In this study, the authors present an infinite‐series‐based approach for the performance analysis of n ‐diversity receivers operating over Rayleigh correlated fading channels in the presence of correlated phase difference. The performance analysis is based on error probability and signal‐to‐noise ratio (SNR) criteria. The authors propose a model to investigate the impact of phase difference between n ‐correlated Rayleigh fading channels. We have derived the closed form expression for phase distribution in a Rayleigh fading environment with the help of some statistical properties. The authors have also derived the joint density function of phase difference and its associated correlated envelopes. With the help of probability distribution function, the authors have observed two cases of equally spaced and loosely spaced antennas and showed that imperfect phase estimation lowers the SNR. The authors also present statistical analysis and the effectiveness of the proposed approximation to predict the variance of the phase difference. The authors have performed Monte Carlo simulation for a subcarrier‐based spectrum to analyse error probability with respect to phase and correlation.

This study is based on improving the visual quality of the images captured under different illumination conditions, i.e. overexposed and underexposed. This study presents a fuzzy image enhancement process based on a finite fuzzy set which is defined to optimise entropy, noise, intensity and edge information. In the proposed fuzzy approach, the overexposed and underexposed images are mapped to form a fuzzy set using membership functions. In the fuzzification process, the degree of belonging of each input to an appropriate fuzzy membership is calculated with respect to intensity, entropy, edge information and background noise. Therefore, the proposed method preserves the details of the image. Indeed, the fuzzy systems are well suited to model the uncertainty that occurs when conflicting operations are performed. Some effective approaches can enhance the image data without increasing noise. However, their ability to reduce the noise during the sharpening process is limited. The proposed method enhances the image by controlling sharpness parameter which affects the visual quality of the image. Both qualitative and quantitative assessments are performed to evaluate the performance of the proposed algorithm.

One of the most obvious characteristics of a good quality fused image is high spectral resolution. It is used to discriminate inner information in an image of low and high resolution by computing respective frequency components. The high‐resolution image results in high correlation between the adjacent bands. The authors have utilised resolution, contrast, and correlation using the wavelet fusion approach to achieve the enhanced image. A wavelet scheme is used to extract low‐ and high‐frequency data, forming wavelet domain components. These components are combined to create a fused wavelet coefficient map. To further improve the fused coefficients, we have used a higher‐order approximation to compute directive details of an image. The high‐frequency components are extracted to obtain edge and texture information to avoid too much spectral information loss because block‐wise wavelet transform decomposition and reconstruction introduces visible blocking artefacts in the image. In this work, phase variation in wavelets is also discussed and error analysis is performed. Comparison of various performance measures using different methods is shown in both qualitative and quantitative results.

The method presented encodes red, green and blue (RGB) images. When RGB images are added, the result inherently becomes darker due to summation of grey‐scale images. This image is enhanced by adjusting brightness and contrast to achieve a visually pleasing image. The method developed uses hue saturation value (HSV) and contrast enhancement (CE) to obtain enhanced color images. It can be used to combine imaging modality of a multimodal data set to represent multimodal data sets in color image without data loss. In HSV color space, grey scale and color information are in separate channels, so the combined images do not suffer from the same darkening contrast as the images combined in RGB color space suffer. The method proposed first involves computation of mapping function, then gradient‐based function is calculated to map image gradients based on grey‐level (GL) intensity and eigenvalue computation is used for CE. Therefore, the contrast of GL components of gradient of an image is enhanced by a mapping function. A better visual output is ensured using the proposed algorithm which is evaluated using performance metrics. When compared to adaptive histogram equalisation and contrast‐based imaging algorithms, the proposed technique gives significant performance in contrast and color enhancement.

Multiple‐input multiple‐output (MIMO) technology can be combined with orthogonal frequency division multiplexing to achieve diversity gain and improvement in system spectrum efficiency. The relative capacity of different system configurations are obtained using various channel characteristics. In this study, the probability density function (PDF) and the cumulative distribution function expressions of the condition number [i.e. the maximum to minimum singular value ratio (MMSVR)] of the channel state information matrix are derived. This ratio is directly related to noise enhancement in open loop (OL) multiuser MIMO systems. The probability density function (PDF) of MMSVR is directly used to compute the channel capacity if specific channels fail at high throughput. Capacity expressions in terms of MMSVR are derived for OL and closed loop (CL) multiuser MIMO systems. The capacity of both OL and CL systems are plotted for different system specifications, different fading channels and compared with each other under both semi and doubly correlated channels. A novel algorithm is developed to compute the channel capacity and PDF of MMSVR of a generic N T × N R MIMO system.

This study investigates the performance of independent and non‐identically distributed (i.ni.d.) α – μ fading channel with threshold conditions. A multiple input multiple output system employing orthogonal space time block codes over α – μ fading channel with i.ni.d. fading parameter and average signal‐to‐noise ratio (SNR) of K users as independent and identically distributed (i.i.d.) is considered. In this study, analytical expressions for bit error rate and average capacity under threshold conditions are derived and their numerical and simulated results are compared for two different scenarios for i.i.d. and i.ni.d. fading parameters under absolute SNR scheduling without threshold conditions. It is shown that the proposed system under threshold conditions improves system performance for various values of code rate, R c , number of receive antennas, n R , and threshold SNR, γ T.

In this paper, the authors study the system performance of adaptive transmission techniques in the presence of adjacent channel interference (ACI). The authors obtain closed‐form expressions for system capacity when employing different adaptive transmission policies with and without diversity schemes. The simulation results of spectrum efficiency in a WiMAX network employing 256 orthogonal frequency division multiplexing subcarriers are obtained for the analytical expressions derived for selection combining diversity under various adaptation policies. Analytical results show that the optimal power and rate adaptation policy provides the highest spectrum efficiency. Both analytical and simulation results are found to be in close agreement with each other, which shows that the obtained analytical results works well with the scenario of ACI. Also, maximal ratio combining scheme yields the highest spectrum efficiency when subjected to ACI.

Ultra wideband (UWB) systems transmit signals across a much wider frequency than conventional systems and are usually very difficult to detect. UWB systems tend to be useful for short‐range indoor applications. However, because of the short duration of UWB pulses, it is easier to engineer extremely high data rates. In multi‐band orthogonal frequency division multiplexing (MB‐OFDM) architecture, designers gain flexibility, reduction in power consumption, high spectrum efficiency and cost. In the earlier study, people shadowing has been considered to model attenuation in a packet‐level UWB channel model. However, in dense short‐range indoor applications, the effect of scatterers, diffractors and reflectors cannot be ignored. This happens mostly when the transmit antenna is omni‐directional. Compared with the earlier work which incorporated only shadowing effects, this study discusses a packet‐level UWB channel model subject to both multipath fading and people shadowing, which can arise even in an indoor channel (e.g. inside a hall of dimensions ∼ 10 m), and is incorporated in an MB‐OFDM system. The performance analysis of the link is made based on link throughput and delay in servicing packets. The numerical results show the relative effects of various fading distributions, viz., Rayleigh, Rician, Weibull and Nakagami, together with people shadowing on the MB‐OFDM system.

In this research work, the authors derive closed‐form expressions for capacity per unit bandwidth (spectrum efficiency) of correlated Rayleigh fading channels under maximal ratio combining diversity at low signal‐to‐noise ratios (SNRs). Spectrum efficiency expressions are derived for M diversity branches under adaptation policies, such as: (i) optimal power and rate adaptation (OPRA) policy, (ii) optimal rate adaptation (ORA) policy and (iii) truncated channel inversion with fixed rate (TIFR) policy. Even at low SNRs, if space diversity is exercised using a single‐input multiple‐output system, spectrum efficiency achieved is higher compared with that achieved when signals are uncorrelated and have no diversity. This forms the focal point of this study. Analytical results show accurately that OPRA policy provides highest capacity over other adaptation policies. The spectrum efficiency for the three policies and outage probability for the low SNR case are derived, plotted and analysed in detail in this work.

The authors analyse ergodic capacity for a system employing multi-element antenna array at the transmitter and receiver side. The signal is assumed to have both line-of-sight and non-line-of-sight (NLOS) components characterised by Rician fading distribution. The presence of the cluster of scatterers which gives rise to NLOS components is modelled using Von Mises Fisher (VMF) distribution. The impact of spatial correlation on capacity is graphically presented using MATLAB. The effect of channel state information at the transmitter side is analysed and plotted. Uniform circular array (UCA), which has been proved to outperform uniform linear array, is used at both the transmitter and the receiver. Furthermore, the effect of the radiation pattern of a UCA on the received signal-to-noise ratio is also plotted. Closed-form expressions for asymptotic tightness and upper bound of the system incorporating VMF distribution are obtained and plotted.

In this study, the authors investigate the first-order finite-state Markov chain modelling of time-varying flat fading channels. The scope of this work is to consider the joint effects of unknown channel phase and amplitude on the received signal. Performance measures such as level crossing rate, steady-state probability, state transition probability and state time duration of the fading models are derived, plotted and analysed. Comparison of the performance measures are made for Rician, Lognormal and Weibull fading distributions.

In this article, the capacity of multiuser multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) system is analysed under Rayleigh, Rician, Lognormal and Weibull fading channels, and compared with each other under both semi- and doubly correlated channels. The distribution of the complex Wishart matrix is utilised to derive closed-form expressions of ergodic capacity of MIMO-OFDM systems under doubly correlated channels when the transmitter has no channel state information (CSI) and the receiver has perfect CSI. The capacity of MIMO-OFDM systems is plotted for various fading channels under different system specifications, such as number of transmit and receive antennas, number of subcarriers and different power levels. The obtained results are used to study the impact of channel correlation on capacity.

In this paper, the performance of short constraint length convolutional codes in imperfect phase tracking conditions is discussed. Convolutional codes are used to provide error protection to a particular user in an Asynchronous CDMA (A- CDMA) system undergoing slow Rician fading. Maximum likelihood decoding with a Viterbi algorithm recovers the information symbols. A Phase Locked Loop (PLL) depicting the variations in the phase error for abrupt phase changes in the input signal is considered. Analytical bounds, which are useful in predicting the performance of the A-CDMA system are derived and plotted for the cases of infinite and finite channel memory. The upper bounds on the unconditional Bit Error Rate (BER) with Viterbi decoding are derived and plotted for the various convolutional codes considered. The simulated BERs are found to agree well with their upper bounds.