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Coded Ofdm Methods For Digital Broadcasting Systems

Nowadays, mobile communication systems require modulation and diversity techniques that ensure data transmission with high rate and low bit error in order to support internet, video and multimedia applications. In this thesis orthogonal frequency division multiplexing OFDM and coding used as a modulation technique in order to cope with mobile communication channel constraints are constraints.

OFDM is a multi-carrier modulation technique in which a single high rate data-stream is divided into multiple low rate data-streams that are modulated using subcarriers which are orthogonal to each other. OFDM has commonly been utilized to transform a frequency selective fading channel into multiple flat fading subchannels. One of the main advantages of OFDM is its multipath delay spread tolerance and efficient spectrum use by allowing overlapping in the frequency domain. Coded OFDM systems are obtained by combining OFDM and channel coding technique and help to achieve high data rates and low bit error rates in mobile communication systems.

In this study the channel estimation and receiver performance of a wireless communication system which is the combination of two channel coding methods and OFDM are investigated. Mutli Level Turbo Coded (MLTC) and Low Density Parity Check (LDPC) coded data symbols are modulated with OFDM method, then the parameters of a wireless time varying channel are estimated and the bit error rate (BER) is calculated. After all, it was concluded that the bit error rate of a coded OFDM system is much better than that of an uncoded OFDM system.