Costas C. Constantinou

Antennas and propagation for body centric wireless communications

Research in antennas and propagation for body centric wireless communications continues to grow, in response to increasing demands for body area networks (BANs) for healthcare, defence and personal communications and entertainment. This paper will briefly review recent international work, and then report on advances in three UK BAN research centres, Birmingham, Queen Mary and Queens Belfast. The demand for greater security in BAN links could be met by the use of 60GHz channels, and the likely channel characteristics will be discussed and initial results given. New insights into surface wave excitation on the human body has enabled a novel low profile antenna to be designed that maximises link performance where very thin antennas are necessary. Finally advances in the numerical computation are reported, in which the importance of relating phantoms directly to patients to give subject specific simulations and to allow improved modelling of internal organs.

Statistical Analysis and Performance Evaluation for On-Body Radio Propagation With Microstrip Patch Antennas

On-body propagation channel measurements using two microstrip patch antennas for various links are presented and statistically analyzed. The attenuation attributed to factors such as the body, head and clothing are: 19.2, 13.0, and 1.7 dB, respectively, when measurement performed in the anechoic chamber. Measured cumulative distribution function (CDF) of data in the chamber and lab fits to lognormal distribution with deviation factors comparable in both cases. The results demonstrate that the human body is a major shadowing contributor in body area network (BAN) radio systems. The performance of potential radio systems under the measured channel variations is also investigated. Excellent system performance is achievable with power levels as low as 0.01mW. These results support the significance of channel characterization and modelling in producing suitable wireless systems for ultra low power BANs

Measurements and Statistical Analysis of On-Body Channel Fading at 2.45 GHz

The fading of an on-body transmission channel at 2.45 GHz is investigated. For the first time a large amount of data has been gathered in practical environments, for realistic activities, and has been subject to statistical analysis. It is clear that significant variations of the path gain and fading can occur due to the movements of body. Extensive statistical analysis has shown that fading in on-body channels is a non stationary process. This letter presents results of a number of significant statistical parameters, including level crossing rate and average fade duration.

A biologically inspired QoS routing algorithm for mobile ad hoc networks

We present an Emergent Ad hoc Routing Algorithm with QoS provisioning (EARA-QoS). This ad hoc Quality-of-Service (QoS) routing algorithm is based on a swarm intelligence inspired routing infrastructure. In this algorithm, the principle of swarm intelligence is used to evolutionally maintain routing information. The biological concept of stigmergy is applied in the process of route maintenance to reduce the amount of control traffic. This algorithm adopts the cross-layer optimisation concept to use parameters from different layers to determine routing avoiding congestion areas. A lightweight QoS scheme is proposed to provide service-classified traffic control based on the data packet characteristics. The simulation results show that this novel routing algorithm performs well in a variety of network conditions.

On-body path gain variations with changing body posture and antenna position

Variability of an on-body transmission channel at 2.45 GHz is investigated. The propagation path gain was measured for a number of antenna positions and at a number of static human body postures as well as during arbitrary movements. Dependence of the path gain on conformal antenna separation is investigated and probability distributions of the path gain during arbitrary movement are derived

A three-dimensional parabolic equation applied to VHF/UHF propagation over irregular terrain

The two-dimensional (2-D) parabolic equation (PE) is widely used for making radiowave propagation predictions in the troposphere. The effects of transverse terrain gradients, propagation around the sides of obstacles, and scattering from large obstacles to the side of the great circle path are not modeled, leading to prediction errors in many situations. In this paper, these errors are addressed by extending the 2-D PE to three dimensions. This changes the matrix form of the PE making it difficult to solve. A novel iterative solver technique, which is highly efficient and guaranteed to converge, is presented. In order to confine the domain of computation, a three-dimensional (3-D) rectangular box is placed around the region of interest. A new second-order nonreflecting boundary condition is imposed on the surface of this box and its angular validity is established. The boundary condition is shown to keep unwanted fictitious reflections to an acceptable level in the domain of interest. The terrain boundary conditions for this 3-D PE method are developed and an original technique for incorporating them into the matrix form of the iterative solver is described. This is done using the concept of virtual field points below the ground. The prediction accuracy of the 3-D PE in comparison to the 2-D PE is tested both against indoor scaled frequency measurements and very high frequency (VHF) field trials.

Simulation and Measurement of Dynamic On-Body Communication Channels

A study is presented of wireless on-body communication links, with the body in motion. This paper compares simulations and measurements of the path gain (PG) on moving male and female bodies. Simulations using avatars derived from an animation software have been performed at 2.45 GHz. Male and female avatars walking and a male rising from a chair have been simulated and the results are compared with measurements carried out in an anechoic chamber. The results show that good agreement between simulation and measurement of slow fading features can be achieved for a reasonable computational effort.

Wireless channels and antennas for body-area networks

In this paper a review of recent research in characterizing on-body wireless channels is presented. Path gain random variations caused by body movements in various environments have been investigated at several frequencies, including 2.45 GHz and 5.8 GHz. In a scattering environment, such as an office, the fading of on-body channels was found to undergo a combination of two types of variation, namely, short-term and long-term variations. The short-term variation is due to multipath fading and can be described by either Rician or Nakagami distribution, and the long-term fading usually follows a log-normal, or gamma distribution. The rates of fading expressed in terms of level crossing rate and average fade duration have been also obtained. The effect of these indings on the system design parameters, such as link reliability, fade margin, and required transmitted power, is discussed. Performance of different types of antennas which can be used in WBAN devices has been evaluated as well. It is found that antenna diversity can be successfully applied in order to mitigate the effects of channel fading and interference.

A biologically inspired congestion control routing algorithm for MANETs

This paper presents EARA-CG, an improved version of a swarm-intelligence ad hoc routing algorithm EARA introduced in the work of Z. Liu et al. (2004). Based on the understanding of the evolutionary cooperation in the biological swarm, we use the principle of swarm intelligence to reinforce good quality routes with only local communication. The concept of stigmergy is adopted to reduce the amount of control traffic. By locally monitoring the network transmission queue and other MAC layer information, this algorithm can forward data traffic through paths that avoid network hotspots. The data traffic influences routing table updates at each node. We also discuss an evaluation methodology to simulate ad hoc networks, and the simulation results show that this novel routing algorithm scales well to a variety of network conditions.

On the modeling of reflected energy from building faces in microcellular mobile radio planning tools

A semideterministic model of electromagnetic scattering from exterior urban building walls that is capable of modeling scattering from large-scale discontinuities such as ledges, windows, etc., is presented. The model is in quantitative agreement with spatiotemporally resolved measurements of scattering from a building wall at 2.4 GHz and can be used to construct relatively simple modified reflection coefficients that can be used in ray-optical microcellular planning tools.