Wireless Body Area Network Channel Research Articles

Deep Learning Based Cooperative MIMO Systems for Wireless Body Area Networks

Wireless Body Area Network (WBAN) is widely applied in various fields, including healthcare, sports, wellness, and assistive technologies, by offering the benefits of convenience, reliability, low latency, privacy, and customization. However, the propagation characteristics of the WBAN channel can impact the reliability of transmission, which is particularly crucial in healthcare systems. To address this issue, this article presents a novel approach using deep learning-based cooperative Multiple-Input Multiple-Output (MIMO) systems that leverage the autoencoder (AE) technique. In our proposed approach, we utilize the AE-based cooperative MIMO systems with two different techniques: Amplify-and-Forward (AE-AF) and Decode-and-Forward (AE-DF). The AE-AF scheme operates without needing training parameters at the relay node, whereas the AE-DF scheme necessitates training parameters at the relay node. Both schemes aim to overcome challenges such as multipath propagation phenomena, thereby enhancing the performance of on-body communication systems. Additionally, we introduce two combinators, Minimum Mean Square Error (MMSE) scheme and Radio Transformation Network (RTN), to effectively mitigate co-channel interference (CCI) in the received signal streams and improve the bit error rate performance of the AE-AF and AE-DF systems. We assess the performance of these systems in scenarios with and without direct links. Simulation results demonstrate significant performance improvements compared to baseline cooperative MIMO systems using MMSE combining, namely AF-MMSE and DF-MMSE systems. Notably, the proposed systems employing RTN combination, including both direct and relay paths, achieve a 7.5 dB gain over the baseline when all nodes are equipped with two transceiver antennas.

Antenna Optimization for WBAN Based on Spherical Wave Functions De-Embedding

Antennas for wireless body area networks (WBANs) need to be modeled with adapted methods because the coupling with the body tissue does not allow for a clear separation between antenna and channel. Especially for dynamically varying on-body channels due to changing body poses, e.g., with head-worn antennas, modeling is challenging and design goals for optimal antennas are difficult to determine. Therefore, in this article, the modeling of WBAN channels using spherical wave functions (SWFs) is utilized for antenna de-embedding and for deriving optimal antenna characteristics that maximize the transmission coefficient for the respective channel. It is evaluated how typical factors influencing WBAN channels (different body anatomies, body postures, and varying positions of the communication nodes) can be modeled statistically with SWF. An optimized antenna design is developed based on the derived optimization method, specifically adapted to the channel of on-body links with eye-wear applications. The results with the optimized antenna are compared to other standard antenna designs and validated against measurements.

Performance Evaluation of an On-Body Wireless Body Network Based on an Ultra-Wideband Physical Layer under a Dynamic Channel Model

Wireless body area networks (WBANs) are attracting attention as an important technology for realizing the Internet of Medical Things (IoMT). In addition, ultra-wideband (UWB) is one of the wireless communication technologies suitable for the IoMT and WBANs. Our previous study investigated the feasibility of WBANs utilizing UWB under ideal and static wearable WBAN channel models. The present research applies a dynamic on-body UWB channel model to a WBAN as a more realistic channel model. The feasibility of a high-reliability UWB-WBAN is demonstrated by evaluating the physical layer performance. Numerical results reveal the maximum number of retransmissions needed to achieve the desired transmission failure ratio for each link type and the corresponding energy efficiency and average number of retransmissions. These findings contribute to the realization of a highly reliable IoMT utilizing UWB-WBANs in a practical environment.

The Attenuation Characteristics of the Body Tissue on Frequency Function in WBAN Channel

The Wireless Body Area Network (WBAN) refers to a communication network between sensors placed on the inside, on the surface, or around the body wirelessly. WBAN system cannot be separated from body tissues. Body tissues also have electrical properties depending on frequency. Therefore, body tissue can affect the phenomena occurring in radio wave propagation in the WBAN channel. One of the phenomena is attenuation. This study investigates the impacts of body tissue on the WBAN channel and the effects of frequency on the attenuation of body tissue in the WBAN channel. The measurement of magnitude response was carried out with the human body as the measurement object by utilizing the S21 parameter measurement with a vector network analyzer. In NLOS conditions, a human body was located between two coplanar Vivaldi antenna. Measurements were conducted on the head, chest, and abdomen. The frequency used was in the range of 2 GHz to 6 GHz. The body tissue attenuation was obtained by finding the difference between the magnitude measurement response on the LOS and NLOS conditions. The attenuation data were analyzed using statistical and numerical analysis to determine the effect of frequency on the attenuation of the human body tissues. Based on the analysis results, it was identified that the frequency affected the human body tissue attenuation. The enhancement attenuation of the human body tissues occurred when the frequency was higher. Moreover, there was a significant difference in the body tissue attenuation in different parts of the body.Keywords: attenuation, body tissues, s-parameters, wireless body area network.

Analyzing the Performance of WBAN Links during Physical Activity Using Real Multi-Band Sensor Nodes

Wireless body area networks (WBANs) present unique challenges due to their specific characteristics of mobility and over-the-body radio propagation. A huge amount of factors—both internal and external to the network—affect WBAN channel conditions, so a reliable and comprehensive theoretical model of these communications is unfeasible and impractical in real scenarios. Thus, an empirical performance analysis of several WBAN channels is presented in this work, based on the receiver signal strength indicator (RSSI) and packet reception rate (PRR) metrics. Four different static and dynamic activities have been characterized: standing, sitting, cycling and walking. This analysis confirms the theoretical notions of path attenuation due to body parts obstructing the signal path, while serving as a benchmark for the design of future algorithms. The experiments have been carried out with real hardware nodes with wireless interfaces in three ISM bands: 433 MHz, 868 MHz and 2.4 GHz, evaluating the effect of the transmit power and node placement for different subjects. In all scenarios, the PRR metric reaches its maximum of 100% for both sub-GHz bands. Finally, our study concludes that the RSSI metric is sufficient to exploit the periodicity of dynamic activities, without the need for any extra hardware resources.

WBAN Channel Modeling for 900 MHz and 60 GHz Communications

This article deals with the experimental characterization of the on-body propagation channel for applications in wireless body area networks (WBANs). The on-body propagation was studied between two quarter-wavelength monopole antennas in the 900 MHz band and between two horn antennas in the 55-65 GHz range. Different locations all over the body, including arm, leg, and front and back of the torso, were studied for two human male subjects. The channel parameters in terms of path gain and delay spread were extracted from measurements for vertical and horizontal polarizations of the antennas in both frequency bands. In addition, a wrist to arm path was studied in the 60 GHz band where the transmitter was rotated in 360° around the arm at a fixed distance from the receiver. We obtained a path gain exponent between 2 and 3 in the 900 MHz band and in the 2.4-6 range for the 60 GHz band. Higher path gains for vertical and horizontal polarizations were obtained in the 900 MHz and 60 GHz bands, respectively. Maximum mean excess delay and root-mean-square delay spread were 6.3 ns and <; 2 ns in the 900 MHz band, respectively, while these values decreased by factors 3 and 10 in the 60 GHz band.

Re-AuTh: Lightweight Re-Authentication with Practical Key Management for Wireless Body Area Networks

The development in wireless body area networks (WBANs) has facilitated a growth in electronic health in terms of quality and efficiency. Telemonitoring systems observe human vital signs without the need for a patient to be present using WBANs. The data sensitivity of WBAN, mobile users and public channels poses a critical challenge to security and privacy in order to prevent unauthorized access to vital health data. Several solutions have been suggested to ensure secure and effective communications in WBANs; nonetheless, these methods tend to have drawbacks, such as efficiency overhead and protection vulnerabilities. This paper proposes a lightweight authentication and also provides a protocol for re-authentication (Re-AuTh). The proposed “Re-AuTh” utilizes identification and authorization tokens to assist the application provider in authenticating and further to authorize medical users. Such tokens also provide a way to achieve effective key management. The Scyther simulation shows that the proposed Re-AuTh has no security vulnerabilities and the informal security analysis further ensures protection of all related possible threats. The performance comparisons with related solutions showed that the proposed Re-AuTh effectively provides security services for WBAN in the medical environment and greatly reduces computation costs at the user side.

A Flexible Enhanced Throughput and Reduced Overhead (FETRO) MAC Protocol for ETSI SmartBAN

Smart body area networks (SmartBAN) is an emerging wireless body area networks (WBAN) standard proposed by the European Telecommunications Standards Institute (ETSI). This paper first examines the potential of SmartBAN medium access control (MAC) layer with scheduled access to support a myriad of WBAN applications, having diverse data rate requirements. Extra scheduled access slots can be allocated to high date rate sensor nodes for managing their data rate requirements. High data rate sensor nodes can also be re-assigned to use the available time slots of low data rate sensor nodes in Inter-Beacon Interval (IBI) by the central hub. But these two schemes incorporate different physical (PHY) and MAC layer overheads related to frame transmission, frame acknowledgement and slot re-assignment. This redundant overhead transmission results in high overhead energy consumption and reduced effective throughput. Therefore, an innovative and flexible enhanced throughput and reduced overhead (FETRO) MAC protocol for scheduled access is proposed in this article. In the proposed scheme, the sensor node data rate requirements are considered while assigning the scheduled access slot duration by allowing minimal changes in the base-line standard implementation. This infers the provision of scheduled access slots with variable slot durations within an IBI. We also evaluate the existing techniques of extra slot allocation and slot re-assignment in SmartBAN as well as the proposed FETRO MAC protocol with variable slot length. The proposed FETRO MAC scheme results in optimizing both the overall throughput and normalized overhead energy consumption per kilo bits per second (Kbps). Additionally, the impact of various WBAN channel models over these throughput management approaches is also investigated. The proposed FETRO MAC protocol with variable slot duration gives an average reduction of 65.5 and 59.16 percent, respectively, in the hub and nodes normalized overhead energy consumption per Kbps outcomes, as compared to the de-facto SmartBAN MAC scheduling strategies.

Characterization of dynamic wireless body area network channels during walking

In this work, finite-difference time-domain was used for the investigation of dynamic wireless body area network channel characteristics during walking, thus accounting for dynamic aspects and body postures. This involves the study of on-body, off-body, and body-to-body communication in an empty environment, at the center frequency of 2.45 GHz. The channels were investigated in terms of fade variation and their corresponding amplitude distributions. For on-body channels, the fade variation was found to be periodic, with larger fade variations for the channels involving the nodes at the hand and thigh. For off-body and body-to-body channels, channels with the absence of line of sight experienced constructive and destructive interference as the distance between the end nodes changes, resulting in larger fade variations. For the amplitude distribution of the channels, a multivariate normal distribution was considered. The distribution has the capability of modeling channels jointly which makes it easier for network analysis and was considered because of the significant correlation between the channels. The resulting estimated multivariate distributions fit well with the simulated data, for on-body, off-body, and body-to-body channels.

Capacity-Outage Joint Analysis and Optimal Power Allocation for Wireless Body Area Networks

Wireless body area networks (WBANs) are characterized by short-range wireless communication between inherently resource-limited sensors that operate in the vicinity of the human body for recording certain physiological signals. One of the main limitations of WBANs is in terms of their available power. Since the nodes are typically battery-driven, an efficient power transmission is essential to guarantee long-lasting communications among nodes without the need for frequent battery replacement or charging. In this study, aiming to improve the WBAN performance, we first investigate the power allocation problem by choosing the ergodic capacity and the outage probability as the desired metrics. Subject to an average power constraint, it can be shown that the power allocation, which is optimal for the ergodic capacity, does not necessarily yield a good result for the outage probability, and vice versa. Therefore, we assert that although both of the aforementioned metrics are recognized as the key performance indicators, the WBAN performance would not be appropriately characterized by considering each of them separately. Consequently, a novel hybrid metric is proposed that jointly accounts for the capacity and the outage. Subject to an average power constraint, we then find the power allocation policy that maximizes the proposed hybrid metric. The entire devised framework is utilized in the context of WBAN channels derived from applying the well-known Bayesian information criterion to a set of publicly available experimental channel data. The numerical results demonstrate the superiority of the proposed power allocation policy compared to the legacy water-filling and truncated-inversion approaches.

Joint VMIMO and LDPC Decoders for IR-UWB Wireless Body Area Network

A complete impulse radio-ultra wide band (IR-UWB) system is proposed to mitigate the impairments concerning on-body to off-body Wireless Body Area Networks (WBAN). The proposed system maintains the practical communication link between on-body sensors to the fusion center or the monitoring device held by the medical representative. Also, these sensors are assigned a recently proposed pulse shaping to mitigate the noise that existed in the IR-UWB WBAN channel. Furthermore, virtual multiple-input multiple-output (VMIMO) is proposed to perform spatial multiplexing between various sensors transmitted data. Moreover, low complex low density parity check (LDPC) encoding/decoding algorithms, including a new low complex hybrid LDPC decoding algorithm, are proposed to reduce the complexity and to enhance the bit error rate of the on-body sensors. Interestingly, low energy consumption at every sensor participating in the on-body to off-body WBAN was achieved by adopting the combination between LDPC decoders and VMIMO technique. According to simulation results, the new system enhanced the BER performance and reduced the complexity of the on-body to off-body IR-UWB communication system effectively.

Temporal correlation model‐based transmission power control in wireless body area network

Researchers have encountered many challenges in developing communication system in wireless body area networks (WBANs). These challenges include the dynamic characteristics of WBAN channels, limited energy resources, and strict requirements, such as high reliability and low latency. To achieve highly reliable and energy-efficient communication in the WBAN, temporal correlation model-based transmission power control (TCM-TPC) is proposed. In this method, the channel condition is firstly determined based on a long-term mean channel gain and the last known channel gain using a temporal correlation model. The channel is estimated as a conditional distribution of channel gains. After that, the transmit output power is selected from the estimated channel to satisfy a pre-defined outage probability. Performance of the proposed TCM-TPC method was evaluated on a network simulator for a walking scenario. The evaluation results showed that the TCM-TPC had up to 1.48% of packet loss, while other TPC methods had up to 6.86% of packet loss. Furthermore, for a high data rate application, the TCM-TPC showed the lowest energy consumption for all sensor nodes.

Reliability and Energy Efficiency Enhancement for Emergency-Aware Wireless Body Area Networks (WBANs)

Medium access control protocols based on time division multiple access (TDMA) can improve the reliability and efficiency of wireless body area network (WBAN). However, traditional static TDMA techniques adopted by IEEE 802.15.4 and IEEE 802.15.6 do not sufficiently consider the channel status or the buffer requirements of the nodes within heterogeneous contexts. Although there are some solutions that have been proposed to alleviate the effect of the deep fade in WBAN channel by adopting dynamic slot allocation, these solutions still suffer from some reliability and energy efficiency issues and they do not avoid channel deep fading. This paper presents two novel and generic TDMA based techniques to improve WBAN reliability and energy efficiency. Both techniques synchronize nodes adaptively while tackling their channel and buffer status in normal and emergency contexts. Extensive simulation experiments using various traffic rates and time slot lengths demonstrate that the proposed techniques improve the reliability and the energy efficiency compared to IEEE 802.15.4 and IEEE 802.15.6 in both situations, the normal and emergency contexts. This improvement has been achieved in terms of packet loss, up to 90%, and energy consumption, up to 13%, confirming the significant enhancements made by the developed scheduling techniques.

Mixed‐signal demodulator for IEEE 802.15.6 IR‐UWB WBAN energy detection‐based receiver

A mixed-signal baseband demodulator for IEEE 802.15.6 impulse-radio ultra-wideband (IR-UWB) wireless body area network (WBAN) energy detection-based receiver is presented. It considers M-ary pulse position modulation (PPM) signalling format conforming to the IEEE 802.15.6 WBAN standard. The demodulator utilises ‘integrate-and-digitise’ approach employing simple mixed-signal circuits. The design is implemented in 0.18 μm CMOS technology operating at 1.8 V supply. The demodulator consists of a mixed-signal windowed integrator, a single-ended successive approximation register analogue-to-digital converter followed by a digital back-end. Further, its performance evaluation is carried out for 2-ary and 16-ary PPM signalling in different WBAN channels.

LDPC Decoding Algorithms for Implant to Implant Wireless Body Area Network

Wireless body area network (WBAN) is a promising network aiming at enhancing the communication in medical applications. It is adopted by medical organizations due to its flexibility in remotely monitoring patient health status. WBANs suffer from many limitations due to excessive channel impairments. Low density parity check (LDPC) codes are proposed to mitigate WBAN's impairments concerning the bit error rate, complexity, and dissipated energy. In this paper, a comprehensive performance analysis of various LDPC decoding algorithms is used to improve communication and reduce complexity in implant to implant WBAN channel. Moreover, a novel low complex LDPC decoding algorithm, which has a performance close to soft decision and a decoding time close to hard decision algorithms is proposed to minimize the dissipated energy. The proposed algorithm can be classified as a hybrid decision algorithm. The results demonstrate extensive analysis and comparisons between hard, soft, and hybrid decision algorithms.

OFDM Performance of Ultra Wideband in Wireless Body Area Network Channel

OFDM Performance of Ultra Wideband in Wireless Body Area Network Channel

OFDM Performance of Ultra Wideband in Wireless Body Area Network Channel

OFDM Performance of Ultra Wideband in Wireless Body Area Network Channel

An Overview of the Electromagnetic Simulation-Based Channel Modeling Techniques for Wireless Body Area Network Applications

Electromagnetic simulation-based channel modeling is presently considered as a promising option for wireless body area network (WBAN) channel modeling. The benefits of simulation-based channel modeling are obvious: realistic channel characteristics for required environments and situations are provided flexibly and cheaply. In addition, the use of simulation-based channel modeling may overcome several challenges related to the use of measurement data, such as uncertainties and inaccuracies due to cabling, unintentional changes in the position of the test person or the antennas and so on. There are several numerical methods suitable for simulation based-channel modeling, both full-wave and an asymptotic solutions. The choice of the numerical approach depends on the nature of the communication links of the wireless body network being considered. This paper presents a general overview, including recent progress, of the electromagnetic simulation-based WBAN channel modeling techniques. Advantages, disadvantages, and the most appropriate applications are described. Furthermore, the features of the different techniques are compared.

Network Coding for Energy Efficient Transmission in Wireless Body Area Networks

Wireless Body Area Networks (WBANs) is a technology that has revolutionized the health-care industry by allowing remote monitoring, early detection and prevention of diseases. Patients can be remotely monitored thanks to implant devices in the body or by placing nodes on different parts of the body. Often the deployed sensor nodes are constraint by limited battery sources and are required to continuously collect the data and transfer it to the sink node, thus requiring energy efficient communication schemes. In addition, in poor channel conditions, this data collection and transfer results in retransmission thus wasting useful energy. This work presents a cooperative network coding based transmission technique for spectrum and energy efficiency in WBANs. The bit error rate (BER) of the network coded path in comparison to direct communication approach is explored. The effect of WBAN path loss due to different node positions is also discussed. It is observed that node position greatly affects path loss and received power which in turn affect the BERs. Simulation results show that network coded cooperative communication strategy in WBAN channel with and without combining outperforms as compared to direct communication.

A Novel Cooperation-Based Network Coding Scheme for Walking Scenarios in WBANs

In Wireless Body Area Networks (WBANs), the tradeoff between network throughput and energy efficiency remains a key challenge. Most current transmission schemes try to cope with the challenge from the perspective of general Wireless Sensor Networks (WSNs), which may not take the peculiarities of WBAN channels into account. In this paper, we take advantage of the correlation of on-body channels in walking scenarios to achieve a better tradeoff between throughput and energy consumption. We first analyze the characteristics of on-body channels based on realistic channel gain datasets, which are collected by our customized wireless transceivers in walking scenarios. The analytical results confirm the rationale of our newly proposed transmission scheme A3NC, which explores the combination of the aggregative allocation (AA) mechanism in MAC layer and the Analog Network Coding (ANC) technique in PHY layer. Both theoretical analyses and simulation results show that the A3NC scheme achieves significant improvement in upload throughput and energy efficiency, compared to the conventional approaches.