Wireless Transmission Capability Research Articles

Towards wireless sensor networks with enhanced vision capabilities

Wireless sensor networks are expected to become an important tool for various security, surveillance and/or monitoring applications. The paper discusses selected practical aspects of development of such networks. First, design and implementation of an exemplary wireless sensor network for intrusion detection and classification are briefly presented. The network consists of two levels of nodes. At the first level, relatively simple microcontroller-based nodes with basic sensing devices and wireless transmission capabilities are used. These nodes are used as preliminary detectors of prospective intrusions. The second-level sensor node is built around a high performance FPGA controlling an array of cameras. The second-level nodes can be dynamically reconfigured to perform various types of visual data processing and analysis algorithms used to confirm the presence of intruders in the scene and to classify approximately the intrusion, if any. The paper briefly presents algorithms and overviews hardware of the network. In the last part of the paper, prospective directions for wireless sensor networks are analyzed and certain recommendations are included.

A wide-band linear amplitude modulator for polar transmitters based on the concept of interleaving delta modulation

Polar transmission techniques offer the capability of multimode wireless transmission and the potential for significant efficiency gains over solutions based on I/Q. However, polar transmitters are difficult to implement because of the wide bandwidths associated with the phase and envelope signals. Moreover, accurate synchronization between envelope and phase components is essential in minimizing distortion. A concept named Interleaving Delta Modulation (iDM) is proposed to overcome some of the issues associated with polar transmission. IDM minimizes distortion and improves efficiency by replacing a stream of fast drive pulses to the amplitude modulator with a parallel stream of slower pulses. Circuitry to implement iDM has been designed, fabricated, and measured in 0.35-/spl mu/m CMOS technology.

Single-RF Diversity Receiver for OFDM System Using ESPAR Antenna with Alternate Direction

This paper presents a single-RF diversity scheme for orthogonal frequency division multiplexing (OFDM) receiver using Electronically Steerable Passive Array Radiator (ESPAR) antenna whose direction changes alternately at the OFDM symbol rate. OFDM is widely used for mobile communication systems because of its broadband wireless transmission capability in a severe time dispersive multipath propagation channel. OFDM is, however, not efficient for mitigating the performance degradation due to fading. Diversity is an efficient technique for solving this problem. Although maximal ratio combining diversity is the most efficient technique, it requires the same number of RF front-end circuitry and analog-todigital converters (ADC) as antennas. Although ESPAR antenna-based diversity technique requires only a single-RF and ADC, the convergence is not fast enough to track fast variation of the channel state. Furthermore, it is not efficient in a frequency selective channel. In this paper, we propose a new OFDM diversity scheme using ESPAR antenna. The proposed scheme is capable of obtaining the diversity gain in a frequency selective fading environment and avoids the slow convergence rate problem in the conventional technique using ESPAR antenna. Computer simulation results show that the proposed scheme gives diversity gain in a frequency selective fading channel.