3 research outputs found

    Optical wireless scattering channel estimation for photon-counting and photomultiplier tube receivers

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    Channel estimation is conceived for optical wireless scattering channels associated with laser diode transmitters and photon-counting/photomultiplier tube receivers. The proposed channel estimation approach consists of two stages, namely, of the estimation of the channel tap second-order moments followed by the estimation of the channel taps based on the estimate of second-order moments. In the first stage, we provide the general framework of the moment estimation complemented by the conception of an estimation approach based on a sparse pilot structure, as well as by the analysis of the estimation error. We also propose a novel sparse pilot design as well as the associated low-complexity channel estimation, and prove the optimality of the proposed channel estimation. In the second stage, we conceive the associated channel tap estimation based on the eigenvalue decomposition of the matrix of estimated second-order moments, and analyze the associated performance. It is shown that as the length of the pilot sequence tends to infinity, the probability of having an estimation distortion above a certain threshold can be reduced arbitrarily small. Simulation results show that the proposed sparse pilot sequence can lead to a smaller estimation error than the pilot design using random 0-1 bits

    Self-Synchronizing Pulse Position Modulation With Error Tolerance

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    Pulse position modulation (PPM) is a popular signal modulation technique which converts signals into M-ary data by means of the position of a pulse within a time interval. While PPM and its variations have great advantages in many contexts, this type of modulation is vulnerable to loss of synchronization, potentially causing a severe error floor or throughput penalty even when little or no noise is assumed. Another disadvantage is that this type of modulation typically offers no error correction mechanism on its own, making them sensitive to intersymbol interference and environmental noise. In this paper, we propose a coding theoretic variation of PPM that allows for significantly more efficient symbol and frame synchronization as well as strong error correction. The proposed scheme can be divided into a synchronization layer and a modulation layer. This makes our technique compatible with major existing techniques such as standard PPM, multipulse PPM, and expurgated PPM as well in that the scheme can be realized by adding a simple synchronization layer to one of these standard techniques. We also develop a generalization of expurgated PPM suited for the modulation layer of the proposed self-synchronizing modulation scheme. This generalized PPM can also be used as stand-alone error-correcting PPM with a larger number of available symbols
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