HBBCL Work on OFDM

Overview of Orthogonal Frequency Division Multiplexing (OFDM)

Orthogonal Frequency Division Multiplexing (OFDM) is a technique with a long history in multicarrier communication. OFDM is rapidly gaining attention in wireless and wireline applications: currently, the IEEE 802.11 and ESTI BRAN committees are incorporating the use of OFDM in the new standards. Our research work on OFDM includes the following:

Low PAPR Codes

For successful implementation of an OFDM system, the transmitter's amplifiers must operate in their linear regions to avoid intermodulation among sub-carriers. Amplifiers with large linear ranges are expensive to build. Thus, it is desirable to use codes whose waveform envelopes have low values of peak-to-average power ratios (PAPRs) so that the amplifiers may be used in their linear ranges. Furthermore, if the the peak transmission power is limited due to constraints in implementation, a high PAPR causes the average transmission power and hence, the range of transmissions to be reduced. In our work in this area we computed fundamental lower bounds on the PAPR for OFDM codes. For small code lengths, we have also constructed codes with low PAPR values based on Reed-Muller codes and Golay sequences over GF(2^k).

Frequency and Timing Estimation

Frequency and timing synchronization are two important practical considerations in the implementation of an OFDM system. Frequency synchronization is required to preserve the orthogonality of the subchannels and timing estimation is required for identification of the start of every new frame. In our current work we propose a new synchronization scheme of low complexity that performs asymptotically close to theoretical limits.

For further information refer to our publications and presentations.