Adaptive power control in wideband CDMA cellular systems (WCDMA) and methods of operation

• US 6,690,652 B1
• Filed: 10/07/1999
• Issued: 02/10/2004
• Est. Priority Date: 10/26/1998
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Sadri, Ali S.
• Primary Examiner(s): Vu, Huy D.
• Assistant Examiner(s): Philpott, Justin M
• Application Number:
  US09/413,991
• Time in Patent Office: 1,587 Days
• Field of Search: 370/277-280, 370/311, 370/318, 370/252, 370/335, 370/342, 455/574, 455/343, 455/522, 379/395.01
• US Class Current: 370/252
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0015 characterised by the adaptation strategy
• CPC Class Codes: H04L 1/0059 Convolutional codes
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27
• CPC Class Codes: H04W 52/221 using past power control commands
• CPC Class Codes: H04W 52/223 predicting future states of the transmission
• CPC Class Codes: H04W 52/267 taking into account the information rate
• CPC Class Codes: H04W 52/42 in systems with time, space, frequency or polarisation diversity

Abstract

A WCDMA system includes a Base Station (BS) transmitter, or forward transmitter and a pilot channel that transmits control signals between the BS and a Mobile Station (MS) to reconfigure their transmitter/receiver. Reconfiguration is performed according to the prediction of the channel attenuation and the threshold set at the BS or MS based on its channel power probability density function separated into three distinct equal probable regions. In one embodiment, Seamless Rate Change (SRC)/Transmitter Power Control (TPC) logic uses the predicted channel attenuation to signal both the transmitter and the receiver in a channel to reconfigure their transmit power level according to the power density function (pdf) of the channel power and threshold level. A transmission rate is reduced when the power level is below the threshold and increased when the channel power is above threshold. The pilot channel is used to signal the mobile station and the base station.

Claims

1. A Wide-band Code Division Multiple Access (“

WCDMA”

) system comprising;

a base station and a mobile station;

a first channel including a baseband signal having a variable transmission rate for data transmission coupling the base station and the mobile station;

a pilot channel including a group of pilot data signals and a group of transmission power control data signals;

means responsive to the baseband signal for predicting power attenuation on the first channels by a probability density function based upon signal fading;

means establishing power thresholds in the first channel using the pilot data signals and based upon the probability density function divided into several ranges in which the probability of the power attenuation in each range is equal to achieve average constant power in the first channel; and

means responsive to the predicting power attenuation means to signal both a transmitter and a receiver in the first channel over the pilot channel to reconfigure the transmission rate according to the predicted power attenuation.

2. The system of claim 1 further comprising:

means for transmitting the base band signal in a series of frames, each frame including a plurality of transmit slots;

means for checking the predicted power attenuation signals in each slot;

means for checking each slot for predicted power attenuation signals indicative of the channel power;

means for increasing transmitter power when the predicted power attenuation falls below a threshold; and

means for reducing the transmitter power when the predicted power attenuation goes above the threshold.

3. The system of claim 1 further comprising:

means for increasing the transmission rate in a channel when the predicted power attenuation in a range goes above a threshold.

4. The system of claim 1 further comprising:

means for decreasing the transmission rate in a channel when the predicted power attenuation in a range falls below a threshold.

5. The system of claim 1 further comprising:

means for transmitting a data signal on the channel using an OFDM code and a long code corresponding to the orthogonal code length negotiated at transmission.

6. The system of claim 1 further comprising:

a QPSK modulator for processing the baseband signals.

7. The system of claim 1 further comprising:

multiplexing means multiplexing the baseband signal with the pilot signal; and

means spreading the multipexed signal by an appropriate orthogonal code and a long code corresponding to the orthogonal code length negotiated at transmission.

8. The system of claim 1 further comprising:

means for receiving a base band signal in a sense of frames, each frame including channel power values;

means for checking two antennas associated with both the base station and the mobile station for the channel power values; and

means for selecting a transmit antenna after comparing the channel power values for each antenna to a threshold.

9. The system of claim 1 wherein the means for reconfiguring the transmission rate further comprises:

means for defining a channel power probability density function separated into three equal first, second and third probability regions; and

means for operating the system in a transmit power control mode in which power is increased to a transmitter if the predicted power attenuation falls into the first probability region;

power to the transmitter is reduced if the predicted power attenuation falls into the third probability region, and no power adjustment is made to the transmitter if the predicated power attenuation falls into the second probability region.

10. The system of claim 1 wherein the means for reconfiguring the transmission rate further comprises:

means for spreading the baseband signal by an appropriate orthogonal code and a long code corresponding to the transmission rate;

means for defining a predicted channel power probability density function separated into three equal first, second and third probability regions; and

means for operating the system in a seamless rate change node in which a frame includes seamless rate change command bits in the pilot channel indicative of the predicted power attenuation whereby a transmit rate for a transmitter is reduced and a longer spreading code is used if the predicted power attenuation falls into the first region;

the transmit rate for the transmitter is decreased and a shorter spreading code is used if the predicted power attenuation falls into the third region and no power adjustment is made to the transmitter transmit rate and spreading code if the predicated power attenuation falls into the second probability region.

11. The system of claim 1 wherein the means for reconfiguring the transmission rate further comprises:

means for operating the system in an adaptive transmitter diversity mode in which one station predicts power attenuation for multiple antenna power thresholds in the first channel based upon a predicted power density function divided into several ranges in which the probability of every range is equal and transmits the predicted power attenuation values for each antenna to the other station via pilot bits;

means at the other station for comparing the predicted power attenuation values for each antenna to a threshold; and

means at the other station for selecting the antenna for signal transmission that has the greatest predicted power values exceeding the threshold.

12. In a wide band code division multiple access (“

WBCDMA”

) system comprising a base station including a transmitter and a receiver, a mobile station including a transmitter and a receiver, dual channels coupled between the base station and the mobile station, each including a baseband signal having a variable transmission rate and a pilot channel coupling the base station and the mobile station, a method for improved throughput, channel capacity and transmit power control of the system, comprising the of;

predicting power attenuation on the dual channels by a probability density function based upon signal fading;

establishing power thresholds in the dual channels using pilot data signal and based upon the probability of the power attenuation divided into several ranges in which the probability of every range is equal to achieve average constant power in the dual channels; and

signaling both a transmitter and a receiver in the dual channels over the pilot channel to reconfigure the transmission rate according to the predicted power attenuation.

13. The method of claim 12 further comprising the step of:

establishing a power threshold in the dual channel based upon a probability density function divided into several ranges in which the probability of every range is equal.

14. The method of claim 13 further comprising the step of:

increasing the transmission rate when the predicted power attenuation in a range goes above a threshold.

15. The method of claim 14 further comprising the step of:

decreasing the transmission rate when the predicted power attenuation in a range falls below a set threshold.

16. The method of claim 15 further comprising the step of:

transmitting a data signal on the dual channels using an OFDM code and a long code according to the transmission rate.

17. The method of claim 12 further comprising the step of:

processing the baseband signal using a QPSK modulator.

18. The method of claim 12 further comprising the steps of:

multiplexing the baseband signal with the pilot signal; and

spreading the multiplexed signal by an appropriate orthogonal code and a long code corresponding to the transmission rate.

19. The method of claim 12 further comprising the steps of:

transmitting the base band signal in a series of frames, each frame including a plurality of transmit slots;

including a group of pilot signals and a group of transmission power control signals in separate slots of a pilot channel;

checking the predicted power attenuation signals in each slot;

checking each slot for predicted power attenuation signals indicative of the channel power;

increasing transmitter power when the predicted power attenuation falls below a threshold; and

reducing the transmitter power when the predicted power attenuation goes above the threshold.

20. The method of claim 12 further comprising the steps of:

receiving a base band signal in a series of frames, each frame including channel power values;

checking two antennas associated with both the base station and the mobile station for the channel power values; and

selecting a transmit antenna after comparing the channel power values for each antenna to a threshold.