Richard F. Ormondroyd

Channel estimation for layered space-time systems

Space-time techniques for multiple-input multiple-output (MIMO) systems potentially provide vast increases in capacity. In order to achieve the quoted capacity gains the MIMO channel impulse response (CIR) must be known or estimated. Thus far, existing MIMO channel estimation techniques have been limited to the narrowband case or cater specifically for coded space-time systems. In this paper, we present a novel training-based MIMO channel estimation scheme for an uncoded layered space-time system that operates in the wideband frequency-selective fading environment. The method uses a pilot matrix consisting of pilot symbols derived from the Paley-Hadamard matrix in order to jointly estimate the individual CIR of the MIMO channel. The orthogonal property of the pilot matrix is utilized to resolve both intersymbol interference and intercarrier interference of the multiple transmit and received signals. The Paley Toeplitz structure is also exploited in order to minimise the length of the pilot sequence for a given length of CIR and thus maximise the effective data throughput. Results are presented which demonstrate the accuracy of the proposed channel estimation scheme and its performance in a layered space-time system.

Comparison of Hough Transform and Particle Filter Methods of Emitter Geolocation using Fusion of TDOA Data

This paper compares the performance of RF emitter geolocation algorithms based on the Hough transform and the particle filter. Three Hough transform methods are considered: (a) the generalized Hough transform, (b) the randomized Hough transform and (c) the hybrid Hough transform. In each case, the emitter is assumed to provide a signal from which time difference of arrival measurements can be made by pairs of mobile receiving platforms, such as fixed-wing UAVs or fast jets as well as rotorcraft. Typical emitters include cellphones and other types of communication equipment. The paper shows that the Hough transform outperforms the particle filter both in terms of the RMS positional error and the computational processing requirements.

Simultaneous detection and parameter estimation of multiple linear chirps

The paper describes a new method for the simultaneous detection and parametric estimation of multiple chirped waveforms using a method based on evolutionary algorithms. Unlike traditional time-frequency analyzers, which provide a distribution of the signal spectrum over a period of time, but do not inherently provide chirp parameters, this new method detects and provides as an output the start and stop frequencies of each chirp, its starting phase and amplitude. The new method is capable of detecting and characterizing multiple chirps which may be overlapping (in time and frequency) and in the presence of significant noise.

Performance of a serial-search synchronizer for fiber-based optical CDMA systems in the presence of multiuser interference

This paper examines the performance of a serial-search synchronization system in the presence of multiple access interference and receiver noise for a non-coherent fiber- based optical CDMA system using optically orthogonal codes. The synchronization performance of two different optical CDMA system, an on-off keyed system and an M-ary pulse- position modulation system with M equals 2, are compared. The effects of the dwell-time, the total number of users, the code weight, decision threshold and optical hard-limiters on the mean acquisition time of the synchronizer are examined. It is shown that an optimum dwell-time exist which minimizes the mean acquisition time.

Fusion of Sensor Data for Source Localization using the Hough Transform

This paper describes a novel source localization algorithm based on the Hough transform that allows different types of sensor data, such as angle of arrival and time difference of arrival data to be fused together by means of a transformation into a consistent parameterized space. A particular advantage of this method is that terrain data can also be fused with the various types of sensor data to aid accurate source localization

Passive emitter geolocation using agent-based data fusion of AOA, TDOA and FDOA measurements

This paper considers the use of the Hough transform image processing method applied to the problem of agent-based multi-platform, multi-sensor emitter geolocation. In this paper, improved geolocation is obtained through the fusion of three different types of measurement: angle of arrival, time difference of arrival and frequency difference of arrival. One of the main aims of this paper is to introduce a novel method of obtaining the weights for optimal combining of the different types of measurement during fusion. Comparative results of the new method obtained by simulation are presented.

An improved digital communication system for doubly-spread underwater acoustic channels using evolutionary algorithms

This paper presents an improved system for high data rate digital acoustic communication over a shallow underwater channel that is doubly spread. The method uses cancellation of interfering multipath signals rather than delay equalisation. In this improved system, an Evolutionary Algorithm is used to obtain an accurate estimate of the Doppler spread. This novel implementation of a Doppler estimator significantly improves the accuracy of the channel estimator thus enabling more effective interference cancellation. BER performance results of the improved system in a typical underwater scenario are presented.

A robust digital communication system for doubly-spread underwater acoustic channels

The performance of underwater acoustic communication systems depends on the timeliness and accuracy of the estimate of the time-varying channel characteristics and the use of an effective algorithm to compensate for the distortion on the received signal caused by the channel. In a previous paper, the authors proposed estimating the characteristics of the doubly-spread underwater channel using a pilot tone in conjunction with a broadband PN pilot sequence and the channel estimate was optimised using an evolutionary algorithm. However, because of frequency selective fading due to multipath propagation, the pilot tone can be severely attenuated, causing unreliable channel estimates. To overcome this, diversity techniques are used here, wherein additional pilot tones are suitably placed to mitigate the frequency selective fading. As a result, both the channel estimates and the overall system performance are more reliable even for the more severe channel being considered here.

Channel estimation for layered space-time systems in time-varying frequency selective wireless channels

A novel training-based channel estimation scheme is presented for an uncoded layered space-time system that operates in a wideband frequency selective fading environment of a time-varying multiple-input multiple-output (MIMO) channel. The method uses a pilot matrix consisting of pilot symbols derived from the Paley-Hadamard matrix to estimate the MIMO channel impulse response. The orthogonality of the pilot matrix resolves both the intersymbol interference and the cochannel interference of the wideband MIMO channel. The Toeplitz-like structure of the Paley-Hadamard matrix is exploited to minimise the length of the pilot sequence, reducing pilot symbol overhead. A decision feedback algorithm is used to track the time-varying MIMO channel. Results are presented which demonstrate the performance of the proposed MIMO channel estimator in a layered space-time system for different mobile velocities and system configurations.

Comparison of Hough Transform and particle filter methods of passive emitter geolocation using fusion of TDOA and AOA data

This paper compares the performance of passive RF emitter geolocation algorithms based on the Hough Transform and the particle filter. Three Hough Transform variants are considered: (a) the generalized Hough Transform, (b) the Randomized Hough Transform and (c) the Hybrid Hough Transform. In each case, the emitter is assumed to provide a signal from which angle of arrival measurements and time difference of arrival measurements can be made by pairs of mobile receiving platforms, such as fixed-wing UAVs or fast jets, as well as rotorcraft. Typical emitters include cellphones and other types of communication equipment. The paper demonstrates that the Hough Transform and the particle filter provide similar performance in terms of robustness of the RMS positional error and the computational time.