William H. Tranter

Wireless communications: past events and a future perspective

the 21 st century. ireless communications has emerged as one of the largest sectors of the telecommunications ,industry, evolving from a niche business in the last decade to one of the most promising areas for growth in the 21st cenW tury. This article explores some of the key technological advances and approaches that are now emerging as core components for wireless solutions of the future.

Dynamic spectrum allocation in cognitive radio using hidden Markov models: Poisson distributed case

Cognitive radio networks can be designed to manage the radio spectrum more efficiently by utilizing the spectrum holes in primary users licensed frequency bands. Recent studies have shown that the radio spectrum is poorly utilized by the licensed users even in urban geographical areas. This spectrum utilization can be improved significantly by making it possible for secondary users (who are not being served by the primary system) to access spectrum holes, i.e., frequency bands not used by licensed users. In this novel work, we use hidden Markov models (HMMs) to model and predict the spectrum occupancy of licensed radio bands. The proposed technique can dynamically select different licensed bands for its own use with significantly less interference from and to the licensed users. It is found that by predicting the duration of spectrum holes of primary users, the CR can utilize them more efficiently by leaving the band, that it currently occupies, before the start of traffic from the primary user of that band. We propose a simple algorithm, called the Markov-based channel prediction algorithm (MCPA), for dynamic spectrum allocation in cognitive radio networks. In this work, we present the performance of our proposed dynamic spectrum allocation algorithm when the channel state occupancy of primary users are assumed to be Poisson distributed. The impact of CR transmission on the licensed users is also presented. It is shown that significant SIR improvements can be achieved using HMM based dynamic spectrum allocation as compared to the traditional CSMA based approach. The results obtained using HMM are very promising and HMM can offer a new paradigm for predicting channel behavior in cognitive radio, an area that has been of much research interest lately.

Dynamic Data Structures for a Direct Search Algorithm

The DIRECT (DIviding RECTangles) algorithm of Jones, Perttunen, and Stuckman (Journal of Optimization Theory and Applications, vol. 79, no. 1, pp. 157–181, 1993), a variant of Lipschitzian methods for bound constrained global optimization, has proved effective even in higher dimensions. However, the performance of a DIRECT implementation in real applications depends on the characteristics of the objective function, the problem dimension, and the desired solution accuracy. Implementations with static data structures often fail in practice, since it is difficult to predict memory resource requirements in advance. This is especially critical in multidisciplinary engineering design applications, where the DIRECT optimization is just one small component of a much larger computation, and any component failure aborts the entire design process. To make the DIRECT global optimization algorithm efficient and robust on large-scale, multidisciplinary engineering problems, a set of dynamic data structures is proposed here to balance the memory requirements with execution time, while simultaneously adapting to arbitrary problem size. The focus of this paper is on design issues of the dynamic data structures, and related memory management strategies. Numerical computing techniques and modifications of Jones original DIRECT algorithm in terms of stopping rules and box selection rules are also explored. Performance studies are done for synthetic test problems with multiple local optima. Results for application to a site-specific system simulator for wireless communications systems (S4W) are also presented to demonstrate the effectiveness of the proposed dynamic data structures for an implementation of DIRECT.

In-building wideband multipath characteristics at 2.5 and 60 GHz

This paper contains measured data for 2.5 and 60 GHz in-building partition loss. Path loss measurements were recorded using a broadband sliding correlator channel sounder which recorded over 39000 power delay profiles (PDP) in 22 separate locations in a modern office building. Transmitters and receivers were separated by distances ranging from 3.5 to 27.4 meters, and were separated by a variety of obstructions, in order to emulate future single-cell-per-room wireless networks. These measurements may aid in the development of future in-building wireless networks in the unlicensed 2.4 GHz and 60 GHz bands.

Convergence analysis of the least squares constant modulus algorithm in interference cancellation applications

This paper examines the convergence behavior of the least squares constant modulus algorithm in an adaptive beamforming application. The improvement in output SIR with each iteration of the algorithm is predicted for several different signal environments. Deterministic results are presented for an environment containing two tones. Probabilistic results are presented for a constant modulus desired signal with a constant modulus interferer and with a gaussian interferer. The asymptotic improvement in output SIR as the output SIR becomes high is also derived.

Globally optimal transmitter placement for indoor wireless communication systems

A global optimization technique is applied to solve the optimal transmitter placement problem for indoor wireless systems. An efficient pattern search algorithm - DIviding RECTangles (DIRECT) of Jones et al.- has been connected to a parallel three-dimensional radio propagation ray tracing modeler running on a 200-node Beowulf cluster of Linux workstations. Surrogate functions for a parallel wideband code-division multiple-access (WCDMA) simulator were used to estimate the system performance for the global optimization algorithm. Power coverage and bit-error rate are considered as two different criteria for optimizing locations of a specified number of transmitters across the feasible region of the design space. This paper briefly describes the underlying radio propagation and WCDMA simulations and focuses on the design issues of the optimization loop.

The performance of Reed-Solomon codes on a bursty-noise channel

The performance of a Reed-Solomon coded binary communication system on a bursty-noise channel is considered. Bursty noise is defined to be background Gaussian noise plus burst noise, where burst noise is defined to be a series of finite-duration Gaussian-noise pulses with fixed duration and Poisson occurrence times. Using the noise model, along with ideal symbol interleaving, decoded bit-error probability bounds are derived for the case where the noise bursts are long with respect to the channel symbol rate. Specific performance results are presented for the (31,15,8) Reed-Solomon Joint Tactical Distribution System (JTIDS) code with a binary phase shift keyed (BPSK) modulation scheme. Simulation results are presented and they compare well with the theoretical results. >

Noise generators for the simulation of digital communication systems

The generation of random numbers, having uniform and Gaussian distributions, with application to the time-domain simulation of communication systems is considered. The specific goal is to identify appropriate noise generation algorithms for use in system simulations for the determination of the symbol error probability of a digital communication system. Several methods of generating both uniform and Gaussian random numbers are examined. The algorithms considered were taken from those discussed in recent literature that appeared most appropriate for the authors problem. The algorithms were programmed in FORTRAN for use on a PC with math-coprocessor. Tests to evaluate the statistical properties of the generators were performed and the results are presented. >

System power consumption minimization for multichannel communications using cognitive radio

Power consumption has been a significant issue for many mobile and wireless devices, especially those with high rate applications. This paper presents a methodology and framework to minimize system power consumption for multichannel communications using cognitive radio (CR) based on the application quality of service requirement, the channel condition, and the radio capabilities and characteristics. The CR framework enables an adaptation process that is aware of the radio (component) capabilities and characteristics. This paper mathematically formulates a system power consumption minimization problem under a rate constraint for multichannel communications and develops numerical solutions. Simulation results show that the knowledge of the radio capabilities and characteristics can help to reduce system power consumption significantly (e.g., up to 55% for a multichannel system with Class A power amplifiers).

Towards integrated PSEs for wireless communications: experiences with the S 4 W and SitePlanner® projects

This paper describes the computational methodologies of two problem solving environments (PSEs) for wireless network design and analysis, one academic (S4W) and one commercial (SitePlanner®). The PSEs address differently common computational issues such as environment specification, propagation modeling, channel performance prediction, system design optimization, and data management. The intended uses, interfaces, and capabilities of the two PSEs are compared and contrasted in a common framework. An important future direction, for these two and all future wireless system design PSEs, is resolving the fundamental impedance mismatch between physical channel modeling and upper level protocol modeling in wireless networks.