JP2004538713A - Method for supporting variable data rates in a CDMA system - Google Patents

Abstract

An improved method (10) for supporting a variable data rate between a transmitter and a receiver in a code division multiple access (CDMA) data communication system is provided. The method includes providing a control channel and at least one application data channel between the transmitter and the receiver (12), and transmitting user data from the transmitter to the receiver via the application data channel (14). ), Transmitting a data rate indicator indicating a data rate at which the user data is transmitted by the transmitter from the transmitter to the receiver via the control channel (16), and using the data rate indicator, Decoding this user data (18) is included.

Description

【Technical field】
[0001]
The present invention relates generally to code division multiple access (CDMA), and more particularly, to a method for supporting variable data rates in a CDMA data communication system.
[Background Art]
[0002]
Wireless telecommunications systems have experienced dramatic growth over the past decade as their system reliability and system capacity have increased. Wireless communication systems are utilized in a variety of applications where landline-based systems are impractical or unusable. Wireless communication systems are also an economically viable alternative to replacing aging telephone lines and outdated telephone equipment. Unfortunately, the portion of the radio frequency band available for use in wireless communication systems is a finite and essential resource that must be shared between various service providers. Thus, there is always a need for improving the efficiency and capacity of wireless communication systems.
[0003]
Code division multiple access (CDMA) has shown particular promise in improving the efficiency and capacity of wireless communication systems. CDMA is a data communication technology based on the principle of spread spectrum communication. In a CDMA system, the same part of the frequency spectrum is used for communication by all system subscribers. Each per-subscriber baseband data signal is multiplied by a code sequence having a rate much higher than the data rate, commonly referred to as a "spreading code." This technique is called "spread spectrum," since the transmission spectrum becomes much wider than the spectrum of the baseband data signal by performing this encoding. The assignment of a unique spreading code to each communication link allows a distinction between subscriber units and their communication. Because communications from different subscriber units are performed by transmissions on the same frequency band, CDMA allows more users to access the wireless network than using other conventional data communication techniques such as time division multiple access or frequency division multiple access. Can be accessed simultaneously.
DISCLOSURE OF THE INVENTION
[Problems to be solved by the invention]
[0004]
In CDMA systems, users sometimes need to transmit data at different data rates. In the variable rate service, the data rate may be changed between frames depending on the application. In one known technique, blind rate detection is used to determine the data rate for a given frame received at the receiver. In this method, the receiver needs to determine the data rate of the received frame prior to the frame processing. Each frame must be processed separately at each possible data rate before the transmitter makes a determination as to which data rate was used. The greater the number of data rates supported by the service, the greater the processing power required on the receiver side, and the more complicated the processing configuration. Therefore, it is desirable to provide a reduced complexity and reliable method for supporting variable data rates in CDMA systems.
[Means for Solving the Problems]
[0005]
According to the present invention, there is provided an improved method for supporting a variable data rate between a transmitter and a receiver in a code division multiple access (CDMA) data communication system. The method includes providing a control channel and at least one application data channel between a transmitter and a receiver, transmitting user data from the transmitter to the receiver via the application data channel, and controlling from the transmitter. Transmitting, over the channel, to the receiver, a data rate indicator indicating a data rate at which the user data is transmitted by the transmitter, and using the data rate indicator to decode the user data at the receiver. included.
[0006]
The present invention, and its objects and advantages, will be more fully understood with reference to the following specification and accompanying drawings.
BEST MODE FOR CARRYING OUT THE INVENTION
[0007]
CDMA techniques are commonly implemented in cellular wireless network communication systems. In a cellular type system, a service area is geographically divided into several adjacent radio coverage areas, called cells. Each cell in the network has at least one base station that establishes a communication link with several mobile stations located in or near the cell. A base station and a mobile station, as is well known in the art, are transceivers that can transmit and receive data signals, and communicate with the mobile station when the mobile station moves from one cell to an adjacent cell. The link is maintained by being handed over to the base station in the adjacent cell. In this way, the mobile station can move between cells without breaking its communication link. Although the following description refers to a cellular wireless network system, it is readily understood that CDMA technology can be used in other types of data communication systems.
[0008]
FIG. 1 is a flowchart illustrating an improved method for supporting variable data rate transmission between a transmitter and a receiver in a CDMA data communication system. The communication link is configured such that a dedicated control channel and at least one application data traffic channel are provided between the transmitter and the receiver as described in step 12. It is envisioned that the control channel operates at a fixed data rate, while the application data channel can support a variable data rate.
[0009]
Data is transmitted in blocks of bits called frames, and the data rate is defined as the number of bits transmitted per frame. To support variable rate transmission, a data rate indicator is transmitted by the transmitter over the control channel to the receiver (14), while simultaneously transmitting user data over the application data channel by the transmitter. (16). According to the invention, the frame size used for the control channel is shorter than the frame size used for the application data channel.
[0010]
In transmitting the data rate to the receiver, a 4-bit binary indicator is preferably used. The value of the indicator has a correlation with a particular data rate (ie, bits per frame) and the corresponding frame period. In this example, when the value of the indicator is “0000”, it indicates the highest supported data rate, and when the value is “1111”, it indicates the lowest supported data rate. The data rate indicator and the corresponding data rate and frame period are stored in a lookup table provided in the receiver. It is assumed that the reference table is arranged in order from the highest data rate to the lowest data rate. In an alternative embodiment, the data rate indicator may indicate the actual data rate used by the transmitter.
[0011]
Upon receiving the data rate indicator from the transmitter, the receiver decodes it. Once the data rate has been determined, the receiver can decode the user data received from the transmitter via the application data channel as shown in step 18. In this way, the user data payload can be different between frames. The data rate indicator need only be sent when the data rate changes, but the data rate indicator can also be sent for each of the user data payloads sent between the transmitter and the receiver. Suppose.
[0012]
In a cellular network system, a base station and a mobile station each have the ability to perform transmission and reception functions. Transmission from the base station to the mobile station is called a downlink or forward channel communication link, while transmission from the mobile station to the base station is called an uplink or reverse channel communication link. Therefore, it is understood that the above-described technique can be applied to transmission in any direction.
[0013]
Various wideband CDMA standards have been proposed for use in third generation wireless personal communication systems. Unlike earlier CDMA standards (eg, IS-95), the proposed wideband CDMA standard includes one or more dedicated control channels that can be used to transmit data rate indicators. The Wideband CDMA standard (commonly referred to as "CDMA2000") proposed by the American Telecommunications Industry Association is one such wideband CDMA standard. As described further below, the improved approach of the present invention is particularly suited for use with CDMA2000. Although the following description refers to CDMA2000, the invention includes (but is not limited to) the wideband CDMA standard proposed by ARIB and ETSI and the wideband CDMA standard proposed by ETRI It is readily understood that other CDMA standards can be implemented.
[0014]
FIG. 2 shows four different dedicated uplink channels proposed for CDMA2000. The fundamental channel 22 and one or more supplemental channels 24 and 26 are for transmitting user data. The dedicated control channel 28 is for transmitting control information, and the pilot channel 30 is for transmitting a timing signal for uplink synchronous detection. The four uplink channels are separated by Walsh codes as is well known in the art.
[0015]
In a preferred embodiment of the present invention, user data is transmitted over either the fundamental channel 22 or the supplemental channels 24 and 26 with a frame length of 20 ms. Further, a dedicated control channel 28 is used to transmit the data rate indicator. Preferably, the dedicated control channel 28 uses a 5 ms frame length with a fixed data rate.
[0016]
Similarly, three individual downlink channels have been proposed for CDMA2000. The fundamental channel and the supplemental channel transmit user data, and the dedicated control channel transmits control information. In the present invention, a dedicated control channel is used to transmit a data rate indicator.
[0017]
While this invention has been described in its presently preferred form, it will be understood that it can be modified without departing from the spirit of the invention as set forth in the appended claims.
[Brief description of the drawings]
[0018]
FIG. 1 is a flowchart illustrating a method for supporting a variable data rate according to the present invention. FIG. 2 is a diagram illustrating four different dedicated uplink channels proposed for CDMA2000.

Claims (10)

Providing a control channel having a fixed data rate between the transmitter and the receiver and providing at least one application data channel;
Transmitting user data in the form of a spread spectrum data signal from the transmitter to the receiver via the application data channel,
Transmitting a data rate indicator indicating a data rate at which the user data is transmitted by the transmitter from the transmitter to the receiver via the control channel;
Decoding the user data based on a portion of the data rate indicator received at the receiver,
A method for supporting a variable data rate between a transmitter and a receiver in a data communication system. The method of claim 1, wherein the step of transmitting user data further comprises changing the data rate at which the user data is transmitted to the receiver. The method of claim 1, wherein the step of transmitting the data rate indicator is performed simultaneously with the step of transmitting user data. The method of claim 3, wherein the data rate indicator is transmitted by a data packet having a fixed length that is less than a fixed length of a data packet used to transmit the user data. Decoding the user data, extracting a data rate corresponding to the user data, storing the data rate in a memory area provided in the receiver, and decoding the user data using the data rate The method of claim 1, further comprising: The method of claim 1, wherein the step of transmitting a data rate indicator further comprises using a dedicated control channel defined by the CDMA2000 standard. Transmitting user data in the form of a spread spectrum data signal over an application data channel;
Transmitting, via a control channel, a data rate indicator indicating a data rate at which the user data is transmitted;
Decoding the user data based on a portion of the data rate indicator received at a receiver;
A method for supporting a variable data rate in a data communication system using a wideband code division multiple access (CDMA) scheme. The method of claim 7, wherein the step of transmitting user data further comprises using at least one of a dedicated fundamental channel and a dedicated supplemental channel defined by the CDMA2000 standard. The method of claim 7, wherein the step of transmitting a data rate indicator further comprises using a dedicated control channel defined by the CDMA2000 standard. The method according to claim 7, wherein the wideband CDMA scheme is selected from a group having a CDMA2000 standard proposed by TIA, a WCDMA standard proposed by ARIB and ETSI, and a TTAI and TTA II standard proposed by ETRI.

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