Use this URL to cite or link to this record in EThOS:
Title: Spectrum efficiency improvement techniques for wireless communications
Author: Zhao, Bo
ISNI:       0000 0004 2703 9941
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2011
Availability of Full Text:
Access from EThOS:
Full text unavailable from EThOS. Restricted access.
Access from Institution:
Ultra-wideband (UWB) and cognitive radio have been proposed as two important approaches to improve the spectrum efficiency of wireless communications. The aim of this thesis is to study these two techniques considering different practical conditions. The study of the UWB technique begins with the analysis of the statistical properties of the sum of path gains using maximum ratio combining technique based on the IEEE UWB channel models. This analysis helps to justify the equivalent tapped-delay-line discrete UWB channel models. Following the study of the UWB channel models, signal-to-interferenceplus- noise ratio is analyzed for direct sequence binary phase shift keying UWB Rake receivers. Closed-form expressions for the signal-to-interferenceplus- noise ratio are derived by taking inter-path interference, inter-chip interference and inter-symbol interference as well as multiple-access interference into account. The analysis framework is further used to optimize the integration interval for UWB transmitted reference receivers. In addition to the signal-to-interference-plus-noise ratio, channel capacity of UWB systems with timing errors is also analyzed in this work. Both additive white Gaussian noise and multipath fading channels are studied. All the necessary interferences are considered. Moreover, transmitted reference systems are also considered as an example of non-coherent UWB systems for the capacity analysis. Novel adaptive receivers are also proposed for multi-user UWB systems in this thesis, as conventional matched-filter detection is not optimal in multi-user environments due to the non-Gaussian multiple-access interference. The new receivers adopt modified correlation operations without designing new decision rules. Numerical results show that the new receivers outperform the conventional receivers in both additive white Gaussian noise and multipath fading channels. For cognitive radio, spectrum sensing based on energy detection is studied. In order to make the analysis closer to practical applications, traffic load of the multiple primary users is taken into account. Expressions for the probability of detection, probability of false alarm and error probability are derived for both standalone spectrum sensing and collaborative spectrum sensing. In addition, the effect of the primary user traffic on the signal-to-noise ratio wall of energy detection is evaluated when noise uncertainty is present. Collaborative user number selection is also investigated in this work. The number of collaborative users is selected to maximize the effective throughput considering both the sensing performance in the physical layer and the throughput performance in the upper layer. Different channel conditions and decision rules are considered. Expressions for the optimum number of collaborative users are derived and verified.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QA Mathematics ; TK Electrical engineering. Electronics Nuclear engineering