Richard C. North

Mitigating error propagation effects in a decision feedback equalizer

We present an approximate analysis approach to the computation of the probability of error and mean burst error length for a decision feedback equalizer (DFE) that takes into account feedback of decision errors. The method uses a reduced-state Markov model of the feedback process and is applicable to linear modulation formats. We use this technique to analyze a DFE design that mitigates the effects of feedback error by incorporating a soft decision device into the feedback path and a norm constraint on the feedback filter weights. We apply the DFE design and analysis approach to a dispersive multipath propagation environment.

The performance of adaptive equalization for digital communication systems corrupted by interference

This paper analyzes the effects of interference on the steady-state performance of several popular adaptive equalization algorithms. It is shown that adaptive equalizers based on the linear equalizer structure have a built-in capability to reject narrowband interference, however the performance deteriorates as the bandwidth of the interference increases. The existence of a time-varying misadjustment component in the adaptive equalizer weight vector is shown to affect the interference cancellation properties. In addition, simultaneous multipath propagation and interference is investigated. These errors on the performance of the adaptive linear equalizer are especially important to applications where intentional or unintentional interferers may be encountered.<<ETX>>

A floating-point arithmetic error analysis of direct and indirect coefficient updating techniques for adaptive lattice filters

The ways in which finite precision arithmetic effects can deleteriously manifest themselves in both the stochastic gradient and the recursive least squares adaptive lattice filters are discussed. closed form expressions are derived for the steady-state variance of the accumulated arithmetic error in a single adaptive lattice coefficient using a floating-point stochastic arithmetic error analysis. The analytical results show that the performance of adaptive lattice filters using a direct updating computational form is less sensitive to finite precision effects than that of adaptive lattice filters using an indirect updating computational form. In addition, a method for reducing the self-generated noise is presented. Experimental results obtained on a 32-b floating-point hardware implementation of the adaptive lattice filters and with computer simulations are included to verify the analytical results describing the effects of finite precision on adaptive lattice filters. >

b-bit serial/parallel multipliers

A generalized β-bit least-significant-digit (LSD) first, serial/parallel multiplier architecture is presented with 1≤β≤n wheren is the operand size. The multiplier processes both the serial input operand and the double precision product β-bits per clock cycle in an LSD first, synchronous fashion. The complete twos complement double precision product requires 2n/β clock cycles. This generalized architecture creates a continuum of multipliers between traditional bit-serial/parallel multipliers (β=1) and fully-parallel multipliers (β=n). β-bit serial/parallel multipliers allow anoptimized integrated circuit arithmetic to be designed based on a particular applications area, power, throughput, latency, and numerical precision constraints.

Channel estimate-based performance prediction for coherent linear modulation on slowly fading channels

This paper describes a framework for predicting the error rate performance of linearly modulated coherent systems operating over frequency selective, slowly fading channels, when the statistics of the bandlimited two-sided discrete FIR model for the channel are available from a channel estimator. This work supports an upcoming experiment in which channel estimates obtained with one modulation scheme will be used to predict the performance of higher order modulation schemes. The focus of this paper is the mathematical framework for the theoretical performance prediction. Linear memoryless modulation is assumed, providing a a very general signal model that includes M-PSK and M-QAM. The channel model is slowly fading, with correlated complex Gaussian taps, incorporating both the flat and frequency selective cases. Expressions for the error probability are presented, and the cases for which closed form or acceptable numerical solutions exist are delineated. A new recursive method for solving the Rician-fading main path case is presented. The high-data-rate maritime line-of-sight channel is used to demonstrate the use fullness of the method.

Probability of error evaluation for multichannel reception of coherent MPSK over Ricean fading channels

This paper presents a recursive method for evaluating the error rate performance of multichannel reception of coherent MPSK systems operating over slowly Ricean fading channels. Each of the multiple channels is assumed to be a bandlimited two-sided discrete path model with complex Gaussian taps. The main path is assumed to be non-zero mean, corresponding to Ricean fading. Maximal ratio combining in the receiver is assumed, and an expression for the received phase density function is developed. A recursive method for solving the resulting error probability expression is then presented. This method is similar to those used for recursive computation of the Marcum Q function, and is both efficient and accurate. The method can be applied for both the flat and frequency selective Ricean fading cases. Examples based on a ship to ship high-data-rate line-of-sight channel model are provided to demonstrate the method.

The Design of a Real-Time Adaptive Filter Development System

Abstract : This paper describes a hardware test platform designed to implement adaptive lattice filters in real-time. To achieve real-time processing speeds, algorithm complexity was accommodated by custom designing the computation engines with respect to the lattice data flow. Execution speeds of the computation engines were dramatically increased by a memory architecture that supports efficient addressing and by providing a floating-point ALU with numerous data paths and efficient implementation of division. Performance is further enhanced by pipelining multiple computation engines. In addition, the architecture is flexible enough to support other filter structures and to allow observation of filter variables as they adapt. With this system, various Adaptive Filter algorithms are being tested in real-time implementations of Adaptive Line Enhancers (ALEs) and Adaptive Noise Cancelers (ANCs) in order to characterize their performance and behavior, especially long term stability and the ability to track non-stationary signals.

Joint Tactical Radio System - empowering the warfighter for joint vision 2020

In this paper we describe the operational benefits of JTRS and the critical contribution this program represents in the Department of Defensepsilas network centric vision. The first increment of JTRS provides radio systems and critical networking capabilities to warfighters representing the tactical edge. This capability is enabled through servicepsilas platform and system-of-system integration activities. Future JTRS increments plan to add additional critical operational capabilities, to include fielding common data and voice waveforms across all operational domains, enhancing interoperability with the United Kingdom and improving spectrum management integration with electronic warfare systems. We will quantify the capability improvements JTRS brings to the warfighter over current systems through an analysis of the Joint Close Air Support (JCAS) mission thread utilizing JP 3-09.3 Close Air Support (CAS) publication [1] and the TWJN CONOPS [2]. This analysis will support the notion that technology introduction needs appropriate Tactics, Techniques and Procedure (TPP) changes to maximize the capability improvements.

The performance of multichannel adaptive equalization for LOS digital communication corrupted by interference

Multichannel adaptive equalization combines the concepts of spatial diversity and temporal equalization to improve receiver performance in a line-of-sight communication environment. We derive the optimal Wiener filter for conditions common to this environment. We specifically analyze the effect of a CW interference on this solution and demonstrate the dependence of receiver performance on the multichannel adaptive equalizer (MAEQ) spatial-temporal beam pattern.

Arithmetic effects in adaptive lattice filters

The performance of adaptive lattice filters in finite precision real-time hardware is largely unknown because of the complexity of implementing lattice algorithms. The authors show how arithmetic effects can deleteriously manifest themselves in both the stochastic gradient and the least squares adaptive lattice filters. Computer simulations and experimental results are used to verify an analytical analysis describing implementation effects of adaptive lattice filters. It is found that the performance of adaptive lattice filters can be substantially improved by manipulating the time recursive coefficients using direct updating techniques. Results are compared to those obtained from LMS (least mean square) transversal adaptive filters.<<ETX>>