Mobile network operators are coping with coverage and capacity issues to meet the ever-increasing amount of mobile data and video traffic from smart phones and tablets. However, conserving capex and opex are top of mind for operators, even before they consider additional revenue opportunities from 4G customers. Currently, the industry is in the midst of upgrading all the traditional macro cells to a new generation of lower cost and more efficient macro base stations with software-defined radios that can serve legacy 2G/3G, as well as new 4G/LTE customers, and at the same time lower operational costs.
The Rise of Ethernet-Based Services
These new macro base stations are all Ethernet-fed, which allows the carriers to decommission all the legacy and costly T1/E1 connections and replace them with Ethernet. The industry, of course, has made this possible by making Ethernet carrier-grade capable of delivering services instead of just connectivity. And in particular, the MEF industry forum, has played an instrumental role in defining and raising the bar in what it meant to deliver Ethernet-based services.
One of these new Ethernet services is timing and synchronization. The previous generation of macro base stations used E1/T1 lines for frequency synchronization, and GPS for time-of-day if required. The new generation of base stations can receive timing over the network using a protocol called IEEE1588v2 (or 1588) Precision Timing Protocol (PTP).
Backhaul Challenges with Small Cells
As consumers buy more and more 4G/LTE-ready mobile devices, operators will need small cells for (4G) capacity – and lots of it. However, small cells introduce a slew of new backhaul challenges because – unlike macro cells – they are actually going to be deployed at street level on top of lamp posts, on top of traffic signals, and attached to the side of buildings. Because fiber connectivity is not viable everywhere, as in the above scenarios, a majority of these small cells will be connected by microwave or millimeter-wave from more central nodes like the macro cell sites where fiber ismore readily available.
Many IP Edge router and Carrier Ethernet switch vendors have already upgraded their equipment with what we call “1588 on-path support” in hardware, such as Vitesse’s VeriTime technology. This enables operators to deliver GPS-class packet timing to macro cell sites over fiber. For microwave and millimeter-wave backhaul, Vitesse believes that delivering GPS-grade 1588 timing over microwave links will be critical for small cell deployments.
The Importance of Timing for Small Cells
For several reasons, timing and synchronization is actually more important for small cells than for macro cells:
- First, small cells are deployed primarily in dense urban corridors at street level, and as such, visibility to GPS satellites is either not available or unreliable, and they are much more susceptible to jamming. Deploying GPS antennas for each small cell would be costly as well.
- Secondly, small cells and macro cells actually have a lot of overlapping coverage in order to deliver the capacity and quality of experience the 4G/LTE user expects. So interference mitigation and management are key. In order to do that, you need to have better control over the phase of the signals – even for FDD LTE, where you would not think phase or time-of-day synchronization was important. So while we were talking better than 1 microsecond alignment and time-of-day accuracy among macro sites, it becomes more like 100ns precision when you take small cell interference management into account.
Investing in New Technology for 4G/LTE
As carriers make the transition to 4G/LTE networks, the number of small cell deployments will only continue to increase to meet upgrade needs. And with the transition to small cells, point to point connectivity from a central site to each small cell is not a viable option. Instead, quality of service support is necessary to ensure that each small cell and traffic class gets their fair share of bandwidth while keep latencies low for the best quality of experience for the user. Therefore, it is critical that carriers and OEMs are investing in and deploying new technology, such as 1588, to not only meet timing requirements but also to ensure they are able to keep up with the both bandwidth and user demands.