1 / 20

CONVOLUTIONAL CODED DPIM FOR INDOOR NON-DIFFUSE OPTICAL WIRELESS LINK

CONVOLUTIONAL CODED DPIM FOR INDOOR NON-DIFFUSE OPTICAL WIRELESS LINK. S. Rajbhandari, Z. Ghassemlooy , N. M. Adibbiat, M. Amiri and W. O. Popoola Optical Communications Research Group, Northumbria University, Newcastle, UK. Contents. Introduction to optical wireless Modulation schemes

keefer
Download Presentation

CONVOLUTIONAL CODED DPIM FOR INDOOR NON-DIFFUSE OPTICAL WIRELESS LINK

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CONVOLUTIONAL CODED DPIM FOR INDOOR NON-DIFFUSE OPTICAL WIRELESS LINK S. Rajbhandari, Z. Ghassemlooy, N. M. Adibbiat, M. Amiri and W. O. Popoola Optical Communications Research Group, Northumbria University, Newcastle, UK

  2. Contents • Introduction to optical wireless • Modulation schemes • Digital PIM • Coded DPIM • Results + comments

  3. Optical Wireless Communication - Introduction • Uses light (visible or Infrared (IR )) as a carrier. • The medium is free-space (outdoor and Indoor) • Line-of-sight (LOS) or diffuse or hybrid • License free with abundance bandwidth, and high data rate • No multipath fading but • Protocol transparent • High security • Free from electromagnetic interference • Compatible with optical fibre (last mile bottleneck?) • Low cost of deployment

  4. OWC - Challenges • Power limitation: due to eye and skin safety • Intersymbol interference due to multipath propagations • Intense ambient light noise • Limited user mobility • Large area photo-detectors - limits the data rate

  5. OWC - Links Rx Tx • LOS • Non-LOS • Multipath Propagation • Intersymbol interference (ISI) • Difficult to achieve high data date due to ISI • LOS • No multipath Propagation • Only noise is limiting factor • Possibility of blocking • Tracking necessary to maintain LOS link Rx Tx

  6. Digital Modulation Schemes • On-off Keying (OOK) • Pulse position modulation (PPM) • Subcarrier modulation • Digital pulse interval modulation (DPIM) • Dual-header pulse interval modulation (DH-PIM)

  7. Frame 2 0 1 0 Frame 3 1 1 0 Frame 4 1 1 1 Frame 1 0 0 0 Information Digital Modulation Schemes DPIM

  8. Digital Pulse Interval Modulation • Variable symbol length Where Tb is input bit rate and Ts is DPIM slot duration • A symbols starts with pulse followed by k empty slots. 1≤ k≤ L and L = 2M • Guard slot(s): Added after the pulse to provides immunity to ISI arising from multipath propagation. • With g guard slots the minimum and maximum symbol durations are * gTs and (L+g)Ts

  9. DPIM- What does it offer? • Bandwidth efficient compared to PPM. • Built-in slot and symbols synchronisation. • Higher through put compared to PPM. • Better performance in diffused environment compared with PPM

  10. DPIM - Convolutional Coding • Has not been done before • Linear block codes like Hamming code, Turbo code and Trellis coding are difficult (if not impossible ) to apply in PIM because of variable symbol length. • Hence, Convolutional code is employed - since the acts on the serial input data rather than the block.

  11. DPIM - Convolutional Coding • (3,1,2) convolutional • encoder . • ½ code rate and • constraint length = 3 • Generator function • g0= [100], g1 = [111] and g2 = [101]

  12. DPIM - Convolutional Coding • 2 empty slots for all the symbols to ensure that memory is cleared after each symbol. • Trellis path is limited to 2.

  13. DPIM - Decoder • Viterbi ‘Hard ‘ decision decoding • The Chernoff upper bond on the error probability is: where Pse is the slot error probability of uncoded DPIM. • It is also possible not use Viterbi algorithm instead one can use a simple look-up table.

  14. DPIM - Block Diagram AWGN R Convolutional Encoder Optical Tx Photodetector DPIM Input Ik Viterbi Decoder Matched Filter Sampler DPIM estimate

  15. Results – Slot Error Rates Upper Bounds • Difficult to ascertain exact hamming distance • Union bound is utilised to evaluate the performance. • A close match at upper bound, less than 0.5 dB gap • The DPIM(2GS) gives the best performance

  16. Results – Slot Error Rates With/Without Guard Slots • Code gain of 4.8 dB • at Pse of 10-4 for all cases. • Increasing number • of guard slot improves • the performance at the • cost of bandwidth. • 0.5 dB improvement • in SNR requirement • for each increment • in number of Guard • slot for M=4

  17. Results - Slot Error Rates With/Without Guard Slots • Higher bit resolution • provides better • performance ( at the • expense of bandwidth) • The code gain is 0.6 • higher for bit • resolution of 5 • compared to 3.

  18. 8 , 16 , 32 - DPIM with one guard band @ R = 100 Mbps Uncoded 8 - DPIM R Coded Upper E Bound 8 - DPIM P , Uncoded 32 - DPIM r o r r Coded Upper e t Bound 32 - DPIM e k c Uncoded a P 16 - DPIM f o Coded Upper y t i Bound 16 - DPIM l i b a b o r P - 2 - 1 0 1 2 3 4 5 6 7 8 Electrical SNR ( dB ) Packet Error Rates - 4 10 - 6 10 - 8 10 - 10 10 - 12 10 PER against the electrical SNR for coded and un-coded 8,16,32 – DPIM(1GS) at 100 Mbps.

  19. Final Comments • Applying Convolutional coding has resulted in improved PER performance for DPIM scheme. • Higher SNR can be achieved at the cost of lower throughput. • Inclusion of one guard slot marginally reduces the probability of an error.

  20. Thank You! 20

More Related