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To achieve better tracking of time-varying channel parameters, a structure using blind adaptive minimum output energy (MOE) detection in conjunction with RAKE combining diversity for direct-sequence code-division multiple-access communications over frequency selective multipath fading channels is introduced. In this MOE-RAKE structure, the signal replicas received from multiple fading paths are first independently produced by a bank of adaptive MOE detectors and then combined by a RAKE receiver for final symbol decision. A normalised, complex-valued stochastic gradient descent algorithm is developed for the blind adaptation used in the MOE-RAKE. Simulation results show that, in the time-invariant channel, the MOE-RAKE has a performance comparable to the previously proposed MOE and outperforms the conventional RAKE. In the time-varying channel, the MOE-RAKE performs better than the other blind multiuser detection techniques. In practice, to further improve the detector performance, a hybrid scheme started with blind adaptation for the initial updates and then switched to the decision-directed algorithm is desired.

In three-dimensional space an embedded network is called gradient-constrained if the absolute gradient of any differentiable point on the edges in the network is no more than a given value m. A gradient-constrained minimum Steiner tree Tis a minimum gradient-constrained network interconnecting a given set of points. In this paper we investigate some of the fundamental properties of these minimum networks. We first introduce a new metric, the gradient metric, which incorporates a new definition of distance for edges with gradient greater than m. We then discuss the variational argument in the gradient metric, and use it to prove that the degree of Steiner points in Tis either three or four. If the edges in Tare labelled to indicate whether the gradients between their endpoints are greater than, less than, or equal to m, then we show that, up to symmetry, there are only five possible labellings for degree 3 Steiner points in T. Moreover, we prove that all four edges incident with a degree 4 Steiner point in Tmust have gradient mif mis less than 0.38. Finally, we use the variational argument to locate the Steiner points in T in terms of the positions of the neighbouring vertices.

Recently Rubinstein et al. gave a new proof of the NP-completeness of the discretized Steiner problem, that is, the problem of finding a shortest network connecting a given set of points in the plane where all vertices are integer points and a discretized metric is used. Their approach was to consider the complexity of the PALIMEST problem, the Steiner problem for sets of points lying on two parallel lines. In this paper, we give a new proof of this theorem, using simpler, more constructive arguments. We then extend the result to a more general class of networks known as APE-Steiner trees in which certain angles between edges or slopes of edges are specified beforehand.

An adaptive nonlinear recursive least square (RLS) algorithm for amplitude estimation in class A noise is presented. For Gaussian input signal and class A noise, its mean and mean-square behaviours are studied. It is shown that the linear RLS and nonlinear RLS algorithm with the clipper function are stable in the mean and mean square. For non-Gaussian input, amplitude estimation in CDMA communication is presented. Simulation results show that the nonlinear RLS can provide good performance close to the Cramer–Rao bound and outperform the nonlinear LMS and the conventional RLS in impulse noise.

Analysis of performance of an L-diversity DPSK nonlinear combiner in frequency nonselective Rayleigh fading channels with impulse noise is presented. By employing the characteristic function, asymptotic and approximate bit error probabilities are derived. Analysis and simulation results indicate that by equipping a nonlinear element in the equal-gain combiner, the new detector can effectively combat impulse noise and fading.

We prove a conjecture of Chung, Graham, and Gardner (Math. Mag.62(1989), 83–96), giving the form of the minimal Steiner trees for the set of points comprising the vertices of a 2k×2ksquare lattice. Each full component of these minimal trees is the minimal Steiner tree for the four vertices of a square.

We construct minimal Steiner trees for any square or rectangular array of integer lattice points on the Euclidean plane.

A new two-stage nonlinear detector for synchronous DS/SSMA communications in impulsive channels is presented and analysed. In the detector, an interference cancellation scheme is used such that the effect of the multiple-access interference on the system performance can be alleviated. For a multiuser system with long spreading sequences an approximate error probability is derived and shows that the new detector is insensitive to the ‘near–far’ effect and gives a near-single-user performance. For cases with short spreading sequences Monte-Carlo simulation is carried out to estimate the error probability and the results show that the detector performs robustly in various mixtures of noise.

The authors present a performance analysis of L-diversity DPSK receivers over frequency non-selective Rayleigh fading channels in Middleton's class A impulse noise. The analysis is exact and is shown by simulation to be accurate.

A new closed form for the bit error rate of a binary non-coherent DPSK receiver with equal gain combining diversity over frequency non-selective m-distributed Nakagami fading channels is presented. The analysis is shown to be efficient and accurate in the simulation.

M-ary FSK transmission with square law combining over frequency non-selective m-distributed Nakagami fading with arbitrary m is studied. A closed form of the symbol error probability is derived and is verified by simulation to be accurate.

A general formula for the bit error probability of M-ary DPSK transmission with equal gain combining diversity over frequency non-selective m-distributed Nakagami fading channels is derived. Simulations have shown that the analysis is efficient and accurate.

An efficient method for evaluating the performance of the nonlinear combiner in L-branch frequency non-selective Rician fading channels with impulse noise is derived and verified by simulations. Analysis shows that the nonlinear combiner is robust against impulse noise and fading.