Journal of Emerging Technologies in Web Intelligence Contents

JOURNAL OF EMERGING TECHNOLOGIES IN WEB INTELLIGENCE, VOL. 2, NO. 2, MAY 2010 117Figure 4. Block diagram of Software RadioA. Smart AntennaAntennas are conducting devices which transmit orreceive electromagnetic radiations. An antenna arrayconsists of distributed antenna elements whose outputsare combined and is a practical tool for enhancingwireless system performance. The choice of an antennafor a software radio is crucial as it is expected to supportmultiple bands [1].It is an antenna array system with in-built signalprocessing “smart” algorithms to help adapt to differentsignal environments. It can also identify the direction ofarrival of the signal; add phases to the signal to create aconstructive radiation pattern to nullify interference.Smart antennas mitigate fading through diversityreception and beam-forming while minimizinginterference through spatial filtering. Software radiosprovide the flexibility needed for effective smart antennasand smart antennas put help in effective implementationand utilization of software radio.B. RF Front EndIt appears before the Intermediate Frequency changestate and after the signal is received from the antenna. Itdoes the job of converting the incoming signal to IFfrequency by using a tunable local oscillator.RF front end design process for a software radio hasthe challenge of catering to a variety of waveforms withwidely changing parameters such as amplitude,frequency, phase etc. Due to this wide spectrum, thepresence of noise and interference is manifold. Thismakes the process of achieving a dynamic range evenmore difficult. The dynamic range is the measure of thehighest and lowest level signals that can besimultaneously contained in a radio. In case of mobilecommunication, increase in dynamic range would meanmore battery consumption, which becomes a major tradeofffor mobile phones.Low level signals suffer from the problem of noise.Noise enters at the bottom of dynamic range due to thethermal effects of the components, deviation inquantization or sampling aperture jitter in an ADC. Highlevel signals are limited by interference. Interference iscaused at the high end due to adjacent channel, cochannelor is self induced by transceiver. Traditionalwireless communication receivers require single RF frontend for each channel. Software radio, however, has onlyone wideband RF front end which can digitize desiredsignal into separated channels via software to provide alow cost solution.C. Analog to Digital ConversionBefore all the processing can be done in the software,the analog signal received at IF stage needs to beconverted to digital samples by use of Analog to Digitalconverter. Ideal Software Radio would require a widebandwidth and good dynamic range from the ADC. Asshown in “Figure 5. , the translation of the signal fromanalog to digital is performed via sampling andquantization. Sampling changes the signal that existscontinuously in time to a signal that is non zero only atdiscrete intervals of time. Quantization changes thecontinuous valued signal to discrete valued signal.Figure 5. Analog to Digital Conversion© 2010 ACADEMY PUBLISHER