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Wireless Links, HFC Extensions and Wireless DOCSIS return for CATV Systems

One-Way Broadband CATV Links

A Point-to-Point broadband wireless link consists of a transmitter at the Headend site and a receiver at one or more hub sites. At the receiver site, the receiver feeds the trunk cable system directly, without the need for interface equipment or facilities of any kind.

Two-Way Broadband CATV Links

Two-Way Broadband CATV Links enable operators to deliver the latest bi-directional services to subscribers on wireless links.

Cable AML's new wireless extension products can provide a wireless return path for data services such as the DOCSIS-based, high-speed Internet Access return signals from cable modems and interactive set-top boxes while simultaneously providing additional capacity downstream -- without sacrificing existing bandwidth .

An upstream return path from 5 to 42 MHz can be implemented from each existing AML receiver to the Headend for single or multiple AML paths by tapping the bandwidth available in the 18 GHz band.

The return path is created when upstream transmitter and receiver pairs, designed especially to return to the Headend the QPSK or 16-QAM modulated signals from subscribers, are added to existing AML systems.

The upstream transmitters are typically located at the AML receive sites. The upstream receivers are located at the Headend. Both units are available at various power levels in indoor and outdoor configurations.

Wireless HFC Extension

Tap the 50 MHz of extra CARS band spectrum available through specific waiver to add bandwidth to existing systems. The frequency band from 13.2 to 13.25 GHz can be used to create an upstream return path. Cable AML's new series of 13 GHz transceivers are the perfect choice for upgrading existing CARS band AML links to provide 2-way data service. A TRX13 model transceiver installed at each end of the link can simultaneously transport both the downstream (forward) channels from 54 MHz up to 552 MHz, and the upstream (return) channels from 5 to 42 MHz. These transceivers are available in both indoor and outdoor models.

Wireless HFC Extensions with 54-550 MHz downstream bandwidth

These links are 2-way, point-to-point links designed to provide 2-way wireless DOCSIS-based data transport in the extended CARS band. The links are implemented with transceivers (integrated transmitters-receiver pairs) and can be used for upgrading existing CARS band (12.7-13.2 GHz) links to provide 2-way data service.

They simultaneously transport both the downstream (forward) cable channels from 54 MHz up to 552 MHz, and the upstream (return) cable channels from 5 MHz to 42 MHz.

Full-Bandwidth Wireless HFC Extension

For applications where additional downstream capacity is required in addition to two-way service, the TRX18-series transceivers are the answer. These transceivers are two-way, wireless, point-to-point, integrated transmitter/receiver pairs designed to extend the traditional CARS band AML downstream capacity from 552 to 870 MHz and to provide 2-way wireless DOCSIS based "upstream" data trunking simultaneously. The additional bandwidth available in the 18 GHz band provides the capacity for the 552 to 870 MHz downstream extension as well as the upstream (return) channels from 5 to 42 MHz. As with the TRX13 series products, these transceivers are available in indoor and outdoor versions.

Wireless DOCSIS Return

The BWA-2000C allows a Cable System to offer DOCSIS Cable Modem service even though the cable plant might not have everywhere the two-way capability required for carrying the DOCSIS upstream or return signal from the subscriber modems.

The system allows the upstream DOCSIS signal to return to the Headend via a wireless link in a licensed band, for example the MDS (2.150-21.62 GHz), MMDS (2500-2686 MHz) or the 3.5 GHz bands.

The operation of the system is better understood by describing separately the downstream and upstream paths of the DOCSIS modem signals.

The downstream signal travels to the subscriber through the cable, much like any other digital carrier or like the analog video channels. The upstream signal returns through a wireless link to the headend. The wireless link need not be at the subscriber premises, it can be further up the cable plant. In fact a wireless transmitter can provide the upstream path to all subscribers that have two-way access from the node.

Downstream Path

At the Headend, there is a DOCSIS-certified CMTS (Cable Modem Termination System), which provides the interface between the Internet and the cable system.

The CMTS interfaces with the cable system by providing one or more 6-MHz data channels in the 88-860 MHz range for the downstream data signal. The downstream data modulation format is 64QAM. The downstream data channel is combined with the video channels and the combined downstream channels are distributed to the local subscribers over the local cable plant. The data carrier level is normally set at 6-10 dB lower than analog video carrier level.

At the subscriber site, the downstream signals from the cable plant are split to two paths. One path through a STB (Set-Top-Box) feeds the TV set and another path goes through a downstream/upstream diplexer to the Cable Modem for the data service.

A subscriber’s PC can be connected directly to the cable modem through a 10-BaseT Ethernet cable. The cable modem can also feed a LAN (Local Area Network) with multiple PCs.

Upstream Path

The upstream data from the subscriber cable modems is sent back to the CMTS via a wireless link.

In the case of the single subscriber, the PC sends the upstream data out, the cable modem modulates the data in QPSK at a frequency in the 5 to 42 MHz range, from where it goes through the diplexer, and is fed to an upstream transmitter, which up-converts the upstream channel frequency to one channel in the upstream band.

The upstream transmitter is connected to a directional antenna which sends the upstream signal to an omni-directional antenna at the Headend, where the upstream signals from all local subscribers are received and sent to the CMTS upstream input ports, as if they were coming from a two-way cable system.

The upstream antenna and transmitter can be shared by all subscribers connected by two-way cable to a node. In this way the cost of this equipment is effectively shared between a few or even many subscribers.

Furthermore, as sections or nodes of the cable system are upgraded for two-way service, the wireless transmitter and antenna can be moved further upstream to provide return path for all subscribers within a node.