AMShare: Distributed Frequency Synchronization of Small Cell Base Transceiver Stations Utilizing Commercial AM Wireless Signals

Abstract

Exponential growth of connected users in recent years and the increasing demands for ubiquitous coverage of wireless services has pushed the mobile operators to invest in innovative technologies that can support more connected users with higher quality of service. The idea of overlay network in cellular networks by adding small cells, has been proposed in recent years to improve network capacity and address the varying demands of mobile users in different areas. In deploying small cells as an overlay network, lots of technical challenges should be addressed. Stringent timing and synchronization requirements of the small cells are one of the challenges in implementing small cell radios. Currently, macro base transceiver stations use GNSS (Global Navigation Satellite Systems) receivers to comply with timing and synchronization requirements of the air interface standard (2G, 3G or LTE). However, the GNSS based synchronization solutions are not economically feasible in small cell implementations. Additionally, GNSS may not work well or at all in some indoor environments or in dense urban areas with high rise buildings where the canyon effect limits the sky view of the reviver. In this research, a new low cost frequency synchronization solution based on the commercial AM wireless signals is proposed. Each BTS in a small cell utilizes the carrier component embedded in a commercial AM wireless signal as the reference clock. Different small cell transceivers can then correct the relative CFO (Carrier Frequency Offset) between them using a common over the air reference clock. As part of the MW (Medium Wave) band, AM wireless signals can penetrate buildings and due to their ground-wave propagation have a relatively stable path that does not affect the transmitted signal. So they can be a good candidate for a synchronization solution. The proposed distributed frequency synchronization method is implemented using off the shelf components and its performance is evaluated in short term and long term measurement periods.