ECG Compression - ECG Acquisition and Automated Remote Processing - page 114

Fig. 5.10 Block diagram of
the ECG transmission system
in GSM network (a) transmit-
end configuration;
(b) receive-end configuration

(a)

ECG data
File/ digitizer

MOD 9001
GSM module

Data compression
algorithm

Formatting of data in GSM
protocol

Transmit-End PC

(b)

Storage, analysis,
interpretation and report
generation

Mobile
phone

Recombination of text
msg to generate
compressed data file

Decompression of data
files to generate ECG
data file

Receive-end PC

The schematic block diagram of the developed system is shown in Fig. 5.10 .In
the transmit end, a PC is used for compression of ECG and transmitting the
messages through the GSM modem at the serial port.

5.4.1 Transmit-End Functions

Since mobile message can accommodate 7-bit ASCII characters, the following
additional functions are necessary at the transmit end:

(a) Conversion of 8-bit ASCII to 7-bit ASCII.
(b) Data framing for sending the compressed packets through short messages.
(c) Introducing packet serial number for easy concatenation at receive end.

These functions are achieved using a MOD 9001 GSM modem and developing
an application software for providing the mobile numbers, ECG file identification
for compression, etc.
The algorithm steps for conversion of 8-bit ASCII characters to 7-bit ASCII are
provided at the End of Chapter Appendix VI . The protocol frame for sending a
single short message through MOD 9001 GSM is shown in Fig. 5.11 .
Actual message is prefixed and suffixed by some additional characters, which
are directives to the microcontroller of the GSM modem for appropriate actions.
The interpretations are given as: