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Abstract
Ultra-Wide Band (UWB) technology is one of the possible solutions for future short-range indoor data communication with uniquely attractive features inviting major advances in wireless communications, networking, radar, imaging, and positioning systems. UWB uses a wide range of spectrum to transmit low-powered, ultra-short radio pulses (commonly monocycle pulses) through the air, and is capable of transmitting data at several hundred Mb/s typically over short distances under restricted power limited. These systems are therefore considered suitable for high-data-rate applications, such as Wireless Local Area Networks (WLAN), streaming media, and for use in battery-powered wireless data devices.
UWB usually refers to impulse based waveforms that can be used with different modulation schemes. The transmitted signal consists of a train of very narrow pulses, normally on the order of nanosecond pulse duration. Each transmitted pulse is referred to as a monocycle (the first derivative of a Gaussian pulse). The information can be carried by the phase, position or amplitude of the pulses. A major challenge when designing UWE systems is choosing the suitable modulation. Data rate, transceiver complexity, and BER performance of the transmitted signal are all related to the employed modulation scheme.
Several classical modulation schemes can be used to create UWB signals, some are more efficient than others. These schemes namely, Pulse Position Modulation (PPM), Pulse Amplitude Modulation (PAM), Binary Phase Shift Keying (BPSK), and On-Off Keying (OOK) are reviewed. The function of the receiver is to extract the information bit sequence modulated on the monocycle train from the distorted and corrupted receiving waveforms with a high accuracy. Having generated a signal with minimal spectral features, it is also necessary to have an optimal receiving system. The optimal receive technique in additive white Gaussian noise (A WGN) environments is a correlation receiver (correlator). A correlator multiplies the received RF signal with a ”template” waveform and then integrates the output of that process to yield a single DC voltage upon which it decides whether the received bit is a logic ’0’ or ’I’. This UWB direct conversion receiver avoids the multiple RF and Intermediate Frequency (IF) stages, local oscillators, and mixers. Since all pulses are sent at baseband, therefore synchronization of a carrier is also not required (carrierIess).
In the thesis, the performance of PPM system, combined with Time Hopping Spread Spectrum (THSS) multiple access technique is evaluated in an asynchronous multiple access free space environment. The multiple access interference is first assumed to be a zero mean Gaussian random process to simulate a scenario of multi user environment. An exact BER calculation is then evaluated based on the characteristic function (CF) method, for TH-PPM UWB systems with multiple access interference (MAl) in A WGN environment. The resulting analytical expression is then used to asses the accuracy of the MAl Gaussian Approximation (GA) first assumed. The GA is shown to be inaccurate for predicting BERs for medium and large signal-to-noise ratio (SNR) values.
Furthermore, the analysis of TH-PPM system is further extended to evaluate the influence of changing and optimizing some of the system or signal parameters. It can be shown how the system is greatly sensitive to variations in some signal parameters, like the pulse shape the time-shift parameter associated with PPM, and the pulse length. In addition, the systelT performance can be greatly improved by optimizing other system parameters like th( number of pulses per bit, Ns, and the number of time slots per frame, Nh. All thes( evaluation are addressed through numerical examples.
Then, we can say that, by improving some signal or system parameters, the BER performance of the system is greatly enhanced. This is achieved without imposing exac1 complexity to the transceiver and with moderate computational calculations.