Optical communications – Multiplex – Code division multiplexing
Reexamination Certificate
2000-03-29
2004-06-08
Pascal, Leslie (Department: 2633)
Optical communications
Multiplex
Code division multiplexing
C348S078000, C348S079000, C475S146000
Reexamination Certificate
active
06748171
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to telecommunication networks, and more particularly, to a system and method for providing high speed data transmission services for multiple classes of services over an optical network.
Optical networks are high-capacity telecommunications networks based on optical technologies and components that provide routing, grooming, and restoration at the wavelength level. They provide higher capacity and reduced costs for new applications such as the Internet, video and multimedia interaction, and advanced digital services. Wavelength division multiplexing (WDM) technology is widely used in optical networks to provide additional capacity on existing fibers. Using the WDM technology, the components of the optical network are defined according to how the wavelengths are transmitted, groomed, or implemented in the network.
WDM technology combines many signals, or “virtual” fibers, onto a single physical fiber by transmitting each signal at a different frequency. Furthermore, with the improvement of optical filters and other laser technology, the number of effective channels on a single physical fiber for carrying the signals is continually increasing. Currently, dense wavelength division multiplexing (DWDM) technology allows a single fiber to provide 40 or 80 channels for carrying signals. Consequently, by implementing DWDM systems and optical amplifiers, networks can now provide a variety of channels with different bit rates, e.g., OC-48 or OC-192, over a single fiber.
One major problem in designing a DWDM system is creating a channel spacing plan. Although the International Telecommunication Union (ITU) has published a standard set of frequencies based on different channel spacing, the 50 GHz and 100 GHz plans are still the most commonly used. Furthermore, as these systems are rapidly deployed, it is most likely that both OC-48 and OC-192 channels will be carried. However, at a low channel spacing plan such as 50 GHz, OC-192 channels can not be adjacent because an interference will ensue (referred to as “neighboring channel interference”). Moreover, this interference problem may not be prevented by simply using filtering mechanisms. Due to this neighboring channel interference, the available number of OC-192 channels for a channel spacing plan of 50 GHz is effectively cut in half.
With the implementation of the optical networks, opportunities exist for providing high speed data communication services for multimedia applications required by today's computer network users. Video, audio, and data information are considered to be the most popular classes of information that need to be supported. Therefore, the optical networks need to integrate a range of services on a single platform, to have system scalability to suit different groups of users, and to provide end-to-end error free communication services for mission critical applications.
It is thus desired to provide a mechanism for supporting multiple classes of communication services on the optical networks while reducing neighboring channel interference and channel dispersion.
SUMMARY OF THE INVENTION
An improved system and method is hereby disclosed for providing high-speed and high capacity data communication services over Wave Division Multiplexing (WDM) optical networks for multiple classes of services.
In one embodiment of a WDM network system, the system can employ a first incoming user data stream to select an n-bit orthogonal code from a predetermined code book, and similarly use a second incoming user data stream to select another n-bit orthogonal code from a different orthogonal code book for a neighboring channel. The selected orthogonal codes are then used to modulate the two incoming light channels for the incoming user data streams. With the modulation, the ON/OFF patterns of the light channels become an exact representation of the selected orthogonal codes. Hence, with an appropriate code plan to arrange the code books, the orthogonally encoded first and second incoming user data streams are interference proof to each other because they are orthogonal to each other. By doing so, the neighboring channel interference can be eliminated for narrowly spaced communication channels such as the OC-192 channels with a 50 GHz spacing.
Since the codes selected to modulate two neighboring channels determine whether the modulated light channels will interfere with each other, designing the predetermined code plan is very important and must assure that each light channel is isolated from its neighbor. In one embodiment of the present invention, a complete set of n-bit orthogonal codes (e.g., C
1
-C
2n
wherein “n” is an integer) can first be partitioned into at least two groups (e.g., an odd group having C
1
, C
3
, . . . , C
2n−1
, and an even group having C
2
, C
4
, . . . C
2n
). The odd group is assigned to a first orthogonal code book, and the even group is assigned to a second orthogonal code book. Since the first and second orthogonal code books are used for two neighboring light channels, neighboring channel interference is minimized. Further, the first orthogonal code book can be used again for modulating a third light channel that borders with the second light channel (but not with the first light channel). This arrangement further ensures that neighboring channels are isolated by using codes orthogonal to each other.
In order to provide multiple classes of services on a quality communication platform, a predetermined group of light channels are first partitioned into sub groups. Each sub group is then assigned to a predetermined class of services such as those exclusively for video, voice, or data. Moreover, for the purpose of restraining the channel dispersion problem, low bit rates are used for light channels having comparatively longer wavelengths, and high bit rates are used for light channels having shorter wavelengths.
In addition to grouping the orthogonal codes and grouping the light channels, another embodiment of the present invention also provides a self channel assignment mechanism so that information can be immediately transmitted on an available light channel. In this embodiment, an Optical Code Sense Multiple Access Protocol is implemented so that the code plan only needs to provide a predetermined set of orthogonal codes for all the light channels. With the implementation of the Optical Code Sense Multiple Access Protocol and a code correlator, all the orthogonal codes used in the network are monitored by each user terminal connected to the network. When an orthogonal code is available for modulating a light channel, a user terminal instantly selects that orthogonal code for modulating the light channel, and starts to transmit information through that modulated light channel.
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International Search Report dated Apr. 19, 2001.
Faruque Saleh
Homayoun Fereidoun
Haynes and Boone LLP
Nortel Networks Limited
Pascal Leslie
Tran Dzung
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