complementary codes with parameters [120, 9, 56] and [136, 9, 64]. Some quasi-cyclic self-complementary codes are also constructed with parameters [496, 11, 240] and [528, 11, 256]. These codes are optimal in the sense that they meet the Grey-Rankin hound. New quasi-symmetric SDP designs are constructed from these codes. Index Terms - Quasi-cyclic codes, quasi-symmetric designs, self-complementary codes.

Byline: Welly T. Firmanto (1), T. Aaron Gulliver (2) Keywords: Reed--Muller codes; fading channels; code combining. Abstract: Radio communications are often desirable for data and voice communications in an indoor environment. Wireless technology offers an improved mobility since the users are not confined to any particular location by wires. This paper investigates the use of Reed--Muller codes in an indoor wireless environment. Code combining is used to exploit the multiple signal copies resulting from the inherent frequency diversity of spread spectrum. The performance of Reed--Muller codes is compared with that of convolutional codes of similar rates and comparable decoding complexity. The complete weight distribution of various Reed--Muller codes is presented. Author Affiliation: (1) Merkuri Utara XI/8, Margahayu Raya, Bandung, Indonesia e-mail (2) Dept. of Electrical and Electronic Engineering, University of Canterbury, Private Bag 4800, Christchurch e-mail Article History: Registration Date: 28/09/2004

This paper considers the combination of multiple copies of a packet to improve the performance of a slotted direct-sequence spread-spectrum multiple-access (DS/SSMA) ALOHA packet radio system with coherent binary phase-shift keying (BPSK) modulation. Both slotted DS/SSMA ALOHA with and without forward error correction (FEC) are considered. For the case with FEC, maximum-likelihood decoding with code combining is used. Code combining allows for the combination of multiple copies of the same packet (which are typically discarded), to obtain a lower code rate for that specific packet, and therefore an improved probability of successful decoding. In both cases, combining multiple copies of the same packet results in a throughput which is an increasing function over a broad range of offered load, so that the system is more reliable from the point of view of stability. In addition, combining provides a higher throughput and a smaller time delay for packet transmission. This is illustrated by means of analytical and simulation results. Index Terms - Automatic repeat request, forward error correction, spread spectrum communication.

Reed-Solomon (RS) error-correcting (EC) codes are often proposed for communication systems requiring burst and/or erasure correction capabilities. In most cases, the modulation symbol size is fixed a priori. Therefore, the effective application of RS coding implies proper matching of the code symbol size with the modulation symbol size. Previous results have assumed that the RS codeword symbol size is an integer multiple of the modulation symbol size or have been based on simple approximations. In this paper, the exact symbol error probability with K-bit M-ary modulation symbols and q-bit RS codeword symbols is presented. Index Terms - Error analysis, error correction coding.

Let [n, k, d: q]-codes be linear codes of length n, dimension k and minimum Hamming distance d over GF(q). The following quasi-cyclic codes are constructed in this paper: [44, 11, 20; 3], [55, 11, 26; 3], [66, 11, 32; 3], [48, 12, 21; 3], [60, 12, 28; 3], [56, 13, 24; 3], [65, 13, 29; 3], [56, 14, 23; 3], [60, 15, 23; 3], [64, 16, 25; 3], [36, 9, 19; 4], [90, 9, 55; 4], [99, 9, 61; 4], [30, 10, 14; 4], [50, 10, 27; 4], [55, 10, 30; 4], [33, 11, 15; 4], [55, 11, 29; 4], [36, 12, 16; 4], [48, 12, 23; 4], [60, 12, 31; 4] All of these codes have established or exceed the respective lower bounds on the minimum distance given by Brouwer. Index Terms - Quasi-cyclic codes, ternary and quaternary linear codes.

In this correspondence, new ternary codes of dimension 6 are presented which improve the bounds on optimal linear codes. These codes belong to the class of quasi-twisted (QT) codes, and have been constructed using a greedy algorithm. This work extends previous results on QT codes of dimension 6. In particular, several new two-weight QT codes are presented. Numerous new optimal codes which meet the Griesmer bound are given, as well as others which establish lower bounds on the maximum minimum distance. Index Terms - Optimal ternary linear codes, quasi-twisted codes.

The largest quasi-cyclic subcode of the Reed-Muller code R(r, m), invariant under the shift [T.sup.[2.sup.m-1]] is determined. This code, denoted QCR(r, m, l), is presented through its module decomposition into cyclic submodules. The smallest regular trellis diagram (SRTD) is defined for block codes. This trellis and its construction algorithm are given for the class of cyclic-form codes. Using the cyclic-form structure of QCR(r, m, l), the [2.sup.l]-section SRTD of this code is determined. The eight-section SRTD is given for the Reed-Muller codes R(r, m). The quasi-cyclic subcodes of R(r, m) with regular [2.sup.l]-section minimal trellis diagrams are presented. Index Terms - Minimal trellis, quasi-cyclic codes, Reed-Muller codes, regular trellis.

In this correspondence, new optimal quaternary linear codes of dimension 5 are presented which extend previously known results. These codes belong to the class of quasi-twisted (QT) codes, and have been obtained using a greedy local search algorithm. Other codes are also given which provide a lower bound on the maximum possible minimum distance. The generator polynomials for these codes are tabulated, and the minimum distances of known QT codes are given. Index Terms - Quasi-twisted codes, optimal quaternary linear codes.

The class of quasi-twisted (QT) codes is a generalization of the class of quasi-cyclic codes, similar to the way constacyclic codes are a generalization of cyclic codes. In this paper, rate 1/p QT codes over GF(3) are presented which have been constructed using integer linear programming and heuristic combinatorial optimization. Many of these attain the maximum possible minimum distance for any linear code with the given parameters, and several improve the maximum known minimum distances. Two of these new codes, namely (90, 6, 57) and (120, 6, 78), are optimal and so prove that [d.sub.3](90, 6) = 57 and [d.sub.3](120, 6) = 78. Index Terms - Quasi-twisted codes, heuristic search, optimal codes over GF(3).

The performance of M-ary differential phase shift keying (MDPSK) in both tone jamming and Gaussian noise is presented. Previous work has been extended by considering larger signal sets and skewed differential phases with unequal decision regions. The error performance when a frequency offset exists between the jamming tone and MDPSK carrier is also considered.

The class of quasi-cyclic (QC) codes has been proven to contain many good codes. To date the known QC codes are primarily rate 1/p and (p - 1)/p binary codes constructed from circulant matrices. These results are extended to QC codes over GF(3) and GF(4). Codes are constructed using integer linear programming and heuristic combinatorial optimization. Many of these attain the maximum possible minimum distance for any linear code with the same parameters, and several improve the maximum known distances. The link between power residue (PR) codes and QC codes is exploited as a means of constructing new QC codes and to initialize the search algorithm. Previously unknown minimum distances for nonbinary quadratic residue codes are given. The minimum distances for the PR codes and the maximum known distances for the QC codes are tabulated.

The class of quasi-cyclic (QC) codes has been proven to contain many good codes. To date the known results are largely codes of the form 1/p and (p - 1)/p constructed from circulant matrices. A generalization of these rate 1/p codes to rate (m - 1)/pm codes is presented based on the theory of 1-generator QC codes. The results of a search for good codes based on heuristic combinatorial optimization are nine codes which improve the known lower bounds on the minimum distance of binary linear codes. Index Terms--Quasi-cyclic codes, heuristic combinatorial optimization, best-known binary linear codes.

In this correspondence, we construct new self-dual codes over [F.sub.4], [F.sub.5], [F.sub.7] with larger minimum weights than the previously known self-dual codes, using construction methods based on circulant and negacirculant matrices. In particular, a self-dual [36, 18, 13] code over [F.sub.7] is constructed which has a larger minimum weight than the previously known [36, 18] codes. Index Terms--Circulant matrix, negacirculant matrix, nonbinary codes, self-dual codes.

Eighteen new codes are presented which improve the bounds on maximum minimum distance for binary linear codes. They are rate (m - r)/pm, [Tau] [greater than or equal to] 1, degenerate quasi-cyclic (QC) codes. Based on the known upper bounds, six of these new codes are optimal. In addition, five two-weight QC codes of dimension 8 are given. Index Terms - Optimal binary linear codes, quasi-cyclic codes.

The synthesis of a quadrupolar ruthenium alkynyl cruciform complex and its reversible conversion to tetravinylidene complex or tetraruthenium(III) tetracationic complex is reported. The reaction provides insight into optical nonlinear behavior of cruciform complexes.

The linear and nonlinear optical (NLO) properties of a series of [D.sub.3] [F(II), Ru(II), Ni(II), Cu(II), Zn(II)]octupolar metal complexes featuring the 4,4'-bis[(dibutylamino)styryl]-2,2'-bipyridine ligand are described. These compounds have displayed relatively large first hyperpolarizabilities and two-photon absorption (TPA) cross section values.

The syntheses of medium-nuclearity very-mixed metal clusters by an unusual combination of core expansion and metal exchange upon reacting M[Ir.sub.3][(CO).sub.11]([eta]-L) (M = Mo, W and L = [C.sub.5][H.sub.5], [C.sub.5]H[Me.sub.4], [C.sub.5][Me.sub.5]) with [[M[(CO).sub.3]([eta]-L)].sup.-] (M = Mo, W and L = [C.sub.5]H[Me.sub.4], [C.sub.5][Me.sub.5]) is reported. The spectroscopic data has suggested that the electron density at these dispartate-metal-containing cluster cores is tunable by progressive cyclopentadienyl alkylation.

Reactions of tungsten-iridium clusters with tungsten phenylethynyl, diruthenium ethynidyl, or ditungsten butadiyndiyl complexes afford a range of products of the same or higher nuclearity. The focus of the study is on molybdenum/tungsten-iridium clusters, reaction with alkynes having afforded products involving alkyne coordination, dimerization, or C triple bond C scission.

Recently, Type II codes over [F.sub.4] have been introduced as Euclidean self-dual codes with the property that all Lee weights are divisible by four. In this paper, a number of properties of Type II codes are presented. We construct several extremal Type II codes and a number of extremal Type I codes. It is also shown that there are seven Type II codes of length 12, up to permutation equivalence. Index Terms--Euclidean self-dual codes over [F.sub.4], Type II codes.

This paper considers the performance of iteratively decoded single parity check (SPC) multidimensional product codes in an additive white Gaussian noise channel. Asymptotic performance bounds are compared to simulation results. A new code structure based on SPC product codes is introduced. This structure involves interleaving between the encoding of each dimension in the product code. Analysis of the weight distribution is used to explain the good performance results for these randomly interleaved SPC product codes. Index Terms--Product codes, random interleaving, single parity check codes.

Previously, self-dual codes have been constructed from Hadamard matrices. In this correspondence, codes constructed from weighing matrices, and in particular conference matrices are presented. A necessary condition for these codes to be self-dual is given, and examples are given for lengths up to 40. Codes constructed from all weighing matrices of order n [is less than or equal to] 13 are also considered. Index Terms--Conference matrices, self-dual codes, weighing matrices.

Let [[n, k, d].sub.q]-codes be linear codes of length n, dimension k, and minimum Hamming distance d over GF (q). In this correspondence, 31 new quaternary (q = 4) codes are constructed which improve the respective lower bounds on minimum distance in Brouwer's tables. Index Terms--Quasi-twisted (QT) codes, quaternary linear codes.

Recently, Type IV self-dual codes over the ring [F.sub.2] + [micro][F.sub.2] of order 4 have been introduced. In this correspondence, we construct five optimal Type IV self-dual codes which are the first examples of such codes for that length. We also give new optimal Type Iv self-dual codes, and Type Iv self-dual codes which improve the upper bounds for minimum weights. Index Terms--Optimal Type IV self-dual codes, Type IV codes over rings.

In 1976, Moore investigated a class of self-dual double-circulant codes based on primes of the form q = 3 mod 8. This paper shows that the corresponding length 168 code contains a weight 28 codeword and thus is not extremal. This answers a long-standing question regarding this code. The next five codes in this class are also shown not to be extremal. Index Terms - Double circulant codes, self-dual codes.

Conway and Sloane have listed the possible weight enumerators for extremal self-dual codes up to length 72. In this correspondence, we construct extremal singly-even self-dual [60, 30, 12] codes whose weight enumerator does not appear in this list. In addition, we present the possible weight enumerators for extremal self-dual codes of length 60. Index Terms - Extremal self-dual codes, double circulant codes.

A class of rate 2/p quasi-cyclic codes can be characterized in terms of m x m circulant matrices. In this correspondence, two new codes with parameters (80, 10, 35) and (95, 10, 42) are presented which improve the known lower bound on the maximum possible minimum distance. The former code can be extended with an even parity check bit to an (81, 10, 36) code that establishes that [d.sub.2](81, 10) = 36. Index Terms - Quasi-cyclic codes, best binary linear codes