Application-layer Coding Research Articles

Making the Most of Sporadic Feedback: Low-Complexity Application Layer Coding for Data Recovery in the Internet of Things

We propose application-layer coding schemes to recover lost data in delay-sensitive uplink (sensor-to-gateway) communications in the Internet of Things. Built on an approach that combines retransmissions and forward erasure correction, the proposed schemes' salient features include low computational complexity and the ability to exploit sporadic receiver feedback for efficient data recovery. Reduced complexity is achieved by keeping the number of coded transmissions as low as possible and by devising a mechanism to compute the optimal degree of a coded packet in O(1). Our major contributions are: (a) An enhancement to an existing scheme called windowed coding, whose complexity is greatly reduced and data recovery performance is improved by our proposed approach. (b) A technique that combines elements of windowed coding with a new feedback structure to further reduce the coding complexity and improve data recovery. (c) A coded forwarding scheme in which a relay node provides further resilience against packet loss by overhearing source-to-destination communications and making forwarding decisions based on overheard information.

Performance Analysis of Fountain Coded Non-Orthogonal Multiple Access With Finite Blocklength

Driven by the increasing demand for high reliability and low latency, finite blocklength communications have recently become the focus of the communication research field. In this letter, to achieve high reliability and low latency communication, we propose the cross-layer design of fountain coded two-user non-orthogonal multiple access (NOMA) system with finite blocklength. Specifically, the message for each user is firstly encoded by an application-layer fountain code at the base station (BS). Then, each fountain-coded packet for each user is encoded by a physical-layer channel code into a frame. Finally, the BS sends the frames to these two users by using superposition modulation. Under the reliability constraints of two users, the relationship among the application-layer code rate, the physical-layer data rate, and the optimal power allocation coefficient is derived to minimize the transmission latency. The numerical analysis and simulation results show that the message transmission latency of the proposed cross-layer scheme is much lower than that of the scheme which only adopts physical-layer channel codes in the finite blocklength NOMA system.

Application Layer Coding for IoT: Benefits, Limitations, and Implementation Aspects

One of the key technologies for future Internet of things (IoT)/machine-to-machine systems is low-power wide area networks, which are designed to support a massive number of low-end devices, often in the unlicensed shared spectrum using random access protocols. However, these usually operate without centralized control and since automatic repeat-request and acknowledgment mechanisms are not very effective due to the strict duty cycles limits and high interference in the shared bands, many packets are lost from collisions. In this paper, we analyze a recently proposed application layer coding scheme introduced in [1] , which aims to recover lost packets by introducing redundancy in the form of a fountain code. We show how latency and decoding complexity is affected by the packet loss rate but also prove that there is a limit to what can be achieved by introducing more redundancy. The analysis is backed up by simulation results.

On Effectiveness of Application-Layer Coding

The effectiveness of application-layer coding in a system with a large number of users is considered. The end users encode data packets before transmitting them. The effect of additional packets on the system performance is twofold: (i) additional packets increase offered load, which results in higher drop probability, and (ii) some of dropped packets can be recovered at the receivers after decoding. It is argued that the space of all systems can be partitioned into two regions where coding is beneficial and detrimental, respectively. In particular, the paper establishes an asymptotic regime that contains the boundary between these two regions. On the boundary, systems with and without coding have the same performance. Informally, our results indicate that application-layer coding improves the performance only in systems with low loss probabilities (without coding), and employing such coding in systems with high loss probabilities only degrades the performance.

Applications Directly Using Cryptography

Sometimes, we need to use cryptographic protection from application layer code. Although requirements for this don't arise that often, when they do, they tend to be met in homegrown, ad hoc ways, and frequently without considering how to best use cryptographic APIs or do key management. In this article, the author considers how to do somewhat better than that.