CN100525277C - Method and apparatus for anti-interference between codes in OFDM system - Google Patents
Method and apparatus for anti-interference between codes in OFDM system Download PDFInfo
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- CN100525277C CN100525277C CNB2006100668742A CN200610066874A CN100525277C CN 100525277 C CN100525277 C CN 100525277C CN B2006100668742 A CNB2006100668742 A CN B2006100668742A CN 200610066874 A CN200610066874 A CN 200610066874A CN 100525277 C CN100525277 C CN 100525277C
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Abstract
The invention relates to a method for preventing code interference in the orthogonal frequency division multiplexing system, and relative device. Wherein, said method comprises: the base station or user terminal, according to the transmitted data, estimates the time delay expansion of channel between each user terminal and base station; the base station or user terminal, according to said time delay expansion and the circulatory prefix length, fixes the displace range of prefix in the transmitted data, and according to said displace range, to circulatory displace bit of transmitted data. The invention can realize the full utilization of CP, via circulatory displacing bit of the prefix of each path, to improve the anti-ISI ability.
Description
Technical field
The present invention relates to network communications technology field, relate in particular to the method and the device of anti-intersymbol interference in a kind of ofdm system.
Background technology
In OFDM (OFDM) system, high-speed data-flow at first is divided into the data flow of a series of more low rate, these low rate data streams corresponding on a series of subcarrier parallel transmission, these subcarriers are orthogonal, so the OFDM OFDM of gaining the name.Just because of the orthogonal property of these subcarriers, transmitting terminal and receiving terminal can utilize inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT) fast algorithm respectively in the ofdm system, greatly reduce the implementation complexity of transceiver.
For the low rate data streams of a plurality of parallel transmissions, each symbol is elongated on time domain, therefore diminishes for the relative symbol duration of temporal diffusing capacity that expansion causes for multidiameter delay.Further, if each OFDM symbol is introduced the guard time of certain-length, the intersymbol interference of OFDM can be eliminated fully so; In guard time, signal is the cyclic extensions of OFDM symbol, therefore, is referred to as to disturb (ICI, Inter-Carrier Interference) between subcarrier that Cyclic Prefix (CP, Cyclic Prefix) avoided causing because of symbol time is elongated like this.
Usually adopt the radiation pattern of burst (Burst) in the ofdm system, therefore, for synchronous having relatively high expectations, general beginning at each Burst, insert one or two known OFDM symbols as leading (Preamble), like this, at receiving terminal, receiver can obtain according to known Preamble synchronously, the FFT window when determining follow-up OFDM symbol demodulation then.
As shown in Figure 1, if the starting point of FFT window has been eliminated intersymbol interference (ISI) so fully in the CP of OFDM symbol scope and between last figure A and B, has extraordinary ability of anti-multipath; But, if the starting point of FFT window is positioned at outside the CP, will introduce bigger ISI so, thereby worsen systematic function.
When definite FFT position of window, carry out related operation with local known Preamble sequence and received signal, the relevant peak value place that exports is as the original position of FFT window.For convenience, FFT window length is made as N, CP length is made as L.
Figure 2 shows that the ISI inhibition method of prior art one, just Preamble is not made any shifting processing at transmitting terminal, though the relevant peaks position mean of this scheme is positioned at the optimum position, but because the existence that noise and multipath disturb, the possibility that relevant peaks comes across after the optimum position is relatively large, has introduced bigger ISI like this.In addition, when in the sub-district, disposing CP length, need be provided with according to the requirement that the time delay of maximum is expanded, thereby for most of SS, the length of CP is long, has caused the wasting of resources like this.
As shown in Figure 3 in the scheme of prior art two, transmitting terminal is shifted for introducing a fixed cycles to Preamble people, perhaps, of equal valuely in the past reach in the position of the artificial relevant peaks of receiving terminal, the possibility that appears at after the optimum position of relevant peaks reduces greatly like this, thereby has reduced the probability that ISI occurs.
This method is compared the obvious anti-ISI ability that improved with preceding a kind of method, but its shortcoming also is apparent in view, reason is to adopt the method for fixed cycles displacement, and this fixing displacement is restriction with the ability of anti-multipath of not damaging the SS with maximum delay expansion, different SS is not distinguished.This method does not make full use of vacant CP, does not have further deeply to excavate the ability of anti-ISI.
Summary of the invention
In view of above-mentioned existing in prior technology problem, the purpose of this invention is to provide the method and the device of anti-intersymbol interference in a kind of ofdm system.
The objective of the invention is to be achieved through the following technical solutions:
The method of anti-intersymbol interference in a kind of ofdm system comprises:
A, base station or user terminal are according to the time delay expansion of channel between each user terminal of data estimation that is transmitted between base station and each user terminal and base station;
B, base station or user terminal are determined leading shift range in the transmission data according to the time delay expansion of user terminal and this user's circulating prefix-length, and according to leading the carry out cyclic shift of this shift range to the transmission data.
Described shift range is leading displacement is not more than the leading maximum shift value that is allowed, and wherein the maximum shift value draws according to the circulating prefix-length of bursty data and the time delay expansion that estimates.
The method of described anti-intersymbol interference comprises:
The centralized inhibition that realizes by the base station, or the distributed inhibition that realizes by each user terminal;
Wherein, described centralized inhibition comprises:
The uplink burst data that the base station sends according to a user terminal is estimated the time delay expansion of channel between this user terminal and base station;
Draw the leading maximum shift value that allows in the transmission data according to the circulating prefix-length of bursty data and the time delay expansion that estimates;
User terminal is according to leading the carry out cyclic shift of maximum shift value to the transmission upstream data, and the distance of cyclic shift is not more than the maximum shift value;
Carry out and the leading identical adjustment of upstream data the leading of downlink data according to the actual shift value base station;
Described distributed inhibition comprises:
The downlink burst data that user terminal is sent to this user terminal according to the base station estimates the time delay expansion of channel between this user terminal and base station;
Draw the maximum shift value of leading permission in the transmission data according to the circulating prefix-length of bursty data and the time delay expansion that estimates, and this maximum shift value is sent to the base station;
The base station is according to leading the carry out cyclic shift of maximum shift value to the downlink data that sent, and the cyclic shift distance is not more than the maximum shift value;
User terminal carries out and the leading identical adjustment of downlink data the leading of upstream data that is sent according to the actual shift value.
The estimation of channel delay expansion need repeat according to pre-set time interval between base station and each user terminal.
The device of anti-intersymbol interference in a kind of ofdm system comprises:
Time delay expansion determination module is used for determining the time delay expansion of channel between base station and each user terminal;
Circular shift module is used for expanding respectively to the leading cyclic shift of carrying out in data that each channel transmits according to the time delay of channel between base station and user terminal.
Described circular shift module comprises:
Maximum shift value determination module is used for the maximum shift value according to the definite leading permission of this circuit-switched data of time delay expansion of each circuit-switched data that is obtained by time delay expansion determination module;
Shift module is used for the maximum shift value that allows according to the data leading cyclic shift of carrying out to this circuit-switched data, and the ultimate range of cyclic shift is no more than the maximum shift value.
As seen from the above technical solution provided by the invention, the present invention is by being respectively the leading cyclic shift of carrying out of every circuit-switched data, realized the making full use of of CP saved resource, further improves the ability of anti-ISI.
Description of drawings
Figure 1 shows that the window's position schematic diagram of fast Fourier transform FFT;
Figure 2 shows that the relevant peaks position view of prior art one;
Figure 3 shows that the relevant peaks position view of prior art two;
Figure 4 shows that the relevant peaks position view of the embodiment of the invention one;
Figure 5 shows that the schematic diagram of the embodiment of the invention two by centralized inhibition SI;
Figure 6 shows that embodiment of the invention threeway crosses the schematic diagram of distributed inhibition ISI;
Figure 7 shows that the device schematic diagram of the embodiment of the invention four.
Embodiment
Core of the present invention is according to the data of transmitting between base station and a plurality of user terminal data transmission channel to be carried out the time delay expansion respectively to detect; According to the time delay expanding value of channel and the length of datacycle prefix, determine the largest loop shift value K that every circuit-switched data allows, respectively according to the K value of each circuit-switched data the leading cyclic shift of carrying out, to suppress the intersymbol interference of every circuit-switched data to each circuit-switched data.
More specifically say, the present invention includes and detect the time delay expansion, determine the largest loop shift range of permission and, finally, reduce the intersymbol interference of every circuit-switched data by cyclic shift to leading cyclic shift three parts of carrying out in the data.
Time delay expansion to the transmission data among the present invention detects and can be undertaken by BS, also can be undertaken by SSi (SSi represents one of a plurality of user terminal SS), both of these case can finally be realized the inhibition of the present invention to intersymbol interference, but every kind of situation all has oneself treatment step when concrete enforcement.
Initiates the time delay expansion by BS and detect, and the method for inhibition intersymbol interference is:
BS carries out the time delay spread estimation according to the data of this Burst to the channel that transmits this Burst after receiving the uplink burst data Burst that sends from SSi, measures the time delay expansion of this channel in BS
BS is according to current C P length and the time delay expansion that estimates
, definite maximum shift value K that allows, and with K value notice SSi;
BS is when being notified to SSi with the K value, and BS is shifted to the Preamble in the downlink data with reference to the K value;
SSi carries out same adjustment according to the displacement of BS to the up Preamble that sends.
The method of being initiated time delay expansion detection and inhibition intersymbol interference by SSi is:
SSi carries out the time delay spread estimation according to this Burst after receiving the descending Burst that sends from BS, draws the time delay expansion of BS for this SSi
:
SSi is according to current C P length and the time delay expansion that estimates
, the maximum shift value K that determine to allow, and the K value sent to BS;
When SSi sent to BS with the K value, SSi was shifted to the Preamble in the upstream data with reference to the K value;
BS adjusts the descending Preamble that sends according to the shift value K of SSi indication, displacement K position.
Owing to the channel quality between base station and each user terminal may change over time, therefore the present invention need repeat according to pre-set time interval the estimation of channel delay expansion between base station and each user terminal, when channel quality changes, estimate the time delay expansion that changes the back channel, and determine cyclic shift value according to new time delay expansion.
Below in conjunction with the specific embodiment of the invention accompanying drawing the present invention is elaborated.
Figure 4 shows that the relevant peaks position view of the embodiment of the invention one;
Main thought of the present invention is, (SS, SubscriberStation) length of the different time delay expansion of channel and Cyclic Prefix is that leading (Preamble) in the transmission data determines the cyclic shift distance in the channel according to base station and each user terminal.As shown in Figure 4, concerning each SS, neither damage the ability of anti-multipath, improved the ability of anti-ISI again to greatest extent, thereby improved the performance of whole system.
According to above-mentioned thought, at first need to determine the time delay expansion of channel between BS and each SS, expansion draws maximum permission shift value and carries out cyclic shift according to time delay.
According to the difference of time delay expansion detection method, specific embodiments of the invention can be divided into two kinds of situations that suppress intersymbol interference, and a kind of is the centralized inhibition that detects the time delay expansion in BS, and another kind is the distributed inhibition that detects time delay in SS.
Figure 5 shows that the schematic diagram of the embodiment of the invention two by centralized inhibition ISI.
The embodiment of the invention is concentrated and to be suppressed at the BS side and to finish, and its concrete steps comprise:
Step 51, SSi send up Burst data to BS;
After step 52, BS receive the up Burst that sends from SSi, transmission channel between BS and this SSi is carried out the time delay spread estimation, estimation time delay expansion in BS according to this Burst
:
Step 53, BS are according to the CP length of transmission data and the time delay expansion that estimates
, determine the maximum shift value K that allows;
Step 541, BS are notified to SSi with this K after obtaining the K value;
Step 542, BS are when being notified to SSi with the K value, and according to the displacement of K value, the ultimate range of displacement is not more than K to the Preamble of downlink data;
Step 55, SSi are carried out identical adjustment according to the actual shift value of BS to the Preamble of upstream data.
According to the IEEE802.16-2004 agreement, under existing framework, need not agreement flow process, message changed and just can realize centralized inhibition, BS can pass through a set message, with the shift value notice SS that determines, this message is UL-MAP physically modifying cell (Physical Modifier IE), and is as shown in table 1:
| Syntax | Size | Notes |
| PHYMOD_UL_IE() { | ||
| The last between-line spacing that Extended UIUC has expanded is used code | 4bits | PHYMOD＝0×01 |
| Length length | 4bits | Length=1 length=1 |
| Preamble Time Shift leading time displacement | 8bits | Preamble Time Shift leading time displacement |
| } |
Table 1
The value that the Preamble Time Shift of BS in can the utilization table notifies corresponding SS to be shifted, the binary number representation that the size of shift value is 8bit with a maximum length.
Like this, when carrying out centralized inhibition intersymbol interference and suppressing, at first send data by SS to BS, BS sends back to SS with the shift range that the K value that estimates promptly draws, and SS is shifted to leading according to this scope, has realized concentrating inhibition from the closed loop of SS-BS-SS.
Figure 6 shows that embodiment of the invention threeway crosses the schematic diagram of distributed inhibition ISI.
The distributed SS of being suppressed at side is finished, and its concrete steps comprise:
Step 61, base station BS send descending Burst data to SSi;
After step 62, SSi receive the descending Burst that sends from BS, transmission channel between this SSi and BS is carried out the time delay spread estimation, estimation time delay expansion in BS according to this Burst
:
Step 63, SSi are according to the CP length of transmission data and the time delay expansion that estimates
, determine the maximum shift value K that allows;
Step 641, SSi send to BS with the K value after obtaining maximum shift value K;
When step 642, SSi sent to BS with the K value, SSi was shifted according to the K value to Preamble in the upstream data according to the K value, and the ultimate range of displacement cannot surpass the K value;
Step 65, BS carry out same adjustment according to the actual shift value of SSi to the Preamble in the downlink data.
In present embodiment three, K is worth the mode of carrying identical with mode among the embodiment two.
The embodiment of the invention four device schematic diagrames as shown in Figure 7, this is the device of anti-intersymbol interference in a kind of ofdm system, it is characterized in that, comprising:
Time delay expansion determination module is used for determining the time delay expansion of each circuit-switched data between base station and each user terminal;
Circular shift module is used for according to the expansion of the time delay of each circuit-switched data between base station and user terminal respectively to the leading cyclic shift of carrying out of each circuit-switched data.
Described circular shift module comprises:
The maximum shift value is determined submodule, is used for the time delay expansion according to each circuit-switched data that is obtained by time delay expansion determination module, determines the maximum shift value of the leading permission of this circuit-switched data;
The displacement submodule is used for the maximum shift value that allows according to the data leading cyclic shift of carrying out to this circuit-switched data.
The above; only for the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, and anyly is familiar with those skilled in the art in the technical scope that the present invention discloses; the variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of claim.
Claims (6)
1, the method for anti-intersymbol interference in a kind of ofdm system is characterized in that, comprising:
A, base station or user terminal are according to the time delay expansion of channel between each user terminal of data estimation that is transmitted between base station and each user terminal and base station;
B, base station or user terminal are determined leading shift range in the transmission data according to the time delay expansion of user terminal and this user's circulating prefix-length, and according to leading the carry out cyclic shift of this shift range to the transmission data.
2, the method for anti-intersymbol interference in a kind of ofdm system according to claim 1, it is characterized in that, described shift range is leading displacement is not more than the leading maximum shift value that is allowed, and wherein the maximum shift value draws according to the circulating prefix-length of bursty data and the time delay expansion that estimates.
3, the method for anti-intersymbol interference in a kind of ofdm system according to claim 1 is characterized in that the method for described anti-intersymbol interference comprises: the centralized inhibition that is realized by the base station, or the distributed inhibition that is realized by each user terminal;
Wherein,
Described centralized inhibition comprises:
The uplink burst data that the base station sends according to a user terminal is estimated the time delay expansion of channel between this user terminal and base station;
Draw the leading maximum shift value that allows in the transmission data according to the circulating prefix-length of bursty data and the time delay expansion that estimates;
User terminal is according to leading the carry out cyclic shift of maximum shift value to the transmission upstream data, and the distance of cyclic shift is not more than the maximum shift value;
Carry out and the leading identical adjustment of upstream data the leading of downlink data according to the actual shift value base station;
Described distributed inhibition comprises:
The downlink burst data that user terminal is sent to this user terminal according to the base station estimates the time delay expansion of channel between this user terminal and base station;
Draw the maximum shift value of leading permission in the transmission data according to the circulating prefix-length of bursty data and the time delay expansion that estimates, and this maximum shift value is sent to the base station;
The base station is according to leading the carry out cyclic shift of maximum shift value to the downlink data that sent, and the cyclic shift distance is not more than the maximum shift value;
User terminal carries out and the leading identical adjustment of downlink data the leading of upstream data that is sent according to the actual shift value.
4, the method for anti-intersymbol interference in a kind of ofdm system according to claim 1 is characterized in that, the estimation of channel delay expansion need repeat according to pre-set time interval between base station and each user terminal.
5, the device of anti-intersymbol interference in a kind of ofdm system is characterized in that, comprising:
Time delay expansion determination module is used for determining the time delay expansion of channel between base station and each user terminal;
Circular shift module is used for expanding respectively to the leading cyclic shift of carrying out in data that each channel transmits according to the time delay of channel between base station and user terminal.
According to the device of anti-intersymbol interference in a kind of ofdm system shown in the claim 5, it is characterized in that 6, described circular shift module comprises:
Maximum shift value determination module is used for determining according to the time delay expansion of each circuit-switched data that is obtained by time delay expansion determination module the maximum shift value of the leading permission of this circuit-switched data;
Shift module is used for the maximum shift value that allows according to the data leading cyclic shift of carrying out to this circuit-switched data, and the ultimate range of cyclic shift is no more than the maximum shift value.
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| WO2008084634A1 (en) * | 2007-01-10 | 2008-07-17 | Nec Corporation | Transmission of mbms in an ofdm communication system |
| CN101282571B (en) * | 2007-04-05 | 2011-12-28 | 中兴通讯股份有限公司 | Method for constructing relay section code-guiding sequence |
| CN101940046B (en) | 2008-02-04 | 2015-07-22 | 诺基亚通信公司 | Mapping a cyclic shift to a channel index for ACK/NACK resource allocation |
| CN101754261B (en) * | 2008-12-11 | 2012-10-17 | 华为技术有限公司 | Signal detection method, system and device |
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