Our day to day activities are increasingly relying on Internet access and data services, even when we’re engaged with an activity like watching a sporting event in a stadium. These dynamic user expectations, coupled with modern infrastructure, make a compelling case for the use of a cloud radio access (C-RAN) network to meet this demand.
With a traditional LTE (News - Alert) approach to meeting mobile Internet demand, a base station combines a baseband unit and the radio, amplifier, filter and antenna into a single installation location. For a small cell, this could be an all-in-one unit. The mobile backhaul is required to transport IP and for some traffic streams there is some tolerance for controlled latency and jitter.
With C-RAN, however, there is s separation of functionality so performance and efficiency goals can be met. Details of this are explained in a recent Alcatel-Lucent white paper, Mobile Fronthaul for Cloud-RAN Deployment: Efficient Use of Optical Infrastructure for Remote Radio Architectures.
As the paper notes, the baseband unit is separate from the other functions. This separation and the associated centralization of processing in the baseband unit can enable improved coordination of radio capabilities, an important feature for LTE and LTE-Advanced where such techniques can bring increased efficiency through interference mitigation and installation simplicity. A standard pooled server approach also can be used in supporting baseband processing, thus supporting the trend toward network functions virtualization.
Yet, for C-RAN to take hold, as Alcatel-Lucent (News - Alert) Senior Marketing Manager John Davies points out in a recent podcast on mobile fronthaul, both mobile backhaul and fronthaul must keep pace.
There are several ways that the remote radio heads, which deliver the radio, amplification, filtering and antenna, can connect to the baseband unit via the common public radio interface (CPRI) standard. This includes dedicated fiber, an optical transmission network, a passive optical network, microwave, or a wavelength-based system (WDM).
According to the Alcatel-Lucent white paper, WDM delivers the best fronthaul for C-RAN architectures.
“WDM offers a good combination of characteristics for CPRI transport,” elaborated Davies in a recent TechZine blog post. “In particular, coarse wavelength-division multiplexing (CWDM) brings low delay and high throughout yet is economical, both in equipment costs and in its use of fiber resources.”
CWDM fits well with the unpredictable nature of remote placement that can often accompany small cells places in outdoor locations.
“With no active electronics, and relatively simple optics, a CWDM transport solution can be deployed in all outdoor environments providing significant CAPEX/OPEX (News - Alert) savings,” Davies noted. “There are no specialized enclosures, no requirement for battery backup and minimum power is consumed. CWDM technology provides a cost-effective transport option necessary to support the projected RRH small cell roll-outs.”
CWDM also supports the strict delay requirements needed for the CPRI protocol. Lacking active electronics along the optical path between the radio heads and the baseband unit means that the only source of transport-incurred latency is from signal propagation.
When it comes to delivering the LTE experience users desire, a C-RAN approach using CWDM is an effective combination.
Edited by Peter Bernstein