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In this paper, a cocktail approach is proposed to delicately integrate the two conventional countermeasures, i.e., the fractional pilot reuse and time-shifted pilots (TSP) schemes, for the pilot contamination problem in the full-duplex massive multiple-input multiple-output system. Specifically, the TSP scheme is applied to duplicate for the inner and edge regions of a cell such that the number of accommodated users can be doubled. To achieve this, the base station should operate in the full-duplex mode; also, the pilot symbols rather than the pilot sequences are used to attain the user diversity gain. The simulation results verify the accuracy of the numerical analysis and the remarkably boosted sum rate for both the downlink and uplink cases. [ABSTRACT FROM AUTHOR]

In this paper, we consider the joint power and modulation optimization in two-user non-orthogonal multiple access (NOMA) channels based on error-rate performance criterion and finite-alphabet inputs. Specifically, with joint maximum-likelihood detection being employed at each user's receiver, the users’ transmission power levels are jointly determined with the 4-QAM constellation of one of the users being rotated such that the probability of dominant pairwise error event in the NOMA channel is minimized. Toward solving the joint power and modulation problem, our results are twofold. First, with $M$ antennas at the receiver, closed-form expressions for the optimal angles as a function of $M$ , the channel coefficients, and the users’ power levels are derived. Second, closed-form expressions are derived for the joint power allocation with optimal rotation by casting the joint optimization as a piecewise convex optimization problem over its sub-domains. Using the proposed joint optimization, the error-rate performance of NOMA improves significantly and it outperforms traditional NOMA power allocation methods for the selected transmission rates. The proposed approach thus represents a rather distinct approach in NOMA optimization, and it is applicable in the uplink NOMA where users share the same time/frequency channel or in the downlink NOMA where users are multiplexed in the power domain. [ABSTRACT FROM AUTHOR]

In this paper, we study the energy efficiency (EE) of a downlink multicell massive distributed antenna system (DAS) in the presence of pilot contamination (PC), where the antennas are clustered on the remote radio heads (RRHs). We employ a practical power consumption model by considering the transmit power, the circuit power, and the backhaul power, in contrast to most of the existing works which focus on colocated antenna systems (CASs), where the backhaul power is negligible. For a given average user rate, we consider the problem of maximizing the EE with respect to the number of antennas of each RRH $n$, the number of RRHs $M$, and the number of users $K$ and study the impact of system parameters on the optimal $n$, $M$, and $K$. Specifically, by applying random matrix theory, we derive the closed-form expressions of the optimal $n$ and find the solution of the optimal $M$ and $K$ under a simplified channel model with maximum ratio transmission. From the results, we find that, to achieve the optimal EE, a large number of antennas is needed for a given user rate and PC. As the number of users increases, EE can be improved further by having more RRHs and antennas. Moreover, if the backhauling power is not large, a massive DAS can be more energy efficient than a massive CAS. These insights provide a useful guide to the practical deployment of massive DASs. [ABSTRACT FROM PUBLISHER]

In this paper, we consider unicast/multicast multicell cooperative transmission with interference among users/user groups. In this context, we derive the optimal minimum variance distortionless response (MVDR)-based successive minimum variance beamforming (SMVB) scheme that achieves a superior sum-rate performance compared with the block diagonalization scheme. Subsequently, we derive an optimal joint power allocation and broadcast beamforming scheme for multicell cooperative broadcast transmission for a pooled power constraint at the base stations. This scheme is extended to include per base station power constraints by formulating it as a relaxed semi-definite program (SDP). We also consider the multicell cooperative uplink scenario and derive a successive multiuser (MU) uplink beamforming (SMUB) scheme that maximizes the signal-to-interference-plus-noise ratio (SINR) of each user. Next, we consider imperfect channel state information (CSI) and derive a robust beamforming scheme for the downlink, based on minimizing the worst-case interference by formulating it as a second-order cone program. It is demonstrated that the corresponding robust beamformer for the uplink transmission can be derived by employing the multidimensional covariance fitting approach. Simulation results are presented to demonstrate the superior sum-rate performance of the proposed multicell transmission schemes. The performance is also compared with several bounds for cooperative multicell scenarios. [ABSTRACT FROM AUTHOR]

In this paper, an in-band full-duplex based two-way cooperative (TWC) scheme is presented where, both downlink and uplink transmissions by two users are accommodated in two phases. We consider a system when a node can be a relay with its own communication requirements. A relay user receives far user's downlink data from a base station (BS) and uplink data from a far user, and can transmit its own uplink data to BS in phase 1. Then, the relay user delivers far user's data by decode-and-forward strategy through exclusive OR operation, and receives its own downlink data from BS in phase 2. Considering the traffic features of delay-sensitive uplink and high rate downlink, we adopt a power allocation with high-priority uplink transmission and opportunistic downlink transmission. Analysis on outage probability and ergodic rate is provided and validated by Monte Carlo simulations. It is demonstrated that TWC scheme outperforms one-way cooperative non-orthogonal multiple access scheme in terms of ergodic rate and uplink outage probability under reasonable self-interference cancellation capability. [ABSTRACT FROM AUTHOR]

In full-duplex cloud radio access network systems, the uplink received signal of each remote radio head (RRH) contains downlink-to-uplink (D2U) interference signal which is a linear combination of the transmit signals of nearby RRHs including itself. Since the fronthaul links that connect RRHs to a baseband processing unit (BBU) have finite capacity, the RRHs forward quantized versions of the uplink received signals to the BBU. To improve the fidelity of the quantization, it is important to suppress the impact of the D2U interference signals prior to the quantization. This paper tackles the problem of jointly optimizing the D2U interference suppression and fronthaul quantization strategies with the goal of maximizing the sum rate of uplink user equipments. To tackle the formulated non-convex problem, we derive an iterative algorithm based on the successive convex approximation approach. To save the complexity, a simpler algorithm, which non-iteratively pre-fixes the D2U interference suppression matrices, is also proposed. Extensive numerical results confirm the advantages of the proposed schemes compared to conventional schemes. [ABSTRACT FROM AUTHOR]

In this paper, we study a network information flow problem for cellular multiuser two-way relay networks (MU-TWRNs) where uplink and downlink messages are exchanged through a multiantenna relay node using two-way relaying. Both single- and two-cell scenarios are investigated. In particular, for the two-cell scenario, we consider two schemes with and without base station (BS) cooperation, respectively. By comparing the degrees-of-freedom (DOF) upper bounds obtained via cut-set theory, we derive the feasibility conditions to achieve the optimal DOF for all the schemes. These DOF bounds are shown to be achieved by suitably applying some physical-layer signaling techniques, such as physical-layer network coding, signal alignment, block diagonalization, and the newly proposed successive interference nulling. By comparing one-way relaying in terms of the normalized DOF, we observe that the proposed two-way-relaying-based scheme can double the performance with symmetric antenna configurations; however, the gain is reduced under unbalanced antenna configurations. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the resource allocation problem in two-tier heterogenous networks (HetNets) with massive MIMO, where two frequency bands, cellular frequency band and millimeter wave frequency band, are used for wireless backhaul links. To coordinate the interference among small cells (SCs), SCs are grouped into multiple SC clusters (SCCs), where SC users are jointly served by SC base stations (BSs) (SBSs) belonging to the same SCC. To eliminate the multi-user and inter-tier interference, we propose a block diagonalization based precoding scheme at macro-BS and each SCC, where the transmit precoding matrix for users is projected onto the null space of interference channels. Following this, we formulate a power allocation optimization problem to maximize the downlink sum rate of the system subject to per-SCC power and users’ quality of service requirements. Since the formulated problem is nonconvex, we transform it into a convex one by appropriate approximation, and a constrained concave convex procedure based iterative algorithm is proposed to obtain the solution. Furthermore, we prove that the obtained solution converges to the local optimum. Meanwhile, according to the structure of the original formulated problem, we divide it into multiple subproblems and propose an optimal iterative water-filling algorithm. Next, we extend the original problem with per-SBS power constraint, which results in that the precoding of each SCC has to be redesigned. On this basis, we propose an iterative water-filling algorithm to obtain the optimal power allocation and precoding. Numerical results are presented to verify the performance of our proposed algorithms. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the interference alignment (IA) for the multiple-input–multiple-output (MIMO) multicell downlink networks in the context of a square channel matrix. We propose a novel joint user grouping and base station (BS) association algorithm. Furthermore, we design the transmit and receive beamforming matrices in closed forms by using a generalized eigenvalue decomposition (GEVD)-based IA scheme, which can exploit the special structure of a square channel matrix against the existing algorithm. Moreover, we provide three theorems to characterize the maximum achievable degrees of freedom (DoF) of the proposed GEVD-based IA scheme. Compared with the existing IA scheme, the proposed GEVD-based IA scheme can reduce the dimension of subspace occupied by the intercell interference (ICI) more efficiently, hence providing achievable DoF higher than or equal to that of the existing IA scheme. [ABSTRACT FROM AUTHOR]

As a benefit of sophisticated interference cancelation techniques, full-duplex (FD) transceiver design may become feasible, even possibly on the aggressive time-scale of fifth-generation (5G) wireless communication systems. Hence, we further develop the recent bidirectional relaying [i.e., the two-way half-duplex (HD) relaying] aided cooperative network to its more radical counterpart, which entirely consists of FD entities for the sake of adapting to emerging FD communication scenarios. In more detail, the proposed bidirectional relaying-aided FD network operates in a decode-and-forward (DF) style and exploits the advanced network coding (NC) concept. We analyze its achievable error-free data rate, where the effects of both the self-interference (SI) and of the geographic location of the relay node (RN) are evaluated. Furthermore, the potential variations of the networking scenario are also taken into account. Based on this theoretical analysis, the optimum rate allocation scheme maximizing the system's error-free data rate is found. Our results demonstrate that a significant spectral efficiency gain is achieved by the proposed system. [ABSTRACT FROM PUBLISHER]