Survey of cross‐technology communication for IoT heterogeneous devices
2019; Institution of Engineering and Technology; Volume: 13; Issue: 12 Linguagem: Inglês
10.1049/iet-com.2018.6069
ISSN1751-8636
AutoresYing Chen, Ming Li, Pengpeng Chen, Shixiong Xia,
Tópico(s)Wireless Body Area Networks
ResumoIET CommunicationsVolume 13, Issue 12 p. 1709-1720 Review ArticleFree Access Survey of cross-technology communication for IoT heterogeneous devices Ying Chen, Ying Chen orcid.org/0000-0001-9444-1357 China University of Mining and Technology, Xuzhou, 221116 People's Republic of ChinaSearch for more papers by this authorMing Li, Ming Li China University of Mining and Technology, Xuzhou, 221116 People's Republic of ChinaSearch for more papers by this authorPengpeng Chen, Pengpeng Chen China University of Mining and Technology, Xuzhou, 221116 People's Republic of ChinaSearch for more papers by this authorShixiong Xia, Corresponding Author Shixiong Xia shixiongxia.cumt@outlook.com China University of Mining and Technology, Xuzhou, 221116 People's Republic of ChinaSearch for more papers by this author Ying Chen, Ying Chen orcid.org/0000-0001-9444-1357 China University of Mining and Technology, Xuzhou, 221116 People's Republic of ChinaSearch for more papers by this authorMing Li, Ming Li China University of Mining and Technology, Xuzhou, 221116 People's Republic of ChinaSearch for more papers by this authorPengpeng Chen, Pengpeng Chen China University of Mining and Technology, Xuzhou, 221116 People's Republic of ChinaSearch for more papers by this authorShixiong Xia, Corresponding Author Shixiong Xia shixiongxia.cumt@outlook.com China University of Mining and Technology, Xuzhou, 221116 People's Republic of ChinaSearch for more papers by this author First published: 01 July 2019 https://doi.org/10.1049/iet-com.2018.6069Citations: 11AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract The ever-developing Internet of Things (IoT) drives the prosperity of ubiquitous connections among heterogeneous wireless devices (e.g. WiFi, ZigBee and Bluetooth) that follow different standards. Wireless devices share unlicensed industrial, scientific and medical bands, offering an opportunity for cross-technology communication (CTC), where coexistence and cooperation mechanisms of wireless technologies incur the problem of coexistence. This study is purposed to present a rounded state-of-the-art survey on CTC from the hardware perspective, CTC techniques are roughly divided into two types: hardware based and hardware free. In hardware-based strategies, a dedicated hardware is required to send information to wireless devices for enabling direct communication. The hardware-free schemes, by contrast, enable heterogeneous wireless devices to communicate directly by exchanging information or data without the dedicated hardware. Recent advances in CTC are reviewed in both types by expatiating on how heterogeneous wireless devices are achieving direct communication. The authors compare some CTCs with respect to throughput, communication range, energy efficiency and cost, in addition, they present open research issues of two types. 1 Introduction In recent decades, the developing era of Internet of Things (IoT) has brought great convenience to modern life. This also inspires the rapid development of wireless technologies, such as IEEE 802.11b/g, IEEE 802.15.4 and Bluetooth to accommodate different system performance requirements (e.g. communication range, throughput, latency, and energy consumption). Many of these technologies coexist and share the same spectrum, e.g. 2.4G ISM band, where they intensely compete for channel and interfere with each other, which is available to spectrum resources [1-3], leading to cross-technology interference (CTI) and causing considerable spectrum inefficiency and low-reliability [4]. CTI is a common issue in industrial, scientific and medical (ISM) unlicensed band, for example Angrisani et al. [2] observed the mutual interference between ZigBee and WiFi in real environment. Observation result shows that the packet loss rate of ZigBee networks varies from 0 to 85% under different WiFi traffic load. Therefore, channel access competition leads to the problems of inefficiency and inequality, especially among various wireless technologies. The main reason is that many network coordination protocols, like TDMA and RTS/CTS, are useless in heterogeneous wireless technologies. Albeit different technologies share the same ISM band, their channels occupy different bandwidths and are overlapped. Fig. 1 illustrates the spectrum usage among Bluetooth, ZigBee and WiFi. Different devices operating on the public spectrum will introduce CTI with each other and bring wireless communication performance to deteriorate or even destroy. From pioneering papers to recent advances in communicating on commodity devices under CTI can be divided into bridging wireless technologies and cross-technology communication (CTC). Fig. 1Open in figure viewerPowerPoint Interactions between 802.15.1 (Bluetooth), 802.15.4 (ZigBee) and 802.11b (WiFi) [5] Traditionally, bridging wireless technologies achieve an indirect connection among heterogeneous devices through multi-radio gateways. Gateway, also known as a protocol converter, is an inter-network connector used for information transmission and exchange between networks. With multiple wireless interfaces equipped, a local gateway can translate data from different devices abiding by different communication standards. For example, ZigBee technology and Bluetooth technology, respectively, complete the communication between devices under the drive of different network protocols, packet encapsulation is also quite different in the process of data transmission. To achieve communication between ZigBee devices and Bluetooth devices, a ZigBee and Bluetooth dual radio gateway can convert the two types of data. The functions required by this gateway include: (i) The ability to communicate individually with ZigBee devices and Bluetooth devices. (ii) The ability to convert ZigBee packets and Bluetooth packets to each other. According to function (i), the gateway must be a dual-stack device; function (ii) requires that the gateway needs a data processor to parse and encapsulate the data packet. Therefore, the working principle of the gateway is that the data processor receives data through a single-sided protocol stack device, according to the data format of the package on this side for data analysis (i.e. stripping address information and control information in the data packet) to load data; afterwards, according to the data packet format on the other side for encapsulating data (i.e. adding address information and control information). Protocol conversion is achieved through the process of data parsing and data re-encapsulating. This allows that ZigBee devices receive Bluetooth packets, Bluetooth devices can receive ZigBee packets. A general-purpose IoT gateway on a smartphone can be used to perform the data processing [6]. Vivek and Sunil [7] proposed a WiFi–ZigBee gateway, which provided user terminals and system functions with an appropriate application interface to establish the connection and managing bidirectional data communication. Considering that most IoT devices are small-scale and battery-powered, Galinina et al. [8] exploited Bluetooth low energy (BLE) to enable energy-efficient data transmission. Currently, Shim et al. [9] designed a ZigBee–BLE gateway direct communication system to control and manage home appliances. These IoT systems are implemented indirectly through multi-radio gateways that introduce additional hardware, maintenance costs, deployment complexity, and traffic overhead into and out of the gateway. To settle the inherent issues of bridging wireless technologies, recent advances in CTC have been introduced to establish direct communication across technologies. Consequently, network coordination protocols (e.g. TDMA and RTS/CTS) can be stretched out to extensive application in across-wireless technologies. The overview of CTC is shown in Fig. 2. In brief, the core idea of CTC implementation is that wireless devices operating in the public spectrum need to sense the presence of signal via channel energy detection, such as channel state information (CSI) and received signal strength indicator (RSSI). Under the restriction of incompatible physical layers, heterogeneous wireless devices, equipped with different technologies, are incapable of decoding each other's information. However, they can identify each other's existence via channel energy sensing. In other words, CTC mechanisms are based on the channel sensing technique and sense energy patterns which heterogeneous devices can recognise. For example, a ZigBee device cansense the channel energy when dedicated WiFi packets are transmitted from a WiFi device. Various CTC mechanisms include requiring dedicated hardware (hardware-based) and not requiring dedicated hardware (hardware-free). These CTC mechanisms have a wide range of IoT applications, for example the technology of direct communication from WiFi to ZigBee can be applied to control devices in smart homes [10]. Fig. 2Open in figure viewerPowerPoint Overview of CTC Existing wireless communication environment where heterogeneous technologies operate in the same unlicensed 2.4 GHz ISM band, a consequence of this is that there will be an opportunity to establish a direct CTC among these technologies. Replacing existing hardware or building new dedicated hardware to enable direct CTC is motivated by the fact that heterogeneous technologies have different corresponding protocols in PHY and MAC layers. For example, in [11], an inter-technology communication constructs the sequence of energy pulses whose gaps conveying information for the coexisting technology, and perceives the gaps between them to create a side channel between wireless nodes. Requiring the design of additional equipment with low-power is investigated in recent works [12, 13], which can establish a direct connection between heterogeneous devices. To enable WiFi to sense the existence of ZigBee, an alternative approach [13, 14] employs a dedicated helper node which sends a busy-tone through a created channel for minimising interference. Recently, many scholars have become interested in medical applications including smart contact lens platforms [15-18] that measure biomarkers such as glucose, cholesterol and sodium for diabetes management; and implanted neural devices which are used to treat epilepsy, Parkinson's disease [19], reanimation of limbs [20] and development of brain–computer interfaces [21]. These implanted devices have the potential to change chronic medical condition's management and enable novel interactive functions by using backscatter communication (BackCom) systems. The key challenge of achieving these goals is that implanted devices cannot use conventional radios to generate WiFi, Bluetooth or ZigBee transmission signals due to strict power limitations, and therefore, cannot communicate directly with mobile devices (e.g. smartphones, watches and tablets). Although hardware-based techniques have achieved better results in improving the performance of cross platforms. In effect, the workload of direct communication across heterogeneous systems is only limited. Moreover, they need to modify existing hardware or deploy new hardware, which is too expensive for existing off-the-shelf devices. And the extra demand fordedicated hardware makes CTC unrealistic in some application scenarios. On the other hand, to achieve direct communication among commercial devices in the same spectrum, the highlight of hardware-free techniques is that the proposed designs are committed to constructing CTC among heterogeneous devices without requiring additional hardware, while still complying with existing standards. In this paper, hardware-free are divided into packet-level modulation and physical-level modulation. Existing CTCs commonly use packet-level modulation, where embedding symbols with the use of durations of packets [22-24], timing [25-27], packet energy [28, 29], sequence patterns [30, 31] and all types of frames [10, 32, 33] to convey the data. Bring significant benefits including, but not limited to CTI moderation and effectiveness. As physical-level modulation [34-40], this pioneering works pick up coarse-grained ‘packets’ as the basic modulation, where one packet is able to express at most several bits. Bitrates are inherently limited due to coarse-grained ‘packets’ as the basis for modulation. Therefore, the physical-level emulation technique is proposed by He et al., which is a new direction for CTC schemes without hardware. We compared hardware-based CTCs and hardware-free CTCs qualitatively rather than quantitatively, which is displayed in Table 1. Compared with hardware-based CTCs, hardware-free CTCs, adoptable and cost-effective solutions for deployed billions of devices, eliminate the need for any hardware change and are fully compatible with disparate commodity devices. Hardware-free schemes achieve CTC on commodity devices without the requirement of additional hardware, which outperforms hardware-based schemes in terms of cost-effectiveness and energy saving, while weakening in terms of reliable protection and spectrum efficiency, because of no guarantee for interference in the overcrowded ISM band without hardware. Table 1. Hardware-based CTCs versus hardware-free CTCs Adoptability Cost-effectiveness Energy saving Reliable protection Spectrum efficiency hardware-based CTCs yes high high weak low hardware-free CTCs no low low strong high In this paper, an in-depth survey on CTC schemes is given. From the pioneering papers to the current state-of-the-art technologies, they are all collected and classified according to definite standard. A detailed comparison of these works is given, the main contributions of our work include: (i) To the best of our knowledge, this is the first survey work in this field, which focuses on CTC from the perspective of hardware. (ii) We depict the system performances of CTCs for both categories, and also illustrate the different application scenarios of two categories. (iii) Finally, the open research issues are discussed, current issues and research trends on CTC techniques are also presented. The remainder of this paper is structured as follows: the application scenarios, categorised by hardware-based and hardware-free, are briefly presented in Section 2. Section 3 reviews hardware-based CTCs. Hardware-free CTCs are described in Section 4, followed by open issues and future directions are discussed in Section 5. Finally, Section 6 concludes the survey. 2 Application scenarios Different devices deployed in IoT have different purposes depending on their characteristics and they cannot directly communicate with each another. Fig. 3 illustrates that WiFi supports transmission rate from 6 to 54 Mbps utilising quadrature amplitude modulation (QAM) or orthogonal frequency division multiplexing (OFDM) technology, while the ceiling transmission rate of ZigBee is 250 kbps utilising direct sequence spread spectrum (DSSS) or offset quadrature phase-shift keying (OQPSK) in 2.4 GHz ISM band. The advantage of WiFi is that its propagation distance is relatively long, it can directly access the Internet without a bridge and communicate with mobile phones seamlessly. The main disadvantage is that WiFi chips have a slightly larger package size and higher power consumption. In contrast to WiFi, ZigBee technology is relatively mature with a low-power, while the drawbacks are low-speed, poor wall performance and short communication distance, usually about 100 m. Fig. 3Open in figure viewerPowerPoint WiFi and ZigBee are targeted at different applications Heterogeneous devices deployed in IoT systems need to exchange information, the current methods are achieved indirectly via bridging wireless technologies, the result of this will introduce extra hardware cost, deployment complexity and so on. Contrary, CTC techniques build a direct link among existing billions of heterogeneous devices, which suffer from different hardware constraints and have different protocols in PHY and MAC layers without the pre-deployed gateways. A WiFi AP controls all smart home ZigBee-enabled devices in one hop without a gateway. For example, WEBee [34] realises bidirectional communication between WiFi and ZigBee by using a signal emulation method. CTC systems have changed at the breathtaking speed these years with the developing era of IoT. According to whether hardware devices are required for communicating between heterogeneous wireless technologies, we divide existing CTC techniques into two folds: hardware based and hardware free. Generally speaking, CTCs leverage dedicated hardware to send information for enabling wireless technology communication belonging to hardware-based. Alternatively, these schemes belong to the hardware-free without needing hardware to support communication. To understand the distinct requirements for the IoT devices, Fig. 4 furnishes the category of CTC from a hardware perspective. In this section, we present various application scenarios ranging from hardware-based to hardware-free. Fig. 4Open in figure viewerPowerPoint Category of CTC 2.1 Hardware based Coordination: Coordination is the main concern for CTC techniques, because heterogeneous technologies (e.g. WiFi, ZigBee and Bluetooth) operate in the same ISM band causing competition for spectrum resources and making CTI. For example, WiFi channels and ZigBee channels are distributed to different frequencies, although the bands are not completely overlapped. The cooperation among devices is crucial, because devices cannot directly decode standardised messages from other technologies. Modulation technique and demodulation technique: To achieve communication between heterogeneous wireless devices, the gateway uses a radio designed for a specific frequency band to modulate or demodulate. CTC schemes require both devices for modulation technique on sender and demodulation technique on the receiver. In particular, demodulation on ZigBee devices must be effective in both power and calculation. Sufficient throughput: The most important performance of CTC is throughput, which stands by the total data traffic in bits per second successfully received [41]. To encode more bits once and further increase throughput, general methods use the energy levels of amplitude modulation. Typically designed hardware generates throughput between a few Kbps and a few Mbps, and canbe placed in the home or on the body anywhere [13]. Therefore, the wireless links connected the dedicated hardware to wired gateway ought to offer uplink throughput of several Mbps and a range of 1–5 m. Energy efficiency: These devices require long periods of operation without replacing the battery or even without batteries. In the actual situation, the radio of designed device should provide the necessary throughput and range, and use tens of milliwatts of power to work without a battery. Thus, this will eliminate the need for a dedicated power infrastructure gateway (like an RFID reader). Therefore, maximise the power-transfer efficiency is a significant design issue. Reliability: The reliability of CTCs is to support explicit channel coordination by extending local mechanisms globally across wireless technologies. Reliability is a key factor in evaluating a CTC scheme, for example with long-distance transmission in an indoor or an outdoor, one CTC scheme can also have a higher frame reception rate. And it also manifests a moderate decrease in throughput as the length and number of transmitted frames increase. Next, an example is used to introduce the application scenario of hardware-based techniques, BackCom systems are already used in healthcare system applications, as shown in Fig. 5. BackCom systems belong to hardware-based strategies and comprise a tag, a Bluetooth watch and a smartphone (e.g. a WiFi device). The Bluetooth watch radiates a continuous wave (CW) at two frequency tones used to encode bits. CW akin to Bluetooth signal can be crafted to get the sensed electronic health information of BackCom tag, this information is collected by the smartphone through backscatter modulation. Due to the difference between Bluetooth CW frequency and WiFi signal, the BackCom tag can switch the Bluetooth CW to the WiFi channel by adopting a frequency-shift keying (FSK) modulation. Future IoT applications require BackCom systems to achieve long-distance, low-latency and high-speed communication between dense IoT devices, and also enable communication among heterogeneous devices. Unlike traditional gateway tags that only need to report their ID information, BackCom tags also need to sense and calculate which consume more energy. Fig. 5Open in figure viewerPowerPoint BackCom system applying in healthcare system 2.2 Hardware free Robustness to wireless channel noise: As wireless device attempts to compete for the channel access in the ISM band, this causes the ISM band to become crowded. Indubitability, this will incur ineluctable wireless noise affecting the receiver's energy pattern. In a nutshell, the performance of hardware-free schemes is enhanced by reducing noise. According to the channel quality, using the packet timing adaptively adjusts the length of receiving window to improve the data rate. For example, WiZig [32] stretches the window length when the channel quality is poor, while shortens the receiving window length when the channel quality is good. RSS sampling speed: The RSS sampling speed in low-power devices is another most important part for the propagation [42], however, it is inherently limited as CTCs adopt coarse-grained ‘packets’ as the basis for modulation. For example, the bit rate of BLE to ZigBee communication in the state-of-the-art is limited to 18 bps [25], a consequence of this is a low throughput. Mobility: Achieving direct communication among the mobility of IoT devices without pre-deployed gateways or other dedicated hardware is the primary concern for the design CTC schemes. Once CTCs achieve mobility, CTCs will be widely used in the vehicular ad-hoc network, battlefield, inventory tracking, wearables and so on. Specially, Alsamhi et al. [43] discussed mobile devices via using artificial intelligence in ad-hoc network for vehicle communication. Achieving direct communication among the mobility of IoT devices without pre-deployed gateways or other dedicated hardware is the primary concern for the design CTC schemes. Once CTCs achieve mobility, CTCs will be widely used in the vehicular ad-hoc network, battlefield, inventory tracking, wearables and so on. Specially, Alsamhi et al. [43] discussed mobile devices via using artificial intelligence in ad-hoc network for vehicle communication. Cost: To realise direct communication among heterogeneous wireless technologies, hardware cost, infrastructure cost, maintenance cost and installation cost have been recognised as of key element for CTCs. Compared with bridging wireless technologies, CTC can achieve low cost, for example a smart home is equipped with ZigBee devices that are controlled by a WiFi AP in one hop without a gateway. Efficiently transmitting information: Energy savings used by communication devices should be considered in IoT, therefore Alsamhi et al. [44] pointed out the importance of more energy-efficient technologies, since different technologies use different physical layers and protocols, they cannot directly communicate with each other. Furthermore, the authors of [41] explored the importance of efficient transition on wireless communication services on the Internet of public safety things. As a current trend, the IoT provides instant access to everything in many applications, including homes, ubiquitous healthcare systems and business, to improve human health and well-being. The application of IoT to smart homes, people can easily control various equipment (climate control systems, carports, TVs, furniture, goods and so on) via mobile phones under the help of CTCs. For example, a smart home application scenario, where WiFi mesh networks have been employed to provide Internet connectivity [45]. Given the WiFi interface in the active state will consume a considerable amount of power, which is the main source of energy consumption and affects the user experience. Esense [22], one of the packet-level modulations, uses an extremely low power ZigBee radio to wake up a WiFi interface. In this condition, the WiFi can be turned off when idle and remotely woken up by its neighbours through Esense messages, which are received on the low-power ZigBee radio. For example, temperature, humidity, light and smoke sensors are deployed in a smart home, various of them can be controlled by a smartphone. And this information is transmitted over the Internet to the WiFi APs, which transmit the control information to various sensors via CTC. 3 Hardware-based CTCs Owing to the additional wireless traffic can be caused by the relay traffic of the gateway. Moreover, the key challenge is that gateway cannot use conventional radios to generate WiFi, Bluetooth or ZigBee transmissions and consequently cannot communicate directly with each other. Particularly, to achieve this goal, there is a pressing need for a CTC technique [46], which enables to interpret signals coming from another technology without dual-radio gateways. Considering this circumstance, numerous coordination-based methods are springing up to settle direct communication among heterogeneous wireless technologies. Meanwhile, there are several candidates that achieve the same goal and require dedicated hardware through backscatter communication systems classified as BackCom-based. In this section, substantial resolutions and systems of hardware-based CTCs in recent years are reviewed, mainly in two aspects: coordination based and BackCom based. 3.1 Coordination-based systems A coordination-based approach is considered as an effective way to solve the problem of direct communication among heterogeneity devices, such as [3, 11, 14, 47-49]. One of the works [47] studies on how to actively ensure the coexistence of disparate wireless devices. Other works [3, 48, 49] use indirect coordination mechanism, by taking advantage of transmitting busy-tone or preamble, which consists of multiple energy pulses to prevent other signal interference; or by modulating the payload length to encode channel access parameters [49]. Gummadi et al. proposed Metronome [47], a policy framework demanding an arbitrator, which allocates these parameters, including transmit power and carrier sensing threshold to communicate with different wireless devices. Metronome is implemented to be used with the universal software radio peripheral (USRP) hardware and GNURadio software for the monitors, which collect wide-band spectrum activity information around a receiver in order to robustly compute the signal and interference power. While this policy framework only applies to static networks, due to the mobile node's arbitrator should be restarted the spectrum survey and reallocated parameters. Zhang and Kang [14] proposed another framework, cooperative busy tone (CBT) which enhances the mutual observability between ZigBee and WiFi to resolve the coexistence between them. The core idea of CBT is to equip hardware to improve the visibility of ZigBee signals, thereby boosting the throughput of WiFi and reducing performance overhead compared with the legacy ZigBee protocol. Cooperative carrier signalling (CCS) [3] adopts a mechanism similar to CBT, i.e. a cooperative busy-tone mechanism with a busy tone scheduler that enables a ZigBee node to select a busy-tone concurrently with the desired transmission. CCS also harnesses a special coordinator to make busy-tone when there exists ZigBee transmissions. The result of this is to enhance the ZigBee's visibility to WiFi. To achieve lightweight coordination of WiFi and ZigBee, Zhang and Kang [11] also put forward a method, gap sense (GSense) is the straight-forward way to design dedicated hardware, which is a novel mechanism to coordinate heterogeneous devices, and does not modify PHY layer modulation schemes or spectrum widths. The GSense's preamble is composed of multiple energy pulses with quiet periods (gaps) in between, which is designed to maximise the signal-to-noise ratio and detection probability for ensuring sufficient capacity to accommodate the coordination information. For example, ZigBee devices first send preambles to build an energy pattern in the air. Then, when the WiFi device detects this energy pattern, it delays its transmission to avoid interference. This method is very promising, but it cannot be actualised in commercial devices, due to its inefficient communication. ZigBee devices with less ability often have unpredictably low throughput due to strong WiFi interference. Based on the ability of the ZigBee protector to reserve the ZigBee device's channel, a novel time-reservation scheme, named narrow band protection (NBP), is presented by Lim et al. [48]. To protect ongoing ZigBee transmissions, the NBP protector automatically perceives ongoing ZigBee packet by cross-correlating it with the pre-defined pseudo-random noise (PN) sequences. Next, the protector switches to the adjacent channel and issues a reservation signal for the duration of the estimate, preventing the WiFi node from tr
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