M. Darnell

Trellis Decoding Technique for Array Codes

Array codes were first introduced by Elias [1], and have been proposed for many burst and random-error control applications [2–5]. The essence of an array code is that the combination is based on a geometrical construction, the component codes are simple and decoding of array codes is relatively easy. The simplest array code is the row-and-column parity code, which also is called a two-coordinate, bidirectional, bit and block parity and has been widely used in data transmission systems and computer memories [2]. The code may be square or rectangular and has parameters (n1n2,k1k2,dmin), where (n1,k1) and (n2,k2) are row and column codes respectively, and minimum Hamming distance dmin=4. These codes are easy and flexible to design and relatively simple to decode. However these codes do not have the full power of block linear code of length n=n1n2, and the conventional decoding algorithms [2] for array codes, do not make use of maximum power of the code and are not maximum likelihood decoding algorithms.

Balanced quadriphase sequences with near-ideal autocorrelations

We describe a generalization of balanced binary sequences to quadriphase sequences. Given any prime p/spl equiv/1 mod4 and any positive integer m, a class of balanced quadriphase sequences of length p/sup m/-1 with near-ideal periodic autocorrelation properties is constructed. The quadriphase sequences are optimal under the condition of balanced sequence elements.

Polyphase sequences with good periodic and aperiodic autocorrelations

Polyphase sequences with ideal periodic autocorrelation functions and favorable aperiodic autocorrelation functions are considered. The properties of such polyphase sequences are studied. It is proved that there exist other Golomb (1965) sequences of length L whose maximum out-of-phase value is bounded by /spl radic/(L/c), where c is an positive number.<<ETX>>

Perfect sequences derived from M-sequences

New classes of multi-level and complex sequences with perfect periodic autocorrelations are presented. The sequences are derived directly from certain M-sequences over rational and Gaussian integers.

Adaptive nested trellis decoding for block codes

A new adaptive trellis decoding technique for block codes is proposed. The technique is based on an encoding technique which allows the design of almost all known linear codes together with their minimal trellises. The proposed adaptive trellis decoding technique allows the implementation of a single soft maximum likelihood trellis decoder for decoding of different codes. It has been shown that both the encoding and decoding techniques can be implemented with a low complexity and cost.

Fast 3-D algorithm for the 3-D IDCT

We introduce a fast three-dimensional algorithm for the calculation of the three-dimensional inverse discrete cosine transform (3-D IDCT). The derivation of the algorithm is presented and its arithmetic complexity is analysed and compared to that of the familiar row-column-frame (RCF) method. The proposed algorithm is found to reduce the number of multiplications by about 41%, whilst keeping the number of additions the same. Also, based on computer run-time, it is found to reduce the time involved in calculating the 3-D IDCT significantly. This makes the developed algorithm more suitable for 3-D image and video compression decoders involving the 3-D IDCTs.

High performance reconfigurable digital signal processing for the time varying channel

In the time varying channel there is a requirement for the communication system to vary its function to adapt to the changing transmission conditions. The need for greater transmission capacity puts increasing demand on the processing requirements of such systems. This paper describes the concept of reconfigurable digital processing and highlights some of the problems encountered while designing such systems. An example of a reconfigurable channel coding algorithm is presented which illustrates the difficulty of designing reconfigurable systems particularly for adaptable communications systems such as those used for HF communication. This example illustrates the use of reconfigurable systems based around Golay and Hamming codes which are commonly used in HF systems. A design methodology is presented with software and hardware tools to enable the reconfigurable processing designer to easily design a reconfigurable digital processing system for communication in a time varying environment.

Decision feedback MLD for CTDMA system

A decision feedback maximum likelihood detection scheme (DFMLD) is developed to support code time division multiple access (CTDMA) systems operating in a fully loaded mode. CTDMA systems have been proposed as a candidate for the third generation mobile communication systems to combine the advantages of constant envelope transmission of CDMA and the good user separation of TDMA.

RS-CDMA: a quasi-synchronous CDMA scheme to support uplink operation of mobile communication

A despreading scheme employing inverse filtering is introduced to exploit the frequency diversity of a multipath signal in such a way that the path with the strongest power is enhanced while the others are cancelled almost completely. Based on this scheme, a quasi-synchronous CDMA system, termed rotated spectrum code division multiple access (RS-CDMA), is proposed as an alternative to the previously proposed CTDMA to support uplink operation of mobile communications with good performance as well as high spectrum efficiency. The principle and simulation results of the performance are given.

Low-complexity trellis decoding of linear block codes

A new encoding technique which allows the design of a wide variety of block codes is introduced. Based on this technique, minimal trellises of the codes are designed.<<ETX>>