Showing papers by "Stephen McLaughlin published in 2006"

Method of operating a telecommunications network

Abstract: A method of selecting one of a plurality of candidate devices (1-6) forming at least part of a wireless personal area network (WPAN) to be a controller of the WPAN. For each candidate device (1-6), distances between that candidate device and other devices of the WPAN are assessed. A centrally located one (3) of the candidate devices is selected to be the controller, taking said distances into account. The residual battery energy of the candidate devices may also be taken into account.

Mobile ad-hoc network

Abstract: A method of assessing a communication route comprising a plurality of links between nodes in a mobile ad-hoc network comprises calculating the two-hop residual bandwidth of each node I of the route as B I ⁡ ( t ) = B - ∑ J ∈ N ⁡ ( I ) ⁢ B ⁡ ( J ) ϕ where B is the raw channel bandwidth, the summation is the overall consumed bandwidth from node I's two-hop neighborhood nodes, JeN(I) and φ is a factor to account for protocol overhead, which may include handshaking, packet collision, re-transmission and/or back-off scheme traffic. An estimated transmission time for each of a plurality of links between said nodes may be calculated taking said two-hop residual bandwidth into account. For each possible route, a route efficiency function is determined at least by summing the estimated transmission times for all the links in the route, and the route in which the value of the route efficiency function is smallest is selected.

Hybrid wireless communication system and communication method using the same

Abstract: Disclosed is a hybrid wireless communication system and a communication method in the system. The system supports time and frequency division duplexing modes and includes a base station having a cellular communication range based on a cellular mode and mobile stations within the cellular communication range. The base station divides each available frequency resource into frames for communication, and each frame switches between a real-time service mode and a non-real-time service mode at a switching time within the frame. Communication is performed with the mobile stations within the cellular communication range via at least one of an uplink and a downlink in the real-time service mode of each frame according to the frequency division duplexing mode. Communication is performed with the mobile stations via the uplink and the downlink in the non-real-time service mode of each frame according to an ad hoc mode based on the time division duplexing mode.

Block error correcting codes using finite-field wavelet transforms

Abstract: This paper extends the popular wavelet framework for signal representation to error control coding The primary goal of the paper is to use cyclic finite-field wavelets and filter banks to study arbitrary-rate L-circulant codes It is shown that the wavelet representation leads to an efficient implementation of the block code encoder and the syndrome generator A formulation is then given for constructing maximum-distance separable (MDS) wavelet codes using frequency-domain constraints This paper also studies the possibility of finding a wavelet code whose tail-biting trellis is efficient for soft-decision decoding The wavelet method may provide an easy way to look for such codes

Managing change within IBM's complex supply chain

Abstract: Purpose – The purpose of this research is to report on research to date concerning the creation of a hybrid model for managing performance and decision making with elements of an IBM supply chain.Design/methodology/approach – As part of a wider research programme this paper utilises survey, focus group and case analysis techniques to examine the supply chain interactions.Findings – A cross‐functional process‐orientated team was assembled to look at the end‐to‐end process logic, skills alignment, effective codified knowledge systems, and the prioritisation of change to overcome inhibitors of change originating from functional/IT‐focused processes/solutions.Research limitations/implications – The results of this paper have, as yet, not been validated beyond the process performance targets set by IBM. Validation across and within industry boundaries, based on survey and case analysis, is about to commence.Practical implications – Too often “management” play too active a role in the operational aspects of tea...

An SOS-Based Blind Channel Shortening Algorithm

Abstract: A new SOS-expressed blind channel shortening algorithm is proposed. It is based on a necessary and sufficient condition that guarantees detection of all possible shortening equalizers before the best one is selected. The unique existing SOS-based blind channel shortening algorithm meets the same objective but has a much higher complexity.

Towards multi-mode terminals

Abstract: The increasing demand for wireless based services continues to grow with a multiplicity of standards developing. This is driving a need to develop integrated mobile terminals which have multi-mode capabilities, i.e., multiple communication systems which can coexist. The attention of this paper is focused on the coexistence of multiple communication systems via a simple hardware based structure with the algorithms and architectures developed within the framework of multi-mode terminals. The term multi-mode in this paper is limited to a set of standards and to a receiver that is expected to handle different systems with a low hardware complexity. Dedicated hardware is shared and reused by different systems. Existing specifications DAB, DVB-T, HIPERLAN-2 and UMTS are considered as examples in this paper, although the methodology could be applied to other systems. The systems considered can be classified into two categories: multi-carrier systems and single-carrier systems. This paper considers multi-mode terminals from both the algorithm and the architecture viewpoint, reducing receiver complexity by taking advantage of the commonalities among different specifications and receiver requirements. As an example, a joint channel estimation, chip-level frequency domain equalization and parallel interference cancellation structure for WCDMA is presented

The use of the fractional Fourier transform with coded excitation in ultrasound imaging

Abstract: Medical ultrasound systems are limited by a tradeoff between axial resolution and the maximum imaging depth which may be achieved. The technique of coded excitation has been used extensively in the field of RADAR and SONAR for some time, but has only relatively recently been exploited in the area of medical ultrasound. This technique is attractive because allows the relationship between the pulse length and the maximum achievable spatial resolution to be changed. The work presented here explores the possibility of using the fractional Fourier transform as an effective means for the processing of signals received after the transmission of linear frequency modulated chirps. Results are presented which demonstrate that this technique is able to offer spatial resolutions similar to those obtained with a single cycle duration signal.

Timing Recovery With Frequency Offset and Random Walk: Cramer–Rao Bound and a Phase-Locked Loop Postprocessor

Abstract: We consider the problem of timing recovery for bandlimited, baud-rate sampled systems with intersymbol interference and a timing offset that can be modeled as a combination of a frequency offset and a random walk. We first derive the Crameacuter-Rao bound (CRB), which is a lower bound on the estimation error variance for any timing estimator. Conventional timing recovery is based on a phase-locked loop (PLL). We compare the conventional timing-recovery method with the CRB for realistic timing parameters for the magnetic recording channel, and observe a 7 dB signal-to-noise ratio gap between the two. Next, we propose a PLL postprocessor based on the maximum a posteriori estimation principle that performs to within 1.5 dB of the CRB. This postprocessor performs time-invariant filtering and time-varying scaling of the PLL timing estimates. The refined timing estimates from the postprocessor are then used to get refined samples by interpolating the samples taken at the PLL's timing estimates. Finally, we present suboptimal implementations that allow a performance-complexity tradeoff

GEN04-2: M-ary, Binary, and Space-Volume Multiplexing Trade-offs for Holographic Channels

Abstract: In this paper, we consider the tradeoffs of binary and M-ary signaling in page-oriented holographic storage systems that multiplex pages using two methods: conventional angle multiplexing throughout the volume and localized recording. We study the mutual information transfer, which is increasingly easy to achieve in practice, between the recorded and recovered data and use it to assess the trade-offs in these systems. We use the transmission model developed by Heanue, Bashaw, and Hesselink [7] for deriving the mutual information bound on capacity and examine the interplay between the storage density and the number of recorded pages within the medium. This result is useful for deciding the number of recorded pages and the desired level of a multi-level modulation code for maximizing the storage density in a volume holographic memory. We analyze our results for localized and angle multiplexed recording and compare the performance in these two cases.

Stationarity Analysis of Ambient Noise in the Baltic Sea

Abstract: Most signal processing techniques are only valid if the assumption of stationarity is true. This is the basis for making reliable and consistent estimates. Stochastic processes can be categorised by their stationarity properties ranging from stationary to non-stationary processes. The degree of stationary has implications on a number of factors in signal processing, but mainly on the level of reliability of any estimate. Estimates from highly non-stationary data can at times be so bad that the variance of the estimate is by far greater than the estimate itself. In this paper, the degree of stationarity is addressed from a stationarity length point of view and sonar data is tested using the Kolmogorov-Smirnov two sample test.

Estimating Errors in Transmission Systems Due to Impulse Noise

Abstract: Impulse noise is a major limiting factor to the performance of digital subscriber lines, powerline communication systems, and digital TV. Research has shown that the impulse noise in all those transmission media has very similar statistical properties. Using noise distribution parameters for the specific case of telephone lines, this paper suggests a Bernoulli–Weibull model of impulse noise in the local loop at symbol level. This model is then applied to develop closed-form expressions for the error probability of PAM and single carrier QAM. A novel extension of the distribution of the impulse noise amplitudes to two dimensions is introduced to enable the analysis of two-dimensional modulations, such as QAM. It is shown that earlier noise models, which assume Gaussian distributed impulse amplitudes or Rayleigh distributed powers, produce overly optimistic results for the errors owing to impulse noise in comparison with the Bernoulli–Weibull model presented here. The error performance of multicarrier QAM (DMT) is also evaluated based on the Bernoulli–Weibull model, however this is done numerically owing to the lack of an analytical solution. It is shown that multicarrier QAM performs better than single carrier systems but only for low impulse power and low impulse probability. The analytical framework presented here is also directly applicable to powerline transmission and DVB-T systems as they have very similar impulse noise statistics to those in telephone lines.

Capacity Enhancement Using Ad Hoc Pico-Cells and TDD Underlay

Abstract: This paper introduces a new technique for efficiently incorporating multihop communications in a wideband code division multiple access (WCDMA) system with a clustered user distribution. For each cluster of users a mobile station (MS) is selected as a gateway to act as a relay between the other MSs and the base station (BS). The under-used resources from the FDD (frequency division duplex) uplink band are utilized for communication within the cluster (TDD underlay). This model is simulated for a number of scenarios and scheduling algorithms. It is demonstrated that the proposed enhancements lead to an improvement in the spectral efficiency of the system of up to 50%.

MIMO Cooperative Diversity Strategies for Frequency Selective Fading Relay Channels

Abstract: This paper presents a family of cooperative diversity strategies for the fading relay channel in an initially frequency flat fading environment. The relay channel used in this paper operates in what is termed as MIMO cooperative diversity mode, where the source transmits to both relay and destination terminals in the first instance. Both the source and relay then transmit to the destination in the second instance. Initially the current cooperative diversity frameworks are extended to consider system constraints to make a direct and fair comparison with the single-hop case. In-particular a power constraint is put on the system and the optimal transmit power levels are presented. The framework is then extended to consider the frequency selective channel by consider an Orthogonal Frequency Division Multiplexing (OFDM) framework. The amount of collision in frequency can be varied and then analysed. This paper shows that full collision is the preferred transmission scheme.

Bit Stuff Encoding for (0, G/I) Constraints

Abstract: (0,G/I) constraints arise in magnetic recording systems that use partial-response equalization with maximum-likelihood sequence detection (PRML). In this paper, we present simple variable-rate and fixed-rate encoding algorithms for (0,G/I) constraints that come quite close to the constraint capacity. Both algorithms are based on the concept of bit stuffing. We first describe the variable-rate encoding algorithm, and discuss rate computations based on a Markov chain model. The average encoding rates for 1 les G les 15 and 14 les I les 10 are tabulated. It is seen that the variable-rate bit stuff algorithm generates greater than 99% efficiency (0,G/I) codes for a wide range of the values of G and I. Then we present a fixed-rate version of the variable-rate stuff algorithm, and tabulate required parameters for the design of fixed-rate (0,G/I) codes with rate close to 100/101 and 200/201

Capacity Lower Bounds for Two-Dimensional M-ary (0, k) and (d, ∞) Runlength-limited Channels

Abstract: We present lower bounds on the two-dimensional capacity for two sets of symmetric and asymmetric M-ary runlength-limited constraints. The bounds extend and generalize our previous work on binary constraints. We also give sequential coding algorithms achieving the derived capacity lower bounds.

Conditioning Lofargrams Using Empirical Mode Decomposition

Abstract: Recorded sonar data is processed in many different ways to extract target information from the source signals. Trying to separate different sources of sound, or identifying vessels by examining the emitted tonals, is often done in the time-frequency domain, e.g. using the lofargram. Narrowband components appear as long-time duration lines and transients as broadband short-time duration pulses. The transients may be generated by the same source as the tonal lines or by other sources in the vicinity, or they can be a part of the additional ambient noise. If transients and narrowband components are mixed in the estimation window, distortion and masking of the lines may occur especially in low SNR regimes. A method for improving the visibility of relevant spectral lines in a lofargram is applied. Instead of using filtering or outlier rejection methods to condition the data, the signal is decomposed by using the method of empirical decomposition.

On the performance enhancement of the Empirical Mode Decomposition

Abstract: Empirical mode decomposition (EMD) has lately received much attention due to the many interesting features exhibits However it lacks a strong theoretical basis which would allow a performance analysis and, hence, the enhancement and optimization of the method in a systematic way In this paper, the investigation of EMD is realized by means of a genetic algorithm (GA) based optimization The above study results in novel directions for both the performance enhancement and also the theoretical investigation of the method

Route selection in a mobile ad-hoc network

Abstract: A method of assessing a communication route comprising a plurality of links between nodes in a mobile ad-hoc network comprises calculating the two-hop residual bandwidth of each node I of the route as B I ( t ) = B − ∑ J ∈ N ( I ) B ( J ) φ where B is the raw channel bandwidth, the summation is the overall consumed bandwidth from node I 's two-hop neighborhood nodes J ∈ N(I), and ϕ is a factor to account for protocol overhead, which may include handshaking, packet collision, re-transmission and/ or back-off scheme traffic. An estimated transmission time for each of a plurality of links between said nodes may be calculated taking said two-hop residual bandwidth into account. For each possible route, a route efficiency function is determined at least by summing the estimated transmission times for all the links in the route, and the route in which the value of the route efficiency function is smallest is selected.

Distributed Channel-Adaptive Fair Allocation for IEEE 802.11e WLAN

Abstract: Distributed channel-adaptive fair allocation (DCAFA) is proposed to extend the IEEE 802.11e enhanced distributed coordination function (EDCF), by halving the contention window (CW) after zeta consecutive successful transmissions to reduce the collision probability when channel is busy. The scheme computes an adaptive threshold function for each priority queue by taking into account the channel load. Simulation results show that DCAFA outperforms EDCF in-terms of global throughput, throughput of traffic class, frame discard probability and average delay in medium and high load cases. They also show that the proposed analytical model is accurate and achieves a high degree of fairness among applications of same priority level