Method and rake receiver for phasor estimation in communication systems

• US 7,167,506 B2
• Filed: 03/02/2001
• Issued: 01/23/2007
• Est. Priority Date: 03/03/2000
• Status: Expired due to Fees

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems Incorporated (Broadcom, Inc.)
• Inventors: Baltersee, Jens, Fock, Gunnar, Schulz-Rittich, Peter
• Primary Examiner(s): Corrielus; Jean B.
• Application Number:
  US09/798,813
• Publication Number:
  US 20010038665A1
• Time in Patent Office: 2,153 Days
• Field of Search: 375/260, 375/130, 375/142, 375/143, 375/144, 375/147, 375/148, 375/150, 375/152, 375/285, 375/316, 375/346, 375/348, 375/349, 375/350
• US Class Current: 375/148
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• CPC Class Codes: H04B 1/7117 Selection, re-selection, allocation or re-allocation of paths to fingers, e.g. timing offset control of allocated fingers
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0214 of a single coefficient

Abstract

The invention relates to a channel estimation algorithm is proposed for a RAKE receiver for CDMA communication systems operating in the downlink of a mobile communication scenario yielding an improved phasor estimation. Received signals are distributed to a plurality of receiver fingers of a RAKE receiver. Each receiver finger i is assigned to a signal path of the transmitted signal which is subject to phase shift and power dissipation due to reflection, diffraction and scattering. According to the invention the approach partly cancels multipath/multiuser interference and offers the advantage of being able to cope with physically closely spaced multipaths.

Claims

1. A RAKE receiver for processing a received electromagnetic signal being a superposition of signal components of different signal propagation paths, the RAKE receiver comprising:

an analog-to-digital converter adapted to digitize the received signal;

a correlator adapted to decorrelate the digitized signal using a code sequence;

first circuitry adapted to generate received symbols from the decorrelated signal;

second circuitry adapted to generate, from the received symbols, derotated symbols for a first signal component corresponding to a first signal propagation path;

third circuitry adapted to generate, using the received symbols and the derotated symbols, an estimated phasor for the first signal component, wherein the derotated symbols are used to generate symbol decisions for the received electromagnetic signal; and

fourth circuitry adapted to generate a corrected phasor for the first signal component from the estimated phasor by reducing multipath interference from one or more other signal components corresponding to one or more other signal propagation paths, wherein the second circuitry is adapted to generate the derotated symbols using the corrected phasor.

2. The RAKE receiver of claim 1, wherein the multipath interference has a bandwidth substantially equal to the bandwidth of the received signal.

3. The RAKE receiver of claim 1, wherein the estimated phasor is a maximum likelihood estimated phasor.

4. The RAKE receiver of claim 1, wherein the second circuitry is adapted to multiply the received symbols by the corrected phasor to generate the derotated symbols for the first signal component.

5. The RAKE receiver of claim 1, wherein the third circuitry is adapted to generate the estimated phasor for the first signal component based on said symbol decisions derived from the derotated symbols for the first signal component.

6. The RAKE receiver of claim 5, wherein the third circuitry is adapted to generate the estimated phasor for the first signal component by:

summing the derotated symbols for the first signal component with derotated symbols for each of the one or more other signal components to generate an input to a decider adapted to generate the symbol decisions;

applying complex conjugation to the symbol decisions to output complex-conjugated symbol decisions; and

multiplying the complex-conjugated symbol decisions by the received symbols for the first signal component.

7. The RAKE receiver of claim 1, wherein the third circuitry is adapted to generate the estimated phasor for the first signal component based on pilot symbols.

8. The RAKE receiver of claim 1, wherein the third circuitry comprises a switch adapted to select either (i) symbol decisions derived from the derotated symbols for the first signal component or (ii) pilot symbols for use in generating the estimated phasor.

9. The RAKE receiver of claim 1, wherein the fourth circuitry is adapted to generate the corrected phasor for the first signal component using the estimated phasor for the first signal component and one or more other estimated phasors for the one or more other signal components.

10. The RAKE receiver of claim 9, wherein the fourth circuitry is adapted to generate the corrected phasor for the first signal component using timing error signals for the first and the one or more other signal components.

11. The RAKE receiver of claim 1, wherein the fourth circuitry is adapted to:

estimate the multipath interference for the first signal component; and

subtract the estimated multipath interference from the estimated phasor to generate the corrected phasor.

12. The RAKE receiver of claim 1, wherein the fourth circuitry is further adapted to filter the corrected phasor to remove multipath interference.

13. The RAKE receiver of claim 1, wherein the fourth circuitry comprises a Wiener filter adapted to filter the corrected phasor to remove multipath interference corresponding to white noise.

14. The RAKE receiver of claim 1, wherein:

the multipath interference has a bandwidth substantially equal to the bandwidth of the received signal;

the estimated phasor is a maximum likelihood estimated phasor;

the second circuitry is adapted to multiply the received symbols by the corrected phasor to generate the derotated symbols for the first signal component;

the third circuitry comprises a switch adapted to select either (i) symbol decisions derived from the derotated symbols for the first signal component and the one or more other signal components or (ii) pilot symbols for use in generating the estimated phasor;

if the switch selects the symbol decisions for use in generating the estimated phasor, then the third circuitry generates the estimated phasor for the first signal component by;

summing the derotated symbols for the first signal component with derotated symbols for each of the one or more other signal components to generate an input to a decider adapted to generate the symbol decisions;

applying complex conjugation to the symbol decisions; and

multiplying the complex-conjugated symbol decisions by the received symbols for the first signal component;

the fourth circuitry is adapted to;

estimate the multipath interference for the first signal component using (i) the estimated phasor for the first signal component and one or more other estimated phasors for the one or more other signal components and (ii) timing error signals for the first and the one or more other signal components; and

subtract the estimated multipath interference from the estimated phasor to generate the corrected phasor; and

the fourth circuitry comprises a Wiener filter adapted to filter the corrected phasor to remove multipath interference corresponding to white noise.