Coded OFDM for broadband indoor wireless systems

In this paper we investigate the use of OFDM for broadband indoor wireless links as a means of dealing with the multipath propagation problem. We consider three solutions capable of simplifying the system. First, we consider differential encoding, so that phase estimation is not required. The second solution consists of the use of special coding schemes that are capable of spreading the information bits among the subcarriers, so that the BER performance is not deteriorated by badly attenuated subcarriers. Two coding schemes are compared, a Walsh coding scheme and 4-state trellis-coded modulation. As a third solution, we consider a Nyquist sampling rate OFDM. We show that the Nyquist sampling rate OFDM signal, which is supposed to be dependent on a perfect receiver timing, can be made resistant to a receiver timing mismatch by using the coding schemes and by decreasing the rolloff factor of the Nyquist pulse, with extra benefits of greater bandwidth efficiency and lower added noise