nk-pulse position modulation for optical wireless communication

Abstract

An original analysis is presented for n k -PPM in which the information is conveyed by the position of k pulses, each within their own frame of n slots, giving n k PPM symbols. Comparisons are made with multiple PPM (MPPM) and it is demonstrated that n k -PPM offers improved orthogonality, a simplified circuit implementation and comparable receiver sensitivity.Introduction: Conventional n-ary pulse position modulation (PPM) has been proposed for optical fibre [1], optical wireless [2] and optical satellite [3] channels, owing to its enhanced sensitivity performance. In this format, L bits (where L is termed the coding level) of pulse code modulation (PCM) are encoded into PPM by positioning a single pulse in one of 2 L time slots. Since a single pulse is conveying L bits of information there is an immediate reduction in average power when compared to PCM. However, this comes at the cost of increased bandwidth consumption. For example, with a coding level of L ¼ 10, 1024-ary PPM conveys 10 bits of information by a single pulse but the slot duration is 10=1024 narrower than the PCM bit period leading to a prohibitive bandwidth expansion of 1024=10 ¼ 102.4. Multiple PPM [4][5][6][7][8] has been proposed as a technique for offering improved receiver sensitivity over PCM under bandwidth-constrained environments such as the optical wireless channel. In multiple PPM, k-pulses are positioned within a time frame containing S slots leading to S

Spectral characterisation of variable weight MPPM modulation technique

“…Introduction: In wireless optical communication systems, specially those based on diffuse link configurations, rate-adaptive transmission schemes are preferred in order to make communication suitable in adverse channel conditions, depending on the available SNR until a sufficiently low error probability can be attained [1]. Although conventional pulse-position modulation (PPM) has been widely reported in the literature, recently a multiple PPM (MPPM) technique has been proposed in wireless optical systems in order to reduce the average optical power transmitted [2], such as the n k -PPM technique [3], the spectral evaluation of which was described in [4]. In previous work by the present authors a novel rate-adaptive transmission scheme using block coding of variable Hamming weight was presented.…”

Spectral characterisation of nk pulse position modulation format

“…Unfortunately, S k is rarely a power of two, which leads to complex encoding and decoding circuitry. In [6], a new format, termed as n k -PPM, was proposed for the optical wireless channel.…”

Spectral characterisation of shortened pulse position modulation format

“…expansion and so alternative, more bandwidth efficient schemes have been proposed such as multiple PPM [5] and n k -PPM [6].…”