Telecommunications – Wireless distribution system
Reexamination Certificate
2000-02-15
2002-04-23
Maung, Nay (Department: 2681)
Telecommunications
Wireless distribution system
C455S003050, C379S056200, C370S277000, C370S486000, C370S487000, C725S110000, C725S111000, C725S119000, C725S123000
Reexamination Certificate
active
06377782
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to data communications and more specifically to transmission and receipt of data via a linear broadband network.
BACKGROUND OF THE INVENTION
There currently exists a complex and robust wired television cable infrastructure that is commonly referred to as the Hybrid Fiber Coax (“HFC”) network. The HFC network is an example of a linear broadband network having substantially linear and broadband frequency characteristics. A linear broadband network exhibits linearity in that there are substantially no exponential terms in a gain function of the network over a frequency band of operation. As one of ordinary skill in the art appreciates, an all fiber and an all coaxial cable network is also a linear broadband network. The HFC network merely happens to be the most prevalent linear broadband network in use at the time of the filing of the present patent application. The HFC network has typically been used for delivery of television signals to subscribers. Each subscriber, which represents either an individual or a business, is connected to the cable TV HFC network through coaxial cables running from a headend in a trunk and branch configuration to individual subscribers. Over time, the cable TV HFC network has been upgraded by replacement of some of the coaxial cable trunk lines with fiber optic cable, which has led to this infrastructure being referred to as the HFC network. The connection between the HFC network and the subscriber premises is conventionally made with a coaxial cable, referred to as a subscriber drop, which spans the connection between a tap connected to the HFC network and a client device, which is most cases is a television set, located in the subscriber premises.
Deregulation of the communications industry has made it permissible for the telephony companies to supply television and video services and cable companies to supply telephony and data services. Accordingly, there is an interest among the cable TV service providers to grow their market share by being able to offer all communications services. The cable TV service providers are in a unique position in that they already have a linear and broadband network that reaches many existing subscribers. Their main historical business being television delivery, the cable companies have focused primarily on the forward or downstream path. In order to be a full service provider, however, the return or upstream path from the subscriber to the headend must be provided. For example, there is a growing demand for communication services that require higher performance from the communication infrastructure, such as higher speed Internet access, interactive television, video conferencing, and telephony. As the demand grows, there will be increasing demands placed on the quality and speed of the downstream and upstream paths. Providing subscriber access to the upstream path presents a challenge to the cable TV service providers. The cable TV service providers have provided a high quality network up to the curb (tap). However, the subscriber drop and client devices have been a source of significant noise resulting from bad connectors, unterminated connections, frayed cables, faulty wiring, breached shielding, noise generated by subscriber appliances, etc. The noise leaks into subscriber wiring and onto the subscriber drop, presenting itself on the upstream path of the HFC network as unwanted signal energy. The very nature of the trunk and branch configuration of the hybrid fiber coax network causes the noise to accumulate on the upstream path as the branches of the network converge. The noise from each subscriber adds together to reduce the overall signal-to-noise ratio of the return signal.
The signal-to-noise ratio of a communications signal is directly related to the effective bandwidth of the channel. Decreasing the signal-to-noise ratio, therefore, increases the bit error rate of a channel. As signal-to-noise ratio decreases, the data transmission rate must slow to a level that provides a sufficiently low bit error rate. The lowering of the data transmission rate is in direct contravention to the objective of the cable TV service providers in supplying high-speed communication services. The signal-to-noise ratio problem is exacerbated when the composite signal reaches an optical laser that is used to power the return transmission fiber. The absolute power level of the signal is limited because the laser has a fixed modulation index. In other words, as the noise level increases, the available signal strength decreases. This limits the cable service provider's option of amplifying the signal to achieve an acceptable signal-to-noise ratio. In data transmission applications, it is possible to employ loss packet retransmission to correct for noise that degrades the integrity of the upstream information. As speeds increase, however, retransmission consumes valuable bandwidth that would otherwise be used for additional upstream information. Consequently, noise limits the overall capacity of the network, thereby increasing the cost of the service to subscribers. There is a need, therefore, to improve upstream capacity on the network by reducing the injection of upstream noise.
U.S. Pat. No. 5,867,485 issued to Chambers et al. and assigned to Bellsouth Corporation, proposes a low power microcellular wireless drop for a full duplex interactive network in which a cable connecting a bi-directional fiber network to a subscriber premises is replaced by two wireless transceivers. A Network Interface Unit multiplexes and de-multiplexes signals transmitted and received from a number of subscriber appliances. These signals are transmitted and received by a roof or eaves mounted antenna. The upstream signal is up-converted, amplified, and filtered before being transmitted to a receiver. The system disclosed is a linear processing system, which amplifies the noise presented to the upstream path by the subscriber premises. Disadvantageously, the linear processing propagates any in-band noise and reduces the signal-to-noise ratio. The downstream signal is filtered, amplified, and down-converted before entering the Network Interface Unit and de-multiplexed to the appropriate appliance. The wireless drop succeeds in isolating the subscriber premises from the bi-directional fiber network, but does not remove the noise injected into the upstream signal. There remains a need, therefore, for a method or system to limit the noise ingress into the upstream path.
SUMMARY OF THE INVENTION
According to one aspect of an embodiment of the present invention, a method of communicating information from a client device to a linear broadband network having substantially linear and broadband frequency characteristics comprises the steps of generating an upstream baseband signal having a predefined format. The method further comprises modulating the upstream baseband signal onto at least one upstream wireless radio frequency carrier to generate at least one first upstream modulated carrier signal and transmitting the at least one first upstream modulated carrier signal wirelessly. The method further includes receiving the at least one first upstream modulated carrier signal at a network access interface device coupled to the linear broadband network and demodulating the at least one first upstream modulated carrier signal to produce an upstream demodulated baseband signal. The method then comprises modulating the upstream demodulated baseband signal onto at least one upstream linear broadband radio frequency carrier to produce at least one second upstream modulated carrier signal having a signal format compatible with the linear broadband network.
According to another aspect of the present invention, a method of communicating bi-directional information between a client device and a linear broadband network having substantially linear and broadband frequency characteristics comprises the steps of generating an upstream baseband signal, having a predefined format, and modulating the upstream baseb
Bishop Donald M.
Green George R. J.
Shyu Archie R.
Cochran William W.
Maung Nay
MediaCell, Inc.
Persino Raymond B.
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