Resultado de la Encuesta Aplicada al personal de la Cooperativa de Ahorro y

Validation results of the set of physical parameters are presented in the Fig. 5.12 - 5.17. The set of results are plotted with distance in x asis and RSSI in y axis. Different data sets of transmitting power are used for plotting. In order to compare the results meaningfully, different antenna orientation are chosen as the criteria for analysis. In Fig. 5.12, the antenna orientation is chosen as a classifier. The results are presented based on the Scenario in the following subsections.

SC1In Scenario 1, where the nodes are placed inside the flesh, the attenuation of signal is very high even in the smaller distances. The plot show in Fig. 5.12, at 0 degree which represents the antenna are placed closed to each other, even at 2 cm separation, a transmission of 5 dbm is received as -20 dbm. This indicates almost 25 % of the signal is attenuated even at such lower distances. Increasing the distances indicate that the RSSI is decreasing linearly. This boils down to the fact that ” as the distance increases, the received signal strength decreases”. However, it is interesting to note that the decrease in RSSI is not completely linear at higher distances. The relationship between RSSI and distance become logarithmic after 12 cms inside the flesh.

2 4 6 8 10 12 14 16 −110 −100 −90 −80 −70 −60 −50 −40 −30 −20 −10 Distance cm RSSI dbm

Distance vs RSSI (Orientation = 0 degree)

Tx 5dbm Tx 0dbm Tx −10dbm Tx −15dbm Tx −30dbm

Figure 5.8: RSSI vs Distance at 0 degree antenna orientation 2 4 6 8 10 12 14 16 −110 −100 −90 −80 −70 −60 −50 −40 −30 −20 Distance cm RSSI dbm

Distance vs RSSI (Orientation = 90 degree)

Tx 5dbm Tx 0dbm Tx −10dbm Tx −15dbm Tx −30dbm

Figure 5.9: RSSI vs Distance at 90 degree antenna orientation 2 4 6 8 10 12 14 16 −120 −110 −100 −90 −80 −70 −60 −50 −40 −30 −20 Distance cm RSSI dbm

Distance vs RSSI (Orientation = 180 degree)

Tx 5dbm Tx 0dbm Tx −10dbm Tx −15dbm Tx −30dbm

Figure 5.10: RSSI vs Distance at 180 degree antenna orientation 390 400 410 420 430 440 450 460 470 −110 −105 −100 −95 −90 −85 −80 −75 Frequency MHz RSSI dbm Freqeuncy vs RSSI

Figure 5.11: RSSI vs Frequency at a fixed tx power, distance, orientation

Figure 5.12: Received signal strength information (RSSI) for in-body to in-body communication SC1

SC2 In Scenario 2, where the nodes are placed inside the flesh and outside the flesh, the attenuation of signal is lesser than the SC1. The plot show in Fig. 5.17, at 0 degree which represents the antenna are placed closed to each other, even at 2 cm separation, a transmission of 5 dbm is received as -10 dbm. This indicates 20 % of the signal is attenuated even at lower distances. Increasing the distances indicated that the RSSI is decreasing linearly. However, as obtained in the case of SC1, the decrease in RSSI is not completely linear at higher distances. The relationship between RSSI and distance become logarithmic even after 10 cms inside the flesh when the node is communicating to the node outside the flesh.

CHAPTER 5. CHARACTERISATION OF PHY LAYER OF AN IMPLANATABLE SENSOR NODE 2 4 6 8 10 12 14 16 −110 −100 −90 −80 −70 −60 −50 −40 −30 −20 Distance cm RSSI dbm

Distance vs RSSI (Orientation = 90 degree)

Tx 5dbm Tx 0dbm Tx −10dbm Tx −15dbm Tx −30dbm

Figure 5.13: RSSI vs Distance at 0 degree antenna orientation 2 4 6 8 10 12 14 16 −110 −100 −90 −80 −70 −60 −50 −40 −30 −20 −10 Distance cm RSSI dbm

Distance vs RSSI (Orientation = 0 degree)

Tx 5dbm Tx 0dbm Tx −10dbm Tx −15dbm Tx −30dbm

Figure 5.14: RSSI vs Distance at 90 degree antenna orientation 2 4 6 8 10 12 14 16 −120 −110 −100 −90 −80 −70 −60 −50 −40 −30 −20 Distance cm RSSI dbm

Distance vs RSSI (Orientation = 180 degree)

Tx 5dbm Tx 0dbm Tx −10dbm Tx −15dbm Tx −30dbm

Figure 5.15: RSSI vs Distance at 180 degree antenna orientation 390 400 410 420 430 440 450 460 470 −110 −105 −100 −95 −90 −85 −80 −75 Frequency MHz RSSI dbm Freqeuncy vs RSSI

Figure 5.16: RSSI vs Frequency at a fixed tx power, distance, orientation

Figure 5.17: Received signal strength information (RSSI) for in-body to on-body communication SC2

SC3The Scenario 1 where the nodes are placed outside the flesh, the attenuation is similar to that of the communication in free space. The plot show in Fig. 5.22, at all the orientations, the attenuation follows the same pattern. However, it is interesting to note that the decrease in RSSI is still linear at higher distances. There is no logarithmic dependency at higher distances. The effect of orientation is not a major contribution in the RSSI information in free space. The antenna in this case is faced towards the air, and not sandwiched between PCB and skin.

2 4 6 8 10 12 14 16 −120 −110 −100 −90 −80 −70 −60 −50 −40 −30 −20 Distance cm RSSI dbm

Distance vs RSSI (Orientation = 180 degree)

Tx 5dbm Tx 0dbm Tx −10dbm Tx −15dbm Tx −30dbm

Figure 5.18: RSSI vs Distance at 0 degree antenna orientation 2 4 6 8 10 12 14 16 −120 −110 −100 −90 −80 −70 −60 −50 −40 −30 −20 Distance cm RSSI dbm

Distance vs RSSI (Orientation = 180 degree)

Tx 5dbm Tx 0dbm Tx −10dbm Tx −15dbm Tx −30dbm

Figure 5.19: RSSI vs Distance at 90 degree antenna orientation 2 4 6 8 10 12 14 16 −120 −110 −100 −90 −80 −70 −60 −50 −40 −30 −20 Distance cm RSSI dbm

Distance vs RSSI (Orientation = 180 degree)

Tx 5dbm Tx 0dbm Tx −10dbm Tx −15dbm Tx −30dbm

Figure 5.20: RSSI vs Distance at 180 degree antenna orientation 390 400 410 420 430 440 450 460 470 −110 −105 −100 −95 −90 −85 −80 −75 Frequency MHz RSSI dbm Freqeuncy vs RSSI

Figure 5.21: RSSI vs Frequency at a fixed tx power, distance, orientation

Figure 5.22: Received signal strength information (RSSI) for on-body to on-body communication SC3

In general all the cases indicate that the RSSI is linearly decreasing with distance, which can be formulated as RSSIα _k Distance ·(µ·T xpower)

where, k&µare constants. In order to match the standards of MICS, the transmission power should not be higher than 25µW. By referring to the datasheet of antenna and CC430 it is found that at a transmitting power of -10dbm the EIRP of the node will not exceed 25µW. However, no hardware measurement is made in order to verify the EIRP. Also, lowering the power further below -10dbm will not be able to communicate at distances greater than 5cms. A distance of 16 cms is chosen in order to match the requirements of pace-maker and drug-delivery device standards, where the distance between the sensor and the device cannot be larger than 16 cms. Larger distance will reduce the sensitivity of the sensor, hence the distance can be ranged from

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

3-15 cms. The antenna orientation is chosen to be 0 degree, because at higher distances, it is found that the node cannot have a higher RSSI values. Having lower RSSI values may result in the higher error rates in data transmission, which will not be reliable for in-body communication. In order to evaluate the set 2 parameters of the PHY layer, the optimum parameters are set based

Parameter Value Transmission power -10dbm Transmission distance SC1 - 16 cms SC2 - 40cms SC3 - 100 Frequency of operation 433MHz Antenna orientation 0◦

Table 5.6: Optimum values derived from validating the set of physical parameters

on the analysis. The optimum is chosen where the node is able to receive valid signal strength meeting the MICS standards.