Multiple user digital receiver apparatus and method with time division multiplexing

• US 5,621,730 A
• Filed: 12/07/1992
• Issued: 04/15/1997
• Est. Priority Date: 06/13/1991
• Status: Expired due to Term

• Current Assignee: Microelectronics Technology Inc (MTI Laboratory Inc)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Kelley, Edwin A.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): HOM, SHICK C
• Application Number:
  US07/986,180
• Time in Patent Office: 1,590 Days
• Field of Search: 370/20, 370/50, 370/70, 370/72, 370/84, 370/112, 370/77, 381/4, 381/7, 381/13, 375/17, 375/103, 375/241
• US Class Current: 370/345
• CPC Class Codes: G01S 19/13 Receivers
• CPC Class Codes: G01S 19/35 Constructional details or hardware or software details of the signal processing chain
• CPC Class Codes: G01S 19/36 relating to the receiver frond end
• CPC Class Codes: H04B 1/0003 Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain digital baseband systems H04L25/00; digital modulation/demodulation H04L27/00; CDMA H04B1/707; TDMA H04B7/2643; image transmission H04N5/00
• 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 1/0017 Digital filtering H04B1/001 takes precedence; digital filters per se H03H17/00
• CPC Class Codes: H04B 1/006 using switches for selecting the desired band H04B1/0057 takes precedence
• CPC Class Codes: H04B 1/16 Circuits
• CPC Class Codes: H04B 1/26 for superheterodyne receivers multiple frequency-changing H03D7/16
• CPC Class Codes: H04B 1/406 with more than one transmission mode, e.g. analog and digital modes
• CPC Class Codes: H04H 40/00 Arrangements specially adapted for receiving broadcast information

Abstract

A digital receiver apparatus and method, designed for multiple simultaneous users, digitizes a received analog RF signal and tunes to multiple desired frequencies of the received signal on a time division multiplexed basis. After filtering by a finite impulse response (FIR) filter that also operates in time division multiplexing for multiple service bands, the selected signals are digitally demodulated and signal processed, again on a time-shared basis. Different service bands are accommodated at the same time by separate FIR filters, each including a coefficient memory for its particular service band. The multiplexed frequency signal for each band is multiplied by the coefficients of its respective FIR filter memory in a common complex multiplier. The results are demultiplexed and directed to respective accumulators for decimation in accordance with the FIR coefficient characteristics.

Claims

1. A multiple use radio frequency (RF) receiver, comprising:

means for providing anti-alias filtering for a received analog RF signal;

gain control amplifier means for providing amplification to the filtered and received analog RF signal;

means for digitizing the amplified, filtered and received analog RF signal;

multiple simultaneous digital tuner means for selecting, by time division multiplexing, signals at at least three desired frequencies from the digitized signal, with said desired frequencies distributed at unequal frequency spacings along a frequency spectrum, said digital tuner means consisting of a modified programmable direct digital frequency synthesizer, selecting signals at said desired frequencies from separate RF service bands that are distributed at unequal frequency spacing along said frequency spectrum;

digital filter means for isolating the signals at the desired frequencies selected by said tuner means from interfering signals by time division multiplexing, said digital filter means comprising a plurality of digital finite impulse response, FIR, filters that include respective FIR filter coefficient memories corresponding to said service bands, means for digitally time division multiplexing among said FIR filter coefficient memories, in synchronism with said multiple simultaneous digital tuner means, and means controlling said multiplexing among said FIR filter coefficient memories in synchronism with the selection of signals at said desired frequencies from a digitized signal so that the selected frequency signals for each service band are processed by a corresponding FIR filter coefficient memory for that service band, said FIR filters including respective accumulators for each of said service bands, a complex multiplier for multiplying multiplexed selected frequency signals by the FIR filter coefficients for their respective service bands, and de-multiplexing means for directing the results of said multiplications for each service band to a respective accumulator; and

digital demodulator and signal processing means for digitally demodulating and signal processing the signals at the desired frequencies selected by said tuner means and isolated by said digital filter means, wherein digital demodulation occurs in synchronism with digital tuner multiplexing.

2. The multiple user radio frequency receiver of claim 1 wherein said modified programmable direct digital frequency synthesizer comprises accumulators and generates a staircase of phase values which approximates a ramp at a predetermined frequency.

3. The RF receiver of claim 1, said digital demodulator and signal processing means processing the output of each accumulator separately.

4. The RF receiver of claim 3, said digital demodulator and audio processing means separating the processing of the output of each accumulator by time division demultiplexing.

5. The RF receiver of claim 4, wherein said digital demodulator and signal processing means are implemented by a single digital signal processor programmed to perform said time division multiplexed processing.

6. A multiple use radio frequency (RF) receiver, comprising:

means for providing anti-alias filtering for a received RF signal;

gain control amplifier means for providing amplification to the filtered RF signal;

means for digitizing the filtered and amplified received analog RF signal;

digital tuner means for selecting, by time division multiplexing signals at least three desired frequencies from the digitized signal, with said desired frequencies distributed at unequal frequency spacings along a frequency spectrum, said digital tuner means selecting said signals from a single RF service band;

digital filter means for isolating the signals at the desired frequencies selected by said digital tuner means from interfering signals, said digital filter means comprising a digital finite impulse response, FIR, filter that includes a filter coefficient memory, containing the FIR filter coefficients, for said service band, respective accumulators for the signals at each of said desired frequencies, a complex multiplier for multiplying the signals at the frequencies selected by said tuner means by said FIR filter coefficients from said memory, and demultiplexing means for directing the results of multiplications for each desired frequency to a respective accumulator; and

digital demodulator and signal processing means for digitally demodulating and signal processing the signals at the desired frequencies selected by said tuner means and isolated by said digital filter means.

7. The RF receiver of claim 6, said digital demodulator and signal processing means processing the output of each accumulator separately.

8. The RF receiver of claim 7, said digital demodulator and audio processing means separating the processing of the output of each accumulator by time division demultiplexing.

9. The RF receiver of claim 8, wherein said digital demodulator and signal processing means are implemented by a single digital signal processor programmed to perform time division multiplexed processing.