Mohammad N. Patwary

Effect of Directional Antenna on the Doppler Spectrum in 3-D Mobile Radio Propagation Environment

In this paper, an analytical model is proposed for a macrocellular communication system with directional antennas at elevated base station (BS) to quantify the effect of directivity of the radiated waves from antennas on the Doppler spectrum in a 3-D radio propagation environment. The impacts of antenna beamwidth and motion of mobile station (MS) are thoroughly investigated on the statistical distribution of the power Doppler spectrum. Closed-form expressions for trivariate probability density functions (pdfs) of propagation path distance, power, and Doppler shift are derived. Furthermore, general expressions for joint and marginal pdfs of elevation angle of arrival, power, and Doppler shift are established. Finally, the obtained theoretical results, along with the observations that illustrate the effect of directivity of the antenna beamwidth and the direction of the MSs motion on the distribution characteristics of the power Doppler spectrum, are presented. It is established that for motion of the MS in all directions, the spread in distribution of the Doppler shift observed is significantly reduced due to the use of a directional antenna at the BS with a narrow beam directed toward the desired user. It is also observed that, for a sharp azimuthal beam of directional antenna, the multipath components corresponding to the scatterers in the elevation plane result in the reduction of Doppler shift with an increase in their vertical distance from the MS.

Capacity and coverage increase with repeaters in UMTS urban cellular mobile communication environment

In this letter, we propose to use repeaters to increase system information capacity in urban areas, where path loss exponents are higher (as much as 3.4 or more). There is at least a 10% increase in coverage area when repeaters are placed in every cell within the network to increase system capacity. The overall system information capacity is doubled at propagation exponent 3.7-3.9.

The impact of propagation environment and velocity on the handover performance of LTE systems

In this paper, a generalized model is proposed to analyze the impact of propagation environment and velocity on the handover performance of user equipment (UE) for long term evolution (LTE) systems. An adaptive time window is defined within the generalized model, to provide additional flexibility to perform handover procedure over conventional reference signal received power (RSRP) and reference signal received quality (RSRQ) based procedures. The proposed algorithm reduces the call dropping rate during handover at the cell boundary of urban cells, due to its enhanced degree of freedom in decision making process. In providing so, the process requires additional statistics, which are readily available at the receiver. Therefore, it does not require any additional computational complexity at UE. Finally, to demonstrate the validity of the proposed algorithm, simulation results along with the observations are presented.

Superimposed training-based compressed sensing of sparse multipath channels

In a number of wireless communication applications, the impulse response of multipath communication channels has sparse nature. In this study, physical model for various propagation environments exhibiting sparse channel structure is considered. A superimposed (SI) training-based compressed channel sensing (SI-CCS) technique is proposed for such sparse multipath channels. A non-random periodic pilot sequence is SI over the information sequence at the transmitter, which avoids the use of dedicated time slots for training sequence. At the receiver, first-order statistics and the theory of compressed sensing is applied to estimate the wireless communication channels with sparse impulse response. A simulation analysis is presented to demonstrate the effectiveness of the proposed-channel estimation technique, where mean-square error and bit-error rate are used as the performance measures. Exploiting the proposed SI-CCS technique, the simulation results along with the observations are presented, which illustrate the effect of various channel parameters on the performance of the proposed technique. Furthermore, obtained simulation results for the proposed SI-CCS technique along with its comparison with other techniques in literature are also presented. It is established that for the cases of sparse multipath channels, the proposed SI-CCS technique can potentially achieve significant improvement in the performance of channel estimator over the existing estimation techniques of such sparse channels.

Spectral efficient compressive transmission framework for wireless communication systems

Increasing demand of high-speed data rate is leading to a challenging task to provide services to the users within exponentially growing market for wireless multimedia services. Subsequently, the available radio resources are becoming scarce because of different factors such as spectrum segmentation and dedicated frequency allocation to existing wireless standards. Exploring new techniques for enhancing the spectral efficiency in wireless communication has been an important research challenge. In this study, the enhancement of spectral efficiency of wireless communication systems is considered. A framework is proposed to implement the concept of compressive sampling (CS) for compressing the natural random signals. The performance of proposed framework is evaluated in the context of multiple input multiple output orthogonal frequency division multiplexing system. Simulation-based results show that 25% of resources can be saved by marginal trade-off with the quality of service (QoS) requirement applying CS to the natural random signals. Furthermore, it can be claimed that this QoS trade-off can be optimised with dynamic selection of random measurement matrices.

Subspace compressive GLRT detector for airborne MIMO Radar

In this paper, the design of a subspace compressive GLRT (SSC-GLRT) detector has been pursued for MIMO airborne radar system when the secondary sets of data are available in addition to the primary one. It is observed that with very reduced amount of measurement data at sub-Nyquist rate that is equal to the number of virtual bi-static radar in the presence of a single target, SSC-GLRT provides the same performance as the conventional GLRT with much larger length of the data, i.e., an order of magnitude higher given by the product of the number of elements in the received antenna array and coherent pulse interval (CPI). Therefore, SSC-GLRT is much energy efficient and useful in the scenario where the computational complexity becomes a burden. Also, this paper illustrates an elegant way of mapping the angular and Doppler domain to an one dimensional discrete vector for the formulation of compressive sampling (CS) based ℓ1 reconstruction of the signal subspace when it is unknown so that it can successively be used in SSC-GLRT. The simulation example further corroborates the effectiveness of the proposed SSC-GLRT detector.

3-D Gaussian scatter density propagation model employing a directional antenna at BS

In this paper, a propagation model is presented for the land mobile radio cellular systems with 3-D Gaussian distributed scatterers around Mobile Station (MS). The Base Station (BS) equipped with a directional antenna is located outside of the scattering region. The effect of directional antenna is thoroughly observed on spatial and temporal characteristics of the proposed model. General expressions for joint and marginal probability density functions (PDFs) of Angle-of-Arrival (AoA) observed at MS and BS in correspondence with azimuth and elevation angles are derived. Novel expressions for the trivariate and the bivariate density functions for Time-of-Arrival (ToA) / AoA in correspondence with azimuth and elevation angles are derived. Exploiting the proposed model, the theoretical results along with observations are presented to illustrate the effect of directional antenna on the spatio-temporal characteristics of channel. Obtained theoretical results for spatial statistics at BS are compared with an empirical set of measured data, which also demonstrates the validity of proposed model.

Adaptive compressive sensing for target tracking within wireless visual sensor networks-based surveillance applications

Wireless Visual Sensor Networks (WVSNs) have gained significant importance in the last few years and have emerged in several distinctive applications. The main aim is to design low power WVSN surveillance application using adaptive Compressive Sensing (CS) which is expected to overcome the WVSN resource constraints such as memory limitation, communication bandwidth and battery constraints. In this paper, an adaptive block CS technique is proposed and implemented to represent the high volume of captured images in a way for energy efficient wireless transmission and minimum storage. Furthermore, to achieve energy-efficient target detection and tracking with high detection reliability and robust tracking, to maximize the lifetime of sensor nodes as they can be left for months without any human interactions. Adaptive CS is expected to dynamically achieve higher compression rates depending on the sparsity nature of different datasets, while only compressing relative blocks in the image that contain the target to be tracked instead of compressing the whole image. Hence, saving power and increasing compression rates. Least mean square adaptive filter is used to predicts target’s next location to investigate the effect of CS on the tracking performance. The tracking is achieved in both indoor and outdoor environments for single/multi targets. Results have shown that with adaptive block CS up to 20 % measurements of data are required to be transmitted while preserving the required performance for target detection and tracking.

Characterization of Field-of-View for Energy Efficient Application-Aware Visual Sensor Networks

Energy consumption is one of the primary concerns in a resource-constrained visual sensor network (VSN). The existing VSN design solutions under particular resource-constrained scenarios are application specific, whereas the degree of sensitivity of the resource constraints varies from one application to another. This limits the implementation of the existing energy efficient solutions within a VSN node, which may be considered to be a part of a heterogeneous network. The heterogeneity of image capture and processing within a VSN can be adaptively reflected with a dynamic field-of-view (FoV) realization. This is expected to allow the implementation of a generalized energy efficient solution to adapt with the heterogeneity of the network. In this paper, an energy efficient FoV characterization framework is proposed, which can support a diverse range of applications. The context of adaptivity in the proposed FoV characterization framework is considered to be: 1) sensing range selection; 2) maximizing spatial coverage; 3) adaptive task classification; and 4) minimizing the number of required nodes. Soft decision criteria is exploited, and it is observed that for a given detection reliability, the proposed framework provides energy efficient solutions, which can be implemented within heterogeneous networks. It is also found that the proposed design solution for heterogeneous networks leads to 49.8% energy savings compared with the trivial design solution.

On the spatial characterization of 3-D air-to-ground radio communication channels

A three dimensional (3-D) geometric channel model is proposed for air-to-ground (A2G) communication environments. The proposed model considers air station (AS) and ground base station (BS) located at foci points of a virtual bounding ellipsoid corresponded from the delay of longest propagation path. The scattering region around the ground BS is thus designed based on this virtual bounding ellipsoid truncated by the ground plane and average rooftop level of the BSs surroundings. Closed-form expressions for joint and marginal probability density functions (PDFs) of angle of arrival (AoA) observed at both AS and BS in correspondence with both azimuth and elevation planes are derived. Impact of various physical channel parameters on the elevational and azimuthal angular dispersion is thoroughly observed; which is useful in designing advanced signal processing techniques for directional antennas employed in aeronautical communication links. To establish the models validity, the obtained analytical results are compared with simulation results. For 105 uniformly distributed scattering points, the best matching is observed between simulation and analytical results.