Rapidly fading channels provide Doppler-induced diversity, but are also challenging to estimate. To bypass channel estimation, we derive two novel block differential (BD) codecs. Relying on a basis expansion model for time-varying channels, our differential designs are easy to implement, and can achieve the maximum possible Doppler diversity. The first design (BD-I) relies on a time-frequency duality, based on which we convert a time-varying channel into multiple frequency-selective channels, and subsequently into multiple flat-fading channels using orthogonal frequency-division multiplexing. Combined with a group partitioning scheme, BD-I offers flexibility to trade off decoding complexity with performance. Our second block differential design (BD-II) improves the bandwidth efficiency of BD-I at the price of increased complexity at the receiver, which relies on decision-feedback decoding. Simulation results corroborate our theoretical analysis, and compare with competing alternatives.
Bibliographical noteFunding Information:
Paper approved by R. Raheli, the Editor for Detection, Equalization, and Coding of the IEEE Communications Society. Manuscript received October 18, 2002; revised June 1, 2003 and September 18, 2003. This work was supported through collaborative participation in the Communications and Networks Consortium sponsored by the U. S. Army Research Laboratory under the Collaborative Technology Alliance Program, Cooperative Agreement DAAD19-01-2-0011. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation thereon. This paper was presented in part at the International Conference on Communications, Anchorage, AK, May 11–15, 2003, and in part at the International Conference on Acoustics, Speech and Signal Processing, Hong Kong, April 6–10, 2003.
- Decision feedback
- Differential encoding