WO2008074254A1

WO2008074254A1 - A signal receiving and transmitting method and device based on ofdm

Info

Publication number: WO2008074254A1
Application number: PCT/CN2007/071235
Authority: WO
Inventors: Bin Li; Linfeng Xia; Wei Ruan
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2006-12-19
Filing date: 2007-12-14
Publication date: 2008-06-26
Also published as: CN101119352A

Abstract

A receiving and transmitting method and device based on OFDM are provided, which relate to wireless communication. The performance of signal detection is improved when the signal sequences in frequency domain can't be transmitted completely. In the method and device, firstly the signal sequences for transmitting are transformed by DFT after interweaving or scrambling, secondly the partial DFT results are mapped to the sub carriers of OFDM symbols, the signals are transmitted after OFDM modulation. And the receiver de-interweaves and descrambles the received signals, and abstains the signal sequences transmitted by the sender.

Description

OFDM-based signal receiving and transmitting method and device

The present application claims priority to Chinese Patent Application No. 200610171341.0, entitled " OFDM-based Signal Transmitting Method and Apparatus", filed on Dec. 19, 2006, the entire contents of in.

Technical field

The present invention relates to the field of wireless communications, and in particular, to a signal receiving and transmitting method and device based on OFDM.

Background technique

In recent years, multi-carrier transmission technology represented by Orthogonal Frequency Division Multiplexing (OFDM) has received wide attention. The multi-carrier transmission technique decomposes the data stream into a number of independent sub-data streams, each sub-data stream will have a much lower bit rate if the total data transmission rate is constant. Demodulating the corresponding subcarriers with low rate multi-state symbols formed at such low bit rates constitutes a transmission system in which a plurality of low rate symbols are transmitted in parallel.

As a multi-carrier digital modulation technology, OFDM uses the data to be transmitted as frequency domain information, and encodes the data into a time domain signal in the frequency domain. At the receiving end, reverse process demodulation is performed to obtain the transmitted data. The modulation and demodulation of the OFDM system can be replaced by an Inverse Discrete Fourier Transform (IDFT) and a Discrete Fourier Transform (DFT), respectively. At the transmitting end, the frequency domain data symbols can be transformed into time domain data symbols by an N-point IDFT operation, and after carrier modulation, they are sent to the channel. At the receiving end, the received signal is coherently demodulated, and then the baseband signal is subjected to an N-point DFT operation, so that the transmitted data symbol can be obtained. In practical applications, IDFT/DFT is implemented by Inverse Fast Fourier Transform (IFFT) and Fast Fourier Transform (FFT). The use of FFT technology makes the complexity of OFDM system greatly reduced, coupled with high-performance information processing devices, such as Programmable Logic Device (PLD,), Digital Signal Processor (referred to as Digital Signal Processor). The development and application of "DSP") and microprocessor ("Micro", referred to as "μΡ") make the implementation of OFDM system easier and become the most widely used multi-carrier transmission scheme.

In some scenarios where OFDM technology is used, orthogonal code sequences need to be modulated as information bits. Transmission on OFDM symbols. The 3rd Generation Partnership Project 2 (3GPP2) Air Interface Evolution ("AIE") The preamble of the superframe in the forward physical channel needs to be based on the orthogonal code. The sequence is modulated and transmitted on OFDM symbols. The orthogonal code sequence includes a Walsh code sequence, a DFT code sequence, and the like.

Specifically, the forward physical channel of the 3GPP2 AIE is composed of superframes, and each superframe has a preamble (preamble) for performing forward synchronization acquisition, identifying cells, broadcasting system parameters, and the like. The Preamble is composed of 8 OFDM symbols, and the last 3 OFDM symbols are called TDM1, TDM2, and TDM3. TDM1 is used to transmit the synchronization acquisition sequence, and TDM2 and TDM3 are used to transmit Walsh code sequences, which are used to identify different cells and transmit some system bits. Different cells can identify different cell numbers and the like by selecting different Walsh codes.

For a 5 MHz OFDM system, the number of IFFT points used for OFDM modulation is 512 points, and the length of the Walsh code sequence that TDM2 needs to transmit is 512 codes. In the prior art, a Walsh code sequence of 512 codes is firstly converted into a frequency domain signal by a DFT of 512 points, and then modulated onto a subcarrier of an OFDM symbol by subcarrier mapping, as shown in FIG. For a certain bandwidth OFDM system, it is usually necessary to reserve a certain number of guard subcarriers on both sides of the frequency band to prevent the spectrum of the transmitted signal from leaking and interfering with other frequency bands. If the number of guard subcarriers is Ng, the useful subcarriers are 512-Ng. That is to say, the spectrum signal of the Walsh code sequence of the DFT of 512 points can only be mapped to 512-Ng effective subcarriers during mapping, and Ng/2 points need to be truncated at both ends of the spectrum to be mapped to On the OFDM symbol. The frequency domain signal of the Walsh code sequence is mapped onto the subcarrier wave of the OFDM symbol, and then transmitted through the antenna through OFDM modulation (IFFT conversion).

The receiving end performs correlation detection on the received time domain signal, and determines the sequence number of the transmitted Walsh code to identify different cells.

In practical applications, due to the influence of the protection subcarriers, a frequency domain signal of the Walsh code sequence after the DFT transform is partially truncated during subcarrier mapping, which affects the frequency domain integrity of the Walsh code, and This part of the frequency phrase may carry the most important characteristics required for Walsh code detection. The lack of this part of the spectrum makes the performance of the receiving end detection greatly reduced, and the false detection rate of the Walsh code mapped on the OFDM subcarrier is high.

Summary of the invention

Embodiments of the present invention provide a method and a device for transmitting and receiving signals based on OFDM, so that a signal code When the frequency domain signal of the sequence cannot be completely transmitted, the performance of signal code detection is improved.

The embodiment of the invention provides a signal transmission method based on OFDM, which includes:

After the signal code sequence to be transmitted is interleaved or scrambled, the discrete Fourier transform DFT transform is performed, and the partial result of the DFT transform is mapped to the subcarrier of the OFDM symbol, and then transmitted and modulated by OFDM.

An embodiment of the present invention further provides an OFDM-based signal receiving method, including: deinterleaving or descrambling a received signal, and determining, by using correlation detection, a sequence number of a signal code sent by the transmitting end.

The embodiment of the invention further provides an OFDM-based signal transmitting device, comprising: a unit for interleaving or scrambling a sequence of signal codes to be transmitted;

a unit that performs a DFT transform on an interleaved or scrambled sequence;

Mapping a partial result of the DFT transform to a unit of subcarriers of the OFDM symbol;

A unit that transmits OFDM after subcarriers of OFDM symbols.

An embodiment of the present invention further provides an OFDM-based signal receiving apparatus, including: a unit that receives an OFDM signal;

a unit that deinterleaves or descrambles the received signal;

A unit that performs correlation detection on the deinterleaved or descrambled signal and determines the sequence number of the corresponding signal code. In the embodiment of the present invention, in the case that all the frequency domain signals generated by the DFT cannot be transmitted in the subcarrier of the OFDM symbol, the signal code to be transmitted is interleaved or scrambled before the DFT, and the interlace or scramble can be used to make the signal The frequency spectrum of the number is more "flat", and the distortion generated when the partial frequency domain signal is lost is small, so that it can be more accurately identified.

The orthogonal code usually has a certain regularity. For example, Walsh is symmetric or antisymmetric. Therefore, the frequency domain signal generated by the orthogonal code after DFT transformation is relatively regular. Some important features may only appear on a few frequency domain signals. If these frequency domain signals are not able to be sent out, these important features are lost and cannot be correctly identified by the receiving end. After the orthogonal code to be transmitted is interleaved or scrambled and then enters the DFT, the entire frequency domain signal appears "flat", or important features are scattered throughout the spectrum. Even if part of the frequency domain signal is lost, it is only equivalent to introduction. Some noise does not cause the receiver to be completely unrecognizable.

In some systems, only part of the frequency domain signal may be modulated onto the subcarriers of the OFDM symbol. Sending, for example, when there is a guard band, the subcarrier where the guard band is located will be set to zero, the frequency domain signal at the corresponding position will be lost, and if the hole is required to be punched, the frequency domain signal at the position where the hole is punched will also be lost. By interleaving or scrambling the orthogonal code to be transmitted before the DFT, the orthogonal code detection performance of the receiving end can be effectively improved when a guard band or a hole is required.

DRAWINGS

1 is a schematic diagram of operation of a transmitting end of an OFDM system in the prior art;

2 is a flowchart of a method for transmitting an OFDM-based signal according to a first embodiment of the present invention; FIG. 3 is a schematic diagram of an operation of a transmitting end in an OFDM-based signal transmitting method according to a first embodiment of the present invention;

4 is a schematic diagram showing an operation of a transmitting end in an OFDM-based signal transmitting method according to a second embodiment of the present invention;

5 is a simulation performance curve obtained by a transmitting method according to first and second embodiments of the present invention; FIG. 6 is a device including an interleaving unit and a guard band setting module in an OFDM-based signal transmitting apparatus according to a fourth embodiment of the present invention; Structure diagram

7 is a structural diagram of an apparatus including an interlace unit and a puncturing module in an OFDM-based signal transmitting apparatus according to a fourth embodiment of the present invention;

8 is a structural diagram of an apparatus including an interference unit and a guard band setting module in an OFDM-based signal transmitting apparatus according to a fourth embodiment of the present invention;

9 is a structural diagram of an apparatus including an interference unit and a puncturing module in an OFDM-based signal transmitting apparatus according to a fourth embodiment of the present invention.

detailed description

The invention will be further described in detail below with reference to the accompanying drawings.

In the embodiment of the present invention, the signal code sequence to be transmitted is first interleaved or scrambled, and then DFT transform is performed, and the partial result obtained by the DFT transform is mapped onto the subcarrier of the OFDM symbol, and modulated by OFDM.

The invention has a better effect on the signal code sequence of the spectrum "undulating", such as the orthogonal code sequence 歹|J, and of course other signal code sequences, such as GCL (General chirp-like) sequences. Wait. The following embodiments are described by taking an orthogonal code sequence as an example, but the present invention is not limited to the orthogonal code sequence. Since the orthogonal code is interleaved or scrambled before the DFT transform, the frequency domain signal generated by the orthogonal code after the DFT transform is not too regular, and some important features are scattered to the entire spectrum, and are not concentrated in a few. On the frequency domain signal, even if all the frequency domain signals generated by the DFT cannot be transmitted through the subcarriers of the OFDM symbol, these important features are not lost due to the lack of a few frequency domain signals, so that the receiving end cannot be correctly identified.

The first embodiment of the present invention relates to an OFDM-based signal transmission and reception method. As shown in FIG. 2, at the transmitting end, in step 210, the orthogonal code sequence to be transmitted is first interleaved. The orthogonal code sequence to be sent may be a Walsh code sequence, and is generally used for transmitting cell system information or control information in a control channel, such as TDM2 and TDM3 in the preamble of the forward physical channel of the AIE system, or other orthogonality. A sequence of signal codes whose code sequences or other spectrum "floats".

Next, proceeding to step 220, DFT transform is performed on the interleaved Walsh code sequence. Since the orthogonal codes are usually regular, for example, the Walsh code sequences are symmetric or antisymmetric, the frequency domain signals generated by the orthogonal codes after DFT transformation are compared, and some important features may only appear in a few frequency domains. On the signal, if these frequency domain signals are not able to be transmitted, these important features are lost and cannot be correctly recognized by the receiving end. In the embodiment of the present invention, the Walsh code sequence is first interleaved before the DFT transform, so that important features of the Walsh code sequence are spread to the entire spectrum. Even if some frequency domain signals are lost, only some noise is introduced, and The receiver is completely unrecognizable.

Next, proceeding to step 230, the entire result of the DFT transform is mapped onto the subcarriers of the OFDM symbol.

Next, proceeding to step 240, the result of the DFT transform mapped on the subcarrier serving as the guard band is set as a command.

Next, proceeding to step 250, OFDM modulation is performed on the mapped OFDM symbol, and then transmitted to the receiving end through the antenna.

For example, in the preamble of the forward channel of an OFDM system (512-point IFFT) of 5 MHz bandwidth, TDM2 or TDM3 needs to transmit a 512-bit Walsh code sequence, as shown in FIG. 3, a Walsh code sequence of length 512. After interleaving by the interleaver, the DFT transform is performed by 512 points to become a frequency domain signal, which is mapped to the OFDM symbol by the subcarrier mapper, wherein the subcarrier corresponding to the protection subcarrier is set to zero. After being modulated by an OFDM modulator, it is transmitted through an antenna. At the receiving end, the received signal is first deinterleaved, and then the correlation detection is used to determine the sequence number of the Walsh code sent by the transmitting end.

The second embodiment of the present invention is substantially the same as the first embodiment except that in the first embodiment, before the DFT conversion, the orthogonal code sequence to be transmitted is first interleaved; in the present embodiment, Before performing the DFT transform, the orthogonal code sequence to be transmitted is first scrambled. By scrambling, some important features of the orthogonal code can also be spread to the entire spectrum without being concentrated on a few frequency domain signals, so that even if all frequency domain signals generated by the DFT cannot be transmitted through the subcarriers of the OFDM symbol. Going out, there is no loss of these important features due to the lack of a few frequency domain signals, so that the receiving end can not correctly identify the orthogonal code sequence.

As shown in FIG. 4, the Walsh code sequence of length 512 is first scrambled by a scrambler, and then subjected to DFT transform of 512 points to become a frequency domain signal, and mapped to an OFDM symbol by a subcarrier mapper, where The subcarrier corresponding to the protection subcarrier is set to zero. After being modulated by the OFDM modulator, it is transmitted to the receiving end through the antenna.

At the receiving end, the received signal is descrambled first, and then the correlation detection is used to determine the sequence number of the Walsh code sent by the transmitting end.

Fig. 5 shows simulation performance curves obtained by the two improved transmission methods in the first embodiment and the second embodiment. The curve marked with a circle is a performance curve of the prior art, and a floor effect (Floor) occurs at -10 dB, and the error rate is 5 χ 10- ² . Diamond marked curve plus interleaving curve occurs where the floor effect -8dB, packet error rate 2χ 10- ^3. The curve marked with a triangle is the curve of the scrambling code. It can be seen that the OFDM-based signal transmission method in the present invention greatly increases the detection success rate of the receiving end.

The third embodiment of the present invention is substantially the same as the first and second embodiments, and the only difference is that in the first and second embodiments, after the DFT conversion result, the data corresponding to the guard band is cut off. Mapping to the subcarriers of the OFDM symbol; in the present embodiment, the DFT transform result needs to be punctured to remove the DFT transform result of the puncturing position.

As in the case of setting the OFDM guard band, the puncturing also affects the frequency domain integrity of the Walsh code to be transmitted. Therefore, in order to prevent the receiving end from completely recognizing the Walsh code sequence, the embodiment of the present invention also needs to perform the DFT transform. The transmitted Walsh code sequence is interleaved or scrambled such that some important features of the orthogonal code are spread throughout the spectrum. Then interlaced or scrambled The Walsh code sequence is subjected to DFT transform, and the DFT transform result is punctured, and the remaining DFT transform result after puncturing is mapped onto the effective subcarrier of the OFDM symbol, and is transmitted to the receiving end after OFDM modulation. For example, there are 512 transform results after DFT transform, and 32 of the specified positions are punctured (such as the number 16n, η is an integer from 0 to 31), and the remaining 512-32 = 480 transform results. The 480 transform results are respectively mapped to 480 effective subcarriers of the OFDM symbol (the original OFDM symbol has 512 subcarriers, and the guardian subcarriers are removed and the 480 effective subcarriers are removed after zero frequency), after OFDM modulation. Send to the receiving end. By interleaving or scrambling the orthogonal code sequence to be transmitted, the most important feature of the Walsh code sequence is not concentrated on a few frequency domain signals. Although the receiver cannot receive the complete Walsh code sequence, it is the most important. The feature is not completely lost, which is equivalent to introducing some noise into the received signal, which will not cause the receiving end to completely fail to recognize the Walsh code sequence, and improve the detection efficiency of the receiving end.

A fourth embodiment of the present invention relates to an OFDM-based signal transmitting apparatus, including: an interleaving unit 61, configured to interleave an orthogonal code sequence to be transmitted, as shown in FIG. 6 or FIG. 7, or a scrambling unit 81, Performing scrambling on the orthogonal code sequence to be transmitted, as shown in FIG. 8 or FIG. 9; further comprising a DFT transform unit 62 for performing DFT transform on the interleaved or scrambled sequence; a subcarrier mapping unit, The partial result of the DFT transform is mapped to the subcarrier of the OFDM symbol; the OFDM modulation unit 64 performs OFDM modulation on the subcarrier of the OFDM symbol and transmits it to the receiving end. The orthogonal code sequence to be sent may be a Walsh code sequence, and is generally used for transmitting cell system information or control information in a control channel, such as TDM2 and TDM3 in the preamble of the forward physical channel of the AIE system, or other positive Cross-code sequences or other spectral "fragments" of more severe signal code sequences.

In addition, as shown in FIG. 6 and FIG. 8 , the subcarrier mapping unit 63 further includes: a first mapping module 631 that maps all the results of the DFT transform to subcarriers of the OFDM symbol; and further includes a guard band setting module 632. The result of the DFT transform on the subcarrier to be used as the guard band is set to or, as shown in FIG. 7 and FIG. 9, the subcarrier mapping unit 73 further includes: a puncturing module

731. The DFT transform result is used for puncturing the DFT transform result, and the DFT transform result is used to map the remaining DFT transform result after the puncturing to the effective subcarrier of the OFDM symbol. The most important features of the sequence are not concentrated on a few frequency domain signals, even if the subcarriers in which the guard band is located are zeroed, the frequency domain signal at the corresponding position is missing, or the frequency domain in the punctured position is punctured. The signal is lost, and the most important feature of the Walsh code sequence is not completely lost. It only introduces some noise into the received signal, which does not cause the receiver to completely recognize the Walsh code sequence, which improves the detection efficiency of the receiver. .

A fifth embodiment of the present invention relates to an OFDM-based signal receiving apparatus, including: a unit that receives an OFDM signal; a unit that deinterleaves or descrambles the received signal; and receives a complete Walsh code sequence by the deinterleaving method However, since the Walsh code sequence is interleaved or scrambled at the time of transmission, the most important feature of the Walsh code sequence is not concentrated on a few frequency domain signals, so even if several of the received frequency domain signals are errors The most important feature of the Walsh code sequence is not completely lost, which is equivalent to introducing some noise into the received signal, which does not cause the receiving device to completely fail to recognize the Walsh code sequence, thereby improving the detection efficiency of the receiving device. .

In various embodiments of the present invention, the DFT may be implemented by a Fast Fourier Transform ("FFT").

While the invention has been illustrated and described with reference to the preferred embodiments embodiments The spirit and scope of the invention.

Claims

Rights request

An OFDM-based signal transmission method, comprising:

Discretizing or scrambling the sequence of signal codes to be transmitted, performing discrete Fourier transform; mapping partial results of the discrete Fourier transform onto subcarriers of OFDM symbols, and transmitting by OFDM modulation.

The OFDM-based signal transmission method according to claim 1, wherein the mapping the partial result of the DFT transform to the subcarriers of the OFDM symbol comprises:

All results of the discrete Fourier transform are mapped onto subcarriers of the OFDM symbol; the result of the discrete Fourier transform on the subcarriers used as guard bands is set to zero.

The discrete Fourier transform result is punctured to remove the discrete Fourier transform result of the puncturing position;

The discrete Fourier transform results remaining after the puncturing are mapped onto the effective subcarriers of the OFDM symbol.

The OFDM-based signal transmission method according to any one of claims 1 to 3, wherein the signal code sequence is an orthogonal code sequence.

The OFDM-based signal transmission method according to claim 4, wherein the orthogonal code sequence comprises a Walsh code sequence.

The OFDM-based signal transmission method according to claim 4, wherein the orthogonal code sequence to be transmitted is used to transmit cell system information or control information in a control channel.

The OFDM-based signal transmission method according to claim 6, wherein the cell system information transmitted by the orthogonal code sequence to be transmitted includes: TDM2 in a preamble of a forward physical channel of an air interface evolution system And TDM3.

8. An OFDM-based signal receiving method, comprising:

Deinterleaving or descrambling the received signal;

The detection determines the sequence number of the signal code sent by the transmitting end.

9. An OFDM-based signal transmitting device, comprising:

a unit that interleaves or scrambles a sequence of transmitted signal codes; a unit that performs a discrete Fourier transform on the interleaved or scrambled sequence;

A unit that maps a partial result of the discrete Fourier transform to a subcarrier of the OFDM symbol; a unit that performs OFDM modulation on the subcarrier of the OFDM symbol.

The OFDM-based signal transmitting apparatus according to claim 9, wherein the mapping the partial result of the discrete Fourier transform to the subcarrier of the OFDM symbol comprises: mapping all results of the discrete Fourier transform a module to a subcarrier of an OFDM symbol; a module that sets the result of the discrete Fourier transform on a subcarrier serving as a guard band to zero.

The OFDM-based signal transmitting apparatus according to claim 9, wherein the mapping the partial result of the discrete Fourier transform to the subcarrier of the OFDM symbol comprises: puncturing the discrete Fourier transform result a module for removing discrete Fourier transform results of the punch position;

The discrete Fourier transform results remaining after the puncturing are mapped to modules on the effective subcarriers of the OFDM symbol.

The OFDM-based signal transmitting apparatus according to claim 9, wherein the signal code sequence is an orthogonal code sequence.

13. An OFDM-based signal receiving device, comprising:

a unit that receives an OFDM signal;

a unit that deinterleaves or descrambles the received signal;

A unit that performs correlation detection on the deinterleaved or descrambled signal and determines the sequence number of the corresponding signal code.