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A footwear-centric body area network employing a directional antenna is compared with waist-centric systems using omnidirectional and directional antennas. The effect of body movements on path gain is analysed for two bands at 3.99 and 7.99 GHz. The path gain and data rate results demonstrate that footwear-centric configurations are equivalent to or better than waist-centric body area networks.
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DOI: 10.1049/el.2013.1596
1
Footwear-centric body area network with directional UWB antenna
D. Gaetano, V. Sipal, P. McEvoy, M. J. Ammann, C. Brannigan*, L. Keating* and F. Horgan*
A footwear-centric body area network employing a directional antenna is compared with waist-centric systems using omnidirectional and directional
antennas. The impact of body movements on path gain is analysed for two bands at 3.99 GHz and 7.99 GHz. The path gain and data rate results
demonstrate that footwear-centric configurations are equivalent or better than waist-centric body area networks.
Introduction: In wireless body area networks (WBAN), the hub is typically located at the waist to coordinate data from other sensors [1].
Omnidirectional antennas are employed to cover upper and lower body areas but lower gain patterns can impair link reliability.
As an alternative, a directional Vivaldi antenna for a footwear-centric configuration is reported and assessed in terms of path gain and the
guaranteed minimum data rates defined in the IEEE 802.15.6-2012 standard for WBANs [2, 3]. UWB channels were selected for low power
consumption, resilience to multipath fading and an adequacy for the short propagation range within a body area [2, 3]. Footwear can
comfortably incorporate kinetic-energy harvesting and electronic sensors for medical or sporting applications without a significant adverse
impact on a user’s gait or stride [4, 5].
The footwear Vivaldi antenna is on a substrate 37.1 × 37.1 × 0.2 mm3 with a curve which is described as follows:
x=0.191×e0.173y for 0 < y < 21 mm (1)
It provides a directional radiation pattern towards the upper body which minimizes interference to off-body networks. Waist-centric
measurements were taken with an omnidirectional monopole 20 × 32.8 × 0.2 mm3 positioned in the upper body areas. Cumulative distribution
functions of body area path gain are presented.
Methodology: Both antennas are matched in the bandwidth of interest when in close proximity to the various body areas shown in Fig. 1. The
left shoe, the left waist, the left and right upper arms, the sternum and the 4th vertebrae are representative of candidate sensor positions. Three
link configurations are reported:
Waist-centric hub monopole and node monopole antennas (M/M)
Footwear-centric hub Vivaldi and node Vivaldi antennas (V/V)
Waist-centric hub monopole and node Vivaldi antennas (M/V)
The measurements were performed on two people of 1.75 m height with weights of 70 kg and 80 kg in an 8 × 8 m2 laboratory area with
metallic furniture and a reinforced concrete floor and ceiling. S21 values were recorded at the low and high band frequencies of 3.9936 GHz
and 7.9872 GHz with a bandwidth of 499.2 MHz. These bands were selected as they are the mandatory regional bands for IEEE 802.15.6
UWB impulse radio (IR). 261 link measurements per person for the hub-node combinations were recorded under the following conditions:
(a) 4 second duration for a standing position in a static channel;
(b) 12 second duration while walking in a static channel, and;
(c) 10 second duration while standing in a dynamic channel where people made random movements in the laboratory near the subject.
(a) (b)
Fig. 1 (a) Vivaldi geometry (mm) with (b) hub (H) and node (N) body positions.
Results and Performance Discussion: The Vivaldi antenna is 50% and 56% efficient at 4 GHz and 8 GHz respectively. These simulated results
correspond to applied conditions for the antenna positioned on the lateral side of the left shoe, 10 mm from the foot. It is matched over the
band with gains of 5.1 dBi at 4 GHz and 6.4 dBi at 8 GHz.
Similarly, the monopole antenna is 25% and 48.5% efficient at 4 GHz and at 8 GHz respectively. The simulated results are for the antenna
being displaced 6 mm from the left waist.
Inspection of the data indicates that the right upper arm incurs the least path gain from the left foot and left waist due to direct path
shadowing. Low band path gain results for the three hub-node configurations for right upper arm with the foot and waist on the 70 kg person
are shown in Fig. 2. Despite the increased distances, it is evident that the footwear-centric setup outperforms the waist-centric approach.
2
Fig. 2 Comparison of the measured path gain for the right upper arm.
Fig. 3 Path gain for different node positions.
Cumulative distribution functions (CDFs) of the measured path gain for each of the hub-node configurations are shown in Fig. 3. The
increased horizontal spread of values denotes shadowing, antenna pattern misalignment and fading variations, etc., that are due to body
movement. The high band performs better than the low band for the left and right upper arm. In other cases, the low band is better since there
is less path loss at lower frequencies. In most of the analysed cases, the footwear-centric configuration performs better than the waist-centric
configuration. An exception is the sternum area, where the distance between the hub and sensor node in the waist-centric system is
significantly shorter.
The CDFs results are summarized in Table 1 which shows the achieved maximum data rates for an IEEE 802.15.6 compliant IR-UWB
system. The measured data-rates are based on the received signal strength calculated using the path gain and the maximum transmitter power.
For example, the minimum and maximum data rates of 0.3948 Mbps and 12.636 Mbps correspond to the received signal strength of -91 dBm
-80 -70 -60 -50
0
0.2
0.4
0.6
0.8
1
Path gain [dB]
CDF
Empirical CDF
Waist/Footwear
@ 3.99 GHz
M/M
V/V
V/M
-80 -70 -60 -50
0
0.2
0.4
0.6
0.8
1
Path gain [dB]
CDF
Empirical CDF
Waist/Footwear
@ 7.99 GHz
M/M
V/V
V/M
-80 -70 -60 -50
0
0.2
0.4
0.6
0.8
1
Path gain [dB]
CDF
Empirical CDF
Left Upper Arm
@ 3.99 GHz
M/M
V/V
V/M
-80 -70 -60 -50
0
0.2
0.4
0.6
0.8
1
Path gain [dB]
CDF
Empirical CDF
Left Upper Arm
@ 7.99 GHz
M/M
V/V
V/M
-80 -70 -60 -50
0
0.2
0.4
0.6
0.8
1
Path gain [dB]
CDF
Empirical CDF
Right Upper Arm
@ 3.99 GHz
M/M
V/V
V/M
-80 -70 -60 -50
0
0.2
0.4
0.6
0.8
1
Path gain [dB]
CDF
Empirical CDF
Right Upper Arm
@ 7.99 GHz
M/M
V/V
V/M
-80 -70 -60 -50
0
0.2
0.4
0.6
0.8
1
Path gain [dB]
CDF
Empirical CDF
Sternum
@ 3.99 GHz
M/M
V/V
V/M
-80 -70 -60 -50
0
0.2
0.4
0.6
0.8
1
Path gain [dB]
CDF
Empirical CDF
Sternum
@ 7.99 GHz
M/M
V/V
V/M
-80 -70 -60 -50
0
0.2
0.4
0.6
0.8
1
Path gain [dB]
CDF
Empirical CDF
4th Vertebrae
@ 3.99 GHz
M/M
V/V
V/M
-80 -70 -60 -50
0
0.2
0.4
0.6
0.8
1
Path gain [dB]
CDF
Empirical CDF
4th Vertebrae
@ 7.99 GHz
M/M
V/V
V/M
3
and -76 dBm, respectively. Where the minimum 0.3948 Mbps data rate was not guaranteed due to path gains being less than -76.7 dB, the
outcomes are reported as the percentage of successful 0.3948 Mbps data rate measurements.
Table 1 Achieved maximum data rates for 522 path gain measurements across two people for the M/M, M/V and V/V WBAN configurations.
Frequency
7.99 GHz
Hub and Antennas Postions
Waist-centric [Mbps]
Footwear-centric
[Mbps]
Waist-centric [Mbps]
Footwear-centric
[Mbps]
M/M
M/V
V/V
M/M
M/V
V/V
Footwear/ Waist
6.3
12.6
12.6
0.8
0.8
1.6
Left Upper Arm
0.4
0.4
0.8
0.8
0.4
0.8
Right Upper Arm
0.2%
57%
87%
61%
57%
86%
Sternum
3.2
6.3
6.3
3.2
1.6
0.8
4th Vertebrae
0.4
1.6
3.2
99%
96%
0.8
Inspection of the data rates in Table 1 indicates that the footwear-centric system performs equivalently or better than a waist-centric system,
except for links to the sternum area. In fact, the footwear-centric system is significantly better for nodes on the vertebrae since the hub location
mitigates the shadowing impact. The right upper arm area is the farthest distance and it is not possible to guarantee a minimum data rate for all
the measurements. However, the footwear-centric hub provides better link availability for the lowest data rate.
Conclusion: Antenna designs for footwear-centric wireless body area networks show that they are competitive with waist-centric
configurations in terms of propagation path-gain and compliance with the IEEE 802.15.6-2012 standard for WBANs. A foot-based directional
antenna provides good wireless coverage for typical sensor node positions for standing and walking conditions. It is envisaged that such radio
link advantages will encourage the development of kinetic energy harvesting and other footwear-based electronic sensors for medical and
sporting applications.
Acknowledgments: This work was supported by the Science Foundation Ireland grant 09/IN.1/I2652 and with the Government of Ireland
Fellowship for Engineering, Science and Technology funded by the Irish Research Council.
© The Institution of Engineering and Technology 2013
04 July 2013
doi: 10.1049/el.2013.1596
One or more of the Figures in this Letter are available in colour online.
D. Gaetano, V. Sipal, P. McEvoy and M. J. Ammann
(Antenna & High Frequency Research Centre, Dublin Institute of Technology, Kevin Street, Dublin 8, Ireland)
E-mail: max.ammann@dit.ie
C. Brannigan, L. Keating and F. Horgan
(*School of Physiotherapy, Royal College of Surgeons in Ireland, 123 St Stephen’s Green, Dublin 2, Ireland)
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... Even though both on-and off-body channels have been studied in great detail for frequencies up to 10 literature almost unanimously assumes that the hub is located on the waist of the user. Exceptions are works [7]- [9], which discuss the benefits for a hub located on the footwear. ...
... In fact, other locations offer additional benefits. For instance, in terms of propagation, it may be advantageous to locate the hub in the extremities of the body (head or foot) because the entire body can be covered by directional antennas [7]- [9]. Integration in the footwear enables extension of battery life by harvesting energy from piezoelectric elements integrated in the footwear [9]. ...
... These results further confirm previous works [7]- [9], which pointed out that the waist/hip may not be the most suitable location for hubs in future WBANs because other locations allow the use of directive antennas which reduce the impact of fading and improve the overall path-gain characteristics. ...
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This letter compares the propagation properties of Wireless Body Area Networks for three different locations (head, foot and waist) of the hub/internet gateway on the human body. The wireless channels between the hubs and four nodes (chest, back, and upper arms) are measured for frequencies between 5 and 7 GHz on a female and a male subject performing push-ups and squats. A framework using path gain and fade depth metrics in spider plots is used for cumulative performance description. The results show that the best overall performance is for a hub located on the temple and the worst overall performance is achieved for a hub on the waist. These results are expected to stimulate further research into the optimum hub placement on the human body.
... Emerging opportunities for wearable electronics include sensors for footwear [1][2][3] and associated communications [4] to enable medical [5], occupational [6] and leisure [7] applications. The volume and rigidity of footwear can contain low-profile and conformal components without undue impact on the flexibility of a subject"s foot or natural gait. ...
... The first reported channel link-reliability for footwear to upper body nodes demonstrated the need to consider system performance [4]. In addition, a 2.4-11.0 ...
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Wireless Body Area Networks (BANs) present an exciting opportunity for further growth in wireless connectivity. In this paper, an investigation on how the fading properties for wireless BAN on-body channels scale with bandwidth is made, thereby filling the unexplored gap between fading in narrowband and extremely wideband channels. The fading is found to scale similarly to indoor channels, but the dominance of the first path means that the wideband channel properties are achieved already for bandwidths in excess of 100 MHz. Furthermore, fading in footwear centric and in waist centric system is compared. It is concluded that the footwear centric architecture has similar fading properties for all bandwidths and for all nodes except for the node on the back, where it significantly outperforms the waist centric system.
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Energy Harvesting From Piezoelectric Materials Fully Integrated in FootwearAn Antenna for Footwear 1-6 7.99 GHz Hub and Antennas Postions Waist-centric [Mbps] Waist-centric [Mbps] Footwear-centric [Mbps] V/V 1.6 0.8 86% 0.8 0.8 V/V 12.6 0.8 87% 6.3 3.2 M/M 0
  • Technol Rocha
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  • P Gaetano
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  • L Horgan
Technol., Italy, 2010, pp. 1–6 4 Rocha, J. G., Gonçalves, L. M., Rocha, P. F. and Silva, M. P.: ‘Energy Harvesting From Piezoelectric Materials Fully Integrated in Footwear’, IEEE Trans. Ind. Electron., 2010, 57, (3), pp. 813–819 5 Ammann, M. J., McEvoy, P., Gaetano, D., Keating, L. and Horgan, F.: ‘An Antenna for Footwear’, MobiHealth 3rd International Conference on Wireless Mobile Communication and Healthcare, Paris, 2012, pp. 1-6 7.99 GHz Hub and Antennas Postions Waist-centric [Mbps] Waist-centric [Mbps] Footwear-centric [Mbps] V/V 1.6 0.8 86% 0.8 0.8 V/V 12.6 0.8 87% 6.3 3.2 M/M 0.8 0.8 61% 3.2 99% M/V 0.8 0.4 57% 1.6 96%
On-Body Radio Channel Characterization and System-Level Modeling for Multiband OFDM
  • Q H Abbasi
  • S Member
  • A Sani
Abbasi, Q. H., Member, S. and Sani, A.: 'On-Body Radio Channel Characterization and System-Level Modeling for Multiband OFDM', IEEE Trans. Microw. Theory Tech., 2010, 58, (12), pp. 3485-3492
An overview of IEEE 802.15.6 standard
  • K S Kwak
  • S Ullah
  • N Ullah
Kwak, K. S., Ullah, S. and Ullah, N.: 'An overview of IEEE 802.15.6 standard', Proc. 3rd Int. Symp. Appl. Sci. Biomed. Commun. Technol., Italy, 2010, pp. 1-6