General aspects of coding for optical fibre digital transmission systems are considered in this paper. Simplified mathematical models are developed which reveal the relationship between binary, multilevel and duobinary codes in terms of optical penalty. Various properties of binary block codes are discussed, in particular, how the properties relate to code efficiency.

Invited paper Line coding for optical fibre systems

In conventional ${M}$ -ary differential chaos shift keying modulation (DCSK) systems, the distance between constellation points gets closer as ${M}$ increases, resulting in poor performance. A hybrid modulation scheme based on pulse position modulation (PPM) and DCSK is proposed in this letter to improve bit-error-rate (BER) performance. In this scheme, one part of the bits is modulated by PPM while the other part is modulated by DCSK. Thus, information bearing signals are simultaneously modulated by the information bit and the selected pulse position of PPM which is determined by extra information bits. Analytical BER performance of the proposed scheme is derived and verified by simulations. Results show that the considered scheme outperforms conventional M-DCSK, code index modulation DCSK, and commutation code index DCSK in additive white Gaussian noise and multipath Rayleigh fading channels.

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Hybrid Modulation Scheme Combining PPM With Differential Chaos Shift Keying Modulation

A novel modulation scheme for an indoor optical wireless communication (OWC) system referred to as generalized time slot index modulation (GTIM) is proposed for single-carrier frequency domain equalization (SC-FDE) systems. This scheme is further referred to as SC-GTIM. In SC-GTIM, information bits are flexibly encoded onto both the amplitudes and positions of pulses. A set partitioning algorithm is proposed to construct a codebook for the SC-GTIM system. In this paper, SC-GTIM will be compared with the conventional pulse amplitude modulation-based SC-FDE (SC-PAM) and time slot index modulation-based SC-FDE (SC-TIM). By considering a multipath optical wireless channel and the limited dynamic range of a light emitting diode (LED), a considerable bit error ratio (BER) gain can be achieved by SC-GTIM. It is concluded that SC-GTIM is a promising technique for low to medium spectral efficiency transmission and uplink schemes.

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Generalized Time Slot Index Modulation for Optical Wireless Communications

This paper studies the bit error rate (BER) performance of non-coherent impulse-radio ultra wideband (IR-UWB) correlation receivers in the IEEE 802.15.3a channel for combined binary pulse amplitude modulation-pulse position modulation (BPAM-PPM) scheme. The BER performance is based on the channel averaged signal-to-noise ratio (SNR). The study includes simple transmitted reference (TR), difierential TR (DTR), and energy detection (ED) receiver structures. Moreover, difierent performance parameters are addressed, namely the signal bandwidth integration window factor, number of pulses per bit, and receiver power consumption. ED receivers with BPAM-PPM are shown to outperform simple TR receivers and have a performance which approaches that of difierential TR (DTR) receivers with smaller power consumption for the same design parameters.

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Performance Comparison of Ed, TR and Dtr IR-UWB Receivers for Combined Pam-Ppm Modulation in Realistic UWB Channels

Transmitted reference pulse cluster (TRPC) is an impulse radio technology developed for ultrawideband (UWB) communications that achieves superior performance among non- coherent (NC) schemes with low complexity. It employs binary phase-shift keying (BPSK) in the pulse cluster to carry informa- tion. In this letter, a hybrid pulse position modulation (PPM) and BPSK is introduced into the TRPC to improve energy efficiency and/or increase data rate. Two types of bit-to-pulse cluster map- ping are proposed, one of which is termed Gray PPM-BPSK. It is shown by analysis and simulation that, compared with the original BPSK-TRPC, the new Gray PPM-BPSK-based TRPC not only increases the data rate by a factor of 2 but also achieves 1.5-3-dB coding gain in the BER performance. The performance improvement of the proposed hybrid schemes over BPSK-TRPC and NC PPM is demonstrated over both 3-10-GHz UWB and 60-GHz millimeter-wave channels, making it a promising signaling candidate for these frequency bands. Index Terms—Ultrawideband (UWB), 60 GHz, transmitted ref- erence pulse cluster (TRPC), binary phase-shift keying (BPSK), hybrid modulation.

Hybrid PPM-BPSK for Transmitted Reference Pulse Cluster Systems in UWB and 60-GHz Channels

A combined pulse amplitude modulation (PAM) and pulse position modulation (PPM) technique is proposed and investigated as a feasible solution of the problem of line encoding in optical fibre communication systems The basic idea is that of exploiting PAM and PPM jointly, to give rise to three different waveforms in one signalling period, without resorting to more than two signal levels Some evaluations of the behaviour of this signalling format are reported in terms of coding efficiency, spectral density, timing information, and error probability Alternative receiving schemes are also devised to improve system performance

A PAM-PPM signalling format in optical fibre digital communications

A combined pulse-amplitude/pulse-position modulation tachnique is proposed for digital optical communication systems. Evaluations of its behaviour in terms of coding efficiency, spectral density, timing information content, and error probability are summarised. Alternative receiving schemes are devised to improve system performance.

Luciano Bosotti

Papers

A PAM-PPM signalling format in optical fibre digital communications

A new signalling format for optical communications