Adnan Kavak

Vector channels for smart antennas. Measurements, statistical modeling, and directional properties in outdoor environments

In wireless communications, smart antenna systems that employ antenna arrays coupled with adaptive signal-processing techniques at the basestation improve capacity, coverage, and trunking efficiency. However, design and performance analysis of smart antenna systems strongly depend on channel propagation characteristics of signals present at the antenna array, the so-called vector channels. Here, variation of narrow-band vector channels (spatial signatures) due to a moving terminal is studied in typical suburban settings. Vector channel measurements are taken using a real-time smart antenna system with a uniform circular array at the basestation and a mobile transmitter at several locations. Two different wireless scenarios, namely, pedestrian and car mobile, are implemented to emulate the random movement of the mobile user. In each scenario, the mobile transmitter locations are chosen so that there exists line-of-sight (LOS), nonline-of-sight (NOLOS), or both LOS and NOLOS (mixed) propagation to the basestation. We find that in all cases, the Beta distribution can be used to empirically represent the spatial signature correlations and that large spatial diversity exists in NOLOS cases compared to LOS cases. Also, direction-of-arrivals mostly do not change much with movement in a suburban environment.

The Sectoral Sweeper Scheme for Wireless Sensor Networks: Adaptive Antenna Array Based Sensor Node Management and Location Estimation

We introduce a novel sensor node management and location estimation method referred as sectoral sweeper (SS) scheme that uses an adaptive antenna array (AAA) at a central node in wireless sensor networks (WSNs). With the SS scheme, the central node can activate or deactivate the nodes in a desired region which is specified by beam direction and beam width of the transmit beam and also by minimum and maximum thresholds (Rmin and Rmax) for the received signal strength indicator (RSSI) of signals received by the nodes. In order to perform a specified task that is associated with a Task_id, two different beams are transmitted, which are task region beam and routing region beam to switch the nodes into active or routing modes. Since our scheme does not require any additional software or hardware for node management and location estimation in sensor nodes, the deficiencies of tiny sensors are effectively eliminated. The proposed scheme is shown to reduce the number of sensing nodes and the amount of data traffic in the network, thus leading to considerable savings in energy consumption and prolonged sensor lifetime.

Implementation of floating point arithmetics using an FPGA

Floating point operations, which find their applications in vast areas such as many mathematical optimization methods, digital signal and image processing algorithms, and Artificial Neural Networks (ANNs), require much area and time for ordinary implementation on Field Programmable Gate Arrays (FPGAs). However, meaningful floating point arithmetic implementation on FPGAs is quite difficult with low level design specifications due to mapping difficulties and the complexity of floating point arithmetic. Design and implementation of floating point arithmetic and mapping of this into an FPGA become easier with the emergence of new generation FPGAs and development of high level languages such as VHDL tools. This paper presents the implementation methodologies of various floating point arithmetic operations such as addition, subtraction, multiplication, and division using 32-bit IEEE 754 floating point format. The implementation is performed using Xilinxs Spartan 3 FPGAs. The algorithms and implementation steps used for different operations are discussed in detail. As an example, an ANN application is presented using these algorithms.

Characteristics of vector propagation channels in dynamic mobile scenarios

In wireless communications, the performance of a smart antenna system depends heavily upon vector channels describing channel propagation between an antenna array and a mobile subscriber. The smart antennas perform quite well in stationary mobile environments in which channel propagation characteristics are stable. However, in dynamic wireless environments where the mobile user is in motion, knowledge of how vector channels are affected is necessary for the proper operation of smart antennas. Here, we experimentally investigate the variation of vector channel parameters such as spatial signatures, directions-of-arrival (DOAs), and complex path attenuations with small movement (2/spl lambda/) of the mobile under typical line-of-sight (LOS), line-of-sight with local scatterer (LOSLS), and nonline-of-sight (NLOS) propagation scenarios. The experiments are conducted using a 1.8-GHz smart antenna testbed developed at The University of Texas at Austin and a mobile transmitter. The results show that with small displacements, DOAs remain approximately unchanged and spatial signatures change due primarily to complex attenuations. Spatial signatures are very susceptible to the movement in the NLOS scenario, reaching up to 90% relative angle change within 2/spl lambda/ displacement. However, in the LOS scenario, they exhibit small and periodic fluctuations with a period of 0.6/spl lambda/.

Scalable location estimation using smart antennas in wireless sensor networks

For Wireless Sensor Networks (WSNs), although many localization techniques have been proposed, development of effective localization techniques for sensor nodes, which do not require any hardware or computational burdens on them, continues to be a challenging task. Motivated by this need, this paper proposes a new location discovery scheme in WSNs so called Sectoral Sweeper based Location Estimation (SSLE). Sectoral Sweeper (SS) relies on integration of smart antenna processing capability only at a central node. By expanding the SS scheme, the key idea in the SSLE is to perform two dimensional (azimuth and range) sweeping process over a given sensor field with beamforming capable central node followed by range estimation and direction estimation algorithms. It does not require any hardware or computational load at tiny sensor nodes. Performance evaluation of the SSLE is given in terms of localization error, response message statistics, and complexity analysis for grid and randomly deployed sensor node scenarios under various sweeping conditions. The SSLE performance is also compared with the Centroid method. The advantage of the SSLE is that it is applicable to environments with hard-to-access sensor deployment scenarios and that desired localization accuracy can be obtained by properly adjusting sweeping parameters.

A novel localization technique for wireless sensor networks using adaptive antenna arrays

In this work, we introduce a novel location estimation technique which uses adaptive antenna arrays (AAA) at the central node in wireless sensor networks (WSN). This localization technique can be used at the setup phase in the routing protocol. This technique is based on scanning the desired region in azimuth and radial directions by changing parameters of downlink beam. This sweeping process can activate the nodes in the desired region which is specified by beamwidth and beamdirection of the transmit beam and also by minimum and maximum thresholds (Rmin and Rmax) for the received signal strength indicator (RSSI). Active nodes in the desired region transmit their IDs and RSSI levels via multi hop communication to the central node. Unlike GPS-based or beacon based localization techniques, the proposed technique does not require any modification in the sensor nodes. The accuracy of location estimation depends on beam direction, beamwidth and transmit power for downlink beams. The results show that by carefully adjusting these parameters, desired performance can be achieved.

A Smart Antenna Module Using OMNeT++ for Wireless Sensor Network Simulation

We introduce a smart antenna (SA) module to be used in OMNeT++ for wireless sensor networks (WSN). This module is a collection of tools in OMNeT++ for adding smart antenna capability to a central node in WSNs. It is based on sectoral sweeper (SS) scheme which was shown to provide efficient task management and easy localization scheme. The number of sensing nodes, energy consumption of nodes, and data traffic carried in the network are reduced with the SS. OMNeT++ is an open source object-oriented modular discrete event network simulator consisting of hierarchically nested modules. With the SA module, desired task region can be specified by a task beam with changing beam width and beam direction parameters in the OMNeT++ configuration file. In addition, each node in the network model that uses SA module has capability of Mobility framework which is intended to support wireless and mobile simulations within OMNeT++. The simulation results provide performance evaluation using the developed module in OMNeT++ for WSNs.

Design and Hardware Implementation of a Novel Smart Antenna Algorithm Using TI DSPs

This paper presents design and implementation of a novel smart antenna algorithm referred as space code correlator (SCC). The algorithm is based on storing predetermined array response vectors, and performing code correlation with the desired users code and then spatial correlation of despread signal with stored array response vectors. The design methodology aims to find a beamforming weight vector that provides satisfactory SINR performance with fixed execution time so that convergence problem is avoided. SCC algorithm is implemented on the different Texas Instruments (TI) TMS320C67x floating-point digital signal processors (DSP) taking into account multipath propagation conditions. The implementation steps and results pertaining weight vector estimation time and SINR performance are presented. Results show that with careful selection of DOA search window and multipath SNR level, the SCC algorithm provides implementation time less than 10 ms frame interval of cdma2000 system

Analyzing distributed file synchronization techniques for educational data

“Movement of Enhancing Opportunities and Improving Technology”, abbreviated as Fatih, is among the most important educational projects in Turkey, in which students and teachers can use their tablet PCs to obtain educational data (text, images, media, etc.) stored in cloud servers. However, the limited network bandwidth and increase in both the number of users and their educational data sizes degrade the system performance and even negatively affect the overall usability of the system. Proxy server is a solution approach to both decreasing network traffic and increasing the efficiency in data transfers between end users (tablets) and cloud servers. In case of using a proxy server, synchronization problems arise. In this paper, distributed file synchronization approaches such as SyncML, Rsync and CouchDB have been reviewed and compared for their feasibility of employing in this school level proxy server based distributed systems architecture.

Software radio implementation of a smart antenna system on digital signal processors for cdma2000

This paper presents a software defined radio (SDR) implementation based on programmable digital signal processors (DSP) for smart antenna systems (SAS). We evaluate adaptive beamforming algorithms, namely non-blind-type least mean square (LMS) and blind-type constant modulus (CM) using TI TMS320C6000 high performance DSPs for cdma2000 reverse link. Adaptive beamformers are implemented using TI code composer studio (CCS) that includes assembly language and C code development tools. Performance variation of these sofware radio beamformers in terms of weight computation time and received SINR are compared for different C6000 development boards (TMS320C6701 EVM, TMS320C6711 DSK, and TMS320C6713 DSK) and array topologies under varying multipath propagation conditions. Results show that while antenna array and algorithm type are important for the SINR performance, DSP type becomes important for the weight computation time.