### 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 |
---|---|

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 |

### Fingerprint

### 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

**Diversity-multiplexing tradeoff in OFDMA systems : An H-matching approach.** / Bai, Bo; Chen, Wei; Letaief, Khaled; Cao, Zhigang.

Research output: Contribution to journal › Article

*IEEE Transactions on Wireless Communications*, vol. 10, no. 11, 6030125, pp. 3675-3687. https://doi.org/10.1109/TWC.2011.092011.101114

}

TY - JOUR

T1 - Diversity-multiplexing tradeoff in OFDMA systems

T2 - An H-matching approach

AU - Bai, Bo

AU - Chen, Wei

AU - Letaief, Khaled

AU - Cao, Zhigang

PY - 2011/11

Y1 - 2011/11

N2 - 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 2EHK) 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 2EHK algorithm is negligible compared to the exhaustive search method. In addition, it is also shown that the R 2EHK 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.

AB - 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 2EHK) 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 2EHK algorithm is negligible compared to the exhaustive search method. In addition, it is also shown that the R 2EHK 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.

KW - constraint H-matching

KW - correlated random bipartite graph

KW - diversity-multiplexing tradeoff

KW - OFDMA

KW - outage probability

UR - http://www.scopus.com/inward/record.url?scp=83555163950&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=83555163950&partnerID=8YFLogxK

U2 - 10.1109/TWC.2011.092011.101114

DO - 10.1109/TWC.2011.092011.101114

M3 - Article

VL - 10

SP - 3675

EP - 3687

JO - IEEE Transactions on Wireless Communications

JF - IEEE Transactions on Wireless Communications

SN - 1536-1276

IS - 11

M1 - 6030125

ER -