A Distributed Resource Allocation Scheme for Self-Backhauled Full-Duplex Small Cell Networks

Hybrid duplex wireless networks, use half duplex (HD) as well as full duplex (FD) modes to utilize the advantages of both technologies. This paper tries to determine the proportion of the network nodes that should be in HD or FD modes in such networks, to maximize the overall throughput of all FD and HD nodes. Here, by assuming imperfect self-interference cancellation (SIC) and using ALOHA protocol, the local optimum densities of FD, HD and idle nodes are obtained in a given time slot, using Karush–Kuhn–Tucker (KKT) conditions as well as stochastic geometry tool. We also obtain the sub-optimal value of the signal-to-interference ratio (SIR) threshold constrained by fixed node densities, using the steepest descent method in order to maximize the network throughput. The results show that in such networks, the proposed hybrid duplex mode selection scheme improves the level of throughput. The results also indicate the effect of imperfect SIC on reducing the throughput. Moreover, it is demonstrated that by choosing an optimal SIR threshold for mode selection process, the achievable throughput in such networks can increase by around 5%.

In this paper, we investigate the user scheduling and power allocation scheme for a millimeter wave non-orthogonal multiple access system. To reduce the feedback overhead, random beamforming is adopted at a base station. The optimization problem is formulated to maximize the energy efficiency. To solve this problem, we first address the user scheduling and power allocation problem separately, then an iterative algorithm is proposed to jointly optimize the user scheduling and power allocation. Simulation results show that the proposed scheme achieves higher energy efficiency than the conventional scheme.

Small cell, mmWave, and massive Multi-Input Multi-Output (MIMO) technologies in 5G cellular networks becomes inevitable trend caused by killer applications such as holographic video which is traffic-intensive. In this paper, we study a sequential activation beam selection, user scheduling, and power allocation problem in a mmWave network with massive MIMO utilizing a physical layer preceding technique. We aim to maximize the time-averaged utility of users with a time-averaged transmit power constraint on top of the EdgeSON architecture, which takes advantage of both centralized and distributed characteristics. We decompose the original long-term problem into two-time scales in which solving the problem of choosing beam pattern is run at a slower time scale than solving user scheduling and power allocation. Then, to solve user scheduling and power allocation, we leverage the Lyapunov drift-plus-penalty framework which transforms an original long-term average problem into per-slot modified sub-problems. Since provided per-slot problem to find a set of user scheduling and power allocation is known as NP-hard, we propose a low-complex and practical interference management algorithm, namely CRIM, by introducing two critical users with the highest interference channel gain in intra-BS and inter-BS respectively. Finally, via extensive simulations, we verify and compare the performance of the proposed algorithm and comparing algorithms in a real mmWave network environment.

As explained in many chapters of this book, relaying in principle means indirect data transmission from a source node to a destination node via intermediate relay nodes (RNs), e.g., not so unlike repeaters, gap-fillers, or signal boosters do in old-fashioned wireless systems. On the other hand, the field of information theory has addressed many classical questions related to the performance of idealistic relay links. Relay transceivers in these original research areas conventionally operate in a full-duplex (FD) mode, while later studies on cooperative communication deemed it impossible to begin with and focused almost invariably on half-duplex (HD) relaying. However, modern relay transceivers such as those assumed in the context of this chapter are much more advanced than simple analog amplifiers in terms of their processing capabilities so that, e.g., they can be made robust to interference. Time has thus become right for us to return to the origins of relaying by promoting FD operation as a practical and highly efficient design choice whose technical difficulties can be now overcome. With this background, this chapter provides an overview of essential aspects to be considered when introducing FD operation into relaying systems. Two particular contributions are central for this development, namely introducing transmit power control for FD relaying and comparing the performance of FD relay links to that of their HD counterparts. The main focus herein is on infrastructure relaying although the considered systems have their relatives with cable-connected distributed antennas and mobile relays instead. Thus, the considered relay transceivers are fixed nodes and belong to infrastructure deployed by a network operator. This scope choice differs from earlier mainstream literature which is inclined toward ad hoc mobile relaying by user terminals. When discussing cellular systems, the link elements may be referred to as a base station (BS), a RN, and a user equipment (UE). The BS and RNs form a “backhaul link” while UEs are always connected to a “service link”. There is typically only one relay per each group of destinations (except for special hand-over situations) while backhaul links may involve multihop relaying. Furthermore, the study is formulated in an implicit context to concern a single subcarrier within orthogonal frequency-division multiplexing (OFDM) transmission.

With the recent advances in radio modules capable of carrying out full duplex (FD) communication, the spectrum efficiency promised by the concept of Cognitive radio (CR) can be stretched even further by incorporating full duplex transceivers in CRs. This incorporation brings about certain challenges in the resource allocation. In this work we try to address some of the challenges in joint channel and power allocation. We proposed a decentralized scheme which is capable of selecting which channels to be used as half duplex and which to be used as FD between a pair of CRs. Then we decomposed the problem into two sub-problems one dealing with channel assignment and the other dealing with power allocation. In the power allocation we did not assume the signal to interference plus noise ratio to be high like most work in the literature. The monotonic optimization framework was used to solve the power allocation problem. Then the channel assignment problem was approximated by a linear objective function and was solved as a linear integer program.

Full-duplex (FD) is a principle in which a transceiver can receive and transmit on the same time-frequency radio resource. Assuming perfect self-interference cancellation (self-IC), FD can potentially double the spectral efficiency (SE) of a given point-to-point communication. However in cellular networks, we may be far from this upper bound due to base stations (BSs) and users interference. In particular, even if the overall SE is improved, the uplink (UL) performance is degraded compared to a traditional half-duplex (HD) system. In this paper, we propose and evaluate a new duplex-switching (DS) policy in which BSs can adopt FD- or HD-mode according to the position of their scheduled users. This system is analyzed using stochastic geometry in terms of average SE (ASE) and signal-to-interference-plus-noise ratio (SINR). The proposed scheme allows to trade-off the downlink (DL) for the UL performance when comparing to a FD scenario. In terms of cell performance (UL+DL), our DS policy even outperform both HD and FD systems when the parameters are optimized.

Full-duplex (FD) transmission holds a great potential of improving the sum data rate of wireless communication systems. However, the self-interference introduced by the full-duplex transmitter brings a big challenge to enhance the energy efficiency. This paper investigates the power allocation problem in a full-duplex two-way (FDTW) communication network over an OFDM channel, aiming at improving the sum data rate and energy efficiency. We first characterize the sum rate and energy efficiency achieved in a single-carrier FDTW system. The optimal transmit power that achieves the maximal sum data rate is presented. The energy efficiency maximization problem is solved by using fractional programming. Then we further formulate sum rate and energy efficiency maximization problem in a multi-subcarrier FDTW system. In particular, the sub-optimal transmit power allocation which achieves a decent sum rate improvement is found by using a proposed iterative algorithm. By combining the iterative algorithm and fractional programming, we further maximize the energy efficiency of the multi-subcarrier system. With our proposed algorithm, we can easily obtain an optimal transmit power that approximates the global optimal solution. Simulation results show that using the obtained optimal transmit power allocation algorithm can significantly improve the sum rate and energy efficiency in both single-carrier and multi-subcarrier systems.

In heterogeneous cellular networks (HCNs), the growing demand of small cell data traffic puts great pressure on the capacity limited backhaul links. Resource allocation is an efficient approach to mitigate the severe interference and improve the network performance in HCNs. However, differentiated backhaul capacity constraints introduce the inherent nonconvexity to the resource optimization problem, which hinders the development of the optimal solutions. In this article, we investigate the joint resource block (RB) and power allocation problem under two different backhaul capacity limitations. First, we consider the small cell backhaul limitation scenario where the backhaul capacity constraint is imposed on each small cell. Then, we extend the resource optimization to the macrocell base station backhaul limitation scenario which considers the overall backhaul capacity constraint on the whole small cell network. Besides, the quality of service (QoS) requirements of users and the cross‐tier interference mitigation are also considered. This resource allocation problem is formulated as a nonconvex mixed‐integer nonlinear programming (MINLP) problem. By variable substitution and constraints relaxation, we convert the original optimization problem into a convex one and obtain the optimal solutions. Accordingly, joint RB and power allocation algorithms are proposed. Numerical results verify the effectiveness of the proposed algorithms and evaluate the impact of different types of backhaul capacity limitations on system performance.

In this paper, we propose an optimal time and power allocation scheme in a wireless power supply full-duplex (FD) relay system, where we consider the number of relay antennas in the energy harvesting stage. At the same time, the energy efficiency optimization problem of the system is structured, where optimization issues related to time allocation factors and power allocation are established. For the FD dual-antenna and the FD single-antenna energy harvesting system, energy efficiency function is proven to be a concave function over the time-switch factor, and the optimal time-switching factor is theoretically obtained using the Lambert function. Then, according to the given value range of the optimal time switching factor, the optimal power distribution scheme is obtained by analyzing the derivative function of the system energy efficiency and using the properties of the Lambert function. The time-switching factor and transmission power are optimally selected at the wireless power supply FD relay. Results reveal that the performance of energy efficiency of the dual-antenna energy harvesting at the FD relay outperforms that of the single-antenna. Moreover, our results demonstrate that FD relay systems always substantially boost the energy efficiency compared with half-duplex (HD) relay systems.

With the advances of green energy technologies, clean and sustainable energy sources have been considered as alternative energy sources for powering cellular networks. However, it is very challenging to exploit the charged energy to satisfy the QoS demands of wireless multimedia services due to the dynamics in the energy charging and discharging processes. In this article, we study how to efficiently utilize the green energy supply to fulfill the QoS requirements of multimedia services in a cellular network. Specifically, we study network deployment and power allocation of small cell BSs in a two-tier cellular network in support of high-rate multimedia services. Our objective is to maximize the transmission efficiency while ensuring energy sustainability in green cellular networks powered by green energy sources. For network deployment, we aim to deploy the minimum number of small cell BSs to meet the high throughput demands of multimedia services and statistically guarantee energy sustainability of wireless networks. In addition, a power allocation scheme with cooperative communication is presented to maximize throughput. It is shown that the network sustainability and throughput of green cellular networks can be significantly improved by using the proposed BS placement and power allocation schemes.

Moving contents proximity to the network edge and proactively caching popular contents at multiple infrastructures are promising directions for solving the backhaul congestion problem. This letter proposes and evaluates a multi-level cache-enabled network, where cache-hit users can fetch their data from the available cache at either small base-stations, unmanned aerial vehicles, or cache-enabled mobile device-to-device users. Cache-miss users, on the other hand, fetch their data from the central cloud via limited capacity backhaul links. This letter considers the problem of maximizing the network weighted-sum rate by jointly determining the users’ mode of operation and their transmit powers, subject to backhaul capacity and transmit power constraints. After showing how the association problem can be formulated as a generalized assignment problem, the letter solves the transmit power problem using an iterative function evaluation apprach. The resulting mode-selection and power-allocation (MSPA) iterative algorithm is then tested through numerical simulations, which suggest that, while being easily implementable, the proposed multi-level caching can substantially relieve the backhaul congestion, especially in dense-networks, and at low-backhaul capacity regimes.

User scheduling and power allocation for downlink multi-cell multi-carrier NOMA systems

Device-to-device (D2D) communications and full-duplex (FD) communications, which can improve the spectrum efficiency (SE) of mobile communications, have received much attention. To further improve the SE, some researchers have begun to integrate FD into D2D communications, which will generate more transmission modes. Since different modes have different advantages and disadvantages, the mode selection problem needs further study. In this paper, we investigate the mode selection problem for FD-enabled two-way D2D communications to improve the SE. Four transmission modes, i.e., FD underlay mode, half-duplex (HD) underlay mode, FD overlay mode and HD overlay mode, are considered. For each mode, we maximize the system SE while fulfilling the minimum rate requirements and maximum transmit power constraints for both cellular and D2D users. For FD underlay mode, the optimization problem can be transformed into a difference of convex functions (D.C.) programming and the concave-convex procedure (CCCP) algorithm can solve the problem efficiently. For HD underlay mode and FD overlay mode, we can use search plus CCCP algorithm to solve the optimization problem. For HD overlay mode, we only need to search for the optimal solution. After obtaining the maximum SE of four modes, we can select the maximum one as the optimal mode. Numerical results are presented to illustrate the effects of the channel gains and self-interference cancellation ability on the maximum SE of four modes and the transmission mode selection.

This paper focuses on multi-user full-duplex (FD) systems. When multiple users share the same resources, using FD degrades the sum capacity compared to using half-duplex (HD) because of the inter-user interference (IUI) that arises between two FD users. This factor highlights the need for a good strategy for switching between FD and HD modes. We address this first by considering a two-user case and deriving the sum capacities. We then consider the general case of K users and compare the average sum capacities for all-FD mode, all-HD mode and the optimal mode case.

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