CN101534539A - Method and device for quickly searching cells - Google Patents

Abstract

The invention discloses a method for quickly searching cells, comprising the following steps of: constructing a fundamental sequence based on a sequence category index; mapping the sequence index to base station identification; conducting Discrete Fourier transform (DFT) or Inverse Discrete Fourier transform (IDFT) to the fundamental sequence; and sending the transformed sequence as a reference sequence. By receiving and processing the reference sequence, a receiving terminal completes the searching of cells quickly. The embodiment of the invention also discloses a transmitting terminal device and a receiving terminal device used for quickly searching cells. The method for searching cells is simple, does not increase the system complexity, and is beneficial to quick cell detection, cell switching, and the like.

Description

A kind of fast cell search method and device

Technical field

The present invention relates to wireless communication field, be specifically related to a kind of sub-district method for fast searching and device.

Background technology

In mobile cellular network, geographical coverage area is divided into many sub-districts, and each sub-district is served by base station (BS).Each sub-district can also further be divided into many sectors.When mobile radio station (MS) when being powered, it need search for BS to register.And when MS found signal weaker from current area, it should prepare other cell/section.Because this point requires the good BS of MS search to communicate, wherein candidate list is provided by current service cell.Quick identification BS is important with the ability of carrying out initial registration or switching for reducing complexity and reducing power consumption.

Can periodic transmission cell specific reference signal (or synchronizing signal) carry out the Cell searching function, carry out exhaustive search, and determine best BS subsequently by attempting to detect each reference signal.Because mobile radio station will receive the signal from other sector or sub-district transmission, therefore, when determining the reference signal of sub-district or sector, the good cross correlation between the reference signal is important.Similar with autocorrelation, the cross correlation between two sequences is corresponding to the difference sequence self of displacement relatively.More accurately, the cross correlation at displacement d place is defined as: in the result who on whole items, sues for peace after element multiplies each other one by one of a sequence and another sequence, this another sequence be with respect to first sequence conjugation and the d item that has been shifted.

OFDM (Orthogonal Frequency Division Multiplexing, be called for short " OFDM ") be a kind of multi-carrier modulation (Multi-Carrier Modulation, be called for short " MCM "), it adopts a plurality of carrier waves, the data flow that will transmit resolves into the bit stream of a plurality of low speed, removes to modulate a plurality of carrier waves respectively with the bit stream of these low speed.Even if the mutual aliasing of frequency spectrum also can keep mutually orthogonal waveform.So just avoid the interference between the signal waveform, also improved the availability of frequency spectrum simultaneously.In ofdm system, be output as the output sum of N separate modulation carrier wave.When these carrier waves added together, a very high peak value may appear.This will cause a very high power peak-to-average force ratio (Peak Average Power Ratio is called for short " PAPR ") problem.In the ofdm system that uses DFT to realize, an OFDM symbol s (n), n=0,1 ..., N-1, PAPR be that the computing formula of unit is as follows with the decibel:

$\mathrm{PAPR}=10\log \left[\underset{k\∈[0,\mathrm{DN}-1]}{\max }\frac{{\left|(\underset{n=0}{\overset{\mathrm{DN}-1}{\mathrm{\Σ}}}s\′\left(n\right)\exp [-j2\mathrm{\πnk}/\left(\mathrm{DN}\right)])\right|}^2}{\frac{1}{\mathrm{DN}}\underset{k=0}{\overset{\mathrm{DN}-1}{\mathrm{\Σ}}}{\left|(\underset{n=0}{\overset{\mathrm{DN}-1}{\mathrm{\Σ}}}s\′\left(n\right)\exp [-j2\mathrm{\πnk}/\left(\mathrm{DN}\right)])\right|}^2}\right]$

Wherein, DN is the size of DFT, and D is an oversample factor.The low PAPR character of reference signal makes reference channel circuitry emission have the reference signal that is higher than data power, so that improve the signal to noise ratio/signal interference ratio on the reference signal that other communication unit receives, provides the channel estimating, synchronous etc. of improvement thus.And if the PAPR value of reference signal is very high, the power amplifier that then needs transmitter operates in a very big range of linearity with low efficiency and needs D/A (D/A) transducer and A/D (mould/number) transducer has very big dynamic range, thereby the expense that the raising system realizes, and therefore become the major defect of OFDM.When the PAPR value of leading (Preamble) sequence is higher than the range of linearity of power amplifier, signal can clipped wave (amplitude limit slicing).The distortion that causes will cause channel estimating or synchronous inaccurate, and cause the deterioration of systematic function.

In the existing protocol the inside, the sequence with the equal power ratio of ebb is used as leading (Preamble) to do synchronously and the function of channel estimating.Wherein a kind of Preamble sequence relatively more commonly used is a binary PN sequence.Used in the IEEE802.16e standard is exactly binary PN sequence, and its PAPR value reaches more than the 4dB.

Summary of the invention

The embodiment of the invention provides a kind of fast cell search method, reaches transmitting end device and receiving end device based on this searching method.

A kind of fast cell search method comprises: structure is based on the basic sequence of sequence classification index; Sequence index is mapped to Base Station Identification; Described basic sequence is carried out discrete Fourier transform (DFT) DFT or inverse discrete Fourier transformer inverse-discrete IDFT, with the sequence after the conversion as the reference sequence; Send reference sequences.A kind of fast cell search method comprises: receive the reference sequences that comprises based on basic sequence; Determine the sequence classification index of described reference sequences; Described sequence classification index is mapped to Base Station Identification.

A kind of transmitting end device comprises original series constructing module, sequence allocation module, reference sequences generation module, wherein:

The basic sequence constructing module is used to construct basic sequence;

The sequence allocation module is used for being mapped to sequence classification index a plurality of uniquely or the single base station sign;

The reference sequences generation module, the basic sequence that is used for distributing to each base station carries out DFT or IDFT, and the sequence that obtains is as the reference sequence.

A kind of receiving end device comprises: reference sequences receiver module, sequence index determination module, Base Station Identification identification module, wherein:

The reference sequences receiver module is used to receive the reference sequences that comprises based on basic sequence;

The sequence index determination module is used to determine the sequence classification index of the reference sequences that receives;

The Base Station Identification identification module, the sequence classification index that is used for determining is mapped to Base Station Identification.

The reference sequences that the embodiment of the invention provides has low PAPR value (near 0dB), and can provide good cell detection performance based on this specific reference sequences.In addition, simple based on the cell detection algorithm of the embodiment of the invention, do not bring any complexity to increase to system, help fast cell detection, sub-district switching etc.

Description of drawings

Fig. 1 is the transmitting terminal process chart of the embodiment of the invention;

Fig. 2 is the optional process chart one of the transmitting terminal of the embodiment of the invention;

Fig. 3 is the receiving terminal process chart of the embodiment of the invention;

Fig. 4 is the optional process chart one of the receiving terminal of the embodiment of the invention;

Fig. 5 is the optional process chart two of the receiving terminal of the embodiment of the invention;

Fig. 6 is the optional process chart two of the transmitting terminal of the embodiment of the invention;

Embodiment

The embodiment of the invention provides a kind of fast cell search method, realizes the quick search of sub-district by structure special reference sequence.The embodiment of the invention also provides a kind of transmitting end device and receiving end device that is used for Cell searching, below is elaborated respectively.

Embodiment one

A, structure reference sequences, the structure of reference sequences depends at least two factors, i.e. number of reference sequences K and required sequence length Np in the network.Present embodiment time domain reference symbol is the OFDM symbol, and this symbol is based on N point discrete Fourier inverse transformation IDFT.

At first construct basic sequence:

$x\left(k\right)=b\·\exp (-j(2\mathrm{\π\μ}\frac{k}{N_G}+c))---\left(1\right)$

Wherein, μ=0,1 ..., N _G" classification " of-1 corresponding sequence,

K=0,1 ..., N _GThe-1st, the index of sequence discipline,

B, c are any real number, and b ≠ 0.For satisfying number of reference sequences purpose requirement in the network, only need satisfy N _GK.

Depend on b, the specific selection of c, each basic sequence classification can have unlimited sequence number, but only has a sequence to be used to construct a reference sequences in each classification.Each classification index " μ " has produced different phase ramp characteristic on each reference sequences.For explaining conveniently, below all with b=1, c=0 does not represent b as example, the value of c only limits to this.

Then to N _GThe basic sequence of individual above-mentioned structure carries out T point (T 〉=N respectively _G) DFT, the sequence that obtains can be expressed as:

$X\left(m\right)=\mathrm{DFT}\left(x\left(k\right)\right)=\underset{k=0}{\overset{T-1}{\mathrm{\Σ}}}x\left(k\right)\exp (-j2\mathrm{\π}(\frac{\mathrm{\μ}}{N_G}+\frac{m}{T})k)---\left(2\right)$

Wherein, k=N _G..., during T-1, x (k)=0.

When $\frac{\mathrm{\μ}}{N_G}+\frac{m}{T}=1$ The time, peak value appears in X (m).

Also can be to the N of structure _GIndividual basic sequence carries out T point (T 〉=N _G) IDFT (contrary DFT), the sequence that obtains can be expressed as:

$X\left(m\right)=\mathrm{IDFT}\left(x\left(k\right)\right)=\underset{k=0}{\overset{T-1}{\mathrm{\Σ}}}x\left(k\right)\exp \left(j2\mathrm{\π}(\frac{m}{T}-\frac{\mathrm{\μ}}{N_G})k\right)---\left(3\right)$

Wherein, k=N _G..., during T-1, x (k)=0.

When $\frac{\mathrm{\μ}}{N_G}=\frac{m}{T}$ The time, peak value appears in X (m).

With above-mentioned be that the set of the sequence of T is gathered as frequency domain reference sequences through the length that obtains after DFT or the IDFT conversion.Equal the situation of Np for T, generating frequency domain reference sequences does not need additional other operations again, referring to Fig. 1; Being not equal to the situation of Np for T, can be that the arrangement set of T is made amendment to length, to generate the frequency domain reference sequences set of Len req, referring to Fig. 2, wherein revises and comprises, to former sequence interpolation, or is truncated to operation such as required sequence length Np.Select suitable DFT/IDFT to count, can so that, be nonzero value having only the data on the subcarrier on all reference subcarrier, data are 0 on other subcarrier, be that frequency domain sequence can be seen an impulse function sequence as, so the frequency domain reference sequences set has optimum cross correlation.

According to the mapping mode of predesignating, with the sequence item be assigned to Np reference subcarrier set in the frequency domain N subcarrier go up (N be the OFDM symbol based on the counting of discrete Fourier transform (DFT) DFT, Np is the above-mentioned required sequence length of mentioning, and required sequence length equals the number of frequency domain reference subcarrier).Through N point IDFT, above-mentioned OFDM symbol frequency domain data is transformed to time domain, as sending sequence, expression formula is:

$\begin{array}{c}s\left(n\right)=\mathrm{IDFT}(X\′(m\′))m\′=\mathrm{0,1},L,N-1\\ =\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}X\′(m\′)\exp (-j2\mathrm{\π}\frac{m\′n}{N})\end{array}---\left(4\right)$

Wherein, X ' (m ') is for finishing the frequency domain sequence after subcarrier shines upon, and m ' is the subcarrier sequence number.

The final reference sequence of launching in the time domain can be a cyclic extensions, and wherein cyclic extensions length typically is longer than desired channel maximum delay spread (LD).In this case, the length of the ultimate sequence that is sent equals N and cyclic extensions length L _CPSum.Cyclic extensions can comprise the combination of prefix, suffix or prefix and suffix.Cyclic extensions is the intrinsic part of ofdm communication system.Can prove that the time domain reference sequences still has optimal cross-correlation.

B, carry out the distribution of reference sequences, promptly uniquely sequence classification index is mapped to a plurality of base stations/single base station sign.Each base station can be at any transmission intercal, with the one or more basic sequences of any number of times ground use.In addition, can give the different basic sequences of each base station assigns, advance the set of reference sequences that obtains after the subsequent treatment by this K basic sequence and be designed to have optimum cross correlation property from K basic sequence set.Actual signal can be the result of the different functions of institute's assigned sequence.For example, applied function is the cyclic shift of sequence.

The also N that can directly step 103 among Fig. 1 be obtained _GIndividual length is K sequence in the set formed of the frequency domain reference sequences of Np, distribute to a plurality of base station/single base stations respectively, and uniquely basic sequence classification index is mapped to a plurality of base stations/single base station sign respectively, then subcarrier mapping, frequency-time domain transformation and cyclic extensions operation only need be carried out in each base station.

C, next carry out Cell searching based on aforesaid operations.

Suppose to have finished OFDM symbol timing and Frequency offset estimation and correction, the timing point from proofreading and correct transforms to frequency domain by DFT with the time domain data that is received, and carries out subcarrier based on the subcarrier mapping mode of transmitting terminal regulation and separates mapping.

The frequency domain data that subcarrier is separated after the mapping is expressed as Y (m), and wherein m (from 0 to Np-1) is the index of reference subcarrier.Discussion by the front knows, the peak of frequency domain data is by the decision of μ value, can calculate the μ value by the peak of Y (m).Also promptly, classification index (or sequence index) information " μ " is carried in the peak of Y (m), by analyzing the peak of Y (m), can detect " μ " corresponding to the reference sequences index.The peak n of Y (m) _MaxBe confirmed as with the mapping relations of corresponding transmitting sequence classification index μ:

$\mathrm{\μ}=N_G(1-\frac{n_{\max }}{T}),$ (corresponding to X (m)=DFT (x (k)))

Or $\mathrm{\μ}=N_G\frac{n_{\max }}{T},$ (corresponding to X (m)=IDFT (x (k))), wherein n _MaxPeak for Y (m).The μ that is calculated by above formula is integer not necessarily, at this situation, gets the integer value that the approaches above result of calculation most value as μ.

Can obtain the peak discerned and the mapping relations between the sequence classification index thus.Sequence classification index is corresponding to the source base station sign that sends reference sequences.Receiving terminal can calculate the source base station sign, and then finish Cell searching according to the position of the signal peak that receives like this.Referring to Fig. 3.

Can use conventional peak-value detection method, compare with threshold value, or directly peak value detects or the like as amplitude with sample.If there are a plurality of receiving sequences, then will show a plurality of peak values.

Also the μ that is discerned can be mapped in the additional possible transmitted sequence indices set, this transmitted sequence indices set is corresponding near the μ that is discerned.Referring to Fig. 4.When some values " μ " tight spacing of in system, using, noise or disturb can make peak value appear near but be not to be positioned at the same position place that expectation is used for index " μ ".By near peak value, searching for, can discern more than a candidate sequence index and be used for further inspection (as in a plurality of reference signal transmission periods).For example, to the result on a plurality of reference signal transmission periods make up, comparison, majority voting or the like, to help a value or a plurality of value of " μ " that identification received.In a word, we can be mapped to the μ that is discerned in the additional possible transmitted sequence indices, and this transmitted sequence indices is corresponding near the μ that is discerned.

Detecting under the situation of a plurality of sequences, can use the method for counteracting, to improve the possibility that detects the weak order row.Referring to Fig. 5, can at first discern first reference sequences, estimate to relate to the channel response of known reference sequence, re-construct received signal part by first known array and channel response contribution thereof, from received signal, remove this part, and execution is similar to step required in first Sequence Detection to obtain second sequence index subsequently.Can continue by this process, up to detecting full sequence.

At receiving terminal, can also after the removal channel effect, carry out operations such as peak value detection again by earlier reference symbol being carried out channel equalization.

Embodiment two

Small region search method that present embodiment provides and embodiment one are similar.Structure basic sequence method is with embodiment one, just directly to basic N _GThe sequence of length is made amendment, and makes its sequence length equal Np, and then carries out middle DFT or IDFT operation among the embodiment one, and this moment, counting of DFT/IDFT was Np, and subsequent operation is identical with embodiment one.Referring to Fig. 6

The processing method of receiving terminal is μ and n with embodiment one _MaxBetween relational expression become:

$\mathrm{\μ}=N_G(1-\frac{n_{\max }}{T}),$ (corresponding to X (m)=DFT (x (k)))

Or $\mathrm{\μ}=\frac{n_{\max }}{T}{N}_G,$ (corresponding to X (m)=IDFT (x (k))), wherein n _MaxPeak for Y (m).Sequence classification index is corresponding to the source base station sign that sends reference sequences.Receiving terminal can calculate the source base station sign, and then finish Cell searching according to the peak that receives signal like this.

Corresponding to above-described small region search method, the embodiment of the invention also provides a kind of transmitting end equipment and receiving device.

Transmitting end equipment comprises basic sequence constructing module, sequence allocation module, reference sequences generation module.Wherein,

The basic sequence constructing module is used to construct basic sequence;

The sequence allocation module is used for being mapped to sequence classification index a plurality of uniquely or the single base station sign;

The reference sequences generation module, the basic sequence that is used for distributing to each base station carries out DFT or IDFT, and the sequence that obtains is as the reference sequence.

Here, the basic sequence constructing module comprises the basic sequence of particular category index μ based on formula (1) structure.

Receiving device comprises, reference sequences receiver module, sequence index determination module, Base Station Identification identification module.Wherein,

The reference sequences receiver module is used to receive the reference sequences that comprises based on basic sequence;

The sequence index determination module is used to determine the sequence classification index of the reference sequences that receives;

The Base Station Identification identification module, the sequence classification index that is used for determining is mapped to Base Station Identification.

The reference sequences that the embodiment of the invention provides has low PAPR value (near 0dB), and can provide good cell detection performance based on this specific reference sequences.In addition, simple based on the cell detection algorithm of the embodiment of the invention, do not bring any complexity to increase to system, help fast cell detection, sub-district switching etc.

One of ordinary skill in the art will appreciate that all or part of step in the whole bag of tricks of the foregoing description is to instruct relevant hardware to finish by program, this program can be stored in the computer-readable recording medium, and storage medium can comprise: ROM, RAM, disk or CD etc.

Use specific case herein principle of the present invention and execution mode are set forth, the explanation of above embodiment just is used for helping to understand method of the present invention and core concept thereof; Simultaneously, for one of ordinary skill in the art, according to thought of the present invention, the part that all can change in specific embodiments and applications, in sum, this description should not be construed as limitation of the present invention.

Claims (10)

1, a kind of fast cell search method is characterized in that, comprising:

Structure is based on the basic sequence of sequence classification index; Sequence classification index is mapped to Base Station Identification; Described basic sequence is carried out discrete Fourier transform (DFT) DFT or inverse discrete Fourier transformer inverse-discrete IDFT, with the sequence after the conversion as the reference sequence; Send reference sequences.

2, small region search method according to claim 1 is characterized in that, described basic sequence expression formula is

$x\left(k\right)=b\·\exp (-j(2\mathrm{\π\μ}\frac{k}{N_G}+c))$

Wherein, μ represents described sequence classification index, and k represents the index of sequence discipline, and b, c are any real number, and b ≠ 0, N _GBy the required number of reference sequences decision of reality.

3, small region search method according to claim 1, it is characterized in that, described described basic sequence is carried out after discrete Fourier transform (DFT) DFT or the inverse discrete Fourier transformer inverse-discrete IDFT, further comprise: the sequence after the conversion is made amendment, and described modification comprises interpolation or blocks.

4, small region search method according to claim 1 is characterized in that, after the basic sequence of described structure based on sequence classification index, further comprises: basic sequence is made amendment, and described modification comprises interpolation or blocks.

5, a kind of fast cell search method is characterized in that, comprising:

Reception comprises the reference sequences based on basic sequence; Determine the sequence classification index of described reference sequences; Described sequence classification index is mapped to Base Station Identification.

6, small region search method according to claim 5 is characterized in that, described definite sequence classification index comprises that receiving terminal according to the peak that receives signal, calculates sequence classification index.

7, a kind of transmitting end device is used for fast cell search, it is characterized in that, comprises original series constructing module, sequence allocation module, reference sequences generation module, wherein,

The basic sequence constructing module is used to construct basic sequence;

The sequence allocation module is used for being mapped to sequence classification index a plurality of uniquely or the single base station sign;

The reference sequences generation module, the basic sequence that is used for distributing to each base station carries out DFT or IDFT, and the sequence that obtains is as the reference sequence.

8, transmitting end device according to claim 7 is characterized in that, described basic sequence is based on sequence classification index.

9, a kind of receiving end device is used for fast cell search, it is characterized in that, comprising: reference sequences receiver module, sequence index determination module, Base Station Identification identification module, wherein,

The reference sequences receiver module is used to receive the reference sequences that comprises based on basic sequence;

The sequence index determination module is used to determine the sequence classification index of the reference sequences that receives;

The Base Station Identification identification module, the sequence classification index that is used for determining is mapped to Base Station Identification.

10, receiving end device according to claim 9 is characterized in that, described sequence index determination module calculates sequence classification index according to the position of the signal peak that receives.

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