Rapidly ramping mobile traffic is forcing a sea change in mobile infrastructure and standards. Users and enterprises are shifting their focus on more efficiently using mobile devices and infrastructure to drive value. As a result there is an impending ‘data tsunami’. For mobile and network operators, keeping pace with such ramping demand is essential to staying relevant. One of the key ways of adding capacity (through upgrading the network to LTE-advanced or beyond) is more efficient methods of coordination. This in turn ramps up the requirements for precise timing. Another way is through deployment of outdoor and indoor small cells, ad-hoc femtocells.
Heterogeneous Network (the 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 1.1 µs. For more advanced LTE-A systems, the requirement is even more stringent.
|LTE||Frequency Transport / Air Interface||Phase|
|FDD||16 ppb / 50 ppb||None|
|TDD||16 ppb / 50 ppb||± 1.1 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 cells, deploying GNSS at every cell has been the traditional method for delivering precise synchronization. While this leads to expensive holdover mechanisms, the cost envelope is proportional to a macro-cell deployment economics. However, when these cells are shrunk and become small cells, and they are moved indoors or deployed in urban canyons, the same method is no longer economically or operationally viable. Moreover due to external vulnerabilities of GNSS and the need for more resilient sync architecture it is essential to have alternate sources of sync such as packet based IEEE 1588 PTP and SyncE in addition to GNSS.
For small cells, having a 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 three objectives: enables rapid and ubiquitous deployment, lowers operational cost and improves 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 Ethernet is usually used to provide traffic backhaul. In such deployments, packet based IEEE 1588 PTP synchronization is a better choice. Deploying an inexpensive embedded local Grandmaster at the premises is a cost effective way of distributing sync via existing in-building LAN networks. Qulsar is pioneering network-edge deployed “Synchronization software as a service” (P/SaaS), to make such deployments even more cost effective and scalable.
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 unpredictable RF reception indoors and challenges of GNSS installation indoors. Qulsar is pioneering a wireless in-building synchronization technology that will make such deployments even less expensive and very convenient.
Femtocell for Residential and SOHO Coverage
For macro cells, Qulsar's embedded Managed Timing Engine (M64 and M68) or the more robust Managed Timing Clock (M88 Series) can be deployed as an IEEE 1588 PTP slave and integrated into the macro cell timing card.
For femtocell, Qulsar's embedded Managed Timing Module 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.
A new option for small cells or femtocells is the licensable reference design of QNgine S.
For residential and some enterprise femtocells using wireless backhaul, Qulsar’s wireless sync (Quki) may be more appropriate.
For use as a HetNet synchronization source, the Managed Timing Engine Board 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.
Most cost effective and robust would be to deploy Qulsar’s P/SaaS platform, the Qg 2 at the network edge.