WO2013091155A1

WO2013091155A1 - Carrier frequency offset estimation method and device

Info

Publication number: WO2013091155A1
Application number: PCT/CN2011/084198
Authority: WO
Inventors: 李焱
Original assignee: 中兴通讯股份有限公司
Priority date: 2011-12-19
Filing date: 2011-12-19
Publication date: 2013-06-27
Also published as: CN103988475A; CN103988475B

Abstract

Disclosed is a carrier frequency offset (CFO) estimation method. The method includes: according to different frame timings and CP modes, respectively performing self-relevance estimation and accumulation on a non-service downlink signal in a received downlink subframe; and comparing the modulus value of the obtained accumulation result and selecting an accumulation result with a bigger modulus value to perform CFO estimation. The present invention uses a non-service downlink signal in a downlink subframe to perform CFO estimation according to the features of an LTE system and can solve the problem that the CFO estimation performance is reduced if there is no downlink service scheduling and can avoid affecting subsequent SSS detection.

Description

Carrier frequency offset estimation method and device

The present invention relates to the field of wireless communications, and in particular, to a carrier frequency offset (CF0) estimation method and apparatus. Background technique

In a wireless communication system, when the carrier frequency of the base station and the user equipment (UE) is inconsistent, it will be represented as CF0 on the receiver. Most wireless systems, especially Orthogonal Frequency Division Multiplexing (OFDM) systems, are very sensitive to CFOs.

The CFO can seriously affect the performance of the receiver, so the initial CFO estimate is very important. In the initial synchronization in the Long Term Evolution (LTE) system, the correlation is usually performed by using the Primary Synchronization Signal (PSS), and the timing of 5 ms can be obtained.

Since the OFDM symbol has a Cyclic Prefix (CP), the frequency offset estimation can be performed by using an autocorrelation method, which is also a commonly used method in the OFDM system. In the normal CP (Normal CP) mode in the LTE system, each subframe is composed of 14 OFDM symbols. When there is no traffic scheduling, only a few OFDM symbols have data transmission thereon, and no other locations transmit signals. At this time, when all the OFDM symbols in the entire subframe 0 or 5 are used for estimation, the correlation result on the majority of the OFDM symbols is noise, and the estimation performance is seriously degraded. Summary of the invention

In view of this, the main object of the present invention is to provide a CFO estimation method and apparatus, which can solve the problem of reduced CFO estimation performance when there is no downlink traffic scheduling.

In order to achieve the above object, the technical solution of the present invention is achieved as follows:

A carrier frequency offset (CFO) estimation method, the method comprising: Perform autocorrelation estimation and accumulation on the non-service downlink signals in the received downlink subframes according to different frame timings and CP modes, respectively;

Compare the modulus values of the obtained cumulative results, and select the cumulative result with large modulus values to estimate the CFO. Further, the method further includes:

The user equipment UE performs frame synchronization on the received subframe according to different frame timings and CP modes;

It is judged whether the signals transmitted by the subframes after synchronization in different frame timings and CP modes are non-service downlink signals, respectively.

The frame timing includes a 10 ms frame timing of a start position of a frame header of a radio frame when a primary synchronization sequence (PSS) position is known.

The performing auto-correlation estimation on the non-service downlink signals in the received downlink subframes and accumulating is:

And using a cyclic prefix OFDM of the OFDM symbol in the received non-traffic downlink signal to perform autocorrelation with a portion of the CP corresponding to the OFDM symbol;

The results of the autocorrelation corresponding to the OFDM symbols are accumulated.

The non-service downlink signal includes one or more of a cell reference signal, a broadcast channel, a primary synchronization signal, and a secondary synchronization signal.

A CFO estimating device, including a CFO estimating module, further comprising: an autocorrelation module, an accumulation module, and a selection module; wherein

The auto-correlation module is configured to perform autocorrelation estimation on the non-service downlink signals in the received downlink subframes according to different frame timings and CP modes, respectively.

The accumulation module is configured to separately accumulate results of the autocorrelation estimation to obtain a cumulative result;

The selection module is configured to compare the modulus values of the accumulation result, and select a cumulative result with a large modulus value to perform CFO estimation by the CFO estimation module. Further, the device further includes: a frame synchronization module and a judging module; wherein the frame synchronization module is configured to respectively perform frame synchronization on the received subframe according to different frame timings and CP modes;

The determining module is configured to determine whether the signal transmitted by the subframe after synchronization in different frame timings and CP modes is a non-service downlink signal.

The frame timing includes a 10 ms frame timing of a start position of a frame header of a radio frame when the PSS position of the main synchronization sequence is known.

The auto-correlation module is configured to perform autocorrelation with a CP of the OFDM symbol in the received non-service downlink signal and a corresponding part of the CP in the OFDM symbol.

The accumulation module is specifically configured to accumulate results of autocorrelation of corresponding OFDM symbols.

According to the characteristics of the LTE system, the CFO estimation is performed by using the non-service downlink signal in the downlink subframe, which can solve the problem that the CFO estimation performance is degraded when there is no downlink service scheduling, and can avoid affecting the subsequent secondary synchronization signal (Secondary Synchronization Signal, SSS) detection. DRAWINGS

1 is a schematic diagram showing an implementation flow of a CFO estimation method according to the present invention;

2 is a schematic diagram of selection of an OFDM symbol in a CFO estimation method according to the present invention;

Fig. 3 is a schematic structural view of a CFO estimating apparatus of the present invention. detailed description

The basic idea of the present invention is: Since the detection of the CFO is after the PSS, the uplink and downlink configuration of the base station is unknown, at this time, the UE has only a half frame timing of 5 ms, and the 10 ms frame timing needs to be determined after the SSS detection; and some signals, such as Broadcast Broadcast Channel (PBCH) The transmission period is 10 ms, but the UE has not yet obtained the frame timing. Therefore, in order to make the best use of the available signals, it is also necessary to preset the frame timing to perform frame synchronization on the received subframes, and perform correlation and accumulation separately, and finally select a CFO estimation with a larger modulus value;

According to different frame timings and CP modes, auto-correlation estimation and accumulation are performed on the non-service downlink signals in the received downlink subframes respectively; comparing the obtained modular values of the cumulative results, and selecting a cumulative result with a large modulus value to perform CFO estimation .

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

FIG. 1 shows an implementation flow of a CFO estimation method according to the present invention. As shown in FIG. 1, the method includes the following steps:

Step 101: Perform autocorrelation estimation and accumulation on the non-service downlink signals in the received downlink subframes according to different frame timings and CP modes.

Specifically, the CP of the OFDM symbol in the non-service downlink signal in the received downlink subframe may be auto-correlated with the corresponding part of the CP in the OFDM symbol, where the CP is to copy a part of the OFDM symbol. Come over, placed in front of the OFDM symbol, so the CP is generally shorter than the OFDM symbol, the corresponding portion refers to the OFDM conforming to the copy as part of the CP; and the result of the autocorrelation of the corresponding OFDM symbol is accumulated. Here, the non-service downlink signal includes one or more of a Cell-Specific Reference Signal (Cell RS), a Broadcast Broadcast Channel (PBCH), a PSS, and an SSS.

Before the step, the method further includes: performing, by the UE, frame synchronization on the received subframe according to different frame timings and the CP mode, where the different frame timing includes a 5 ms half frame timing and a known primary synchronization sequence PSS. The 10 ms frame timing of the start position of the frame header of the radio frame at the time of the position.

Step 102: Compare the modulus values of the obtained cumulative results, and select a cumulative result with a large modulus value. CFO estimates.

The above method will be further described in detail below with reference to the selection of OFDM symbols in the above CFO estimation method shown in FIG. 2:

Step 1: performing frame synchronization on the received subframes according to two frame timings, and selecting a signal from the correlation estimation;

Since the CFO detection is after the PSS, the uplink and downlink configuration is unknown at this time. The UE can only perform CFO detection using subframes 0, 1, and subframes 5, 6, because these subframes are downlink or special subframes. Since no frame synchronization is performed at this time, the UE cannot determine whether the current downlink subframe is subframe 0 or subframe 5. The CP mode of OFDM includes normal CP (Normal CP) and extended CP (Extended CP). Therefore, it is necessary to simultaneously detect multiple possibilities. In each of the possible cases, it is determined whether the received OFDM symbol belongs to a downlink signal that must be transmitted, such as Cdl RS, PBCH, PSS, SSS or other non-traffic signals;

^sy _m ,hy ^ ^{here h} y ^ - ^N ^

Where hy represents the OFDM symbol corresponding to different frame timings, and N is various possibilities. Normally, there are 2 CP modes and 2 frame timings, so N=4. as shown in picture 2.

Step 2: performing autocorrelation estimation and accumulation on the selected OFDM signal;

For each selected OFDM symbol "S uses its own CP for autocorrelation:

Rxx'hy = R _xx ,h _y + x _{sym hy} (k)x _{sym hy} (k) - x _{sym hy} (k - n _cp )x _{sym hy} (k - n _cp - n _FFT ) where ^ represents the received The signal, n _FFT , and _ncp represent the number of samples of the OFDM symbol and the CP, respectively, and the correlation length is the number of CP points.

The results of the autocorrelation estimates of the corresponding OFDM symbols are accumulated according to each possibility:

Where ^ represents the number of accumulated OFDM symbols; here, the accumulated OFDM symbols may be within a subframe, or may be multiple subframes. Step 3: Compare the cumulative results of the autocorrelation estimation results obtained at the above two frame timings, and select the cumulative result for which the CFO estimation is to be performed.

Compare the modulus values of the two frame timings and the cumulative results obtained by the two CP modes, and select a set of correlation results with the largest modulus to estimate the carrier frequency offset. For details, refer to the following formula:

Leg = ax(abs(R _hy )) Step 4, perform CFO estimation on the cumulative result obtained by the selection;

According to the previous step, the selected cumulative result is calculated by the following formula, and the correct CFO estimation is obtained. The specific process is basically the same as the existing CFO estimation, and will not be described again.

Δ / = L _arct K , leg) )

2π - ΑΤ Re legs)

Where ΔΓ is the time interval of the two sampling points for autocorrelation, here the length of the OFDM symbol.

3 shows the structure of the CFO estimating apparatus of the present invention. As shown in FIG. 3, the apparatus includes: a CFO estimating module 31, an autocorrelation module 32, an accumulating module 33, and a selecting module 34; wherein the autocorrelation module 32 And performing auto-correlation estimation on the non-service downlink signals in the received downlink subframes according to different frame timings and CP modes;

The accumulating module 33 is configured to accumulate results of the autocorrelation estimation respectively to obtain a cumulative result;

The selection module 34 is configured to compare the modulus values of the accumulation result, and select a cumulative result with a large modulus value to be estimated by the CFO estimation module 31 for the CFO.

Further, the device further includes: a frame synchronization module 35 and a judging module 36; wherein the frame synchronization module 35 is configured to respectively perform frame synchronization on the received subframe according to different frame timings and CP modes;

The determining module 36 is configured to determine whether the signal transmitted by the subframe after the synchronization of the frame timing and the CP mode is a non-service downlink signal, where the different frame timing includes a 5 ms half frame timing and is a known primary synchronization sequence. 10ms frame setting of the start position of the frame header of the radio frame at the PSS position Time.

The auto-correlation module 32 is configured to perform auto-correlation with a CP in an OFDM symbol in the received non-service downlink signal and a corresponding part of the CP in the OFDM symbol; Accumulating the results of the autocorrelation of the corresponding OFDM symbols;

The above is only the preferred embodiment of the present invention and is not intended to limit the scope of the present invention.

Claims

Claim

A carrier frequency offset CFO estimation method, the method includes: performing autocorrelation estimation on a non-service downlink signal in a received downlink subframe according to different frame timings and a cyclic prefix CP mode, respectively Accumulate

Compare the modulus values of the obtained cumulative results, and select the cumulative result with large modulus values to estimate the CFO.

The method according to claim 1, wherein the method further comprises: the user equipment UE separately performing frame synchronization on the received subframe according to different frame timings and CP modes;

3. The method according to claim 2, wherein the frame timing comprises a 10 ms frame timing of a start position of a frame header of a radio frame when a PSS position of the main synchronization sequence is known.

The method according to claim 1, wherein the auto-correlation estimation is performed on the non-service downlink signals in the received downlink subframes and accumulated as:

And utilizing the OFDM of the OFDM symbol in the received non-service downlink signal to perform autocorrelation with the corresponding part of the CP in the OFDM symbol;

The method according to claim 1, wherein the non-service downlink signal comprises one or more of a cell reference signal, a broadcast channel, a primary synchronization signal, and a secondary synchronization signal.

A CFO estimating device, comprising a CFO estimating module, wherein the device further comprises: an autocorrelation module, an accumulation module, and a selection module;

The accumulation module is configured to separately accumulate results of the autocorrelation estimation to obtain a cumulative result; The selection module is configured to compare the modulus values of the accumulation result, and select a cumulative result with a large modulus value to perform CFO estimation by the CFO estimation module.

The device according to claim 6, wherein the device further comprises: a frame synchronization module and a determination module; wherein

The frame synchronization module is configured to separately perform frame synchronization on the received subframe according to different frame timings and CP modes;

8. The apparatus according to claim 7, wherein the frame timing comprises a 10 ms frame timing of a start position of a frame header of a radio frame when a PSS position of the main synchronization sequence is known.

The apparatus according to claim 6, wherein the auto-correlation module is specifically configured to utilize a cyclic prefix CP of an OFDM symbol in the received non-service downlink signal and the CP corresponding to the OFDM symbol. Partially autocorrelated;

10. The apparatus according to claim 6, wherein the non-service downlink signal comprises one or more of a cell reference signal, a broadcast channel, a primary synchronization signal, and a secondary synchronization signal.