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FIBRE OPTIC CABLING
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By John Chamberlain , Director , Office of the CTO
www . commscope . com
Time and costs savings can be significant when using hybrid cabling solutions to meet growing mobile data demands
To meet the rising demand for wireless bandwidth while lowering costs , operators deploy remote radio units ( RRUs ) at the top of the tower . However , there is still a debate about the best way to connect those RRUs to the DC power supply and baseband unit .
The typical approach has been to use a separate ‘ home run ’ of fibre and power cables for each RRU . This design is familiar to installers and uses standardised components , but adding at least two cables to each RRU , on towers already heavily loaded with existing cables , can be complex and timeconsuming . Cabling a three-sector site with two RRUs per sector can take a full working day .
The hybrid fibre approach In the past few years , mobile operators have been increasing their use of an alternative connection method : hybrid cable , which combines power and fibre in a single ruggedised cable . Long used in outside plant telco applications , hybrid cable can be configured and deployed to support a variety of applications , including fibre-to-the-antenna ( FTTA ). There are two hybrid methods : hybrid direct and hybrid sector .
For high-density sites , operators use the hybrid direct model where multiple fibre and power cables are aggregated into a single large trunk cable that runs up the tower . The trunk cable terminates just below the RRUs with a pre-connected breakout canister . From here , individual jumpers connect the appropriate fibre / power pair in the trunk cable to the corresponding RRU . Each hybrid direct trunk cable can carry enough fibre and power connections to support up to nine RRUs . This minimises installation complexity and conserves tower space .
For lower density sites , the hybrid sector option is like traditional discrete cabling except that it requires only one cable per RRU instead of two . Individual hybrid cables – each containing power and fibre for one RRU – are deployed directly from the baseband unit to the RRUs . Compared to the traditional discrete FTTA solution , the hybrid sector cabling enables installers to cut the installation time nearly in half while offering a comparable price point .
Saving installation time Hybrid cable has been gaining traction lately as operators look for new ways to reduce deployment time and costs . In December 2015 , productivity researchers from Scott-Grant Ltd compared the time required to cable a typical three-sector cell site using the hybrid direct , hybrid sector , and traditional discrete cabling models . The site selected had three sectors and was 27m ( 88ft ) tall with one passive antenna and two RRUs per sector . From start to finish , the hybrid direct method was approximately 55 % faster than the traditional discrete model , while the hybrid sector method was about 48 % faster .
If we extrapolate these savings across hundreds or thousands of sites , the financial impact can be quite significant . In the UK , for example , using the hybrid direct model instead of the traditional discrete model to cable a 500 site expansion project could save 1,442 hours – equal
to 180 eight-hour days . Factoring in the local labour rates and availability of qualified installers , this can lower overall installation costs by about 25 %.
These results also indicate that for lower density installations of up to six RRUs , the hybrid sector solution provides a more cost- and time-efficient approach . For higher density sites involving more than six RRUs , the cost and time benefits of the hybrid direct approach increase as the number of RRUs increases .
Additional benefits If one considers the design of the HFF direct cable , applications for site and infrastructure sharing , commonly mandated in markets across Europe , become apparent . With the traditional point-to-point discrete cable , each fibre is dedicated to the RRU of a specific operator , eliminating the possibility of sharing . In the hybrid direct cable each fibre is still dedicated to a specific RRU , but the trunk configuration enables installation of up to nine RRUs . Therefore , on a threesector site , one cable can support three operators , each using one air interface .
Network managers can also use hybrid technology to build in excess capacity by loading more fibres in the trunk than initially needed . This allows them to bring new antennas and technologies on line as needed by simply running individual jumpers from the breakout connector to the RF device . The ability to pre-provision the network in anticipation of new antennas can significantly accelerate time to market .
When compared to the traditional discrete model , both the hybrid sector and the hybrid direct solutions offer savings on long-term operating expenses . By reducing the number of cables needed – along with the associated hangers , clips and other supporting structures – network managers can decrease the tower load , enabling lower lease costs or making it possible to add more equipment to the tower .
At the same time , both the hybrid direct and hybrid sector solutions minimise the number of discrete fibre cables exposed to environmental threats like wind , ice , animals and installer traffic . This can have a substantial impact on the network ’ s reliability . For example , a network of 1,000 towers – each with four antennas and 12 RRUs – requires 24,000 individual fibre cables . A 5 % failure rate in the connections would translate to 1,200 incidences of RRUs going offline during the year .
Shifting to Hybrid Models Over the past several years , the wireless industry has seen a significant shift in cell site architecture . The mass deployment of RRUs has created challenges regarding the best way to get fibre and power to the top of the tower . Currently , there are two popular technologies – traditional discrete cabling and the hybrid approach featuring hybrid sector and hybrid direct . For years , purchase decisions regarding most types of cable , FFTA included , have hinged on price . However , there are several important variables beyond price that significantly impact the total cost of installation .
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