Multilevel perfect sequences over integers are introduced which include the conventional binary perfect sequences as special cases. Such sequences can be derived from multilevel cyclic Hadamard matrices over integers. It is proved that integer-valued perfect sequences of odd lengths with the energy being non-square integers do not exist, and the existence of four-level perfect sequences of lengths up to 11 over the alphabet sets {+/- 1, +/- 2} and {+/- 1, +/- 3} is completely determined.

The presence and availability of several independent wired and wireless networks within a communication environment has led to the channel adaptive multiple I/O (CAMIO) protocol being developed as an appropriate and novel technique for data transmission. The proposed system utilises an intelligent multiplexing technique that enables the transmission/reception of multiple data sources via several wired/wireless networks simultaneously. Real-time configuration and adaptation capabilities when data sources/channels are dynamically added/deleted/modified are described. Data prioritisation methods, combined with traffic control and congestion-reactive techniques, are presented. Simulation results demonstrate that the use of the CAMIO protocol over multiple transmission/reception channels increases the overall data transmission rate, handles the delivery of time-sensitive packets and maintains the quality of service, especially in situations where one or more communication channels fail to operate.

This paper evaluates the BER performance of a spatial multiplexing system over finite scattering channel. We employ a `DBLAST-like' space-time convolutional code, which directly maps a convolutional code frame to a space-time code word. The finite scatterers channel model is used to account for the limited multipath scattering which occurs in practical channels. In the receiver, iterative joint MMSE detection, decoding and interference cancellation is applied to improve the system performance. Numerical results are presented to illustrate the performance of this spatial multiplexing system over this channel. We analyse the impact of this channel model on the system performance and examine the performance improvement obtained by the use of the iterative receiver

A novel multiple access coding approach for mobile networked systems is presented based on complex quadraphase coding. matched error control coding and channel adaptation. This approach provides an adaptive multiple-access communications capability where residual spreading gain. coding gain. data rates and channel loading are variables. Based on a blind estimate of the channel state. these parameters can be optimised to satisfy user Quality of Service Requirements. With these techniques, the foundation is laid for a new class of Collaboratively Coded Multiple Access Systems that can operate stand-alone or as hybrid CDMA/CCMA communications systems. A principal advantage of this approach is that high user and service density can be accommodated while the overall system complexity can be managed to tractable levels.

Perfect sequences find application in many areas including synchronisation techniques, channel estimation, fast start-up equalization, pulse compression radars and CDMA systems. This paper will first discuss the necessary and sufficient condition for, and some useful properties of, perfect sequences. Then, a comprehensive description of various perfect sequences is given. The emphasis will be on the synthesis of different perfect sequences, including two-valued perfect sequences, ternary perfect sequences, polyphase perfect sequences and modulatable perfect sequences. The perfect array and other related topics are also discussed briefly.

Since their introduction by Berrou et al [1] in 1993, Turbo codes have generated considerable interest within the coding community as they offer near-Shannon limit performance. As yet, there is little application of these codes in practical systems and the vast majority of results thus far have been from simulations. The paper will discuss Turbo codes with particular reference to their application in radio channels and offers practical solutions for future implementation.

A practical approach is described for adaptively multiplexing in real-time T of N users in a multi-channel communications system using a majoritive logic multiplexer and quasi-othogonal binary coding. The adaptive multiplexer employs the users' class of service and channel noise constraints to optimize T and fidelity criteria.

Low frequency sub-surface radio is used for communications with miners and cavers. The signal attenuation is dependent on frequency and on the electrical conductivity of the ground. In addition, the optimum frequency for communications is dependent on depth below the surface; and on the degree of noise and cochannel interference. An adaptive communications system makes use of a channel-sounding technique by transmitting a wideband signal and deriving the signal/noise ratio (SNR) as a function of frequency. The communications system can thereby alter its transmission frequency, and other parameters, to optimise SNR under different conditions. The same principles are relevant to applications in sub-surface radiolocation, archaeology and geophysics.

The three-dimensional cosine transform (3-D DCT) is used for 3-D image compression and related applications. Its calculation involves a very large number of arithmetic operations and hence fast algorithms are needed for its computation. In this paper, the row-column-frame (RCF) and the 3-D vector radix (3-D VR) algorithms, which are usually used for the calculation of the 3-D DCT and its inverse, are investigated and compared based on their arithmetic operations and computer-run times. Both comparisons show that the 3-D VR algorithm is clearly faster and more efficient than the RCF approach.

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.

In an application to measure subterranean radio propagation, a wide-band low-frequency channel sounder makes use of a modified pseudo-random binary sequence with an imperfect (non-impulsive) auto-correlation function (ACF). The transmitting antenna for this system is essentially an induction loop, and the extreme wideband nature of the system requires this to be operated untuned. The resultant low efficiency is countered by signal-averaging techniques at the receiver, requiring accurate synchronisation to the transmitter, which is achieved using a code- or delay-locked loop. Accurate system identification and synchronisation is possible because cross-correlation is carried out between the non-ideal transmitted sequence and its inverse reference. A simple algorithm is presented for calculating the inverse of an arbitrary sequence under the operation of cross-correlation, and some properties of inverse sequences are discussed.

The contribution of this paper is to derive a novel figure of merit that can be measured in practice for symbol synchronisers. It is used to estimate the probability of symbol error, including the effect of symbol slip, for different frame and signaling alphabet sizes. The new figure of merit proves to provide a significantly more accurate characterisation than previously published methods. Specifically, by applying the novel figure of merit, the paper compares the symbol synchronisation performance of a conventional digital phase locked loop (DPLL) symbol synchroniser with that of modulation-derived synchroniser (MDS) under additive white Gaussian noise (AWGN) channel conditions.

A new video compression algorithm based on a temporal blocking structure, rather than the more conventional spatial blocking structure, is described. This blocking structure forms the basis of an adaptive vector quantisation (VQ) algorithm, the performance of which is then compared with a similar adaptive VQ scheme based on a spatial blocking structure.

A physically based method has been developed to simulate the wideband HF ionospheric propagation channel relevant to the case of wideband spread spectrum HF communications and also other HF applications such as digital broadcasting and over-the-horizon radar. It is based on the consideration and solution of the equations governing pulse signal propagation through a fluctuating time varying random ionosphere. The wideband scattering function has been constructed as the appropriate Fourier transform of the correlation function of a channel impulse response. Numerical codes have been written, which allow numerical simulation of the wideband scattering function of the HF sky wave ionospheric fluctuation channel for any given model of the background ionosphere and time varying ionospheric turbulence with an anisotropic inverse power law spatial spectrum and frozen drift of the ionospheric inhomogeneities. When employed in the simulation of the scattering function for real conditions of propagation, the method provides the possibility of analysing the propagation effects for different relative bandwidths of the background channel, fluctuating channel and transmitted pulse. The effects of the transmitted pulse bandwidth and anisotropy of the irregularities have been studied. The numerical results have been obtained and presented, which demonstrate the contribution of the effects enumerated in the wideband scattering function of the HF ionospheric 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

The paper describe techniques by which an HF channel impulse response measurement capability can be added to existing ITU broadcast field strength monitoring terminals. This additional capability can be provided via a simple software upgrade. Obviously, due to the relatively low clock rate of the complementary sequences and the restricted transmission bandwidth, the time resolution of the impulse response estimate is somewhat limited. However, the resolution is sufficient to identify the multipath conditions which are likely to have a detrimental effect on the majority of HF data modems.

Requirements for future mobile communications systems are demanding. This paper presents techniques and a development system for the research, design & development of reconfigurable digital signal processing for software radio based systems. Software radio is an essential technology required for the realisation of 3G to meet requirements such as seamless global roaming and protocol independence. This development system ensures that the use of FPGA is practical and realistic when considering the high data rate and multifunctional requirements of 3G systems.

In a digital communication system, synchronisation between the transmitter and the receiver is essential to ensure reliable data transmission. There are three main categories of synchronisation associated with a typical data receiver system i.e.: (i) carrier synchronisation; (ii) symbol synchronisation; and (iii) frame synchronisation. The aims of the research are to acquire carrier, symbol and frame synchronisation with: (i) minimum transmission overheads (intrinsic synchroniser); (ii) minimum synchroniser complexity; and (iii) an adaptive synchronisation capability. This paper emphasises symbol synchronisation. Since one of the aims of the research is to acquire symbol synchronisation with minimum overheads, data derived synchronisation is emphasised here. Data derived synchronisation is a method of symbol synchronisation that allows timing information to be extracted from the message signal itself. There are three types of data derived symbol synchronisation algorithms available. The modulation derived synchronisation (MDS) is chosen as the basis of this paper. (7 pages)