According to Cisco Global Visual Networking Index (VNI) June 2014, mobile data traffic will grow at a compound annual growth rate (CAGR) of 61 percent between 2013 and 2018 reaching 15.9 exabytes per month by 2018. As a result of this data tsunami, delivering additional capacity and coverage through deployment of small cells, ad-hoc femtocells and other spectrum improvement techniques is of paramount importance to mobile network operators.
Cisco VNI 2014: Mobile Data Traffic by 2018
Heterogeneous Network (HetNet) is a network densification architecture where small cells are deployed under a macro cell umbrella to augment indoor coverage in buildings, multi-tenant dwelling units, enterprises; and outdoor coverage in dense urban canyons. Sometimes deploying small cells in clusters outdoors maybe a more cost effective solution than adding a macro cell. Other applications for small cells to enhance capacity include traffic hotspots such as retail, stadiums and event venues.
Heterogeneous Radio Access Network
To enable reliable and robust delivery of network services, precise and performance assured synchronization is not only essential, but fundamental to the network densification strategy. LTE heterogeneous networks call for tighter timing requirements. While LTE FDD networks require only frequency synchronization, LTE TDD systems have an additional phase requirement of 1.5 µs. For more advanced LTE-A systems, the requirement is even more stringent.
|LTE||Frequency Transport |
/ Air Interface
|FDD||16 ppb / 50 ppb||None|
|TDD||16 ppb / 50 ppb||± 1.5 µs|
|MBSFN / eICIC etc.||16 ppb / 50 ppb||± 1.32 µs|
|LTE-A (COMP)||16 ppb / 50 ppb||± 0.5 µs|
In traditional 3G networks, synchronization was delivered using TDM line timing or GNSS. 4G LTE networks however are IP based and with the deployment of HetNets, operators need to revamp their synchronization delivery architecture.
For macro cell, deploying only GNSS at every cell leads to expensive holdover mechanisms. Moreover due to external vulnerabilities of GNSS and the need for more resilient sync architecture it is essential to have alternate back-up sources of sync such as packet based IEEE 1588 PTP and SyncE in addition to GNSS.
For small cells, having multi-sync architecture enables ease of installation, high availability and reduced operational costs. Acquiring time and phase via GNSS at the macro aggregation point or at the cell edge by placing a mini Grandmaster and then distributing sync via IEEE 1588 PTP to all the small cells to hold time and phase is an efficient sync architecture that achieves the twin objectives of cost and resiliency.
Macro and Small Cell Synchronization
In scenarios where small cells are deployed to enhance indoor coverage, for example dense urban venues such as stadiums, convention centers, shopping malls, enterprises and multi-tenant buildings where generally Ethernet cabling exists to provide traffic backhaul; packet based IEEE 1588 PTP synchronization techniques are better choices. Deploying an inexpensive embedded local Grandmaster at the premises is a very cost effective way of distributing sync via existing in-building LAN networks.
Small Cell Synchronization for Office Campus and Multi-tenant Dwelling Units
For ad-hoc femtocells deployed in homes and SOHOs to augment indoor coverage, delivering synchronization via home based backhaul (ISP connection) is the most viable approach. GNSS for femtocells is expensive and not feasible given the RF losses and challenges of GNSS reception and installation indoors.
Femtocell for Residential and SOHO Coverage
For macro cells, Qulsar's embedded Managed Timing Board (P62) can be deployed as an IEEE 1588 PTP slave and integrated into the macro cell timing card. It takes in IEEE 1588 PTP and/or ToD from GNSS as input and delivers 1PPS, Frequency 5/10/20/25 MHz and ToD as output. It offers a choice of different oscillators to provide holdover capability when the source of sync is lost.
For small cells, Qulsar's embedded Managed Timing Module (M62) or Managed Timing Board (P62) can be deployed as IEEE 1588 PTP slave/client and integrated into the small cell electronics. The module is an extremely cost and power efficient solution based on a low cost oscillator. For holdover it is recommended to use the Managed Timing Board (P62).
For femtocell, Qulsar's embedded Managed Timing Module (M62) can be deployed as IEEE 1588 PTP slave/client and integrated into the femtocell electronics. The module is an extremely cost and power efficient solution.
For use as a HetNet synchronization source, the Managed Timing Board (P64) can be deployed as an IEEE 1588 PTP embedded Grandmaster (Edgemaster) at the macro cell aggregation point or at the edge of the Mobile Backhaul. It has the ability to act as the PRTC source with GNSS enabled.