With increasing customer or subscriber demand for transmitting and receiving increasingly greater amounts of information, telecommunication and broadband cable communication companies are being pushed to upgrade their wide area network (WAN) or broadband access communication network infrastructures. In order to supply more information in the form of video, audio and telephony at higher rates, higher bandwidth communication network upgrades or new deployments are required. Twisted wire pair cable, such as used in plain old telephone services, do not support high bandwidths over a great distance; and while coaxial cables, such as used in cable television services, do a better job, it too has reach and bandwidth limitations. Optical fiber can provide virtually unlimited bandwidth thus enabling broadband and multimedia services.
Modern telephone wide area network access infrastructures, such as fiber in the loop networks (FITL), utilize a combination of fiber optics and twisted wire pair to send and receive data communications to and from a subscriber. While modern cable wide area network access infrastructures, such as Hybrid Fiber Coaxial networks (HFC), utilize a combination of fiber optic and coaxial cable to send and receive data communications to and from a subscriber. Generally, subscribers are served by twisted wire pair in the last mile or so of the telecommunication networks or by coaxial cable within the last two to three miles or so of cable networks. In order to achieve greater bandwidth rates at a subscriber location, the fiber optic network must be brought closer to the subscriber so that the copper drop (e.g., twisted wire pair or coaxial cable) is of a sufficiently short distance and will be capable of supporting increased data transfer rates.
One major problem with bringing fiber cable within a short distance of a subscriber location is the added burden of maintaining the multitude of optical to copper drop sites. These drop sites are network elements that are called optical network units (ONUs) or optical network terminals (ONTs) in telecommunication networks and optical node (or simply a node) in hybrid fiber cable networks and generally serve to convert information between the optical domain of a fiber and electrical domain of a twisted pair or coaxial cable.
A significant part of the provisioning and maintenance of these drop sites by Service Providers or their affiliates (e.g., broadband access service provider, application service providers, internet service providers, managed service providers, master managed service providers, managed internet service providers, telecommunication service providers, campus service providers, cable service providers) is supplying the electrical power required. Optical fiber itself is not capable of carrying the electricity to power these drop sites. This creates a challenge in planning, distributing and deployment of electricity to power the drop site energy needs. Furthermore, reserve power must also be provided if the main power supply to the drop site fails and with enough reserve powering capacity capable of meeting performance and reliability requirements of the network for several hours or even days. This is often the case with Lifeline telephony service, which is required in plain old telephone service networks. Lifeline telephone means that the subscriber telephones must remain energized and operational during an AC supply power interruption or outage at the subscriber premise.
The drop sites are typically centrally powered from a Service Provider or affiliates' distributed copper facility or a power node located near a cluster of drop sites, or locally powered from a nearby commercial or utility electrical power source, or with solar photovoltaic energy.
In the case of centralized power, power is typically provided over new or existing copper facilities from a central office (CO). Power can also be provided on separate twisted wire pair or coaxial cable that are bonded to the outside of a fiber cable bundle, woven within a fiber optical cable bundle or deployed separately with the fiber during installation of the fiber from the central office. However, centralized power is a strategy that requires a separate power network to be deployed that is separate from the information network. With increasing distances between a central office or head end to the remote drop sites increased voltages are required on the power network to feed the drop site energy needs. Increased voltages raise craft safety issues. Alternatively, the power network may be augmented with power nodes located near a cluster of drop sites, however additional metallic enclosures increase susceptibility to electrical surges caused by lightning and power-line induction. Furthermore, there is the 24-hour a day cost of supplying electricity to the power network, as well as regular maintenance and support of the power network itself including regular replacement of batteries for Lifeline services, which are generally located at the CO or head end.
In the case of locally powered drop sites, power is derived near a drop site and reserve power is provided with batteries at the drop site. The primary energy source for this architecture is commercial AC power tapped directly from a power utility's facility. The power supply is placed in a small environmentally hardened enclosure that could be co-located with a drop site; however, the batteries are generally in the same enclosure as the drop site. This results in a large number of battery sites and power access points. Generally the cost of this type of system is high primarily due to the cost of connecting drop sites to a commercial power source. Regional power utility companies may insist on metered connections to their power grid, incurring a one-time ac meter installation and connection charge to be levied. Additionally a minimum monthly meter charge may be levied regardless of usage. This poses a major problem when the monthly energy consumption of a drop site is significantly lower than the minimum charge.
In the case of electrically powering the communication network infrastructure locally with solar power, this strategy minimizes some of the disadvantages of centralized and locally powering such as vulnerability to lightning and limited battery reserve, allowing fiber to be the sole distribution facility. Solar panels and large batteries are co-located at drop sites, which power the drop sites continuously without any connection to any power grid. However, its use is limited to areas with direct access to sunlight as the output of solar panels decreases with a reduction in incident solar energy. Therefore, this strategy cannot be used everywhere. In addition, solar power requires batteries of large capacity (Wh) to be installed.
As such, a need exists for powering a fiber optic communication network element that brings optical access fiber within a short distance of a subscriber premise or customer location. The electrical powering strategy or architecture of the fiber optic wide area network must be capable of supporting and operating the multitude of drop sites or network elements in a cost effective and maintainable manner.