Subblock-Constrained Codes for Real-Time Simultaneous Energy and Information Transfer

TL;DR

This paper investigates subblock-constrained coding strategies for energy-harvesting receivers, balancing energy delivery and information transfer, and introduces methods to optimize capacity while ensuring sufficient energy within each subblock.

Contribution

It characterizes the capacity of subblock-constrained codes, compares constant subblock-composition codes with variable compositions, and analyzes the tradeoffs between energy delivery and information rate.

Findings

CSCCs incur a rate loss compared to CCCs.

Allowing variable subblock compositions improves capacity.

Real-time energy use has less penalty than real-time information use.

Abstract

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 consider a discrete memoryless channel and characterize achievable information rates when the energy content in each codeword is regularized by ensuring that sufficient energy is carried within every subblock duration. In particular, we study constant subblock-composition codes (CSCCs) where all 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 to 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 show that CSCC capacity can be improved by allowing different subblocks to have different composition while still meeting the subblock energy constraint. We provide numerical examples highlighting the tradeoff between 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 than the ability to use information in real-time.