Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1997-09-24
2001-09-18
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S342000, C370S468000
Reexamination Certificate
active
06292476
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to communications. More particularly, the present invention relates to a novel and improved communication system wherein a user transmits variable rate data on an allocated traffic channel, but when the user's variable transmission exceeds the capacity of the allocated traffic channel, the user is provided temporary use of an overflow channel to use with the allocated traffic channel in order to transmit the high rate data.
II. Description of the Related Art
The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of system users are present. Other multiple access communication system techniques, such as time division multiple access (TDMA), frequency division multiple access (FDMA) and AM modulation schemes such as amplitude companded single sideband (ACSSB) are known in the art. However the spread spectrum modulation technique of CDMA has significant advantages over these modulation techniques for multiple access communication systems. The use of CDMA techniques in a multiple access communication system are disclosed in U.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS”, assigned to the assignee of the present invention, of which the disclosure thereof is incorporated by reference. The use of CDMA techniques in a multiple access communication system is further disclosed in U.S. Pat. No. 5,103,459, entitled “SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM”, assigned to the assignee of the present invention, of which the disclosure thereof is incorporated by reference.
The method and apparatus for the generation of a pseudorandom noise (PN) signal that is well suited for CDMA applications is disclosed in U.S. Pat. No. 5,228,054 issued Jul. 13, 1993, entitled “POWER-OF-TWO LENGTH PSEUDO-NOISE SEQUENCE GENERATOR WITH FAST OFFSET ADJUSTMENT”, assigned to the assignee of the present invention, of which the disclosure thereof is incorporated by reference.
CDMA by its inherent nature of being a wideband signal offers a form of frequency diversity by spreading the signal energy over a wide bandwidth. Therefore, frequency selective fading affects only a small part of the CDMA signal bandwidth. Space or path diversity is obtained by providing multiple signal paths through simultaneous links from a mobile user through two or more cell-sites. Furthermore, path diversity may be obtained by exploiting the multipath environment through spread spectrum processing by allowing a signal arriving with different propagation delays to be received and processed separately. Examples of path diversity are illustrated in copending U.S. Pat. No. 5,101,501 entitled “SOFT HANDOFF IN A CDMA CELLULAR TELEPHONE SYSTEM”, and copending U.S. Pat. No. 5,109,390, entitled “DIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM”, both assigned to the assignee of the present invention and incorporated by reference herein.
An additional technique that may be used to increase the efficiency of the allocation of the communication resource is to allow the users of the resource to provide data at varying rates thereby using only the minimum amount of the communication resource to meet their service needs. An example of a variable rate data source is a variable rate vocoder, which is detailed in U.S. Pat. No. 5,414,796, issued May 9, 1995, entitled, “VARIABLE RATE VOCODER,” assigned to the assignee of the present invention and incorporated herein by reference. Since speech inherently contains periods of silence, i.e. pauses, the amount of data required to represent these periods can be reduced. Variable rate vocoding most effectively exploits this fact by reducing the data rate for these periods of silence.
In a variable rate vocoder of the type described in aforementioned U.S. Pat. No. 5,414,796, approximately 40% of the speech packets are coded at full rate. In the vocoder described in the patent application, the encoding rate is selected in accordance with the packet energy. When the packet energy exceeds a full rate threshold the speech is coded at full rate. In U.S. patent application Ser. No. 08/288,413, entitled, “IMPROVED METHOD AND APPARATUS FOR SELECTING AN ENCODING RATE IN A VARIABLE RATE VOCODER,” assigned to the assignee of the present invention and incorporated herein by reference, a method for determining based on characteristics of the speech packet if some of the packets to be coded at full rate can be coded at a lower rate without sacrificing perceived quality.
A variable rate speech encoder provides speech data at full rate when the talker is actively speaking, thus using the full capacity of the transmission packets. When a variable rate speech coder is providing speech data at a less that maximum rate, there is excess capacity in the transmission packets. A method for transmitting additional data in transmission packets of a fixed, predetermined size, wherein the source of the data for the data packets is providing the data at a variable rate is described in detail in U.S. Pat. No. 5,504,773, issued Apr. 2, 1996, entitled “METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION,” assigned to the assignee of the present invention, of which the disclosure thereof is incorporated by reference herein. In the above-mentioned patent application a method and apparatus is disclosed for combining data of differing types from different sources in a data packet for transmission.
SUMMARY OF THE INVENTION
A communications resource is typically divided into communications channels. Typically, each of these channels has the same capacity. A communications system could re-allocate the channels to the users for each transmission. This would theoretically allow for a maximally efficient allocation of the communication resource because each user would be using only the amount of the resource absolutely necessary. However, this technique would result in unacceptable complexity in the resulting receiver and transmitter design.
In the present invention, an efficient method of transmitting and receiving variable rate data is disclosed. In the present invention, each user is provided with a voice or data channel, also referred to as a traffic channel, specifically allocated for that user. In addition, each user is provided with selective access to a pool of overflow channels which are for use by all users of the communications resource. If a user needs to transmit at a rate higher than the capacity of the allocated traffic channel then the user transmits the information using both the allocated traffic channel and an overflow channel.
In the exemplary embodiment, the communication system is a code division multiple access (CDMA) communication system as is described in detail in the aforementioned U.S. Pat. Nos. 4,901,307 and 5,103,459. In the exemplary embodiment each of the traffic channels are orthogonal to one another. Each traffic channel is spread by a unique Walsh sequence that is orthogonal to the other Walsh sequences. The spread signals are then spread by pseudorandom noise (PN) sequences and then transmitted.
In the exemplary embodiment, the overflow channels are not provided with unique orthogonal Walsh spreading sequences, because this would decrease system capacity. Instead the system spreads the overflow channel portion of the information by a Walsh sequence that is not unique from those used in spreading the traffic channels. This portion is then spread by a PN sequence. The PN sequence is unique from the PN sequence used to spread the traffic channel of the same Walsh sequence. In the exemplary embodiment the traffic channel and the overflow channel use, although not necessarily, the same Walsh spreading sequence.
In the exemplary embodiment, the receiver continuously monitors both the traffic channel and the overflow channel. If the receiver determines that information is being transmitted on both
LaRocca Judith
Miller David S.
Zehavi Ephraim
Minhas Sandip (Micky) S.
Nguyen Chau
Nguyen Phuongchau Ba
Ogrod Gregory D.
Qualcomm Inc.
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