Received signal processing device, communication system, and received signal processing method

Patent metadata

Field	Value
Publication number	US-9722768-B2
Application number	US-201415034282-A
Country	US
Kind code	B2
Filing date	Nov 13, 2014
Priority date	Nov 15, 2013
Publication date	Aug 1, 2017
Grant date	Aug 1, 2017

Abstract

A carrier recovery unit is provided including: separation-and-output section that outputs separated symbol group formed into block; a priori state-estimation section that obtains a priori estimate acquired by estimating values processed this time from among values of intra-block frequency and central phase processed last time; provisional compensation section that provisionally compensates the phase of each separated symbol based on the a priori estimation phase; decision section that performs decision based on the reference signal for the symbol before decision, and obtains symbol after decision; error-estimation section that calculates the frequency and phase errors; a posteriori state-estimation section that obtains a posteriori estimate based on the frequency and phase errors; actual compensation section that actually compensates the phase based on the a posteriori estimation phase; and feedback processing section that feeds back the a posteriori estimate as the values processed last time to the a priori state estimation section.

First claim

The invention claimed is:

1. A received signal processing device that regards, as one process, phase compensation for one separated symbol group acquired by separating every certain number of symbols of a modulated received signal and making the symbols form a block, and sequentially performs the process multiple times according to the number of the separated symbol group, the device comprising: a carrier recovery unit that includes:
a separation and output section that temporally separates the symbols input into the block in a constant time interval, for every constant number of symbols to obtain the separated symbol group, and outputs the group in a sequence of the separated symbols constituting the separated symbol group;
an a priori state estimation section that obtains an intra-block a priori estimation frequency and an intra-block a priori estimation central phase, as a priori estimates that are estimates of values processed k th time, from values processed (k−1) th time of one intra-block frequency determined based on phase variation of each of the separated symbols with respect to time, and one intra-block central phase determined as a temporal center of each phase of each of the separated symbols;
a provisional compensation section that calculates an a priori estimation phase of each of the separated symbols from the a priori estimate, and provisionally compensates the phase of each of the separated symbols based on the a priori estimation phase;
a decision section that regards, as a symbol before decision, each of the separated symbols whose phase has been provisionally compensated, performs decision for the symbol before decision based on a reference signal set according to a modulation scheme of the received signal, and obtains a symbol after decision that coincides with a reference point of the reference signal;
an error estimation section that calculates a frequency error between an observed value of the intra-block frequency and the intra-block a priori estimation frequency which are determined based on the symbol before decision and the symbol after decision, and calculates a phase error between an observed value of the intra-block central phase and the intra-block a priori estimation central phase which are determined based on the symbol before decision and the symbol after decision;
an a posteriori state estimation section that corrects the a priori estimates based on the frequency error and the phase error, and obtains an intra-block a posteriori estimation frequency and an intra-block a posteriori estimation central phase as a posteriori estimates obtained by estimating most likely values processed k th time that are of the intra-block frequency and the intra-block central phase;
a compensation section that calculates an a posteriori estimation phase of each of the separated symbols from the a posteriori estimate, and actually compensates the phase of each of the separated symbols based on the a posteriori estimation phase; and
a feedback processing section that performs a feedback process so that the a priori state estimation section can adopt the a posteriori estimates as the values processed (k−1) th time of the intra-block frequency and the intra-block central phase, and obtains the a priori estimates for the separated symbol group in the next phase compensation.

2. The received signal processing device according to claim 1 , wherein the number of symbols of the separated symbol group obtained in the separation and output section is 2 to 1,024.

3. The received signal processing device according to claim 1 , wherein the error estimation section calculates the frequency error and the phase error through maximum likelihood estimation.

4. The received signal processing device according to claim 1 , wherein the a posteriori state estimation section includes a Kalman filter that outputs the a posteriori state vector as the a posteriori estimate and the a posteriori error covariance matrix where the a priori estimate and the value of the a priori error covariance matrix have been corrected, based on an input of the a priori error covariance matrix for controlling the frequency error, the phase error, the a priori state vector as the a priori estimate, and a gain, and the feedback processing section performs the feedback process so as to input the a posteriori estimate and the a posteriori error covariance matrix into the a priori state estimation section to allow the a priori state estimation section to output, to the Kalman filter, these items as the a priori estimate and the a priori error covariance matrix for the next phase compensation.

5. The received signal processing device according claim 1 , further comprising an actual decision section that includes:
a decision element that decides a reference point having a shortest Euclidean distance on a complex plane among multiple reference points constituting a reference signal determined according to a modulation scheme for digital modulation with respect to one received symbol of a digitally modulated received signal output from the carrier recovery unit; and
a reference signal update section that corrects a position of the decided reference point so as to approach a position of the received symbol, based on a following expression [1], and updates the reference point of the reference signal used in the decision element to the corrected reference point,
r n+1 =r n +μ( x n −r n )  [1]

where in the expression [1], n denotes the number of updating the reference point, r n denotes a two-dimensional vector representing the position of the reference point on the complex plane subjected to an n-th updating, x n denotes a two-dimensional vector representing the position of the received symbol on the complex plane subjected to the n-th updating, μ represents an infinitesimal numerical value that is 10 −10 or more and 0.1 or less, and r n+1 denotes a two-dimensional vector representing the position of the corrected reference point on the complex plane.

6. The received signal processing device according to claim 5 , further comprising a section of calculating the amount of phase correction that adopts, as a control signal, the phase difference between the received signal and the decision signal that is a decision result of the decision element based on the reference signal updated by the reference signal update section with respect to the received signal, and calculates the amount of phase correction according to the phase variation of the received signal occurring owing to the fluctuation of the frequency difference between the carrier frequency of the received signal and the frequency of a local oscillator used in the receiver.

7. The received signal processing device according to claim 5 , further comprising an adaptive equalizer that adopts, as the error signal, the difference between the received signal whose noise component has been filtered out according to a tap coefficient and the decision signal that is a decision result of the decision element based on the reference signal updated by the reference signal update section with respect to the received signal, controls the tap coefficient so that the error signal can have a minimum intensity, and performs the equalization process for the subsequent received signal.

8. The received signal processing device according to claim 7 , wherein the adaptive equalizer includes a polarization separation processing section that applies a polarization separation process to a polarization-multiplexed received signal.

9. A communication system comprising:
a receiver that includes the received signal processing device according to claim 5 ;
a transmitter that transmits a transmission signal to the receiver; and

Assignees

• Nat Inst Advanced Ind Science & Tech

Inventors

• Inoue Takashi

Classifications

• H04L1/1819

  with retransmission of additional or different redundancy · CPC title

• H04L27/38 Primary

  Demodulator circuits; Receiver circuits · CPC title

• H04L7/0079

  Receiver details · CPC title

• H04B10/6165

  Estimation of the phase of the received optical signal, phase error estimation or phase error correction · CPC title

• H04B10/6164

  Estimation or correction of the frequency offset between the received optical signal and the optical local oscillator · CPC title