This paper proposes a novel downlink precoding method for a cell-free massive multiple-input multiple-output (CF-mMIMO) network, requiring no channel state information sharing between the access points via fronthaul l...
详细信息
This paper proposes a novel downlink precoding method for a cell-free massive multiple-input multiple-output (CF-mMIMO) network, requiring no channel state information sharing between the access points via fronthaul links. By drawing analogies between a CF-mMIMO network and an artificial neural network, the proposed algorithm borrows the idea of backpropagation to train the precoders and the combiners through over-the-air ping-pong signaling between the access points and user equipments. It utilizes manifolds optimization to meet the per-AP power constraint and is named as distributed quasi-neural network precoding on manifold (DQNPM). The DQNPM algorithm can accommodate a large category of objective functions for fully distributed implementation. Numerical simulations show that our method outperforms the state-of-the-art approaches, and is robust against pilot contamination.
Most works on cell-free massive multiple-input multiple-output (MIMO) consider non-cooperative precoding strategies at the base stations (BSs) to avoid extensive channel state information (CSI) exchange via backhaul s...
详细信息
Most works on cell-free massive multiple-input multiple-output (MIMO) consider non-cooperative precoding strategies at the base stations (BSs) to avoid extensive channel state information (CSI) exchange via backhaul signaling. However, considerable performance gains can be accomplished by allowing coordination among the BSs. This paper proposes the first distributed framework for cooperative precoding design in cell-free massive MIMO (and, more generally, in joint transmission coordinated multi-point) systems that entirely eliminates the need for backhaul signaling for CSI exchange. A novel over-the-air (OTA) signaling mechanism is introduced such that each BS can obtain the same cross-term information that is traditionally exchanged among the BSs via backhaul signaling. The proposed distributed precoding design enjoys desirable flexibility and scalability properties, as the amount of OTA signaling does not scale with the number of BSs or user equipments. Numerical results show fast convergence and remarkable performance gains as compared with non-cooperative precoding design. The proposed scheme can also outperform the centralized precoding design under realistic CSI acquisition.
This paper is concerned with the design of distributed precoding in the multiple access (MA) phase for two-way relaying communication (TWRC) systems using OFDM. The error probability analysis is conducted to establish...
详细信息
This paper is concerned with the design of distributed precoding in the multiple access (MA) phase for two-way relaying communication (TWRC) systems using OFDM. The error probability analysis is conducted to establish the diversity and coding gains for three error types in the MA phase. Then, the design criteria of distributed precoding to achieve the maximum diversity and coding gains are given. The frequency-grouped linear constellation precoding (F-GLCP) is first investigated and shown not to be able to achieve the maximum diversity gain under type-3 errors. A novel frequency-time GLCP (FT-GLCP) that performs precoding in both the frequency and time domains is then proposed. It is proved that the proposed FT-GLCP is able to achieve the maximum diversity gain under type-3 errors while maintaining the maximum diversity and coding gains under type-1 and type-2 errors. To corroborate the theoretical analysis, simulation results are provided to show the advantage of the proposed FT-GLCP over other schemes in both Rayleigh and Rician fading channels.
Cell densification is a key driver to increase area spectral efficiencies in multi-antenna cellular systems. As increasing the density of base stations (BSs) and users that share the same spectrum, however, both inter...
详细信息
Cell densification is a key driver to increase area spectral efficiencies in multi-antenna cellular systems. As increasing the density of base stations (BSs) and users that share the same spectrum, however, both inter-user-interference (IUI) and inter-cell interference (ICI) problems give rise to a significant loss in spectral efficiencies in such systems. To resolve this problem under the constraint of local channel state information per BS, in this paper, we present a novel noncooperative multi-user multiple-input multiple-output (MIMO) precoding technique, called signal-to-interference-pulse-leakage-pulse-noise-ratio (SILNR) maximization precoding. The key innovation of our distributed precoding method is to maximize the product of SILNRs of users per cell using local channel state information at the transmitter (CSIT). We show that our precoding technique only using local CSIT can asymptotically achieve the multi-cell cooperative bound attained by cooperative precoding using global CSIT in some cases. We also present a precoding algorithm that is robust to CSIT errors in multi-cell scenarios. By multi-cell system-level simulations, we demonstrate that our distributed precoding technique outperforms all existing noncooperative precoding methods considerably and can also achieve the multi-cell bound very tightly even with not-so-many antennas at BSs.
This paper investigates the distributed precoding for network massive multi-input multi-output (MIMO) communications without data sharing between cells. In order to restrict the information exchange, which imposes sig...
详细信息
ISBN:
(纸本)9781665491228
This paper investigates the distributed precoding for network massive multi-input multi-output (MIMO) communications without data sharing between cells. In order to restrict the information exchange, which imposes significant requirements on signaling overhead, we first reformulate the original weighted sum-rate maximization problem into a cell-specific form. With this reformulated problem, we take a virtual weighted sum-rate, whose expression only depends on precoders in a single cell and some initial values, as the objective function of an approximated problem. A stationary point of this non-concave virtual weighted sum-rate maximization problem is then achieved iteratively through the minorize-maximize (MM) algorithm. After exchanging a virtual covariance matrix generated locally, each base station (BS) can solely optimize its precoding matrix in parallel without any exchange during the optimization procedure. Numerical results show that the proposed method performs well in the sense of achievable sum-rate.
A downlink adaptive distributed precoding scheme is proposed for coordinated multi-point (CoMP) transmission systems. The serving base station (BS) obtains the optimal precoding vector via user feedback. Meanwhile, th...
详细信息
A downlink adaptive distributed precoding scheme is proposed for coordinated multi-point (CoMP) transmission systems. The serving base station (BS) obtains the optimal precoding vector via user feedback. Meanwhile, the precoding vector of each coordinated BS is determined by adaptive gradient iteration according to the perturbation vector and the adjustment factor based on the vector perturbation method. In each transmission frame, the CoMP user feeds the precoding matrix index back to the serving BS, and feeds back the adjustment factor index to the coordinated BSs, which can reduce the uplink feedback overhead. The selected adjustment factor for each coordinated BS is obtained via the precoding vector of the coordinated BS used in the previous frame and the preferred precoding vector of the serving BS in this frame. The proposed scheme takes advantage of the spatial non-correlation and temporal correlation of the distributed MIMO channel. The design of the adjustment factor set is given and the channel feedback delay is considered. The system performance of the proposed scheme is verified with and without feedback delay respectively and the system feedback overhead is analyzed. Simulation results show that the proposed scheme has a good trade-off between system performance and the system control information overhead on feedback.
The amalgamation of cell-free networks and reconfigurable intelligent surface (RIS) has become a prospective technique for future sixth-generation wireless communication systems. In this paper, we focus on the precodi...
详细信息
The amalgamation of cell-free networks and reconfigurable intelligent surface (RIS) has become a prospective technique for future sixth-generation wireless communication systems. In this paper, we focus on the precoding and beamforming design for a downlink RIS-aided cell-free network. The design is formulated as a non-convex optimization problem by jointly optimizing the combining vector, active precoding, and passive RIS beamforming for minimizing the weighted sum of users' mean square error. A novel joint distributed precoding and beamforming framework is proposed to decentralize the alternating optimization method for acquiring a suboptimal solution to the design problem. Finally, numerical results validate the effectiveness of the proposed distributed precoding and beamforming framework, showing its low-complexity and improved scalability compared with the centralized method.
The capacity of Multiple-Input Multiple-Output networks (MIMO) is seriously degraded by interference. Many solutions have been given to overcome this problem, such as network MIMO and maximum signal to leakage plus no...
详细信息
The capacity of Multiple-Input Multiple-Output networks (MIMO) is seriously degraded by interference. Many solutions have been given to overcome this problem, such as network MIMO and maximum signal to leakage plus noise ratio (max-SLNR). In this letter, a downlink distributed precoding method is proposed to nullify the intra-cell interference and mitigate the negative effect on other cell users. This method can keep the merits of network MIMO and max-SLNR while overcoming their shortcomings. Numerical results show that the proposed precoding method outperforms Block Diagonalization (BD), max-SLNR and Block Diagonalization with Other Cell Interference (BD-OCI).
In order to alleviate the multipath interference of the MIMO multi-relay system and improve the system spectrum efficiency, this paper presents a cyclic delay distributed precoding relay scheme. The channel state info...
详细信息
ISBN:
(纸本)9781479900749
In order to alleviate the multipath interference of the MIMO multi-relay system and improve the system spectrum efficiency, this paper presents a cyclic delay distributed precoding relay scheme. The channel state information (CSI) sent from the source node, according to its phase information and relay node's matrix match, sends the signals to destination node via specific relay node, rather than the tradition broadcasts to all repeaters. Then at the relay node, we design a distributed precoding cyclic delay relay scheme to improve and balance the destination node's received signal power. At last, the receiver achieves the signals coherent combination and completes the system design. Simulation results show the proposed distributed precoding scheme improves the system capacity, reduces the encoding complexity, and is well suited for multi-relay system.
User-centric (UC) based cell-free (CF) structures can provide the benefits of coverage enhancement for millimeter wave (mmWave) multiple input multiple output (MIMO) systems, which is regarded as the key technology of...
详细信息
ISBN:
(纸本)9781728186788
User-centric (UC) based cell-free (CF) structures can provide the benefits of coverage enhancement for millimeter wave (mmWave) multiple input multiple output (MIMO) systems, which is regarded as the key technology of the reliable and high-rate services. In this paper, we propose a new beam selection scheme and precoding algorithm for the UC CF mmWave MIMO system, where a weighted sum-rate maximization problem is formulated. Since the joint design of beam selection and precoding is non-convex and tractable with high complexity, this paper designs the beam selection and precoding separately. Particularly, the proposed beam selection aims at reducing the inter-cluster inter-beam interference, then we also propose a precoding algorithm based on the weighted sum mean-square error (WSMSE) framework, where the precoding matrix can be updated in a distributed manner. We further employ the low-rank decomposition and Neumann series expansion (NSE) to reduce the computational complexity of the precoding. Simulations and complexity analysis verify the effectiveness of the proposed algorithm with a considerable reduction in computational complexity.
暂无评论