With the prevalence of smartphones and newer Internet-enabled technologies such as Google (News - Alert) Glass on the horizon, Internet connectivity is expected and demanded no matter where the user is located. This is particularly the case at large sporting events such as the Sochi Olympics and the upcoming FIFA World Cup where mobile operator backhaul and fronthaul networks must be ready to provide high-performance and readily available access in densely populated areas where heavy simultaneous session traffic is expected and hence where not just connectivity but the user experience presents major challenges.
In such situations, especially given the transition to LTE (News - Alert)-Advanced, there’s a compelling case for the use of a cloud radio access network (cloud RAN) architecture for mobile fronthaul as explained in a recent video by Jon Davies Senior Marketing Manager, Alcatel-Lucent (News - Alert), which speaks to the highlights of his recent TechZine posting on the subject, Mobile Fronthaul Optimized For Cloud RAN.
For those not familiar, a C-RAN architecture includes remote radio heads (RRHs) connected to the baseband unit (BBU) using a common public radio interface (CPRI), as outlined in a recent fronthaul white paper by Alcatel-Lucent. The RRHs include the radio itself, associated amplification and filtering, plus the antenna. The BBU is implemented separately and carries out the centralized signal processing functions. This separation and the associated centralization of processing in the BBU, can enable improved coordination of radio capabilities across a set of RRHs.
CPRI is a digital interface standard for encapsulating radio samples between a radio and a digital baseband processing unit. CPRI is not packet-based; instead, signals are multiplexed in a low latency timeslot-like fashion. CPRI defines a maximum latency, a near zero jitter, and a near zero bit error rate. According to the Alcatel-Lucent paper, a value of .4 milliseconds for transport leaves an acceptable delay budget for processing requirements and propagation delay. The capacity required is up to 10 Gb/s, with distances of up to 40km between the remotes and the BBU.
Both mobile backhaul and fronthaul must keep pace if this architecture is to work which means having in place a service aggregation router to facilitate the migration to IP/MPLS. However, in the case of fronthaul there are several approaches that can be used.
The first option for mobile fronthaul is the use of dedicated fiber. This can be a good option for network operators with a large installed base of available fiber, although the cost of deploying new fiber limits dedicated fiber as an option in many cases.
Optical transmission network (OTN) is a second option. OTN brings forward error correction (FEC) and can increase the reach of metro optical networks, but it requires careful consideration to keep latency within acceptable bounds.
A third option is passive optical network (PON). PON is an attractive option for CPRI transport in high traffic areas such as stadium environments and urban neighborhoods where small cell deployments often exist.
Microwave is another option when the distances are 1 kilometer or less. But current transport technology can only support of a subset of the CPRI line bit rate options, according Davies.
Wavelength based systems (WDM) present perhaps the best option for C-RAN, according to the blog, delivering a good combination of characteristics for CPRI transport.
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 technology fits well with the unpredictable nature of remote placement, often outdoors e.g. in stadiums and on street ‘furniture,’” noted Davies in the TechZine article. “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.”
There are no specialized enclosures, no requirement for battery backup and minimum power is consumed, and CWDM technology provides a cost-effective transport option necessary to support the projected RRH small cell roll-outs.
As operators work to ensure that Internet connectivity reaches customers in every situation, C-RAN employing the CPRI standard and set up with CWDM mobile fronthaul is a compelling option for making that possible.
Edited by Peter Bernstein