Orthogonal frequency-division multiplexing (OFDM) converts a frequency-selective fading channel into parallel flat-fading subchannels, thereby simplifying channel equalization and symbol decoding. However, OFDM's performance suffers from the loss of multipath diversity, and the inability to guarantee symbol detectability when channel nulls occur. In this paper, we introduce a linear constellation preceded OFDM for wireless transmissions over frequency-selective fading channels. Exploiting the correlation structure of subchannels and choosing system parameters properly, we first perform an optimal subcarrier grouping to divide the set of subchannels into subsets. Within each subset, a linear constellation-specific precoder is then designed to maximize both diversity and coding gains. While greatly reducing the decoding complexity and simplifying the precoder design, subcarrier grouping enables the maximum possible diversity and coding gains. In addition to reduced complexity, the proposed system guarantees symbol detectability regardless of channel nulls, and does not reduce transmission rate. Analytic evaluation and corroborating simulations reveal its performance merits.
Bibliographical noteFunding Information:
Paper approved by C. Tellambura, the Editor for Modulation and Signal Design of the IEEE Communications Society. Manuscript received June 29, 2001. This work was supported in part by the National Science Foundation Wireless Initiative under Grant 9979442, in part by the Army Research Office under Grant DAAG55-98-1-0336, and in part by the Army Research Laboratory/Collaborative Technology Alliance (CTA) under Grant DAAD19-01-2-011. This paper was presented in part at the 35th Asilomar Conference on Signals, Systems, and Computers, Pacific Grove, CA, November 4–7, 2001.
- Diversity methods
- Linear constellation precoding
- Orthogonal frequency-division multiplexing (OFDM)