Radar systems in the United Kingdom (UK) prior to World War 2 (WW2) were predominantly land-based equipments that typically operated at frequencies below 50 MHz. The first airborne radar systems operated at Very High Frequencies (VHF, about 200 MHz) and it was recognised that operation at even higher frequencies would be required to achieve the required resolution and to fit into the airframe. However, it was not possible at that time to achieve the required transmitter power. This paper describes the technical advances during WW2 in the design of the cavity magnetron, which first enabled the generation of kilowatts of microwave power, making particular reference to the work of Randall, Boot and Sayers, who were recognised in the June 2024 IEEE historical plaque erected at the University of Birmingham, UK. This paper refers to and references the many prior magnetron innovations and also includes provides a discussion on the very significant subsequent contributions by Megaw and Gutton in developing a practical device, suitable for mass production, which ultimately provided the required high-power output. These and other advances—in durability, compactness, efficiency, stability, and ever more power—unlocked the development of airborne radar, such as ASV (Air to Surface Vessel) systems that were fundamental to winning the Battle of the Atlantic; AI (Airborne Intercept) radars for night fighters; and air to ground mapping bombing aids.

The first working telegraphs were built by several individuals in the 1830s and they began to be adopted into practical use in the 1840s prior to the laying of the first undersea telegraphic cable across the English Channel, before attempting to cross the Atlantic Ocean. A string of subsequent failures on undersea cables led to an acceptance of a need to measure, accurately, the resistance of both the wire and insulation. Prior to 1860, there was no widely accepted system of electrical units or standards. This article gives an overview of the historical development of the Ohm as a unit. In Section I, we discuss the telegraphic communication. Section II considers electrical resistance, Section III reports on the work of the British Association (BA) Committee, and Sections IV and V discuss the recognition and subsequent developments. This month's history article takes a look at how the British Association Committee on Electrical Standards built the first internationally recognized material resistance standard, the BA unit of Resistance, subsequently called the Ohm.

The month’s regular papers issue covers machine learning at the wireless network edge, soft-informationbased localization techniques, and Antenna-in-Package technology.

Spatial modulation (SM) is a unique single-stream, multiple-input multiple-output (MIMO) transmission technique. One key property of the SM is that a single transmit antenna is activated at any given time, which completely avoids inter-channel interference in a single-user scenario. In the context of multi-user cellular networks, inter-cell interference (ICI) mitigation becomes the main challenge for the SM. Network MIMO is a technique that employs precoding to enable ICI cancellation among neighbouring cells. However, the cell-edge users might still experience a high level of the ICI due to the significant channel attenuation. In this paper, we propose a novel cooperative scheme based on the SM, named cooperative SM (CoSM). The basic concept is to reschedule the transmit antennas of multiple base stations for multiple co-channel users, so as to maximize the antenna diversity gain. Unlike the traditional antenna selection for a single user, the involvement of multiple users might cause conflict due to the selection of the same antenna. An antenna rescheduling scheme (ARS) is thus proposed to address this issue. The performance of the ARS is theoretically analyzed, and closed-form expressions are derived for the probability distribution of the received SNR. Also, a novel three-tier cellular architecture is proposed to accommodate the CoSM within the context of the network MIMO. Results show that the CoSM can improve signal-to-interference-plus-noise ratio by up to 4 dB over the network MIMO. In addition, compared with spatial multiplexing using the same ARS, the CoSM can halve the energy consumption while achieving the same bit error rate.

In this paper, the performance analysis of Receive Space Modulation (RSM) in the shadowing Multiple-Input Multiple-Output (MIMO) broadcast channel is presented. This is undertaken by considering Zero Forcing (ZF) precoding and both small and large scale fading. In particular, a closed form and accurate framework for the evaluation of the Symbol Error Rate (SER) is derived. In addition, the diversity order and the coding gain of the new architecture are also obtained. The derived framework can be directly extended to the conventional spatially multiplexed shadowing MIMO broadcast channel. It is shown that RSM achieves the same diversity order and, in certain scenarios which are well defined, higher coding gain than spatially multiplexing (SMX). Also, the performance difference between RSM and SMX in the shadowing broadcast channel is mathematically quantified. Finally, numerical results that verify the new framework and conclusions are provided.

One of the major purposes for fifth generation (5G) communications waveform design is to relax the synchronization requirements for supporting efficient massive machine type communications (MTCs). Polynomial cancellation coded orthogonal frequency-division multiplexing (PCC-OFDM) and universal filtered multi-carrier (UFMC) are designed to reduce the sidelobes of the OFDM waveform to protect against intercarrier interference (ICI) in the 5G uplink. To the best of our knowledge, there is no analysis of the effect of ICI for the UFMC system with time offset transmissions that many arise in MTC scenarios. Furthermore, there is no study on reducing the computational complexity of the UFMC system. This paper provides closed-form expressions for time offsets interference in such a case for OFDM, PCC-OFDM, and UFMC. This paper also presents theoretical analysis for the signal-to-interference-plus-noise ratio, achievable rate, and bit error ratio performance. The results show that PCC-OFDM significantly protects against ICI at the cost of halving the spectral efficiency. UFMC improves the ICI and intersymbol interference protection performance, especially when the length of time offset is very small, at the cost of significantly increasing the computational complexity. Finally, this paper proposes the overlap and adds UFMC and a variant of UFMC using infinite impulse response prototype filter banks to reduce the processing complexity.

In this paper, for the first time real--world channel measurements are used to analyse the performance of spatial modulation (SM), where a full analysis of the average bit error rate performance (ABER) of SM using measured urban correlated and uncorrelated Rayleigh fading channels is provided. The channel measurements are taken from an outdoor urban multiple input multiple output (MIMO) measurement campaign. Moreover, ABER performance results using simulated Rayleigh fading channels are provided and compared with a derived analytical bound for the ABER of SM, and the ABER results for SM using the measured urban channels. The ABER results using the measured urban channels validate the derived analytical bound and the ABER results using the simulated channels. Finally, the ABER of SM is compared with the performance of spatial multiplexing (SMX) using the measured urban channels for small and large scale MIMO. It is shown that SM offers nearly the same or a slightly better performance than SMX for small scale MIMO. However, SM offers large reduction in ABER for large scale MIMO.

A virtual‐multiple‐input–multiple‐output (MIMO) wireless system using the receiver‐side cooperation with the compress‐and‐forward (CF) protocol, is an alternative to a point‐to‐point MIMO system, when a single receiver is not equipped with multiple antennas. It is evident that the practicality of CF cooperation will be greatly enhanced if an efficient source coding technique can be used at the relay. It is even more desirable that CF cooperation should not be unduly sensitive to carrier frequency offsets (CFOs). This study presents a practical study of these two issues. Firstly, codebook designs of the Voronoi vector quantisation (VQ) and the tree‐structure VQ (TSVQ) to enable CF cooperation at the relay are described. A comparison in terms of the codebook design and encoding complexity is analysed. It is shown that the TSVQ is much simpler to design and operate, and can achieve a favourable performance‐complexity tradeoff. Furthermore, this study demonstrates that CFO can lead to significant performance degradation for the virtual‐MIMO system. To overcome this, it is proposed to maintain clock synchronisation and jointly estimate the CFO between the relay and the destination. This approach is shown to provide a significant performance improvement.

A cooperative virtual multiple-input multiple-output (MIMO) system using two transmit antennas that implements bit-interleaved coded modulation (BICM) transmission and compress-and-forward (CF) relay cooperation among two receiving nodes is presented here. To perform CF cooperation, we propose to use standard source-coding techniques for virtual MIMO detection, based on the analysis of its expected rate bound and the tightness of the bound. Since the relay and the destination are closely spaced, the authors first assume an error-free conference link between them, to focus on investigating the achievable gain from the CF cooperation. Then the system throughput expression and upper bounds on the system error probabilities over block fading channels are derived. The results show that the relay enables the proposed cooperative virtual-MIMO system to achieve almost ideal MIMO performance with low source-coding rates. Furthermore, when we consider a non-ideal cooperation link for practical considerations, a channel-aware adaptive CF scheme is proposed, so that the relay could always adapt its source-coding rate to meet the data rate on the non-ideal link. Owing to the short-range communication and the proposed scheme, the impact of the non-ideal link is too slight to impair the system performance significantly.

In this paper a hybrid one-bit feedback algorithm is proposed to achieve carrier phase alignment at the receiver for distributed transmit beamforming. The proposed iterative algorithm employs two schemes to speed up the convergence process, which exploit negative feedback information in a single time slot (Scheme 1) and in successive time slots (Scheme 2) respectively, whereas previously proposed algorithms in the literature discard this information. We show that the proposed algorithm yields a significant improvement in the convergence speed compared to the original algorithm. Furthermore, we modify the proposed algorithm to be capable of tracking time-varying channels which have variable rates of phase drift. The modified hybrid algorithm has the ability to adjust perturbation sizes adaptively without the knowledge of channel state information and is suited for practical implementations.

In this paper, we investigate the impact of receiver interference cancellation (IC) techniques on the base station (BS) downlink transmission power for a multiple-input multiple-output (MIMO) communication system with inter-cell interference. Besides the power amplifier module whose power consumption is determined by the required transmission power, we also consider the signal processing module when characterizing the total power consumption of the BS. Rather than specifying absolute values, we define the power consumption of the signal processing module as a proportion of the power consumption of the power amplifier module. We investigate the influence of both the signal processing module and receiver IC techniques on the total power consumption of the BS. Results show that besides receiver IC techniques, the power consumed at the signal processing module should not be overlooked when evaluating the BS total power consumption. Particularly, when the power consumption of the signal processing module becomes too dominant, it may contribute more to the increase of the BS total power consumption as compared to the additional power needed by the power amplifier module to combat inter-cell interference. Furthermore, any transmission power savings that are potentially obtained from receive diversity gain and receiver IC techniques may not be justified if the signal processing consumes too much power relative to that of the power amplifier.

In this study, the potential of reducing radio base station operational energy consumption is discussed in terms of deploying sleep modes. By periodically switching off the base station transmission, or using fewer transmit antennas, the energy consumption of base station hardware decreases. By delivering less control signalling overhead, the radio frequency energy consumption can also be reduced. Taking the long-term evolution system as an example, up to 90% radiated energy reduction can be obtained in low traffic conditions by employing time-domain optimisation in each radio frame. The optimum on/off duty cycle is derived, enabling the energy consumption of the base station to scale with traffic load. In the spatial domain, an antenna selection criterion is proposed, indicating the most energy-efficient antenna configuration as a function of users' locations and quality of service requirements. Without time-domain sleep modes, using fewer transmitter antennas could outperform full antenna transmission. However, with time-domain sleep modes, using all available antennas is generally the most energy-efficient choice.

Motivated by the recent concept of Space-Time Shift Keying (STSK), we propose a novel cooperative STSK family, which is capable of achieving a flexible rate-diversity tradeoff, in the context of cooperative space-time transmissions. More specifically, we first propose a Coherent cooperative STSK (CSTSK) scheme, where each Relay Node (RN) activates Decode and-Forward (DF) transmissions, depending on the success or failure of Cyclic Redundancy Checking (CRC). We invoke a bit to-STSK mapping rule, where according to the input bits, one of the Q pre-assigned dispersion vectors is activated to implicitly convey log2Q bits, which are transmitted in combination with the classic log2L-bit modulated symbol. Additionally, we introduce a beneficial dispersion vector design, which enables us to dispense with symbol-level Inter-Relay Synchronization (IRS). Further more, the Destination Node (DN) is capable of jointly detecting the signals received from the source-destination and relay destination links, using a low-complexity single-stream-based Maximum Likelihood (ML) detector, which is an explicit benefit of our Inter-Element Interference (IEI)-free system model. More importantly, as a benefit of its design flexibility, our cooperative CSTSK arrangement enables us to adapt the number of the RNs, the transmission rate as well as the achievable diversity order. Moreover, we also propose a Differentially-encoded cooperative STSK (DSTSK) arrangement, which dispenses with CSI estimation at any of the nodes, while retaining the fundamental benefits of the cooperative CSTSK scheme.

In this paper a novel detection algorithm for spatial modulation (SM) based on sphere decoder (SD) tree search idea is proposed. The aim is to reduce the receiver complexity of the existing optimal decoder while maintaining an optimum performance. The algorithm performs a maximum likelihood (ML) search, only over those points that lie inside a sphere, centered at the received signal, of given radius. It is shown with the aid of analytical derivations, that for a SNR (signal-to-noise ratio) between 2~dB and 18~dB at least 45% and up to 85% reduction in the number of complex operations can be achieved with a close to optimal bit-error-ratio (BER) performance.

Trellis Coded Spatial Modulation (TCSM) is a novel transmission technology for Multiple-Input-Multiple-Output (MIMO) systems, which has been recently proposed to improve the performance of Spatial Modulation (SM) over correlated fading channels. The fundamental principle of TCSM is to use convolutional encoding and Maximum-Likelihood Sequence Estimation (MLSE) decoding to increase the free distance between sequences of spatial constellation points, thus improving, especially over spatially correlated fading channels, the end-to-end system performance. In this paper, we propose tight analytical bounds for performance analysis of TCSM over correlated fading channels. In particular, the contributions of this paper are as follows: i) we propose two asymptotically tight (for high Signal-to-Noise-Ratios, SNRs) upper bounds for the analysis of uncoded SM schemes, which offer a better accuracy than already existing frameworks, ii) we propose a simple Chernoff bound for performance analysis of TCSM, which, although weak, can well capture the diversity order of the system, and iii) we propose an asymptotically tight (for high SNRs) true union bound for the accurate performance prediction of TCSM over correlated fading channels. Analytical frameworks and findings will also be substantiated via Monte Carlo simulations.

In this paper an improved iterative algorithm is proposed for distributed transmit beamforming to achieve carrier phase alignment at the receiver. The transmitters adjust their phase offsets based on one-bit feedback from the receiver in each time slot. The proposed algorithm has an improvement in the convergence speed of phase alignment compared to a previously proposed algorithm in the literature by exploiting one-bit feedback information more efficiently. Simulation results show that the improved algorithm on average has a 20% faster convergence speed. The minimum number of time slots required to achieve specified beamforming gains and the corresponding perturbation steps are obtained by Monte Carlo simulations.

Trellis coded modulation (TCM) is a well known scheme that reduces power requirements without any bandwidth expansion. In TCM, only certain sequences of successive constellation points are allowed (mapping by set partitioning). The novel idea in this paper is to apply the TCM concept to the antenna constellation points of spatial modulation (SM). The aim is to enhance SM performance in correlated channel conditions. SM considers the multiple transmit antennas as additional constellation points and maps a first part of a block of information bits to the transmit antenna indices. Therefore, spatial multiplexing gains are retained and spectral efficiency is boosted. The second part of the block of information bits is mapped to a complex symbol using conventional digital modulation schemes. At any particular time instant, only one antenna is active. The receiver estimates the transmitted symbol and the active antenna index and uses the two estimates to retrieve the original block of data bits. In this paper, TCM partitions the entire set of transmit antennas into sub-sets such that the spacing between antennas within a particular sub-set is maximized. The scheme is called trellis coded spatial modulation (TCSM). Tight analytical performance bounds over correlated fading channels are proposed in this paper. In addition, the performance and complexity of TCSM is compared to the performance of SM, coded V-BLAST (vertical Bell Labs layered space-time) applying near optimum sphere decoder algorithm, and Alamouti scheme combined with TCM. Also, the performance of all schemes with turbo coded modulation is presented. It is shown that under the same spectral efficiency, TCSM exhibits significant performance enhancements in the presence of realistic channel conditions such as Rician fading and spatial correlation (SC). In addition, the complexity of the proposed scheme is shown to be 80% less than the V-BLAST complexity.

This paper reports a number of individual research activities being performed as part of the UK mobile virtual centre of excellence, mobile VCE, an industry-university research partnership conducting precompetitive research for 4G systems.

This paper analyses candidate adaptive algorithms for operating antenna arrays on the downlink of wideband code division multiple access (WCDMA) systems, including diversity, beamforming and hybrid schemes. The algorithms are simulated and compared with each other under different channel environments and for various numbers of transmit antennas. Furthermore, a new blind downlink technique is proposed, which optimises performance in all channel environments according to a flexible criterion and yields the best performance among the presented blind techniques.

The combination of Walsh coding with a layered space-time architecture is investigated. This provides a system with flexible coding rates and low complexity linear decoding. The codes allow exploitation of the diversity of the multiple antenna channel while allowing code rates up to 1, while still providing a performance improvement over an uncoded system. Simulations provide comparison with repetition coded and uncoded systems.

A novel approach to selectively enhance important facial features in very low bit-rate head and shoulders video sequences is described. The selected facial features (eyes, nose and mouth) are tracked from frame to frame and their positions are used to rank image blocks according to their perceptual importance. This ranked list of blocks is used to generate an independent bit stream which can be used to enhance regions of interest in the reconstructed image, depending on the available transmission bit rate. The technique is demonstrated as an add-on to an available H.263 encoder and decoder. Results are presented which show the effectiveness of the method for common image sequences.

A novel approach to selectively enhancing important facial features in head and shoulders video sequences is described. The selected facial features (eyes, nose and mouth) are tracked from frame to frame and their positions are used to rank image blocks according to their perceptual importance. This ranked list of blocks is used to generate an independent bit stream which can be used to enhance regions of interest in the reconstructed image, depending on the available transmission bit rate. The technique is demonstrated as an add-on to an available JPEG-2000 encoder and decoder. Results are presented which show the effectiveness of the method for common image sequences. The applicability of this technique to inter-frame encoded motion compensated video is noted.

The UTRA TDD signalling mode is considered, which uses a combination of the multiple access schemes FDMA, TDMA and CDMA, which is termed TD-CDMA. In CDMA cellular mobile systems both intersymbol interference (ISI) and multiple access interference (MAI) cause degradations to the system performance. In TD-CDMA a joint detection CDMA (JD-CDMA) processor performs unbiased signal estimation to eliminate both ISI and MAI within the reference cell. This paper reports an extension of the previously reported receiver processor to achieve intercell interference cancellation to reduce the interference from the adjacent cells.

A Walsh coded OFDM system is described which could provide an alternative to convolutional coding in packet based wireless LAN systems. This allows lower complexity decoding and lower peak-to-average power ratios. This system is compared with a hard decision decoded convolutional receiver, based on the OFDM specifications for the IEEE 802.11 and ETSI HIPERLAN/2 physical layer standards. In multipath environments, the high diversity Walsh coded OFDM system shows large improvements over uncoded systems and similar performance to the more computationally complex convolutional receivers.

A CDMA unslotted ALOHA system using MMSE multi-user detection is proposed. In the CDMA unslotted ALOHA system, a user station can transmit a packet asynchronously, and so the number of simultaneously transmitted packets fluctuates moment by moment. This fluctuation affects the performance of the MMSE multi-user detection. At first, we employ the Wiener filter detector assuming perfect information as an upper bound of the performance of the proposed system. Then, we apply an adaptive filter to CDMA unslotted ALOHA to compensate for the birth/death of a packet.

Detection algorithms for single user wireless communication using multiple antennas at both the transmitter and receiver in a Rayleigh (flat) fading environment are compared. The system includes N transmitting antennas, M receiving antennas (N/spl les/M) and repetition coding at the transmitter (delay diversity). The linear decorrelating (LD) and minimum mean squared error (MMSE) detectors are compared with their D-BLAST and V-BLAST versions using bit error ratio versus signal-to-noise ratio simulation. For BPSK, the MMSE detector and its BLAST versions perform best and yield almost indistinguishable BER curves. The LD detector performs worst. For fixed N, as M increases, all the BER curves converge. The effect of error propagation in the BLAST schemes is shown to be non-negligible.

We consider the reverse link of a cellular direct sequence CDMA system with the aim of increasing the system's capacity. The capacity of a conventional (matched filter) receiver can be increased by employing sectorized antenna arrays or multiuser detection techniques. Our results confirm that the potentially complex approach of beamforming followed by multiuser detection further increases capacity. To reduce complexity, bit detection techniques based on partitioning the users into spatial equivalence classes by beamforming and then employing standard multiuser detection techniques within each class are investigated. Subtractive interference cancellation yields the lowest bit error ratios and is the least computationally complex method of multiuser detection under consideration.

This paper discusses the use of coherent demodulation for antenna array receivers employing direct sequence spread spectrum techniques and M-ary orthogonal modulation. Three different approaches are discussed. The first is a conventional receiver using training sequences and decision feedback for channel estimation. The other two techniques employ decisions from a simple noncoherent combining (O) receiver to circumvent the need for training sequences. The bit error ratio (BER) performance of coherent M-ary orthogonal modulation is derived. Some qualitative analysis is also presented for the algorithms, and simulation results are used to compare their performance in different scenarios.

Model-based video coding requires the application of both image processing and machine vision techniques for proper fitting of the semantic model and its subsequent tracking throughout the rest of the sequence of a certain type (e.g. 'head-and-shoulders' or 'head-only'). A method of automatic semantic wire-frame fitting and tracking based on principal component analysis using an independent reference data-base of facial images is presented. The method has been tested on widely used 'head-and-shoulders' video sequences with very good results. It was possible to accurately retrieve the position of the desired facial features in all cases. The position of the facial features in initial frames was subsequently used in automatic tracking. Experimental results are also presented.

Data rate management of compressed digital video has been treated mainly from the teletraffic control point of view, i.e. by modelling traffic or controlling congestion via network protocols. Relatively less attention has been focused on video rate management in the source coding side. We consider that it is more efficient and less costly to control the video rate at the video source than handling network congestion due to an extremely large quantity of incoming variable bit rate (VBR) video traffic. Thus this paper investigates effective rate control algorithms for video encoders. Considering the non-stationary nature of the video rate originated from scene variations (i.e. the wide band nature of digital video), we adopted and compared the performance of two nonlinear approaches; radial basis function (RBF) estimation using a neural network-based approach and fuzzy logic control as a nonlinear feedback control.

This paper addresses the problem of wire-frame tracking by accurate analysis of the motion and the shape of the facial features in head-and-shoulders scenes. Accurate wire-frame tracking is of paramount importance for correct reconstruction of the encoded image, especially in the areas occupied by the lips and the eyes. An entirely new algorithm for tracking the motion of a semantic wire-frame (Candide) by analysis of the principal components of sub-images containing important facial features of the speaker's face is proposed. This algorithm is suitable for tracking both global motion (motion of the speaker's head) and local motion (motion of the facial features). The algorithm was tested on numerous head-and-shoulders sequences with excellent results.

A nonlinear predictive approach has been employed in MPEG (Moving Picture Experts Group) video transmission in order to improve the rate control performance of the video encoder. A nonlinear prediction and quantisation technique has been applied to the video rate control which employs a transmission buffer for constant bit rate video transmission. A radial basis function (RBF) network has been adopted as a video rate estimator to predict the rate value of a picture in advance of encoding. The quantiser control surfaces based on nonlinear equations, which map both estimated and current buffer occupancies to a suitable quantisation step size, have also been used to achieve quicker responses to dramatic video rate variation. This scheme aims to adequately accommodate non-stationary video in the limited capacity of the buffer. Performance has been evaluated in comparison to the MPEG2 Test Model 5 (TM5) in terms of the buffer occupancy and picture quality.

This paper considers the performance of four channel identification techniques for code division multiple access (CDMA) antenna array receivers. These techniques are based on the assumption that the interference is spatially white: they provide a spatial "matched filter" solution. Perturbation formulae are presented for estimating the attainable signal to interference and noise ratios (SINR) for these techniques. Some simulation results are also presented to compare the convergence performance of these methods.

This paper presents a comparative study of accurate automatic semantic wire-frame fitting methods for extremely low bit-rate model-based moving image communication systems. Efforts are concentrated on the accurate fitting of the semantic wire-frame in areas occupied by important facial features (the lips, the eyes and the nose). The automatic fit in the areas occupied by those features is crucial for the correct reconstruction of the transmitted scene. The algorithms are based on the analysis of a facial code-book and are designed to provide the final and most accurate fit of the Candide wire-frame model to the facial features of the speaker in a typical videophone scene (head-and-shoulders). The results obtained from tests carried out on the images from the MIT facial data-base are presented and compared.

A method of automatic wire-frame fitting for semantic-based moving image coding is proposed. The algorithm describes a technique for detailed fitting of the wire-frame in the areas occupied by important facial features (lips, eyes, eyebrows, nose). The algorithm utilises a preprocessed data-base of facial images. Only the monochrome edge maps are used in the automatic wire-frame fitting algorithm. This reduces the space required for storage of the reference data-base. The images from the data-base are pre-processed and manually fitted with the wire-frame model as part of the data-base preparation. The processing of an unknown image is therefore accomplished in a fast and efficient manner. A new measure of the accuracy of the automatic wire-frame fitting is proposed. Encouraging results, as presented in this paper, were obtained.

The paper investigates adaptive equalization of time-dispersive mobile radio fading channels and develops a robust high performance Bayesian decision feedback equalizer (DFE). The characteristics and implementation aspects of this Bayesian DFE are analyzed, and its performance is compared with those of the conventional symbol or fractional spaced DFE and the maximum likelihood sequence estimator (MLSE). In terms of computational complexity, the adaptive Bayesian DFE is slightly more complex than the conventional DFE but is much simpler than the adaptive MLSE. In terms of error rate in symbol detection, the adaptive Bayesian DFE outperforms the conventional DFE dramatically. Moreover, for severely fading multipath channels, the adaptive MLSE exhibits significant degradation from the theoretical optimal performance and becomes inferior to the adaptive Bayesian DFE.>

A multi-stage blind clustering algorithm is proposed for equalisation of multi-level quadrature amplitude modulation (M-QAM) channels. A hierarchical decomposition divides the task of equalising a high-order QAM channel into much simpler sub-tasks. Each sub-task can be accomplished fast and reliably using a blind clustering algorithm derived originally for 4-QAM signals. The constant modulus algorithm (CMA) is used as a benchmark to assess this multi-stage blind equaliser. It is demonstrated that the new blind algorithm achieves much faster convergence and is very robust when input symbols are not sufficiently white. This multi-stage clustering equaliser only requires slightly more computations than the CMA and, like the latter, its computational complexity does not increase as the levels of digital symbols increase.>

The operation of a decision-directed RAKE receiver is described which has the advantage of not requiring any overhead for training bits. The performance is illustrated using bit error rate (BER) graphs obtained from Monte Carlo simulations. The receiver is simulated using a fast fading (100 Hz Doppler) mobile channel at a bit rate of 4.8 kbit/s for a 900 MHz carrier. The receiver is not greatly affected by error propagation. However, the lag on the channel impulse response estimate is the major limitation on the system performance and it introduces an irreducible BER. Results are shown for the maximal ratio, equal gain, and differential phase combining schemes.>

The application of a radial basis function network to digital communications channel equalization is examined. It is shown that the radial basis function network has an identical structure to the optimal Bayesian symbol-decision equalizer solution and, therefore, can be employed to implement the Bayesian equalizer. The training of a radial basis function network to realize the Bayesian equalization solution can be achieved efficiently using a simple and robust supervised clustering algorithm. During data transmission a decision-directed version of the clustering algorithm enables the radial basis function network to track a slowly time-varying environment. Moreover, the clustering scheme provides an automatic compensation for nonlinear channel and equipment distortion. Computer simulations are included to illustrate the analytical results.

The radial basis function network offers a viable alternative to the two-layer neural network in many applications of signal processing. A common learning algorithm for radial basis function networks is based on first choosing randomly some data points as radial basis function centers and then using singular-value decomposition to solve for the weights of the network. Such a procedure has several drawbacks, and, in particular, an arbitrary selection of centers is clearly unsatisfactory. The authors propose an alternative learning procedure based on the orthogonal least-squares method. The procedure chooses radial basis function centers one by one in a rational way until an adequate network has been constructed. In the algorithm, each selected center maximizes the increment to the explained variance or energy of the desired output and does not suffer numerical ill-conditioning problems. The orthogonal least-squares learning strategy provides a simple and efficient means for fitting radial basis function networks. This is illustrated using examples taken from two different signal processing applications.

The application of two distinct approaches to the diagnosis of faults in digital communication equipment is examined. The selected artificial-intelligence approaches use either rule-based or machine-learning techniques. Faults up to 8-dB TWT (traveling-wave tube) overdrive, 10% spacing error in the signal constellation, and 5 degrees nonorthogonality in the modulating carriers are introduced on an 11-GHz radio. Each approach shown is capable of diagnosing both the type and magnitude of the introduced faults, subject to certain constraints for each system. Results indicate that the machine learning system is more appropriate than the rule-based system for providing optimal adjustment of the radio, where the underlying mechanisms are too complex to allow simple rules of thumb to be applied. However, the rule-based technique has been shown to be suitable for areas with large nonlinearities. A combination of the two techniques would solve some of the problems caused by the suitability of each method to a specific problem type, the rule-based approach covering the areas with large nonlinearities and the machine learning system the more linear regions. This would help in simplifying the implementation as it would minimize the number of rules required for each different radio type.>

This paper presents a comparison of the effects of finite arithmetic on least mean squares (LMS) and block least mean squares (BLMS) adaptive algorithms. It is demonstrated, using both simulation and analytic results, that the BLMS algorithm consistently achieves improved converged noise performance compared to an LMS algorithm using the same word lengths. In the case dealt with here the improvement is equivalent to an excess 2-3 bits in word length.

A new calibration algorithm to compensate for sensor positioning errors in direction finding (DF) arrays is introduced. Transmissions with known bearings are analysed to determine the true sensor positions, which are subsequently used by a conventional bearing estimation algorithm to determine the angles of arrival of unknown transmissions. The proposed calibration algorithm is based on Schmidt's MUSIC method for bearing estimation. Simulation results illustrate the effects of sensor positioning errors, the improvements obtained using the new algorithm, and its robustness in the presence of other sources of error, such as uncorrelated noise and finite averaging.

This paper presents a new Block Least Mean Squares(BLMS) adaptive filter structure by exploiting the use of an efficient circular convolution algorithm known as the rectangular transform(RT). The BLMS algorithm is presented as an approximation to a recursive block least squares (RBLS) algorithm. The analysis is used to develop the computationally superior overlap save adaptive filter structure even though the structure of the overlap add adaptive filter may be easily worked out in a similar manner. The computational requirements of the proposed filter are investigated and compared with an FFT based filter. The proposed filter is found to be a useful alternative to its FFT counterpart. For completeness, the convergence properties of the filter obtained from simulations are also included.

A new realisation of adaptive filter is reported which employs a cascade of forward and inverse surface acoustic wave (SAW) analogue Fourier transform processors interconnected via a digital interface. The interface multiplies the transformed input by a set of weights stored in RAM and compares the products against a separately supplied desired complex spectrum. The resulting error is used to update the RAM weights via a feedback loop. The use of frequency domain processing in the adaptive filter offers faster convergence than conventional time domain adaptive transversal filters, and the incorporation of SAW chirp transform techniques extends the adaptive filter to MHz's of signal bandwidth.

This paper compares the relative advantages of discrete and integrated circuit transversal and lattice adaptive filter designs. It discusses the trade-offs between the traditional transversal filter and the gradient adaptive lattice (GAL), showing that the reliable rate of convergence of the lattice is offset by a greater complexity and algorithm noise. Two 16-stage hardware implementations are described. One is a TTL GAL equaliser based on a single 12-bit parallel multiplier. The second is a suite of 5 custom NMOS bit-serial arithmetic LSI chips, which together make a lattice prediction-error filter. Both implementations offer 12-bit precisions and bandwidths of over 8 kHz. This shows that the increased complexity of the lattice approach can easily be accommodated in custom VLSI circuit designs.

The application of certain prototype devices, already realized in the complementary surface acoustic wave (SAW) and magnetostatic wave (MSW) technologies, is examined in the context of analogue and digital microwave communications equipments. The specifications of Gaussian response IF bandpass filters and satellite channel multiplexing filters are detailed in the context of SAW designs. Extensions of SAW filter technology to the construction of IF remodulating modems incorporating frequency modulated oscillators and discriminators are examined. Stable SAW oscillators are also reviewed in the context of lightweight, rugged, spacequalified local oscillator drives. The application of MSW technology to the design of a group delay equalizer for millimetric waveguide long-haul digital communications equipments is surveyed. Finally, the paper addresses the design of fixed and variable delay lines realized in both technologies, and SAW code generators, for application to path-length equalization and test{ng of high data rate microwave radio relay systems, respectively.