RECEIVER APPARATUS FOR RECEIVING A MULTICARRIER SIGNAL

• US 20120039379A1
• Filed: 06/16/2006
• Published: 02/16/2012
• Est. Priority Date: 06/16/2005
• Status: Active Grant

• Current Assignee: ST-Ericcson SA (Telefonaktiebolaget LM Ericsson)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: Husen, Sri Andari, Filippi, Alessio, Voorthuisen, Phjm Van
• Granted Patent: US 8,345,809 B2
• Time in Patent Office: Days
• US Class Current: 375/230
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 27/2665 Fine synchronisation, e.g. by positioning the FFT window
• CPC Class Codes: H04L 27/2688 Resistance to perturbation, e.g. noise, interference or fading
• CPC Class Codes: H04L 27/2691 involving interference determination or cancellation

Abstract

In time varying OFDM systems, the effect of a non-ideal time synchronization may lead to a poor performance in terms of decoded average bit error rate versus the signal-to-noise ratio. The receiver apparatus (3) of the transmission system (1) estimates a subcarrier-dependent channel frequency response and determines an intercarrier interference spreading on the basis of a cyclic shift in symbols carried by the subcarriers. Therewith, an intercarrier interference included in an OFDM signal can be canceled, even in case of a non-ideal time synchronization.

Claims

1. Receiver apparatus for receiving a multicarrier signal comprising subcarriers, wherein symbols are modulated onto the subcarriers, which receiver apparatus comprises an estimation unit for estimating a subcarrier-dependent channel frequency response and for determining an intercarrier interference spreading on the basis of a cyclic shift in said symbols, an equalizer unit for at least approximately canceling an intercarrier interference included in said multicarrier signal received on the basis of at least said channel frequency response estimated and said intercarrier interference spreading determined.

2. Receiver apparatus according to claim 1, characterized in that said estimation unit determines a zeroth order time derivative of said channel frequency response for said subcarriers and at least a first order time derivative of said channel frequency response for said subcarriers according to a first or higher order approximation so as to estimate said channel frequency response, that said estimation unit determines said intercarrier interference spreading on the basis of an intercarrier interference spreading that is fixed for parallel subcarriers and said cyclic shift, and that said equalizer unit determines a signal output on the basis of the sum of said zeroth order time derivative applied on said symbols and said intercarrier interference spreading applied after said first order time derivative on said symbols.

3. Receiver apparatus according to claim 1, characterized in that said estimation unit determines said zeroth order time derivative of said channel frequency response for said subcarriers as a matrix for said zeroth order time derivative of said channel frequency response, said first order time derivative of said channel frequency response for said subcarriers as a matrix for said first order time derivative of said channel frequency response, said fixed intercarrier interference spreading as a matrix for said fixed intercarrier interference spreading, and said cyclic shift as a complex-valued function depending on a shift variable and said subcarriers, that said estimation unit determines a matrix for said intercarrier interference spreading on the basis of said cyclic shift function and said fixed intercarrier interference spreading matrix, that said equalizer unit determines a vector of said signal output as a sum of a product of said matrix for said zeroth order time derivative of said channel frequency response and a vector of said symbols of said subcarriers, and a product of said matrix for said intercarrier interference spreading, said matrix for said first order time derivative of said channel frequency response and said vector of said symbols of said subcarriers.

4. Receiver apparatus according to claim 3, characterized in that said estimation unit determines said intercarrier interference spreading matrix so that an element in a specific row and a specific column is calculated as a product of an element in said specific row and said specific column of said fixed spreading matrix and a complex value of said cyclic shift function, wherein said complex value of said cyclic shift function is determined as a complex exponential function of a product of an imaginary unit, two times Ludolf'"'"'s number, said shift variable and a fraction value consisting of a numerator that is a difference between said row number and said column number, and a denominator that is the total number of columns of said intercarrier spreading matrix or the total number of subcarriers.

5. Receiver apparatus according to claim 2, characterized in that said estimation unit estimates said first order time derivative of said channel frequency response as a subcarrier-dependent first order time derivative.

6. Receiver apparatus according to claim 5, characterized in that said estimation unit estimates said first order time derivative of said channel frequency response for a specific symbol as a difference of a zeroth order time derivative of said channel frequency response for a symbol succeeding said specific symbol with respect to a time coordinate and a zeroth order time derivative of said channel frequency response for a symbol preceding said specific symbol with respect to said time coordinate.

7. Receiver apparatus according to claim 1, characterized in that said equalizer unit at least approximately cancels said intercarrier interference of each of said subcarriers on the basis of an intercarrier interference from at most a predetermined number of adjacent subcarriers.

8. Transmission system for transmitting a multicarrier signal from a transmitter apparatus to a receiver apparatus, wherein the multicarrier signal comprises subcarriers, wherein said transmitter apparatus modulates symbols on said subcarriers, and wherein said receiver apparatus is arranged according to claim 1.