Estimating Eb/Nt in a CDMA system using power control bits
View Patent ↗A portable communication device including a power control system which estimates E b /N t by determining the variance of the noise components of PCBs that are received on the fundamental traffic channel. The power control system includes a demodulator for demodulating a BPSK modulated (or PAM) first signal from a base station, a noise variance calculation circuit that samples the perpendicular noise component of the demodulated signal to determine a noise variance, a power estimation circuit that measures the power of the demodulated signal and provides an estimate of the power of the first signal by eliminating the noise variance from the demodulated signal, and a comparator that compares the ratio of the power estimate and the noise variance to a threshold. The comparator output is a power up or power down signal to the base station.
1. A power control system including:
a demodulator that demodulates a power control bit (PCB) having a power value, the demodulated PCB including a noise component that is perpendicular to a signal axis of the PCB;
a first circuit coupled to the demodulator for receiving the demodulated PCB, the first circuit determining a noise variance of the demodulated PCB from the perpendicular noise component;
a second circuit coupled to the demodulator and the first circuit, the second circuit providing an estimate of the power value of the PCB by eliminating the noise variance of the perpendicular noise component from the demodulated PCB; and
an estimator coupled to the first circuit and the second circuit, the estimator calculating the ratio of the power value estimate and the noise variance.
2. The system of claim 1 wherein the estimator compares the ratio to a threshold value to provide one of a power up and power down signal to a base station.
3. The system of claim 1 wherein the PCB is a BPSK modulated signal.
4. The system of claim 1 wherein the PCB is a PAM signal.
5. The system of claim 1 wherein the first circuit samples a single demodulated PCB to provide an instantaneous noise variance value.
6. The system of claim 1 wherein the first circuit samples a plurality of demodulated PCBs to provide an average noise variance value.
7. The system of claim 6 wherein the plurality of demodulated PCBs are within a PCG.
8. The system of claim 1 wherein the second circuit provides an instantaneous estimate of the power value of the PCB.
9. The system of claim 1 wherein the second circuit computes a power value for a plurality of PCB to provide an average power value estimate.
10. The system of claim 1 wherein the second circuit employs a histogram-based approach to determine whether the average power value estimate is above or below a predetermined threshold.
11. A power control system for making inner loop forward control power decisions and generating a corresponding power control signal for transmission to a base station, including:
a demodulator that demodulates a power control bit (PCB) from the base station, the PCB having a power value, the demodulated (PCB) including a noise component that is perpendicular to a signal axis of the PCB;
a noise variance calculation circuit coupled to the demodulator for receiving the demodulated PCB, the noise variance calculation circuit sampling the perpendicular noise component to determine a noise variance of the demodulated PCB;
a power estimation circuit coupled to the demodulator and the noise variance calculation circuit, the power estimation circuit providing an estimate of the power value of the PCB by eliminating the noise variance of the perpendicular noise component from the demodulated PCB; and
an estimator coupled to the noise variance calculation circuit and the power estimation circuit, the estimator calculating the ratio of the power value estimate and the noise variance; and
a comparator for comparing the ratio to a threshold value to provide one of a power up and power down signal to the base station.
12. The system of claim 11 wherein the PCB is a BPSK modulated signal.
13. The system of claim 11 wherein the PCB is a PAM signal.
14. The system of claim 11 wherein the noise variance calculation circuit samples a single demodulated PCB to provide an instantaneous noise variance value.
15. The system of claim 11 wherein the noise variance calculation circuit samples a plurality of demodulated PCBs to provide an average noise variance value.
16. The system of claim 15 wherein the plurality of demodulated PCBs are within a PCG.
17. The system of claim 11 wherein the power estimation circuit provides an instantaneous estimate of the power value of the PCB.
18. The system of claim 11 wherein the power estimation circuit computes a power value for a plurality of PCBs to provide an average power value estimate.
19. The system of claim 11 wherein the power estimation circuit employs a histogram-based approach to determine whether the average power value estimate is above or below a predetermined threshold.
20. A method for making control power decisions including the steps of:
demodulating a PCB from a base station;
sampling a noise component of the demodulated PCB which is perpendicular to the fade line to determine the Nt associated with the demodulated PCB;
estimating the E b associated with the PCB by eliminating the variance of the sampled perpendicular noise component from the square of the demodulated PCB;
computing an estimated E b /N t ;
comparing the estimated E b /N t to a threshold value; and
providing one of a power up and power down signal to the base station depending upon whether E b /N t is greater than or less than the threshold value.
21. The method of claim 20 wherein the PCB is a BPSK modulated signal.
22. The method of claim 20 wherein the PCB is a data bit.
23. The method of claim 20 wherein the noise component of a single demodulated PCB is sampled to provide an instantaneous estimate of the variance of the sampled noise component.
24. The method of claim 20 wherein the device samples a plurality of demodulated PCBs to provide an average of a plurality of estimates of the variance of the sampled noise component.
25. The method of claim 24 wherein the plurality of demodulated PCBs are within a PCG.
26. The method of claim 20 wherein E b is estimated for a plurality of PCBs to provide an average estimate of E b .