Recent trends in Wireless Body Area Network (WBAN) - Springer Link

Health Technol. (2014) 4:239–244 DOI 10.1007/s12553-014-0083-x

REVIEW PAPER

Recent trends in Wireless Body Area Network (WBAN) research and cognition based adaptive WBAN architecture for healthcare Dheeraj Rathee & Savita Rangi & S. K. Chakarvarti & V. R. Singh

Received: 31 January 2014 / Accepted: 7 May 2014 / Published online: 24 May 2014 # IUPESM and Springer-Verlag Berlin Heidelberg 2014

Abstract In healthcare domain, Wireless Body Area Network (WBAN) has transpired as a prominent technology which is capable of providing better methods of real time patient health monitoring at hospitals, asylums and even at their homes. In recent times, WBAN has gained great interest and proved one of the most explored technologies by health care facilities because of its vital role and wide range of application in clinical sciences. WBAN involve communication between very small sensor nodes with frequently changing environment, hence lots of issues still need to be addressed. Some of the major issues are Physical layer issues, interoperability & mobility issue, reliability, resource management, usability, Energy consumption and QoS issues. This research paper includes a comprehensive survey of recent trends in WBAN research, provides prospective solutions to some major issues using cognitive approach and a proposed concept of Cognitive Radio based WBAN architecture. Thus a conventional WBAN architecture can be improvised to an adaptive, more reliable and efficient WBAN system using Cognitive based approach.

D. Rathee (*) : S. Rangi : S. K. Chakarvarti Department of ECE, FET, Manav Rachna International University, Faridabad, India e-mail: [email protected] S. Rangi e-mail: [email protected] S. K. Chakarvarti e-mail: [email protected] V. R. Singh National Physics Laboratory, New Delhi 110012, India e-mail: [email protected] V. R. Singh PDM Educational Institutions, Bahadurgarh, India

Keywords Wireless Body Area Networks . Cognitive Radio . MAC layer . Healthcare . WBAN applications

1 Introduction WBAN is a wireless networking technology, based on Radio Frequency (RF) that interconnects a number of small nodes with sensor or actuator capabilities. These nodes operate in close vicinity to, on or few cm inside a human body, to support various medical area and non-medical area applications [1]. WBAN technology is highly appreciated in the field of medical science and human healthcare [2–5]. Also significant contribution is delivered in the field of Biomedical and other scientific areas [6]. Moreover, its applications are widespread in non-medical areas like consumer electronics and personal entertainment. In late 1990s, researchers & academicians showed interest in cognitive radio (CR) technology. The general idea of CR was given in 1999 by Mitola [7]. Cognitive radio enhances the software radio with radio-domain protocols, and extends the flexibility of user defined services using a radio knowledge based programming language. Thus an ideal platform is provided by Software radio for the practical realization of cognitive radio. Cognitive Radio (CR) is a platform for opportunistic and cooperative control to primary (licensed) section of the electromagnetic spectrum by secondary (unlicensed) users. CRT includes sensing its electromagnetic operational environment by sensors. CR enabled BAN will plan and take decisions on its outcomes considering system’s priorities, end goals and other constraints and further focus on improving the efficiency of wireless resource usage. With these self-awareness and environment awareness capabilities the novel WBAN system can apply best strategies to meet its requirements. Further details about CRT can be referred from [8–19]. During the last 12 years, the technology grows at rapid speed.

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The utility of CR has been recognised by ETSI and IEEE. IEEE is playing an important role in developing CR technology by forming IEEE standard 1900 with its workgroups 1–6 [20].

2 Current trends in WBAN research A lot of research work is undergoing on WBANs. The main issues concentrated upon are scale of network, result accuracy, node density, power supply, mobility, data rate, energy consumption, QoS, and Real time communication. WBAN nodes use miniaturized batteries due to their small size. Hence the network must work and perform in a power efficient manner so that the life duration of power sources can be maximized. Most of the work in this particular domain has been on development of better MAC protocols for energy efficient processing. Presently, there are two different approaches of MAC protocol designing for sensor networks. First one is Contention- based MAC protocol design. Example of this type of MAC protocol is Carrier Sense Multiple Access – Collision Avoidance (CSMA/CA). This design has their nodes priorities for channel access before transmitting data. The benefits of CSMA/CA based protocols include almost no time synchronization constraints, easy adaptability to network variations and scalability. The other approach is Schedulebased MAC protocol. Example of this type of protocol is a TDMA based, in which time slotted access to the channel is provided. Hence different users get separate time slots for data transmission. These slots can be of fixed or variable duration. Time Slot Controller (TSC) is used for providing time slots. The benefits of this approach are reduced idle listening, overheading and collision. TDMA based approach is highly used in energy efficient MAC protocol [21]. According to [22], IEEE 802.15.4 is not capable of providing energy efficient communication for WBAN applications. There are many loop holes that must be filled for their use in medical area. Hence another improved standard, i.e. IEEE 802.15 with task group 6 (BAN) has been formulated [23]. The purpose of this standard is to provide new MAC and physical layers for WBAN. The Physical layer (frequency bands) is categorized as Narrowband, Ultra Wide Band (UWB) and Human Body Communication (HBC). The MAC layer includes following three modes [24]: 1. Beacon mode with a beacon period superframe boundaries 2. Non Beacon mode with superframe boundaries 3. Non Beacon mode without superframe boundaries In [24], it is also shown that the efficiency for CSMA\CA based MAC layer can be improved by increasing payload size

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and thereby bandwidth. Another work undertook the approach of Clear-Channel Assessment and Collision Avoidance (CCA\CA) with TDMA in generation of energy-efficient MAC layer [25]. Marinkovic et al. [26] presents a low duty cycle, TDMA based energy efficient MAC protocol. The novel MAC protocol includes collision free data transfer (TDMA) and energy efficiency because of sleep time application for sensors, without the need of channel listening. Hence, communication is done for small overhead and minimum time spent on idle listening. The protocol is implemented on analog device development platforms (ADF70XXMBZ2) with RF transceivers. A novel approach of heartbeat powered the MAC protocol is given by [27]. This protocol is TDMA based and used for body sensor networks (BSNs). The work includes usage of heart beat rhythm to perform time synchronization and hence provides an energy-efficient MAC layer by avoiding power consumption associated with time synchronization beacon transmission. Fang, et al. proposed a new MAC protocol, BODYMAC, for WBANs [28]. This protocol uses efficient and flexible bandwidth allocation schemes and introduction of sleep modes to reach the desired requirements of dynamic application in WBANs. The bandwidth allocation flexibility of BodyMAC is improved by dynamic bandwidth allocation mechanism like burst bandwidth. Results showed that the average delay is decreased by almost 30 % and improved bandwidth utilization efficiency was achieved. But the effect of deep channel fading and central packet introduction is not considered during the simulation process. In [29], Timmons, et al. introduced another novel Mac protocol, MedMAC. The protocol features contention free TDMA channel access scheme, a novel low-overhead TDMA synchronization mechanism, energy-efficient, and dynamically adjusting time slots, optimal contention period and use of sleep modes. Adaptive Guard Band Algorithm (AGBA) is used to maintain synchronization of devices during sleeping period, using beacons. The protocol is useful in only low & medium data rate medical application of WBAN. A cross-layer fuzzy-rule scheduling algorithm was introduced to replace conventional first-come-first-serve transmitting discipline for MAC layer processing by Otal et al. [30]. Hence a new Distributed Queuing Body Area Network (DQBAN) MAC protocol was introduced to get high reliability and application based QoS requirements (reliability & message latency) for packet transmission. Energy consumption was reduced but not significantly. Latre, et al. also proposed a cross-layer protocol, CICADA, for WBAN application [31]. CICIADA or Cascading Information by Controlling Access with Distributed slot Assessment was based on tree structures. A control cycle and a data sub-cycle were used collectively to achieve low


delays and better energy efficiency while preserving network flexibility. Al Ameen et al. [32] proposed a novel wake-up mechanism for implanted devices to communicate in Wireless BANs. The proposed MAC protocol was energy-efficient and minimizes time delays, but functionality is restricted to implant devices only. In [33], Liu et al. introduced a novel dynamic model for small scale direct methanol fuel cells. In this fuel cells are directly coupled with PSO algorithm to increase the battery life. A hybrid approach to context –aware MAC protocol was introduced using TDMA-based and contention-based algorithms by Choi et al. [34]. Channel fading due to adaptively modified frame structure was also managed using a new control mechanism while bursty, periodic and emergency data traffic was controlled by polling-based and scheduled-based techniques. Simulation results were better than conventional system but reliability and efficiency was quite low. Huq et al. [35] proposed an energy efficient MAC layer protocol for master node and attached nodes in WBAN system. Performance of the system was better with high number of nodes as the size the conventional MAC superframe structure was reduced by removing redundant periods. Thus the average power consumption per bits was drastically reduced but reliability was still an issue. In [36], a highly reliable Medical emergency body (MEB) MAC protocol was proposed by dynamical insertion of listening windows in contention free periods. The results showed better and reliable system but high power consumption and susceptibility to outer interferences were still present. In [37], increased sleep time and low duty cycle per beacon was introduced in form of a statistical MAC layer protocol for heterogeneous traffic networks. The system was experimented in HBC platform and resulted in an energy efficient and compact protocol but the system reliability was low because of non-transmission of lost messages during inactive periods. A survey on various context-aware MAC layer and application layer protocols was given in [38]. It was concluded that limited solutions are available particularly in MAC layer area for context-aware data transmission. Most of the work that has been discussed above speaks about providing novel energy-efficient MAC layer protocols or better power supplying devices. Although none of them have succeeded in making significant energy efficient systems with better throughput.

3 Proposed architecture for adaptive WBAN using a CRT The proposed architecture is to merge two most significant technologies of current time i.e. Conventional WBAN and Cognitive Radio Technology (CRT), to get a highly efficient and reliable Wireless Body Area Network that revolutionizes

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the future of WBAN. The novel cognitive approach based wireless BAN, can lead to a considerable improvement in resource efficiency (spectrum management), networking efficiency and energy efficiency. Research Design includes proposed architecture of WBAN with Cognitive abilities. The architecture includes the following three levels of communication (Fig. 1). 3.1 Level 0 This level includes Intra-WBAN communication. This includes the following components: 3.1.1 Core and actuator nodes (sensors/actuators) A number of sensor nodes operating on the body, inside the body or in close proximity (less than 2 cms) to collect data on physical signals (bio-signals) from human body (detection\acquisition), process them (if necessary) according to requirements and finally transmit them to a centralized on body network controller. It consists of a micro sized processor with memory, a power unit & a transceiver. Intelligent Core and access nodes (sensors/actuators) can be designed with the help of cognitive approach. Sensor nodes are designed using appropriate methods and ability to access self and environment information. Thus intelligent nodes will perform their operation in highly reliable and energy efficient manner, using cognitive approach. The intelligent sensors are capable of adjusting not only to communication limitations but also to the information requirements. Cognitive features that can be incorporated in sensors are goal evaluation, real time and energy efficient monitoring, intelligent processing and wireless cognitive connectivity with Network Coordination Unit. 3.1.2 CRT based Network Coordination Unit (NCU) This device is placed on body of a patient or the person under consideration itself. The main purpose of NCU is to communicate core and access nodes (sensors/actuators), process the compiled data and transmit to Central Controlling Unit (CCU) at Level 1. CRT based NCU is capable of performing a number of cognitive functions like to improve Data fusion, spectrum sensing (b/w nodes & NCU), configurable networking, node parameters (mobility, battery life, working, connectivity) sensing, energy efficient and reliable data routing and wireless cognitive connectivity with CCU. The basic components of CRT based NCU would be a small size processing unit, memory unit and a transceiver. 3.2 Level 1 This communication level consists of Inter-WBAN networking. Here a number of NCUs are connected wirelessly to a

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Fig. 1 Basic architecture of CR enabled WBAN

CRT enabled the Central Controlling Unit (CCU) and main function of CCU is to communicate with a number of NCUs within a particular area (hospital, building, asylum etc.) using CRT approach. This unit will be static and hence power supply and connectivity issues are not so important, but the rest of the issues are quite vital. Cognitive functions that can be incorporated in CRT enabled CCU are spectrum sensing (b/w NCUs & CCU), Energy efficient and highly reliable routing protocols, Efficient MAC protocol, NCU parameters (mobility & location, battery life, working, calibration and connectivity) maintenance, QoS awareness and end-to-end goal maintenance. The basic components of the CRT based CCU will be a heavy processor, large memory unit and a transceiver. 3.3 Level 2 This communication level will be beyond WBAN networking. CRT based CCU will be connected wirelessly to any of the following: &

Doctor or Medical Attendant or Supporting staff

& &

Emergency Services e.g. ambulance or risk management unit Hospital or Healthcare Unit

3.4 Cognitive functions incorporated The cognitive functions that would be applied to different networking layers in CRT enabled WBAN are as follows: 3.4.1 Spectrum sensing The major cognitive approach to the WBAN is Spectrum Sensing. WBAN can communicate through licensed bands (MICS, WMTS) or through the unlicensed band like ISM (2.4 GHz) band. Both communication systems require information about the primary users (licensed) and white spaces (empty spectrum holes) in the spectrum. It has been seen that much of the licensed spectrum remains unused most of the time and unlicensed band is overcrowded as most of the medical devices communicate in this band only. Thus efficient


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exploitation of the spectrum is quite vital. CR enabled WBAN can use cooperative or opportunistic spectrum sensing techniques for spectrum aware processing. 3.4.2 Resource allocation Resource Allocation in CR enabled WBAN is very crucial as it controls the interference caused to other communication systems as well as to its own network. It includes Power and frequency allocation schemes which can be done in proper manner to minimize the interaction of WBAN with other networks like Bluetooth, LANs etc. and to minimize interference between different BNUs (inter-WBAN). QoS and endto-end goals consideration is also taken into account during resource allocation in CR enabled WBAN. This function in the CR - WBAN will be able to utilize dynamic spectrum resources efficiently to maximize network throughput performance. It will also ensure minimization of harmful interference from Secondary Users to Primary Users. Moreover, CRT is capable enough to convert the resource gains into performance gains efficiently. 3.4.3 CRT enabled MAC protocol Energy efficiency is another important requirement in WBAN (as explained earlier) and an efficient MAC protocol is the most suitable level in the protocol stack to address the energy consumption issue. CR enabled MAC protocol will use the information about spectrum, resource allocation and QoS issues to provide an optimum Spectrum access scheme. The novel MAC layer will support distinct applications and transmission of heterogeneous data with high level QoS. The fundamental task of CR-enabled MAC protocol is to avoid collisions and repeated data transmissions while maintaining maximum throughput, communication reliability, minimum latency and maximum energy efficiency. In CR enabled WBAN MAC layer is tightly coupled with high level layers and PHY layer. 3.4.4 Spectrum-aware routing protocol Spectrum-aware routing protocol enhances the cognitive functions of link and network layers. This protocol became crucial when the physical layer nature is dynamical. In WBAN, high overhead problem is quite natural hence intelligent routing protocol is must. Spectrum awareness feature gives conventional routing protocol a fair idea about changing spectrum and hence CR enabled BAN will possess adaptable routing protocol for better performance. CR-BAN transport protocols will constitute efficient end-to-end layer applications. Spectrum sensed data can be implemented during protocol generation.

Fig. 2 Layered architecture of CR enabled WBAN

3.4.5 QoS awareness and end-to-end goal achievement QoS and end-to-end goals are crucial parameters for any Efficient & reliable system. QoS awareness is a CRT function that is very much related to multiple layers of the network while end-to-end goals are directly related to the application layer. Desired goals would be achieved by intelligent processing and smart communication of data within different layers of network while considering QoS awareness. Also reliability of the system would improve by constant monitoring of end-to end goals, comparing them with desired QoS parameters and reconfiguration of network. Another view of CRT based WBAN architecture is shown below in Fig. 2 which includes layer wise WBAN working using cognitive approach.

4 Conclusion This paper included current research trends in WBAN with deep review of MAC layer research. We also proposed the concept of CRT based Adaptive WBAN architecture for efficient and reliable results. CRT based functions for different layers of the network were also modelled and discussed in detail. Future work may involve practical testing of the proposed concept. Conflict of interest The authors declare that they have no conflict of interest.

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