Method and apparatus for multipath signal compensation in spread-spectrum communications systems

• US 6,990,158 B2
• Filed: 04/23/2004
• Issued: 01/24/2006
• Est. Priority Date: 07/31/2000
• Status: Expired due to Term

• Current Assignee: Qualcomm technologies international, ltd. (Qualcomm, Inc.)
• Original Assignee: RF Micro Devices Incorporated (Qorvo, Inc.)
• Inventors: King, Eric J., Shan, Peijun
• Primary Examiner(s): BURD, KEVIN MICHAEL
• Application Number:
  US10/831,026
• Publication Number:
  US 20040196933A1
• Time in Patent Office: 641 Days
• Field of Search: 375/346, 375/348, 375/350, 375/233, 375/229, 375/232, 375/235, 375/347, 375/285, 455132-148
• US Class Current: 375/346
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 1/7113 Determination of path profile
• 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: H04B 2201/70707 Efficiency-related aspects

Abstract

An equalizer operates on chip or sub-chip resolution input samples of a received spread-spectrum multipath signal to remove interference from one or more secondary propagation path signals within the multipath signal. The equalizer may be configured for cancellation of secondary signals arriving before and after a main propagation path signal. The length of sample delay buffers and the input sample rate determine the maximum secondary signal delay accommodated by the equalizer. The equalizer makes a hard-decision about the phase value of each input sample and buffers these hard-decision values for use in secondary signal cancellation. The hard-decision values are used to rotate the phase of corresponding path coefficients. These adjusted values are fed back for subtraction from input samples for post-cursor cancellation, and fed forward for subtraction from delayed input samples for pre-cursor cancellation.

Claims

1. An apparatus comprising:

a compensation circuit adapted to receive input samples from a received multipath signal and compensate input samples using secondary signal estimates to form compensated samples;

an estimation circuit adapted to receive magnitude and phase information corresponding to a secondary path signal in the received multipath signal and output a current secondary signal estimate for a current input sample based on the magnitude and phase information and a selected one in a running sequence of past nominal phase values derived from prior input samples;

a hard-decision circuit adapted to determine a nominal phase value for each input sample, wherein said hard-decision circuit outputs a selected one from a defined set of nominal phase values as the nominal phase value;

a buffer circuit adapted to maintain the running sequence of past nominal phase values in successive buffer positions corresponding to successively greater sample time offsets with respect to the current input sample; and

a buffer interface circuit adapted to receive path delay information corresponding to the secondary path signal and provide said estimation circuit with the selected past nominal phase value by retrieving the past nominal phase value currently held in one of said buffer positions corresponding to a sample time offset equal to the received path delay information;

wherein said apparatus is operative to remove secondary path signal interference from the input samples for output as compensated samples to an associated communications system.