| In this dissertation, the system performance of multiple access schemes in Ultra Wideband (UWB) communications is evaluated in a multipath and multiuser fading environment. Three multiple access schemes, namely Time Hopping (TH), Direct Sequence (DS) and hybrid Direct Sequence-Time Hopping (DS-TH) are investigated. The TH multiple access has been well studied in Radar communication systems. This research extends the previous studies by applying all kinds of pulse modulations, including pulse position modulation, pulse shift keying and pulse amplitude modulation. The idea of the DS multiple access schemes is also generalized from the well-known Direct Sequence-Code Division Multiple Access (DS-CDMA) cellular systems to UWB radios. It is shown that the DS multiple access has the potential to reach higher data transmission rates and that TH techniques are more resistant to fading. The DS-TH multiple access schemes are proposed by combining the advantages of both TH and DS multiple access schemes. Results show that the DS-TH ultra wideband achieves better system performance while maintaining the required data transmission rate and multiple access capacity. The system performance is illustrated and examined in terms of the signal to noise plus interference ratio, bit error rate and outage probability. |
