Plan de Cuentas – Normas Internacionales de Información Financiera

The impact of flesh in the radio communication is not completely standardized. Different design of hardware may influence the meat differently. First step is to understand the effect of flesh on the designed hardware. This understanding should be normalized and an optimum should be chosen for the further experiments for the performance measurement of the network.

5.3.1

Parameters of physical layer configuration

The hardware designed supports different configurations for the PHY and MAC layer. The configurations of physical layer should be verified with real world physical characteristics such as distance, antenna orientation, etc. To understand the different configuration for the PHY layer, different parameters should be studied and the effect of the parameters in the network performance is needed. This is explained as follows,

• Transmission (Tx) Power : The power at which the power is delivered to the antenna. It is measured in the units of dbm. If the antenna is exactly matched with the output impedance of the radio chip, the power delivered at the antenna should ideally match the transmission power. Varying Tx power will result in the variation in the signal received at the receiver end. Lower the RSSI, higher the bit error rate and lesser the number of successful transmission. In order to save power at both receiver and the transmitter, an optimum level of Tx power should be chosen.

• Tx Rate : The rate at which the data is sent. The unit is bytes per second. Higher the transmission rate, quicker the transmission and hence power will be saved. However, if the receiver misses any information, the re-transmission has to be done, which again

CHAPTER 5. CHARACTERISATION OF PHY LAYER OF AN IMPLANATABLE SENSOR NODE

contradicts to the power consumption. Also, the network throughput is increased with higher data rates. However, the same failure rate effect the effective throughput of the network.

• Frequency of Tx : Higher the frequency, lesser the propagation inside the human body. As the human body is conductive, RF properties in air donot follow inside the body. The in-body communication as mentioned earlier is standardized to operate in MICS band. However, it can be useful to investigate if the network performance is increased with a different frequency inside the meat.

• Distance : The distance between Tx and Rx is not software configurable, however, the varying the distance will change the physical layer configuration. In order to cope up with the changes in distances, the maximum limit of the distance is found out with different configurations of the PHY.

• Orientation : The orientation of antenna inside the meat. The orientation is again not a software defined PHY parameter, but it is taken into consideration for evaluating the PHY of hardware. Different scenarios of communication will be explained in the section 5.3, out of which is the communication of nodes placed in different location inside the body. For this configuration, the antenna orientation can be a possible factor to decide on the location of the implants. Moreover, other scenarios such as inbody to outbody communication will also benefit from the antenna orientation.

All these options are possible to configure though software with the given implant. The distance and orientation are taken care in the implantation of the sensor node in the sub-cutaneous layer of the given meat.

5.3.2

Medical scenarios for different configurations

The IEEE 802.15 Task group 6 have defined four main configurations for in-body communic- ation [31] :

• Scenario (SC) 1 : In-body to in-body communication

• SC2 : In-body to on-body communication

• SC3 : On-body to on-body communication

• SC4 : On-body to external nodes communication

PHY layer parameters for all the four configurations will be evaluated. Different medical scenarios for these configurations are foreseen as follows,

SC1 : The in-body to in-body communication is necessary when an implant medical device needs to communicate to the implanted sensor. Consider a patient who has a drug-delivery device and pace maker implanted. The drug delivery device will deliver the insulin for the regulating the blood glucose level. The effect of blood glucose level has impact on the heart rate. Lower the glucose level, lower the heart rate is the medical symptom [3]. In such a situation the patient will have sensors implanted for measuring the glucose level and hear rate. In the event of an high heart rate, the pacemaker should regulate the rhythm of the heart. To confirm that the heart rate is changing because of the glucose level, the pace maker should communicate to the glucose sensor and also send command to the drug delivery implant, while regulating the pace of the

heart by itself. All the data communication in this case is inside the human body, provided the pacemaker acts as the controller. The data communication should be reliable and also quicker to save the life of the patient.

SC2: Consider the same scenario explained above. If the controller is not the pace-maker then an external controller outside the body must communicate to the implants for the same action to take place. However, for tele-medicine application where the sensor data and operation of the implanted medical devices are to be logged externally to a server. In such cases, logging of the periodic data to an external device is mandatory.

SC3: The on-body sensor nodes are the nodes which monitor the physiological and physical activities non-invasively. These sensor nodes must communicate to the controller or the data logger which is also placed external to the body. This communication is not critical and can take place with less priority than the in-body sensor nodes. The effect of shadowing and fading due to human body is considered in this situation i.e, placing a node in the chest of a human (ECG) and another node in the leg (activity sensor)of human will severely face the effects of shadowing from human body. Validating the PHY layer parameters for this scenario is also considered in this thesis.

SC4 : The communication between external controller which is attached to the surface of the body to the external internet server placed in the vicinity of the human. The telemedicine ap- plication requires this communication path for remote monitoring of the patient and healthcare. This communication model need not be considered for the evaluation of PHY since it is out of scope of the thesis.