On Cognitive Radio-based Wireless Body Area Networks for Medical Applications

Aqeel Raza Syed, Kok-Lim Alvin Yau Department of Computer Science and Networked System

Faculty of Science and Technology, Sunway University, Malaysia 12010591@imail.sunway.edu.my, koklimy@sunway.edu.my

Abstract—Wireless Body Area Network (WBAN) is

envisioned to provide a wide range of health-care services to patients in medical environment such as hospitals and clinics. This increases the deployment of wireless platforms in medical environment that bring new challenges, such as interference with neighboring medical devices and the degradation of Quality of Service (QoS) performance, which may be critical to patient’s safety. Cognitive Radio (CR) is next-generation wireless communications, and artificial intelligence has been widely adopted to provide self-learning in order to observe, learn and take action against its operating environment. The application of CR in medical wireless environment can cater to the aforementioned challenges. In this paper, we present a review on the limited literature on CR-based WBAN, highlighting some pioneering schemes in this area. We present two architectures, two state-of-the-art applications of CR (i.e. Electro-Magnetic Interference (EMI) reduction and QoS enhancement), as well as a number of schemes in CR-based WBAN. While there are numerous research efforts investigating CR and WBAN respectively, the research into CR-based WBAN remains at the infancy stage. This paper discusses various open issues related to CR-based WBAN in order to spark new interests in this research area.

Keywords—Cognitive radio, wireless body area networks, context awareness, intelligence

I. INTRODUCTION The revolution of ubiquitous and pervasive computing has

significantly increased the demand for spectrum resulting in spectrum scarcity. Cognitive Radio (CR), which is the next generation wireless communication system, has emerged as a promising technique to address spectrum scarcity. The CR technology enables unlicensed users (or Secondary Users, SUs) to access underutilized licensed (or white space) spectrum opportunistically whenever licensed users (or Primary Users, PUs) are in idle state [1]. The SUs can access licensed and unlicensed bands in order to improve spectrum efficiency. In licensed bands, PUs have higher priority to access the channels than SUs; while in unlicensed bands, there is lack of the concept of PUs and SUs such that every user has the same priority to access the channels.

Cognitive radio can be applied to medical applications, such as telemedicine systems, Wireless Body Area Networks (WBANs), bio medical devices and mobile hospital information systems, to provide social advantages. For instance, wireless communications enable medical staff to continuously monitor a patient’s data gathered by sensors worn

by the patients, and so it greatly improves the patient’s mobility, which is impossible with the traditional wire-connected devices. Furthermore, the medical staff can be gathered the data seamlessly either in mobile or static condition through mobility management (i.e. roaming and handoff strategies) [2]. While in [3], traditional wireless technologies, such as IEEE802.11 and Bluetooth, have been applied in hospital and home environments for different medical applications, CR offers several added advantages in line with its intrinsic characteristics, such as the use of licensed spectrum and opportunistic access. The application of CR in medical environment has been very limited, and remains in its infancy stage while there has been numerous research efforts investigating CR and WBAN respectively in recent years, and so this is the focus of this paper.

This paper presents limited state-of-the-art applications of CR to medical applications in order to promote research interest in this area. The limited literature on CR-WBAN has been the motivation for this paper. Our contributions are as follows. The next subsections present overviews of CR and medical applications respectively. Section 2 presents CR-based architectures for medical applications. Section 3 presents an overview of the application of CR to medical applications. Section 4 presents the application scheme of Cognitive Radio-based Wireless Body Area Networks (CR-WBANs). Section 5 presents open issues. Section 6 presents conclusions.

A. Cognitive Radio Equipped with the capability to observe and learn from the operating environment, SU transceivers can adapt their respective wireless transmission parameters and make decisions to optimize network performance. For instance, in [2], medical equipment can be categorized as PUs, which have higher priority (i.e. EMI-sensitive medical devices), and SUs, which have lower priority (i.e. non-EMI-sensitive medical devices), in a hospital environment. The SUs observe the channels (i.e. white spaces), learn to select transmission parameters (e.g. channels and modulation techniques), and use the channels in order to maximize the throughput performance of SUs, while reducing the interference to PUs. For this purpose, SUs must sense the spectrum on a regular basis [4].

Cognitive Radio has unique attributes of ‘learn’, ‘sense’, and ‘adapt’. Generally speaking, CR provides two main advantages. Firstly, cognition capabilities enable SUs to acquire appropriate information about transmission parameters (i.e. transmission power) through learning mechanism, and to

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capture the underutilized spectrum through sensing the operating environment. Secondly, re-configurability enables SUs to dynamically adjust their transmission parameters (i.e. transmission power) respectively through adaptation mechanism based on the surrounding operating environment.

B. Medical Applications Medical or health care applications provide patient monitoring, diagnostic, therapy and imaging functions [5]. The advent of wireless technologies in medical environment significantly enhances the aforementioned objectives of medical applications and offers several advantages. Firstly, it provides remote monitoring and physical rehabilitation applications that help to ease the operations of medical staff. Secondly, it improves patient’s mobility, which speeds up the recovery process after surgical procedures. Thirdly, it reduces medical expenses due to earlier discharge from hospital [4].

This subsection presents four types of wireless medical applications, namely, Wireless Body Area Networks (WBANs), bio-medical devices, telemedicine systems and mobile hospital information systems.

1) Wireless Body Area Networks Wireless Body Area Networks (WBANs) are active

wireless-enabled components that provide remote monitoring of patients and the elderly at hospitals and home using telemedicine systems [6]. WBAN is comprised of sensors, which are embedded on medical devices (e.g. Electrocardiogram (ECG), Electromyogram (EMG) and blood-oxygen saturation) devices and controllers. Sensors are usually connected with the controller through a star topology. Furthermore, sensors require less transmission power to send their data to the controller. Generally speaking, the controllers gather and process sensing outcomes from the sensors, and subsequently send the processed outcomes to access points, which may connect to inventory systems, mobile hospital information systems (e.g. patient database) or even the internet.

2) Bio-medical Devices Bio-medical devices are passive in nature. Specifically,

these devices do not transmit information through wireless communications; however their electronic components may become malfunction due to their sensitivity to Electro-Magnetic Interference (EMI) caused by high transmission power of neighboring wireless devices. Examples of bio-medical devices are incubators, infusion pumps, anesthesia machine and defibrillators [2].

3) Telemedicine Systems Due to the limited resources (e.g. staff and equipment) and

increasing demand of health-care services in medical environment such as hospitals and clinics, telemedicine systems [5] can be deployed to monitor patients’ at home. In this system, the data collected by WBAN (see section 1.2.1) is forwarded to remote data processing center (e.g. mobile hospital information systems) through wireless networks such that IEEE802.15 and IEEE802.11 [3]. Telemedicine systems, such as multimedia (i.e. video and audio) e-health applications, have high bandwidth requirement, and it is sensitive to end-to-end delay and packet loss rate because of the data being transferred are of highly sensitivity, which is crucial to the

patient safety. For instance, tele-diagnostic with interactive audio and video transmissions provide remote consultations among physicians during operations and surgeries, remote diagnosis, and patient information transfers [2].

4) Mobile Hospital Information Systems Mobile hospital information systems handle all patients’

traffics traversing into and out of the hospital premises. It provides storage, retrieval and processing of patients’ medical records. It has high bandwidth requirement and sensitive to packet loss rate due to the criticality of the patients’ medical records [2]. Mobile hospital information systems may connect to patients’ WBAN through the underlying wireless network (e.g. IEEE802.11 and 3G).

II. COGNITIVE RADIO-BASED ARCHITECTURE FOR MEDICAL APPLICATIONS

Generally speaking, there are limited literatures on CR-WBAN architecture. This section presents two types of CR-based architectures for medical applications, namely three-tier WBAN architecture and central controller-based architecture. The three-tier WBAN architecture has been deployed in hospital and home environment, and it adopts hierarchical structure in which every patient is equipped with sensors and controller, which communicates with the access point in order to access the mobile hospital information systems. The central controller-based architecture has been deployed in hospital environment equipped with medical infrastructure (see Figure 2), and it adopts a master-slave structure in which a single controller acts as a master, and wireless-enabled devices act as slaves, which cover areas in the hospital premise.

A. Three-Tier WBAN Architecture In [4], Chavez-Santiago & Balasingham, propose a three-tier WBAN architecture consists of intra-, inter- and beyond-WBAN models as shown in Figure 1. The intra- and inter-WBAN models provide short-range communications (i.e. a few hundred meters); while the beyond-WBAN model provides long-range communications (i.e. a few kilometers). The prime objective of CR in this architecture is to alleviate interference level and to enhance Quality of Service (QoS) performance in the first two tiers. Next, we summarize these models.

Fig 1. Three-Tier WBAN architecture

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1) Intra-WBAN Model In intra-WBAN model, WBAN sensors communicate with

WBAN controllers, which is part of the inter-WBAN model. The sensors, which are wearable, are operating at close proximity to a patient’s body (e.g. a few centimeters), and so sensor’s communication must consume less power in order to reduce electro-magnetic effects of radio waves on a patient’s body. Furthermore, these sensors should have minimal electronic design complexity and have longer battery life, so that patients can comfortably wear these devices for a longer period of time. These requirements of low design complexity and low energy consumption make WBAN sensor devices inappropriate to implement CR functions (e.g. channel sensing and switching), which may consume high energy levels.

2) Inter-WBAN Model In inter-WBAN model, WBAN controllers communicate

with access points. In most cases, the access points are connected to inventory systems, patient database and internet. The access points can be configured by a handset, such as PDA and notebook. The access point serves as a communication bridge in between intra- and beyond-WBAN models. This model can adopt a centralized or distributed topology so that wireless sensors and controllers can communicate with each other in a single or multiple hops. CR functionalities can be implemented by the controllers and access points because they have greater processing capabilities than WBAN sensors.

3) Beyond-WBAN Model In beyond-WBAN model, the access points communicate

with base stations, and this model has been widely investigated in the traditional CR networks [7]. The beyond-WBAN model can provide a wide range of medical applications through communications between WBAN with medical team (e.g. doctors and nurses), medical database in the hospital, emergency healthcare facilities, and family connections.

B. Central Controller-based Architecture In [2], Phunchongharn et al. propose a central controller-based architecture equipped with CR capabilities. It comprises of three components, namely CR controller, inventory system, and CR clients as shown in Figure 2. The CR controller receives information from the inventory system as time goes by, and informs the CR clients about the allowable transmission power. In this architecture, CR controller plays the role of master, and it is responsible to allocate transmission opportunities to CR clients that are slaves. This architecture operates in unlicensed channel, uses a single channel each for data and control packets, and applies spectrum overlay techniques [8]. Next, we summarize the three components.

1) Inventory System Inventory systems keep track of inventory information,

such as physical location, EMI immunity level, activity status (i.e. busy or idle) and priority level (i.e. PU or SU), for all medical devices in the hospital. For instance, RFID readers are deployed in the vicinity of hospitals so that it can keep track of the inventory information through communications with RFID tags, which are attached to various medical devices.

2) Cognitive Radio Controller Cognitive radio controller acts as a master and a central

player which allocates transmission opportunities among its clients. Equipped with two radio interfaces, it can transmit and receive data simultaneously on two distinctive channels (i.e. data and control channels). It performs two main tasks. Firstly, it gathers information from inventory systems to determine transmission parameters (i.e. SU transmission power). Secondly, it uses EMI-aware approach to inform CR clients to control their transmission power respectively.

3) Cognitive Radio Client Cognitive radio clients are slaves in nature, and it depends

on the controller to assign transmission parameters (i.e. SU transmission power) and allocate transmission opportunities to them. CR client are attached to the medical devices, are equipped with a single radio interface, and so it can transmit and receive data with CR controller in either control or data channel only.

III. APPLICATIONS OF COGNITIVE RADIO TO MEDICAL APPLICATIONS

This section presents two types of applications of CR in medical applications that include reducing interference and enhancing QoS performance.

A. Reducing Interference Cognitive radio can be applied to reduce the interference introduced by the conventional wireless communications in medical applications, particularly Electro-Magnetic Interference (EMI) to EMI-sensitive medical devices. For instance, Bluetooth and ZigBee operate in the same or overlapping frequency bands, such as the 2.4 GHz (or the Industrial, Scientific and Medical, ISM) band, and so the applications may interfere with each other.

Reducing EMI interference helps to achieve promised QoS level and accuracy in medical devices. The EMI interference can cause malfunction (e.g. automatic shutdown and restart, and waveform distortion) that critically affect the operation and communication of various EMI-sensitive medical devices, such as infusion pumps, EMG monitor and ECG monitor, putting the wellness of the patients at risk [2], [4].

Fig 2. Central Controller-based architecture

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Furthermore, CR controller adjusts the transmission parameters (e.g. transmission power) of SUs (e.g. non-EMI sensitive devices) based on EMI constraints to minimize interference to PUs (e.g. EMI sensitive devices). For instance, RFID in [2], which provides accurate estimation and patient monitoring, is applied to implement EMI-aware communications. The patients’ location is identify, and subsequently the location information is used as constants to minimize interference to PUs.

B. Enhancing Quality of Service Performance Cognitive Radio can be applied to enhance the QoS performance of wireless communications among medical devices, particularly in transmission power reduction and channel access, by defining the priority levels of different medical devices as PUs and SUs [2]. For instance, CR applies an EMI-aware handshaking protocol for channel access, and QoS differentiation is provided to different kinds of medical devices or applications with different levels of priorities (i.e. telemedicine system as PU, and mobile hospital information systems as SU), in which PUs have higher priority than SUs.

There may be several traffic classes based on QoS requirements, such as bandwidth, delay and jitter. For instance, in [2], there are four classes, namely real-time critical, real-time non-critical, remote control, and office/support applications. Enhancement of QoS helps to protect the bio-medical devices from harmful interference by controlling the transmission power of PUs and SUs users. Another major challenge associated with QoS provisioning is the co-existence of multiple networks (e.g. IEEE 802.11 and IEEE 802.5), which may cause interference to medical devices, and so the QoS is unpredictable [6].

IV. APPLICATION SCHEMES IN COGNITIVE RADIO-BASED WIRELESS BODY AREA NETWORKS: STATE-OF-THE-ART

While there are considerable research efforts in CR, little has been done in CR-WBAN. This section presents the limited schemes of CR-WBANs in the literature. The schemes have been designed to reduce interference and provide QoS enhancement in CR-based WBAN.

A. Reducing Interference In [9], Nazir and Sabah propose a cooperative relay communication technique to adjust short-range transmission power and to enable channel access using game theory in order to provide robust transmission, as well as to reduce energy consumption and interference to medical devices in WBAN (see Section 1.2.1). It adopts the three-tier WBAN architecture (see Section 2.1). It improves robustness to minimize transmission failure as a result of physical body movements because any transmission failure may put the wellness and safety of patients’ at risk. In cases of failed transmissions (e.g. due to device failure, fading and interference) between a transmitter and a receiver, cooperative communication enables a node to choose an alternative neighbouring node as relay in order to forward data packets to its receiver. Game theory describes the behaviour of players who are interacting with each other in order to maximize network-wide performance

[10]. Game theory is applied to maximize a utility function, which takes account of throughput, transmission power level, SNR and channel gain. Higher values of utility function indicate greater robustness, energy efficiency and lower interference.

In [11], Dong et al. propose a CR-based mobile ad hoc network for WBAN (see section 1.2.1), which is equipped with a WBAN controller responsible for managing all available wireless networks (e.g. IEEE 802.11 and IEEE.802.15.4a) in order to allocate spectrum resource efficiently with interference avoidance using physical locations of bio-medical devices (see section 1.2.2) based on power compression and channel coding approaches. It adopts the three-tier WBAN architecture (see Section 2.1). In order to reduce the interference caused by sensors to EMI-sensitive bio-medical devices, the WBAN controller estimates the physical location of these devices and adjusts the transmission parameters (i.e. channel frequency and transmitting power) of the sensors. In order to estimate the physical locations of the devices, the WBAN controller estimates the distance between the sensors and the devices based on received signal strength, as well as time and angle of arrival of the signal. An enhanced graph colouring approach called Utility Graph Colouring (UGC) [12], is used to improve spectrum utilization in addition to interference avoidance, rather than merely minimizing the number of colours (or channels) in a graph, which is commonplace in the traditional graph colouring approach. UGC has been shown to increase spectrum reuse in which each channel can accommodate higher number of users, and hence it improves spectrum utilization. Additionally, correlated information (e.g. patient’s systolic and diastolic pressure) is compressed using information theory approach [13] so that transmission can be reduced in order to further reduce interference. Data compression is performed on correlated information, such as patient’s systolic and diastolic pressure information. The UGC and information theory approaches have been shown to improve throughput.

In [2], Phunchongharn et al. (2010) apply CR to reduce interference to medical applications such as telemedicine systems (see section 1.2.3) and mobile hospital information system (see section 1.2.4), and to prioritize transmissions with different levels of QoS requirements (i.e. packet delay and packet loss) in a hospital environment. For instance, telemedicine systems (or PUs) have higher priority level than mobile hospital information system (or SUs). It adopts a central controller-based architecture (see Section 2.2). In order to reduce the interference caused by SUs and to provide prioritized transmissions, two types of channel access mechanisms, namely common control channel broadcasting and EMI-aware request-to-send/clear-to-send (RTS/CTS), are proposed. In the common control channel broadcasting approach, the CR controller is responsible to control transmission parameters (i.e. transmit power) of its clients. Generally speaking, it calculates and broadcasts the maximum allowable transmission power in order to minimize interference to medical devices. The calculation of the maximum allowable transmission power of PUs’ and SUs’ are dependent on the physical location and EMI immunity of the medical devices. In the EMI-aware RTS/CTS approach, the CR controller receives requests from clients to assign transmission power, and it

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grants permissions only if the priority level of the client, the minimum QoS requirements, and EMI constraints of medical devices are fulfilled; otherwise, a negative CTS is returned to terminate the client. Compared to the traditional approaches, this scheme has been shown to reduce interference, and to improve QoS metrics (i.e. average packet delay and packet loss probability of PUs, as well as packet loss probability of SUs). Average packet delay is the time taken for a three-way handshaking between a user and a controller; while packet loss probability is the probability that a packet arrives to a full queue, and is dropped subsequently. There are two types of queues, one for PUs and another one for SUs. Since PUs have higher priority, their queue is smaller, and so PUs have lower average transmission delay.

B. Enhancing Quality of Service (QoS) In [6], Feng et al. propose two channel sensing mechanisms, specifically, periodic sensing and triggered sensing schemes for two types of telemedicine traffics with different priorities (i.e. urgent traffic and periodic traffic) in order to reduce transmission delay in WBAN (see Section 1.2.1). It adopts the three-tier WBAN architecture (see Section 2.1) in which the Cognitive Base Station (CBS) is equipped with multiple transceivers. The main difference between periodic sensing and triggered sensing schemes is that channels are sensed periodically in periodic sensing scheme, whereas the channels are sensed immediately whenever the current operating channels are occupied with PU activities in triggered sensing scheme. Therefore, whenever PU activities reappear, periodic sensing can only sense for new channels during the start of the next coming sensing period. Hence, as a comparison, the triggered sensing provides better QoS (i.e. throughput and transmission delay). The urgent traffic has the highest priority among all telemedicine traffics, and so transmission opportunities reservation is made in every beacon period. Due to the low amount of urgent traffic, a WBAN controller must respond to a periodic beacon sent by its CBS in order to prevent the reserved transmission opportunities being wasted. The periodic traffic, such as monitoring data, may have different priority levels. For instance, information of heart activity has higher priority than body temperature. Transmission opportunities reservation is made for higher priority traffic; while WBAN controller with lower priority traffics are assigned transmission opportunities according to the amount of traffic in their buffer. Triggered sensing has been shown to reduce transmission delay and increase throughput.

In [14], Yu et al. propose a home-based BAN architecture such as telemedicine systems (see Section 1.2.3), that provides transmission reliability in order to minimize Bit Error Rate (BER) and improve energy efficiency. Energy-efficient system enables the architecture to operate in low power (energy) levels, which reduces the radiation effects of electro-magnetic waves on human body. It adopts the three-tier WBAN architecture (see Section 2.1). It is comprised of sensors (see Section 1.2.1) and WBAN controller, which is comprised of a medical instrument and gateway. The medical instrument acts as a convergence node for all sensed data from the sensors. The gateway is equipped with cognition capabilities and cooperative communication functionalities, and it acts as an

access point, which further communicates with the mobile hospital information systems via the internet. Cognition capabilities enable a user to shift from one network to another intelligently for better and opportunistic use of spectrum; while cooperative communication functionalities enable a node to choose an alternative neighbouring node as relay in order to forward data packets to its receiver. Two cooperative communication schemes are proposed, namely Energy-conserved Cooperative Transmission (ECT) and Reliability-driven Cooperative Transmission (RCT). In the ECT scheme, there are distinctive power levels, and the total power level of sensors and multiple access points must be constrained in order to minimize energy consumption. In RCT, the power optimization criteria, in which the power level of sensors is constrained and the power level of access point is maximized, is adopted in order to achieve the necessary threshold value of BER for reliable transmissions. It has been revealed that the increment of transmission power enhances the communication reliability in both cooperative communication schemes, namely ECT and RCT, and decreases BER significantly. Cooperative communications also significantly decrease BER and energy consumption compared to non-cooperative communications.

V. OPEN ISSUES This section presents five open issues.

A. Introducing Cognitive Attributes to Sensors Radios equipped with cognition capabilities may incur higher energy consumption while performing the cognition attributes (i.e. learn, sense and adapt). Furthermore, SUs transceivers may switch their respective transmission parameters (i.e. channel frequency and transmission power) according to the type of operating network (e.g. IEEE802.11 and IEEE801.16) being selected. This aspect of cognition environment requires WBAN devices (i.e. sensors and controllers) to be equipped with an electronic circuit that can perform all these cognition attributes efficiently. This increases the complexity of circuit design of WBAN devices. While various CR-WBAN architecture have been proposed in the literature, such as [4] and [14], these cognition attributes have been applied at the WBAN controller only, rather than sensors. By introducing cognition attributes to sensors, the CR-WBAN will become fully cognitive, and this helps the sensors to make independent decisions (e.g. network selection) in order to reduce interference to medical devices and to improve QoS of CR-WBAN. The challenge is that this may introduce complexity to the sensor circuitry, which causes inconveniency to patients.

B. Extending Central Controller-based Architecture with Several Controllers

Using a single controller with higher transmission power in a central controller-based architecture (see Section 2.2) to cover all areas (e.g. patients’ rooms, operation rooms and corridors) in a hospital may increase interference to bio-medical devices [2]. In contrast, using a single controller with lower transmission power, the transmission range may be difficult to cover all areas. As a consequence, this may increase interference, as well as lead to degraded QoS performance.

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Hence, a single controller may not be sufficient. This architecture can be extended by deploying a hierarchical-based model comprised of multiple controllers with CR capabilities in order to adjust its transmission power to CR clients so that interference to the bio-medical devices can be reduced. The extended architecture can be similar to a conventional Global System for Mobile Communications (GSM) [15]. In GSM, the Base Transceiver Stations (BTSs), which form the lowest level of the hierarchy, communicate with their respective Base Station Control lers (BSCs), and the BSCs communicate with the Main Switching Centre (MSC), which form the highest level of the hierarchy. The hierarchical model provides several advantages including larger coverage area and increased network capacity and these can be achieved without increasing interference to PUs. There are several challenges associated with this model. For instance, it may increase the overhead (e.g. average transmission delay and control messages) due to multi-hop transmissions.

C. Enhancing QoS Performance There has been limited research on the enhancement of QoS performances (i.e. throughput, end-to-end delay and packet loss rate) in CR-WBAN. CR has been applied to provide QoS differentiation for different types of traffic classes.

Generally speaking, there have been limited traffic classes in CR-WBAN, which are normally categorized as PUs and SUs, even though higher number of available traffic classes may exist. In [2], four classes (i.e. real-time critical, real-time non-critical, remote control, and office/support applications) have been suggested; however, only two traffic classes were investigated, in which PUs and SUs are categorized as high-priority and low-priority traffic classes, respectively. Further investigation can be pursued to increase the number of available traffic classes in CR-WBANs.

Priority-based scheduling schemes can be applied to provide context-based QoS differentiation. For instance, a traffic priority may vary with respect to the severity of the patients’ health conditions (i.e. the degree or severity of life-threatening conditions) or the importance of a particular room or area (i.e. the degree of importance of the Intensive-Care Unit (ICU) and surgery rooms, as well as the hall way). Further investigation can be pursued to investigate context-based QoS differentiation in CR-WBANs, such as dynamic assignment of the PU and SU status, and the introduction of more priority levels. The traffic classes may be defined based on the objective of the networks, such as throughput and end-to-end delay requirements of the various applications.

D. Reducing Interference to Medical Devices using Non-RFID Approach

In order to reduce the interference to bio-medical devices, accurate detections of the physical locations of these devices may be helpful. Radio Frequency Identification (RFID)-based transceivers have been proposed in [2] to embed RFID readers and tags into bio-medical devices in order to detect their respective physical locations. Even though RFID transceivers may be suitable due to its low-power transmissions; however,

it has been shown in [16] that, it may cause interference to bio-medical devices. Hence, CR-WBANs may be designed to avoid using physical location information, or to apply other approaches (e.g. angle of arrival) to obtain the information. Without accurate location information offered by RFID, there may be greater challenge to reduce SUs’ interference to PUs, as well as to reduce the amount of overhead incurred in identifying the physical locations.

E. Enhancing Security Aspects Medical information in regards to patients, services, and

facilities is highly secured, and so authentication and encryption mechanisms must be put in place in order to mitigate eavesdropping and other kinds of intrusion activities, particularly the manipulation of the patient information [2]. Additionally, in CR networks, a node must observe and learn from its operating environment, which may have been manipulated by the attackers. Consequently, the nodes may not achieve their optimal performance. The challenge is that, the use of CR must not jeopardize the security aspects and introduce high amount of overheads that may affect the efficiency of the WBAN. To the best of our knowledge, there is lack of literature on the security aspects of CR-WBAN.

VI. CONCLUSIONS In this paper, we call for more investigation into Cognitive

Radio-based Wireless Body Area Networks (CR-WBANs) to address two critical concerns poised to the traditional Wireless Body Area Networks (WBANs): reduction of Electro-Magnetic Interference (EMI) to medical devices, particularly life-threatening bio-medical devices, and the enhancement of Quality of Service (QoS) performances (i.e. throughput and delay). This paper presents two architectures (i.e. three-tier WBAN and central controller-based architectures), two applications of CR (i.e. Electro-Magnetic Interference (EMI) reduction and QoS enhancement), as well as a number of schemes in CR-based WBAN. At present, the three-tier WBAN primarily investigates the mitigation of interference between tier-1 (i.e. Intra-WBAN) and tier-2 (i.e. Inter-WBAN); while the central controller-based architecture present a hospital environment, categorize different traffic classes with respect to their QoS, priority and transmission power levels in order to reduce interference. CR has been applied to reduce EMI through efficient spectrum utilization and by defining suitable power levels of medical devices; and to enhance the QoS by describing priorities level of medical devices and applications based on severity of patient’s conditions. Due to the limited literature, this research area remains at infancy stage. Hence, this paper discusses various open issues in this new area in order to spark new research interests.

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