1. Sujan Rajbhandari PGNET2006 1 Performance of Convolutional Coded Dual Header Pulse Interval Modulation in Infrared Links S. Rajbhandari, Z. Ghassemlooy, and N. M. Aldibbiat Optical Communications Research Group, School of Computing, Engineering and Information Sciences, The University of Northumbria, Newcastle, U.K. Web site: http://soe.unn.ac.uk/ocr

2. Sujan Rajbhandari PGNET2006 2 Optical Wireless – Advantage  High unregulated bandwidth, 200 THz in the 700- 1500 nm range  No multipath fading  Low cost  Small cell size  Can not penetrate through wall- same frequency can be utilized in adjacent rooms

3. Sujan Rajbhandari PGNET2006 3 Issues for Practical Implementations  Intense ambient noise.  Average transmitted power is limited due to eye safety reasons.  Can not penetrate through wall-need to instant infrared access point.  Large area photo-detectors - limits the bandwidth.

4. Sujan Rajbhandari PGNET2006 4 Modulation Techniques  Modulation scheme must be power efficient as far as possible because the maximum power that can be transmitted is limited because of eye safety.  On-Off Keying (OOK), Pulse Position Modulation (PPM), Digital Pulse Interval Modulation (DPIM), Dual Header Pulse Position Modulation (DH-PIM), Differential Amplitude Pulse-Position Modulation (DAPPM)

5. Sujan Rajbhandari PGNET2006 5 Modulation Techniques

6. Sujan Rajbhandari PGNET2006 6 DH-PIM  Header and Information section for every symbol.  Two headers, having same time duration.  Information section consist of empty slots which are equal to the decimal equivalent or decimal equivalent of one’s complement of the symbol depending upon the symbol.  Power efficient compared to OOK  Bandwidth efficient compared to PPM and DPIM.  Built in slot and symbol synchronisation capability.

7. Sujan Rajbhandari PGNET2006 7 Why use Error Control Coding ?  Improves the reliability of system.  Improves the Signal to Noise ratio (SNR) required to achieve the same error probability.  Efficient utilization of available bandwidth and power.

8. Sujan Rajbhandari PGNET2006 8 Convolutional Coded DH-PIM(CC-DH-PIM)  Linear block codes and Trellis coding is difficult (if not impossible ) to apply in DH-PIM because of variable symbol length.  So either convolutional code or modification of convolutional codes are only alternatives.  There has no report that the convolutional code is applied to DH-PIM system as far as author’s knowledge.

9. Sujan Rajbhandari PGNET2006 9 System Block Diagram

10. Sujan Rajbhandari PGNET2006 10 State Diagram Depending upon the symbol and preceding symbol, four headers are possible. Generally headers are [11 10 11] or [11 01 01] for symbol of magnitude less than (2 M- 1 )/2 or greater than or equal this value respectively. The header can be [00 10 11 ] or [00 01 01] if the present symbol is preceded by symbol of magnitude 2 M-1. So there is only limited paths in trellis diagram. No state transition form ‘d’ to ‘d’. The transfer function and error bound needs to be modified for CC-DH-PIM encoder.

11. Sujan Rajbhandari PGNET2006 11 CC-DH-PIM Symbol OOK (M=3) DH-PIM 2 CC-DH-PIM 2 CC-DH-PIM 2 preceded by 2 M -1 00010011 10 1100 10 11 001100 011 10 11 0000 10 11 00 010100 0011 10 11 00 0000 10 11 00 00 011100 00011 10 11 00 00 0000 10 11 00 00 00 100110 00011 01 01 11 00 0000 01 01 11 00 00 101110 0011 01 01 11 0000 01 01 11 00 110110 011 01 01 11 0000 01 01 11 11111011 01 0100 01 01

12. Sujan Rajbhandari PGNET2006 12 Error Bound Error Bound for general convolutional encoder

13. Sujan Rajbhandari PGNET2006 13 Error Bound  The upper error bound for CC-DH-PIM is less than or equal to the error bound for general encoder  Fixed header patterns limits trellis paths.  Only finite set of paths.

14. Sujan Rajbhandari PGNET2006 14 Comparisons of Uncoded and Coded DH-PIM A code gain of greater than 3 dB for slot error rate of 10 -4

15. Sujan Rajbhandari PGNET2006 15 Comparisons of Different Modulation Scheme Show up to 10 -10 ! CC-DH-PIM 1 offer the best performance compared with PPM and DH-PIM.

16. Sujan Rajbhandari PGNET2006 16 Convolutional Coded DH-PIM having different constraint Length Improved performance can be obtained by increasing the constraint length of encoder at the cost of complexity.

17. Sujan Rajbhandari PGNET2006 17 Conclusions  Applying convolutional coding to the DH-PIM improves the performance of system.  (3,1,2) Convolutional encoded DH-PIM requires 4-5 dB less SNR compared to uncoded DH-PIM.  Further improvement can be obtained by increasing the constraint length.

18. Sujan Rajbhandari PGNET2006 18 Thank you!