Wireless Communications

Scalable On-body Pathloss Models Based on Surface Wave Propagation for Wireless Body Area Networks

Research grant by DFG (German Research Foundation)

Timeframe: End 2014 - ongoing

DFG MA 4981/6-1:

Introduction

Nowadays the use of wireless communication technologies for the intercommunication of body-worn applications is increasing rapidly. These applications range from security technologies, multimedia products and telemetric sports applications to healthcare systems. Especially the combination of these applications offers a wide variation of possible realizations. In accordance with the ongoing miniaturization of wearable devices the interaction between the antenna and the user becomes more severe. Along with the lack of the traditional free-space antenna theory in describing the excitation of on-body surface waves, this leads to insufficient insight in the development of such body centric systems so far. Therefore, the aim of this research proposal is a derivation of scalable, physically motivated pathloss models for wireless body area networks that can later be used to develop optimized design strategies. The models shall be closely connected to basic geometric and dielectric parameters of the on-body channel, making it scalable.

Corresponding to the preceding research activities of the applicant a developed antenna de-embedding approach will be used to separate antenna and channel characteristic. Based on this, the pathloss models will be derived by the adaption of the ground wave propagation theory (e.g. from terrestrial and naval wireless communications). Here, each modification step towards a more realistic model is verified by numerical simulations and practical measurements.

Finally, the physically motivated pathloss models are calculated for different on-body propagation links. Here, the underlying modeling process contains the basic geometric features, the frequency, the dielectric tissue values of the on-body channel and the antenna integration setup itself. By variation of these explicit parameters the model can be adapted to a wide class of specific propagation scenarios.

 surfwave_fig_1

 

Antenna de-embedding

To evaluate the properties of an antenna in terms of on-body propagations the electric current distribution on the antenna is calculated by the FDTD method. At this point even the interaction with the human body is modeled by a anatomical or simplified human body model. Using the Norton surface wave theory, the contribution of each current element to the on-body antenna far field can be modeled. Separating the corresponding antenna far field in its TM- and TE-components, even the derivation of on-body antenna parameters are realized. This enables a comparison of different antenna types in terms of on-body communications and a discussion of the underlying wave species.

surfwave_fig_2

 

Channel modeling

The assumed on-body far field model is restricted to a flat surface and therefore to line-of-sight links only. The consideration of various shaped surfaces is realized by a combination of flat and cylindrical models. Therefore, the total propagation distance is segmented into related sub-distances. This enables a combination of adapted far field models of each distance segment. Driving key point  of this assumption is that even non-line-of-sight regions can be separated into a TM- and TE-far field.
surfwave_fig_3

 

Total propagation link

The combination of on-body parameters and channel models enable a systematic segmentation and combination of various propagation scenarios. By this approach a wide class of scalable pathloss models can be realized, and smart antenna concepts can be developed which aim for specific propagation qualities.

surfwave_fig_4

 

 

Publications

  1. Grimm, M. and Manteuffel, D., "Body Worn Antenna Systems for Health Care related On- and Off-body Communications", 4th International Conference von Wireless Mobile Communication and Healthcare, Athens, Greece, November 3-5 2014. DOI
  2. Grimm, M., and Manteuffel. D, "On-Body Far Field Description by two Equivalent Electric Sources", Antennas and Propagation Society International Symposium (APSURSI), 2015 IEEE, Vancouver, Canada, pp.1068-1069, 19-24 July 2015. DOI
  3. Grimm, M. and Manteuffel, D., "On-Body Antenna Parameters," Antennas and Propagation, IEEE Transactions on. (accepted for publication). DOI 
    [Abstract]
     

    Within the scope of on-body communications an approach is presented which is capable to describe the radiated on-body field of arbitrarily shaped antenna structures. The method is based on a segmentation of the excited current distribution on the antenna body by a finite number of small electric dipoles. To consider the presence of the human body, which affects the underlying radiation mechanism significantly, the model is implemented by the use of the Norton surface wave theory. Based thereon, a method is presented to model the onbody far field of an antenna by two equivalent electric dipoles, a TM and a TE source. Based on this assumption the directivity and the effective antenna area are defined for on-body propagation scenarios. The radiation characteristic of body worn antennas is discussed in terms of their radiation characteristic using the example of tilted half-wave dipoles and a planar inverted-F antenna. The last part of the study discusses a pathloss model which is calculated from the underlying antenna parameters. Numerical full-wave simulations, based on the FDTD method, and measurements in an anechoic chamber, verify the results.

    [BibTeX]
     
    @ARTICLE{7277023,
    
    
    author={Grimm, M. and Manteuffel, D.},
    
      journal={Antennas and Propagation, IEEE Transactions on}, 
    
     title={On-Body Antenna Parameters}, 
    
      year={2015},
    
      volume={PP},
    
      number={99},
    
      pages={1-1},
    
      keywords={Antenna theory;Dipole antennas;Mathematical 
    model;Optical surface waves;Surface impedance;Surface waves;Body area 
    networks;antenna theory;on-body directivity;on-body propagation;wearable
     antennas},
    
      doi={10.1109/TAP.2015.2482499},
    
      ISSN={0018-926X},
    
      month={},}