Keying

About: Keying is a research topic. Over the lifetime, 6598 publications have been published within this topic receiving 82943 citations.

Multilevel amplitude shift keying in dispersion uncompensated optical systems

Abstract: The authors model and characterise the performance of 10 Gbit/s 4-ary amplitude shift keying (ASK) systems in dispersive environments at 1550 nm. Both non-return-to-zero (NRZ) and return-to-zero (RZ) formats are examined, with comparisons to on-off keying (OOK) in each case. Both single amplified links and cascaded fibre-amplifier links are modelled. While 4-ary ASK systems suffer a back-to-back sensitivity penalty of up to 7 dB with respect to OOK, they offer a significantly reduced dispersion sensitivity, particularly for RZ formats. This suggests advantages for M-ary coding in future systems employing optical time division multiplexing. Optimal level spacing for ASK is analysed and approximations for different noise regimes are shown to fit well to detailed calculations. Sensitivity to extinction ratio is examined; RZ systems are shown to have higher sensitivity than NRZ for both 4-ary and OOK. Finally, the authors show that frequency drift, or equivalently, a de-tuning in the centre frequency of the optical filter, is more severe for OOK than for 4-ary ASK, especially in the case of non-fully dispersion uncompensated systems.

Noncoherent Amplify-and-Forward Cooperative Networks: Robust Detection and Performance Analysis

Abstract: We develop closed-form generalized likelihood ratio test (GLRT) sequence detectors for multi-relay amplify-and-forward (AF) cooperative networks employing M-ary differential phase-shift keying (M-DPSK) and noncoherent M-ary frequency-shift keying (M-FSK). The proposed detectors achieve robust performance in a wide range of fading environments where prior knowledge of channels, signal powers, noise variances, and relay functionalities is unavailable to the destination. A comprehensive error probability performance analysis is carried out in Rayleigh fading. Specifically, we derive unified pairwise error probability (PEP) expressions for both detectors in a dual-hop network, which are valid for arbitrary modulation order M and arbitrary sequence length Ns. We also derive unified bit-error probability (BEP) expressions for both detectors employing binary signalings in various networks for Ns = 1. It is further shown that both detectors achieve near full diversity orders. Finally, the superiorities of the proposed detectors over the state-of-the-art noncoherent detectors are justified through extensive comparisons in practical scenarios. For example, in a multi-relay network where the relays are uniformly distributed between the source and destination, the proposed detector for noncoherent FSK with Ns = 1 outperforms the well-known maximum energy selector by almost 15 dB in high signal-to-noise ratios.

Digital pulse interval modulation for IR communication systems a review

Abstract: This paper presents a brief review of infrared communications systems, modulation techniques and in particular, a digital pulse modulation scheme known as digital pulse interval modulation (DPIM) for infrared (IR) communication systems employing intensity modulation with direct detection (IM/DD). DPIM code characteristics, power spectral density and error probability in terms of the packet error rate are discussed. Performance comparison is made with that of on–off keying (OOK) and pulse position modulation (PPM). For comparison, relevant expressions for both OOK and PPM are also presented. Using a threshold-detector-based receiver, we show that DPIM outperforms both OOK and PPM in terms of power efficiency and PPM in terms of bandwidth efficiency, by taking advantage of its inherent variable symbol duration. However, using a maximum-a posteriori (MAP) detector it provides marginally inferior error rate performance compared with PPM.

Modeling and optimization of a single-drive push–pull silicon Mach–Zehnder modulator

Abstract: We present an equivalent circuit model for a silicon carrier-depletion single-drive push–pull Mach–Zehnder modulator (MZM) with its traveling wave electrode made of coplanar strip lines. In particular, the partial-capacitance technique and conformal mapping are used to derive the capacitance associated with each layer. The PN junction is accurately modeled with the fringe capacitances taken into consideration. The circuit model is validated by comparing the calculations with the simulation results. Using this model, we analyze the effect of several key parameters on the modulator performance to optimize the design. Experimental results of MZMs confirm the theoretical analysis. A 56 Gb/s on–off keying modulation and a 40 Gb/s binary phase-shift keying modulation are achieved using the optimized modulator.

Performance of Optical Spatial Modulation with Transmitters-Receivers Alignment

Abstract: This letter proposes significant enhancement in optical spatial modulation (OSM) performance by aligning the transmit and receive units. OSM is a recently proposed pulsed modulation technique for indoor optical wireless (OW) communication . In OSM, multiple transmitters are considered where only one transmitter is active at a time and the others are turned off. The incoming bit sequence activates one of the transmit units, i.e. the transmit units are considered as a spatial constellation points and each unique sequence of incoming bits is mapped to one of the constellation points. It is shown that the proposed transmit-receive unit alignments for OSM enhances the performance by more than 14 dB in signal to noise ratio (SNR). In addition, the resultant scheme is shown to be very efficient in terms of power and bandwidth as compared to on-off keying (OOK), pulse position modulation (PPM), and pulse amplitude modulation (PAM).