03-12-2012, 06:10 PM
Radio Propagation Measurement And Channel Modelling For Wireless Body Area Network (WBAN)
1Radio Propagation.docx (Size: 283.23 KB / Downloads: 51)
Abstract
The increasing use of wireless network in most application has driven the development of wireless body area network (WBAN). In this project, a simple and efficient channel model is proposed for WBAN. This is done by estimating two parameters which are path loss coefficient, and polarization loss factor, of the Friis Formula. For this purpose, two microstrip patch antennas which operates in the range of 2.4 GHz has been designed, simulated, fabricated and tested to be used in the transmitter and receiver end of the WBAN system. The signal strength between the transmitter and receiver antennas has been measured for possible distances within the WBAN usage environment. By comparing the theoretical and simulation results of the signal strength, the value of and are obtained to model the channel for WBAN.
INTRODUCTION
Wireless Body area network (WBAN) is a network of body-attached (wearable/implanted) devices that monitor body parameters/ movements, which is essential for healthcare services of the future. FCC (Federal Communication Commission) of the US has considered the frequency range of 2.4 GHz to be allocated for WBAN. In these networks, various sensors are attached on clothing or on the body or even implanted into the human body [1]. The wireless nature of the network and the use of various type of sensor may offer many applications such as to monitor body parameters or detect movements in order to improve health care and the Quality of Life [2]. The sensors of a WBAN measure for example the heartbeat, the body temperature or record a prolonged electrocardiogram [3].Several research regarding the channel models for WBAN systems have been done which can be categorized into implanted BAN and wearable BAN. The communication links for WBAN between in-body device, on-body device and near-body device have been studied.
CHANNEL MODELING FOR WBAN SYSTEM
A communication channel can be referred to as a physical transmission medium such as a wire or to a logical connection over a multiplexed medium such as a radio channel. A channel is used to transmit an information signal from transmitter to the receiver. A channel has a certain capacity for transmitting information, often measured by its bandwidth in Hz or its data rate in bits per second. It can be modeled physically by calculating the physical processes which modify the transmitted signal. An important step in the development of a WBAN system is the characterization of the electromagnetic wave propagation from devices that are close to or inside the human body [4]. It involves communication from the human body to distances ranging from a few centimeters to 3 meters, to or from devices on the body, implanted in the body or wearable.
EXPERIMENTAL SETUP
This project consists of two parts. In the first part, the antennas that will be used to measure the power received via the WBAN channel were fabricated. In the second part, the channel measurement was done in order to finally obtain the parameters α and β of the Friis Equation.
Antenna Simulation
After the parameter had been computed using formulas given, the simulation of the microstrip patch antenna is done using Computer Simulation Technology Microwave Studio (CST MWS) software. CST MWS is a specialist tool for the fast and accurate 3D electromagnetic simulation. So, from this simulation, we can simply obtain and investigate a few parameters which are very important in designing the antenna [5].
SECOND PART
The measurement of signal strength in this project was done using two microstrip patch antenna operating in the range of 2.4GHz that act as transmitter and receiver. Since this project will focused more on patient monitoring which include in the on-body to on-body scenario, the measurement will be done for on body and near body communication links. To achieve this, one antenna is attached on the body and the other antenna is put near the body but with different distances. The signal strength of these two devices for different distances is measured using vector network analyzer (VNA) and plotted in MATLAB. By modifying the and of the Friss formula, new channel model will be produced. So, this project is divided into two parts:
Antenna Face to Face Test
In this part, two antennas are being used; one antenna is used as transmitter and the other one is used as receiver. The transmitter antenna is connected to Port 1 of VNA and it is fixed to one location. The receiver antenna is connected to Port 2 of VNA and then distance of the receiver is varied in range of 10mm<R< 2000mm. This range of distance is being used in this test because 10mm lies in the far field and the distances are the most likely distances between a Tx and Rx WBAN system. The S21 parameter is measured using Vector Network Analyzer (VNA) to see the signal strength between the transmitter and receiver when the distance between them is varied. S21 refers to the signal
exiting at Port 2 for the signal incident at Port 1 which represents the power received at antenna 2 relative to the power input to antenna 1 [6].
CONCLUSION
In this paper, the channel model for WBAN had been proposed based on experimental radio channel modeling campaign for on-body measurement. Two parameters that have been used to determine the channel model are path loss coefficient.