Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.556707
Title: Investigations into multi-antenna ultra-wideband channels in local and body area network environments
Author: Thompson, William Henry
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2012
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Abstract:
Understanding the effects of the propagation medium is essential in the design of efficient multi-antenna wireless communications systems. Ultra-wideband (UWB) intentional radia- tion offers great potential for short-range applications. However, due to the wideband charac- teristics of these signals, in-band frequency variation may impact system performance. This thesis addresses this issue and builds on the characterisation of the frequency dependence of multi-antenna UWB channels in local area network (LAN) and body area network (BAN) scenarios. Here, the frequency dependence of channel capacity and sub channel correlation properties are characterised for multi-antenna UWB channels. The LAN channel measurements were preformed in office environments using arrays of biconical antennas, under line-of-sight (LOS) and non-LOS (NLOS) channel conditions, over a frequency range of 4 to 10 GHz. The BAN measurements were performed in an office environment, using two different types of antennas located at several locations on the user's body, and covering the band from 4 to 9 GHz. For the LAN deployment, analysis reveals that, as frequency increases, the channels' spatial diversity potential increases at a faster rate in LOS channels than in NLOS channels, even though the overall diversity measure was still, on average, 31 % higher in the NLOS channels. The channel capacity characteristics are found to be dependent on the method of power control used to normalise the channel. If the channels are normalised to equal power in subbands then the capacity is found to be higher for the NLOS channels. However, when the path loss is included in the channel, the channel gain is found to dominate the capacity estimations. A comparison of channel measurements taken using virtual and physical arrays, shows that the use of virtual arrays (common in the literature) out performed the channel capacity of physical array measurements in 77 % of the cases tested. A novel antenna mounting method was developed to enable reliable BAN characterisation. This technique was shown to significantly decrease the electromagnetic coupling between the antenna and user, creating a non-user dependent antenna. The multi-antenna BAN measure- ments highlight an increased variability in the properties compared to the LAN measurements, with variations in the BAN capacity up to eight times higher over the UWB bandwidth than NLOS LAN measurements. The higher variation in capacity was caused by propagation paths travelling over the user's body; these paths were often found to increase the power difference and correlation between subchannels. However, when the channel gains were included into the capacity estimations, this propagation around the user was found to increase the received power, and again showed that the capacity is strongly linked to the received power.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.556707  DOI: Not available
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