The type of network used for communication among a laptop and smartphone using bluetooth is a

7.6.1 Personal Area Networks

A personal area network is a network concerned with the exchange of information in the vicinity of a person. Typically, these systems are wireless and involve the transmission of data between devices such as smartphones, personal computers, tablet computers, etc. The purpose of such a network is usually to allow either transmission of data or information between such devices or to server as the network that allows further up link to the Internet. Developments in the area of Personal Area Networks (PANs) are largely overseen by the IEEE 802.15 working group [18].

2.2 The Technology Trends

Ubiquitous computing comprises a broad and dynamic spectrum of technologies. Two of the most common placeholders for these devices are the personal technologies and smart environments.

Personal Area Network (PAN): It is an interconnection of personal technology devices to communicate over a short distance, which is less than 33 feet or 10 meters or within the range of an individual person, typically using some form of wireless technologies. Some of these technologies are:

Bluetooth technology: The idea behind Bluetooth is to embed a low cost transceiver chip in each device, making it possible for wireless devices to be totally synchronized without the user having to initiate any operation. The chips would communicate over a previously unused radio frequency at up to 2 Mbps. The overall goal of Bluetooth might be stated as enabling ubiquitous connectivity between personal technology devices without the use of cabling as written in Mckeown (2003a).

High rate W-PANs: As per standard IEEE 802.15 TG3, launched in 2003, these technologies use higher power devices (8 dBm) than regular Bluetooth equipment (0 dBm) to transmit data at a rate of up to 55 Mbps and over a range of up to 55 m Ailisto et al (2003).

Low power W-PANs: As per standard IEEE 802.15 TG4, these technologies are particularly useful for handheld devices since energy consumption for data transmission purposes, and costs, are extremely low. The range of operation of up to 75 m is higher than current Bluetooth applications, but the data transfer rate is low (250 Kbps) Ailisto et al (2003).

BodyArea Network (BAN): Wireless body area networks interlink various wearable computers and can connect them to outside networks and exchange digital information using the electrical conductivity of the human body as a data network. Advantages of BANs versus PANs are the short range and the resulting lower risk of tapping and interference, as well as low frequency operation, which leads to lower system complexity. Technologies used for wireless BANs include magnetic, capacitive, low-power far-field and infrared connections Raisinghani et al (2004).

Sensors and Actuators: Sensors are essential in capturing physical information from the real world. Different types of sensors are needed for different phenomena. These devices collect data about the real world and pass it on to the computing infrastructure for enabling decision-making. They can detect and measure mechanical phenomena of the user like movements, tilt angle, acceleration and direction. Actuators provide the output direction from the digital world to the real world. These devices allow a computing environment to affect changes in the real world.

Smart Tags: The smart tags contain microchips and wireless antennas that transmit data to any nearby receiver which is acting as a reader. Beyond just computing a price, the smart tags will enable companies to track a product all the way. New tags can recognize more than 268 million manufacturers, each with more than 1 million products. They use Radio frequency identification (RFID) system, which encompasses wireless identification through radio transmission.

12.6 Summary

Several WPAN are described in this chapter. Bluetooth consists of two versions—BR/EDR, which we refer to as legacy Bluetooth, and BLE. BR/EDR is used mostly for streaming data applications like wireless headphones and loudspeakers. BLE, with its four defined roles and device capabilities, serves control and monitoring functions as well as one-way beacons, where very low energy consumption for long battery life is a necessity. Both versions operate on world-wide 2.4 GHz unlicensed frequency channels using frequency hopping medium access. Problems and solutions for coexistence between Bluetooth and IEEE 802.11 devices are discussed.

The IEEE 802.15.4 standard and Zigbee implementations for personal area networks are designed for short-range network topologies and use in low cost, low power devices. Several frequency ranges and modulation techniques are defined to suit sub-1 GHz regulations in different countries and regions, in addition to operation on the 2.4 GHz band.

Other WPAN standards for specific application requirements are discussed. They include 6LoWPAN, Thread, WirelessHART, Z-Wave, DASH7, and ANT.

UWB is a WPAN technology that stands apart from the others from the point of view of operating frequencies, bandwidth, data rates and consequently its applications. Two signal generation techniques are explained—impulse radio and multiband OFDM. Due to spreading signal energy over a wide bandwidth, UWB does not interfere with narrow band communications over the same frequency range. Also, its wide bandwidth makes it particularly suitable for short range high precision wireless distance measurement.

Bluetooth (IEEE802.15.1 and .2)

Bluetooth is a personal area network (PAN) standard that is lower power than 802.11. It was originally specified to serve applications such as data transfer from personal computers to peripheral devices such as cell phones or personal digital assistants. Bluetooth uses a star network topology that supports up to seven remote nodes communicating with a single basestation. While some companies have built wireless sensors based on Bluetooth, they have not been met with wide acceptance due to limitations of the Bluetooth protocol including:

Relatively high power for a short transmission range.

Nodes take a long time to synchronize to network when returning from sleep mode, which increases average system power.

Low number of nodes per network (<=7 nodes per piconet).

Medium access controller (MAC) layer is overly complex when compared to that required for wireless sensor applications.

Bluetooth

Bluetooth is another WPAN standard, operating in the 2.4 GHz range using a method called frequency-hopping spread spectrum. It is designed to operate at a distance of between 10 and 100 m, although it typically operates at 10 m or less. Its development began in 1989 at Ericsson Mobile under the title ‘short-link’ radio technology, to allow communication with wireless headsets and was named Bluetooth in 1997 while it was being repurposed by Intel for communication between mobile phones and computers. A master device can communicate with up to seven devices within an ad-hoc Bluetooth network, called a piconet, within which master/slave roles can be switched. Bluetooth was standardised as IEEE 802.15.1. It has undergone continuous evolution, with Bluetooth 4.0 also known as Bluetooth Smart incorporating Bluetooth LE (low energy) being adopted in 2010. There are a number of home automation devices that are Bluetooth enabled, such as locks, blinds and LED lighting, but what makes this technology so important in the assisted living arena is its mass market penetration via computers and especially smartphones. A large-scale proliferation of Bluetooth-enabled sensors and compatible apps in the health and well-being sphere can be seen. Bluetooth LE in particular offers many possibilities in terms of wearable devices that can communicate with smartphones. Most new smartphones running Android, iOS and Windows are now offering Bluetooth LE as standard.

Bluetooth

Bluetooth was developed as a PAN for connecting computers, cell phones, and other devices up to a range of about 30 feet. It is a low-speed data transmission method. Bluetooth operates in the same 2.4- to 2.483-GHz unlicensed spectrum as Wi-Fi. It uses a technique known as frequency-hopping spread spectrum (FHSS), where the data is divided into chunks and transmitted via a carrier that hops from one random frequency to another. Data is transmitted at a 1-Mbps rate using FSK. An enhanced data rate form of Bluetooth is also available to transmit at higher speeds up to 3 Mbps. The range is 10–50 m depending on the environment. The standard is managed by the Bluetooth Special Interest Group.

More recent versions of Bluetooth use a different form of FHSS and are designed to operate on less power. Called Bluetooth Low Energy (BLE) it is available in several forms for data rates of 1 or 2 Mbps. BLE nodes can operate for years from a single button cell because of the very low current drain. A newer version of BLE called Bluetooth 5 uses different modulation and coding schemes to achieve data rates to 2 Mbps over a longer range up to 50 m or more.

One of the basic features of Bluetooth is that it is capable of forming small networks called piconets. It does this by linking two Bluetooth devices together. One serves as a master controller, and it can connect to seven other Bluetooth slave devices. Once the PAN has been set up, the various connected devices can exchange information with one another through the master.

By far the most common application for Bluetooth is cordless headsets for smartphones. Other common uses are Bluetooth speakers for smartphones or tablets as well as hands-free systems in automobiles. But you will also encounter it in some wireless connections between a PC and a mouse or keyboard. Bluetooth may be the most widely used wireless standard in the world because it is used in so many smartphones, laptops, and other consumer equipment. Billions of Bluetooth chips have been sold.

Acronyms

6LoWPAN

IPv6 over Low Power Wireless Personal Area Networks

acknowledgement

Advanced RISC Machine

Bluetooth Low Energy

Central Processing Unit

Cyclic Redundancy Check

Carrier Sense Multiple Access with Collision Detection

Denial of Service

Digital Subscriber Line

Electronic Product Code

European Union

Frequency Division Multiplexing

File Transfer Protocol

Global System for Mobile communications

Hypertext Transfer Protocol

Information and Communication Technologies

Internet of Medical Things

Internet of Things

Internet of Things Security Foundation

Intelligent Transportation System

ITU Telecommunication Standardization Sector

Long Range Wide Area Network

Machine to Machine

Media Access Control

Massachusetts Institute of Technology

MQ Telemetry Transport

Near Field Communication

Personal Digital Assistant

Power line Digital Subscriber Line

Power Line Networking

Quality of Service

Random Access Memory

Radio Frequency IDentification

Real Time Operating System

Simple Mail Transfer Protocol

Service Oriented Architecture

Transmission Control Protocol

Universal Mobile Telecommunications System

Universal Product Code

Uniform Resource Identifier

Uniform Resource Locator

Universally Unique IDentifier

Vehicle-to-Infrastructure

Vehicle-to-vehicle

Wireless Personal Area Network

Wireless sensor networks

ZigBee Coordinator

ZigBee End Device

ZigBee Router

2.1.3 6LoWPAN

The IPv6 over Low power Wireless Personal Area Networks or 6LoWPAN was created by a concluded working group in the Internet area of the IETF to fulfill the necessity to allow any kind of device, even the smallest ones with limited power usage and processing capabilities, to participate in the Internet of Things.

6LoWPAN is a combination of IEEE 802.15.4 and IP in a simple, well understood way. The key features of this protocol are the encapsulation definition and header compression that allow the compatibility between local area networks and wide area networks with IEEE 802.15.4-based networks.

Since 6LoWPAN pertains to the network layer of the OSI model, it does not have a specific transmission specification. Instead, the underlying link layer protocol is responsible for providing them. As mentioned before, this protocol has been designed to work on top of IEEE 802.15.4 based networks which provides the transmission characteristics already explained in Section 2.1.1.

3.1 Introduction/Motivation

With the advancement of medical science, the average longevity of human is increasing day-by-day resulting in more elderly population in many countries (United Nations Department of Economic and Social Affairs, 2013). This trend demands new ways of medical care that acts proactively rather than being reactive. Currently, treatment is provided to handle emergencies. However with more elderly population, day-to-day monitoring is needed for early detection of any anomaly in vital signs. Hospitals cannot handle this huge load. Rather, the living environment at home can be made smart enough to monitor and detect any vital signs and communicate it to the proper place, like a nursing center or the hospital. As mentioned in Wang et al. (2015), “Ambient Assisted Living (AAL) enhances the independent living ability of the elderly through various intelligent services, reducing the need for direct care giving, indoors or outdoors”. The use of wireless technology, in particular medical applications of wireless sensor networks and wireless body area networks in AAL, improves the existing health-care and monitoring services especially for the elderly and chronically ill. A recent report (Prescot, 2013), forecasts that the number of home monitoring systems with integrated communication capabilities will grow at a compound annual growth rate (CAGR) of 26.9% between 2011 and 2017, to reach 9.4 million connections worldwide. These figures imply that the demand for health-care devices and AAL systems is increasing to involve citizens' in personal health-care, support independent living and economize the health-care expenses. These solutions provide a number of benefits including, remote monitoring and reduced costs for managing the health-care systems. With remote monitoring, the identification of emergency conditions for at risk patients will become easy and the people with different degrees of cognitive and physical disabilities will receive proper assistance to have a more independent and easy life. First responders could receive immediate notifications from such smart environments on any changes in patient status, such as respiratory failure or cardiac arrest (Shnayder et al., 2005).

A typical AAL system consists of diverse technologies and systems incorporating medical sensors, wireless sensor and actuator networks (WSANs), RFID tags and readers, computer systems, computer-networks, software applications, and databases, which are interconnected to exchange data and provide services in an ambient assisted environment (Lloret et al., 2015; Gambi et al., 2015). Wireless communication serves as a key enabling technology to support connectivity among different components of the system including, medical sensors, ambient sensors, home gateways and wireless routers that enable the logging/monitoring applications to report data in soft real-time to health-care professionals. Most of the existing solutions include one or more types of sensors carried by the patient, forming a Body Area Network (BAN), and one or more types of sensors deployed in the environment forming a Personal Area Network (PAN). These two are connected to a backbone network via a gateway node. In general, two classes of sensors can be used for monitoring in AAL: sensors to monitor the environment and wearable sensors to sense a person's context and activity. Data from these two networks of sensors should be analyzed to monitor any vital sign. For instance, the heartbeat sensor may give higher reading when a person is jogging, so does the temperature sensor. Thus, to filter out false positives, data from the accelerometer and location of the sensor are very important to appropriately contextualize the information.

In AAL system comprising BAN and PAN sub-components, one of the most precious resource is energy. Since sensor nodes rely on battery power and can only operate as long as their batteries maintain power, their hardware systems (micro-controller and radio communication subsystems e.g. ZigBee or 802.15.4) should be designed for low power consumption. Generally speaking, the amount of energy consumed in radio communication is significantly higher than the energy consumed by micro-controller. Since, the AAL system depends on communication activities to relay the sensor data across BAN and PAN subsystems, the energy efficiency remains a key challenge for end-to-end communication. These challenges necessitate that energy efficient communication protocols are designed. In addition to the energy efficiency, AAL systems also need to address many more complex challenges including, reliability of communication, security, privacy, user mobility, interference and quality of service (QoS) (Porambage et al., 2015). A brief description of these challenges is provided below;

Reliable communication: Interfacing different communication technologies should be reliable enough to transport the important medical data (physiological sensor readings, patient's vital signs etc.). Any loss is not acceptable.

Security and privacy: Handling massive private data-Any violation of privacy and hence data integrity is extremely important. The data may consists of sensitive and private medical or personal data which should be adequately protected.

Multiple receivers: Data could be sent to doctors or a display unit at the room. So multi-cast rather than uni-cast is more suitable.

In-network aggregation cannot be applied as it is not meaningful to combine data from multiple patients.

User mobility: Mobility of the patient results in the change of topology with time as BAN connects to different point of attachment.

An example architecture of AAL system is shown in Figure 3.1. As can be seen, the BAN constitutes tier-1 where body sensors communicate directly or indirectly to the BAN coordinator. In tier-2, information is received from the BAN coordinator to local access point or a home gateway, smart devices acting as a gateway of a simple workstation that is connected to the Internet. The information received by any tier-2 device is finally transmitted to tier-3 via the Internet or cellular network. Such a system can operate in a centralized or distributed fashion. Wearable sensors carried by a person constitute a BAN configuration consisting of a BAN coordinator and multiple sensors like the one shown in Figure 3.1. The sensors communicate with the BAN coordinator following IEEE 802.15 standard, or other communication protocols (Spinsante et al., 2015). These BAN coordinators may have a direct or indirect connection to some central device (PDA or nursing station coordinator) in tier 2 in the building (Aquino-Santos et al., 2013), the main coordinator (say) following IEEE 802.11 LAN standard. This point of attachment can be distributed as well. For instance, whenever a patient moves, the BAN coordinator registers itself to the nearest tier 2 device (Khan et al., 2013). Tier 2 devices further connect to Internet or wireless mobile network in tier 3 providing global access to sampled information from AAL BAN and PAN.

The rest of this chapter is organized as follows. Section 3.2 explores the related work focusing on system and network architecture, as well as inter-BAN communication. Section 3.3 articulates the problem formulation for the energy efficient route calculation. In Section 3.4 we present the evaluation results for the proposed protocol. Finally, the summary and conclusions are provided in Section 3.5.

4.3 The IEEE 802.15 Technologies: Wireless Personal Area Networks

WSN is often deployed under the auspice of the wireless personal area network (WPAN), which was initially designed to have characteristics of low complexity, low data rate, and low energy consumption. WSN facilitates large-scale and fast deployment, as well as low implementation cost. It supports short-range wireless communications and is typically adopted in industry and smart homes. WSNs have been widely used in diverse applications, such as surveillance for crimes, traffic congestion avoidance, telemedicine and e-healthcare, and environmental monitoring. Nevertheless, sensor networks used in power systems are mostly wired-based and are not interconnected [4]. Moreover, WSNs deployed in the smart grid system have more stringent requirements than those in other applications in terms of communications link quality, radio frequency (RF) interference, quality of service (QoS) provisioning, latency, and security [3, 4,12,13]. Several challenges have been identified in the studies, among which severe interference in shared ISM bands with the existing communications networks is a main concern.

In order to alleviate the problem, techniques such as multichannel access [14], WiFi features adoption [15], and cognitive radio [16] integrated in WSNs were proposed to enhance the performance of the smart grid communications. Utilizing the channel resource over time (e.g., parallel transmission using dual transceivers) helps address the coexistence issue, as well as reduce traffic loads (including retransmission) and energy consumption to some degree. It may also mitigate the packet loss caused by collision, congestion, and wireless impairments. In other words, spectrum sensing management, data traffic management, and power control management are important elements that predominantly determine how optimized the network performance can be achieved, subject to the constraints of complexity, cost, overhead, and power consumption.

By the second quarter of 2011, the IEEE 802.15 Working Group (WG) for WPAN consisted of nine Task Groups (TGs) [17], as described in Table 4.2

Table 4.2. IEEE 802.15 Task Groups

Wireless MAC and PHY specifications have been defined for different WPAN purposes among TGs [18]. IEEE 802.15.1 was originally developed by the Bluetooth Special Interest Group. It defines PHY and MAC for the conventional WPAN. The coverage of wireless connectivity with fixed or portable/handheld digital wireless devices operated by a person or object is up to 10 m (in radius) of a personal operating space (POS). Unlike ZigBee, Bluetooth supports much shorter range and coordinates no more than seven devices in its network. Besides, it is power-hungry (i.e., the supported lifetime is only a few days) due to the FHSS (frequency-hopping spread spectrum) technology employed in the PHY. Similarly, Z-Wave Alliance [19], a proprietary standard designed for home automation operating in around 900 MHz, is not as popular as ZigBee.

IEEE 802.15.2 addresses the limitation of coexistence of IEEE 802.15.1-2002 WPANs and IEEE 802.11b-1999 WLANs operated in unlicensed ISM frequency bands. It provides a number of modifications to other standards in IEEE 802.15 for enhancing coexistence with other wireless devices, as well as recommended practices for IEEE 802.11-1999 devices to facilitate coexistence with IEEE 802.15 devices.

IEEE 802.15.3 was meant for wireless multimedia to support high data rates in WPAN required for time dependent and different consumer applications, such as large file transfer in video and digital still imaging. IEEE 802.15.3b adds enhancements to improve the efficiency of IEEE 802.15.3 including the newly defined MLME-SAP (MAC layer management entity-service access point), ACK (acknowledgment) policy and implied-ACK, LLC/SNAP (logical link control/subnetwork access protocol) data frame, and a method for CTA (channel time allocation). IEEE 802.15.3c, namely mmWave, enables data rates greater than 5 Gbps operating in the 60 GHz band and defines a beam-forming negotiation protocol to improve the communications range for transmitters. It also supports aggregation of incoming data and ACKs, respectively, into single packets to improve MAC efficiency by reducing retransmission overhead as well as facilitating coexistence with microwave systems in WPAN. Applications such as real-time video streaming, HDTV, video on demand, and content downloading are supported.

IEEE 802.15.4b, i.e., 802.15.4-2006, the basis for the ZigBee specification, adds enhancements and corrections to IEEE 802.15.4-2003. Major modifications are reducing unnecessary complexities, increasing flexibility in security key usage, and supporting additional frequency bands in various countries. IEEE 802.15.4a [20] provides enhanced resistance to multipath fading with very low transmit power. In order to alleviate the problem, two alternative PHYs were developed. One is to use an ultra wideband (UWB) impulse radio operating in the unlicensed UWB spectrum (i.e., sub-GHz or below 1 GHz, 3–5 GHz, and 6–10 GHz) to increase the precision ranging capability to an accuracy of one meter or better. Another one is to employ chirp spread spectrum (CSS) in the unlicensed 2.4 GHz ISM band to support long-range links or links for mobile devices moving at high speed by adopting the unique windowed chirp technique in order to enhance robustness and mobility. The CSS method outperforms 802.15.4b (250 Kbps), 802.15.3 (22 Mbps), 802.15.1 (1 Mbps), and 802.11b (1, 2, 5.5, 11 Mbps) operating in the 2.4 GHz ISM band. Moreover, IEEE 802.15.4c defines an alternate PHY in addition to those in IEEE 802.15.4b and IEEE 802.15.4a to support one or more of the Chinese 314–316 MHz, 430–434 MHz, and 779–787 MHz bands. It also provides modifications to MAC needed to support the associated PHY. IEEE 802.15.4d specifies alternate PHYs for the Japanese 950 MHz band, and modifies MAC to support the new frequency allocation. By the time of this publication, IEEE 802.15.4-2011 which is a revision of the 2006 version will be published as a single document to consolidate the previous three amendments (i.e., 2 PHYs and 1 MAC) in order to avoid inadequacies or ambiguities discovered in the earlier standards. Table 4.3 provides detailed information on specifications for IEEE 802.15.4b/a/c/d.

Table 4.3. PHY Specifications in IEEE 802.15.4a, b, c, and d

IEEE 802.15.5 provides an architectural framework enabling WPAN devices to promote interoperable, stable, and scalable wireless mesh topologies. The features include the extension of network coverage without either increasing the transmit power or receiver sensitivity, enhanced reliability via route redundancy, easier network configuration, and longer battery life on devices. Lee et al. [21] discussed issues of addressing and unicast/multicast routing. They further investigated the mesh routing in HR-WPAN supporting QoS by using hierarchically logical tree and address blocks. Solutions of energy saving from asynchronous and synchronous aspects as well as the support of portability for mobile devices in LR-WPAN were further presented. Other WGs in progress [17] include the following:

TG4e enhances and adds functionality to the IEEE 802.15.4-2011 MAC. The improvement will support the industrial markets and permit compatibility with modifications being proposed within the Chinese WPAN. It will further enable various application spaces including factory/process/building automations, asset tracking, home medical health/monitor, and telecommunications applications.

TG4f works on the specifications of an active RFID (RF IDentification) tag device. Such a device is typically attached to an asset or a person with a unique identification. It acquires the ability to produce its own radio signal by employing ambient energy harvested from the surrounding environment.

TG4g is creating a PHY amendment to IEEE 802.15.4-2011 to provide a globally fundamental standard for the smart utility neighborhood (SUN) network operating in the 700 MHz–1 GHz and 2.4 GHz ISM bands with data rates supported in between 40 kbps and 1 Mbps. The associated IEEE 802.11ah developing standard, which will define the use of frequencies below 1 GHz for WiFi networks, has been considered as a direction for the IEEE 802.15.4g participants.

TG6 is developing a standard optimized for very-low-power devices worn on/around or implanted in human/animal bodies to serve a variety of applications for medical purposes and others.

TG7 introduces a new communications technology that is different from the traditional RF technology and uses visible light having wavelength between ~400 nm (750 THz) and ~700 nm (428 THz). This technology has mainly been tested in restricted areas such as aircraft, spaceships, and hospitals. Moreover, the group is also looking into the future of LED (light-emitting diode) evolution for applications of illumination, display, ITS, and others, in the interest of its attractive potential for environmental protection, energy saving, and efficiency.

IGthz intends to explore the feasibility of the terahertz frequency band roughly from 300 GHz to 3 THz for wireless communications.

WNG is charged by the IEEE 802.15 Wireless Next-Generation standing committee to facilitate and stimulate presentations and discussions on new wireless related technologies within the defined scope.

Notably, some of these standards will be completed by early 2012; meanwhile, it can be foreseen that more Working Group activities will be formed to address related issues with respect to the IEEE 802.15 standard. Readers are referred to Reference [17] for the corresponding updates. Nonetheless, among the aforementioned standards, IEEE 802.15.3 HR-WPAN and IEEE 802.15.4 LR-WPAN are the most promising technologies to support smart grid applications with various bandwidth requirements. SUN, specified by the IEEE 802.15.4g Task Group (TG4g), has been developed to tackle a number of technical challenges in communications systems for the utility operators: (1) how to manage high volumes of metering data and control messages among a large number of meters/sensors (or nodes) in SUN networks throughout the AMI, and (2) how to establish self-configuring and self-healing utility networks in an efficient and cost-effective manner. The legacy IEEE 802.15.4 has been amended to provision the PHY (by TG4g) and MAC (by the IEEE 802.15.4e Task Group or TG4e) layer requirements in the SUN design. Three modulation formats in the PHY layer proposal are the multirate frequency shift keying (MR-FSK), multirate orthogonal frequency division multiplexing (MR-OFDM), and multirate offset quadrature phase shift keying (MR-OQPSK) [59]. Depending on different regions and network requirements (e.g., dense urban areas versus distant rural locations), various modulation modes, data rates, bandwidths, and channel spacing must be adaptively configured and allocated. The primary issue in SUN is coexistence with homogeneous and heterogeneous systems, especially in sharing the same network resources. Utilizing sub-GHz frequency bands (i.e., license-exempt bands below 1 GHz)1[59] as well as facilitating multi-PHY management (MPM) with the common signaling mode (CSM)2[60] is a foreseeable solution to signal interference in SUN networks.

In addition to the proposals of the state-of-the-art PHY schemes for SUN, most of the MAC protocols specified in IEEE 802.15.4 are adopted for SUN only with minor changes. Therefore, we will review a number of issues and challenges in the following section that have been addressed based on recent LR-WPAN studies predominantly in MAC designs. The survey on network measurements in the legacy IEEE 802.15.4 protocol will provide useful collation for investigation of SUN networks research.