Contender waveforms for Low-Power Wide-Area networks in a scheduled 4G OFDM framework

Yoann Roth,Laurent Ros,Jean-Baptiste Doré,Vincent Berg

doi:10.1186/s13634-018-0566-4

Abstract

When designing new solutions for Low-Power Wide-Area (LPWA) networks, coexistence and integration into existing 4G frameworks should be considered to ease the deployment procedure and reduce costs. In a previous work, Turbo-FSK was proposed as a potential physical layer for LPWA networks. With its constant envelope and high energy efficiency, the scheme is a serious contender for this type of networks. We propose to study the system in the Orthogonal Frequency Division Multiplexing (OFDM) framework, currently used by existing cellular networks and also considered for the recently standardized Narrow-Band IoT (NB-IoT). Several extensions of the Turbo-FSK scheme are presented. A hybrid modulation alphabet, combining orthogonal with linear modulations, is introduced, and the substitution of Frequency Shift Keying (FSK) modulation for another orthogonal modulation based on Zadoff-Chu (ZC) sequences is considered. Simulations are run under various conditions including Rayleigh fading channel with mobility, demonstrating that the Turbo-FSK scheme is able to achieve performance close to the Turbo Coded Orthogonal Frequency Division Multiplexing (TC-OFDM) when a low rate is considered. When considering hybridation of the alphabet, limitations appear for higher data rate, which can be overcome by changing the orthogonal alphabet. The study of the variation of the envelope of the compared solutions emphasizes the crucial trade-off between performance and efficiency of the power amplifier (PA), a main concern for low-power applications. While using the proposed solutions, we demonstrate that energy consumption can be reduced by up to a factor of 2.5.

Highlights

The Internet of Things (IoT) is expected to interconnect objects using both existing communication technologies and new emerging technologies [1, 2]
We proposed the integration of Turbo-Frequency Shift Keying (FSK) in the Orthogonal Frequency Division Multiplexing (OFDM) framework and extended the original scheme to the Coplanar Turbo-FSK, which employs a hybrid modulation alphabet, and to the Coplanar Turbo-ZC, which uses another orthogonal alphabet based on ZC sequences
We demonstrated the possibility for the proposed techniques to use a transmitter and a receiver based on an OFDM-like architecture

Summary

Introduction

The Internet of Things (IoT) is expected to interconnect objects using both existing communication technologies and new emerging technologies [1, 2]. A solution relying on a turbo receiver, the Turbo-FSK, was introduced in previous literature [6] It allows for very low levels of sensitivity to be achieved thanks to the use of a combination of orthogonal modulation, a convolutional code, and an iterative receiver. These steps depend on the choice of the technique and are presented later The output of this block is represented by a matrix of size NA × Ns, where NA is the number of active frequencies and Ns the number of time slots (or OFDM symbols). 2.1.4 Receiver In order to retrieve the information that was mapped in the frequency domain at the transmitter side, a DFT of size NFFT is applied on each OFDM symbol, using the FFT algorithm. The information bits are estimated by the decoder and the CRC is computed to evaluate if the packet contains any error

TC-OFDM and TC-SC-FDMA

Results and discussion

Conclusions