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Accelerating DAS Deployments in Fiber Constrained Locations

Fiber-fed DAS systems are growing in popularity as the demand for ubiquitous high-speed mobile services grows in all indoor locations. Nevertheless, in many locations installing new fiber is challenging both from a technical and an economic perspective, and operators need solutions to re-use existing fiber and maximize the number of DAS radio nodes served using existing fiber. In this case study, we explore how a leading telecommunications infrastructure operator in France deployed advanced mobile services in road tunnels using DAS technology fed by a LambdaGainTM DWDM passive wavelength distribution platform from FONEX 

Project Overview 

The objective of the project was to deliver 3G/4G mobile coverage in several road tunnels. Our client, a neutral host infrastructure operator offering services to four mobile service providers, required a Distributed Antenna System (DAS) located along the length of each tunnel to offer continuous high-speed mobile coverage. Each tunnel had a less than a dozen radio nodes, but the distance from the radio nodes to the host base station location required a fiber length of up to 10 kilometers to connect the radio heads to the DAS headend. 


Confronted with the challenge of boosting mobile bandwidth and reliability in a rigorous environment, our client sought a robust fiber-based bandwidth distribution system to feed the selected DAS system, while the laying the groundwork for future technology evolution.  


To ensure a successful deployment, the infrastructure operator needed a fiber distribution system to overcome key challenges and restrictions imposed by the tunnel environment: 


  • Limited fiber resources:  Only one fiber strand per tunnel was available to connect radio nodes to the DAS headend. 
  • Demanding speed & range requirements:  The fiber distribution system would have to transport multiple 10G CPRI signals across several kilometers of fiber to serve DAS radio nodes located the length of the tunnels. 
  • Harsh environmental conditions & space constraints: Environmental conditions in the tunnels included extreme temperatures, humidity, and dust, all of which required ruggedized optical add/drop terminals to facilitate installation and minimize space utilization in equipment rooms. 
  • Limited electrical power: accessing power within tunnels can be challenging, and the ideal fiber feeder system should be fully passive to avoid the complexity of powering fiber transport equipment.  


After evaluating various technology options, the infrastructure operator opted to deploy the LambdaGain passive DWDM wavelength distribution platform because of its ease of deployment, ruggedness, reliability, and cost-effectiveness. Moreover, the LambdaGain platform offered the benefits of DWDM for increased deployment flexibility and future-proofness: the platform can support additional channels compared to CWDM technology, will support higher speeds suitable for 5G (i.e. 25Gbps and beyond), and can support extended range with the use of amplifiers.  

LambdaGain Solution Elements

The LambdaGain wavelength distribution platform used to feed the DAS is composed of passive Mux/Demux equipment which is energized by LambdaGain pluggable optics located in the DAS headend and remote radio units.  


The solution components include: 


  • High capacity LGX Single Fiber DWDM Mux/Demux to aggregate multiple 10G CPRI signals from the DAS headend. The headend Mux/Demux was deployed using standard chassis-mounted equipment, alongside the DAS headend. For this application, headend DWDM multiplexer capacities of 8 and 16 wavelengths were used, and wavelength capacities of up 48 lambdas are available for applications requiring more capacity per node.  

LambdaGainTM 16-Channel DAS Headend Mux/Demux unit 

  • Ruggedized low channel count single fiber DWDM Drop/Pass modules at DAS radio node locations within the tunnel. The Drop/Pass modules used industrial temperature range mux/demux modules (-40°C — 85°C), packaged in weather-resistant enclosures to facilitate installation without rack equipment, and protect the optical gear from dust, contamination, and accidental contact. For this application, remote DWDM Drop/Pass capacities of 2 wavelengths were used. Wavelength capacities can be adapted to each application depending on the required number of radio units at each remote location.  

LambdaGainTM DAS Remote Drop/Pass unit in weatherproof enclosure 

  • DWDM SFP+ pluggable optics installed in the DAS headend optical interface module and the within the DAS repeaters and RRHs (Remote Radio Heads). To ensure suitability for the DAS environment, industrial temperature (-40°C 85°C) DWDM SFP+ pluggable optics were selected. LambdaGain compatible optics are adapted and tested to guarantee optimal performance with the DAS system, which was supplied by a leading DAS technology vendor. 

LambdaGainTM is a leading supplier of compatible SFPs for RAN nodes including DAS platforms

Solution Benefits

  • Maximize capacity of limited available fiber: the operator was able to cost-effectively bring additional bandwidth to the radio nodes using a single fiber, leveraging the scalability of the LambdaGain DWDM passive wavelength distribution platform. 
  • Futureproof Design: The choice of a DWDM solution ensures that the infrastructure operator is ready to support technological advancements, providing a futureproof investment. LambdaGain Mux/demux systems are fully compatible with CPRI, eCPRI, 25G, and beyond, ensuring readiness for future evolution without the need for replacement.  
  • Versatile Deployment Options: the infrastructure operator could easily deploy the LambdaGain passive platform into the existing equipment locations in the tunnels, reducing costs and ensuring adaptability and flexibility, thanks to the platform’s rugged environmental characteristics, compact size, and optimized packaging options. 
  • Industrial Temperature options: leveraging LambdaGain’s optical expertise, the operator had access to advanced DWDM pluggable transceivers suitable for harsh environment like highway tunnels. 


Building on the tailored characteristics of the LambdaGain DWDM wavelength distribution solution, the infrastructure operator economically augmented DAS system capacity and reliability in challenging tunnel environments. Commuters speeding through the tunnels will have access to uninterrupted high-speed mobile connectivity for an improved customer experience on all four mobile service providers’ networks.  


This case study highlights how DAS system operators can leverage passive DWDM technology to enhance mobile communication capacity and reliability in challenging environments like a highway tunnel, despite obstacles including limited space and power, complex fiber connectivity and harsh environmental conditions. Commuters in France can now enjoy seamless 3G/4G coverage as they traverse highway tunnels, while operators can count on a clear roadmap to 5G. 


Contact Us 


If you are facing a challenging DAS project and would like support on how to incorporate passive optical wavelength distribution technology in your application, please  Contact us.

About FONEX data systems inc.


FONEX data systems inc. (FONEX), delivers optimised, purpose-built solutions for wire-line and wireless telecommunications service providers across Canada, the USA, and Europe. We combine over 30 years of expertise in telecommunication architectures, standards, and trends with a leading edge portfolio of carrier-class products to meet and exceed our customers’ business, technical and operational requirements. Find out more about FONEX here.

Fernando Donoso

Product Marketing Manager