Code Construction Method Research Articles

Systematic space-time trellis code construction for correlated Rayleigh-fading channels

The potential for capacity increase in multiple-antenna wireless communication systems has drawn considerable attention to space-time codes. However, most of the existing space-time code construction methods have assumed ideal channel models: either quasi-static fading or fast fading. In this work, we propose a systematic space-time trellis code construction method for correlated fading channels. We derive the performance criteria that take into account both spatial and temporal channel correlation, assuming that the space-time correlation matrix is of full rank. Moreover, we introduce a new design criterion and analyze the properties of the space-time trellis codes satisfying the proposed criterion. Using the design criterion, we develop a code construction procedure that jointly considers diversity advantage and coding advantage for an arbitrary number of transmit antennas and any memoryless modulation. The flexibility of the proposed code construction method is demonstrated by designing space-time trellis codes for two, three, and four transmit antennas with quaternary phase-shift keying (QPSK), 8PSK (phase-shift keying), and 4ASK (amplitude-shift keying) modulations. The simulation results demonstrate that not only can our method generate new codes for an arbitrary number of antennas, but in some special cases, where previously proposed codes exist, our codes also perform very well.

Systematic Design of Space-Time Trellis Codes for Diversity and Coding Advantages

The emerging need for high data rate wireless services has raised considerable interest in space-time coding. In this work, we propose a systematic code construction method that jointly considers diversity advantage and coding advantage for an arbitrary number of transmit antennas and any memoryless constellation. Our approach is to directly assign channel symbols to transmit antennas at different states by exploiting the properties of the state transitions in the trellis. The code construction problem is reduced to a combinatorial optimization problem and a computationally efficient suboptimal solution is proposed. The flexibility of the method is demonstrated by designing space-time trellis codes for QPSK, 8PSK, 16PSK, asymmetric QPSK AND 4ASK constellations, Space-time code construction for a large number of transmit antennas (6,8, and 10) is also considered. The simulations show that our design procedure results in codes that outperform the ones constructed by previously existing methods. The achievable performance gain is governed by the distance structure of the chosen constellation.

Optimal two-level unequal error control codes for computer systems

Error control codes are now successfully applied to computer systems and communication systems. When we consider some types of computer words or communication messages, the information in some part of the word is more important than the other. Address and control information in computer words and communication messages and pointer information in database words are good examples. The more important the part of the word is, or the less reliable the part is, the more strongly it should be protected from errors. Based on this, this paper proposes a new class of codes, called unequal error control codes, which have some unequal error control levels in the codeword, that is, have some distinct code functions in the codeword and protect the part of the word from errors according to its importance or reliability level. From a simple and practical viewpoint, this paper adopts the model of the codeword which includes two unequal levels: one having strong error control level in some part of the codeword, called fixed-byte, and the other having relatively weak error control level outside the fixed-byte. This paper deals with three basic unequal error control codes. For all types of codes, the paper clarifies necessary and sufficient conditions and bounds on code length and demonstrates code construction method of the optimal codes and evaluation of these codes from the perspectives of error correction/detection capability and decoder hardware complexity.

Linear codes for the sum mod-2 multiple-access channel with restricted access

Transmission of information through a multiple-access-modulo-2 adder channel is addressed for the situation that out of a fixed family of N potential users at most some m, m<N are active simultaneously. The authors assign codes to the N users in a way that the receiver is able to correct any t or less errors and separate the s/spl les/m messages without a priori knowledge of the subset of active users. A decoding procedure is presented. The efficiency of the method of code construction is demonstrated by some examples and by an upper bound, that asymptotically tends to zero, on the loss of rate.<<ETX>>

Theory and design of t-unidirectional error-correcting and d-unidirectional error-detecting code

The basic theory of t-UEC d-UED codes is developed. Methods for construction of such codes from symmetric error-correcting and asymmetric error-correcting codes are developed. Some bounds for t-EC d-UED codes are improved. Encoding/decoding procedures for these codes are discussed. >

Majority logic combination sequences using m-sequences for rapid acquisition in direct sequence/spread spectrum communication systems

Rapid acquisition is an important problem in the direct sequence spread spectrum communication system, especially when code length is long. This paper proposes a novel code construction method of making rapid acquisition, in which majority logic combination sequences constructed from M-sequences mutually of prime length (hereafter M-MAJ sequences) are used. By tacking cross-correlation of incoming M-MAJ sequence with component M-sequences at the receiver, acquisition time can be reduced considerably. Calculated results of the average acquisition time and comparisons with conventional code construction methods (JPL sequence, concatenated sequence) are shown.