Consider an energy-harvesting receiver that uses the same received signal both for decoding information and for harvesting energy, which is employed to power its circuitry. In the scenario where the receiver has limited battery size, a signal with bursty energy content may cause power outage at the receiver, since the battery will drain during intervals with low signal energy. In this paper, we analyze subblock energy-constrained codes (SECCs), which ensure that sufficient energy is carried within every subblock duration. We consider discrete memoryless channels and characterize the SECC capacity and the SECC error exponent, and provide useful bounds for these values. We also study constant subblock-composition codes (CSCCs), which are a subclass of SECCs where all the subblocks in every codeword have the same fixed composition, and this subblock composition is chosen to maximize the rate of information transfer while meeting the energy requirement. Compared with constant composition codes (CCCs), we show that CSCCs incur a rate loss and that the error exponent for CSCCs is also related to the error exponent for CCCs by the same rate loss term. We exploit the symmetry in CSCCs to obtain a necessary and sufficient condition on the subblock length for avoiding power outage at the receiver. Furthermore, for CSCC sequences, we present a tight lower bound on the average energy per symbol within a sliding time window. We provide numerical examples highlighting the tradeoff between the delivery of sufficient energy to the receiver and achieving high information transfer rates. It is observed that the ability to use energy in real-time imposes less of penalty compared with the ability to use information in real-time.

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Abstract-We consider the problem of binary code design for simultaneous energy and information transfer where the receiver completely relies on the received signal for fulfilling its real-time power requirements. The receiver, in this scenario, would need a certain amount of energy (derived from the received signal) within a sliding time window for its continuous operation. In order to meet this energy requirement at the receiver, the transmitter should use only those codewords which carry sufficient energy. In this paper, we assume that the transmitter uses on-off keying where bit one corresponds to transmission of a high energy signal. The transmitter uses only those codewords which have at least d ones in a sliding window of W = d + 1 bits. We show that with this constraint, the noiseless code capacity is achieved by sequences generated from a finite state Markov machine. We also investigate achievable rates when such constrained codes are used on noisy communication channels. Although a few of these results are well known for run-length limited codes used for data storage, they do not seem to appear in literature in the form presented here.

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