Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
In recent years there has emerged an ever increasing need of a wireless technology that will provide high data rates for short ranges in order to create seamless wireless interfaces between home-and office-environment devices with its periferials. A technology that a substantial part of wireless industry has turned its attention to is called Ultra Wide Band (UWB). There exist two proposals for a UWB standard today, one using OFDM and another one pulses with extremely short duration and wide bandwidth called UWB impulse radio. In this master thesis the latter approach intended for use in single-user scenarios is investigated.
UWB impulse radio is a fairly controversial technology due its extremely wide bandwidth. It is thus subject of strict regulations from, up to now only, FCC, a US frequency regulatory agency, in order for the technology not to interfere with licensed radio services operating in frequency bands covered by UWB. UWB impulse radio uses a carrierless approach of transmitting data, where pulses with short duration and low power are modulated in either time (Pulse Position Modulation or PPM) or amplitude (Pulse Amplitude Modulation or PAM). A major issue in the use of impulse radio are the spectral lines, or spikes, created in the frequency spectrum due to somewhat regular repetition of pulses, which results in the need of heavily reducing the transmitted power in order to comply with the FCC rules. One way of reducing the spectral spikes is to obtain randomness in polarity of the pulses. A new modulation scheme is therefore proposed called Pulse Position and Polarity Modulation or PPPM, where the transmitted pulses are modulated both in time and polarity. To improve the performance of the system, the performance of two error-correction coding schemes using the chosen approach are examined. In order to find out if this approach could be in fact used as a solution of providing high data rates for short-range communications a requirement is put forward that the BER at the receiver side should not exceed 10−5 at a distance less than 10 m away from the transmitter.
Due to a very high multipath resolution of UWB impulse radio technology, a RAKE receiver is used at the receiver end along with error correction coding in order to improve the performance of the system. Since UWB-IR is intended for use in mostly indoor environments it should be able to coexist with already existing radio technologies operating in the same band and in the same environment as UWB, such as IEEE 802.11a. Also, it should be fairly immune to timing jitter, which is a small randomness in timing base due to imperfections of pulse generators and sampling units. The simulations show that the latter requirement is met. It also shown that the 2-PPM scheme is useless if being used without any spectral-spike-reduction methods. But the most important conclusion based on simulation results is that the initial requirements are set too high to be met by the chosen approach. The conclusion is therefore drawn that it cannot be seen as a reliable solution for high-data-rate services in wireless personal area networks.
2005. , 42 p.
Slimane, S. Ben