RF and fiber worlds collide at cell sites

Staff writer
29 Sep 2014

Rajesh Rao, regional VP of sales for JDSU, Asia Pacific and Japan, discusses how distributed case station architectures are creating new challenges for cell technicians – and how to overcome them

Telecomasia.net: Remote radio heads have changed the way we think about cell site architectures, but they also introduce new challenges for cellcos. What are the key ones?

Rajesh Rao: Conventional cell sites locate radio equipment at the base of the tower, transmitting RF signals via coax to antennas at the top. However, these coax-based feeders produce the majority of problems in cell sites due to inherent loss, susceptibility to interference, and cable and connector deterioration that creates signal reflections and intermodulation. Modern cell sites have a distributed architecture with two radio elements: the base band unit (BBU) installed at the base of the tower, and the remote radio head (RRH) installed at the top. These two elements communicate using the CPRI protocol via fiber links. This distributed architecture significantly reduces the problems of signal loss and reflections in conventional cell sites.

Since all RF interfaces reside on the RRH, any RF maintenance requires reaching the tower top to gain access to the RRH. This increases opex and safety concerns.

What additional challenges arise from DAS (Distributed Antenna Systems) and small cell deployments?

Networks now consist of a variety of RANs: Hetnets, DAS, small cells, Wi-Fi and macro. As far as DAS and small cells are concerned, the main challenge is placement. Over 50% of cell sites aren't placed optimally and thus negatively affect mobile service. Then there's the cost and time of turn-up, which can't be the same as macro sites. DAS can also be very complex with its distributed antenna architectures. The issue of interference and alignment with macro towers must be properly managed.

Recently, the Small Cell Forum − in partnership with ETSI and hosted by Orange − organized the second Small Cell LTE Plugfest in June 2014. The Plugfest allows operators, network element providers and test vendors to get together, test architectures, and share intelligence in an open environment. Issues with small cells were addressed along with multi-vendor interoperability and LTE elements such as VoLTE.

Do real-time IP-based services like VoLTE create additional headaches for operators?

VoLTE delivers HD voice with fast connection times over LTE. Many operators see the network advantages of using LTE to carry voice with the associated operational savings as well as the benefits of better quality voice for the user. Yet VoLTE creates headaches for operators. It needs guaranteed service end to end, so that means the RF, RAN, edge, IMS and core all need to work. Testing voice quality before the service is deployed is crucial and you have the added complexity of IMS signaling to manage.

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