### Abstract

OFDMA is a promising technique because it is capable of improving the transmission reliability and efficiency of multi-user wireless communications. However, previous works on the performance of OFDMA did not properly consider the fundamental relationship between multiplexing and diversity in OFDMA systems. As a comprehensive performance metric, the diversity-multiplexing tradeoff will be applied in this paper to evaluate the subcarrier allocation scheme. The OFDMA system will be formulated into a correlated random bipartite graph model, in which, whether the edges occur or not depends on the distribution of the channel fading. The H-matching method, which is used to determine the maximum collection of vertex-disjoint copies of a fixed sub-graph H contained in a given graph, will then be developed to address the optimal subcarrier allocation problem. Theoretical analysis will show that the proposed H-matching method achieves the optimal outage performance at a given target multiplexing gain, which implies that the optimal diversity-multiplexing tradeoff can be achieved by only allocating subcarriers. Although the H-matching problem is NP-complete, the proposed Random Rotation and Expansion based Hopcroft-Karp (R ^{2}EHK) algorithm can still achieve the asymptotically optimal outage performance (i.e., optimal diversity-multiplexing tradeoff) with a sub-linear complexity. Furthermore, the channel state information needed is only one bit per subcarrier. Simulation results will verify the theoretical analysis and will show that the performance loss of the R ^{2}EHK algorithm is negligible compared to the exhaustive search method. In addition, it is also shown that the R ^{2}EHK algorithm has at least a 2 dB SNR gain compared to the interleaved subcarrier allocation with water-filling power allocation in IEEE 802.16 standards.

Original language | English |
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Article number | 6030125 |

Pages (from-to) | 3675-3687 |

Number of pages | 13 |

Journal | IEEE Transactions on Wireless Communications |

Volume | 10 |

Issue number | 11 |

DOIs | |

Publication status | Published - Nov 2011 |

Externally published | Yes |

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### Keywords

- constraint H-matching
- correlated random bipartite graph
- diversity-multiplexing tradeoff
- OFDMA
- outage probability

### ASJC Scopus subject areas

- Electrical and Electronic Engineering
- Computer Science Applications
- Applied Mathematics

### Cite this

*IEEE Transactions on Wireless Communications*,

*10*(11), 3675-3687. [6030125]. https://doi.org/10.1109/TWC.2011.092011.101114