With the mobile telecommunications space facing an onslaught of data-hungry subscribers and their migration to LTE, operators have embarked on a quest to pack even more service in smaller and smaller service areas. The frontier of these smaller service areas have come to be characterized as small cells. The issue is getting communications into and out of these small service areas. Capacity, coverage and interference all need to be addressed. Some have proposed serving small cells via Centralized Radio Access Networks (C-RAN). To implement a C-RAN, one of the requirements is a newer concept that has come to be termed “fronthaul.”
In a June 2013 meeting of the Telecom Council, Aviat Networks’ chief technology officer, Paul Kennard, took on fronthaul and the challenges it presents for LTE, small cell and C-RAN. In his presentation, he weighed the advantages and obstacles of fronthaul. While the chief advantage of distributing Remote Radio Heads (RRH) around the cell can help alleviate coverage, capacity and interference concerns, it is not easy to reach these RRH locations with fiber in the mostly urban areas where this deployment scenario will be needed most. This is especially true of non-traditional implementation of small cells on light standards, signposts and other non-tower infrastructure collectively known as “street furniture.” Wireless backhaul solutions will continue to be necessary in the grand scheme of things.
More is available on fronthaul in the Telecom Council presentation below as is in an associated webinar.
In the United States, the fixed service for wireless communications usually operates in bands licensed either on a link-by-link basis or by block allocation. So why is the 5.8GHz ISM band so important and why should the industry be concerned about current FCC proposals to change the rules of operation in this band.
Many operators use this band because they can install and operate a link in a very short period—much quicker than the usual route of prior coordination and license application that is required in other bands. There are numerous reasons why this approach is attractive, even if it is difficult to guarantee Quality of Service (QoS) in ISM. A common use of this approach sees the operator set up a link in the 5.8GHz band to get the link up and running while in parallel it goes through the coordination process for the same link in the L6GHz band. Then when that license is granted, the operator will move the link to the L6GHz band. This has the advantage that the same antenna may be reused and sometimes the same radio with just a filter change. Another use of the 5.8GHz band for fixed service links is in support of disaster relief efforts where because there is no need for prior coordination that means vital communications links can be up and running very quickly.
Under the current FCC Part 15 rules, equipment can be certified using section 15.247 whereby the above scenarios are attractive to operators as they mimic the conditions that can be found in the L6GHz band. However, the FCC has issued a notice of proposed rulemaking, NPRM, which will change this by requiring a reduction in conducted output power of 1dB for every dB of antenna gain over 23dBi for Part 15.247 point-to-point links. At present, the conducted power at the antenna port in this frequency range is limited to 1 watt, but there is no penalty applied to the conducted power in relation to higher gain antennas on point-to-point links. Should this proposal by finalized then this would reduce the effective range of point-to-point links in this band and would so change the dynamics that the ability to deploy a link in the 5.8GHz band and then “upgrade” to the L6GHz band at a later date would no longer be a feasible option. We would encourage all readers, especially those using the 5.8GHz band to file a comment with the FCC regarding Proceeding 13-49 that this particular change would be detrimental to many fixed link operators, as well as those who rely on this band for fast deployment during disaster recovery.
For more information on this proceeding, email Aole Wilkins at the Office of Engineering and Technology.
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