TRANSMITTER AND RECEIVER FOR, AND METHOD OF, TRANSMITTING AND RECEIVING SYMBOLS OVER TIME VARYING CHANNELS WITH DOPPLER SPREAD

Abstract

A communication frame for an OTFS transmission system includes at least one first-type and at least one second-type block. At least the first-type block includes data signals two-dimensionally arranged along the delay domain and the Doppler domain of which at least one has a superimposed pilot signal. The second-type block includes data signals two-dimensionally arranged along the delay domain and the Doppler domain which may or may not have superimposed pilot signals. At least one second-type block is preceded and followed, in the delay-domain, by first-type blocks, the first-type blocks preceding and following a second-type block having at least one identical data symbol and associated superimposed identical pilot symbol at an identical location in the two-dimensional arrangement. An OTFS transmitter generates and transmits the communication frame, and a receiver uses its properties for compensating oscillator frequency offset and channel estimation.

Claims

1-9. (canceled)

10. A receiver for an OTFS transmission system comprising a first receiver-side transformation unit and a second receiver-side transformation unit, wherein the receiver is adapted to receive a time-domain signal representing a communication frame including at least two first-type blocks and at least one second-type block, wherein at least the two or more first-type blocks comprise data signals two-dimensionally arranged along the delay domain and the Doppler domain of which at least one has a superimposed pilot signal, wherein the one or more second-type blocks comprise data signals two-dimensionally arranged along the delay domain and the Doppler domain or data signals two-dimensionally arranged along the delay domain and the Doppler domain of which at least one has a superimposed pilot signal, wherein one second-type block or a succession of second-type blocks is preceded and followed, in the delay-domain, by first-type blocks, the first-type blocks preceding and following the one second-type block or the succession of second-type blocks having at least one identical data symbol and associated superimposed identical pilot symbol at an identical location in the two-dimensional arrangement, the time-domain signal being transmitted over a communication channel and received at an input of the first receiver-side transformation unit, which outputs a two-dimensional representation of the received communication frame in the time-frequency domain, and wherein the output of the first receiver-side transformation unit is provided to an input of the second receiver-side transformation unit, which outputs a two-dimensional representation of the received communication frame comprising pilot and data signals in the delay-Doppler domain, wherein the receiver comprises an Oscillator Frequency Offset (OFO) estimator unit that is configured for performing an initial OFO estimation and compensation using symbols carried in the first-type block of the received communication frame, and further comprises an iterative two-stage channel estimation and equalization unit that is configured for determining a residual OFO and performing a channel estimation using all symbols of the received communication frame.

11. The receiver (300) of claim 10, wherein the OFO estimator unit is configured to perform an auto-correlation on the received OTFS symbols carried in the first-type block of the received communication frame, and wherein the initial OFO estimate is provided to the iterative two-stage channel estimation and equalization unit (320).

12. The receiver of claim 10, wherein the iterative two-stage channel estimation and equalization unit is configured for implementing an initial channel estimation followed by an initial equalization and symbol estimation, and further configured for implementing an iterative channel estimation followed by respective equalization and symbol estimation, for the joint estimation of the remaining OFO and the channel.

13. The receiver of claim 12, configured to provide at least the pilot signals output from the second receiver-side transformation unit to a first channel estimation unit, which outputs an initial estimation of the time-domain channel matrix, wherein the initial estimation of the time-domain channel matrix, as well as at least the data signals output from the second receiver-side transformation unit or the pilot and data signals output from the second receiver-side transformation unit, are provided to an equalizer, which outputs an estimated set of at least data signals, wherein the estimated set of at least data signals, as well as at least the pilot signals output from the second receiver-side transformation unit or the pilot and data signals output from the second receiver-side transformation unit, are provided to a second channel estimation unit, which outputs a second estimation of the time-domain channel matrix, wherein the output of the second channel estimation unit, as well as at least the data signals output from the second receiver-side transformation unit or the pilot and data signals output from the second receiver-side transformation unit, are provided to the equalizer-unit, which outputs a further estimated set of at least data signals, wherein the receiver is adapted to iteratively repeat the channel estimation in the second channel estimation unit and estimating an estimated set of at least data signals in the equalizer unit until a termination criterion is met.

14. The receiver of claim 13, wherein the first channel estimation unit is adapted to perform a channel estimation based on a basis expansion modelling of a first Basis Expansion Modelling (BEM) order of the time-varying communication channel.

15. The receiver of claim 13, wherein the second channel estimation unit is adapted to perform a channel estimation based on a basis expansion modelling of a second BEM order of the time-varying communication channel.

16. The receiver of claim 10, wherein the first receiver-side transformation unit is adapted to perform a finite Fourier transform, an inverse Heisenberg- or Wigner-transform and/or wherein the second receiver-side transformation unit is adapted to perform a decoding and/or a symplectic finite Fourier transform.

17. (canceled)

18. The receiver of claim 10, wherein an equalizer of the iterative two-stage channel estimation and equalization unit is configured for implementing a message passing, a zero-forcing and/or a minimum mean square error equalization.

19. The receiver of claim 10, further comprising a control unit that is adapted to receive information about the absolute speed and direction of the receiver over ground, the absolute speed and direction of the transmitter over ground and/or the relative speed between the receiver and the transmitter, and is further adapted to determine a BEM order, and/or is adapted to receive the BEM order used at the transmitter for composing the communication frame, and is adapted to pass the received information and/or the BEM order to the first and/or second channel estimation units of the iterative two-stage channel estimation and equalization unit.

20. A wireless device for an OTFS transmission system comprising a receiver according to claim 10.

21-26. (canceled)

27. A method of receiving a binary data sequence over an OTFS communication channel susceptive to doubly-selective fading, comprising: receiving a continuous time-domain signal representing a communication frame including at least two first-type blocks and at least one second-type block, wherein at least the two or more first-type blocks comprise data signals two-dimensionally arranged along the delay domain and the Doppler domain of which at least one has a superimposed pilot signal, wherein the one or more second-type blocks comprise data signals two-dimensionally arranged along the delay domain and the Doppler domain or data signals two-dimensionally arranged along the delay domain and the Doppler domain of which at least one has a superimposed pilot signal, wherein one second-type block or a succession of second-type blocks is preceded and followed, in the delay-domain, by first-type blocks, the first-type blocks preceding and following the one second-type block or the succession of second-type blocks having at least one identical data symbol and associated superimposed identical pilot symbol at an identical location in the two-dimensional arrangement, the time-domain signal being received over the OTFS communication channel, transforming, in a first receiver-side transformation unit, the continuous time-domain signal representing the communication frame into a two-dimensional arrangement of information symbols in the time-frequency domain that is available at an output of the first receiver-side transformation unit, transforming, in a second receiver-side transformation unit, the two-dimensional arrangement of information symbols comprising pilot and data signals in the time-frequency domain into a two-dimensional communication frame comprising pilot signals and data signals in the delay Doppler domain that is available at an output of the second receiver-side transformation unit, estimating an OFO from the first-type blocks of the communication frame, providing the estimated OFO to a channel estimation unit, for incorporating the OFO estimate into the CE function applied, providing the first-type blocks or the first-type blocks and the second-type blocks output from the second receiver-side transformation unit to a first channel estimation unit, for obtaining a first estimation of the time-domain channel matrix at an output of the first channel estimation unit, removing the pilot symbols from the received communication frame, using the first estimation of the time-domain channel matrix, providing the communication frame with the superimposed pilot symbols removed as well as the first estimation of the time-domain channel matrix, to an equalizer, for obtaining an estimated set of at least data signals at an output of the equalizer, estimating, in a second channel estimation unit, an estimation of the time-domain channel matrix, from the first-type block and the second-type block, as well as from the estimated set of at least data signals that are most recently output from the equalizer unit, providing the estimation of the time-domain channel matrix available at an output of the second channel estimation unit, as well as the first-type blocks and second-type blocks output from the second receiver-side transformation unit to the pilot removal unit, removing the pilot symbols from the received communication frame, using the estimation of the time-domain channel matrix available at an output of the second channel estimation unit, providing the communication frame with the superimposed pilot symbols removed as well as the estimation of the time-domain channel matrix available at an output of the second channel estimation unit, to the equalizer-unit, for obtaining a further estimated set of at least data signals at an output of the equalizer, and iteratively repeating estimating the time-domain channel matrix in the second channel estimation unit, removing the pilot symbols, and estimating sets of at least data signals in the equalizer until a termination criterion is met.

28. The method of claim 27, wherein the first transforming, in the first receiver-side transformation unit, comprises subjecting the continuous time-domain signal representing a communication frame to a finite Fourier transform, an inverse Heisenberg-, or Wigner-transform and/or wherein transforming, in the second receiver-side transformation unit, comprises subjecting the two-dimensional arrangement of information symbols comprising pilot and data signals in the time-frequency domain to a symplectic finite Fourier transform.

29. (canceled)

30. The method of claim 27, wherein estimating the OFO from the first-type blocks of the communication frame comprises: separating the first-type blocks from the received communication frame performing an autocorrelation on at least on the superimposed pilot symbols contained therein, and extracting the OFO information from the autocorrelation.

31. The method of claim 27, wherein obtaining the first estimation of the time-domain channel matrix in the first channel estimation unit comprises performing a channel estimation based on a basis expansion modelling of the time-varying communication channel of a first BEM order.

32. The method of claim 27, wherein estimating estimations of the time-domain channel matrix in the second channel estimation unit comprises performing a channel estimation based on a basis expansion modelling of the time-varying communication channel of a second BEM order.

33. The method of claim 27, wherein obtaining an estimated set of at least data signals in the equalizer comprises subjecting at least the data signals to a message passing, a zero-forcing and/or a minimum mean square error equalization.

34. The method of claim 27, further comprising: receiving, in a control unit, information about the absolute speed and direction of the receiver over ground, the absolute speed and direction of the transmitter over ground and/or the relative speed between the receiver and the transmitted, and/or the BEM order used at the transmitter for composing the communication frame, determining the respective BEM order to be used in the first and/or in the second channel estimation unit, and providing the respective determined BEM order to the first and/or to the second channel estimation unit.

35. A non-transitory computer program product comprising computer program instructions which, when executed by a microprocessor, cause the computer and/or control hardware components of an OFTS transmission system comprising a first receiver-side transformation unit and a second receiver-side transformation unit, wherein the receiver is adapted to receive a time-domain signal representing a communication frame including at least two first-type blocks and at least one second-type block, wherein at least the two or more first-type blocks comprise data signals two-dimensionally arranged along the delay domain and the Doppler domain of which at least one has a superimposed pilot signal, wherein the one or more second-type blocks comprise data signals two-dimensionally arranged along the delay domain and the Doppler domain or data signals two-dimensionally arranged along the delay domain and the Doppler domain of which at least one has a superimposed pilot signal, wherein one second-type block or a succession of second-type blocks is preceded and followed, in the delay-domain, by first-type blocks, the first-type blocks preceding and following the one second-type block or the succession of second-type blocks having at least one identical data symbol and associated superimposed identical pilot symbol at an identical location in the two-dimensional arrangement, the time-domain signal being transmitted over a communication channel and received at an input of the first receiver-side transformation unit, which outputs a two-dimensional representation of the received communication frame in the time-frequency domain, wherein the output of the first receiver-side transformation unit is provided to an input of the second receiver-side transformation unit, which outputs a two-dimensional representation of the received communication frame comprising pilot and data signals in the delay-Doppler domain. and wherein the receiver comprises an Oscillator Frequency Offset (OFO) estimator unit that is configured for performing an initial OFO estimation and compensation using symbols carried in the first-type block of the received communication frame, and further comprises an iterative two-stage channel estimation and equalization unit that is configured for determining a residual OFO and performing a channel estimation using all symbols of the received communication frame to execute the method of claim 27.

36. A non-transitory computer readable medium or data carrier retrievably transmitting or storing the computer program product of claim 35.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0121] In the following section exemplary embodiments of the invention will be described in greater detail with reference to the drawing. In the drawing,

[0122] FIG. 1 shows a block diagram of a general OTFS transmission system,

[0123] FIG. 2 schematically shows the superimposed pilots and their power allocation,

[0124] FIG. 3 shows an exemplary visualisation of the Doppler spectrum shifts in an OTFS communication channel in the presence of OFO,

[0125] FIGS. 4A-4F depict exemplary OTFS frame pattern according to an aspect of the present invention at the transmitter,

[0126] FIG. 5 shows a block diagram of the OFO estimation, channel estimation and equalization of an exemplary receiver in accordance with an aspect of the present invention,

[0127] FIG. 6 shows a flow diagram of a method of transmitting a binary data sequence over an OTFS communication channel,

[0128] FIG. 7 shows a flow diagram of a method of receiving a binary data sequence over an OTFS communication channel susceptive to doubly-selective fading,

[0129] FIG. 8 shows an exemplary block diagram of an apparatus configured for executing the method of transmitting in accordance with an aspect of the invention, and

[0130] FIG. 9 shows an exemplary block diagram of an apparatus configured for executing the method of receiving in accordance with an aspect of the invention.

[0131] Throughout the figures identical or similar elements may be referenced using the same reference designators.

DETAILED DESCRIPTION OF EMBODIMENTS

[0132] FIGS. 1 to 4F have been described further above and will not be discussed again.

[0133] FIG. 5 shows a schematic block diagram of the initial OFO estimation and compensation and the joint residual OFO and channel estimation in an exemplary receiver 300 in accordance with an aspect of the present invention. After executing the SFFT and Wigner transforms, the received symbols in the delay-Doppler domain y[k, l] are available for further processing.

[0134] The OFO estimation 312, channel estimation 320 with the iterative two-stage CE blocks 321, 322, and equalization 326 replace the generic channel estimation and equalization block 310 shown in FIG. 1. All other elements of the receiver 300 shown in FIG. 1, i.e., first and second receiver-side transformation units 304 and 306, respectively, are identical and are not shown in the figure.

[0135] The first-type blocks carrying data symbols and superimposed pilots and the second-type blocks carrying either data symbols only or data symbols and superimposed pilots in two-dimensional arrangements that are output from the second receiver-side transformation unit 306 as signal y[k, l] in the delay-Doppler domain may first be provided to the OFO estimator unit 312. OFO estimator unit 312 comprises a block separation unit 314, which separates the first-type blocks from the second-type blocks of the communication frame, and provides the first-type blocks to an autocorrelation unit 316. The autocorrelation may include or be followed by an Eigenvalue decomposition (not shown in the figure). The result of the autocorrelation is provided to the OFO extraction unit 318, which determines the OFO and provides it to a BEM bases generation unit 319. Based on the OFO estimate {circumflex over ()} output from the OFO extraction unit 318 BEM bases generation unit 319 determines the BEM bases to be used in the channel estimation units 321 and 322, and forwards corresponding information accordingly to the first and second channel estimation units 321, 322.

[0136] The first-type blocks carrying data symbols and superimposed pilots output from the low-rate block extraction unit 314, or the entire frame represented by signal y[k, l] comprising first-type blocks and second-type blocks in the delay-Doppler domain are provided to a first channel estimation unit 321, which performs a superimposed pilot-aided, OFO-included first channel estimation using a GCE-BEM channel model with a first BEM order s. The first BEM order s may be small, using a low-resolution T, albeit at the cost of a slower convergence. However, the first BEM order s may also be rather large, using a higher resolution T, resulting in a faster convergence. First channel estimation unit 321 outputs a first or initial channel estimation .sub.t.sup.i=0 , which is provided to an input of a pilot removal unit 324.

[0137] The communication frame represented by signal y[k, l] comprising first-type blocks and second-type blocks in the delay-Doppler domain are also provided to an input of a pilot removal unit 324 and to an input of a second channel estimation unit 322.

[0138] Pilot removal unit 324 uses the respective most recent channel estimation output by either the first channel estimation unit 321 or the second channel estimation unit 322 to remove the superimposed pilot signals present in the signal y[k, l], using the knowledge of the construction of the transmitted communication frame, i.e., the arrangement and power level thereof, leaving only the data signals. The output signal .sub.d.sup.i of pilot removal unit 324 is provided to equalizer unit 326. Equalizer unit 326 determines and outputs estimations {circumflex over (x)}.sub.d.sup.i of the transmitted data symbols.

[0139] Once the initial channel estimation in the first channel estimation unit 321 and the initial estimation {circumflex over (x)}.sub.d.sup.i0 of the transmitted data symbols have been executed, the respective most recent set of estimated data symbols {circumflex over (x)}.sub.d.sup.i is provided to an input of the second channel estimation unit 322 in an iterative fashion. The second channel estimation unit 322 performs data-aided, OFO-included channel estimations on the superimposed pilots comprised in the signal y[k, l] and the estimations {circumflex over (x)}.sub.d.sup.i of the transmitted symbols fed back to the second channel estimation unit 322 from equaliser unit 326 as pseudo pilots in addition to the superimposed pilots, using a GCE-BEM channel model with a second BEM order .sub.L and a second resolution T. The second channel estimation unit 322 may use a higher BEM order .sub.L and a higher resolution T than the first channel estimation unit, although same BEM orders .sub.L and resolutions T are also conceivable.

[0140] In each iteration the respective most recent output of the second channel estimation unit 322, which represents a channel estimation .sub.t.sup.i1, is input to the pilot-removal unit 324. Based thereon, pilot removal unit 324 removes the superimposed pilots from the received signal vector y[k, l] in the delay-Doppler domain, and provides an estimation of a signal representing only the received data signal .sub.d.sup.i, to an input of equaliser unit 326. Equaliser unit 326 outputs estimations {circumflex over (x)}.sub.d.sup.iof the transmitted data symbols that are improved over the previous ones. Iterations may be repeated until a termination criterion is fulfilled.

[0141] FIG. 6 shows a flow diagram of a method 400 of transmitting a binary data sequence over an OTFS communication channel. In step 402 a binary data sequence is mapped into a two-dimensional communication frame in the delay-Doppler domain, comprising a first-type block and a second-type block, in accordance with the first aspect of the invention. In step 404 the two-dimensional communication frame in the delay-Doppler domain is transformed into a two-dimensional arrangement of information symbols in the time-frequency domain. In step 406 the two-dimensional arrangement of information symbols in the time-frequency domain is transformed into a continuous time-domain signal representing the communication frame, which is transmitted over the channel in step 408. Prior to transforming the two-dimensional arrangement of information symbols in the delay-Doppler domain into a two-dimensional arrangement of information symbols in the time-frequency domain a power allocation ratio between pilot and data signals and/or a number of data symbols having superimposed pilots may be determined or adapted in optional step 410, which is set in optional step 412.

[0142] FIG. 7 shows a flow diagram of a method 500 of receiving a binary data sequence, carried in a communication frame in accordance with the first aspect of the present invention, over an OTFS communication channel susceptive to doubly-selective fading. In step 502 a continuous time-domain signal representing the communication frame is received over the communication channel. In step 504 the continuous time-domain signal representing the communication frame is transformed into a two-dimensional arrangement of information symbols in the time-frequency domain. In step 506 the two- dimensional arrangement of information symbols comprising pilot and data signals in the time-frequency domain is transformed into a two-dimensional communication frame in the delay-Doppler domain, comprising a first-type block and a second-type block, in accordance with the first aspect of the invention. In step 508 an OFO is estimated from the first-type blocks of the communication frame and provided, in step 510, from an OFO estimator 312 to a channel estimation unit 321, 322, for incorporating the OFO estimate {circumflex over ()} into the CE function applied. In step 512 an initial estimation of a time-domain channel matrix is obtained in a first channel estimation unit 321 that performs a channel estimation, on the first-type block or on the first-type and the second-type block, based on a basis expansion modelling of the time-varying communication channel of a first BEM order and at a first resolution. In step 514 the pilot symbols are removed from the received communication frame represented by the first-type and the second type blocks, and the resulting signal is provided to an equalizer unit 326. In step 516 an estimated set of at least data signals is determined in equalizer unit 326, based on the channel estimation and the communication frame in the delay-Doppler domain. Step 518 checks if a termination criterion is met, which in the positive case, Yes-branch of step 518, signals that the estimated received symbols can be output to a de-mapper, in step 522, and ultimately can be output as a received binary sequence. If the termination criterion is not met, No-branch of step 518, a further estimation of a time-domain channel matrix is obtained, in step 520, in a second channel estimation unit 322 that performs a channel estimation based on a basis expansion modelling of the time-varying communication channel of a second BEM order and at a second resolution, using the previously estimated data signals in addition to the pilot signals. The result of the further channel estimation is provided to the pilot symbol removing step 514, and the equalizing step 516 and the checking step 518 for the termination criterion are repeated.

[0143] Optionally, in step 524, a BEM order s that was used in the transmitter may be received, or information permitting determining a BEM order to be used in the channel estimation. In step 526 the BEM order s to be used is determined, and provided to the channel estimation unit in step 528.

[0144] FIG. 8 shows an exemplary block diagram of a transmitter 200 in accordance with the second aspect of the invention configured for executing the method 400 of transmitting in accordance with the fourth aspect of the invention. The transmitter 200 comprises a microprocessor 220, a volatile memory 222, a non-volatile memory 224, and a communication interface 226 for transmitting to a receiver 300 via an antenna 206. The aforementioned elements are communicatively connected via at least one data connection or bus 228. The non-volatile memory 224 stores computer program instructions which, when executed by the microprocessor 220, cause the receiver 200 to execute the method 400 in accordance with the fourth aspect of the present invention as presented above. It is noted that one or more of the various function blocks of the transmitter described with reference to FIG. 1, e.g., the first transmitter-side transformation unit 202 and the second transmitter-side transformation unit 204, may be fully or partially be implemented in software executed by the microprocessor 220.

[0145] FIG. 9 shows an exemplary block diagram of a receiver 300 in accordance with the third aspect of the invention configured for executing the method 500 of receiving in accordance with the fifth aspect of the invention. The receiver 300 comprises a microprocessor 330, a volatile memory 332, a non-volatile memory 334, and a communication interface 336 for receiving from a transmitter via an antenna 302. The aforementioned elements are communicatively connected via at least one data connection or bus 338. The non-volatile memory 334 stores computer program instructions which, when executed by the microprocessor 330, cause the receiver 300 to execute the method 500 in accordance with the fifth aspect of the present invention as presented above. It is noted that one or more of the various function blocks of the transmitter described with reference to FIG. 1, e.g., the first receiver-side transformation unit 304, the second receiver-side transformation unit 306, the OFO estimation 312, the first channel estimation unit 321, the second channel estimation unit 322, the pilot removal 324 and the symbol estimation and detection in the equalizer unit 326 may be fully or partially be implemented in software executed by the microprocessor 330.

DEFINITIONS AND LIST OF REFERENCE NUMERALS (PART OF THE DESCRIPTION)

[0146] f.sub.c carrier frequency [0147] f subcarrier spacing [0148] L channel length [0149] M number of delay bins of the communication frame [0150] N number of Doppler bins of the communication frame [0151] P.sub.T total transmission power [0152] pilot power allocation ratio [0153] s BEM order in the initial channel estimation [0154] L BEM order in the subsequent, iterative channel estimation [0155] AWGN additive white Gaussian noise [0156] BEM basis expansion model [0157] CE-BEM complex exponential BEM [0158] GCE-BEM generalized CE-BEM [0159] DFT discrete Fourier transform [0160] KL-BEM Karhunen-Loeve BEM [0161] MSE mean square error [0162] OTFS orthogonal time frequency space [0163] SNR signal-to-noise-ratio [0164] BER bit error rate [0165] OFDM orthogonal frequency division multiplexing [0166] MP message passing [0167] SFFT symplectic finite Fourier transform [0168] 200 transmitter [0169] 202 first transmitter-side transformation unit [0170] 204 second transmitter-side transformation unit [0171] 206 antenna [0172] 220 microprocessor [0173] 222 volatile memory [0174] 224 non-volatile memory [0175] 226 communication interface [0176] 228 data connection/bus [0177] 300 receiver [0178] 302 antenna [0179] 304 first receiver-side transformation unit [0180] 306 second receiver-side transformation unit [0181] 310 channel estimation and equalisation block [0182] 312 OFO estimator [0183] 314 low-rate block extraction [0184] 316 auto correlation [0185] 318 OFO extraction [0186] 319 OFO-included BEM bases generation [0187] 320 two-stage CE and EQ [0188] 321 first channel estimation unit [0189] 322 second channel estimation unit [0190] 324 pilot removal unit [0191] 326 equalizer unit [0192] 330 microprocessor [0193] 332 volatile memory [0194] 334 non-volatile memory [0195] 336 communication interface [0196] 338 data connection/bus [0197] 500 method of receiving [0198] 502 receive continuous time-domain signal [0199] 504 transform continuous time-domain signal into a two-dimensional arrangement of information symbols in the time-frequency domain [0200] 506 transform a two-dimensional arrangement of information symbols in the time-frequency domain into a two-dimensional communication frame in the delay-Doppler domain [0201] 508 estimate OFO [0202] 510 provide OFO estimation to channel estimation [0203] 512 initial channel estimation [0204] 514 remove pilots [0205] 516 estimate symbols in equalizer unit [0206] 518 termination criterion met? [0207] 522 output most recent estimation to de-mapper [0208] 520 estimate channel in second channel estimation unit [0209] 524 receive BEM order used in transmitter [0210] 526 determine BEM order to be used in receiver [0211] 528 provide BEM order to channel estimation