Receiver apparatus for receiving a multicarrier signal
View Patent ↗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.
1. A receiver apparatus configured to receive a multicarrier signal comprising subcarriers, wherein multiple symbols are modulated onto the subcarriers, the receiver apparatus comprising:
an estimation unit configured to:
estimate a subcarrier-dependent channel frequency response;
determine an intercarrier interference spreading on the basis of a cyclic shift in the symbols by determining a zeroth order time derivative of the channel frequency response for the subcarriers and at least a first order time derivative of the channel frequency response for the subcarriers according to a first or higher order approximation so as to estimate the channel frequency response; and
an equalizer unit configured to at least approximately canceling an intercarrier interference included in the multicarrier signal received on the basis of at least the channel frequency response estimated and the determined intercarrier interference spreading.
2. The receiver apparatus according to claim 1 , characterized in that the estimation unit is configured to determine the intercarrier interference spreading on the basis of an intercarrier interference spreading that is fixed for parallel subcarriers and the cyclic shift, and that the equalizer unit is configured to determine a signal output on the basis of the sum of the zeroth order time derivative applied on the symbols and the intercarrier interference spreading applied after the first order time derivative on the symbols.
3. The receiver apparatus according to claim 2 , wherein the estimation unit is configured to estimate the first order time derivative of the channel frequency response as a subcarrier-dependent first order time derivative.
4. The receiver apparatus according to claim 3 , wherein the estimation unit is configured to estimate the first order time derivative of the channel frequency response for a specific symbol as a difference of a zeroth order time derivative of the channel frequency response for a symbol succeeding the specific symbol with respect to a time coordinate and a zeroth order time derivative of the channel frequency response for a symbol preceding the specific symbol with respect to the time coordinate.
5. The receiver apparatus according to claim 1 , wherein the estimation unit is configured to determine the zeroth order time derivative of the channel frequency response for the subcarriers as a matrix for the zeroth order time derivative of the channel frequency response, the first order time derivative of the channel frequency response for the subcarriers as a matrix for the first order time derivative of the channel frequency response, the fixed intercarrier interference spreading as a matrix for the fixed intercarrier interference spreading, and the cyclic shift as a complex-valued function depending on a shift variable and the subcarriers, that the estimation unit is configured to determine a matrix for the intercarrier interference spreading on the basis of the cyclic shift function and the fixed intercarrier interference spreading matrix, the equalizer unit is configured to determine a vector of the signal output as a sum of a product of the matrix for the zeroth order time derivative of the channel frequency response and a vector of the symbols of the subcarriers, and a product of the matrix for the intercarrier interference spreading, the matrix for the first order time derivative of the channel frequency response and the vector of the symbols of the subcarriers.
6. The receiver apparatus according to claim 5 , wherein the estimation unit is configured to determine the 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 the specific row and the specific column of the fixed spreading matrix and a complex value of the cyclic shift function, wherein the complex value of the cyclic shift function is determined as a complex exponential function of a product of an imaginary unit, two times Ludolf's number, the shift variable and a fraction value consisting of a numerator that is a difference between the row number and the column number, and a denominator that is the total number of columns of the intercarrier spreading matrix or the total number of subcarriers.
7. The receiver apparatus according to claim 1 , wherein the equalizer unit is configured to at least approximately cancels the intercarrier interference of each of the subcarriers on the basis of an intercarrier interference from at most a predetermined number of adjacent subcarriers.
8. A transmission system configured to transmit a multicarrier signal from a transmitter apparatus to a receiver apparatus, wherein the multicarrier signal comprises subcarriers, wherein the transmitter apparatus is configured to modulate symbols on the subcarriers, and wherein the receiver apparatus is arranged according to claim 1 .
9. A receiver apparatus configured to receive a multicarrier signal comprising subcarriers, wherein multiple symbols are modulated onto the subcarriers, the receiver apparatus comprising:
an estimation unit configured to:
estimate a subcarrier-dependent channel frequency response; and
determine an intercarrier interference spreading on the basis of a cyclic shift in the symbols; and
an equalizer unit for at least approximately canceling an intercarrier interference included in the multicarrier signal received on the basis of at least the channel frequency response estimated and the determined intercarrier interference spreading,
wherein the estimation unit is configured to determine the zeroth order time derivative of the channel frequency response for the subcarriers as a matrix for the zeroth order time derivative of the channel frequency response, the first order time derivative of the channel frequency response for the subcarriers as a matrix for the first order time derivative of the channel frequency response, the fixed intercarrier interference spreading as a matrix for the fixed intercarrier interference spreading, and the cyclic shift as a complex-valued function depending on a shift variable and the subcarriers, that the estimation unit is configured to determine a matrix for the intercarrier interference spreading on the basis of the cyclic shift function and the fixed intercarrier interference spreading matrix, the equalizer unit is configured to determine a vector of the signal output as a sum of a product of the matrix for the zeroth order time derivative of the channel frequency response and a vector of the symbols of the subcarriers, and a product of the matrix for the intercarrier interference spreading, the matrix for the first order time derivative of the channel frequency response and the vector of the symbols of the subcarriers.
10. A receiving method for receiving a multicarrier signal comprising subcarriers, wherein multiple symbols are modulated onto the subcarriers, the method comprising:
estimating a subcarrier-dependent channel frequency response;
determining an intercarrier interference spreading on the basis of a cyclic shift in the symbols by determining a zeroth order time derivative of the channel frequency response for the subcarriers and at least a first order time derivative of the channel frequency response for the subcarriers according to a first or higher order approximation so as to estimate the channel frequency response; and
approximately canceling an intercarrier interference included in the multicarrier signal received on the basis of at least the channel frequency response estimated and the determined intercarrier interference spreading.
11. The method according to claim 10 , further comprising:
determining the intercarrier interference spreading on the basis of an intercarrier interference spreading that is fixed for parallel subcarriers and the cyclic shift; and
determining a signal output on the basis of the sum of the zeroth order time derivative applied on the symbols and the intercarrier interference spreading applied after the first order time derivative on the symbols.
12. The method according to claim 11 , further comprising estimating the first order time derivative of the channel frequency response as a subcarrier-dependent first order time derivative.
13. The method according to claim 12 , further comprising estimating the first order time derivative of the channel frequency response for a specific symbol as a difference of a zeroth order time derivative of the channel frequency response for a symbol succeeding the specific symbol with respect to a time coordinate and a zeroth order time derivative of the channel frequency response for a symbol preceding the specific symbol with respect to the time coordinate.
14. The method according to claim 10 , further comprising:
determining the zeroth order time derivative of the channel frequency response for the subcarriers as a matrix for the zeroth order time derivative of the channel frequency response, the first order time derivative of the channel frequency response for the subcarriers as a matrix for the first order time derivative of the channel frequency response, the fixed intercarrier interference spreading as a matrix for the fixed intercarrier interference spreading, and the cyclic shift as a complex-valued function depending on a shift variable and the subcarriers;
determining a matrix for the intercarrier interference spreading on the basis of the cyclic shift function and the fixed intercarrier interference spreading matrix; and
determining a vector of the signal output as a sum of a product of the matrix for the zeroth order time derivative of the channel frequency response and a vector of the symbols of the subcarriers, and a product of the matrix for the intercarrier interference spreading, the matrix for the first order time derivative of the channel frequency response and the vector of the symbols of the subcarriers.
15. The method according to claim 14 , further comprising:
determining the 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 the specific row and the specific column of the fixed spreading matrix and a complex value of the cyclic shift function, wherein the complex value of the cyclic shift function is determined as a complex exponential function of a product of an imaginary unit, two times Ludolf's number, the shift variable and a fraction value consisting of a numerator that is a difference between the row number and the column number, and a denominator that is the total number of columns of the intercarrier spreading matrix or the total number of subcarriers.
16. The method according to claim 10 , further comprising approximately canceling the intercarrier interference of each of the subcarriers on the basis of an intercarrier interference from at most a predetermined number of adjacent subcarriers.
17. The method according to claim 10 , further comprising transmitting a multicarrier signal from a transmitter apparatus to a receiver apparatus, wherein the multicarrier signal comprises subcarriers, wherein the transmitter apparatus is configured to modulate symbols on the subcarriers.