Future Enhancements: Wireless Cable, HDTV, Cable Telephony, Interactive Television

Some of the future enhancements for CATV include wireless cable, cable telephony, video on demand (VOD), and interactive television.

Wireless Cable
“Wireless Cable” is a term given to land based (terrestrial) wireless distribution systems that utilize microwave frequencies to deliver video, data, and/or voice signals to end-users. There are two basic types of wireless cable systems, multichannel multipoint distribution service (MMDS) and local multichannel distribution service (LMDS).

Multichannel video and data services are being offered over microwave frequencies. The data-over-cable service interface specification (DOCSIS) with a few modifications can also be used in 2.6 GHz wireless multipoint, multichannel distribution service (MMDS), and 28 GHz local multipoint distribution service (LMDS) systems [14]. The DOCSIS specification is being adapted for the wireless cable marketplace. A consortium called “Wireless DSL” is working to produce an adapted version of DOCSIS called DOCSIS+ that is suitable for offering cable modem technology via microwave transmission. The DOCSIS+ standard has been proposed to the IEEE 802.16 for conversion into an official standard.

Figure 1 shows a LMDS system. This diagram shows that the major component of a wireless cable system is the head-end equipment. The head-end equipment is equivalent to a telephone central office. The head-end building has a satellite connection for cable channels and video players for video on demand. The head-end is linked to base stations (BS) which transmits radio frequency signals for reception. An antenna and receiver in the home converts the microwave radio signals into the standard television channels for use in the home. As in traditional cable systems, a set-top box decodes the signal for input to the television. Low frequency wireless cable systems such as MMDS wireless cable systems (approx 2.5 GHz) can reach up to approximately 70 miles. High frequency LMDS systems (approx 28 GHz) can only reach approximately 5 miles.


Figure 1: Local Multipoint Distribution System (LMDS)

High Definition Television (HDTV)
High definition television (HDTV) is a TV broadcast system that proves higher picture resolution (detail and fidelity) than is provided by conventional NTSC and PAL television signals. HDTV signals can be in analog or digital form.

The specifications for HDTV digital systems allow for many types of data services in addition to digital video service. Digital HDTV channels carry high-speed digital services that can be addressed to a specific customer or group of customers that are capable of decoding and using those services. Examples of these services include: special programming information, software delivery, video or audio delivery (like pay-per-view programming), and instructional materials.

The data rate available for additional services is dynamic and ranges from a few kbps to several Mbps, depending on the video and audio program content. The gross data rate of the HDTV system is 19 Mbps. The amount of this data rate that is used by the HDTV video signal depends on the compression technology. Video data compression produces a data rate that changes dependent on the original video signal. When the video program contains rapidly changing scenes, most of the 19 Mbps signal is required for transmission. If the video signal is not changing rapidly, much of the 19 Mbps can be used for other types of services.

Transmission of the additional services has a lower priority than transmission of the primary program. If the primary service (HDTV) consumes a large part of the data (such as a rapidly changing video action scene), the customer may have to wait for some time prior to receiving large blocks of data.

Cable Telephony
Cable telephony is the providing of telephone services that use CATV systems to initiate, process, and receive voice communications. Cable telephony systems can either integrate telephony systems with cable modem networks (a teleservice) or the cable modem system can simply act as a transfer method for Internet telephony (bearer service). Because of government regulations (restrictions or high operational level requirements) in many countries, some cable operators are delaying the integration of telephone services with cable network. In either case, cable telephony systems are data telephony systems that include a voice gateway, gatekeeper, and a media interface.

Voice gateway is a network device that converts communication signals between data networks and telephone networks. A gatekeeper is a server that translates dialed digits into routing points within the cable network or to identify a forwarding number for the public telephone network. A multimedia transfer adapter converts multiple types of input signals into a common communications format.

Figure 2 shows a CATV system that offers cable telephony services. This diagram shows that a two-way digital CATV system can be enhanced to offer cable telephony services by adding voice gateways to the cable network’s head-end CMTS system and media terminal adapters (MTAs) at the residence or business. The voice gateway connects and converts signals from the public telephone network into data signals that can be transported on the cable modem system. The CMTS system uses a portion of the cable modem signal (data channel) to communicate with the MTA. The MTA converts the telephony data signal to its analog audio component for connection to standard telephones. MTAs are sometimes called integrated access devices (IADs).


Figure 2: Cable Telephony

Because of the high data transmission capability of cable television systems, cable telephony system can provide video telephony service. Video telephony is a telecommunications service that provides customers with both audio and video signals between their communications devices.

Interactive Television
Interactive television is a combination of cable, television, multimedia, PCs, and network programming that allows dynamic control of media display using inputs from the end-user. Interactive television has three basic types: “pay-per-view” involving programs that are independently billed, “near video-on-demand” (NVOD) with groupings of a single film starting at staggered times, and “video-on-demand” (VOD), enabling request for a particular film to start at the exact time of choice. Interactive television offers interactive advertising, home shopping, home banking, e-mail, Internet access, and games.

Video on demand (VOD) is a service that allows customers to request and receive video services. These video services can be from previously stored media (entertainment movies or education videos) or have a live connection (sporting events in real time).

A limited form of VOD is called near video on demand (NVOD). Near video on demand is a video service that allows a customer to select from a limited number of broadcast video channels. These video channels are typically movie channels that have pre-designated schedule times. Unlike full VOD service, the customer is not able to alter the start or play time of these broadcast videos.

Pay per view (PPV) is a process that allows customers to request the viewing of movies through an unscrambling process. PPV movies are usually broadcasted to all customers in a cable television network. To prevent unauthorized viewing, each PPV channel has its own scrambling code. To provide a customer with a reasonable selection of movies, the same movie is broadcasted on different channels with start intervals that range from 15 to 60 minutes. To provider twenty PPV movies, approximately 80 to 160 television channels would be required.

Analog cable systems provide up to 800 MHz of bandwidth. Using 6 MHz wide video channels, this allows up to 120 analog video channels. By digitizing each 6 MHz channel and using compressed digital video (10:1 compression), this increases the capacity of a cable system to over 500 digital television channels.

Cable converter boxes, known as set-top boxes, have different reception and decoding capabilities. Set-top boxes are required to convert distributed signals into a format suitable for viewing. Set-top boxes also can coordinate access to video on demand channels.

Electronic programming guide (EPG) is an interface (portal) that allows a customer to preview and select from possible list of available content media. EPGs can vary from simple program selection to interactive filters that dynamically allow the user to filter through program guides by theme, time period, or other criteria.

Figure 3 shows a video on demand system. This diagram shows that multiple video players are available and these video players can be access by the end customer through the set-top box. When the customer browses through the available selection list, they can select the media to play.


Figure 3: Video on Demand (VOD)

Hypervideo is a video program delivery system that allows the embedding of links (hotspots) inside a streaming video signal. This allows the customer (or receiving device) to dynamically alter the presentation of streaming information. Examples of hypervideo could be pre-selection of preferred advertising types or interactive game shows.

Synchronized television (syncTV) is a video program delivery application that simultaneously transmits hypertext markup language (HTML) data that is synchronized with television programming. Synchronized television allows the simultaneous display of a video program along with additional information or graphics that may be provided by advertisers or other information providers.