Network Timing for the 3G and 4G/LTE Small Moblie Backhaul: the Future is Here

By    February 12, 2014

Mobile subscribers continue to consume more data with smartphones and other mobile devices. In response to that, service providers are trying to deliver the best customer experience with their available spectrum.  Small cells serve a unique purpose in this quest – they allow service providers to inject more capacity and coverage into highly congestion areas. Outdoor small cells are the solutions for 3G and 4G/LTE networks that look to inject capacity where people eat, drink and congregate. In order to maintain high service levels (mobile handoffs, billing, spectrum/frequency re-use, etc.) and smooth hand-off to the macro base-stations, small cells must follow strict timing parameters as defined by the 3GPP. 

With most small cells being deployed at the street level, installed on light posts, street lamps and the sides of building, often the best solution to backhaul small cells is sub-6GHz wireless broadband.  Backhaul needs to be small, unobtrusive and deliver high data capacity in near and non-line of sight situations. One critical feature that can’t be overlooked is the ability to deliver precise timing to small cells. The traditional use of GPS receivers is not always practical in small-cell deployments because line of sight is required, which can be challenging in urban canyons.  

As operators transition to 4G / LTE, timing requirements become more stringent with requirements for not only frequency, by phase as well. Synchronous Ethernet (SyncE) or Precision Time Protocol (PTP) IEEE1588-2008, also known as 1588v2, are two of the three go to standard alongside GPS to meet the operators timing requirements.  SyncE delivers frequency synchronization, and IEEE 1588-2008 delivers network based frequency and phase synchronization designed to meet LTE-A and LTE-TDD timing requirements.      

LTE advanced mobile networks allow a budget of 550ns contributed time error end-to-end with each hop adding no more than 50ns.  IEEE 1588-2008 accomplishes this over a wireless link by   time stamping each packet that arrives and then calculating the time spent in transit.  

The PTP 650S is a small cell backhaul solution, which can be integrated seamlessly into the overall 3G/4G/LTE network architecture.  The PTP 650S acts as an IEEE 1588-2008 transparent clock correcting for the residence time of packets on the wireless link. The resulting backhaul operates with precise timing and frequency references, guaranteeing maximum stable throughput and ensuring network reliability. Testing results show a constant time error (cTE) in many cases less than 10ns vs. the LTE-Advanced target of 50ns which makes the PTP 650S ready for the future today.

At Cambium Networks we continue to develop technologies that are ready to deploy today and firmly aligned to service provider requirements for performance and reliability. With features such as 1588 and Synchronous Ethernet, the PTP 650S is ready for the future as 3G 4G/LTE small cell architectures continue to evolve.