Masts are a common method of deploying basestation- or broadcast-type antennas for mobile communications. Antennas with a mast-like structure usually have a vertical polarization owing to the currents following the vertical metallic mast structure. Horizontal polarization is also of interest for mast-like antennas but is difficult to realize. This paper presents a design concept for a mast-like antenna structure that can give horizontal-polarization with simple azimuthal beam selection capability. The mast-like structure comprises identical isosceles triangular waveguides arranged in a cylinder. The slot elements are located on the outward-facing wall of each of the triangular waveguides. Different configurations for the slots are chosen based on the apex angle of the triangular waveguide, which in turn depends on the required number of azimuthal beams. Design examples with different angular coverage are demonstrated using simulation. We include an adaptation of the design for a surface mounting form, using half of the mast-like cylindrical form.

The use of extra slots in a slotted waveguide array for improving the impedance bandwidth is investigated. This has not been widely studied previously, probably because the directive pattern is a primary parameter for the waveguide array and extra elements are prone to spoiling the control of the pattern. However, the pattern is not a primary design parameter for most mobile terminals, and here we seek a wide bandwidth for a smaller antenna than the traditional waveguide array, which is suitable for a mobile terminal. The extra slots can be viewed as parasitic elements, analogously to free-space thin wire parasitic, but the designs are not interchangeable with wire antennas. This is because the waveguide - both the internal and external structure - constrains the excitation of the slot elements in a different way to that of the wire antenna analogies. Simple-to-build designs are sought where the slot elements are on only one of the waveguide broad walls. The approach is experimental (simulation) which allows rapid and accurate evaluation of different configurations. We do not optimize a configuration because any optimal design will depend on the specific structure of the mobile terminal supporting the antenna. For the basic stand-alone waveguide, a -6dB impedance bandwidth of about ~30% is demonstrated using four slot elements in a short waveguide.

The slot array antenna is used for pattern-critical applications including satellite communications and radar. In most mobile communications antennas, the pattern detail at the mobile terminal is not critical because of the distributed target of a multipath propagation environment. Motivated by a need for bicycle connectivity, this paper looks to waveguide-excited slot antennas on the bicycle frame. The idea is to have a radio mounted internally and radiating from of multiple slots distributed along the frame. The main drawbacks of waveguide slot arrays is their bandwidth sensitivity to dimensional variations; and in the case of a bicycle frame, there is variability in the waveguide cross section, length, and in bends along the waveguide. The use of slots on the different facets of the waveguide are shown to improve the bandwidth and help compensate for the frame length variability.

It is known that speech intelligibility degrades with additive noise and reverberation, and that quantitative parameters such as fidelity and signal-to-noise ratio can be improved by using microphone arrays with various beamforming algorithms. However, it is not clear how the array configuration impacts the intelligibility of speech. Numerical experiments, using widely-used models, provide the most convenient comparison, and the approach allows rapid assessment of parameters such as the array configuration, the number and spacing of the elements, and modeled features such as room reflection coefficients. For a typical reverberant room with a single wanted source and two unwanted sources (interferers), we compare the performance of two ceiling-mounted configurations - the uniform linear array (ULA) and a uniform circular array (UCA). The microphones are taken as omnidirectional and equispaced along the array loci, and we use a standard gain-constrained power minimization beamformer. In this study, a limiting performance is presented by emphasizing the early reflections over the late ones for the prior steering vector. Under this steering vector condition, for the same number of elements, the UCA easily outperforms the ULA on known quality and intelligibility metrics. For both arrays in this room scenario, all the metrics increase with an increasing number of microphones, although for one intelligibility metric, diminishing returns set in at about 12 microphones.

Immersive communication systems promise a greatly improved user experience through the use of advanced technologies tailored to various human senses, such as sight, hearing, and touch. This paper focuses on a simulation study of three-dimensional (3-D) sound field reproduction (SFR) for immersive communication. At the transmitting end, the incident sound field is captured via a microphone array, active talkers are detected, and a clean version of the signals corresponding to active talkers are found by existing methods. The captured information is transmitted to the receiving end, where a 3-D sound field from virtual sources corresponding to active talkers is synthesized around listeners' heads by the proposed SFR method. In our system, the radiation patterns of the higher order (directive) loudspeakers are optimized by the constrained matching pursuit algorithm. Implementation of the directive loudspeaker patterns is not addressed here, and their deployment is assumed. Simulation results quantify the benefit of higher order loudspeakers for speech sound field synthesis in reverberant rooms.

A multiuser multi-input multi-output (MU-MIMO) downlink system with block diagonalization-based precoding is presented with a study of the impact of limited bandwidth resource for the feedback-links on the sum capacity. The channel estimation is acquired at each user via downlink training, and the linear quantized form of estimated channels is fed back to the base station (BS) via noisy, finite-rate channel state information (CSI) feedback-links. Two architectures for CSI feedback are considered: parallel feedback where there is a feedback-link for each user; and serial feedback where a single feedback-link is used for all the users. The sum capacity is formulated as a function of the link parameters, enabling optimization of the number of training symbols and required feedback bits with the criterion of maximum sum capacity. The approach allows a performance comparison for different feedback architectures, the number of transmit antennas, and the number of users. The effect of time variations of the channel is analyzed via simulation, quantifying the loss of sum capacity relative to the case with perfect CSI for different Doppler frequencies.

This paper presents a comparison between several loudspeaker placement methods for sound field reproduction (SFR). The goal of these placement methods is to reduce the SFR error under a power constraint by selecting suitable locations for the loudspeakers. The first method is based on singular value decomposition of the acoustic transfer function (ATF) matrix. Depending on the configuration, an ideal ATF matrix is created and, then, approximated by selecting the appropriate locations for the loudspeakers. Another method is based on the constrained matching pursuit (CMP) algorithm, in which candidate locations of the loudspeakers are selected iteratively to minimize the approximation error of the desired sound field. The third method is based on sparsity-promoting sound field approximation using the least absolute shrinkage and selection operator. Loudspeaker placements obtained using these methods are compared against benchmark configuration of uniformly distributed loudspeakers. The comparison indicates that for constrained power, the CMP-based placement has the least reproduction error.

A new method is presented for optimizing loudspeaker placement, radiation patterns, and excitations for Sound Field Reproduction (SFR). A power constraint is included which is to help control the sound increase in the regions away from listening volume. For a known primary source, the loudspeaker locations and patterns are jointly optimized by Constrained Matching Pursuit (CMP), and this can be undertaken offline, i.e., before system operation. The excitations of the designed loudspeakers are then determined by conventional Lagrangian optimization. Simulations for free space conditions show that the new method yields a lower reproduction error under a power constraint than other SFR methods.

This paper presents three beamforming designs for multiuser multiple-input and multiple-output with orthogonal frequency-division multiplexing, where the transmit and receive beamformers are obtained iteratively with closed-form steps. In the first case, the transmit (Tx) beamformers are set and the receive (Rx) beamformers are calculated. It works by projecting the Tx beamformers into a null space of appropriate channels. This eliminates one interference term for each user. Then the Rx beamformer for each user maximizes its instantaneous signal-to-noise ratio (SNR) while satisfying an orthogonality condition to eliminate the remaining interferences. The second case is jointly optimizing the Tx and Rx beamformers from constrained SNR maximization. It uses the results from the first case. The third case is also for joint optimization of Tx-Rx beamformers but combines constrained SNR and signal-to-interference-plus-noise ratio maximization. The minimum number of antennas required is derived as part of the formulation. All cases can include a linear constellation precoder for extracting multipath diversity. Finally, the required feedback rates are derived and compared to existing beamforming methods. Using the standardized statistical channel model for IEEE 802.11n, our simulations demonstrate faster beamforming, improved error performance, and the ability to extract multipath diversity which is not possible in the least-square approach.

This paper addresses adaptive modulation and power allocation for maximizing the practicable sum capacity (sum of the uncoded throughputs of the users) of a multiuser multiple-input single-output MU-MISO) system. Since the optimal solution, dirty paper encoding (DPC), is complicated to implement, we use the simpler linear precoding based on signal- to-leakage-plus-noise ratio (SLNR). For different choices of constellation sizes, the maximum practicable sum capacities and their corresponding optimal power allocations are obtained via individual non-convex optimization. The best constellation sizes for each user are then identified through a search for the highest maximized practicable sum capacity. Simulations demonstrate the significant performance improvement from this approach compared to existing power allocation schemes. Finally, a selection procedure between different constellation sets is presented to obtain the highest practicable sum capacity while maintaining the instantaneous BER of each user below a target value. This approach allows management of the trade-off between the capacity and error performances.

Water-filled eigenchannels offer the highest multi-input multi-output MIMO information-theoretic capacity, but digital techniques such as quadrature amplitude modulation and finite block lengths will degrade the capacity from the Shannon limit to the capacity of a digital link. Furthermore, eigen-MIMO requires channel overheads, such as estimating the channel state information CSI and feeding it back to the transmitter, which further compromise the capacity. In this paper, the joint influence of channel estimation and imperfect feedback on the information-theoretic capacity and the practicable capacity is analyzed. The channel is modeled as static over a MIMO channel block. In each block, the forward channel is used for CSI estimation and for the payload data transmission. In the back direction, the channel is used to feed back a quantized form of the CSI to the transmitter with a throughput constraint. These three channel usages are combined into an effective simplex channel simplifying the capacity analysis. The capacities are formulated as functions of the link parameters, enabling optimization of the number of training symbols, the feedback duration, and the power allocation for training and data transfer, with the criterion of maximum capacity. The results presented are subject to the usual approximations used in communications theory. Copyright © 2012 John Wiley & Sons, Ltd.

With a view to the suppression of unwanted sound, a planar array of loudspeakers is used to recreate a sound field in a nearby cubic listening area. Using free-space propagation, the formulation for selecting optimal locations of loudspeakers is developed so that numerical experiments can give a feel for the best possible suppression. First, to provide a benchmark, a target Acoustic Transfer Function (ATF) matrix is found that minimizes the reproduction error for a number of uniformly placed loudspeakers. Then the same number of loudspeakers is positioned by selecting from densely placed candidates so that their ATF matrix best approximates the target sound field. For recreating the field of a point source located in the direction of the array, the loudspeaker array with selected locations is shown to improve the reproduction accuracy over a reasonable bandwidth.

Coordinated Multi-Point (CoMP) for Long Term Evolution Advanced (LTE-A) systems refers to a range of techniques to increase the capacity averaged over the cell, and also at the cell edge where the path loss is usually highest. In this paper, the problem of power allocation is first addressed for maximizing the sum capacity at each point of the coverage area in a CoMP multi-user downlink. Then, based on targeting the minimum value of the maximized sum capacity, a design approach is presented for obtaining an optimal size of the cells in a wireless network. The approach guarantees that the sum capacity at each point of the coverage area is above the target value. The path loss model is pivotal for the outcome of this type of performance analysis and the ensuing system design. Here, a simplistic, standard path loss model is used, but the approach can use other models.

The K-user interference channel describes K wireless pairs sharing the same spectrum simultaneously through the use of multiple antennas. In this paper, we present fast joint beamformer design to simultaneously minimize leakage interference (LI) and maximize both the individual signal powers (SPs) and the SINRs. This is a multi-objective, multi- variable problem which is treated here for the first time. We show that a fixed point of a nonexpansive vector field is guaranteed. This fixed point is a solution because it is a stationary point of the equally weighted sum of objective functions. Moreover, this stationary point ensures a minimum quality of service (QoS) for all users. Simulation demonstrates that the solution of the LI-SP-SINR problem is superior to max min SINR by having both a lower symbol error rate and a higher sum rate. Finding the solution also has lower complexity than MSE minimization and the max min SINR problem.

Range‐based localisation and tracking methods use the time‐of‐arrival (TOA) between the mobile station and several base stations, but the multipath propagation of non‐line‐of‐sight channels complicates the estimation and processing. For channel modelling, the Gaussian scatterer distribution model has been reported to have a reasonable match between its TOA probability density distribution (PDF) and measured TOA data. In this study, this TOA PDF is adapted, along with selection from multiple motion models of the mobile station, for a new location and tracking algorithm. Since the TOA PDF is non‐Gaussian and is a non‐linear function of the position of the mobile, particle filtering is used which increases the complexity of the algorithm. The focus is on the tracking performance, and this is evaluated by simulation using idealised statistical channels, allowing direct comparison between different location algorithms. In this context, the presented algorithm is more accurate than the benchmarks of extended Kalman filter tracking, and positioning using least squares.

Deployment of relays with data storage capability is progressively becoming popular in the literature as it provides significant performance improvement over relays with non-storage capability. In this paper, we consider a multi-branch multi-hop decode-and-forward (DF) relay system. We assume each relay has data storage and the data can be stored temporarily if the next channel is not good enough to transmit through. We derive an asymptotic and approximate outage probability expression for the considered system under generalized fading channel. Based on the derived expression, we formulate an optimization problem which allocates source and relay transmit powers under different system requirements.

Error performance and power allocation for multi-hop decode-and-forward (DF) systems are addressed. The different channels treated are Rayleigh, Rician, Nakagami-m, and Nakagami-q, and these are collectively referred to as generalized fading. The modulation can be any linear scheme. The asymptotic (high SNR) error rate expression is derivedwhich can incorporate independent and non-identically distributed (i.n.d.) channels in different hops. Power allocation schemes for the source and collaborating nodes are also presented for enhancing the power efficiency of modeled multi-hop performance. Simulations confirm the error expressions, and demonstrate, under considerable assumptions in transmission systems modeling, the performance of a DF multi-hop systems, including with optimal power allocation. The formulation allows (i) the configuration of modeled multi-hop systems from a wide variety of radio links including diversity-enabled ones or non-fading ones, and (ii) the evaluation of their end-to-end, high-SNR, optimized error performance.

For high data rate multiple-input multiple-output (MIMO) systems, a joint blind channel estimation and data recovery algorithm is presented for where the relative speed of the transmit/receive terminals may change. This changing speed is called manoeuvering. The blind technique is based on non-stationary independent component analysis with a generalised exponential density function to separate each source signal, and it uses particle filtering to track the time-varying channel. The presented technique also uses a hard decision switching block which adaptively selects between discrete speeds of a manoeuvering terminal. The speed can be therefore tracked within a mobile data communication link, that is, by using only the received data information signal. The performance is evaluated by simulation and is compared with optimal coherent detection as benchmark. A large degradation in system error performance is observed if the switching block is disabled within the algorithm, confirming its advantage. Moreover, to assess the impact of the presented blind channel estimation on system error performance more directly, a fair comparison with a known blind technique based on Kalman filtering and two known pilot-aided systems is presented with the assumption of non-manoeuvering terminals. Improved performance is observed using the presented technique.

Eigen-multiple-input multiple-output (MIMO) with water-filling gives the maximum information-theoretic capacity, but realising this maximisation is not straightforward because practical factors are omitted. Adaptive modulation and error coding are combined for finding the maximum practicable capacity (throughput of correctly detected bits) in eigen-MIMO. Quadrature amplitude modulation (QAM) is the logical choice of modulation and here Reed–Solomon (RS) coding is used. RS coding has the advantages of algorithmic simplicity, low-memory requirements, and decoder complexity, and its unique closed-form error probability makes it possible to obtain an optimal power allocation, signal constellation size(s), and code rate(s) on the eigenchannels, for the maximum practicable capacity. The proposed adaptive scheme is applied to two architectures for the encoders/decoders (CODECs): outer coding, where a single CODEC is deployed for the overall serial data; and inner coding, where there is a CODEC for each eigenchannel. The optimal power allocation is different to the water-filling used for the information-theoretic capacity. Also, simple and accurate approximations are found for the bit-error rate (BER) of a single Rayleigh channel and of a 2×2 system. Finally, a selection procedure between different system configurations is presented for obtaining the highest practicable capacity subject to either average or instantaneous output BER.

A Rice factor (K) estimator is described which uses simple operations on the phase of the well-defined Rice channel. Multiple receive channels, such as used in MIMO communications, enable spatial sampling which enhances the accuracy. For an example configuration of four uncorrelated receive antennas with a ten wavelength linear trajectory in isotropic scattering, the estimator works well for small to medium K (i.e., K ≲ 7). Limitations of the estimator include an assumption of isotropic scattering and that the angle-of-arrival of the dominant component is fixed and cannot be perpendicular to the mobile trajectory.

Water-filled eigenchannels offer the highest MIMO information-theoretic capacity. However, in practice there are many factors, such as digital modulations instead of Gaussian signals, finite block lengths, and imperfect power allocation, that combine to degrade the capacity from the Shannon limit to the practicable capacity - the uncoded throughput - of a digital link. Complexity reduction is also an important factor for a practical system. In this paper, we address the problem of power allocation for maximizing the practicable capacity in eigen-MIMO with the total input power constraint and perfect channel state information (CSI) at the transmitter. We use non-adaptive modulation at the transmitter in order to avoid the high complexity in both the electronics and the protocol - of adaptive modulation. The optimum power allocation reveals new and interesting capacity behavior, and it turns out to be different than that of the water-filling.

An adaptive coding scheme for spectral efficiency improvement in eigen-MIMO is presented. It uses Reed-Solomon (RS) codes with non-adaptive QAM. Non-adaptive modulation is of interest since it reduces the high complexity - in both the electronics and the protocol - required for deploying the more commonly treated adaptive modulation. RS codes have practical advantages in terms of their algorithmic simplicity, memory requirements and decoder complexity. Unlike many codes, an analytical solution for the error probability is available for RS coding. This facilitates finding the jointly optimal code rate(s) and power allocation on the eigenchannels, with the criterion of maximum instantaneous practicable capacity (data throughput). The adaptation is applied to two different architectures of the encoders/decoders (CODECs) for eigen-MIMO, and their performances are compared with the uncoded case. The outer coding architecture refers to a single CODEC working on the overall serial data, and inner coding refers to separate CODECs for different eigenchannels. The adaptive RS system with optimum power allocation reveals new capacity behavior which is different to that of water-filling. For the moderate values of SNR (6-20 dB) typical of wireless systems, the improvement in the capacity over the no-coding case is greater for the inner coding architecture.

A new blind channel estimation technique is presented for non-linear/linear equalisation in a frequency-selective Rayleigh fading channel. At each symbol interval, a decision algorithm first makes a primary data estimate based on constrained linear minimum mean square error criterion, and then this is applied to subsequent channel estimation. Channel estimates are obtained in the form of two alternative, related methods: directly from the Wiener solution or Kalman-based recursion. The former performs better but requires more values from the normalised time-correlation function. The performance is evaluated by simulation, allowing fair comparison with the benchmark of equalised coherent detection; optimal uncoded orthogonal frequency division multiplexing with perfect channel state information at the receiver; the conventional decision-directed Kalman filtering which employs channel tracking with delay; and for the special case of flat fading, an optimised, pilot symbol-assisted modulation system.

Abstract Radio channels are usually modeled as a well‐defined Rice process. The statistics of its wrapped phase (i.e., phase values in [−π,π)), such as the mean, variance, and probability density function (pdf), are known. The absolute phase, i.e., the accumulated phase change over an observation interval, is considered here as a new channel variable. Its use for channel characterization can extend to cognitively track users. However, there is very little knowledge about the statistics of the absolute phase. In fact, the known, associated effects of the absolute phase, such as various click noise contributions, are not consistently treated or interpreted in the literature. The definitions of absolute phase, based on both unwrapping and on other methods previously discussed for FM receivers, lay a basis for analysis of the mean, variance, and pdf of the absolute phase for a well‐defined Rice process. The conditions are identified for approximate pdf models to hold, and it is noted that pdfs for the absolute phase for small or medium Rice factor and small observation interval are open problems. Simulations are used to support the analysis and discussion. Copyright © 2009 John Wiley & Sons, Ltd.

This paper describes blind channel estimation for MIMO systems where there are nonlinear distortions in the receiver. The usual source of nonlinearity at the receiver is the front-end amplifier. A recursive algorithm estimates and tracks the channel through unscented transformation. Bussgang's theorem is used to model the in-band distortion comprising a bandpass, memoryless nonlinearity. Simulations demonstrate the excellent accuracy of the algorithm and its power in compensating the effects of distortion. A realistic nonlinearity is almost completely compensated, for small- to mid-values of SNR.

This paper presents a new iterative blind channel estimation technique for systems employing maximum-ratio combining with correlated receive antennas operating over Rayleigh flat fading channels. A decision algorithm first obtains a primary data estimate of the transmitted symbol based on the constrained linear minimum mean square error criterion. Then this estimate is applied to subsequent optimal minimum mean square error channel estimation. Performance is evaluated by simulation and favorable comparison is presented with the known results of optimal coherent detection as well as a known blind technique which employs Kalman filtering to track the channel. The impact of antenna cross correlation is also investigated by simulation.

In this paper, we study the influence of training-based channel estimation on the information-theoretic capacity of closed-loop MIMO systems with imperfect channel state information (CSI) feedback. First, a lower bound on capacity is formulated as a function of various parameters such as received signal-to-noise ratio, number of training symbols, feedback delay time, and the feedback noise variance. Next, we maximize the bound by obtaining the optimal allocation of power for training and data along with the optimal training interval. Fair comparison, through simulation, is also made with the maximized capacity of an open-loop MIMO system. An increase in capacity is still observed over the open-loop capacity for low to mid values of SNR. However, as the result of the imperfect feedback, the open-loop system has higher capacity that the closed-loop system for high SNR. This contribution helps sets the scene for looking at the realizable capacity, which involves the details of a specific communication system.

The inverse discrete Fourier transform (IDFT) technique has been used for simulating mobile channels in 2D isotropic scenarios because of its speed and simplicity. For simulating channels in directional scenarios, the IDFT can still be used, but it is not well developed. In this paper, a more generalized mobile channel simulator, using the IDFT, for directional scenarios is presented. The 2D directional scenario is modeled by the von Mises distribution. Derived quantities, here demonstrated using the level crossing rate and correlation, can have some differences from the theoretical forms. However, the performance of the statistics simulated using the IDFT is adequate for many simulation requirements.

The absolute phase is the accumulated phase change over an observation interval. It is a new variable for the mobile channel and can be simply derived from the wrapped phase or from the quadrature components. The absolute phase offers extra information about the channel, fostering new techniques for channel characterization and location estimation. However, the absolute phase has not been used in mobile communications. In this paper, the absolute phase is introduced including its mathematical definition and two different formulations. The mean of the absolute phase is derived for the mobile channel with directional scattering, including isotropic scattering as a special case. Simulations are used to support the analysis and discussion.

This paper presents blind channel estimation for Alamouti coding operating in time-correlated Rayleigh channels. A decision algorithm first obtains primary data estimates of the transmitted symbols based on the constrained linear minimum mean square error criterion, and these are applied to subsequent optimal minimum mean square error channel estimation. Performance is evaluated by simulation under the assumption of perfect timing, and presented against the known results of optimal coherent detection. The error performance is shown to be better than the Kalman filtering approach. The impact of finite cross correlations between the receive antennas is also investigated by simulation.

A novel approach to joint blind channel estimation and data recovery is presented for high date rate multiple-input multiple-output (MIMO) systems operating over flat Rayleigh channels. The technique is based on independent component analysis (ICA) with particle filtering to track the time-varying channel. Given one value from the channel matrix coefficients' second-order statistics, non-stationary independent component analysis with a generalized exponential density function is used to separate each source signal. The performance is evaluated by simulation and is compared with optimal coherent detection as benchmark. Improved performance is demonstrated over the "conventional" blind approach with Kalman-based estimation, and over two known pilot-aided systems. Finally, the effect of time-selectivity of the channel on error performance is also assessed by simulation.

The von Mises distribution is a convenient model for directional scenarios owing to its circular support, simple bell-shaped form, and smooth transition amongst many distributions. In this paper, we use the von Mises distribution as the angular power distribution to quantify the spacing for antennas to be uncorrelated. The results are well-defined and provide a stable and versatile framework for the design and configuration of spaced antennas in directional scenarios. Example solutions are given for a power correlation coefficient of 0.5 and a wide range of directionality expressed as the half-power beamwidth.

We present a new perspective on the use of channel state information (CSI) at the transmitter of orthogonal frequency-division multiplexing (OFDM) systems. While conventional closed-loop OFDM systems attempt to pre-equalize the channel through power loading, we propose an average signal- to-noise ratio (SNR) maximizing strategy based on the allocation of pilot locations. Our derivation for the average output SNR of OFDM systems with interpolated channel estimation reveals a combinatorial optimization problem in terms of the pilot- symbol locations. Using this framework, we arrive at the SNR gain achieved in using uniform and non-uniform pilot locations. Further, we present simple sub-optimum solutions based on decoupled optimization and show how minor adjustments of these solutions can also lead to very favorable error rate performances. The proposed solutions are simulated in a wide range of Doppler frequencies and compared to uniform pilot allocation in terms of average symbol error rate.

As more users share the radio spectrum, communications systems become limited by interference. The situation can be improved by using smart antennas, including beam-scanning systems, for increased gain and interference suppression. The design of beam-scanning arrays typically involves a tradeoff between the coverage (the set of directions over which beams can be directed) and the scan angle. Wide coverage, which is typical for mobile communications, requires large scan angles from single arrays and this results in scan loss and greater cross-polarization which degrade the SNIR. Large coverage angles with low scan loss can only be realized with multi-faceted or conformal arrays. The multi-faceted arrays are simpler to manufacture. For hemispherical coverage, the basic array configurations are the pyramid and the pyramidal frustum. The design for the optimal geometry (face elevation angle) of pyramidal frustum arrays is addressed using a novel minimax-based approach and the methodology for the choice of the number of faces is presented. The coverage is the partial (rotationally symmetric) hemisphere. Applications for these wide coverage array systems are widespread, ranging from fixed and mobile satellite terminals, landmobile vehicular antennas, basestations for indoor and outdoor networks, to radar surveillance and radio astronomy.

We present a novel transceiver design for orthogonal frequency-division multiplexing (OFDM) wireless systems employing pilot symbol aided channel estimation (PSACE). The design is based on the insertion of known pilots into the time- frequency OFDM grid in a controlled cyclic fashion to exploit time diversity in the pilot tones without consuming additional bandwidth resource. Semi-blind iterative detection based on the expectation-maximization algorithm along with optimum combining is employed at the receiver. Despite moderately increased transceiver complexity, simulations show that the proposed design has superior error rate performance compared to conventional PSACE methods for the same pilot overhead.

Knowledge of the propagation channel makes it possible for multiple-input multiple-output (MIMO) links to achieve higher system capacities by means of beamforming on the stronger channel eigenvectors. Assigning dedicated low bit rate feedback links is an efficient and practical method of providing transmitters with the required channel state information. One of the key problems in limited feedback precoding is the design of finite indexed codebooks known a priori to both the transmitter and receiver.Previous design methods include signal-to-noise ratio maximization through Grassmannian line packing, distortion minimization via vector quantization and antenna selection algorithms. In this paper we propose a new method that utilizes the dominant right singular vector of the MIMO channel to construct quantized unitary precoders. We show that although sub-optimum, this method can produce full diversity order codebooks. Using Monte-Carlo simulations, we compare the performance of the this method with optimum Grassmannian precoders and also antenna selection and subset selection algorithms.

The impact of communications signal processing such as QAM modulations (instead of Gaussian signals), finite block lengths (instead of infinitely long codes), and using simpler algorithms (instead of expensive-to-implement ones), etc., is a lower practicable capacity efficiency than that of the Shannon limit. In this paper, the theoretical and practicable capacity efficiencies for known-channel MIMO are compared for two idealized channels. The motivation is to identify worthwhile trade-offs between capacity reduction and complexity reduction. The channels are the usual complex Gaussian random i.i.d., and also the complex Gaussian circulant. The comparison reveals new and interesting capacity behaviour, with the circulant channel having a higher capacity efficiency than that of the random i.i.d. channel, for practical SNR values. A circulant channel would also suggest implementation advantages owing to its fixed eigenvectors. Because of the implementation complexity of water filling, the simpler but sub-optimum solution of equal power allocation is investigated and shown to be worthwhile

Frequency selective channels can be measured by either a continuous wave frequency sweep, which gives directly the transfer function, or by sounding the channel with pulses, which results in the impulse response. When the sounding pulse becomes a chirp-type waveform, the two approaches become similar. Simple rectangular pulses can be used for partial, but usually sufficient, channel characterization. In this paper, the process is described for resolving impulse response components into bins smaller than the duration of the sounding pulse and smaller than the reciprocal of the channel bandwidth. From such "super-resolution", the delay spread of the propagation channel can be established accurately even when it is much less than the sounding pulse duration, allowing longer, higher energy pulses to be used for channel characterization. The process is demonstrated using subtractive deconvolution where a loop gain of unity is shown to be stable; and a modified inverse filter technique, in which the modification caters for the spectral zeros of the sounding pulse.

Empirical justifications for the lognormal, Rayleigh and Suzuki (1977) probability density functions in multipath fading channels are examined by quantifying the rates of convergence of the central limit theorem (CLT) for the addition and multiplication of random variables. The accuracy of modeling the distribution of rays which experience multiple reflections/diffractions between transmitter and receiver as lognormal is quantified. In addition, it is shown that the vector sum of lognormal rays, such as in a narrow-band signal envelope, may best be approximated as being either Rayleigh, lognormal or Suzuki distributed depending on the fading channel conditions. These conditions are defined statistically.

Some of the radio frequency power transmitted from typical handheld terminals is absorbed in the head. This power loss is a drain on the communications link budget which translates to reduced battery time, and also carries a perception that there could be biological ramifications. The presence of the head affects the impedance seen at the antenna port, and this effect is known to be sensitive to the geometric details and also to vary considerably between individuals. Here, single-cut pattern measurement with power integration is discussed for estimating the absorbed power. This means that the power in the single pattern cut should be proportional to the total radiated power. In practice, this is not always the case, but indicative and useful results can still be obtained. Experimental results using a phantom head are given and simple retrofit parasitic shields are shown to decrease the absorbed power.

The Rayleigh-like distributed envelopes encountered in mobile communications occupy a wide dynamic range, typically 10 dB above the local mean to 40 dB below the local mean, with the range decreasing for increasing bandwidth. The local mean varies owing to shadow fading, by tens of dB, and on top of this, the inverse-distance loss can vary by some 50 dB within a cell. In characterizing the Rayleigh-like fading in real-world channels, measuring equipment needs to be expensive to cover such a dynamic range or else signal limiting occurs. For diversity channel evaluation, the correlation coefficient between channels is required in order to establish the potential diversity gain. This paper gives a statistical formulation for the effect of soft- and hard-clipped envelopes used for the correlation coefficient. It is shown that even hard-clipped envelopes are useful for diversity channel evaluation using the correlation coefficient.

For frequency selective channels, the delay spread is one measure for the channel distortion. This channel characterization is possible by either a CW frequency sweep, which gives directly the transfer function, or by sounding the channel with pulses which results in the impulse response. When the sounding pulse becomes a chirp-type waveform, the two approaches are distinguished more by implementation rather than by concept. Simple rectangular pulses can be used for partial, but usually sufficient, channel characterization. In this paper, the process is described for resolving impulse response components into bins smaller than the duration of the sounding pulse and smaller than the reciprocal of the channel bandwidth. From such super-resolution, the delay spread can be established accurately even when it is much less than the sounding pulse duration, allowing longer, higher-energy pulses to be used for channel characterization. The process is demonstrated by generating the super-resolved real-only impulse responses from the real-only responses of an experimental multipath channel. Two algorithms are presented and compared, These are subtractive deconvolution where a loop gain of unity is shown to be stable; and a modified inverse filter technique, in which the modification caters for the spectral zeros of the sounding pulse. The experiments demonstrate explicitly how receiving antennas can be used to control the amount of multipath channel degradation.

A signal combination technique, based on the spectral replication property of sampling, is presented. The technique uses second-order bandpass sampling to provide some phase control over the component signals. Although the phase control is not independent between the signals and is further constrained by inherent amplitude scaling, quasi-independent control can be achieved. The performance of the combination technique is established for two applications. These applications are diversity antenna combination and demodulation of slow frequency-hopping spread spectrum.>