Arash Asadi

A Survey on Device-to-Device Communication in Cellular Networks

Device-to-device (D2D) communications was initially proposed in cellular networks as a new paradigm for enhancing network performance. The emergence of new applications such as content distribution and location-aware advertisement introduced new user cases for D2D communications in cellular networks. The initial studies showed that D2D communications has advantages such as increased spectral efficiency and reduced communication delay. However, this communication mode introduces complications in terms of interference control overhead and protocols that are still open research problems. The feasibility of D2D communications in Long-Term Evolution Advanced is being studied by academia, industry, and standardization bodies. To date, there are more than 100 papers available on D2D communications in cellular networks, but there is no survey on this field. In this paper, we provide a taxonomy based on the D2D communicating spectrum and review the available literature extensively under the proposed taxonomy. Moreover, we provide new insights into the over-explored and under-explored areas that lead us to identify open research problems of D2D communications in cellular networks.

A Survey on Opportunistic Scheduling in Wireless Communications

Wireless technology advancements made opportunistic scheduling a popular topic in recent times. However, opportunistic schedulers for wireless systems have been studied since nearly twenty years, but not implemented in real systems due to their high complexity and hardly achievable requirements. In contrast, todays popularity of opportunistic schedulers extends to implementation proposals for next generation cellular technologies. Motivated by such a novel interest towards opportunistic scheduling, we provide a taxonomy for opportunistic schedulers, which is based on scheduling designs objectives; accordingly, we provide an extensive review of opportunistic scheduling proposals which have appeared in the literature during nearly two decades. The huge number of papers available in the literature propose different techniques to perform opportunistic scheduling, ranging from simple heuristic algorithms to complex mathematical models. Some proposals are only designed to increase the total network capacity, while others enhance QoS objectives such as throughput and fairness. Interestingly, our survey helps to unveil two major issues: (i) the research in opportunistic is mature enough to jump from pure theory to implementation, and (ii) there are still under-explored and interesting research areas in opportunistic scheduling, e.g., opportunistic offloading of cellular traffic to 802.11-like networks, or cooperative/distributed opportunistic scheduling.

WiFi Direct and LTE D2D in action

With the evolution of high-performance multi-radio smartphones, Device-to-Device (D2D) communications became an attractive solution for enhancing the performance of cellular networks. Although D2D communications have been widely studied within past few years, the majority of the literature is confined to new theoretical proposals and did not consider implementation challenges. In fact, the implementation feasibility of D2D communications and its challenges are still a relevant research question. In this paper, we introduce a protocol that focuses on D2D communications using LTE and WiFi Direct technologies. We also show that currently available WiFi Direct features permits to deploy the D2D paradigm on top of the LTE cellular infrastructure, without requiring any fundamental change in LTE protocols.

On the compound impact of opportunistic scheduling and D2D communications in cellular networks

Opportunistic scheduling was initially proposed to exploit user channel diversity for network capacity enhancement. However, the achievable gain of opportunistic schedulers is generally restrained due to fairness considerations which impose a tradeoff between fairness and throughput. In this paper, we show via analysis and numerical simulations that opportunistic scheduling not only increases network throughput dramatically, but also increases energy efficiency and can be fair to the users when they cooperate, in particular by using D2D communications. We propose to leverage smartphones dual-radio interface capabilities to form clusters among mobile users. We design simple, scalable and energy-efficient D2D-assisted opportunistic strategies, which would incentivize mobile users to form clusters. We use a coalitional game theory approach to analyze the cluster formation mechanism, and show that proportional fair-based intra-cluster payoff distribution brings significant incentive to all mobile users regardless of their channel quality.

Energy efficient opportunistic uplink packet forwarding in hybrid wireless networks

Opportunistic schedulers have been primarily proposed to enhance capacity of cellular networks. However, little is known about opportunistic scheduling with fairness and energy efficiency constraints. In this work, we show that adapting opportunistic scheduling can dramatically ameliorate energy efficiency for uplink transmissions, while achieving near-optimal throughput and high fairness. To achieve this goal, we propose a novel two-tier uplink forwarding scheme in which users cooperate, in particular by forming clusters of dual-radio mobiles in hybrid wireless networks.

DRONEE: Dual-radio opportunistic networking for energy efficiency

Reducing the power consumption of smartphones is becoming more and more important as smartphones become an indispensable component of our daily activities. In this work, we propose a novel scheme, so called DRONEE, that dramatically ameliorates energy efficiency for uplink transmissions, while achieving near-optimal throughput and high fairness levels in cellular networks. Our proposal consists in a novel two-tier uplink forwarding scheme in which users cooperate by forming clusters of dual-radio mobiles for hybrid wireless networks. The impact of our proposal is threefold: (i) energy efficiency is boosted by allowing mobiles to relay the cellular traffic through intra-cluster ad hoc communications, which leads to reduction of power-hungry cellular transmissions; (ii) cellular capacity is augmented by scheduling uplink transmissions from mobiles with the best channel; (iii) almost perfect fairness is achieved by allowing users to share the cellular resources within their cluster. We corroborate the practical relevance of our proposal by providing a first-order discussion on the implementability of DRONEE using LTE and WiFi Direct.

On the efficient utilization of radio resources in extremely dense wireless networks

The emergence of popular wireless technologies such as LTE and WiFi, and the exponential growth in the usage of these technologies, has led to extremely dense wireless networks. There are many proposals for coping with such densification. In particular, we evaluate the compound effect of inter-cell interference schemes and spectrum efficient intra-cell relay techniques, which have been individually proposed recently as separate solutions. We provide a jointly coordinated intracell and inter-cell resource allocation mechanism that opportunistically exploits network density as a resource. We show that intracell opportunistic relay, based on WiFi communications, reduces the complexity of Inter-Cell Interference Coordination (ICIC) and boosts the efficiency of ICIC in LTE. The superiority of the proposed solution to the legacy cellular network operation is proven via simulations.

Network-Assisted Outband D2D-Clustering in 5G Cellular Networks: Theory and Practice

We introduce a channel-opportunistic architecture that enhances the user experience in terms of throughput, fairness, and energy efficiency. Our proposed architecture leverages D2D communication and it is built on top of the forthcoming D2D features of 5G networks. In particular, we focus on outband D2D where cellular users are allowed to exploit both cellular (i.e., LTE-A) and WLAN (i.e., WiFi Direct) technologies to establish a D2D connection. In this architecture, cellular users form clusters, in which only the user with the best channel condition communicates with the base station on behalf of the entire cluster. Within the cluster, the unlicensed spectrum is utilized to relay traffic. In this article, we provide analytical models for the proposed system and study the impact of several payoff distribution methods commonly adopted in the literature on coalitional game theory. We then introduce an operator-controlled relay protocol based on the D2D features of LTE-A and WiFi Direct, and demonstrate the feasibility and the advantages of D2D-assisted cellular communication with our SDR prototype.

An SDR-based experimental study of outband D2D communications

Device-to-Device communications represent a paradigm shift in cellular networks. Analytical results on D2D performance are very promising, but there is no experimental evidence that validates these results to date. This paper is the first to provide an experimental analysis of outband D2D schemes. Moreover, we design DORE, a complete framework for handling channel opportunities offered by outband D2D relay nodes. DORE consists of resource allocation optimization tools and protocols suitable to integrate QoS-aware opportunistic D2D communications within the architecture of 3GPP Proximity-based Services. We implement DORE using an SDR framework to profile cellular network dynamics in presence of opportunistic outband D2D communication schemes. Our experiments reveal that outband D2D communications are suitable for a large variety of delay-sensitive cellular applications, and that DORE enables notable gains even with a few active D2D relay nodes.

5G Millimeter-Wave and D2D Symbiosis: 60 GHz for Proximity-Based Services

The characteristics of two key communication technologies in 5G, namely, D2D and mmWave, are complementary. While D2D facilitates the communication of nearby mobile nodes, mmWave provides very high throughput short-range links by using carrier frequencies beyond 30 GHz, and reduces interference by using directional communication. This directly addresses two critical issues in cellular networks, namely, the increasing number of users and the high throughput requirements. In this article, we explore the above symbiosis of D2D and mmWave. More precisely, we integrate mmWave communications into the 3GPP framework for D2D communication, that is, ProSe. To this end, we design the message exchange among entities in the ProSe architecture to support the discovery, establishment, and maintenance of mmWave links. Further, we evaluate the performance of an mmWave D2D system for the case of a picocell operating in the 60 GHz band. We experimentally analyze the benefits of combining D2D and 60 GHz communication. Our results show that this combination improves performance in terms of throughput by up to 2.3 times.