Multiplex communications – Communication over free space – Repeater
Reexamination Certificate
2000-08-18
2004-08-03
Hsu, Alpus H. (Department: 2665)
Multiplex communications
Communication over free space
Repeater
C370S324000, C370S350000, C370S509000, C375S240280, C375S368000, C455S013400, C714S775000, C714S776000, C714S783000
Reexamination Certificate
active
06771615
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to communication systems, and is more particularly related to synchronizing segmented messages in a satellite communication system.
2. Discussion of the Background
Modern satellite communication systems provide a pervasive and reliable infrastructure to distribute voice, data, and video signals for global exchange and broadcast of information. These satellite communication systems have emerged as a viable alternative to terrestrial communication systems. A popular application, for instance, is direct television broadcasting, which has provided a competitive alternative to cable television systems. Irrespective of the application, a satellite communication system must be designed to support the largest possible traffic capacity, which can translate to lower cost per telephone circuit, or television service, for example, and thus, to increased revenue for the system operator. The largest factors that affect capacity of a satellite communication system are the satellite transmission power and bandwidth.
In addition to data traffic, control messages are transmitted over the satellite links to provide a number of necessary functions, such as session establishment/termination and power management. Power control messages are transmitted from the satellite to terminals (forward link), and from terminals to satellites (return link) to regulate the proper power requirements of the terminal. Satellite terminals transmit power control messages to the satellite to specify the proper amount of transmission power that the satellite terminals require to receive signals from the satellite without experiencing severe signal distortion. During fading conditions, such as rain or snow, the satellite terminals need greater power than under normal environmental conditions. In some situations, the satellite terminals may even reduce their power requirements if the weather is especially conducive to strong signal reception.
A control message is typically fragmented into a number of blocks or segments, which are multiplexed over a number of frames. Specifically, these power control messages are multiplexed with other data traffic in the return link of the satellite communication system. The receiver needs to determine which of the frames corresponds to the start of the messages. In the forward link, messages are synchronized to the frame numbers, such that the receiver knows, prior to their reception, which is the first frame of each message. However, in the return link, the messages are not synchronized to the frame numbering to minimize delay of the underlying control loops. As a result, message synchronization poses a problem, in that there is no guarantee that a message will be received in the correct sequence. Clearly, if the control message cannot be restored in the proper sequence, the message cannot be correctly interpreted (i.e., data corruption).
To ensure that these message blocks can be reordered properly, one conventional approach is to employ overhead bits that provide sequence numbers for each message block. In this manner, the receiver detects the start of the message by examining the sequence number of the message blocks; for example, a sequence number of one would indicate the beginning. Because control messages detract from the useful bandwidth of the satellite system, it is important to minimize or eliminate the use of overhead bits. Thus, a drawback with the traditional approach is that overhead bits are required to provide synchronization of the control messages, which effectively reduces system throughput. In another conventional system, the return link receiver synchronizes the message framing by observing the contents of the messages; however, this disadvantageously results in processing delays.
Based on the foregoing, there is a clear need for improved approaches to synchronizing messages.
There is also a need to increase the efficiency of the satellite system.
There is also a need to enhance transmission capacity.
Based on the need to maximize the useful bandwidth of a communication system, an approach for synchronizing messages without introducing overhead is highly desirable.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a method is provided for performing message synchronization. The method includes encoding a message for transmission over a communication channel. In addition, the method encompasses interleaving the encoded message according to a predetermined interleaving pattern, and applying a mask pattern that has a prescribed sequence of bits to the interleaved message. The prescribed sequence is ordered to eliminate an all zero bit pattern and an all ones bit pattern. Further, the method includes segmenting the masked message into a plurality of blocks, in which each of the blocks has a fixed length. The method also includes multiplexing each of the blocks with data traffic for transmission over the communication channel. Under this approach, synchronization errors are reduced.
According to another aspect of the invention, a communication system for providing message synchronization comprises an encoder that is configured to encode a message for transmission over a communication channel. An interleaver is coupled to the encoder and is configured to interleave the encoded message according to a predetermined interleaving pattern. An adder is configured to add a mask pattern that has a prescribed sequence of bits to the interleaved message. The prescribed sequence is ordered to eliminate an all zero bit pattern and an all ones bit pattern. A multiplexer is configured to multiplex the masked message with data traffic for transmission over the communication channel. The masked message is segmented into a plurality of blocks, in which each of the blocks has a fixed length. The above arrangement advantageously provides enhanced system performance.
In yet another aspect of the invention, a computer-readable medium containing program instructions for execution on a computer system, which when executed by a computer, cause the computer system to perform method steps for providing message synchronization is disclosed. The method includes encoding a message for transmission over a communication channel. In addition, the method encompasses interleaving the encoded message according to a predetermined interleaving pattern, and applying a mask pattern that has a prescribed sequence of bits to the interleaved message. The prescribed sequence is ordered to eliminate an all zero bit pattern and an all ones bit pattern. Further, the method includes segmenting the masked message into a plurality of blocks, in which each of the blocks has a fixed length. The method also includes multiplexing each of the blocks with data traffic for transmission over the communication channel. This approach advantageously enhances system throughput.
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Park Yunsang
Parr Michael
Hsu Alpus H.
Hughes Electronics Corporation
Whelan John T.
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