## Abstract

This paper considers the effect of spatial correlation between transmit antennas on the sum-rate capacity of the MIMO Gaussian broadcast channel (i.e., downlink of a cellular system). Specifically, for a system with a large number of users n, we analyze the scaling laws of the sum-rate for the dirty paper coding and for different types of beamforming transmission schemes. When the channel is i.i.d., it has been shown that for large n, the sum rate is equal to M log log n +M log P/M + o(1) where M is the number of transmit antennas, P is the average signal to noise ratio, and o(1) refers to terms that go to zero as n → ∞. When the channel exhibits some spatial correlation with a covariance matrix R (non-singular with tr(R) = M), we prove that the sum rate of dirty paper coding is M log log n + M log P/M + logdet(R) + o(1). We further show that the sum-rate of various beamforming schemes achieves M log log n+M log P/M +M log c+o(1) where c ≤ 1 depends on the type of beamforming. We can in fact compute c for random beamforming proposed in [1] and more generally, for random beamforming with precoding in which beams are pre-multiplied by a fixed matrix. Simulation results are presented at the end of the paper.

Original language | English (US) |
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Pages (from-to) | 562-672 |

Number of pages | 111 |

Journal | IEEE Transactions on Communications |

Volume | 57 |

Issue number | 2 |

DOIs | |

State | Published - 2009 |

### Bibliographical note

Funding Information:The work of T. Y. Al-Naffouri has been supported by King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia. The work of M. Sharif and B. Hassibi is supported in part by the NSF under grant no. CCR-0133818 and CCR-0326554, by the David and Lucy Packard Foundation, and by Caltech Lee Center for Advanced Networking. The work of T. Y. Al-Naffouri was supported by University Project no. IN070342, Deanship of Scientific Research, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia.

## Keywords

- Broadcast channel
- Channel state information
- Multi-user diversity
- Transmit correlation
- Wireless communications

## ASJC Scopus subject areas

- Electrical and Electronic Engineering