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Title: Wireless Multicarrier Communications with Carrier Interferometry Codes and Iterative Receiver
Authors: Mukherjee, M.
Keywords: Electrical Engineering
Issue Date: 2015
Publisher: IIT Patna
Abstract: Multicarrier based multiple access schemes are actively considered to supporthigh speed traffic on wireless channel. Traditional Code Division Multiple Access (CDMA) system based on single carrier provides low complexity for signal generation and is suited for voice communication and low data rate applications. As multimedia applications gain significant importance in present and future communication systems, there is a need to design communication system to transmit at different data rates with required Quality of Service (QoS). Such heterogeneous information sources are inherently multirate in nature. There has been significant interest in combining CDMA and Orthogonal Frequency Division Multiplexing (OFDM), such as Multicarrier Code Division Multiple Access (MC-CDMA) system to design multiple access scheme more robust against Intersymbol Interference (ISI) over multipath channel for high data rate transmission. However, contiguous wideband of the scare frequency spectrum is not easily available to support high data rate on wireless channel. Design of non-contiguous multicarrier transmission to support single rate and multiple data rates is one of the major research challenges in wireless communications. As in CDMA, MC-CDMA also suffers from Multiple Access Interference (MAI) that limits the number of active users. Furthermore, increasing the number of active users beyond the orthogonal dimensions, i.e., overloading the channel is a challenging task in interference limited multiuser environment. Design of second set of orthogonal spreading codes for additional users is a major research challenge in overloaded system. Also, efficient multiuser detector in overloaded scenario with reasonable complexity is desirable. The focus of this thesis is on the design of multicarrier multiple access schemes based on orthogonal codes for single rate and multirate communications over multipath fading channel. A novel MC-CDMA scheme is proposed which employs two levels of orthogonal spreading using Carrier Interferometry (CI) codes and orthogonal Walsh Hadamard (WH) codes with improved performance. Iterative receivers for fully loaded and overloaded channels have been proposed and extensively studied for these schemes. Three new schemes using multicarrier techniques have been proposed to support variable data rates in multimedia communications. Furthermore, the proposed schemes support integer as well as fractional multiple of basic data rate to meet different multimedia transmission requirements. The system design is also extended to overloaded scenario to investigate the robustness of the system under such loading conditions in multirate environment. Bit error rate performance of these variable rate schemes are extensively evaluated over multipath fading channel using suitable iterative receiver schemes. Deactivation of arbitrary number of subcarriers in non-contiguous allocation results in non-orthogonal transmission using traditional WH codes. Orthogonal Binary codes, a variant of WH code and orthogonal CI code can be generated for any integer length, which make these codes suitable for non-contiguous spectrum allocation. A new variable rate scheme is proposed which combines CI code with orthogonal Binary code to support variable rate transmission for fully loaded and overloaded system over non-contiguous spectrum allocation. Multicarrier based systems like OFDM and MC-CDMA are highly sensitive to phase noise. The carrier phase jitter is the phase error between carriers used for up-converting the baseband signal and the phase-locked carrier at the receiver for down-converting the radio frequency signal. Detrimental effect of phase jitter has been analyzed for single rate and multirate systems, and the analytical results match well with the simulated results. Furthermore, the BER performance of proposed variable rate multicarrier schemes with phase jitter has been evaluated for contiguous and non-contiguous allocation over AWGN and multipath fading channels.
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