Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1999-05-28
2003-10-14
Bost, Dwayne (Department: 2681)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S150000, C375S340000, C375S341000, C370S342000
Reexamination Certificate
active
06633601
ABSTRACT:
TECHNICAL FIELD
The present claimed invention relates to the field of cellular telephony. More specifically, the present claimed invention relates to frame rate determination in variable rate communication systems such as Code Division Multiple Access (CDMA) cellular systems.
BACKGROUND ART
Cellular telephony has become a widely available mode of communication in modern society. Variable rate communication systems, such as Code Division Multiple Access (CDMA) spread spectrum systems, are among the most commonly deployed cellular technology. Variable rate communication systems transmit data in units called data frames and, as its name indicates, at various frame rates. Moreover, in the case of CDMA systems, frame rate information is not transmitted from the originating base station to the receiver, which is typically a mobile receiver unit like a handset. Thus, the receiver needs to determine the frame rate of any and all data frames received from the originating base station on a frame-by-frame basis. As such, the receiver needs to have a method for determining what frame rate a given data frame is being transmitted at when a data frame is received.
Generally, within a CDMA environment with a large number of users on the system, a high level of channel noise is usually present. In particular, each user is a source of noise to every other user on the same system. In the prior art, the symbol error rate, which is calculated based on hard-limited symbols, is used for frame rate determination. Nevertheless, it has been determined that such symbol error rate can often be a highly inaccurate predicate of the frame rate of a data frame when the data channel is very noisy. Such prior art approaches to frame rate determination are thus not practicable in a variable rate communication system with a noisy data channel. Therefore, a method and device which can accurately determine the frame rate of a data frame in a high noise level environment is needed.
Additionally, a method and device for determining the frame rate of a data frame in a high noise level, variable rate communication system must not require significant revamping of such existing communication systems. That is, in implementing a viable method and device for frame rate determination in a variable rate communication system, components that are well known in the art and are compatible with existing communication systems need to be used so that the cost of realizing the method and device is low. In so doing, the need to incur costly expenditures for retrofitting existing communication systems or for building custom components is eliminated.
Thus, a need exists for a method and device for frame rate determination in a variable rate communication system. A further need exists for a method and device which meets the above listed need wherein the method and device operates accurately in the presence of significant channel noise. Still another need exists for a method and system which meets both of the above cited needs and wherein the method and device is easy to implement and is conducive to use with existing variable rate communication systems.
DISCLOSURE OF THE INVENTION
The present invention provides a method and device for determining a frame rate of a data frame transmitted over a variable rate communication system. The present invention accomplishes the above achievements with a method and device which performs frame rate determination using correlation metrics and frame quality indicators. The present invention delivers accurate frame rate determination even in an environment with a high level of channel noise by using correlation metrics based on soft symbols rather than hard-limited symbols as are used in the prior art. Moreover, the present invention is easy to implement either by hardware or software, and is also conducive to use with existing variable rate communication systems such as a CDMA spread spectrum system.
Specifically, in one embodiment, the present invention receives demodulated soft symbols representing a data frame transmitted at a certain frame rate. The present invention then generates a plurality of decoded bit streams from the demodulated soft symbols, where each of the plurality of decoded bit streams is for testing one of a plurality of rate hypotheses for the frame rate of the data frame. The present invention next re-encodes each of the plurality of decoded bit streams to generate a plurality of re-encoded bit streams, each of which corresponds to one of the plurality of decoded bit streams. Then, the present invention generates a plurality of correlation metrics by correlating each of the plurality of re-encoded bit streams with the demodulated soft symbols, and also generates a plurality of frame quality indicators, such that a frame quality indicator is generated for each of the plurality of decoded bit streams which has a cyclic redundancy code (CRC) coupled thereto. Using the plurality of correlation metrics and the plurality of frame quality indicators, the present invention determines the frame rate of the transmitted data frame. In so doing, this embodiment of the present invention provides a method for frame rate determination in a variable rate communication system.
In another embodiment, the present invention includes the above recited steps and further the present invention processes the demodulated soft symbols using a first symbol manipulation scheme and, from the processed demodulated soft symbols, generates a first decoded bit stream for testing a first rate hypothesis for the frame rate. The present invention also processes the demodulated soft symbols using a second symbol manipulation scheme and, from the processed demodulated soft symbols, generates a second decoded bit stream for testing a second rate hypothesis for the frame rate.
The present invention also describes in detail the device for performing the steps of the above described method.
These and other advantages of the present invention will no doubt become clear to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various drawing figures.
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Bost Dwayne
Davis Temica M.
Koninklijke Philips Electronics , N.V.
Zawilski Peter
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