SUMMARYThis paper assesses the performance of dual header pulse interval modulation (DH-PIM) over indoor optical wireless systems. DH-PIM being anisochronous scheme offers a built-in symbol synchronization capability. Theoretical and simulation results demonstrate that DH-PIM offers shorter symbol length, improved transmission rate and bandwidth requirement and a comparable power spectral density profile compared with digital pulse interval modulation (DPIM) and pulse position modulation (PPM) schemes.It is shown that DH-PIM 2 ; with wider pulse duration is the preferred option when the available channel bandwidth is limited and higher optical power is tolerable. Whereas DH-PIM 1 ; with narrower pulse width, exhibits comparable power requirements but a marginally higher bandwidth compared with DPIM, and is also more bandwidth efficient than PPM at the cost of increased power requirement. However, at higher bit resolutions, i.e. M57; DH-PIM 1 is both bandwidth and power efficient compared with PPM. Error rate analysis show that DH-PIM offers improved packet error rate compared with on-off-keying (OOK) and DPIM, but marginally inferior as compared with PPM. The power requirement and penalty due to intersymbol interference for non-dispersive and dispersive channels is analysed and the results show that for given parameters, DH-PIM requires marginally higher optical power compared with PPM and DPIM, but it supports the same bit rate at much less bandwidth requirement.

Fluorescent lamps introduce a periodic interference signal in optical wireless receivers, which has the potential to severely degrade link performance. Usually, electrical high-pass filtering is employed to mitigate the effects of this interference, but this results in baseline wander or intersymbol interference. Digital pulse interval modulation (DPIM) is a modulation technique which has been shown to be suitable for deployment in optical wireless communication systems and this paper examines the effect of baseline wander on systems employing DPIM. A new expression is given for the slot autocorrelation function of DPIM and, from this, the power spectral density is calculated. The error performance of DPIM, as a function of high-pass filter (HPF) cut-on frequency, is compared with the more established techniques of on-off keying using non-return to zero signalling (OOK) and pulse position modulation (PPM), using both numerical analysis and computer simulation.

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