Long Term Evolution is expected to step up wireless networks’ ability to handle increased demand for capacity and make networks more efficient. But once releases reach LTE-Advanced, the possibilities for smarter traffic increase, and LTE topology promises to change how carriers design their networks by adding new network elements and capabilities.
X2 TRAFFIC: CHANGING NETWORK TOPOLOGY
One of the biggest changes in LTE topology is the introduction of x2 traffic, where intelligent base stations can transmit information directly to one another, rather than communicating solely with the core network (see diagram from Ceragon below).
According to a report by the Next Generation Mobile Network Alliance,(1) the backhaul traffic for eNodeB contains user data for one or more cells, plus traffic forwarded over the x2 interface during handovers, plus overheads for transport protocols and security. x2 traffic is supposed to make handover and rapid coordination of radio resources faster and more efficient by placing the intelligence at the base stations, rather than the core, according to Cambridge Networks (2).
Ceragon diagram showing LTE x2 traffic between base stations.
This LTE topology difference can be compared to the difference between a hub-and-spoke topology and a mesh topology. It also allows for network intelligence to be applied closer to the cell site, rather than all traffic needing to be transported to the network core and then back to the site — which cuts down on latency.
However, legacy network equipment which communicates directly with the core will probably be in place for a significant time period, according to Ananth Nagarajan, senior director of product management at Juniper Networks.
“The newer base stations have all the intelligence, but you can’t expect the old base stations to just go away immediately,” he said. So the changeover to widespread LTE topology will take time.
HetNets: The New LTE Topology
Vendors are seeing high levels of interest in the area of small cells: pico, femto, and micro cells, which are small-scale wireless sites that can cover areas as small as a home or apartment unit, the floor of a building, or an entire building.
Those changes in the network landscape, generally called Heterogeneous Networks or HetNets, are expected to include large-scale deployments of small cells.
However, backhauling small cells remains an unsolved challenge. Other aspects of small cells that still need to be address include how to ensure proper hand-offs from macro cell sites, as well as interference among small cells and macro sites. All of those challenges must be dealt with while keeping small cells cost-efficient for carriers to deploy and operate.
ABI Research recently projected that the microwave small cell backhaul equipment market alone will reach $6.4 billion by 2017. That figure represents an annual growth rate of 35% from a forecast $1.5 billion this year. According to a report by Infonetics, however, the small cell space will not be big enough for all the vendors who wish to play in it.
According to ABI, small cell backhaul over fiber will grow from 7% of the market to almost 24%, with fiber favored by China and North America. NLOS and line-of-site microwave technologies are projected to capture most of the market, with Wi-Fi backhauling about 12% of small cell backhaul by 2017.
Wireless local area networks (WLANs) are likely to look different in terms of Wi-Fi, as well. The Broadband Alliance is trialing New Generation Network (NGN) advancements for Wi-Fi, also known as Hot Spot 2.0; the technology is expected to make up part of the new LTE topology landscape and enable Wi-Fi to feel more like cellular, with automatic authentication and roaming.
Additional sources:
1. NGMN Alliance white paper, Guidelines for LTE Backhaul Traffic Estimation. http://www.ngmn.org/uploads/media/NGMN_Whitepaper_Guideline_for_LTE_Backhaul_Traffic_Estimation.pdf
2. Cambridge Broadband Networks white paper, Backhauling X2. http://cbnl.com/sites/all/files/userfiles/files/Backhauling-X2_0.pdf
