Rodrigo L. Batista

A survey of converging solutions for heterogeneous mobile networks

In 5G systems, the current machine-tomachine communications using Wi-Fi or Bluetooth provide a good opportunity to dramatically increase overall performance. Converged mobile networks can provide M2M communications with significant performance improvements by sharing unlicensed spectrum bands in cellular networks, such as Long Term Evolution-Advanced, by using cognitive radio technology. Thus, the converged mobile network will become one of the most popular future research topics because mobile multimedia content services have been generally accepted among mobile device users. In this article, we provide an overview of converged mobile networks, investigating different types of converged mobile networks, different types of convergence, and the current problems and solutions. This survey article also proposes potential research topics in converged mobile networks.

SINR Balancing Combined with SDMA Grouping in CoMP Systems

SDMA grouping algorithms are usually employed in order to find a suitable set of User Equipments (UEs) for spatial multiplexing. The largest SDMA group is not always the best SDMA group in a given transmission such that higher gains might be achieved by dynamically adjusting the SDMA group size. Besides, algorithms that balance the SINR among different links might ensure a certain level of link quality and so provide a more reliable communication for the scheduled UEs. This paper provides system-level analyses for strategies of Radio Resource Allocation in CoMP systems, which consider dynamic SDMA grouping, joint precoding and power allocation for SINR balancing. Our results show that Sequential Removal Algorithms and SINR balancing provide gains of system spectral efficiency.

What happens with a proportional fair cellular scheduling when D2D communications underlay a cellular network

Device-to-Device (D2D) communications are seen as promising technology for future wireless systems. However, while underlying cellular networks they can negatively affect the performance of cellular communications when intra-cell spectrum sharing is enabled. The impact of D2D communications is not only seen on the cellular throughput, but also on the decision-making of the cellular scheduling policy. In this paper, we provide an impact assessment of D2D communications on the performance of Proportional Fair (PF) scheduling for a Long Term Evolution (LTE) multi-cell scenario through system-level simulations. Results show that due to excessive interference generated by D2D communications and depending on the accuracy of the link quality measure used to estimate the instantaneous data rate, a PF cellular scheduling policy may get stuck in an infinite loop and continuously selects the same User Equipments (UEs), which reduces the cellular throughput, or even approaches the performance of a Maximum Rate (MR)-based policy, thus affecting service coverage and fairness.

Power control schemes for energy efficiency of cellular and device-and-device communications

Device-to-Device (D2D) communications underlying cellular networks are a way to increase the network capacity and potentially save the battery lifetime of closely located physical devices. However, D2D communications can generate significant interference to the cellular network when the same resources are shared by both systems. Therefore, the design of Power Control (PC) schemes is required to keep the interference under control, get energy-efficient transmissions and protect cellular devices. In this work, we investigated operating points of the Soft Dropping Power Control (SDPC) and Open-Loop Power Control (OLPC) schemes for energy efficiency of cellular and D2D communications in uplink OFDMA systems. Results indicate that the SDPC performs better for cellular links and OLPC provides higher gains for D2D links in terms of energy efficiency. While high values of pathloss compensation factor α have been widely used in OLPC studies for the LTE standard, α ϵ {0.4, 0.5} has provided high energy efficiency gains for D2D links. Also, by properly setting the parameters of the OLPC applied to D2D links in uplink and considering the most favorable scenario for sharing resources in all cells, the minimum cost for having spectral efficiency gains for D2D communications represents an impact of 11 % on the system spectral efficiency of cellular communications.

Uplink Power Control with Variable Target SINR for D2D Communications Underlying Cellular Networks

Researches in Power Control (PC) schemes are fundamental to provide efficient algorithms and understand their behavior in Device-to-Device (D2D) scenario. The aim of the current study is to investigate Open Loop Power Control (OLPC), Closed Loop Power Control (CLPC) and indicate Soft Dropping Power Control (SDPC) like an alternative PC scheme to D2D communications underlaying a cellular network. We briefly review PC schemes, suggest a new point of dynamic offset compensation factor σ setting the issue in CLPC and evaluate its performance in terms of spectral and power efficiency. Results demonstrate that SDPC keeps a reasonable spectral efficiency and provides a gain of 70% in power efficiency in relation Long Term Evolution (LTE) PC schemes for cellular communications, and the factor σ = 0.8 can modify the behavior of CLPC because increases the Signal to Interference-plus-Noise Ratio (SINR) of the worst users.

UE grouping and mode selection for D2D communications underlaying a multicellular wireless system

Network-assisted Device-to-Device (D2D) communication is a promising technology for next generation wireless systems being seen as a means to improve spectrum utilization and reduce energy consumption. However, D2D communications can generate significant interference to cellular communications when resources are shared by both types of communication. Aiming at the reduction of the intracell interference and spectral efficiency improvement, we formulate and analyze methods to group conventional and D2D-capable User Equipments (UEs) for shared resource usage and to decide if D2D-capable UEs should communicate directly or via the Evolved Node B (eNB). The results show that D2D communications can improve the spectral efficiency of the system and that most of this improvement can be achieved by suitably grouping the UEs for sharing resources.

Radio resource allocation strategies for multi-antenna CoMP systems

In the context of Long Term Evolution (LTE)-Advanced, the transmission points responsible for Coordinated Multi-Point (CoMP) transmission can be arranged in a distributed way and each one can be equipped with multiple antennas. In such scenario, efficient Radio Resource Allocation (RRA) strategies are required to exploit the available spatial degrees of freedom, coordinate the resources usage and manage the interference. This work provides system-level analyses for several RRA strategies in multi-antenna CoMP systems. The results show significant benefits in terms of system spectral efficiency for different spatial transmission strategies, including the combination of spatial multiplexing and spatial diversity.

Interference Mitigation Using Band Selection for Network-Assisted D2D Communications

For systems with reuse factor less than one, the co- channel interference can drastically reduce the gain of primary networks, which limits the whole system performance. This paper exploits the selection of Downlink (DL) or Uplink (UL) band to be reused by a Device-to-Device (D2D) link. The band selected by the method is based on a radio distance metric, such as received power. Despite being a simple concept, results have shown that band selection can effectively mitigate the interference caused by D2D communications in a Long Term Evolution (LTE) network. Therefore, the coexistence of cellular and D2D communication modes becomes possible in time, frequency, and space.

Network-Assisted Neighbor Discovery Based on Power Vectors for D2D Communications

Device-to-Device (D2D) communication is seen as a promising technology to increase the capacity of current wireless systems without extra electromagnetic spectrum bands. However, before starting a D2D communication, Mobile Stations (MSs) must be aware of their neighbors, through a discovery process. While operating in cellular networks, such process may benefit from the network-assistance. In this paper, we propose a method based on the available network power measures to improve the discovery process. Results show that our proposal is less complex but still outperforms traditional methods when considering the time to detect all neighbors.

Radio Resource Management for Coordinated Multipoint Systems

This chapter revisits many of the issues concerning radio resource management with a focus on the upcoming systems embodying the Coordinated Multipoint (CoMP) technology. Nowadays CoMP-based systems have attracted special attention due to their potential benefits in terms of spectral efficiency and coverage. As a part of 3GPP Long Term Evolution—Advanced, CoMP technology promises substantial improvement of the users’ experience at the expense of requiring a reliable and efficient connection among the evolved Node Bs (eNBs). If multiple users and eNBs are coordinated using a suitable technique, the concerns about interference can be greatly alleviated and, consequently, also the restrictions on sharing the radio resources. In this chapter, the grouping of users and eNBs is explored in two different occasions. First, coordinated strategies process the Channel State Information (CSI) for scheduling users in order to improve the system performance; afterwards, clustering of eNBs is described as an attractive approach to deal with the processing and signaling overheads brought by CoMP. The chapter presents an analysis of different algorithms, as well as case studies illustrating some key concepts through computer simulations.