Multiplex communications – Channel assignment techniques – Adaptive selection of channel assignment technique
Reexamination Certificate
1998-12-30
2002-04-30
Luu, Le Hien (Department: 2152)
Multiplex communications
Channel assignment techniques
Adaptive selection of channel assignment technique
C370S431000
Reexamination Certificate
active
06381248
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to information network architecture. In particular, the present invention is directed to a method and apparatus to provide two-way broadband communications over any network, especially where the bandwidth of the existing network is limited.
BACKGROUND OF THE INVENTION
With the growth of the Internet and increasing public reliance upon digital information technology, the demand for broadband communications services such as real-time audio and video has increased. Although there have been significant advances in server and router capacity, information theory and coding and compression techniques, the bandwidth capacity of the physical network remains the primary bottleneck for broadband communications.
The existing cable network provides a potential source for delivering bi-directional broadband services. In order to provide two-way broadband services, the cable industry faces the challenge of cost-effectively transforming a traditional uni-directional cable system, which was designed for broadcast services with tree-and-branch architecture, into a two-way broadband digital platform. Cable networks, either pure coaxial networks or modem hybrid fiber/coaxial (HFC) networks, utilize broadband coaxial cable to connect customers to either the remote fiber nodes or the cable headend. Along the coaxial cable, multiple coaxial amplifiers are deployed to overcome the cable loss. Although the passive elements of the cable network, the fiber, coaxial cable itself, taps and couplers, can provide up to 1 GHz of bandwidth, the amplifiers spanning the coaxial cable have inherent bandwidth limitations (typically, 350 MHz, 550 MHz or 750 MHz), which limit the overall bandwidth capacity of the network.
A conventional solution to these bandwidth limitations involves two upgrade components. First, in order to accommodate broadband signals, the existing coaxial amplifiers are replaced with higher bandwidth bi-directional coaxial amplifiers. Second, due to the fact that losses along the coaxial cable are directly proportional to the frequencies at which signals are transmitted along the cable, the spacing between amplifiers is reduced, which requires the deployment of additional amplifiers. The cable industry has followed this conventional upgrade strategy by upgrading the currently deployed 350 MHz or 550 MHz coaxial amplifiers to 750 MHz amplifiers, and enabling bi-directional capability using low-frequency (5-40 MHz) upstream technology.
However, there are major shortcomings to this conventional approach. First, upstream channel performance is limited. Because the cable network was designed to deliver analog television signals, which occupy the frequency range from 50 MHz through the bandwidth of the coaxial amplifiers themselves, upstream communications are limited to the frequency band of 5-40 MHz. Although this upstream bandwidth may be adequate for existing applications such as web browsing, bandwidth intensive applications such as videoconferencing and other multimedia applications are not possible using the conventional upgrade technology. In addition, ingress noise in that frequency range severely limits channel performance and reducing ingress noise necessitates performing complicated signal processing and spectrum management, translating into higher terminal costs.
Second, the conventional cable upgrade approach is expensive and complex, requiring the deployment of additional amplifiers and network re-engineering. As higher frequencies are used, additional amplifiers are necessary to overcome the increased loss associated with these signals. Noise and reliability concerns, on the other hand, demand the use of fewer amplifiers in cascade. Resolution of this conflict requires network re-branching and re-engineering leading not only to more amplifiers; in the field but also a more complicated coax plant. These difficulties translate into higher costs and operational complexities raising serious questions about the adequacy, quality and reliability of the resulting transport capability.
Third, even with higher bandwidth amplifiers (750 MHz) there still exists a large portion of unexploited bandwidth 750 MHz-1 GHz. Thus, the conventional upgrade approach does not efficiently utilize the available bandwidth in the network.
Mini-Fiber Node (mFN) technology, provides a solution to the limitations imposed by the conventional approach by introducing a low-cost converter node or mFN adjacent to each coax amplifier. The mFNs directly couple into passive coax cable and connect to the headend with separate optical fiber. The mFN then utilizes abundant noise-free bandwidth at higher frequencies, available over the passive coax cable and optical fiber for bi-directional communications.
However, depending on the topology and demography of the embedded cable networks, deploying fiber to each distribution coaxial amplifier may be expensive, especially if an amplifier serves only a few users.
Delivering broadband services using the existing cable infrastructure and mFN technology requires a two-fold solution. First, fiber deployment must be controlled in order to reduce costs. Second, the upgrade solution must be transparent such that the path between the mFN and users is passive at the high frequency band, therefore eliminating the complexities of RF amplifications in that path and the associated cost of modifying existing systems.
SUMMARY OF THE INVENTION
The present invention comprises a method and apparatus for delivering bi-directional broadband communications over an existing network. The present invention is applicable in any existing network where multiple primary remote nodes (PRNs) are allocated along a communication path, which partition the communication path into multiple segments. Typically, the overall system bandwidth is limited by the bandwidth of these PRNs, but the communication path itself has a much larger bandwidth.
For example, one embodiment of the present invention provides for the upgrade of a traditional uni-directional HFC network into a bi-directional broadband communications network. According to this embodiment, a converter apparatus is deployed adjacent to certain PRNs and each converter is directly connected with the central office over additional bi-directional paths. Using this topology, each converter provides access to the communication path downstream of its associated PRN. Multiple secondary nodes (SRNs) are then deployed at the remainder of the PRNs downstream from the converter. The SRNs are capable of bypassing bi-directional traffic between the downstream and upstream segments of the communication path segmented by the PRNs, at a frequency band outside or inside the bandwidth of the PRNs. In one embodiment, some of the SRNs directly connect to the converter over a separate path in order to overcome the loss over the communication path.
Through the introduction of the SRNs, the present invention provides a cost effective mechanism for the deployment of separate broadband fiber transmission paths for transmitting bi-directional broadband signals between the converters and the central office and reducing the amount of fiber deployment.
REFERENCES:
patent: 5073930 (1991-12-01), Green et al.
patent: 5864672 (1999-01-01), Bodeep et al.
patent: 5959658 (1999-09-01), Gnauck et al.
patent: 6195362 (2001-02-01), Darcie et al.
AT&T Corp.
Luu Le Hien
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