Dual Header Pulse Interval Modulation (DH-PIM) Dr. Nawras Aldibbiat Professor Z Ghassemlooy Optical Communications Research Group School of Computing, Engineering & Information Sciences, Northumbria University Tel:

Outline of the Presentation Introduction DH-PIM principles Power spectral density Artificial light interference Slot & packet error probabilities Optical power & B/W requirements. Multipath propagation Conclusions

Introduction DH-PIM was first introduced in 2000: N. M. Aldibbiat & Z. Ghassemlooy: “Dual header-pulse interval modulation (DH ‑ PIM) for optical communication systems”, CSNDSP 2000, Bournemouth, UK, pp , July Why DH-PIM? Is it ideal for Indoor optical wireless systems?

Introduction Line-of-Site Non-Line-of-Site HybridDirected Non-directed

Pulse Time Modulation Tree DH-PIM Pulse Time Modulation Analogue Digital Isochronous Anisochronous DPWM MPPM PPM PCM DPIWM DPPM DPIM Anisochronous Isochronous PIWM PIM PFM SWFM PWM PPM

Pulse Modulation Symbol Structure

DH-PIM symbol structure

Symbol Length

M [slot] Average symbol length [Ts] PPM DPIM DH-PIM 1 2 Average Symbol Length

Transmission bandwidth DH-PIM requires less bandwidth compared with PPM & DPIM. Bandwidth normalised to OOK: M [slot] Normalised bandwidth requirements DH-PIM DPIM PPM

Transmission Packet Rate M [bit] Normalised packet transmission rate DH-PIM DPIM PPM B req = 1 MHz

x B req [Hz] packet transmission rate [packet/sec] M = 5 PPM DH-PIM DPIM Transmission Packet Rate - cont.

Transmission Capacity M [slot] Normalised transmission capacity DH-PIM DPIM PPM

DH-PIM system block diagram Transmitter Channel Receiver

DH-PIM Transmitter

DH-PIM Receiver

Simulation Waveforms (16-DH-PIM 1 )

Simulation Waveforms (16-DH-PIM 1 ) - cont.

Simulation Model

Power Spectral Density

Power Spectral Density - cont.

DH-PIM 1

Power Spectral Density - cont. DH-PIM 2

M [bit] P D C - n o r DH-PIM DC component of the PSD

M [bit] P s l 0 t - n o r DH-PIM Slot component of the PSD

Artificial light interference Artificial light (e.g. Fluorescent) induces periodic interference that contain harmonics at low frequencies This interference can be reduced by employing a high-pass filter, but … this results in baseline wander, which is more severe in modulation schemes that contain high power at DC and low frequencies. Therefore … there is a trade-off between the extent of artificial light interference rejection and the severity of baseline wander 

Artificial light interference Normalised frequency (f / R b ) PSD (linear units) M = 4 (L = 16) DH-PIM (alpha=2) DH-PIM (alpha=1) DPPM OOK-NRZ PSD for OOK, DPPM and DH-PIM (  =1 and  = 2) for M = 4

Artificial light interference – cont. Simulation block diagram 1 Assumptions: -a rectangular pulse shape -an equal average transmitted optical power for all systems

Artificial light interference – cont. - 8-DH-PIM 1 on non-dispersive channel - For f c /R b < 0.01, an additional 5 dB of power is required when R b is increased from 1 Mbps to 10 Mbps and from 10 Mbps to 100 Mbps. - for f c /R b > 0.01, the power requirement starts to increase more swiftly for 1 Mbps than 10 Mbps and 100 Mbps.

Artificial light interference – cont. - 8-DH-PIM 1 assuming multipath propagation -Normalised delay spread (NDS) = RMS delay spread (DT) / Bit rate (RB) - For f c /R b < 0.01, the power requirements are constant for all values of NDS with NDS of 0.1 displaying the highest value - For f c /R b > 0.01, the power requirements increase exponentially reaching the same value for f c /R b > 0.5

Artificial light interference – cont. -R b = 1Mbps and no multipath dispersion -DH-PIM 1 has marginally higher power penalty than DPIM and PPM but lower than OOK - For f c /R b = 0.1: DH-PIM displays far less power penalty than OOK but 1.6 dB and 1 dB additional power penalty compared with PPM and DPIM, respectively. This is because at low frequency region, the PSD of DH-PIM is higher than PPM and DPIM and lower than OOK

Slot/packet error rate Assumptions: The input signal is composed of binary independent, identically distributed bits of ‘1’s and ‘0’s The matched filter is sampled at the slot frequency f s The channel is a distortion free channel No bandwidth limitations imposed by the transmitter and receiver The dominant noise source is the background shot noise No interference due to artificial light Packet length G = 1KB bits Equal occurrence of H 1 and H 2

Slot error rate for DH-PIM is given by: for PIM: : average transmitted optical power, R: a photodetector responsivity. 0 < k < 1 is the threshold factor. where

Slot error rate Vs. SNR OOK The higher the M, the better the slot error rate performance. Simulated results match the predicted ones. SNR OOK [dB] Slot error rate M = 3 M = 4 M = 5 DH-PIM (alpha=1) *** Simulated __ Predicted 12,000 consecutive random bits were used in simulation. Slot error rate is shown down to due to computational power.

Slot error rate - cont. DH-PIM and DPIM offer improved slot error performance compared with OOK, but inferior to that of PPM. At slot error rate of PIM and DH-PIM (  = 1) display an improvement of ~5 dB over DH-PIM (  = 2) SNR OOK [dB] Slot error rate OOK DH-PIM (alpha=2) PIM PPM L=16 slot (M=4 bits) DH-PIM (alpha=1)

Packet error rate For DPIM: For DH-PIM: G is the packet length in bits. The packet error rate is given by

Packet error rate Vs. SNR OOK G = 1KB bits. DH-PIM and DPIM offer improved packet error performance compared with OOK, but inferior to that of PPM. At packet error rate of PIM and DH-PIM (  = 1) display an improvement of ~5 dB over DH-PIM (  = 2) SNR OOK [dB] Packet error rate OOK DH-PIM (alpha=2) PIM PPM L=16 slots (M=4bits) DH-PIM (alpha=1)

DH-PIM packet error rate - cont. G = 1KB bits The higher the M, the better the packet error rate performance. The smaller the , the better the packet error rate performance. DH-PIM

Retransmission Parameters: ret = 1, 3, 4 and 5 Majority decision scheme retransmission rate M = 2, 3, 4 and 5 Bit resolution α = 1 and 2 No of slots in the wide pulse of the header N_bits = 60,000 No of bits in the simulation K = 50% Threshold factor R b = 1 MB/S Bit rate η = e-023; One-sided PSD of the noise I_bg = 200 µAmp Background noise current R = 0.6 Receiver responsivity. SNR = -10:14 signal-to-noise ratio in dB. Simulation block diagram:

Retransmission - cont. At SER = DH-PIM with Ret = 3 gives an improvement of ~ 1 dBm over standard DH-PIM DH-PIM with Ret = 5 gives an improvement of ~ 2 dBm over standard DH-PIM

Retransmission - cont. At SER = DH-PIM with Ret = 3 gives an improvement of ~ 1 dBm over standard DH-PIM DH-PIM with Ret = 5 gives an improvement of ~ 2 dBm over standard DH-PIM

Optical Power Vs. bandwidth requirements The average optical power is calculated at packet error rate of for a packet length of 1KByte. To minimise the optical power and bandwidth, the parameter combinations are: DH-PIM (L=16,  =1) DH-PIM (L=64,  =2) DPIM L = 16

Multipath Propagation

x T s Cascaded system impulse response 32-DH-PIM 1, R b = 1 Mbps D T = D T = 0.01 D T = 0.1 D T = 0.2 _____ __ ___ _ Impulse Response

Diffuse Systems - Eye Diagram NDS = x NDS = x 10 -3

Optical Power Requirements

RMS delay spread / T b Normalised optical power requirements (dB) DH-PIM 1 2 DPIM PPM OOK L = 32 Optical Power Requirements - cont.

Optical Power Penalty

RMS delay spread / T b Optical power Penalty (dB) DH-PIM 1 2 DPIM PPM OOK L = 32 Optical Power Penalty - cont.

Conclusions Compared with PPM and DPIM, DH-PIM offers: –shorter symbol length –higher transmission rate –less bandwidth requirements –simple slot synchronisation –built-in symbol synchronisation DH-PIM offers improved error performance compared with OOK, but inferior to PPM and similar to DH-PIM

Conclusions - cont. The optimum system performance in terms of optical power and bandwidth requirements is achieved at DH-PIM (L=16,  =1), DH- PIM (L=64,  =2) and DPIM L = 16. A trade-off between the extent of artificial light interference rejection and the severity of baseline wander. Retransmission of DH-PIM symbols for 3 times or more gives significant improvement to the probability of errors at the expense of reducing the throughput

Final Remarks Acknowledgements: –Professor Fary Ghassemlooy (Associate Dean For Research) –Dr. R. McLaughlin (Sheffield Hallam University) Two MSc students are working on DH-PIM: –Wasiu Popoola: Equalisation –Olusegun Sanyaolu: Coding We’re seeking collaboration with staff or students from Informatics regarding mathematical analysis

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