Abstract
This paper considers a downlink cellular network where multi-antenna base stations (BSs) simultaneously serve their associated multi-antenna users. Each BS is distributed according to a homogeneous Poisson point process and uses zero-forcing beamforming for spatial division multiplexing with partial channel state information (CSI). During downlink transmission, each user combines the multiple antenna outputs and quantizes the CSI to feed back to its associated BS. Specifically, this paper focuses on antenna combining at the receiver. Conventional quantization-based combining (QBC) effectively reduces the quantization error; however, inter-cell interference in the cellular networks degrades the QBC gain. This degradation is analyzed using a spherical-cap approximation of vector quantization (SCVQ). From the SCVQ, the ergodic spectral efficiency and the optimal number of feedback bits are investigated, and it is shown that the QBC degrades the gain of the effective channel. To address this problem, an optimization solution is proposed that selects the antenna combining to maximize the spectral efficiency. The solution is also derived by considering the expected beamforming vectors of other cells. It is demonstrated by simulation that the proposed solution outperforms the conventional methods.
Highlights
Multi-input multi-output (MIMO) is a promising technology to meet the demand for high speed in wireless communications
For base stations (BSs) geometry, a homogeneous Poisson point process (PPP) with density λ = 10−5 /π is considered with a pathloss exponent α = 4
From the comparison of the existing methods, it was found that the inter-cell interference limits the gain of the quantization-based combining (QBC)
Summary
Multi-input multi-output (MIMO) is a promising technology to meet the demand for high speed in wireless communications. The SCVQ model is approximated on the assumption of many feedback bits From this approximation, it is shown that the QBC method reduces the dimension of the effective single antenna channel to Nt − Nr + 1 where the numbers of transmit and receive antennas are Nt and Nr respectively. The required number of other cells to measure the inter-cell interference is derived from the simulation This remainder of this paper is organized as follows; Section 1 describes the system model and performance metrics; Section 2 explains the antenna combining techniques such as MRC and QBC; Section 3 derives the performance for interference limited MIMO cellular networks; Section 4 presents the proposed antenna combining selection and the simulation results, and Section 5 concludes the paper. The sets N, R, and C denote the set of natural numbers, real numbers, and complex numbers, respectively
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