Milad Mazi Esfahani
AMShare: Distributed Frequency Synchronization of Small Cell Base Transceiver Stations Utilizing Commercial AM Wireless Signals
The exponential growth of connected devices 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 the 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 receiver. In this seminar, a new low-cost frequency synchronization solution based on the commercial AM wireless signals is proposed. Each BTS (Base Transceiver Station) in a small cell tracks the carrier component embedded in the commercial AM wireless signal as the reference clock. Different small cell transceivers can then be locked to this reference and correct the relative CFO (Carrier Frequency Offset) between them using a common over the air clock signal. As part of the Medium Wave (MW) band, AM wireless signals can penetrate buildings and due to their ground-wave propagation have a relatively stable path that does not affect the quality of the carrier component in the transmitted signal. So, the carrier component of the AM wireless signals can be a good candidate as the reference clock in synchronization solutions. The proposed distributed frequency synchronization method is implemented using commercial off the shelf components (Analog Device evaluation boards AD7760, AD7626, AD9681 and Rhode & Schwarz signal acquisition solutions RTE 1034 and RTO 1044) and its performance is evaluated in both short term and long term measurement periods. Finally, implementation results are discussed, and some directions for future research are provided.