, Volume 71, Issue 2, pp 1557-1576

Adaptive Bit Loading and Puncturing Using Long Single Codewords in OFDM Systems

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Abstract

Adaptive puncturing over single codewords offers a new dimension in the family of adaptive coding and modulation techniques for communication systems. In the context of orthogonal frequency-division multiplexing systems, adaptive puncturing provides variable transmission rates across tiles within a single code-word (SCW). This contrasts with the more common multiple code-words (MCWs) structure, where variable rates are obtained using multiple codewords each is uniformly punctured. In this paper, an adaptive puncturing, interleaving, and bit loading schemes are proposed and an extensive performance evaluation is provided for both convolutional and turbo codes. The adaptively punctured SCW structure is compared to the MCWs, as well as to the per-frame adaptation. The comparisons are made using various adaptive loading methods for both constant and variable bit rate wireless applications. The SCW structure provides significantly improved goodput compared to the other two schemes, particularly for turbo-coded transmission. An analytical approximation for the goodput is obtained for both the SCW and the MCWs structures in the case of convolutional codes. The tile size effect is also investigated and it is shown that the SCW offers flexibility over the MCWs structure, since the tile size does not impose any restriction on the codeword length.

This work was supported by a grant from the Egyptian National Telecommunications Regulatory Authority (NTRA).