Applying diversity to OFDM

Author

I. Raad, SECTE, University of WollongongFollow

Year

2008

Degree Name

Doctor of Philosophy

Department

School of Electrical, Computer and Telecommunications Engineering - Faculty of Informatics

Recommended Citation

Raad, I., Applying diversity to OFDM, Doctor of Philosophy thesis, School of Electrical, Computer and Telecommunications Engineering - Faculty of Informatics, University of Wollongong, 2008. https://ro.uow.edu.au/theses/3050

Abstract

In today's world, wireless communications has become an essential part of every day life. An example of this is the exchange and transmission of data in many forms. Multi-user access systems provide a method to allow multiple users to transmit and exchange this type of information concurrently. Due to its orthogonality, Orthogonal Frequency Division Multiplexing (OFDM) has been used in Ultra Wide Band (e.g. MB-OFDM), WLAN (such as IEEE802:11a and IEEE802:11g) and mobile broadband systems (such as 3GPP LTE) as an e±cient scheme to achieve the expected outcomes for today's society needs for communications. Although OFDM achieves an excellent transmission rate and its application can be seen in everyday life, it still su®ered from corruption especially in indoor wireless environments in applications such as Wireless Local Area Networks (WLANS) in business o±ces, universities and shopping centers as an example. In these types of environments OFDM su®ers the greatest in degradation of performance. This degradation is due to multipath and fast frequency channels. Many solutions for this performance degradation have been proposed and the application of di®erent types of diversity has been used. This thesis proposes three applications of three di®erent types of diversity to improve the OFDM system performance in terms of Bit Error Rate (BER). Firstly, a new spreading matrix called the Rotation Spreading matrix used to introduce frequency diversity to OFDM is proposed. This new spreading ma- trix employs the use of a rotation angle to increase the correlation between the transmitted symbols to ensure in an indoor environment the system maintains an excellent performance. This thesis provides many studies through experi- ments and simulations of this new spreading matrix against other well known matrices such as the Hadamard and the Rotated Hadamard. This includes the introduction of methods to increase the size of this new matrix to ensure it is scalable to higher order matrices. Secondly, time diversity is employed through the use of delaying the block sym- bols of Block Spread OFDM (BSOFDM) to allow each symbol of an OFDM packet to be transmitted across independent channels. Thirdly, a new scheme called Parallel Concatenated Spreading Matrices OFDM is presented which employs coding gain to improve the overall BER performance of Block Spread OFDM in frequency selective channels. As a direct result of the solutions and methods proposed in this thesis to im- prove the OFDM system, 15 international peer reviewed publications have been achieved. Two of these include book chapters.