Quantitative Interference and Capacity Analysis of Broadband Multi-Hop Relaying Networks

Broadband Wireless Access Networks (BWANs) such as Worldwide Interoperability for Microwave Access (WiMAX) and Long Term Evolution (LTE) provide significant opportunities for increased throughput and affordable service. Such BWANs are typically based on orthogonal frequency division multiple access (OFDMA). OFDMA is desirable as it divides the available OFDM subcarriers to a number of subchannels. One or more sub-channels are assigned to one user. To achieve high data rates, it is necessary to increase the number of subcarriers per OFDM symbol. However, as the number of subcarriers increases, the frequency spacing between subcarriers in the OFDM symbol is reduced. This makes the OFDM system more sensitive to phase noise, which destroys the orthogonality of the subcarriers causing inter-carrier interference (ICI). Also, as the number of users increases in the system, more users will share the same OFDM symbol. This increases the subcarriers collision and makes OFDMA systems more sensitive to the resulting interference. BWANs are, however, challenged by limited capacity in busy cells and also suffer from coverage holes.;In this thesis, we address the interference issues in multi-hop BWANs and propose a solution using directional antennas in order to deal with some interference effects, and hence improve the bit error rate (BER) performance in the system. Specifically, we develop an analytical model to study the effects of the nonlinearity of high power amplifier (HPA) and the Doppler Shift on the transmitted OFDM symbols over multi-hop relying channels. Our research also includes a development of an analytical model to capture the effect of sub-carriers collision in OFDMA systems. Finally, the capacity of multi-hop relaying OFDMA systems employing the amplify-and-forward (AF) scheme at relay stations as well as taking into consideration the ICI effect, is quantified. The results show that the BER performance is degraded as the HPA nonlinearity and the mobile station's speed increase. Also, the symbol error rate (SER) performance is degraded as the number of subcarriers collisions increases. It is reported that these effects cause some loss of the capacity of the MMR system.;Mobile multi-hop relaying (MMR) system has been adopted in several BWANs as a cost-effective means of extending the coverage and improving the capacity of these wireless networks. In a MMR system, the communication between the source node and destination node is achieved through an intermediate node (i.,e., Relay Station). It is widely accepted that multi-hop relaying communication can provide higher capacity and can reduce the interference in BWANs. Such claims though have not been quantified. Quantification of such claims is an essential step to justify a better opportunity for wide deployment of relay stations.