Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1998-09-30
2003-09-23
Decady, Albert (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S704000
Reexamination Certificate
active
06625776
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to satellite communication systems, and more particularly to a method for adaptive error coding in a processing communication satellite system which optimizes data throughput in accordance with changing signal propagation conditions.
Satellites have long been used to provide communications capabilities on a global scale, allowing various earth terminals to communicate with each other via a satellite relay system. Typically, a satellite includes multiple uplink and downlink antennas, each of which provides communications bandwidth to a large coverage area (or “footprint”) using multiple spot beams. The area covered by a spot beam is often referred to as a “cell”.
A sophisticated processing satellite that demodulates and decodes uplink data and then switches that data and re-encodes and re-modulates it on the downlink may be used in the satellite relay system. Typically, a Network Operation Control Center (NOC) is also provided to generate command signals that control the satellite relay system and coordinate assignment of traffic channels in uplinks and downlinks. A typical system employs frequency and time division multiplexing (FDMA/TDMA) on uplinks and time division multiplexing (TDM) on downlinks. However, other multiplexing schemes may readily be used in either of the links.
Because the data sent to and from the satellite is susceptible to significant degradation by, for example, atmospheric conditions such as rain or by satellite antenna pointing error, the data is encoded with error detection and correction codes. Two types of error detection and correction codes are typically used, convolutional codes and block codes. Characteristics of the various techniques, for error control are extensively covered in the literature. In modern satellite communication systems a “concatenated” set of error detection and correction codes is typically applied to the data. Concatenated coding refers to the sequence of coding in which a second coding operation is performed upon already encoded data. The “outer code” of the concatenated coding is the first code applied (typically a block code), while the “inner code” of the concatenated coding is the second code applied (typically a convolutional code in downlink usage or a short block code in uplink usage).
A block code essentially adds parity bits to each predefined number of bits in a data channel (an information block). In processing satellites, a variety of block codes known as Reed-Solomon codes are typically used to outer encode both the uplink and downlink signals. The block outer encoded data is then further encoded with a convolutional code on the downlink or a short block code on the uplink to reduce the bit error rate (BER) to a tolerable level (the BER is the ratio of incorrectly received information bits to the total number of received information bits). The ratio of the number of information (or data) bits to the number of data bits plus error correction bits is commonly called the “code rate”.
The earth terminals which communicate via the satellite may be separated by a great distance and typically experience different and independent levels of signal degradation. In addition, the gain in the antenna's footprint and the antenna pointing errors are typically different for each terminal.
Most ground stations, however, do not concurrently experience the worst case signal degradation at any given time. In the past, concatenated error detection and correction codes have been used to achieve performance tailored to the worst-case signal degradation. Thus, in the past, bandwidth has been wasted by over-encoding the uplink and downlink with error correcting data that is not needed by the ground station most of the time. Wasted bandwidth results in inefficient communication, reduced throughput, and lost revenue. Additionally, past systems have failed to provide a simple relationship between changes in coding (or even a simple, effective inner code to replace the convolutional code) that allowed efficient processing on the satellite.
Furthermore, previous terminals continued transmission even when signal conditions deteriorated beyond the correction ability of the strongest error detection and protection code. Again, bandwidth, time, and power are wasted because the receiver cannot accurately decode the data transmitted to it under such conditions. Thus, even systems that change transmitter coding to a lighter or heavier level, such as that illustrated in U.S. Pat. No. 5,699,365 entitled “Apparatus and method for adaptive forward error correction in data communications” by Klayman, allow the transmitters to continue transmitting beyond the ability of the receiver to decode the data.
A need has long existed in the industry for an efficient and effective method for adaptive error coding in a satellite communications system.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an adaptive coding scheme for a processing satellite.
It is another object of the present invention to provide a mechanism by which originating terminals may suspend transmission when their data cannot be reliably decoded by destination terminals and to resume transmission when conditions warrant.
Yet another object of the present invention is to adaptively apply coding either to data transmitted in an uplink from an affected terminal “A”, to a corresponding terminal “B”, or to data transmitted in the downlink to an affected terminal A which is being relayed from a corresponding terminal B or both, and to do so independently for the uplink from A and the downlink to A and without requiring adaptation of links between the corresponding terminal B and the satellite.
Another object of the present invention is to provide hysteresis between adaptive changes in coding.
Still another object of the present invention is to provide a relationship between coding levels that allows the coded data to be handled efficiently.
One preferred embodiment of the present invention provides a method for adaptive error control coding of data in a downlink. The method includes the steps of receiving at terminal A a first signal containing light coded data transmitted in A's downlink from the satellite and determining a first data error rate associated with said first signal. When the first data error rate exceeds a first threshold (for example, a light-to-heavy threshold), the method commands the originating terminal B to subsequently select addressing which will result in transmission of heavy coded data in the downlink to A. The heavy coded data has a code rate less than that of the light coded data.
The method also continues to receive at the destination terminal A the first signal containing light coded data in A's downlink from the satellite and continues to determine the first data error rate associated with the first signal. If and when the first data error rate subsequently falls below a second threshold, the method commands the originating terminal B to subsequently select addressing which will result in transmission of light coded data (i.e., if it was currently transmitting heavy coded data) in the downlink to A.
Furthermore, the method may establish an enter-suspension threshold and determine a second data error rate associated with the heavy coded data. The method may then command each originating terminal B to suspend transmission when the second data error rate exceeds the enter-suspension threshold. Additionally, the method may establish an exit-suspension threshold separated from the enter-suspension threshold by a suspension hysteresis. The method may then command the first originating terminal B to resume transmission when the second data error rate falls below the exit-suspension threshold.
Heavy coded data in the downlink is typically associated with a rate 3/8 inner convolutional code applied at the satellite, while the light coded data in the downlink is typically associated with a rate 3/4 convolutional code. In the uplink from originating terminal B, h
Linsky Stuart T.
Perahia Eldad
Wilcoxson Donald C.
Wright David A.
Chaudry Mujtaba K.
McAndrews Held & Malloy Ltd.
Northrop Grumman Corporation
LandOfFree
Adaptive coding scheme for a processing communications... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Adaptive coding scheme for a processing communications..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Adaptive coding scheme for a processing communications... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3097578