Sporadic channel filtering

• US 9,246,721 B1
• Filed: 05/18/2015
• Issued: 01/26/2016
• Est. Priority Date: 12/16/2014
• Status: Expired due to Fees

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Martinez, Vincent Pierre
• Primary Examiner(s): Tran, Khai
• Application Number:
  US14/714,857
• Time in Patent Office: 253 Days
• Field of Search: 375/296, 375/298, 375/350, 331/17
• US Class Current: 1/1
• CPC Class Codes: H03F 3/24 of transmitter output stages
• CPC Class Codes: H04B 1/0007 wherein the AD/DA conversion occurs at radiofrequency or intermediate frequency stage
• CPC Class Codes: H04B 1/001 Channel filtering, i.e. selecting a frequency channel within the SDR system multiplexing of multicarrier modulation signals being represented by different frequencies H04L5/06; multiplexing of multicarrier modulation signals H04L5/023
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence
• CPC Class Codes: H04B 2001/0408 with power amplifiers
• CPC Class Codes: H04L 25/03834 using pulse shaping
• CPC Class Codes: H04L 25/08 Modifications for reducing interference; Modifications for reducing effects due to line faults ; Receiver end arrangements for detecting or overcoming line faults
• CPC Class Codes: H04L 27/2607 Cyclic extensions
• CPC Class Codes: H04L 27/2627 Modulators

Abstract

A digital up-converter (DUC) circuit for performing digital channel filtering of an incoming baseband digital signal. The proposed circuit reduces the complexity of the channel module filter of the DUC. This is achieved by taking advantage of the structure of the underlying symbol waveforms carried by the incoming baseband digital signal which have one or more known discontinuities comprising random amplitude and/or phase. Namely, the channel filter module is activated only for the digital samples located around the known discontinuities and is deactivated for the remaining digital samples. Further, the switching of the channel filter module from one state to another can be performed according to a smooth function so that further discontinuities are not introduced in the incoming baseband digital signal. A method and a computer program are also disclosed.

Claims

1. A digital up-converter, DUC, circuit for performing digital channel filtering of an incoming baseband digital signal and up-converting the filtered incoming baseband digital signal into an intermediate Frequency, IF, baseband digital signal, the incoming baseband digital signal comprising digital samples representative of a plurality of contiguous symbols having at least a first discontinuity comprising random amplitude and/or phase, between symbols taken two-by-two, the DUC comprising:

a channel filter module arranged to perform digital channel filtering on the digital samples, the channel filter module having an active mode and a standby mode of operation, wherein;

in the active mode, digital channel filtering is performed; and

,

in the standby mode, digital channel filtering is not performed;

a processing unit, such as a processor, operably coupled to the channel filter module and arranged to set the channel filter module;

in the active mode, for a given number N of digital samples around the first discontinuity; and

,

in the standby mode, for the remaining digital samples;

wherein the given number N of digital samples is substantially lower than the number of digital samples associated with one symbol.

2. The DUC circuit of claim 1, wherein:

the symbols are OFDM symbols, each having respective cyclic prefix, CP, thereby creating a second discontinuity comprising random amplitude and/or phase, between the CP and respective OFDM symbol taken two-by-two; and

,

the processing unit is further arranged to set the channel filter module in the active mode, for a given number M of digital samples around the second discontinuity;

wherein the given number M of digital samples is substantially lower than the number of digital samples associated with one OFDM symbol.

3. The DUC circuit of claim 1, wherein the processing unit is further arranged to switch the channel filter module between the active mode and the standby mode according to a smooth weight function.

4. The DUC circuit of claim 3, wherein the smooth weight function is a raised cosine waveform.

5. The DUC circuit of claim 3, wherein the processing unit switches for the first and/or second discontinuity during a cycle of the smooth weight function.

6. The DUC circuit of claim 1, wherein the channel filter module comprises a FIR low-pass filter.

7. A transmitter unit for a wireless communication system, the transmitter unit comprising:

the digital up-converter, DUC, circuit of claim 1; and

,

a digital baseband interface operably coupled to the DUC and arranged to provide the incoming baseband digital signal.

8. The transmitter of claim 7, wherein the digital baseband interface comprises one the Open Base Station Architecture Initiative, OBSAI, or the common public radio interface, CPRI.

9. A method of performing digital channel filtering of an incoming baseband digital signal in digital up-converter, DUC, circuit and up-converting the filtered incoming baseband digital signal into an intermediate Frequency, IF, baseband digital signal, the incoming baseband digital signal comprising digital samples representative of a plurality of contiguous symbols having at least a first discontinuity comprising random amplitude and/or phase, between symbols taken two-by-two, the method comprising:

providing a channel filter module arranged to perform digital channel filtering on the digital samples, the channel filter module having an active mode and a standby mode of operation, wherein;

in the active mode, digital channel filtering is performed; and

,

in the standby mode, digital channel filtering is not performed;

providing a processing unit, such as a processor, operably coupled to the channel filter module and arranged to set the channel filter module;

in the active mode, for a given number N of digital samples around the first discontinuity; and

,

in the standby mode, for the remaining digital samples;

wherein the given number N of digital samples is substantially lower than the number of digital samples associated with one symbol.

10. The method of claim 9, wherein:

the symbols are OFDM symbols, each having respective cyclic prefix, CP, thereby creating a second discontinuity comprising random amplitude and/or phase, between the CP and respective OFDM symbol taken two-by-two; and

,

the method further comprising;

setting the channel filter module in the active mode, for a given number M of digital samples around the second discontinuity, wherein the given number M of digital samples is substantially lower than the number of digital samples associated with one OFDM symbol.

11. The method of claim 9, further comprising switching the channel filter module between the active mode and the standby mode according to a smooth weight function.

12. The method of claim 11, wherein the smooth weight function is a raised cosine waveform.

13. The method of claim 11, wherein the switching for the first and/or second discontinuity is performed during a cycle of the smooth weight function.

14. The method of claim 9, wherein the channel filter module comprises a FIR low-pass filter.

15. A computer program product stored in a non-transitory computer-readable storage medium that stores computer-executable code for performing digital channel filtering of an incoming baseband digital signal and up-converting the filtered incoming baseband digital signal into an intermediate Frequency, IF, baseband digital signal, the incoming baseband digital signal comprising digital samples representative of a plurality of contiguous symbols having at least a first discontinuity comprising random amplitude and/or phase, between symbols taken two-by-two, the computer-executable process causing a processor computer to perform the method according to claim 9.