23,602 research outputs found

    Superadditivity of Quantum Channel Coding Rate with Finite Blocklength Joint Measurements

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    The maximum rate at which classical information can be reliably transmitted per use of a quantum channel strictly increases in general with NN, the number of channel outputs that are detected jointly by the quantum joint-detection receiver (JDR). This phenomenon is known as superadditivity of the maximum achievable information rate over a quantum channel. We study this phenomenon for a pure-state classical-quantum (cq) channel and provide a lower bound on CN/NC_N/N, the maximum information rate when the JDR is restricted to making joint measurements over no more than NN quantum channel outputs, while allowing arbitrary classical error correction. We also show the appearance of a superadditivity phenomenon---of mathematical resemblance to the aforesaid problem---in the channel capacity of a classical discrete memoryless channel (DMC) when a concatenated coding scheme is employed, and the inner decoder is forced to make hard decisions on NN-length inner codewords. Using this correspondence, we develop a unifying framework for the above two notions of superadditivity, and show that for our lower bound to CN/NC_N/N to be equal to a given fraction of the asymptotic capacity CC of the respective channel, NN must be proportional to V/C2V/C^2, where VV is the respective channel dispersion quantity.Comment: To appear in IEEE Transactions on Information Theor

    An efficient CDMA decoder for correlated information sources

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    We consider the detection of correlated information sources in the ubiquitous Code-Division Multiple-Access (CDMA) scheme. We propose a message-passing based scheme for detecting correlated sources directly, with no need for source coding. The detection is done simultaneously over a block of transmitted binary symbols (word). Simulation results are provided demonstrating a substantial improvement in bit-error-rate in comparison with the unmodified detector and the alternative of source compression. The robustness of the error-performance improvement is shown under practical model settings, including wrong estimation of the generating Markov transition matrix and finite-length spreading codes.Comment: 11 page
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