The need for more throughput in wireless cellular networks has been increasing in recent years. It has led to an increase in operational costs due to higher energy use as operators deploy more cell sites or increase transmission power at existing ones to satisfy demand. Energy costs are a major expense, and reducing them is a priority. This article presents a scheduler which aims to solve the problem of energy efficient resource allocation in orthogonal frequency division multiple access (OFDMA) cellular systems. The suggested approach is to make the resource scheduling process also consider energy costs as well as allow it to manipulate these by exploiting time/frequency vs energy efficiency trade-offs that are present in the system. The energy efficient score-based scheduler (EESBS) is a novel scheduler which takes energy costs into account when allocating resource blocks (RBs) to users. This allows it to promote energy efficiency in the system alongside throughput and fairness maximization. One of the means it has to manipulate users' expended energy is the bandwidth expanded mode (BEM). BEM is a technique that allows the scheduler to decrease a user's energy consumption by allocating it more RBs and maintaining a constant data rate. This is possible when the energy consumption is dominated by the energy used for data communication as opposed to control channel overhead transmission. Time compression mode (TCoM) is a technique that is complementary to BEM. It allows for energy savings through a reduction of the number of allocated RBs to a user when the energy consumption is dominated by the transmission of signaling traffic. Both BEM and TCoM need to be employed by an energy-aware scheduler like EESBS in order to extract the maximum performance gains. A realistic framework modeling future cellular systems is established to test the performance of the proposed techniques. Within this framework, EESBS generates an average energy saving of 29% over a frequency selective proportional fair (FsPF) benchmark. EESBS coupled with BEM or TCoM achieves a saving of 38% over the same benchmark. These savings are achieved with no detriment to user satisfaction in terms of achieved data rate.

Multiple-antenna techniques constitute a key technology for modern wireless communications, which trade-off superior error performance and higher data rates for increased system complexity and cost. Among the many transmission principles that exploit multiple-antenna at either the transmitter, the receiver, or both, Spatial Modulation (SM) is a novel and recently proposed multiple-antenna transmission technique that can offer, with a very low system complexity, improved data rates compared to Single-Input- Single-Output (SISO) systems, and robust error performance even in correlated channel environments. SM is an entirely new modulation concept that exploits the uniqueness and randomness properties of the wireless channel for communication. This is achieved by adopting a simple but effective coding mechanism that establishes a one-to-one mapping between blocks of information bits to be transmitted and the spatial positions of the transmit-antenna in the antenna-array. In this article, we summarize the latest research achievements and outline some relevant open research issues of this recently proposed transmission technique.

A practical virtual multiple-input multiple-output (MIMO) system that implements compress-and-forward (CF) cooperation is proposed in this paper. Bit-interleaved coded modulation (BICM) technique is implemented here to provide forward error correction and improve the system performance. A closed-form union bound for the system error probability is derived, based on which we prove that the smallest singular value of the cooperative channel matrix dominates the system error performance. Accordingly, an adaptive rate CF scheme is proposed, which uses the smallest singular value as the switching criterion. Depending on the instantaneous channel conditions, the relay could therefore choose various quantization rates. It is shown that the adaptive rate CF scheme eliminates unnecessary complexity for the quantization at the relay, and enables the virtual-MIMO system to achieve almost MIMO 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.

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.

Mobile systems developers have combined three key techniques to achieve the high data rates offered by current mobile broadband connections. They will layer on even more complexity to achieve the Gbit/s rates forecast for future 4G communications systems.

Finding faces, locating important facial features and model fitting are required in a range of applications including model based video coding. In this paper we present a technique for locating important facial features in head and shoulders colour images. A fast and effective method of detecting skin, while excluding eyes, using PCA transformed CIE-Lab colour space, is described. Candidate eye regions are then processed using region growing and eigenimages using the distance from feature space approach. False matches are eliminated using facial geometry constraints. Nose and mouth features are also located using eigen images in search regions derived from the eye positions. Further facial characteristics are identified and automated fitting of a global head model is achieved using a genetic algorithm based approach. Results from applying our technique to a large database of facial images (XM2VTS) are presented.

The UK's higher education funding bodies periodically carry out an assessment of the quality of research at British universities and higher education colleges. The results of the assessment enable approximately. #1 billion of public funds for research to be distributed selectively each year on the basis of quality. The most recent assessment was carried out in 2001 (the first was conducted in 1986...

The implementation of a multi carrier-code division multiple access (MC-CDMA) base station receiver incorporating decision statistic ordered successive interference cancellation multi-user detection in low power CMOS hardware is investigated. Serial and parallel cancellation architectures are compared and it is shown that the parallel one operates in far fewer clock cycles than its serial counterpart. A detailed description of architecture is given including the parallel algorithm used to implement the multi-user detection. Results show the power consumption and fixed point performance of the circuit.

Detection algorithms for single-user wireless communications in a Rayleigh flat-fading environment, using multiple antennas at both the transmitter and receiver are described and compared, assuming repetition coding. The linear decorrelating detector and minimum mean squared error detector are compared with nonlinear decision feedback detectors based on BLAST. Due to the effects of error propagation in the BLAST-type schemes, the MMSE detector performs best.

The implementation of multi-carrier code division multiple access (MC-CDMA) receivers in digital hardware is considered. A low power algorithm is proposed which treats the received signal as a block of symbols, rather than processing the symbols individually. This reduces power by holding one input to the multiplier circuits used in the multi-carrier combiner multiplication constant for a number of clock cycles. This produces a 50% reduction in power consumption for a multi-user detection combiner circuit. This algorithm is also extended to the fast Fourier transform (FFT) block and allows an overall power drain reduction of 13% for the whole receiver. A software configurable version of the circuit, which allows a trade-off between power reduction and processing delay, is also described.

A novel interference cancellation detector, which combines an initial phase of cancelling one or more users per iteration depending on the tentative decision metrics, followed by maximum likelihood detection for the last few users, is proposed for multi-carrier CDMA uplink communication. Simulation results compare the system with a number of other multi-user detection receivers for an uplink multipath multi-user problem. The number of iterations and computation complexity are compared with a successive interference cancellation approach. The influence of the near-far effect and of poor channel estimation is also investigated

A novel algorithm for carrier frequency offset correction in MC-CDMA is investigated. The algorithm uses coherently detected data symbols to provide phase offset information, which is used to modify the carrier frequency and successively reduce the offset with every data symbol. Comparison between this frequency correction algorithm, a closely related phase compensation algorithm and a two-symbol maximum likelihood estimation algorithm is provided.

Automatic wire-frame fitting and automatic wire-frame tracking are the two most important and most difficult issues associated with semantic-based moving image coding. A novel approach to high-speed tracking of important facial features is presented as a part of a complete fitting-tracking system we have developed. The method allows real-time processing of head-and-shoulders sequences using software tools only. The algorithm is based on eigenvalue decomposition of the sub-images extracted from subsequent frames of the video sequence. Since each facial feature (the left eye, the right eye, the nose and the lips) is tracked separately, the algorithm can be easily adapted for a parellel machine. The algorithm was tested on numerous widely used head-and-shoulders video sequences containing speaker's head pan, rotation and zoom with remarkably good results. The experiments we have carried out prove that it is possible to maintain tracking even when the facial features are partially occluded.