Time-Synchronization of CCSK Short Frames

Efficient short Packet transmission is a key technique of the Internet of Things systems. When the data payload is small, the header used to help the receiver synchronization process becomes no longer negligible and should be shortened, and ideally removed. A Preamble-less frame generated using a non-binary error control code associated with a Cyclic Code Shift Keying (CCSK) modulation has been recently proposed. The paper presents a pragmatic approach to mitigate the time synchronization ambiguity at two levels: at symbol level thanks to an over-modulation of the CCSK symbols, and at chip level thanks to the Non-Binary code properties. Simulation results showed the efficiency of the proposed approach, where the blind frame synchronization is successfully performed at -10 dB.

I. Introduction

The transmission of short packets constitutes a key prerequisite for developing future Internet of Things (IoT)-based applications [1]. Usually, the frame is composed of a payload, some redundancy to correct transmission errors, and metadata known at the receiver side to help the synchronization task [2]. However, in short packet transmission, the payload is shortened and started to be comparable in size to the data used for detection and synchronization tasks. Therefore, this synchronization data cost is no longer negligible, and new efficient framing techniques are required. Moreover, Polyanskiy has demonstrated in [3], that asynchronous wireless transmission, even with short packets, does not affect the capacity of the channel. Hence, this means that classical approaches that utilize coordination between synchronization and collision avoidance are far from being optimum since the energy used for coordination is simply wasted.