Sum Power Minimization for Cellular Systems With Underlay D2D Communications

Abstract-The paper studies a scheme that jointly considers beamforming based MU-MIMO and NOMA in a downlink cellular network with underlaid D2D users. Two different MU-MIMO beamforming schemes are developed. The first beamforming scheme aims to eliminate the interference caused by different beams while the second one aims to cancel out the interference from base stations to D2D users. An optimization problem is formulated to maximize the total system sum throughput of both cellular users and D2D users. Since the optimization problem is NP hard and difficult to solve, we develop a suboptimal sequential solution by determining the zero-forcing beamforming matrix for MU-MIMO first. Then a user grouping and optimal power allocation algorithm is proposed in order to maximize the capacity of cellular users in each beam. Simulation results show that MUMIMO beamforming, NOMA and D2D together will significantly improve the overall system throughput.

<p>Device-to-device (D2D) communication can effectively use cognitive radio network approach to coexist with cellular users. For such a cognitive D2D system, two approaches (underlay and overlay) are considered to manage the spectrum sharing among the cellular (primary) users and the D2D (secondary) users. Energy efficiency (EE) is crucial in both these cases due to limited battery capacity and quality of service requirements of the D2D users. This study effectively models the power allocation problem of such a cognitive D2D system by maximising the EE of the D2D users subject to a minimum rate requirement for both the D2D users and the cellular users. This leads to a non-linear fractional optimisation problem which is more complicated and computationally intractable. Alternatively, geometric water-filling approach have been utilised for power allocation to solve this optimisation problem which results in an ‘exact’ and ‘low complexity’ solution. Simulation results reveal the benefits of the proposed algorithm.</p> <p><br></p>

This paper proposes orthogonal frequency division multiple access (OFDMA) based multiuser hybrid cooperative- D2D (C-D2D) communication system with the best user selection. In the proposed model, the listen-before-talk (LBT) algorithm with an energy detection method has been used to check the WiFi spectrum availability. Based on the spectrum availability, the system adapts to any one of the two modes, namely in-band C- D2D or out-band C-D2D. Further, the best user selection scheme is applied to a system wherein multiple D2D users coexist with a cellular user in the same cell. In particular, among the M available D2D pairs, selected D2D user helps the cellular user by relaying D out of N subcarriers to the base station (BS). Based on the availability of Wi-Fi, either N-D subcarriers of the cellular spectrum or N subcarriers of the Wi-Fi spectrum will be shared among M D2D users for D2D transmission. Closedform expressions of outage probability for cellular and D2D users are derived. Results show that the proposed hybrid C-D2D communication system with the best user selection outperforms the conventional C-D2D framework.

Device-to-Device (D2D) communication has recently emerged as a promising technology to improve the capacity and coverage of cellular systems. To successfully implement D2D communications underlaying a cellular network, resource allocation for D2D links plays a critical role. While most of prior resource allocation mechanisms for D2D communications have focused on interference within a single-cell system, this paper investigates the resource allocation problem for a multicell cellular network in which a D2D link reuses available spectrum resources of multiple cells. A repeated game theoretic approach is proposed to address the problem. In this game, the base stations (BSs) act as players that compete for resource supply of D2D, and the utility of each player is formulated as revenue collected from both cellular and D2D users using resources. Extensive simulations are conducted to verify the proposed approach and the results show that it can considerably enhance the system performance in terms of sum rate and sum rate gain.

Device-to-device (D2D) communication exploits the proximity between two devices to enhance the overall spectrum utilization of a crowded cellular network. Two conventional frameworks that are generally used to realize a D2D communication are underlay D2D (U-D2D) and cooperative D2D (C-D2D) communications. Both frameworks have their own merits and demerits in terms of interference management, implementation complexity, and achievable spectral efficiency (SE). For instance, the performance of U-D2D is limited by the amount of interference from the D2D to the cellular user (CU), whereas for C-D2D the performance suffers due to a division of transmission into two orthogonal time phases. In this paper, we propose two novel extensions of conventional D2D communication frameworks, which alleviate their drawbacks and also improves the performance of the overall cellular network. The first proposed framework is an adaptive interference aware U-D2D communication framework. Through this framework, the CU can be protected from the excessive interference of the D2D transmitter (DT), thus maintaining the desired quality of service at CU. The second proposed framework is an adaptive C-D2D communication framework. This framework employs adaptive modulation and coding and bit error rate-based selection and combining to enhance the performance of cellular and D2D users. As a proof-of-concept demonstration and performance assessment, both the frameworks have been implemented on a National Instruments Universal Software Radio Peripheral platform. The measurement results and on-field trials show that the proposed frameworks improve the bit error rate (BER) and the SE of the overall system. Results also interpret that the adaptive C-D2D outperforms the adaptive interference aware U-D2D in terms of BER and SE.

Recently, device-to-device (D2D) communication and full duplex communication are both considered key technologies for 5G networks. In this paper, two novel cooperative modes are developed for full duplex D2D communication underlaying cellular networks: the network MU-MIMO based mode (N-mode) and the sequential forwarding mode (S-mode). In the N-mode, two D2D users work as network MIMO to forward the data to cellular users and thus leverage the channel diversity. In the S-mode, the spatial distribution of D2D users and cellular users is explored to improve the transmission rate. Based on these modes, two D2D users share the downlink resources with two nearby cellular users simultaneously to achieve both proximity gain and reuse gain. Moreover, these modes are well suited for edge cellular users. To optimize the performance of the two modes, optimal power allocation is conducted by considering the influence of residual self-interference at full duplex radios and the requirements of the minimum transmission rate for both cellular users and D2D users. Simulation results show that, compared with the dedicated mode, the sum rate of cooperative modes in the perfect self-interference cancellation case can achieve 32% overall improvement and about 70% improvement in the scenario with non-edge D2D users and edge cellular users. With residual self-interference at a full duplex radio, the overall performance improvement is reduced to 15%. However, the cooperative modes can still achieve 40% improvement in the scenario with non-edge D2D users and edge cellular users.

Throughput maximization in multi-slice cooperative NOMA-based system with underlay D2D communications

Device-to-device (D2D) communications allows two adjacent mobile terminals transmit signal directly without going through base stations, which has been considered as one of the key technologies for future mobile networks. As full-duplex (FD) communications can improve the performance (i.e., throughput, energy efficiency (EE)) of communications systems, it is commonly used in practical D2D communications scenarios. However, FD-enabled D2D communications also results in self-interference. To fully realize the potential benefits of FD-enabled D2D communications, an effective resource allocation mechanism is critical to avoid not only the self-interference of FD-enabled D2D communications but also the interference between D2D users (DUs) and cellular users (CUs). In this paper, we investigate the resource allocation issue for FD-enabled DUs and traditional CUs. Considering the asymmetry of energy and spectrum resources of DUs and CUs, we propose a power-spectrum trading mechanism to achieve mutual benefits for both types of users. A concave-convex procedure algorithm is employed to solve the optimization problem of power allocation, and then a maximum weighted bipartite matching based method is proposed to select proper D2D pairs to maximize the overall system throughput. Numerical results show that the proposed scheme can remarkably improve the overall throughput and EE of FD-enabled D2D communications system.

Device-to-device (D2D) underlay networks enable high data rates and low end-to-end delay and improve spectral/energy efficiency and offload cellular traffic. However, D2D communication also results in interference between CUs and D2D terminals, negatively impacting capacity. Is there a critical set of system parameters (density of D2D users (DUs), cellular base stations (BSs), transmit power, etc.) that can ensure that the benefits of D2D underlay operation can outweigh its drawbacks? We seek to address this fundamental question in the context of the tradeoff between ergodic capacity and power consumption. Toward this end, we first quantify the ergodic capacity metric for a realistic network where D2D pairs are spaced randomly and experience Rician fading. Based on a stochastic-geometry-based network model, we derive, for the first time, closed-form results for ergodic capacity of both cellular users (CUs) and DUs. Second, we identify the D2D user density and transmit power that maximizes the ergodic capacity of the network. Specifically, a two-stage scheme is proposed to optimize ergodic capacity while minimizing overall power consumption. The results from this analysis provide a framework to uncover desirable system design parameters that offer the best gains in terms of capacity.

Device to device (D2D) communication technology is widely considered in 5G for providing higher data rates and increase network capacity. The performance benefits of D2D communication are best achieved if it takes place in shared mode in which it reuses the spectrum being utilized by conventional cellular users. This induces significant challenges in allocating resources because of severe interference among D2D and cellular users. Moreover, centralized resource allocation techniques proposed in literature for D2D users can no longer be practical in dense heterogeneous networks considered for 5G. In this paper, we present a distributed learning based spectrum allocation scheme in which D2D users learn the environment and autonomously select spectrum resources to maximize their Throughput and Spectral Efficiency (SE) while caus- ing minimum interference to the cellular users. We have employed distributed learning in a stochastic geometry based realistic network. Our evaluation results show that the employed learning scheme enables users to achieve high Throughput and Spectral Efficiency while meeting QoS requirements of macro and femto tier.

In this paper we investigate the effect of interference caused by in-band full-duplex radios in device-to-device communication (D2D). While using full-duplex radios in D2D, both users transmit, compared to half-duplex D2D in which one user transmits. This is going to cause more interference in underlay D2D communication since D2D link operates on the same radio resource blocks as cellular users. We consider uplink radio resource reuse of cellular users by D2D communication, and try to maximize the number of possible D2D links constrained to the interference on the cellular user. The number of D2D pairs that can be active in the full-duplex mode is smaller than in the half-duplex mode due to more interference from transmissions of both D2D nodes. We compare the total rate of half-duplex and full-duplex modes and evaluate the benefits of full-duplex radios.

The coverage probability of both the cellular users and the Device-to-Device (D2D) users are analyzed. We assume that the cellular users are able to communication with the Base Station (BS) either by relying on the assistance of Full-Duplex (FD) mode relays or via direct user-to-BS links with high-enough Signal-to-Interference-plus-Noise-Ratio (SINR). Note that the FD-mode devices are capable of simultaneously operating in two modes, i.e. the D2D mode and the cooperative relay mode, with the sum power consumption at these devices kept constant. The closed-form expressions for coverage probability of both tier users are derived. After that, numerical analyses are provided, showing that the coverage probability of the both the cellular and the D2D users can be substantially influenced by a variety of parameters, including the power allocation factor of the relays, the density of users, and the self-interference imposed on the FD mode relays, etc. Furthermore, in the D2D enabled networks, it is shown that the FD relay aided transmission is beneficial to enhancing the coverage probability of the cellular users if the target SINR is lower than 5 dB.

Device‐to‐device (D2D) technology is a promising communication paradigm that enables direct communication between spatially close devices. The D2D technology is very appealing from the standpoint of efficient spatial reuse of resources since it permits to establish communications in networks with higher density of users. Consequently, the introduction of D2D will lead to network performance improvement in terms of spectral and energy efficiency, power consumption, delay reduction, as well as coverage extension. However, implementing D2D technology in 5G networks comes with a set of technical challenges, mainly due to interferences incurred between D2D links and between D2D and cellular users. This article provides a survey of the main interference management frameworks in D2D network in general and underlay D2D communication, in particular. Interference management‐based frameworks can be divided into two main categories: (i) power control and resource management schemes and (ii) advanced physical layer schemes, such as interference cancellation, interference alignment, and multiantenna systems. We provide a brief description of the main studies for the aforementioned categories and discuss the main results.

The performance of device-to-device (D2D) communication in a cellular network depends on the resource sharing between D2D links and cellular users. Existing researches on resource sharing mainly focus on power control between the D2D users and cellular users that operate in the same frequency band. However, the D2D outage probability performance is hampered by the cellular interference to D2D links. Therefore, the D2D users may not achieve satisfactory SINR performance when D2D users and cellular users are geographically located in a small area; as a result, the outage probability performance would be significantly degraded. In this paper, we provide a novel resource sharing strategy to mitigate the interference from cellular users to D2D receivers by utilizing the low energy characteristics of signals in the guard band and analyze the D2D outage probability performance mathematically. Both the mathematical analysis and numerical results show that the proposed resource sharing strategy provides 1.2 dB SNR gain in D2D outage probability performance while guaranteeing the cellular throughputs.

Cellular based M2M systems generate massive number of access requests which create congestion in the cellular network. The contention-based random access procedures are designed for cellular networks which cannot accommodate a large number of M2M traffic. Moreover, M2M systems share same radio resources with cellular users. Resource allocation problem becomes a challenging issue in cellular M2M systems. In this thesis, we address these two problems by analyzing a contention-based slotted Aloha random access procedure for M2M networks using different performance metrics. The impact of massive M2M traffic over cellular traffic is studied based on different arrival rate, random access opportunity and throughput. An analytical model of selecting a base station (eNB) along with load balancing is developed. Finally, two methods have been presented and evaluated with M2M traffic. First one is dynamic access class barring method which controls RAN level congestion by selecting an appropriate eNB and applying load balancing method. Second one is relay-assisted radio resource allocation method which maximizes the sum throughput of the system by utilizing the available radio resource blocks and relay nodes to the MTC systems. Numerical results show that frame transmission rate influences the selection probability of the base stations. Moreover, the dynamic access class barring parameter along with frame transmission rate improve the overall throughput and access success probability among base stations as well as avoid overload situation in a particular base station.