Broadbandindia Magazine

Cable television headend is a master facility for receiving television signals for processing and distribution over a cable television system. The headend facility is normally unstaffed and surrounded by some type of security fencing and is typically building or large shed housing electronic equipment used to receive and re-transmit video over the local cable infrastructure. One can also find headends in power line communication (PLC) substations and Internet communications networks. This invention relates to cable television delivery systems for providing television programing to consumer homes in digital format. More particularly, the invention relates to new technology for the cable headend portion of a cable television delivery system capable of handling digital video/audio signals.

Background

The cable headend is a key part of a cable television delivery system and requires redesign. Analog cable television delivery systems operate with an analog cable converter box in the viewer home which uses a television to display video programs. The converter box is connected via cable to a cable headend site. Typically, each analog cable headend site has multiple satellite dishes. Each analog cable headend site’s satellite dishes normally receive transponded signals from one or two satellites. A satellite has multiple satellite transponders. Although uplink sites and satellite dishes can transmit and receive multiple video/audio program signals, currently, each satellite transponder normally carries only one video/audio program at any given time. Typically, a transponder is dedicated to one channel of video programming. Further, there is generally one Integrated Receiver and Decoder per transponder (or channel) at the analog cable headend to receive the signal from the transponder.

In summary, current analog technology requires the combination of one uplink site, one satellite transponder, and one cable headend satellite dish to deliver each analog video/ audio program to the cable headend. The cable headend uses several analog video/audio signals from multiple dishes and multiple transponders to provide multi-channel analog signals. The cable headend then transmits these analog signals on different transmission frequencies to the cable converter boxes in the viewer homes where one channel is selected.

Each television channel for analog video/audio transmissions for television is in a 6 MHz segment of bandwidth. An industry standard of 6 MHz was set in the year 1939 and the NTSC standard is still 6 MHz per channel of analog video. As television program delivery technology moves into the digital world the 6 MHz segments have no real technical significance, except in hybrid analog-digital converters. In addition, today’s cable television delivery systems carry signals which are scrambled for security reasons. Each vendor uses scrambling techniques that are incompatible with the every other vendor. There are two primary cable industry leaders in scrambling formats, Scientific-Atlanta, Inc. and General Instrument Corporation.

Currently, a two step scrambling/descrambling process is used in cable television program delivery systems. During the first step, program signals are scrambled prior to satellite transmission and are descrambled at the cable headend. During the second step, program signals are transmitted in scrambled format to the viewer homes where an authorized converter box descrambles the signals. Primarily, two types of scrambling techniques are used between the cable headend and converter boxes in subscriber homes, video inversion and synch suppression. Thus, the final descrambling takes place at the converter box in the viewer homes using one of these two techniques.

General Instruments is by far the industry leader and has a virtual “lock” on the market for signal scrambling from origination point to cable headend. From the cable headend to the subscriber home, General Instruments and Scientific Atlanta have the greatest market shares, but face competition from competitors such as Zenith and Pioneer. Scientific Atlanta and General Instruments are also the primary producers of set top terminals for the U.S. cable industry. Therefore, cable headends may only service one vendor’s converter boxes. Generally, cable headend scrambling equipment services either Scientific Atlanta converters or General Instrument’s converters. No standard scrambling or security measures have been agreed upon by the industry. In some cases, manufacturers can produce descramblers that are compatible with another’s system.

Although no standard method for digital coding of moving pictures and audio has been established, the television industry through the International Organization For Standardization is working on a digital coding standard. The use of digital video/audio signals for delivering cable television programming will require changing today’s cable television delivery system. In particular, the analog cable headend described above will not operate in the digital environment. Methods of encryption and decryption also need to be examined.

Digital cable headend

Today’s television delivery systems are designed to deliver digital video/audio signals from the signal source to viewer televisions. Developments in digital bandwidth compression technology will allow for much greater throughput of television program signals over existing or slightly modified transmission media. The cable television delivery systems must be redesigned to take advantage of digital technology. A preferred embodiment of the present invention is a digital cable headend system that allows full utilization of digital technology in a cable television delivery system. The cable headend is a key component of a digital cable television delivery system.

The cable headend is the central component for receiving , combining and routing program signals to the viewer homes. The cable headend of the present invention provides much greater capability and flexibility than existing cable headends. Specifically, the Combiner, in combination with other components of the digital cable headend of the present invention, solves many technical problems and challenges.

Digital Technology

The introduction of digital program signal technology presents several new challenges to cable television delivery systems. Digital technology will provide cable headends with hundreds of channels of programming. With this overwhelming number of programs, there must be a method of selecting or cherrypicking desired programs and/or filtering out unwanted programs received from a transponder. Also, since the programs are too numerous to pass through the limited bandwidth space in the concatenated cable to the viewer homes, the bandwidth available to homes must be effectively and efficiently managed. A limited number of programs must be selected to send to viewer homes.

In addition, the available bandwidth may differ from viewer home to viewer home. For example, a cable headend may service some cable viewers with a 550 MHz bandwidth signal (typically 50 MHz to 550 MHz) and some viewers with a 750 MHz bandwidth system. The cable headend must transmit the correct combined signal to the appropriate viewers. In a similar fashion, if concatenated cable systems with identical bandwidths require different offering of program selections, the cable headend must fashion two different combined signals with identical bandwidth, one for each concatenated cable system.

Satellite transponders act as conduits for the delivery of the digital program signals to cable headends. These satellite transponders send data in various data packet formats, at different data rates, and encrypted in one of several possible formats. Therefore, a cable headend must be able to receive, filter, combine and route signals received at different data rates for distribution to viewer homes.

This requires the cable headend to delay and synchronize signals as necessary. The present invention solves these problems and others. The cable headend also accommodates local cable and television companies with program time for local advertising and/or feature programming time availability in digital or analog form. Local digital or analog signals may be combined with satellite signals at the headend.

Combiner

An important component of the new cable headend configuration is the Combiner. The basic functions of the Combiner are selecting video signals to be combined, handling video/audio signals at varying data rates (as necessary), packet switching and ensuring the integrity of the combined signal. The basic components of the preferred Combiner are a Control CPU, digital logic, and a serialize. The Control CPU in conjunction with digital logic performs the intelligent functions of the Combiner.

Specifically, the Control CPU and digital logic select the video signals to be combined and ensure the integrity of the combined signal. This procedure is accomplished on the video data packet-by-packet. A variety of combinations of hardware and software may be used to perform the Combiner functions. Combiners may be used in parallel or in series as needed to accomplish proper output of signal to set top boxes. The Combiner may be used in conjunction with various digital and analog cable headend configurations.

Four different categories of headends are described, mixed analog and digital, digital only, digital-in-analog-out, and a more complex embodiment which transmits television program information on a data signal to the set top terminal. These embodiments may each be built in a modular fashion and may service multiple concatenated cable systems having different available bandwidths.

Encoder

FEATURES :

Supports MPEG-2 MP@ML (4: 2: 0) coding profile NMS: Local/Remote net administration possible LCD display, flexible in operation Highly reliable design

Modulator

FEATURES

Complying DVB standard Support full range variable data rate, bandwidth and QAM mode stuffing PID filter, re-reflection, PSI/SI Information synchronization updating Code stream real-time monitoring, empty packet filtering Support editing of NIT table PCR adjusting, Output symbol rate variable: 3-7Ms/ s. Fixed or agile channel output. Providing RF output monitoring port-20dB NMS: Local or Remote administration & control possible

Modulator

FEATURES

Complying DVB-S / MPEG-II standard QPSK modulation mode, compatible with SCPC and MCPC Automatic forward error correction (FEC) Last Program memory in case of power failure ASI output interface

Digital Signal Processing

Digital channels are usually received on an L band QAM stream from a satellite, which uses multiplexing. Using special receivers such as the Motorola MPS, the signal can be demultiplexed or “Demuxed” to extract specific channels from the multiplexed signal. At this point, local insertion may be performed to add content specifically targeted to the local geographic area.

Digital Signal Modulation

Cable television signals are then mixed in accordance with the cable system’s channel numbering scheme using a series of cable modulators (one for each channel), which is in turn fed into a frequency multiplexer. Once processed, the television signals are sent over the cable system’s coaxial cables and continuously re-amplified as needed. Digital channels are modulated as well; however, instead of each channel being modulated on to a specific frequency, multiple digital channels are modulated on to one specific NTSC frequency. Using QAM (Quadrature Amplitude Modulation), a CATV operator can place usually up to eight channels on one specific frequency so channel 2 may actually be carrying channels 2-10 in your city. STB’s (Set top boxes) or Cable Cards are required to receive these digital signals and are provided by the cable operator themselves.

Multiplexer

FEATURES

Complying ISO13818 standard. Support MPEG-2 transport stream re-multiplexing. Multiplexing SPTS and MPTS Transport stream.

SDT NIT table Insertion Able to connect independent scrambler for scrambling to specific or Service.

Generating SPI/ SI information. Support PCR adjusting and PID re-reflection.

Able to extract PSI/SI information from any route of SPTS/ MTPS.

Support EMM/ ECM/ EPG information insertion,EPG Regeneration.

Able to interpolate data, and re-multiplex and transport any kind.

Support statistical multiplexing.

Support the cascading connection of several equipments. NMS for Central net administration, remote and maintenance· Alarm display.

Support network upgrade

NMS-5000

FEATURES

Can control and monitor all the equipments of Digital headend The major functions include: add/ delete frequency point (FP), add/ delete equipment Save/load setting, modify equipments information, read the help information, resume factory setting, exit program etc.

Information window: Displays equipments information such as equipment model, IP Address,version number etc.

Alarm window

Displays Alarm information and Alarm date Operation window: Displays relevant interface according to the equipment chosen, users can set the detailed parameters here Software

It is a high-level flow chart of the software resident at the Control CPU to operate the Combiner. The Control CPU sends appropriate instructions to various components of the Combiner to ensure the selection of appropriate videos and that the video signals are combined in an appropriate manner. The software routines may be hardwired as part of the Combiner.

Digital Reception

Many digital cable systems use services like HITS (“Headend in the Sky”, a unit of Comcast, which carry hundreds of channels on just a few satellites; this is commonly used by small systems to expand service without adding expensive new dishes or other equipment.

Some cable TV systems receive the local television stations’ programming by dedicated digital fiber-optic line, installed between the local station and the headend. A device called a modulator at the local station’s facilities feed their programming over this line to the cable TV headend, which in turn receives it with another device called a demodulator. It is then distributed through the cable TV headend to subscribers. This is usually more reliable than receiving the local stations’  broadcasts over the air with an antenna. However, off-air reception is used as a backup by the headend in case of failure.

Other sources of programming include those delivered via fiber optics, telephone wires, the Internet, microwave towers and local community access channels that are sent to the cable headend on an upstream frequency over the cable system itself, or via a dedicated line set up by the cable company, as mentioned earlier for reception of local television stations’ programming by the headend.