Transmitter linearization
An apparatus and method for reducing unwanted spectral emissions of a complex signal to be transmitted comprising calculating the nth power of the complex signal to be transmitted, calculating the complex conjugate of the nth power of the complex signal to be transmitted, applying a scaling factor to the complex conjugate to form a scaled correction signal, and adding the scaled correction signal to the signal to be transmitted.
1. A method of reducing unwanted spectral emissions of a complex signal for transmission comprising:
calculating an nth power of the complex signal for transmission;
calculating a complex conjugate of the nth power of the complex signal for transmission;
applying a scaling factor to the complex conjugate to form a scaled correction signal; and
adding the scaled correction signal to the complex signal for transmission such that unwanted emissions are reduced when the signal is transmitted.
2. The method of claim 1 further comprising applying a phase change to the scaled correction signal.
3. The method according to claim 1 wherein calculating the complex conjugate comprises retrieving a pre-determined value from a lookup table.
4. The method according to claim 3 wherein the lookup table comprises at least two inputs of at least 3-bits and a 4-bit output.
5. The method according to claim 3 wherein the lookup table comprises hard-wired logic arranged to map input bits to output bits.
6. The method according to claim 2 wherein applying the scaling factor and the phase change comprises multiplying the complex conjugate by a vector comprising A=α·cos θand B=α·sin θ, wherein αis the scaling factor and θ is the phase change.
7. The method according to claim 6 wherein the complex signal for transmission is an LTE signal and A and B are determined based on an RB start value.
8. The method according to claim 6 wherein A and B are determined based on a quadratic profile of a power of the unwanted spectral emissions.
9. The method according to claim 6 wherein the signal for transmission is a WiMAX signal.
10. The method according to claim 1 further comprising calculating a plurality of complex conjugates, applying a scaling factor to each of the complex conjugates to form a plurality of scaled correction signals, and adding each of the scaled correction signals to the complex signal for transmission.
11. The method according to claim 10 further comprising applying a phase change to at least one of the scaled correction signals.
12. The method according to claim 1 where the complex signal for transmission comprises in-phase and quadrature components.
13. The method according to claim 1 wherein the method is carried out in the digital domain.
14. An apparatus arranged to reduce unwanted spectral emissions of a signal for transmission comprising:
a first processor block arranged to calculate an nth power of a complex signal for transmission;
a second processor block arranged to calculate a complex conjugate of the nth power of the complex signal for transmission;
a scaling block arranged to apply a scaling factor to the complex conjugate to form a scaled correction signal; and
a summing block arranged to add the scaled correction signal to the complex signal for transmission such that unwanted emissions are reduced when the signal is transmitted.
15. A non-transitory computer readable medium comprising instructions that when executed by a processor causes the processor to carry out the method of claim 1 .
16. the method according to claim 7 wherein A and B are determined based on an RB start value and an RB num value.