In this chapter we deal with the following nonlinear fractional programming problem: 

$$P:\mathop{{\max }}\limits_{{x \in s}} q(x) = (f(x) + \alpha )/((x) + \beta )$$

where f, g: R n → R, α, β ∈ R, S ⊆ R n . To simplify things, and without restricting the generality of the problem, it is usually assumed that, g(x) + β + 0 for all x ∈ S,S is non-empty and that the objective function has a finite optimal value.

Nonlinear Fractional Programming

In futuristic wireless communications, a massive number of devices need to access networks with diverse quality of service (QoS) requirements. It is estimated that the number of connected devices will exceed 20 billions in 2020, and machine-to-machine (M2M) devices will account for nearly half of total connected devices. However, existing cellular systems and wireless standards, designed primarily for human-to-human (H2H) communications focusing on reducing access latency, increasing data rate, and system throughput, are not well suited for M2M communications that require massive connections, diverse QoS requirements, and low energy consumption. Radio resource management (RRM) in conventional H2H communications aims at improving spectrum efficiency and energy efficiency. Similarly, RRM also plays a vital role in M2M communications. In this paper, we make a comprehensive survey on state-of-the-art research activities on RRM in M2M communications. First, we discuss the issues on RRM for machine-type communications in LTE/LTE-A cellular networks including access control, radio resource allocation, power management, and the latest 3GPP standards supporting M2M communications. Acknowledging the fact that a single technology can not support all M2M applications, we discuss RRM issues for unlicensed band radio access technologies in M2M capillary networks, including IEEE 802.11ah, Bluetooth low energy, ZigBee, and smart metering networks. We also survey M2M RRM methods in heterogeneous networks consisting of cellular networks, capillary networks, and ultra dense networks. Finally, we review recent standard activities and discuss the open issues and research challenges.

Radio Resource Management in Machine-to-Machine Communications—A Survey

Small, compact and embedded sensors are a pervasive technology in everyday life for a wide number of applications (e.g., wearable devices, domotics, e-health systems, etc.). In this context, wireless transmission plays a key role, and among available solutions, Bluetooth Low Energy (BLE) is gaining more and more popularity. BLE merges together good performance, low-energy consumption and widespread diffusion. The aim of this work is to review the main methodologies adopted to investigate BLE performance. The first part of this review is an in-depth description of the protocol, highlighting the main characteristics and implementation details. The second part reviews the state of the art on BLE characteristics and performance. In particular, we analyze throughput, maximum number of connectable sensors, power consumption, latency and maximum reachable range, with the aim to identify what are the current limits of BLE technology. The main results can be resumed as follows: throughput may theoretically reach the limit of ~230 kbps, but actual applications analyzed in this review show throughputs limited to ~100 kbps; the maximum reachable range is strictly dependent on the radio power, and it goes up to a few tens of meters; the maximum number of nodes in the network depends on connection parameters, on the network architecture and specific device characteristics, but it is usually lower than 10; power consumption and latency are largely modeled and analyzed and are strictly dependent on a huge number of parameters. Most of these characteristics are based on analytical models, but there is a need for rigorous experimental evaluations to understand the actual limits.

Performance Evaluation of Bluetooth Low Energy: A Systematic Review

Industrial wireless sensor networks (IWSNs) are used to acquire sensor data that need real-time processing, therefore they require predictable behavior and real-time guarantees. To be cost effective, IWSNs are also expected to be low cost and low power. In this context, Bluetooth low energy (BLE) is a promising technology, as it allows implementing low-cost industrial networks. As BLE is a short-range technology, a multihop mesh network is needed to cover a large area. Nevertheless, the recently published Bluetooth mesh networking specifications do not provide support for real-time communications over multihop mesh networks. To overcome this limitation, this paper proposes the multihop real-time BLE (MRT-BLE) protocol, a real-time protocol developed on top of BLE, that allows for bounded packet delays over mesh networks. MRT-BLE also provides priority support. This paper describes in detail the MRT-BLE protocol and how to implement it on commercial-off-the-shelf devices. Two kinds of performance evaluation for the MRT-BLE protocol are provided. The first one is a worst case end-to-end delay analysis, while the second one is based on the experimental results obtained through measurements on a real testbed.

Multi-Hop Real-Time Communications Over Bluetooth Low Energy Industrial Wireless Mesh Networks

The automotive industry is undergoing major transformation, with the emergence of vehicular networks, intelligent transportation systems, and autonomous cars over the last decade. These technologies are made possible by recent advances of software, hardware, and communication systems, along with the development of various applications and standards. Today, new technologies are incorporated into cars that detect potential road hazards and improve the driving experience. There are three key components being integrated into cars: sensors, information systems, and communication technologies to create connected vehicle networks. Vehicle-to-vehicle (V2V) communication is being used in connected networks to reduce traffic congestion, improve passengers’ safety, and enable the efficient management of vehicles on roads. Here, we present recent research developments and current trends in V2V communications. We discuss architectural issues and wireless technologies that support V2V. We also present recently proposed security solutions for V2V. Finally, we discuss outstanding challenges for enabling the deployment and adoption of V2V technology.

A tutorial survey on vehicle-to-vehicle communications

To support various Internet of Things (IoT) applications, the Bluetooth Low Energy (BLE) standard specifies a wide range of parameter values for the neighbor discovery process (NDP). The parameter values used during neighbor discovery directly affect the performance of the NDP. Therefore, an optimal parameter setting is essential to achieve the best tradeoff between discovery latency and energy consumption. An analytical model can offer a beneficial guideline for such a parameter selection. In this paper, we propose a general model for analyzing the performance of NDP in BLE networks. In the model, the operations of the scanner and the advertiser, which are two main components of NDP, are expressed on the discrete-time axis. Based on the Chinese Remainder Theorem (CRT), the discovery latency and energy consumption of advertiser are derived. The numerical results from our model are almost the same as the simulation results, for any parameter values specified by the standard. When considering that BLE is one of candidate communication technologies for IoT, the proposed model is expected to be very useful in setting the default or initial values of NDP parameters for various IoT applications.

Performance Analysis of Neighbor Discovery Process in Bluetooth Low-Energy Networks

As WiFi becomes a universal means for wireless access to Internet, the multi-cell WLAN with a lot of access points (APs) deployed densely is not seldom but comes to be a typical configuration of WLANs, especially, in the hot-spots such as shopping malls, air ports, universities, and enterprises. Moreover, in the large classrooms or conference rooms, a huge volume of multimedia traffic should be multicasted to the users via a number of APs. Since more than one AP can serve a user in a multi-cell WLAN, the overall WLAN performance highly depends on the user association (UA) scheme that decides the serving AP for each user. On the other hand, since the traffic load in such a multi-cell WLAN varies largely with time (e.g., day-time and night), the sleep mode operation of AP can be very helpful for reducing the energy consumption in the entire system. There have been some UA schemes, each of which takes account of only the load balancing between the APs, only the multicast transmission, or just the sleep mode operation of APs. However, to maximize the performance of a multi-cell WLAN, these three problems should be considered together. In this paper, we propose a UA scheme which simultaneously addresses the load balancing, the multicast transmission, and the AP sleep operation adapting to traffic load. The proposed UA scheme is formulated into a mixed integer linear programming problem which can be optimally solved by using branch and bound technique. We implement the proposed scheme using real devices and compare its performance with those of the existing UA schemes. The experimental results show that the proposed scheme greatly outperforms the existing schemes, in terms of the throughput per working AP, the number of working APs, and a load balancing factor.

A joint user association and load balancing scheme for wireless LANs supporting multicast transmission

The long range wide area network (LoRaWAN) forms a star topology where end device (ED) sends data to network server (NS) through gateway (GW). It requires a GW to be connected to the NS through an IP network as the backhaul link. However, when a LoRaWAN is deployed in a remote area, such connection may not be possible. Thus, it is important that the GW can reach the NS through multihop GW-to-GW (G2G) communication using LoRa technology. To realize it, we propose a multihop G2G communication protocol for LoRa networks. The proposed protocol includes both routing protocol and channel access scheme. A packet aggregation feature is also added for improving the transmission efficiency of GW. The simulation results demonstrate that the proposed protocol successfully enables multihop G2G communication for LoRa networks with reasonably good performance.

Multihop Gateway-to-Gateway Communication Protocol for LoRa Networks

As the IEEE 802.11 (WiFi) becomes the de-facto global standard for wireless local area network (WLAN), a huge number of WiFi access points (APs) are deployed and the mobile users enjoy almost ubiquitous wireless Internet access. When densely deployed APs covering a certain area are managed by a single organization (say, an enterprise), there can exist multiple candidate APs for serving a user. In this case, the user association (UA), i.e., the selection of serving AP, holds a key role in the network performance. In this paper, we propose an efficient UA scheme for load balancing among APs and energy saving in the enterprise WLAN, considering various techniques for performance improvement, such as multicast transmission, multiuser multiple-input and multiple-output, and AP sleeping, together. We formulate the problem into a multiobjective optimization and get the solution as the UA scheme. We develop a WLAN testbed to demonstrate the practicality and feasibility of the proposed scheme. Moreover, through extensive simulations, we also compare the performance of the proposed scheme with those of some other UA schemes. The simulation results show that the proposed scheme outperforms the other schemes in terms of the total system throughput, the throughput per working AP, the energy efficiency, and the load balancing factor.

User Association for Load Balancing and Energy Saving in Enterprise WLANs

Bluetooth Low Energy (BLE) is one of the promising technologies to enable Internet of Things. Many potential BLE applications are delay-sensitive which demand a fast data delivery. However, since BLE coexist with other technologies such as WiFi, ZigBee, microwave, the BLE may experience severe interference. The interference can cause the BLE connection event to be unexpectedly closed which forces the device to enter sleep mode even though there is more data to be sent. This negatively affects the performance of the BLE in terms of transmission delay which makes the BLE not suitable for delay-sensitive applications. To address this issue, we propose an extension of channel access scheme of the BLE in connection state. The proposed scheme is based on the listen-before-talk mechanism where the device should sense the channel before using it. By using Markov analysis, several performance measures are derived. Through numerical result, we show that the proposed channel access scheme can reduce the average transmission delay.

Made Harta Dwijaksara

Papers

Performance Analysis of Neighbor Discovery Process in Bluetooth Low-Energy Networks

A joint user association and load balancing scheme for wireless LANs supporting multicast transmission

Multihop Gateway-to-Gateway Communication Protocol for LoRa Networks

User Association for Load Balancing and Energy Saving in Enterprise WLANs

A channel access scheme for Bluetooth low energy to support delay-sensitive applications