Abstract:
The ubiquity of mobile broadband wireless communication systems in today's world is a testament to the robustness and success of radio-based telecommunications. Since the emergence of commercial cellular systems in the early 1980s, there has been an explosive growth in the demand and development of high data rate, large capacity and low cost wireless systems. Furthermore, the demand for mobile broadband connectivity is growing at an exponential rate with so many devices available to consumers that have inbuilt wireless connectivity, e.g. smart phones, laptops and tablets. However, as more wireless systems are deployed in the license-exempt bands (e.g. the ISM band), they are more likely to interfere with close proximity systems due to the inherent nature of the unlicensed radio spectrum. Interference is one of the key factors that limit the performance of wireless systems. Therefore, to deliver high-performance wireless systems, understanding the interference mechanism(s) to a particular system is crucial. One prominent technology that is gaining popularity with contemporary wireless systems (both in the licensed and unlicensed radio spectra) is Orthogonal Frequency Division Multiplexing (OFDM). Most current wireless local area networks (WLANs) and fourth generation (4G) cellular systems, such as the long term evolution (LTE) have adopted OFDM as their physical layer air interface technology. This popularity of OFDM among contemporary wireless systems is one of the major motivations for the research presented here. This thesis presents an analysis into the error rate performance of OFDM-based wireless networks in the presence of multiple interferers as well as a performance comparison with DS-SS wireless systems under identical environmental conditions. Novel analytical expressions that accurately predict the raw error rate (symbol and bit) performance of a generic M-ary QAM OFDM system in the presence of multiple narrowband and generic Z-ary QAM OFDM interferers are derived. The OFDM interferers are considered to be of the same type as the desired system, e.g. all desired and interfering OFDM systems are IEEE 802.11g WLANs. The analytical expressions are validated against Monte Carlo numerical methods. A computationally efficient algorithm that estimates the OFDM raw error rate performance with sufficient accuracy levels is also proposed. The analytical models developed in this thesis are independent of a particular wireless standard and thus can be used as a tool in the design and planning of OFDM based wireless systems. These models are used in conjunction with experimental RF measurements to test the implications for system deployment in indoor environments.