| 1. |
- Jin, S., et al.
(author)
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Cell coverage optimization for the multicell massive MIMO uplink
- 2015
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In: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 64:12, s. 5713-5727
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Journal article (peer-reviewed)abstract
- We investigate the cell coverage optimization problem for the massive multiple-input multiple-output (MIMO) uplink. By deploying tilt-adjustable antenna arrays at the base stations (BSs), cell coverage optimization can become a promising technique that is able to strike a compromise between covering cell-edge users and pilot contamination suppression.We formulate a detailed description of this optimization problem by maximizing the cell throughput,which is shown to bemainly determined by the user distribution within several key geometrical regions. Then, the formulated problem is applied to different example scenarios. For a network with hexagonal cells and uniformly distributed users, we derive an analytical lower bound of the ergodic throughput in the objective cell; based on this, it is shown that the optimal choice for the cell coverage should ensure that the coverage of different cells does not overlap. For a more generic network with sector- shaped cells and nonuniformly distributed users, we propose an analytical approximation of the ergodic throughput. After that, a practical coverage optimization algorithm is proposed, where the optimal solution can be easily obtained through a simple 1-D line searching within a confined searching region. Our numerical results show that the proposed coverage optimization method is able to greatly increase the system throughput in macrocells for the massive MIMO uplink transmission, compared with the traditional schemes where the cell coverage is fixed.
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| 2. |
- Jin, S., et al.
(author)
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Exploiting statistical and outdated CSI in multiuser downlink transmission
- 2012
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In: International Conference on Wireless Communications and Signal Processing, WCSP 2012; Huangshan; China; 25 October 2012 through 27 October 2012. - 9781467358293
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Conference paper (peer-reviewed)abstract
- In this paper, we propose a multiuser downlink transmission scheme, which exploits both the statistical and outdated channel state information (CSI) at the transmitter. The proposed scheme extends the outdated CSI-aided scheme, first introduced by Maddah-Ali and Tse in [1] (denoted as MAT), by sending symbols demanded by a user along its statistical eigenmodes, instead of directly sending the symbols through separate antennas, and we refer to it as statistical eigenmode-MAT (SE-MAT). Considering zero-forcing receiver, we explicitly prove that the proposed SE-MAT scheme can achieve a higher ergodic sum-rate compared to the original MAT scheme, under different correlation conditions. Moreover, a user selection method which selects statistically orthogonal users for the SE-MAT transmission is proposed to further improve the system performance.
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| 3. |
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| 4. |
- Sun, C., et al.
(author)
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Beam division multiple access for massive MIMO downlink transmission
- 2015
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In: IEEE International Conference on Communications. - 1550-3607. - 9781467364324 ; , s. 1970-1975
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Conference paper (peer-reviewed)abstract
- We study a multiuser multicarrier downlink communication system in which the base station (BS) employs a large number of antennas. By assuming frequency-division duplex operation, we provide a beam domain channel model as the number of BS antennas grows asymptotically large. With this model, we first derive a closed-form upper bound on the achievable ergodic sum-rate before developing necessary conditions to asymptotically maximize the upper bound, with only statistical channel state information at the BS. Inspired by these conditions, we propose a beam division multiple access (BDMA) transmission scheme, where the BS communicates with users via different beams. For BDMA transmission, we design user scheduling to select users within non-overlapping beams, work out an optimal pilot design under a minimum mean square error criterion, and provide optimal pilot sequences by utilizing the Zadoff-Chu sequences. The proposed BDMA scheme reduces significantly the pilot overhead, as well as, the processing complexity at transceivers. Simulations demonstrate the high spectral efficiency of BDMA transmission and the advantages in the bit error rate performance of the proposed pilot sequences.
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| 5. |
- Sun, C., et al.
(author)
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Beam Division Multiple Access Transmission for Massive MIMO Communications
- 2015
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In: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 63:6, s. 2170-2184
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Journal article (peer-reviewed)abstract
- We study multicarrier multiuser multiple-input multiple-output (MU-MIMO) systems, in which the base station employs an asymptotically large number of antennas. We analyze a fully correlated channel matrix and provide a beam domain channel model, where the channel gains are independent of sub-carriers. For this model, we first derive a closed-form upper bound on the achievable ergodic sum-rate, based on which, we develop asymptotically necessary and sufficient conditions for optimal downlink transmission that require only statistical channel state information at the transmitter. Furthermore, we propose a beam division multiple access (BDMA) transmission scheme that simultaneously serves multiple users via different beams. By selecting users within non-overlapping beams, the MU-MIMO channels can be equivalently decomposed into multiple single-user MIMO channels; this scheme significantly reduces the overhead of channel estimation, as well as, the processing complexity at transceivers. For BDMA transmission, we work out an optimal pilot design criterion to minimize the mean square error (MSE) and provide optimal pilot sequences by utilizing the Zadoff-Chu sequences. Simulations demonstrate the near-optimal performance of BDMA transmission and the advantages of the proposed pilot sequences.
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| 6. |
- Wang, J., et al.
(author)
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Precoder Design for Multiuser MISO Systems Exploiting Statistical and Outdated CSIT
- 2013
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In: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0090-6778 .- 1558-0857. ; 61:11, s. 4551-4564
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Journal article (peer-reviewed)abstract
- We propose a multiuser downlink transmission scheme exploiting both statistical and outdated channel state information (CSI) at the transmitter. Based on the outdated CSI-aided transmission scheme introduced in [1] (denoted as MAT), the proposed scheme reduces the original K-user MAT system to a two-user virtual MAT system, through statistical precoding in the first two transmission slots. Thus, the proposed scheme (denoted as V-MAT) reduces efficiently the implementation complexity, while increasing the achievable rate at finite signal-to-noise ratios (SNRs). For the V-MAT scheme, we derive an analytical high SNR rate approximation for correlated Rayleigh fading. Furthermore, for independent and identically distributed Rayleigh fading, we derive an exact rate expression at high SNRs, as well as a tight lower bound which applies for arbitrary SNRs. Then, precoder design is investigated, where an efficient near-optimal solution is proposed for arbitrary number of transmit antennas, and a closed-form optimal solution is derived for the two-antenna case. It is demonstrated that the proposed V-MAT scheme yields higher achievable rate than the original MAT scheme at practical SNRs. Moreover, by combining the V-MAT scheme and the generalized MAT scheme of [2], where precoding is implemented in the third transmission slot, the achievable rate can be further increased.
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