METHOD AND APPARATUS FOR DETERMINING SYMBOLS TRANSMITTED VIA ORTHOGONAL FREQUENCY DIVISION MULTIPLEX SIGNALS

Abstract

An OFDM receiver has a first, pilot-aided channel estimation block, an output of which is provided, along with the received signal, to a first equaliser block. An output of the first equaliser block is provided, along with the received signal, to a second, data-aided channel estimation block. An output of the second channel estimation block is provided, along with the output of the first equaliser block and the received signal, to an adjustable interference cancellation block. The output of the interference cancellation block and the output of the second channel estimation block are provided to a second equaliser block. An output of the second equaliser block is provided to a de-mapping block, and is provided to the second channel estimation block and the interference cancellation block, for allowing an iterative repetition of second channel estimation, interference cancellation and second equalisation for a received signal.

Claims

1. A method of determining symbols transmitted in a transmission block (S[k]) over a wireless channel using orthogonal frequency division multiplex, the transmission block (S[k]) comprising at least one data sub-block and at least one pilot sub-block, the method comprising: a) receiving, in the frequency domain, a transmission block (Y[k]) transmitted via the OFDM transmission channel, b) performing a pilot-aided first channel estimation function on the received transmission block (Y[k]), c) providing the received transmission block (Y[k]) and the output (?.sub.q(/).sub.1) of the pilot-aided first channel estimation function to a first channel equalisation function, wherein an output of the first channel equalisation function is a set of first-iteration estimated symbols (?[k].sub.1), d) providing the received transmission block (Y[k]) and the set of first-iteration estimated symbols (?[k].sub.1) to a data-aided second channel estimation function, e) providing the received transmission block (Y[k]), the set of first-iteration estimated symbols (?[k].sub.1) and the output (?q(/).sub.i) of the data-aided second channel estimation function to an adjustable interference cancellation function, f) providing the output (?q(/).sub.i) of the data-aided second channel estimation function and the output (Y[k]) of the adjustable interference cancellation function to a second equaliser function, wherein an output of the second equaliser function is a set of i-th-iteration estimated symbols (?[k].sub.i), i being larger than 1, wherein each set of i-th-iteration estimated symbols (?[k].sub.i) may include the set of the estimated symbols (?[k].sub.i-1) from the previous iteration as a subset, g) repeating steps e) and f), wherein the received transmission block (Y[k]) and the i-th-iteration set of estimated symbols (?[k].sub.i) is iteratively provided to the data-aided second channel estimation function and the adjustable interference cancellation function, respectively, until a predetermined termination condition is fulfilled.

2. The method of claim 1, wherein the first channel equalisation function has a computational complexity or performance that is lower than that of the second channel equalisation function.

3. The method of claim 1, wherein the pilot-aided first channel estimation function and/or the data-aided second channel estimation function apply a basis expansion model.

4. The method of claim 1, wherein the first channel equalisation function implements a message passing or a minimum mean square error equaliser.

5. The method of claim 1, wherein the second channel equalisation function implements a maximum likelihood sequence estimation equaliser.

6. The method of claim 1, wherein the interference cancellation function is adjustable and is arranged to cancel the intercarrier interference on the non-zero sub-diagonals and super diagonals of the channel matrix (H) in the frequency domain and to convert the channel matrix (H) into a banded diagonal matrix (H.sub.b) with a dispersion width smaller than that of the original channel matrix (H).

7. An OFDM receiver having a first channel estimation block adapted to perform a pilot-aided channel estimation on a received transmission block (Y[k]) in the frequency domain, an output of which first channel estimation block is provided, along with the received signal (Y[k]) in the frequency domain, to a first equaliser block, wherein an output of the first equaliser block is provided, along with the received signal (Y[k]) in the frequency domain, to a second channel estimation block, adapted to perform a data-aided channel estimation on a received transmission block, wherein an output of the second channel estimation block is provided, along with the output (?[k].sub.1) of the first equaliser block and the received transmission block (Y[k]) in the frequency domain, to an interference cancellation block, wherein the output (Y[k]) of the interference cancellation block and the output (?q(/).sub.i; i=2 . . . ) of the second channel estimation block are provided to a second equaliser block, wherein the output (?[k].sub.i; i=2 . . . ) of the second equaliser block is provided to a de-mapping block, and is provided to the second channel estimation block and the interference cancellation block, for allowing an iterative repetition of channel estimation, interference cancellation and equalisation for a received transmission block (Y[k]) in the frequency domain.

8. The OFDM receiver of claim 7, wherein the pilot-aided first channel estimation block and/or the data-aided second channel estimation block are adapted to perform a function applying a basis expansion model.

9. The OFDM receiver of claim 7, wherein the first equaliser block is adapted to perform a message passing or a minimum mean square error equaliser function.

10. The OFDM receiver of claim 7, wherein the second equaliser block is adapted to perform a maximum likelihood sequence estimation equaliser function.

11. A wireless device with an OFDM receiver according to claim 7.

12. 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 OFDM receiver having a first channel estimation block adapted to perform a pilot-aided channel estimation on a received transmission block in the frequency domain, an output of which first channel estimation block is provided, along with the received signal in the frequency domain, to a first equaliser block, wherein an output of the first equaliser block is provided, along with the received signal in the frequency domain, to a second channel estimation block, adapted to perform a data-aided channel estimation on a received transmission block, wherein an output of the second channel estimation block is provided, along with the output of the first equaliser block and the received transmission block in the frequency domain, to an interference cancellation block, wherein the output of the interference cancellation block and the output of the second channel estimation block are provided to a second equaliser block, wherein the output of the second equaliser block is provided to a de-mapping block, and is provided to the second channel estimation block and the interference cancellation block, for allowing an iterative repetition of channel estimation, interference cancellation and equalisation for a received transmission block in the frequency domain, to execute the method of claim 1.

13. A non-transitory computer readable medium retrievably storing the computer program product of claim 12.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In the following section aspects of the invention will be described with reference to the drawings, in which

[0046] FIG. 1 shows an exemplary representation of an OFDM communication system,

[0047] FIG. 2A, 2B shows exemplary representations of elements of a channel matrix H without and with Doppler spread

[0048] FIG. 3 shows an exemplary transmission block comprising data and pilot sub-blocks in a frequency domain representation,

[0049] FIG. 4 shows a flow diagram of an exemplary method in accordance with the invention,

[0050] FIG. 5 shows a block diagram of an exemplary receiver in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0051] FIGS. 1, 2A, 2B, and 3 have been described further above and will not be discussed again. FIG. 4 shows a flow diagram of an exemplary method 100 in accordance with the invention. In step 102 a transmission block transmitted over the OFDM transmission channel is received, in the frequency domain, i.e., after a Fourier transformation and removing the cyclic prefix in step 101. In step 104 a pilot-aided first channel estimation function is performed on the received transmission block. The output of the channel estimation is a set of channel frequency response coefficients for the transmission channel. In step 106 the received transmission block and the channel frequency response coefficients for the transmission channel are subjected to a first channel equalisation function. The output of the first channel equalisation function is a set of first-iteration estimated symbols, which are subjected, in step 108, along with the received transmission block, to a data-aided second channel estimation function. The output of the data-aided second channel estimation function is a further set of channel frequency response coefficients, also referred to as second-iteration set of channel frequency response coefficients, as this is the second channel estimation. In step 110 the second-iteration set of channel frequency response coefficients and the set of first-iteration estimated symbols are subjected to an adjustable interference cancellation function, which outputs a representation of the received transmission block with reduced or at least partly removed intercarrier interference. Next, in step 112, the representation of the received transmission block output from the interference cancellation function and the second-iteration set of channel frequency response coefficients are subjected to a second equaliser function. The output of the second equaliser function is a set of second-iteration estimated symbols, as this is the second time a symbol determination has been carried out on the received transmission block, or a representation thereof. In step 114 the method checks if a termination condition is fulfilled. If the termination condition is not fulfilled, no-branch of step 114, the set of second-iteration estimated symbols and the received transmission block are subjected to the data-aided second channel estimation function in step 108, and the process is repeated in a next iteration, until the termination condition is fulfilled. In this case, yes-branch of step 114, the set of final-iteration estimated symbols may be provided, in step 116, to a de-mapper, for producing a binary data output.

[0052] FIG. 5 shows a block diagram of an exemplary OFDM receiver 200 in accordance with the invention. A received transmission block Y[k] is input to a first pilot-aided channel estimation function block PACE and to a first equaliser function block EQ1/MP, which also receives the output of the first pilot-aided channel estimation function block PACE. The output of the first first equaliser function block EQ1/MP is provided to an interference cancellation function block IC and a second data-aided channel estimation function block DACE. The output of the second data-aided channel estimation function block DACE is also provided to the interference cancellation function block IC. The output of the interference cancellation function block IC is provided to a second equaliser function block EQ2/MLSE, whose output is provided to a de-mapper (not shown in the figure), and to the interference cancellation function block IC and the second data-aided channel estimation function block DACE, allowing for iteratively improving the channel estimation, interference cancellation and equalisation.

[0053] The method and apparatus described hereinbefore provide a signal detection that offers low overall complexity and thus allows for low hardware cost and energy consumption. In addition, the method and apparatus provide fast convergence of the signal detection, which results in a low processing delay.

[0054] The present method and apparatus may be useful in future 6G communication systems, and may also be adopted in lightly modified 5G networks.