Pulse or digital communications – Testing
Utility Patent
1997-02-28
2001-01-02
Pham, Chi H. (Department: 2731)
Pulse or digital communications
Testing
C320S118000, C320S118000
Utility Patent
active
06169763
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of Invention
The present invention relates to communication systems. More particularly, this invention relates to characterization tests of a communication system using frame-aligned test signals.
II. Art Background
Digital communication links are commonly employed to carry digital information from a source location to a physically distinct destination location. One type of digital communication link may be referred to as a frame-based communication link or a packetized communication link. Such a frame-based communication link typically carries digital data within data packets which may also be referred to as frames. Typically, each data packet is carried over the communication link during a separate time interval. Such a time interval for carrying a data packet is referred to as a frame interval.
One prior test system for performing characterization tests on a communication system that includes such a frame-based communication link is disclosed in U.S. patent application Ser. No. 08/496,817, file on Jun. 29, 1995, and entitled “Method and Apparatus for Objectively Characterizing Communications Link Quality.” Such a test system injects a test signal into the communication system being characterized. The test signal is carried through the communication system including the frame-based communication link. The test system then receives back the test signal and evaluates the received test signal to provide characterization of various parameters of the communication system.
The test signals generated by such a test system usually include a series of tone bursts which are carefully selected to exercise differing parameters of the communication system. The characterization tests performed by such a test system are usually enhanced if the tone bursts of a test signal are aligned the boundaries of the frame intervals of the communication link. Such frame alignment typically prevents portions of particular tone bursts from being carried in different frame intervals. Such splitting of the test signal could cause anomalies in the received test signal.
One prior method for aligning a test signal to such frame boundaries involves a trial and error approach of injecting various types of test signals and examining the received test signal. Such an approach requires one to determine whether anomalies in a received test signal are caused by frame misalignment or by the characteristics of the communication link being evaluated. Such an approach increases the time required to evaluate a communication system and typically increases the overall cost of characterizing and maintaining the communication system.
SUMMARY OF THE INVENTION
A method and apparatus is disclosed for aligning a test signal to a frame-based communication system. An alignment test signal having an alternating pattern of frequencies is generated and transmitted over a communication link in the communication system wherein the communication link carries the alignment test signal in a series of frame intervals. The alignment test signal is received after transmission over the communication link as a received alignment test signal and then evaluated for frequency content. The start time of the alignment test signal is adjusted until the frequency content of the received alignment test signal corresponds to the alternating pattern of frequencies. The starting time of the alignment test signal indicates a frame interval boundary once adjustment of the starting time is complete.
The aligned test signal enhances a system for quantitatively evaluating the quality of communication channels within a digital communication system. In an exemplary embodiment, the present invention may be incorporated within a digital cellular communication system in which information is exchanged over spread spectrum communication channels, among a plurality of mobile users, via at least one cell-site.
The test signals may be transmitted from a land line connection through the public switched telephone network (PSTN) and through the wireless channel. The aligned test signal enhances a test that is non-intrusive on the communications link. That is to say, the tests conducted appear to all of the communications systems elements simply as another call.
Other features and advantages of the present invention will be apparent from the detailed description that follows.
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DeJaco Andrew P.
Woodward Scott M.
Bayard Emmanuel
Pham Chi H.
Qualcomm Inc.
Rouse Thomas R.
Wadsworth Philip
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