Seyed Alireza Zekavat

Traffic Pattern Prediction and Performance Investigation for Cognitive Radio Systems

In this paper, we propose a technique for predicting the traffic pattern of primary users in cognitive radio systems. Cognitive radios enable sharing the frequency bands that are licensed to primary users. By forecasting the traffic pattern of primary users, secondary users can estimate the utilization of frequency bands and select one for radio transmission to reduce the frequency hopping rate (the rate of switching from one frequency band to another) and the interference effects, while maintaining a reasonable blocking rate. In this work, we propose an algorithm for the prediction of call arrival rate which exploits the periodicity of the traffic process. In addition, we present an approach for call holding time estimation. The results are incorporated to evaluate the probability of the availability of a frequency band within a time period. Setting a threshold on this probability maintains a tradeoff between the blocking rate of secondary users, interference effects on primary users and spectrum efficiency. Simulations are conducted to investigate the performance of cognitive radio systems with and without traffic prediction.

A Novel Wireless Local Positioning System via a Merger of DS-CDMA and Beamforming: Probability-of-Detection Performance Analysis Under Array Perturbations

This paper investigates the probability-of-detection (POD) performance of a novel wireless local positioning system (WLPS) realized via direct sequence code division multiple access (DS-CDMA) and beamforming techniques. The proposed WLPS has unique signaling schemes that discriminate it from the traditional wireless systems and allows the WLPS to have many civilian and military applications. The WLPS consists of two main parts: 1) the detecting unit, a base station carried by a mobile unit defined as dynamic base station (DBS), and 2) the being detected unit, a transponder (TRX) that is mounted on the targets, each assigned a unique identification code. Each DBS should be capable of detecting and locating all available TRXs in its coverage area. As a result, the main complexity of this system is focused at the DBS receiver. In this paper, we introduce WLPS structure, and both theoretically and numerically compute, and compare the POD performance of the DBS receiver realized by a merger of DS-CDMA and antenna arrays. We also analyze and simulate the performance of this system under perturbations in the DBS antenna array vector. The simulations are particularly performed for vehicular collision avoidance applications

User-central wireless system: ultimate dynamic channel allocation

This paper introduces a new wireless architecture that creates ultimate freedom for dynamic channel allocation (DCA). The architecture is implemented based on the capabilities of cognitive radios. In the current wireless systems, users should subscribe to a service provider (vendor) and receive the service through the spectrum assigned to that vendor at all times. Hence, we call the current wireless systems as vendor-central systems. Vendor-central systems suffer from low utility performance defined in terms of spectrum efficiency, blocking rate, and revenue. In this work, we introduce a futuristic user-central wireless system configuration. In user-central systems, a user has the freedom of receiving the service through an optimum vendor at any time instance and geographical location. The optimum vendor is selected by an intelligent mobile based on parameters such as the vendor signal power, channel availability, congestion rate, cost per second, and quality of service. Here, vendors form a vendor area network (VAN) controlled by an inter-vendor mobile registration center (MRC). This paper discusses the systems structure, call procedure, and utility performance benefits attained by this system

Cloud classification using support vector machines

Cloud classification from GOES 8 (Geostationary Operational Environmental Satellite) imagery data is performed using the infrared (IR) channel only. For each block of the image, first and second order statistics are extracted and used to train and test a classifier. In this paper, cloud classification is performed using a support vector machine (SVM) classifier. This scheme, which is typically used to solve two-class problems, has been extended to classify ten different cloud and no-cloud areas. Preliminary results indicate the promise of this method for meteorological applications.

Smart antenna arrays with oscillating beam patterns: characterization of transmit diversity in semi-elliptic coverage

By applying carefully selected time-varying delays to the array elements of a smart antenna located at the base station (BS), small oscillations are generated in the beam pattern. These oscillations create a time-varying channel demonstrating intra-symbol time variation and characterized by coherence time T/sub C/. At a single-antenna mobile station (MS), the time-varying channel (with coherence time T/sub C/) creates a time diversity which is exploited to enhance the mobiles performance (by introducing oversampling to the mobile receiver). We present a channel model which characterizes the time-varying channel that results from beam pattern oscillation. We then use our channel model to evaluate the coherence time, T/sub C/, at the mobile station (MS). The channel model presented corresponds to the so-called geometric-based stochastic channel model (GSCM), with a semi-elliptic coverage area. This geometric approach allows us to stochastically model the parameters of the time-varying channel impulse response. Simulations based on the GSCM show that 7-fold time diversity can be exploited at the MS (when beam pattern movement is small), which significantly improves the MS receiver probability-of-error performance.

A Novel Semidistributed Localization Via Multinode TOA–DOA Fusion

This paper presents a 2-D semi-distributed localization technique, which is based on the fusion of the positioning data estimated by multiple mobile nodes. The fusion is implemented in the local coordinate of one of the nodes (reference node) and improves the positioning performance of the desired node in the coordinate of the reference node. This paper introduces the proposed localization fusion technique. The fusion weights and positioning error are theoretically derived, and the efficiency of a suboptimal reference node selection method, the positioning error, and the position update rate are evaluated via simulations.

A Novel Implementation of DOA Estimation for Node Localization on Software Defined Radios: Achieving High Performance with Low Complexity

This paper introduces a novel implementation of direction-of-arrival (DOA) estimation for localization of nodes in (mobile) ad-hoc networks. The localization technique is being implemented on a software defined radio (SDR) system. The SDR system needs DOA estimation for: (a) beam-forming and detection, and (b) localization. The detection process needs coarse DOA estimation, while the localization needs a fine one. The technique fuses two known DOA estimation techniques: delay-and-sum and root-MUSIC. The former is a simple technique suitable for on-line (high speed) implementation required for detection. Hence, it would consume less power. The latter is a complex technique that needs higher processing time and consumes more power and would be suitable for off-line DOA estimation. Hence, the fused DOA estimation technique offers high performance with low complexity and power consumption.

A Novel Spatially Correlated Multiuser MIMO Channel Modeling: Impact of Surface Roughness

A novel approach for modeling multiuser multiple-input and multiple-output (MIMO) channels is proposed. Here, the scatterers are modeled as random rough surfaces: Any point on rough surfaces scatters the incident wave into any given direction with certain probability. This leads to correlation across different spatially distributed users. The paper derives closed form expressions for the intra-user (point-to-point) and inter-user (multiuser) correlation of pair-wise channel coefficients. It is observed that the distance of users relative to the scatterer surfaces as well as the degree of roughness impact the correlation region. The technique is applied to both non-line-of-sight (NLOS) and line-of-sight (LOS) scenarios. It is observed that LOS signals drastically boost the correlation of the channel coefficients.

Smart antenna spatial sweeping for combined directionality and transmit diversity

In this paper, we present a novel application for antenna arrays in wireless communication systems. Here, antenna arrays at the base station are used to create 1) directionality which supports spatial multiplexing and 2) a scanning beam pattern, allowing receivers at the mobile unit to subdivide the symbol time into L partitions, each with independent fades. Combining the signals received in different symbol time partitions (at the mobile unit) results in diversity gains. In this way, diversity benefits (due to an antenna array) are achieved at the mobile unit with the smart antenna array located at the base station (rather than in the mobile itself), a significant cost saving for wireless communication systems.

DOA-Based Endoscopy Capsule Localization and Orientation Estimation via Unscented Kalman Filter

The endoscopy capsule is a medical device capable of capturing images inside humans digestion system, specifically the small and big intestine. For medical diagnostics and surgery, it is required to know the position and direction of the image taken inside digestion system. This paper considers an alternative method of presurgery gastroscopy and colonoscopy monitoring procedure that allows the patient to freely move inside the medical ward. The direction-of-arrival (DOA) and inertial measurement unit (IMU) measurements are integrated to track the movement of capsule with respect to patients body reference frame. The DOA is estimated via antenna arrays installed within a medical ward and the IMU is installed on the capsule endoscopy. The IMU sends the position information wirelessly to the antenna arrays in medical ward. Additional beacons are attached to the patient to allow body orientation and absolute position estimation due to the free movement. The nonhomogeneous nature of human body refracts the signal transmitted by the capsule, which leads to a highly nonlinear DOA function. This paper implements the unscented Kalman filter (UKF) to track the capsule by fusing the measurements made by DOA, IMU, and additional beacons attached to the patient. Simulations are conducted to investigate the capsule tracking and orientation estimation performance with respect to DOA resolution and beacons localization accuracy. Results confirm that compared with the DOA resolution, the beacons localization accuracy has a higher impact on the capsule orientation estimation performance. Furthermore, this paper investigates the impact of the number of available antenna arrays on multiplication required by UKF.