Abstract
Cell-free massive multiple-input multiple-output (mMIMO) is regarded as a promising technology in the future wireless communication. This paper aims to minimize the downlink power consumption of cell-free mMIMO system under the downlink rate constraints of users and the power constraints of per-antenna over spatially correlated Rayleigh fading channels. Firstly, this paper studies the performance of two different downlink transmission modes: non-coherent joint transmission and coherent joint transmission. Then, for the two transmission modes, the corresponding downlink power optimization model is established and an efficient power optimization algorithm is proposed based on the Lagrange multiplier (LM) method. Under the power optimization model, this paper analyzes the impact of different factors on the downlink power consumption of cell-free mMIMO system. Simulation results show that coherent joint transmission performs better than non-coherent joint transmission on spectral efficiency (SE) and energy efficiency (EE). In addition, under the same power control strategy, the downlink power consumption of cell-free mMIMO is much lower than co-located mMIMO. Moreover, the total transmission power decreases when more antennas are utilized at each access point (AP) or spatial correlation of channels becomes weak.
Highlights
Massive multiple-input multiple-output technology can provide services for multiple users simultaneously in the same time-frequency resource by deploying a large number of antennas at the base station and using beamforming technology [1]. The application of this technology makes the capacity of the traditional cellular network greatly improved, and makes fifth-generation (5G) communication gradually progress from theoretical research to reality [2], [3]
In the proposed power optimization model, we study the influence of various factors such as the number of antennas, the constraint of user’s spectral efficiency (SE) and channel correlation on the total downlink transmission power of cellfree Massive multiple-input multiple-output (mMIMO)
After receiving the signals sent by all L access point (AP), in order to detect the signals sent by different APs, the k-th user needs to use successive interference cancellation technology
Summary
Massive multiple-input multiple-output (mMIMO) technology can provide services for multiple users simultaneously in the same time-frequency resource by deploying a large number of antennas at the base station and using beamforming technology [1]. In cell-free mMIMO, a large number of access points (APs) equipped with single or multiple antennas provide services to all users at the same time by exploring local channel state information (CSI) and performing joint transmission [6]. Most of recent work on cell-free mMIMO considered coherent joint transmission, different APs must send the same data symbol to the same user [9]–[15]. For non-coherent joint transmission and coherent joint transmission, we obtain the expressions for the downlink SE of cell-free mMIMO over the spatially correlated Rayleigh fading channels. In the proposed power optimization model, we study the influence of various factors such as the number of antennas, the constraint of user’s SE and channel correlation on the total downlink transmission power of cellfree mMIMO. It can be seen from (2) that as σφ increases, the spatial correlation of the channel gradually decreases
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