Use of GSM Modem in ECG Transmission

Transcription

1 Use of GSM Modem in ECG Transmission Chapter 5 A major shortcoming of using internet based SMS is the probability of unavailability of internet connection at remote patient site. Hence, we must need to seek another cost effective alternative for fast transmission-reception of compressed ECG signal. Second Generation (2G) Global System for Mobile Communication (GSM) SMS is found as the most suitable one which may replace internet based free SMS. To implement this, a GSM transceiver module is used at the patient s site to send the compressed ECG signal in form of SMS. The SMS transmission-reception protocol using GSM transceiver module is discussed elaborately in the rest of the section G GSM Transceiver An i-300 GSM modem connected through RS232 computer serial port is used to send SMS. Figure 5.1 shows a snapshot of the used GSM transceiver module. SMS transmission and reception techniques are almost similar to that of the internet based technique. The difference is; GSM modem works on AT commands. AT is the abbreviation of Attention. Every command line starts with AT. That's why these commands are called AT commands. Few examples are: ATD is used for dialing a number, ATA is used for answering an incoming call, CMGS is used to send SMS in text mode etc. The application software developed for this purpose offers to choose the compressed file and transmits the same using the connected GSM modem obeying its protocol. As described in chapter 4, here also, 2G GSM SMS supports only 7-bit ASCII characters ranging from 0 to 127. Therefore every character in the compressed file is mapped into two 7-bit ASCII characters. 2G GSM SMS mostly, supports 7-bit ASCII characters but with few exceptions. Few specific 7-bit characters cannot be transmitted

2 Use of GSM Modem in ECG Transmission 93 through SMS. For example, all characters between (0-31), 59, 61, (91-94), 96 and ( ) cannot be transmitted. ASCII characters of 59 (;), 61 (=), 91 ([), 92 (\), 93 (]), 94 (A), 96 (' ), 123 ({), 124 ( ), 125 (}), 126 (~) and 127 (d) can be transmitted through 2G GSM SMS but, in the received SMS file there will be some other characters except these resulting in the same problem as described in chapter 4. Figure 5.1: Snapshot of the used GSM transceiver module. Schematic of such an ECG transmission protocol using GSM transceiver module is shown in figure 5.2. An Approach to Develop a Remote Tele-cardiology System for Compression, Transmission and Analysis of ECG signal, Submitted by Sourav Mukhopadhyay

3 94 OOQOQQ 0 t # d DOODOODD -ro d i'eegeoq > EDdE-r.EdEDOD D 0 gge-f 8 bit ASCII Characters (0-255) DOIDDO ueoed-r iddeie-r 1 EEEdQO,@eEfE-r iqeqgdqoo > gedf/q ' DDEDh.DO eeeoqo 0 EEhe/u heehoo' ieilqd iiodiooo 8 Bit to 7 Bit ASCII Conversion! "#$%&' O,-./0124 : o?«abcd EGbcd! #$$%%&& acahd%n t>arf8#&! "#$%&' O*,-./0124 :o?«abcd EGbcd! #$$%%&& a CAHD%N {}ARF8#&! '.-./0124 :<>?@ABCD EGbcd! #$$%%&& acahdssn #$%& o«- 7 bit ASCII Chsuactcrs (32-126) Creating small data files each containing bit ASCE characters!''#$%&>0)*+ SMS N SMS 2 SMS 1 Figure 5.2: Schematic of the ECG transmission protocol using GSM transceiver module.

4 Use of GSM Modem in ECG Transmission 95 The algorithm followed here to convert 8 bit to 7 bit ASCII character is very simple and is described below. 5.2 Compressed ECG Transmission using GSM modem At first, 8-bit ASCII characters are divided into 4 groups. All characters between 0-31 are taken under 1st group. Characters ranging from 32 to 127 are in the 2nd group. 128 to 218 belong under 3rd group and rest of the characters i.e. 219 to 255 reside under 4th group. Table 5.1 illustrates the group division. Table 5.1: Character Division Table. 0<~>255 0 <-->31 32 <--> < > < >255 1st group 2nd group 3rd group 4th group Two variables have been taken, named RANGE and DATA to hold two 7-bit ASCII characters. Algorithm applied for 1st group: For this group, RANGE is set to 32 and DATA is set to 32 + that 8-bit ASCII. Therefore, both RANGE and DATA will be always greater than 31 and hence can be transmitted through SMS. Although 27 and 29 fall in this range but, after adding 32 with these two, they become 59 and 61 respectively. These two characters can t be transmitted through SMS. For these two, RANGE is set to 33 and DATA is set to Number+33. RANGE DATA that 8-bit ASCII RANGE DATA 33 Number+33 'An Approach to Develop a Remote Tele-cardiology System for Compression, Transmission and Analysis of ECG signal, Submitted by Sourav Mukhopadhyay

5 96 Algorithm applied for 2nd group: For these numbers, RANGE is set to 34 and DATA is assigned to the same as the original number. Although 59, 61, (91-94), 96 and ( ) fall in this range but these characters can t be transmitted through SMS. Therefore these numbers are modified in a different way. For these numbers RANGE is set to 35 and DATA is set to Number-6. This is nothing but to overcome the difficulty. Algorithm applied for 3rd group: For this group, RANGE is set to 36 and DATA is set to number All characters in this range are 8-bit ASCII. 100 is subtracted to make them 7-bit ASCII and 4 is added to move them up above 31. Here also, the same problem occurs for the numbers 155, 157, ( ), and 192. RANGE and DATA are also modified for these numbers in the same way described earlier. Algorithm applied for 4th group: For the last set of characters ( ), RANGE is set to 38 and DATA is set to Number Also in this range, problem arises for the numbers 246 and 248.

6 Use of GSM Modem in ECG Transmission 97 RANGE DATA 38 Number RANGE DATA 39 Number It is to keep into consideration that, both RANGE and DATA must be valid 7-bit ASCII characters. At last both RANGE and DATA are printed in the output file. Utmost 160 characters can be delivered through a single SMS if the GSM modem is used under text mode. Therefore the developed algorithm divides the compressed data file into small data files each containing bit characters. Out of those 160 characters, the first character is allotted for patient ID, second and third characters are allotted for SMS number and rest 157 characters are used for transmitting the compressed ECG data. Now those small data files are transmitted to doctors or cardiologists mobile phone through the i-300 GSM modem with the help of proper AT commands. Excluding those problematic characters (0-31, 59, 69 etc.), at a time, 84 (128 7-bit ASCII characters - 44 problematic characters = 84) patients compressed ECG files can be transmitted simultaneously to a particular mobile phone and each patient ID can have 7056 (84 X 84) SMSs, if needed. 5.3 SMS reception at remote site The procedure followed here to collect and concatenate SMSs is same as described in chapter 4 (section 4.3). Block schematic of the ECG signal reconstruction protocol is shown in figure 5.3. An Approach to Develop a Remote Tele-cardiology System for Compression, Transmission and Analysis of ECG signal, Submitted by Sourav Mukhopadhyay

7 98 SMS N fi SMS 2 SMS 1 SMS Transfer a ETCg3,-./OX24 ;:o.?0abco jegbcd! lacahd%n l{>arf8#&! O.- -/OX24 ;: o? ABCO jegbcd!,#ssm& iacahdxn {}ARF8#&! *./OX24, : o?@abcd jegbcd! :acaho%n #$%& o l»*l AXC.'il < 1»;mu-U'i s (.>2-1 2f») 7 Bit to S bit ASCII conversion u aigal De-Compression Algorithm <= bduuddu Q pngodoggo i EEg EoG > EGdE-i-, EdEEJQO 0 D gge-r BaiDOu ueaed-r- DQEie-r OEQGda c > gedf/0 DOEOh.DQ eeed3d 0 EEhe/D heehoo ieiiod ildcidco - # 8 bit ASCII Characters (0-255) *&SQ Figure 5.3: Block schematic of the signal reconstruction protocol.

8 Use of GSM Modem in ECG Transmission 99 The algorithm designed here, tracks SMS sender s mobile phone number from the SMS body so that fast communication can be made with patient parties at critical condition. Snapshots of the used Samsung Wave 525 mobile phone and few intermediate processes are shown in figure 5.4. (53- OpcnWMh... j Intonx 5«WHY Scan! to - *)hmr*.r*r-» SMI Caning nrwdl antoi.., ' SCoraotMt to "Otfui t.ia* aid «t»arf G Figure 5.4: Snapshots: (A) Samsung Wave 525 mobile phone, (B) Received SMSs, (C, D, E) Transferring SMSs from mobile phone to memory card, (F) Phone is connected to PC via USB cable and (G) Transferring SMSs from memory card to PC. An Approach to Develop a Remote Tele-cardiology System for Compression, Transmission and Analysis of ECG signal', Submitted by Sourav Mukhopadhyay

9 Software Testing As described in chapter 4, here also, the developed ECG transmission-reception software using i-300 GSM transceiver module is tested on all the 12 leads of most of the ECG data files which are included in table 2.1,2.3, 3.1 and 3.4. Table 5.2 summarizes the performance of the ECG transmission-reception module. ECG data files are individually compressed using each of the lossless, lossy and PLPL compression techniques, transmitted, and finally reconstructed at the receiving end. In this case, it is observed that the utmost time required to send a single SMS using GSM transceiver module from Kolkata to Mumbai is even less than 4 seconds which is lesser than that of the internet based SMS. Table 5.2: Performance of the ECG transmission-reception module using i-300 GSM transceiver. ECG Transmission end ECG Reception end SMS (Patient s site) (Doctor s site) delivery time Compression File Lead No. of CR No. SMS SMS PRD Average ECG samples of SMS generation time concatenation time (in second) (in second) single SMS (in second) PLPL through S0075LRE I SD calculation -do- S0097LRE II -do do- S0056LRE III -do do- S0029LRE avr -do Algorithm (%) time to send a PLPL through R S0304 III -do peak detection -do- S0305 avr -do do- S0004RE avl -do do- S0010RE avf -do Lossy S00171re VI -do do- S0020bre V2 -do do- S00261re V3 -do do- S00291re V4 -do Lossless S0436re V3 -do do- S0457re V4 -do do- S0458re V5 -do do- S0459re V6 -do Here also, as described in section 4.4, no data loss occurs during SMS transmission and the designed software concatenates only those SMSs which are

10 Use of GSM Modem in ECG Transmission 101 delivered sequentially. Figures 5.5 to 5.8 show the original ECG signal (A) at the transmitting end (patient s site), reconstructed ECG signal (B) at the receiving end (doctor s site) and difference between A and B (C). Original ECG Signal at Patient site V o lta g e m m V ) Reconstructed ECG Signal at Doctor site _J I I I I I I I I BOO Figure 5.5: Original ECG signal (A) at the transmitting end (patient s site), reconstructed ECG signal (B) at the receiving end (doctor s site) and difference between A and B (C) using Lossless ECG compression technique: File S0436, Lead V6. 'An Approach to Develop a Remote Tele-cardiology System for Compression, Transmission and Analysis of ECG signal, Submitted by Sourav Mukhopadhyay

11 102 Original ECG Signal at Patient site ' Figure 5.6: Original ECG signal (A) at the transmitting end (patient s site), reconstructed ECG signal (B) at the receiving end (doctor s site) and difference between A and B (C) using Lossy ECG compression technique: File S0021BRE, Lead II. Original ECG Signal at Patient site BOO Difference between Original & Reconstructed ECG Signal Voltage in mv Voltage in mv ' Figure 5.7: Original ECG signal (A) at the transmitting end (patient s site), reconstructed ECG signal (B) at the receiving end (doctor s site) and difference between A and B (C) using PLPL ECG compression technique through R peak detection: File S0304, Lead I.

12 Use of GSM Modem in ECG Transmission 103 Original ECG Signal at Patient site ' X30 Reconstructed ECG Signal at Doctor site Voltage in mv Voltage in mv > ' Difference between Original & Reconstructed ECG Signal Q Figure 5.8: Original ECG signal (A) at the transmitting end (patient s site), reconstructed ECG signal (B) at the receiving end (doctor s site) and difference between A and B (C) using PLPL ECG compression technique through SD calculation: File S0097LRE, Lead I. 5.5 Conclusion Nowadays, 3G technology is also becoming popular in various parts of the country. Instead of 2G GSM network, one can use 3G technology too. But the overall cost of such a system is also to be taken into consideration. In India, mobile telecommunication service providers offer 500 SMSs/INR.40 (US$0.65^) for 2G network which is cheap enough. Moreover the initial cost to have a 2G subscriber identification module (SIM) card is around INR 40 (US$0.65) whereas; it is approximately INR 200 (US$ 3.26) for 3G. SMS is used here because it is an integral part of the original 2G GSM cellular system and for subsequent generations. Cost of such a GSM transceiver module is around INR 1200 (US$ 19) which may vary marginally with different manufacturers. But this is only a one-time investment. Using GSM modem, SMSs can also be sent outside the country but, this facility (international SMS) is not available for An Approach to Develop a Remote Tele-cardiology System for Compression, Transmission and Analysis of ECG signal \ Submitted by Sourav Mukhopadhyay

13 104 internet based SMS. Latest wireless communication technologies such as GPRS and EDGE are superior in data transmission rate compared to 2G GSM technology. These high end communication technologies have become popular in economically advanced metropolitan cities. A comparative chart of various wireless data transmission schemes in terms of cost are given in table 5.3. Table 5.3: Comparative chart of various wireless data transmission schemes in terms of cost. Technology Original ECG file size (2Seconds duration) Compressed data file size No. of SMS required Theoretical data transmission rate/second Actual data transmission rate in remote areas/second Time required to send the file (in Seconds) Cost of GSM transceiver module in US$ File transmission cost in USS* 2G SMS KB 11.48KB [To I X2=20 fl9 [0013 3GSMS I 1 ^ fio fdt I [(U68 GPRS (for 2G SIM) GPRS (for 3G SIM) EDGE (for 2G SIM) EDGE (for 3G SIM) -do- -do Kbit[72] Much less 1 (minimum) 2.59[74] (unto 1 GB) -do- -do- " Kbit Much less 1 (minimum) 4.15[74] (upto 1 GB) -do- -do kbit [73] Much less 1 (minimum) 2,59[74] (upto 1 GB) -do- -do kbit Much less 1 (minimum) 4.15[74] (upto 1 GB) *SMS, EDGE, and GPRS charges are valid for Kolkata circle only. Table 5.3 reveals that, as a whole, use of 2G SMS is more beneficial in terms of cost. Although the theoretical data transmission rates of GPRS or EDGE technologies are much higher than SMS, in remote areas, data transmission rates drastically reduce from their theoretical specifications. After transmission-reception and reconstruction of ECG signal on cardiologist s computer screen, it is the turn for assistance to the cardiologists for their task of proper disease diagnosis. Identification of various ECG peaks and extraction of different time domain ECG features (segments, intervals etc.) are the first step of ECG interpretation. The next chapter (chapter 6) describes a promising and reliable ECG feature extraction algorithm which extracts most of the time domain ECG features with significant accuracy. f US$ rate as on 10th March, 2014.