Small–scale fading characteristics of diversity combining schemes used for body–to–body communications within an urban environment at 2.45 GHz

In this paper, an analysis of spatial diversity and small-scale fading characteristics for body-to-bodycommunications is presented. The measurements were made at 2.45 GHz in an urban environment with uncontrolled pedestrian and vehicular traffic. The virtual array of four distributed receive antennas where situated on the centralchest, central waist, left waist and left wrist of the user’s body. Combining of the received signal measured at each ofthe antennas in the virtual array has shown that an average diversity gain of up to 11.8 dB can be achieved when usingfour distributed antennas and a maximal ratio combining scheme. To model the small-scale fading characteristics obtained at the output of the virtual combiners, we use diversity specific, theoretical probability density functions for multi-branch receivers operating in Nakagami-m fading channels. It is shown that these equations provide an excellent fit to the measured channel data.

Characteristics of shadowed fading in off–body communications channels at 2.45 GHz

In this paper, a number of off-body channels which are susceptible to shadowing caused by the human body are investigated. In particular, the recently proposed shadowed κ–μ fading model is fitted to data obtained from field trials performed in low multipath conditions at 2.45 GHz. It is shown that this model provides a significantly improved fit to off-body channels which are subject to shadowing when compared to other fading models such as lognormal, Nakagami-m and Rice which are commonly applied to model fading in body centric communications channels.

RSSI-based environment identification for 2.45 GHz body area networks

A unique property of body area networks (BANs) is the mobility of the network as the user moves freely around. This mobility represents a significant challenge for BANs, since, in order to operate efficiently, they need to be able to adapt to the changing propagation environment. A method is presented that allows BAN nodes to classify the current operating environment in terms of multipath conditions, based on received signal strength indicator values during normal packet transmissions. A controlled set of measurements was carried out to study the effect different environments inflict on on-body link signal strength in a 2.45 GHz BAN. The analysis shows that, by using two statistical parameters, gathered over a period of one second, BAN nodes can successfully classify the operating environment for over 90% of the time.

Simultaneous Measurements of the Channel Response for Multiple Eavesdroppers Operating in the Vicinity of a Body Area Network at 2.45 GHz

Channel randomness can be exploited to generate secret keys. However, to ensure secrecy, it is necessary that the channel response of any eavesdropping party remain sufficiently de-correlated with that of the legitimate users'. In this paper, we investigate whether such de-correlation occurs for a body area network (BAN) operating in an indoor environment at 2.45 GHz. The hypothetical BAN configuration consisted of two legitimate transceivers, one situated on the user's left wrist and the other on the user's waist. The eavesdroppers were positioned in either a co-located or distributed manner in the area surrounding the BAN user. Using the simultaneous channel response measured at the legitimate BAN nodes and the eavesdropper positions for stationary and mobile scenarios, we analyze the localized correlation coefficient. This allows us to determine if it is possible to generate secret keys in the presence of multiple eavesdroppers in an indoor environment. Our experimental results show that although channel reciprocity was observed for both the stationary and the mobile scenarios, a higher de-correlation between the legitimate users' channels was observed for the stationary case. This indicates that mobile scenarios are better suited for secret key generation.