The trade-off between data rate and range of UWB systems holds great promise for a wide variety of applications in military, civilian and commercial sectors. Radar is considered one of the most powerful applications of UWB technology. The fine positioning characteristics of narrow UWB pulses enables them to offer high-resolution radar (within centimeters) for military and civilian applications. Also, because of the very wide frequency spectrum band, UWB signals can easily penetrate various obstacles. This property makes UWB-based Ground Penetrating Radar (GPR) a useful asset for rescue and disaster recovery teams for detecting survivors buried under rubble in disaster situations.
Small and inexpensive UWB transceivers are excellent candidates for wireless sensor network applications for both military and civilian use. Such sensor networks are used to detect a physical phenomenon in an inaccessible area and transfer the information to a destination. A military application could be the detection of biological agents or enemy tracking on the battlefield. Civilian applications might include habitat monitoring, environment observation, health monitoring and home automation. The precise location-finding ability of UWB systems can be used in inventory control and asset management applications, such as tagging and identification systems. For example, RFID tags. Also, the good performance of UWB devices in multipath channels can provide the accurate Geolocation capability for indoor and obscured environments.
The high-data-rate capability of UWB systems for short distances has numerous applications for home networking and multimedia-rich communications in the form of WPAN applications. UWB systems could replace the cables connecting camcorders and VCRs, as well as other consumer electronics applications, such as laptops, DVDs, digital cameras and portable HDTV monitors.
1.5 ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING (OFDM)
OFDM is a special case of multicarrier transmission, where a signal DataStream is transmitted over a number of lower rate sub carriers. One of the main reasons to use OFDM is to increase the strength against frequency selective fading or narrow band interference.
In a single carrier system, a single fade or interference can cause the entire link to fail, but in multi carrier system, only a small percentage of the sub carriers will be affected. Error correction coding can then be used to detect the wrong sub carriers and correct them.
In a usual parallel data system, the total signal frequency band is divided into N non-overlapping frequency sub-channels. Each sub-channel is modulated with a separate symbol and then the N sub-channels are frequency multiplexed. It is good to avoid spectral overlap of channels to eliminate inter-channel interference. However, this leads to inefficient use of the available spectrum. To avoid the inefficient spectral usage parallel data transform and FDM based overlapped sub channels are used so that each sub band carrying a signaling rate b is spaced b apart in frequency to avoid the use of high speed equalization circuits and to combat impulsive noise and multipath distortion.
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