Method and apparatus for compensating code channel power in a transmitter
View Patent ↗It has now been found that in some transmitter implementations which transmit multiple code channels, for example CDMA transmitters, the observed power for each code channel at the output relative to the other code channels is dependent upon the total transmit power due to non-linearities in the transmitter. Methods and apparatus are provided which use pre-set digital gains or digital gain adjustments to compensate for the non-linearities as a function of total transmit power such that at the output, the desired relative powers are observed.
1. A transmitter comprising:
one or more code channel elements comprising at least one of:
a pilot generator;
a fundamental channel (FCH) encoder;
a supplemental channel (SCH) encoder; and
a dedicated control channel (DCCH) encoder;
each code channel element having a respective digital gain element;
a compensation element adapted to apply a set of digital gains to the digital gain elements in order to apply the set of digital gains to a corresponding set of code channels, the set of digital gains compensating for non-linearities in the transmitter as a function of transmit power to substantially achieve a desired relationship between code channel powers of said set of code channels.
2. The transmitter according to claim 1 wherein the compensation element comprises a memory containing for at least one code channel, a respective pre-set digital gain value for the code channel for each of a plurality of states of the set of code channels, and for a plurality of ranges of total transmit power.
3. The transmitter according to claim 1 wherein the compensation element comprises:
a controller adapted to configure the transmitter to have a selected state of a plurality of states, each state comprising at least one of:
a) a selection of a particular set of code channels from a set of available code channels;
b) a selection of a particular encoder format for at least one code channel;
c) a selection of a particular signal format for at least one code channel; and
d) a selection of a particular data rate for at least one code channel;
a memory containing for each state, a pre-set digital gain value for each code channel for each of a plurality of ranges of transmit power;
wherein for each code channel the controller is adapted to apply the appropriate pre-set digital gain value as a function of the state and total transmit power as one digital gain of said set of digital gains.
4. The transmitter according to claim 1 wherein the compensation element comprises a memory containing for at least one code channel, a nominal digital gain for the code channel for each of a plurality of states of the set of code channels, and for a plurality of ranges of total transmit power, the compensation element further configured to combine a respective gain adjustment with a nominal digital gain value to generate the digital gains to be applied to the digital gain elements for the at least one code channel.
5. The transmitter according to claim 4 wherein the compensation element comprises:
a controller adapted to configure the transmitter to have a selected state of a plurality of states, each state comprising at least one of:
a) a selection of a particular set of code channels from a set of available code channels;
b) a selection of a particular encoder format for at least one code channel;
c) a selection of a particular signal format for at least one code channel; and
d) a selection of a particular data rate for at least one code channel;
the memory containing for each state, a pre-set digital gain adjustment for each code channel for each of a plurality of ranges of transmit power;
wherein for each code channel the controller is adapted to employ an appropriate pre-set digital gain adjustment as a function of the state and total transmit power as said respective gain adjustment.
6. The transmitter according to claim 1 further comprising:
a power control subsystem adapted to control the transmit power.
7. The transmitter according to claim 6 wherein the power control subsystem comprises:
a power control function that provides an output to the compensation element;
an Automatic Gain Controller (AGC) configured to receive an output from the power control function;
a digital-to-analog converter (DAC) configured to receive an output from the AGC and configured to output a control signal to an AGC amplifier that in part controls the transmit power.
8. The transmitter according to claim 1 further comprising a normalizer configured to receive outputs of each of the digital gain elements to normalize the outputs of the digital gain elements with respect to one another.
9. The transmitter according to claim 6 further comprising a Code Division Multiple Access (CDMA) spreader configured to:
receive outputs from the normalizer corresponding to outputs from the digital gain elements; and
generate I and Q outputs.
10. The transmitter according to claim 9 further comprising a digital-to-analog converter (DAC) configured to receive the I and Q outputs from the CDMA spreader in order to convert the I and Q outputs from the digital domain to the analog domain.
11. The transmitter according to claim 10 further comprising:
an IQ modulator;
an automatic gain control (AGC) amplifier;
a power amplifier;
and at least one antenna for transmitting a signal.
12. The transmitter according to claim 11 wherein the AGC amplifier is configured to receive an output from a power control system.
13. The transmitter according to claim 9 further comprising a mixer, to upconvert the signal to be transmitted, positioned between the AGC amplifier and the power amplifier.
14. The transmitter according to claim 1 further comprising a Code Division Multiple Access (CDMA) spreader configured to:
receive outputs of each of the digital gain elements; and
generate I and Q outputs.
15. The transmitter according to claim 14 further comprising a digital-to-analog converter (DAC) configured to receive the I and Q outputs from the CDMA spreader in order to convert the I and Q outputs from the digital domain to the analog domain.
16. The transmitter according to claim 15 further comprising:
an IQ modulator;
an automatic gain control amplifier (AGC);
a power amplifier;
and at least one antenna for transmitting a signal.
17. The transmitter according to claim 16 wherein the AGC amplifier is configured to receive an output from a power control system.
18. The transmitter according to claim 17 further comprising a mixer, to upconvert the signal to be transmitted, positioned between the AGC amplifier and the power amplifier.
19. The transmitter according to claim 1 wherein the compensation element is configured to, for each of at least one channel:
generate a digital gain by using a non-linear function that is a function of transmit power for a current state and for a current transmit power of the respective channel.
20. The transmitter according to claim 1 wherein the code channels are CDMA code channels.