Anshoo Tandon

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

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.

On code design for simultaneous energy and information transfer

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.

Subblock energy-constrained codes for simultaneous energy and information transfer

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. The energy content in the signal may be regularized by partitioning each codeword into smaller subblocks and requiring that sufficient energy is carried in every subblock duration. In this paper, we study subblock energy-constrained codes (SECCs) which, by definition, are codes satisfying the subblock energy constraint. For SECCs, we provide a sufficient condition on the subblock length to avoid power outage at the receiver. We consider discrete memoryless channels and characterize the SECC capacity, and also provide different bounds on the SECC capacity. Further, we characterize and bound the random coding error exponent for SECCs.

Has Green Energy Arrived? Delay Analysis for Energy Harvesting Communication Systems

Energy harvesting communication systems provide a “green” solution by obtaining energy from ambient sources, such as sunlight or vibrations. This energy is stored for transmission of data packets which arrive at the link layer of an energy harvesting transmitter. Since the data and energy arrival processes are independent and random, the data packets wait in a queue for the accumulation of sufficient amount of energy and for service completion of previously arrived packets. Thus, the energy arrival process and the data service process jointly impact the data queue dynamics. This makes the queueing analysis of an energy harvesting communication system challenging. In this paper, we formulate a two stage virtual queueing system which decouples the wait stages for the energy arrival process and the service process. This virtual queueing system leads to closed-form expressions for the average packet delay and the probability of data packet loss due to buffer overflow. We assume that the data and energy arrivals are independent Poisson processes and the service time for data packets may have any general distribution. The expressions for the average packet delay and the probability of buffer overflow are shown to be exact when the service time becomes negligible, and the packet delay gets dominated by data packets waiting for arrival of sufficient energy. These expressions are compared with Monte Carlo simulations and are shown to be robust even when the service time is increased up to sixty percent of the average packet delay.

On the impact of channel coding on average packet delay in a multiuser environment

Delay sensitive applications such as gaming and video streaming require relatively low average packet delay, an important higher layer metric which directly affects the user experience. In this paper, we consider a polling based multiple access scheme and study the impact of channel coding on the average packet delay where the link layer employs Automatic Repeat Request (ARQ) to provide error free packet transmission. The communication model assumes that users share a common physical channel and communicate with a central server which polls them for transmission in a cyclic order. Using an average waiting time analysis, we prove that, compared to an uncoded system, it is sufficient for a coding scheme to reduce the average service time in order to achieve lower average packet delay. We use the bounds on the minimum distance of linear codes to choose that code for which the reduction in the number of retransmissions (due to a decrease in probability of packet error) outweighs the increase in packet time (due to an increase in packet length by channel coding) such that the average service time is minimized. We also show that the percentage reduction in average service time by employing channel coding (compared to an uncoded system) results in corresponding reduction in average transmit energy required for successful transfer of a data packet. Numerical examples are provided to highlight the tradeoffs involved in the choice of an appropriate channel coding scheme.

Real-time simultaneous energy and information transfer

Consider an energy-harvesting receiver that uses the same received signal both for decoding information and for harvesting energy to power its circuitry. When the receiver has limited battery size, a signal with bursty energy content may cause power outage since the battery will drain during intervals with low signal energy. The energy content in the signal may be regularized by requiring that sufficient energy is carried in every subblock duration. In this paper, we study constant subblock-composition codes (CSCCs) where all subblocks in every codeword have the same composition, and this composition is chosen such that the real-time energy requirement at the receiver is met. For a given energy storage capacity at the receiver, we give a necessary and sufficient condition on the subblock length for avoiding outage. We show that CSCC capacity on a discrete memoryless channel can be efficiently computed by exploiting certain symmetry conditions, and compare it with the capacity of constant composition codes. We provide numerical examples highlighting the tradeoff between delivery of sufficient energy to the receiver and achieving high information transfer rates.

Binary subblock energy-constrained codes: Bounds on code size and asymptotic rate

The subblock energy-constrained codes (SECCs) have recently been shown to be suitable candidates for simultaneous energy and information transfer, where bounds on SECC capacity were presented for communication over noisy channels. In this paper, we study binary SECCs with given error correction capability, by considering codes with a certain minimum distance. Binary SECCs are a class of constrained codes where each codeword is partitioned into equal sized subblocks, and every subblock has weight exceeding a given threshold. We present several upper and lower bounds on the optimal SECC code size, and also derive the asymptotic Gilbert-Varshamov (GV) and sphere-packing bounds for SECCs. A related class of codes are the heavy weight codes (HWCs) where the weight of each codeword exceeds a given threshold. We show that for a fixed subblock length, the asymptotic rate for SECCs is strictly lower than the corresponding rate for HWCs when the relative distance of the code is small. The rate gap between HWCs and SECCs denotes the penalty due to imposition of weight constraint per subblock, relative to the codeword based weight constraint.

A Cross-Layer Approach to Reducing Packet Delay in Polling-Based Multiuser Systems

We consider a system where users are polled for transmission by a central server, and the link layer of each user employs automatic repeat request (ARQ) to ensure error-free delivery of packets. We present a cross-layer approach for reducing average packet delay (queuing delay plus service time). It is known that forward error correction (FEC) schemes can potentially lower the average packet delay by reducing the packet error probability (PEP) and, hence, the number of retransmissions. However, more precise results in the literature are few and far between. In this paper, we first establish that relative to an uncoded system, it is sufficient to reduce the average service time (AST) using FEC to achieve lower average packet delay. We then study and quantify the reduction in AST that can be achieved using the best possible FEC codes. The specific findings and contributions from our work are as follows: 1) We provide several bounds on the reduction in AST using the best possible FEC codes; 2) we give a sufficient condition when no FEC scheme can reduce the AST; 3) for Gaussian channels, we find that a relatively high PEP

Constant subblock composition codes for simultaneous energy and information transfer

(\sim\!\!\text{10}^{-2})

Detecting Forwarding Misbehavior In Clustered IoT Networks

, which is obtained using as high a coding rate as possible, typically results in sufficiently small AST; 4) the performance of optimum maximum-likelihood decoding can be approached by a lower complexity bounded distance decoder; and 5) average packet delay can be further reduced in certain cases by opportunistically combining and encoding several packets jointly.