MOCZ for Blind Short-Packet Communication: Some Practical Aspects

TL;DR

This paper explores practical enhancements for the MOCZ scheme, enabling reliable ultra-low latency short-packet transmission in unknown wireless channels by addressing impairments like CFO, timing offsets, and channel effects.

Contribution

It introduces an oversampled zero testing decoder, cyclically permutable codes, and diversity techniques to improve MOCZ performance under real-world impairments.

Findings

CFO causes a common rotation of zeros, which can be identified and compensated.

Embedding CPCs into cyclic codes significantly reduces bit-error-rate.

Receive antenna diversity improves impairment estimation and communication reliability.

Abstract

We will investigate practical aspects for a recently introduced blind (noncoherent) communication scheme, called modulation on conjugate-reciprocal zeros (MOCZ), which enables reliable transmission of sporadic and short-packets at ultra-low latency in unknown wireless multipath channels, which are static over the receive duration of one packet. Here the information is modulated on the zeros of the transmitted discrete-time baseband signal's $z-$transform. Due to ubiquitous impairments between transmitter and receiver clocks a carrier frequency offset (CFO) will occur after a down-conversion to the baseband, which results in a common rotation of the zeros. To identify fractional rotations of the base angle in the zero-pattern, we propose an oversampled direct zero testing decoder to identify the most likely one. Integer rotations correspond to cyclic shifts of the binary message, which we compensate by a cyclically permutable code (CPC). Additionally, the embedding of CPCs into cyclic codes, allows to exploit additive error correction which reduces the bit-error-rate tremendously. Furthermore, we use the trident structure in the signals autocorrelation to estimate timing offsets and the channels effective delay spread. We finally demonstrate how these impairment estimations can be largely improved by receive antenna diversity, which enables extreme bursty reliable communication at low latency and SNR.