Synchronous Design For Low Power Wide Area Networks

Currently, low power wide area (LPWA) networks are hot research areas of Machine-to-Machine (M2M) networks. The LPWA networks belong to Wireless Personal Area Network (WPAN), with the characteristics of low power consumption, low cost, low rate, wide coverage and so on. It will be widely used in lots of scenarios, such as oil and gas pipeline monitoring, water leak detection and transportation industries. The IEEE TG4working group has initialized a draft standard, IEEE802.15.4k, focusing on the specifications of physical layer (PHY) and media access control layer (MAC) for Low Energy, Critical Infrastructure Monitoring (LECIM) networks, which is a typical LPWA networks. The technique of direct sequence spread spectrum (DSSS) is adopted in IEEE802.15.4k PHY layer to provide low receiver sensitivity and wide coverage.Synchronization is crucial in wireless communication systems for data recovering and carrier synchronization is the primary and key technology in synchronization. Frequency offset estimation algorithm for burst communication systems includes differential synchronous method, e.g., Kay algorithm, correlation scheme, e.g., L&R algorithm, Fits algorithm and etc. Kay algorithm could not work at low signal-to-noise ratio (SNR), while the computations of Fits algorithm and L&R algorithm are too complex. Most of existing algorithms are not suitable for the synchronization of LECIM networks. Therefore, the design of new synchronization scheme has great research value.Firstly, we study the characteristics of LECIM networks and IEEE802.15.4k standard to attain the fundamental of synchronization design. Secondly, the existing frequency offset estimation algorithms are overviewed and the performance of various algorithms are compared and analyzed. To satisfy the low receiver sensitivity of LECIM networks, we propose a frequency offset estimation scheme using fast Fourier transform (FFT) with interpolation, which holds lower complexity and more excellent performance than other offset estimation algorithm in burst communication in low SNR. Finally, we build a simulation platform to evaluate the performance of proposed algorithm. Results have shown that the FFT with interpolation algorithm for frequency estimation has error deviation of0-2Hz with samples in0.01ms, under the conditions of large frequency offset deviation as12kHz and low SNR even as-25dB, which fullfil the design requirements of LECIM networks synchronization.