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5.
INTRODUCTION
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The device function consists of acquiring and wirelessly transmitting ECG signal for displaying, processing
and presenting ECG signal for the purpose of supporting the diagnose of patient conditions.
The device does not store nor does associate patient identification data to the acquired signal, nor does it
perform analysis on such signal.
The device transmits a continuous stream of ECG samples at rate of 500 s/s or 1000 s/s and a resolution <
1uV/LSB. The bitrate required by the application is ~90 kbit/s at 500 s/s and ~180 kbit/s at 1000 s/s.
In order to support the application data throughput, the device implements the Bluetooth Serial Port Profile
(SPP) with EDR (Enhanced Data Rate), which nominally provides a bandwidth up to 2 mbit/s.
The SPP adopted by the device ensures that data is either received correctly or not received at all. It is up to
the host application to detect packet losses, handling the data gaps appropriately (e.g. by filling the stream
with invalid dummy samples, signaling transmission errors etc…). This approach has been preferred over
enabling the data retransmission (supported by the module) to reduce the data jitter and transmission delay.
5.7.2. Bluetooth functions
Below are defined all functions implemented wirelessly and possible risks associated with delayed or failed
communications:

The only function implemented is the transmission of acquired (unprocessed/unfiltered) ECG signal.

Risks identified with delayed or failed communication are: “Interruption of Vital Signs display” and
“Loss of data integrity”
5.7.3. Bluetooth Quality of Service
Below is defined the acceptable Quality of Service of our wireless function implemented by Bluetooth
technology with the Bluegiga chip model WT-12:

The required data transfer rate is lower than 200 kbit/s, hence the Bluetooth 2.1 + EDR supports the
application bandwidth demand.

Bluetooth SPP implements data integrity checks reducing the probability of accepting corrupted data
as good. A single packet loss encompasses 2 ms of data (500 s/s).

The jitter should be limited to 50 ms: the absence of retransmissions mechanism limits the jitter to
the device internal processing delays.
Bluetooth implements frequency-hopping techniques to select the channel with lower interference.
5.7.4. Bluetooth specifications
Below the Bluegiga module WT-12 specifications:

Bluetooth™ Class II device

BT protocol specification: 2.1 + E.D.R.

Communication profile: SPP (RFCOMM – virtual serial port)