A Frequency-Diversity System With Diversity Encoder and OFDM Modulation

Abstract

In this work, a diversity encoder maps vectors of N modulated symbols to vectors of N diversity symbols using an orthogonal matrix. Each modulated symbol appears in N diversity symbols. An Orthogonal-Frequency-Division-Multiplexing (OFDM) modulator converts the diversity vectors to OFDM symbols. The number of subcarriers in the OFDM symbol equals N. Each diversity symbol modulates one subcarrier; therefore, each modulated symbol is transmitted by N orthogonal subcarriers. The diversity bandwidth of the modulated symbols is N times the subchannel bandwidth. The modulated symbols experience independent fading gains on each subchannel since the diversity bandwidth (OFDM bandwidth) is chosen to be multiple of the coherence bandwidth of the transmission channel. In the receiver, an OFDM demodulator converts back the OFDM symbols to vectors of diversity symbols. The diversity detector maps the diversity vectors to vectors of modulated symbols. The noise samples at the output of the diversity detector are uncorrelated. Maximum likelihood and linear decorrelator detectors are used as diversity detectors. The transmitter and the receiver of this work are implemented using Field-Programable-Gate-Array (FPGA) technology. The performance of the implemented system is the same as the performance of the N channels diversity system with the Maximal-Ratio-Combiner (MRC) receiver.

Keywords

• Frequency diversity
• orthogonal-frequency-division-multiplexing
• frequency selective fading channels
• maximal-ratio-combiner
• maximum likelihood detector
• linear decorrelator detector