MPEG-2, a significant set of hardware and software standards developed by the Moving Pictures Expert Group, is the leading digital video compression technique for many of the newest video and broadcast applications. MPEG-2 is a more efficient compression technique than MPEG-1. The new set of standards offers a resolution of 720 by 480 pixels at 30 frames per second with full CD-quality audio. It allows for a full screen playback on PCs or TVs. MPEG-2 uses a range of compression ratios, exchanging economies of storage and transmission bandwidth for picture quality.

This article, the first in a series on MPEG-2, will examine several factors that ultimately determine the quality of the signal and the resulting television picture using the MPEG-2 standards. The service provider that thoroughly understands the terms associated with MPEG-2 will be that much closer to comprehending when the new standards should be deployed and what the corresponding benefits will be. MPEG-2 terms include:

Symbol Rate
Symbol rate (or baud rate) measures the number of packets that can be transmitted per second. Each packet contains one or more bits of information.

Forward Error Correction
Forward Error Correction (FEC) is a method of detecting and correcting errors by transmitting redundant bytes in each message. The redundant bytes are then used to detect, isolate and fix any errors that occurred in transmission. If a digital satellite Quaternary Phase Shift Keying (QPSK) transmission has an FEC parameter of 1/2, it indicates that one out of every two bytes sent is used to send the actual signal, while the other byte is used for error correction. Similarly, if the satellite transmission has an FEC parameter of 7/8, seven out of every eight bytes sent are used to send the signal and the remaining one is used to check and correct. Although it appears that an FEC of 1/2 guarantees the most accurate transmission, certain other parameters must be considered, such as bandwidth availability and power.

Modulation Error Ratio
Modulation Error Ratio (MER) is measured in decibels (dB) and gives a quantitative result for modulation quality. It is a ratio of two values: (1) the error power in a signal and (2) the average power present. An MER measurement can indicate how close a signal is to breakdown. It can also detect system noise, modulation problems and other transmission barriers.

Eb/No
Eb/No is the ratio of Energy per Bit to Noise Power.

Bit Error Rate
The Bit Error Rate (BER) is the most important measurement available for digital signals. It is a ratio of two values that represent (1) the number of bits that the decoder cannot interpret upon receiving to, and (2) the total number of bits that have been transmitted. In a typical transmission, an average BER would be approximately 1.0E-3 to 1.0E-5. This translates to a range of one error for every 1,000 bits transmitted to one error for every 100,000 bits transmitted.

Carrier to Noise Ratio
The Carrier to Noise Ratio (C/N Ratio) is used to find the satellite signals and is the second most important factor considered in the installation and setup of the satellite antenna. The stronger the signal, the greater the C/N ratio.

Channel Power
While it is helpful in setting up an analog, terrestrial television, Channel Power (CH PWR) is not used when installing and setting up a digital signal system. Because the Low Noise Block (LNB) device at the satellite dish's focal point generates noise that can be read as a very strong signal, the CH PWR measurement is inaccurate in satellite television setup. However, after the head-end components are set up, the CH PWR can be used along with the C/N Ratio and the BER measurement to measure the signal's quality.

Compression Ratios
Although MPEG-2 supports compression ratios of 200:1, it offers broadcast-TV quality pictures when the compression ratio is 30:1 or less.

Signal Power
Attenuating a signal has a significant effect on its power, which must be accounted for. For example, if a 13 dB signal is attenuated by 3 dB, the signal power is actually halved. In this case, -3dB represents a multiplier of .707. If the voltage is reduced by .707, the current is also reduced by .707 (Ohms Law). Because Power equals Voltage multiplied by Current (P=V x I), .707 x .707 = .5 or half the power. Power is also reduced when a two-way splitter is installed. A two-way splitter is, in effect, a two-way power divider, splitting the power into two equal halves.

Technical Parameters
When installing an SMATV (Satellite Master Antenna Television), CATV (Cable Television) or MATV (Master Antenna System) system, certain technical parameters must be adhered to in order to achieve optimum system performance. The parameters are outlined in the following tables.

The Future of MPEG-2
As of August 2001, an estimated 12.2 million homes subscribed to digital cable services, according to the National Cable & Telecommunications Association (NCTA). The adoption of MPEG-2 standards will result in even greater signal quality, offering the consumer better program offerings and more customer options, such as parental control features. The NCTA predicts that the number of digital cable subscribers will increase to 48.6 million homes by 2006, no doubt due to the constantly improved quality and quantity of digital cable offerings as represented by MPEG-2.

About the Author
Mor Allon, chief executive officer of Ikusi Telecommunications, is a telecommunications industry veteran with more than 20 years of experience in the U.S. and Israel. Headquartered in Upper Saddle River, New Jersey, Ikusi Telecommunications, Inc., is part of the global Spanish conglomerate, IKUSI. The author may be reached with questions or comments via email at allon.m@ikusi.com