D2D User Density Research Articles

Rate analysis of ZF receiver for uplink cell-free massive MIMO systems with D2D communications

This paper proposes a transmission structure of zero forcing (ZF) receiver for uplink cell-free massive multiple-input multiple-output (MIMO) systems with device-to-device (D2D) communications, followed by a rate analysis. We assumed that D2D users (DUEs) can utilize orthogonal radio resources to improve the efficiency of the scarce utilization or repurpose the time–frequency-spectrum resources currently used by the cell-free users (CFUEs). Assuming that the imperfect channel state information (CSI) is realizable, after that, the use-and-forget bounding technique is then used to respectively obtain the closed-form expressions of the CFUEs and DUEs, which provide the lower bounds on the ergodic approximate realizable rate of both communication links. First, we calculate the minimum-mean-square error (MMSE) estimation for all channels. Then, the derived results of the achievable uplink sum rate provide us with a tool that enables us to explain how some important parameters, such as the number of access points (APs)/CFUEs, each AP/CFUE/antenna, and the density of DUEs, affect system performance, highlighting the significance of cooperation between cell-free massive MIMO and D2D communication.

Analysis of D2D-Aided Underlaying Uplink Cellular Networks Using Poisson Hole Process

As one of the key technologies in 5th generation mobile networks, device-to-device (D2D) communication technology can significantly improve spectrum utilization, throughput and energy efficiency as well as reduce congestion in the networks. However, due to the spectrum sharing between D2D users (DUs) and cellular users (CUs), it may also cause serious interferences. In this paper, we adopt appropriate stochastic geometric tools to model and analyze the mutual interferences, based on which the coverage probabilities of different users are derived to evaluate the network performance. Specifically, we model the locations of CUs as a Poisson point process (PPP), while the locations of DUs are modelled as a Poisson hole process (PHP), which is driven by the PPP of CUs’ locations due to the exclusion between the positions of CUs and DUs. Furthermore, the approximated expressions of user coverage probabilities are obtained by two methods, which are consistent with the simulation results. The first method is to dissolve the hole, and the second method is to approximate the PHP through a thinned PPP. In addition, the user ergodic data rates and the sum data rate of the networks are also derived through the second approach. The impacts of key parameters (such as the density of DUs and the size of the warning radius) on the ergodic rates and sum data rate are analyzed.

Interference-aware channel assignment and power allocation for device-to-device communication underlaying cellular network

Device-to-device (D2D) communication is a promising technology in 5G new radio (NR) interface to improve the system performance in terms of high data rate, low latency, coverage extension, traffic offloading, and higher spectrum and energy efficiency. In this study, channel assignment and power allocation techniques for D2D communication underlaying cellular network are proposed, those in turn, lead to a spectrum-efficient system. Firstly, the channel assignment problem is solved by employing channel-characteristics of target link and interference links. Then the power allocation problem is solved by allocating the optimal power to the D2D transmitters with allowable interference. This optimal power allocation approach allows multiple D2D communications to reuse the available cellular uplink resources. Numerical results demonstrate significant throughput gains for D2D communication for different transmission and interference power settings. Network throughput comparison with other existing approaches is provided to confirm the efficacy of the proposed approach. In addition, energy efficiency analysis is carried out by considering D2D transmission power, circuit power consumption, D2D link distance, and D2D user density.

Outage and ASE Analyses for Power Controlled D2D Communication

In fifth-generation technology, device-to-device (D2D) communication underlaid with a cellular network provides a feasible solution for proximity-based wireless applications and services. D2D communication allows a direct connection between two devices without traversing through the base station. It can potentially reduce the data traffic in the cellular networks with improved spectral and energy efficiency. However, interference management is a primary concern when D2D links utilize the same resources occupied by cellular users. In this paper, we propose a location-based power control approach to mitigate the severe interference components for underlaying D2D communication cellular network for multicell scenario. Moreover, outage analysis for the cellular user as well as D2D user is carried out by using the tools from stochastic geometry. Outage performance is further improved by employing a cooperation approach that also enables D2D user's power saving. Further, area spectral efficiency (ASE) analysis is performed using the proposed power control and cooperation approach for the overall system model. We obtain the optimal D2D user density to maximize the ASE. Finally, the numerical results are presented to validate the analytic observations of the proposed framework.

Study on the User Density Identification via Improved Whale Optimization Algorithm in Device‐to‐Device Communication

The present study proposes a new algorithm for device‐to‐device (D2D) user density identification in a 5G network based on resource allocation. The method initially established a multiobjective optimization function that calculates system throughput and quality of service (QoS) of D2D users. The optimal resource allocation result of the multiobjective function is obtained via the improved whale optimization algorithm (IWOA). System throughput after resource allocation exhibits a linear relationship with the number of users. Therefore, the D2D user density areas are accurately identified via the throughput value. The simulation result reveals that the accuracy of D2D user density identification reaches 95%.

Coverage and capacity analysis of relay-based device-to-device communications underlaid cellular networks

Coverage and capacity are the key parameters of 4G and beyond wireless networks. These parameters of Long Term Evolution Advanced (LTE-A) networks can be greatly enhanced by enabling device-to-device (D2D) communication. In this paper, full duplex amplify and forward (FDAF) relay nodes (RNs) have been introduced to assisting cellular and D2D communications. The coverage probability (CP) and transmission capacity (TC) for both the cellular and D2D communications have been analyzed with FDAF relay based network. The D2D users can communicate directly or via relaying with FDAF RNs. Cellular users, D2D users and RNs in the network have been modeled using homogeneous spatial poisson point process (SPPP). The closed-form expressions of CP and TC for cellular as well as D2D communications have been derived by using stochastic geometry. The pairing of D2D users is decided by the shortest distance reduced path loss and formed pair either directly or via RN assistance. The approximate complementary cumulative distribution function (CCDF) of the signal to interference plus noise ratio (SINR) for both the cellular users and the D2D users have been derived. The closed form expressions of CP and TC show that coverage and capacity of both the cellular and D2D communications are influenced by various parameters such as D2D user density, relay node density and the distance of D2D pair. Results show the improvement of CP and TC for cellular and D2D communications with the help of RNs.

Performance maximization of network assisted mobile data offloading with opportunistic Device-to-Device communications

Mobile data traffic inside mobile operator’s infrastructure is increasing exponentially every year. This increasing demand forces mobile network operators (MNOs) to seek for alternative communication methods in order to relieve the traffic load in base stations, especially in highly populated and crowded environments. Network assisted data offload and Device-to-Device(D2D) communications are two prominent methods to help MNOs solve this problem. In this study, a data offload framework is developed that incorporates network assisted multiple attribute decision making (MADM) for best network selection and D2D communications for exploiting user proximity in crowded environments. The performance of the framework is evaluated with simulation results as well as analytic solutions and performance bounds. The simulation results indicate the superiority of incorporating network-based information besides user-based information in offloading decisions and demonstrates the significant benefits of D2D communications when the density of D2D users is properly adjusted. The simulation results depict that up to 168% and 200% increase in user satisfaction and throughput can be achieved under high network load scenarios at optimal D2D density.

Power-Aware Maximization of Ergodic Capacity in D2D Underlay Networks

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.

Energy efficiency and sum rate tradeoffs for massive MIMO systems with underlaid device-to-device communications

In this paper, we investigate the coexistence of two technologies that have been put forward for the fifth generation (5G) of cellular networks, namely, network-assisted device-to-device (D2D) communications and massive MIMO (multiple-input multiple-output). Potential benefits of both technologies are known individually, but the tradeoffs resulting from their coexistence have not been adequately addressed. To this end, we assume that D2D users reuse the downlink resources of cellular networks in an underlay fashion. In addition, multiple antennas at the BS are used in order to obtain precoding gains and simultaneously support multiple cellular users using multiuser or massive MIMO technique. Two metrics are considered, namely the average sum rate (ASR) and energy efficiency (EE). We derive tractable and directly computable expressions and study the tradeoffs between the ASR and EE as functions of the number of BS antennas, the number of cellular users and the density of D2D users within a given coverage area. Our results show that both the ASR and EE behave differently in scenarios with low and high density of D2D users, and that coexistence of underlay D2D communications and massive MIMO is mainly beneficial in low densities of D2D users.

Unmanned Aerial Vehicle With Underlaid Device-to-Device Communications: Performance and Tradeoffs

In this paper, the deployment of an unmanned aerial vehicle (UAV) as a flying base station used to provide on the fly wireless communications to a given geographical area is analyzed. In particular, the co-existence between the UAV, that is transmitting data in the downlink, and an underlaid device-todevice (D2D) communication network is considered. For this model, a tractable analytical framework for the coverage and rate analysis is derived. Two scenarios are considered: a static UAV and a mobile UAV. In the first scenario, the average coverage probability and the system sum-rate for the users in the area are derived as a function of the UAV altitude and the number of D2D users. In the second scenario, using the disk covering problem, the minimum number of stop points that the UAV needs to visit in order to completely cover the area is computed. Furthermore, considering multiple retransmissions for the UAV and D2D users, the overall outage probability of the D2D users is derived. Simulation and analytical results show that, depending on the density of D2D users, optimal values for the UAV altitude exist for which the system sum-rate and the coverage probability are maximized. Moreover, our results also show that, by enabling the UAV to intelligently move over the target area, the total required transmit power of UAV while covering the entire area, is minimized. Finally, in order to provide a full coverage for the area of interest, the tradeoff between the coverage and delay, in terms of the number of stop points, is discussed.

Optimal Mode Selection With Uplink Data Rate Maximization for D2D-Aided Underlaying Cellular Networks

The device-to-device (D2D) communication has been regarded as an effective technique for complementing and enhancing the conventional cellular systems owing to its capability of substantially improving both the spectral and power efficiencies of wireless networks. However, the severe interference imposed on the conventional cellular users (CUs) by the geographically close-by D2D pairs may cause a significant performance erosion in the D2D-aided underlaying cellular networks (CNs). In this paper, performance analysis for the D2D-aided underlaying CNs in terms of throughput is provided. We first derive the closed-form expressions of the coverage probability for both the conventional cellular links and the D2D links, followed by giving out the approximated expressions of the ergodic data rate for both an individual cellular/D2D link and the whole underlaying network. Furthermore, the key parameters (e.g., the density of D2D users (DUs) or CUs, and the average geographical distance between a pair of D2D peers) significantly impacting the channel capacity are adaptively adjusted for maximizing the sum data rate of the proposed underlaying networks. In addition, both theoretical analysis and simulation results reveal the attainability of the maximal throughput by optimizing the critical parameters, such as the density of DUs, provided that the scale factor between the DUs and sum users (i.e., comprising both conventional CUs and DUs) can be effectively balanced subject to the constraints specified in the proposed scheme.

셀룰러 네트워크에서의 대규모 D2D 통신의 실현 가능성 연구

Device-to-device (D2D) 통신은 짧은 전송 거리를 적은 전송 전력으로 인프라를 거치지 않고 직접 통신하여 근거리 서비스를 제공할 수 있는 통신 방법으로 기대되고 있다. 이러한 장점들로 인해, 대규모 D2D 시스템에 대한 수요가 존재할 것이다. D2D 통신 자원이 셀룰러 망에 의해 관리되는 네트워크 지원형 D2D 시스템은 제어 신호를 위한 시그널링 오버헤드 때문에 많은 수의 D2D 기기들을 지원하는 것이 불가능하다. 이런 경우에는 오히려 네트워크 조정을 전혀 하지 않는 것이 하나의 해결책이 될 수 있다. 본 논문에서는 이러한 uncoordinated D2D 시스템을 고려하는데, 이는 많은 수의 D2D 기기들이 대규모로 배치되어 네트워크 조정 없이 동작하는 D2D 시스템을 의미한다. D2D 시스템의 전송 용량을 분석하여, uncoordinated D2D 시스템이 셀룰러 네트워크 내에서 상향링크 스펙트럼을 공유하면서 공존할 수 있는 타당성 조건을 도출한다. 또한, 이러한 D2D 시스템의 적절한 전송 전력 수준 및 링크 거리에 관한 연구 결과를 제시함으로써, 대규모 D2D 통신의 운용점에 관한 가이드라인을 제공한다. Device-to-device (D2D) communication is expected to offer local area services with low transmit power and short link distance, even not via any infrastructures. These advantages will lead to the deployment of D2D systems in a massive scale, where the order of magnitude of D2D user density is higher than that of cellular user density. Network-assisted D2D systems, where D2D resources are managed by cellular networks, are unable to support the large number of D2D devices, due to the signaling overhead for control signals. In this case, no coordination can be an answer. This paper considers uncoordinated D2D systems, which is implemented with a number of D2D devices in a large scale. By analyzing the transmission capacity of D2D systems, we found a feasibility condition under which the uncoordinated D2D communications possibly coexist within cellular networks, sharing the uplink spectrum. In addition, we provide guidelines for the operational points of massive D2D communications, giving some knowledge about proper transmit power level and link distance of uncoordinated D2D.