Multistage interference canceller

• US 6,192,067 B1
• Filed: 12/19/1997
• Issued: 02/20/2001
• Est. Priority Date: 12/20/1996
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Tsutsui, Masafumi, Tanaka, Yoshinori, Seki, Hiroyuki, Kobayakawa, Shuji, Toda, Takeshi
• Primary Examiner(s): TSE, YOUNG TOI
• Application Number:
  US08/995,251
• Time in Patent Office: 1,159 Days
• Field of Search: 375/144, 375/148, 375/285, 375/346, 375/348, 375/140, 370/320, 370/335, 370/342
• US Class Current: 375/144
• CPC Class Codes: H04B 1/71075 Parallel interference cancellation
• CPC Class Codes: H04B 2001/71077 Partial interference cancellation

Abstract

A multistage interference canceller and method for removing interference between users and multipath interference from received signals in multiple stages includes a plurality of despreading units which produce a received symbol vector and an estimated channel value, a synthesis unit which synthesizes the received symbol vector, an amplitude of the received symbol vector and the amplitude of the estimated value from each reverse spreading unit, and a decision unit which executes a hard decision and a soft decision according to a result of comparing the total amplitude of the received symbol vector and the total amplitude of the estimated channel value.

Claims

1. A multistage interference canceller for cancelling interference as a communication system from an input signal, the interference canceller comprising:

a plurality of despreading units inputted with an error signal and an interference replica signal to produce received symbol vector and an estimated channel value;

a synthesis unit to synthesize said received symbol vector, an amplitude of the received symbol vector and an amplitude of the estimated channel value from each despreading unit, respectively;

a decision unit to evaluate said received symbol vector by hard-soft decision according to a result of comparing the total amplitude of the received symbol vector and a total estimated channel value and output an information symbol vector; and

a plurality of spreading units inputted with said information symbol vector and said interference replica signal to produce an interference residual signal and a new interference replica signal outputted to the next stage of the interference canceller.

2. The interference canceller according to claim 1, wherein each despreading unit includes a channel estimation unit and said decision unit includes a comparator which compares the total amplitude of the received symbol vector output from said synthesis unit with the total amplitude of the estimated channel value output from said channel estimation unit, and a hard-soft decision unit which executes a hard decision when the total amplitude of the received symbol vector is equal to or greater than that of the estimated channel value as a result of comparison by the comparator, or soft decision when the result of comparison is otherwise.

3. A method of tentative decision in an interference canceller which includes an interference canceller unit including a despreader, a channel estimation unit, a despreading unit which inputs received signals or error and interference replica signals from a previous stage, a first synthesis unit which synthesizes a signal output from the despreading unit, a decision unit which evaluates a signal output from the first synthesis unit, a spreader, a spreading unit which inputs a decision output signal from said decision unit and the estimated channel value from said despreading unit, and a second synthesis unit which synthesizes the signal output from the spreading unit and outputs an estimated interference residual signal, the method of tentative decision comprising the steps of:

switching of decision operations by said decision unit of the said interference canceller unit;

comparing in said decision unit the total amplitude of a received symbol vector output from the first synthesis unit with the total amplitude of the estimated channel value output from the channel estimation unit;

executing by the decision unit a hard decision when the total amplitude of the received symbol vector output from the first synthesis unit is equal to or greater than the total amplitude of the estimated channel value, or executes soft decision when the total amplitude of the received symbol vector output from the first synthesis unit is less than the total amplitude of the estimated channel value.