A study on the performance improvement for CCK-OFDM wireless LAN modem

Abstract

Complementary Code Keying (CCK) is a variation on $\emph{M}$-ary Orthogonal Keying (MOK) modulation which uses an I/Q modulation architecture with complex symbol structures and Orthogonal Frequency Division Multiplexing (OFDM) is to spilt a high-rate data stream into a number of lower rate streams that are transmitted simultaneously over a number of subcarriers. OFDM based system can be of particular interest because it provides greater immunity to impulse noise and fast fades and it eliminates the need for equalizers, while efficient hardware implementations can be realized using Fast Fourier Transform (FFT). So this method has been proposed and adopted for many types of radio systems such as Wireless Local Area Networks (WLAN) and Digital Video Broadcasting (DVB). However, one of the major drawback of multicarrier signals is their high Peak-to-Average Power Ratio (PAPR). There are many methods to reduce the PAPR. In this thesis, we briefly introduce some techniques to get low PAPR in OFDM. Especially, we observe the special property of Golay complementary code to reduce the PAPR. It is that Golay sequences occur as cosets of the first order Reed-Muller (RM) code within the second order RM code. So we apply this theorem and have some modifications to get the good performance of the system. First, we show the equivalence between CCK codeword and coset of the first order RM code with variables of three for the proposed system. The CCK codewords are Golay sequences which have the PAPR of two at most and can correct one error. Thus, we propose a CCK-OFDM modem to reduce PAPR. Also, we present the performance improvement techniques by increasing the variables of four to correct three errors and reduce PAPR at least 9 dB with this system. Although two Fast Hadamard Trnasform (FHT) blocks of size 8$\times$64 are required at the receiver, we reduce the complexity by using FHT blocks of size 8$\times$64 and 2$\times$4 without deteriorating the performance. We gener...