CN101202728A - Method and system for communication based on OFDM - Google Patents

Abstract

The invention relates to the filed of wireless communication and discloses a method and a system of communication based on an OFDM to lead the performance of an OFDM system to be improved. In the invention, a sequence is proposed. The sequence has lower PAPR value and can be taken as a detecting sequence to carry through detecting distribution or as a nameplate to carry through channel estimation. In order to get the sequence, an initial CAZAC sequence is modified and PAPR value of the modified sequence is acquired by the means like simulation, etc. A better sequence of the PAPR is kept as the detecting sequence to carry through detecting distribution or as the nameplate to carry through channel estimation. By using truncation and sideband invariant switch like a cyclic shift, etc., the initial CAZAC sequence can be modified. When the length of the truncation is confirmed, the best estimation value of truncation length is acquired from the relation between the PAPR and the truncation length according to the simulation result and then searching is carried through on the preset range near the estimation value.

Description

Communication means and system based on OFDM

Technical field

The present invention relates to wireless communication field, particularly based on the communication technology of OFDM.

Background technology

Traditional frequency multiplexing technique is that data are only transmitted on a carrier signal, 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, and 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 data flow of these low speed.If these carrier waves are selected for use with the frequency hopping mode, even if the mutual aliasing of frequency spectrum also can keep mutually orthogonal waveform so.So just avoid the interference between the signal waveform, also improved the availability of frequency spectrum simultaneously.

Because used the MCM technology, OFDM has the stronger ability to anti-multipath, adopted by a lot of wireless communication standards, such as digital video broadcasting (Digital Video Broadcasting, be called for short " DVB ") technology, WLAN (wireless local area network) (Wireless Local Area Network, be called for short " WLAN "), micro-wave access to global intercommunication (Worldwide Interoperability for Microwave Access, be called for short " WiMAX ") and radio area network (Wireless Regional Area Network is called for short " WRAN ").

Module map such as Fig. 1 of OFDM describe.In ofdm system, be output as the output sum of N separate modulation carrier wave.A very high peak value will appear together when these carrier waves add.This will cause a very high power peak-to-average force ratio (Peak Average Power Ratio, be called for short " PAPR ") problem, this power amplifier that 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 believing that the PAPR value of leading to detection sequence or header is higher than the range of linearity of power amplifier, signal can clipped wave (amplitude limit wave absorption).The distortion that causes will cause channel estimating or synchronous inaccurate, and cause the packet error rate performance degradation of (Packet Error Rate is called for short " PER ").

This shows that the height of the PAPR value of channel detection sequence or header has considerable influence to the performance quality based on the system of OFDM.Introduce several typical situations below based on channel detection sequence or header in the system of OFDM.

In WRAN (IEEE802.22), ascending channel detecting is that necessary downlink information that base station (Base Station, be called for short " BS ") obtains carrying out closed loop transmission provides one fast and effective method.For the detection sequence that in the OFDM access scheme, distributes, need have the detection sequence of different length.The sequence of these frequency domains need have constant amplitude (flat frequency frequency spectrum just), and the channel estimation accuracy to all subcarriers is just identical like this.In the cellular OFDM system, each sub-district needs cover (frequency domain) sequence, and its corresponding time domain sequences has good their cross correlation, and He Cheng neighbor cell interference may diminish to tolerance interval like this.For convenience's sake, carry out inverse discrete Fourier transformer inverse-discrete (Inverse Discrete Fourier Transformation by frequency domain sequence, abbreviation " IDFT "), provides the cross-correlation function of the time domain sequences of sequence, abbreviate the time domain correlation function of certain particular sequence as.We represent that the frequency domain sequence that a length is N is s (n), n=0, and 1 ..., N-1, the discrete time-domain sequence S (k) that it is corresponding, k=0,1, N-1 can be obtained by its IDFT,

$S\left(k\right)=\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}s\left(n\right)\exp [-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20061017130500221.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;nk}/N]---\left(1\right)$

Its time domain correlation function then is,

$\mathrm{\&phi;}\left(m\right)=\underset{n=0}{\overset{N-1}{\mathrm{\&Sigma;}}}{S}_1\left(n\right){S_2}^{*}\left((n+m)\mathrm{mod}N\right)---\left(2\right)$

M=0 in the equation, 1 ..., N-1, and () ^*The expression complex conjugate.

In WiMAX (IEEE802.16) and WRAN (IEEE802.22) the inside, the sequence with the equal power ratio of ebb also is used as header (Preamble) to do synchronously and the function of channel estimating.

Current IEEE802.22 draft standard has proposed two candidates' detection sequence, is respectively Golay sequence and GCL (broad sense chirp sequence).Used in the IEEE802.16e standard is the Golay sequence, and its PAPR value is higher than 5dB.

The GCL sequence that the IEEE802.22 draft standard adopts is actually very special CAZAC sequence (constant amplitude zero auto-correlation), the just long Chu sequence of prime number length.Though the time domain cross-correlation function of Chu sequence has reached the amplitude of constant minimum, the time domain cross-correlation function equals the square root of sequence length for all cyclic shifts, but the not homotactic PAPR in the set also is different, when the sequence number of needs is very big, and the poorest 7dB that corrupts to.Its result uses in the sub-district of this difference sequence, and the accuracy of channel estimating and the PER that causes are influenced greatly.

For the binary PN sequence as header, in the IEEE802.22 the inside, PAPR can in IEEE802.16, also exceed 4dB up to 7dB.

Because the PAPR value as the sequence of detection sequence or header is higher, so require the power amplifier of transmitter to operate in a very big range of linearity with low efficiency, and need D/A (D/A) transducer and A/D (mould/number) transducer to have very big dynamic range, thereby improved the expense that system realizes.Surpassed the range of linearity of power amplifier as the PAPR value of infructescence, signal can clipped wave, and the distortion that causes thus will cause channel estimating or synchronous inaccurate, and causes the performance degradation of PER.

Summary of the invention

The technical problem underlying that each execution mode of the present invention will solve provides a kind of communication means and system based on OFDM, makes that the performance of ofdm system is improved.

For solving the problems of the technologies described above, embodiments of the present invention provide a kind of communication means based on OFDM, comprise following steps:

Choose initial constant amplitude zero auto-correlation CAZAC sequence;

Revise initial CAZAC sequence, from each sequence of revising gained, keep peak-to-average power ratio PAPR value and satisfy pre-conditioned sequence;

The sequence that use is retained is surveyed distribution or is carried out channel estimating as header as detection sequence.

Embodiments of the present invention also provide a kind of communication means based on OFDM, when surveying distribution or channel estimating, are N with the length that satisfies following feature _sSequence s _Optimal(n) sequence is as detection sequence or header:

s _optimal(n)＝s ₁(mod[(δ ₂+n)，N _s])exp(i2πnθ/N)

Wherein, s ₁(n)=s (mod[(δ ₁+ n), (N _s+ l)]), 0＜=n＜N _s, θ is a pseudo-random phase, N is the size of discrete Fourier transform (DFT), δ ₁And δ ₂Be cyclic shift or offset parameter, l blocks length, and s (n) is that length is sm ²=(N _s+ l) CAZAC sequence.

Embodiments of the present invention also provide a kind of communication system based on OFDM, and comprising the length that will satisfy following feature is N _sSequence s _Optimal(n) equipment that sends as detection sequence or header of sequence:

s _optimal(n)＝s ₁(mod[(δ ₂+n)，N _s])exp(i2πnθ/N)

Wherein, s ₁(n)=s (mod[(δ ₁+ n), (N _s+ l)]), 0＜=n＜N _s, θ is a pseudo-random phase, N is the size of discrete Fourier transform (DFT), δ ₁And δ ₂Be cyclic shift or offset parameter, l blocks length, and s (n) is that length is sm ²=(N _s+ l) CAZAC sequence.

Each execution mode of the present invention compared with prior art, the main distinction and effect thereof are:

The invention provides a kind of sequence with special characteristic, and use this sequence to survey distribution or carry out channel estimating as header as detection sequence, according to simulation result, this sequence can reduce the PAPR value effectively, thereby improves the performance of ofdm system.

In order to obtain above-mentioned sequence with low PAPR value, initial CAZAC sequence is made amendment, obtain the PAPR value of amended sequence by means such as emulation, keep PAPR sequence preferably, survey as detection sequence and distribute or carry out channel estimating as header.Because be not limited to known arrays such as Golay, GCL, but search in the larger context, increase greatly so obtain the possibility of the better sequence of PAPR value, the result of emulation has also proved and can find the PAPR value than the better sequence of prior art.Because in ofdm system, used the better sequence of PAPR value, so can improve the performance of ofdm system effectively.

Use is blocked and sideband invariant conversion (as cyclic shift etc.), initial CAZAC sequence is made amendment, the cross correlation that can keep sequence, and can go out a sequences of sets from an initial CAZAC sequence transformation, thus can satisfy the needs of surveying distribution and channel estimating.

When determining to block length, can be earlier according to simulation result from PAPR with block the relation of length and obtain optimum estimated value of blocking length, search near the preset range this estimated value again, obtain making the minimum optimum of PAPR to block length.So to estimate the result who finally obtains generally better because have, because only near estimated value, search for, so the workload of search is less.

Each sequence that is assigned to different districts is used the displacement of pseudorandom linear phase on frequency domain, or be equivalent in time domain application pseudorandom cyclic shift.Thereby the neighbor cell interference that each user is suffered has been carried out randomization, avoided occurring certain user and be subjected to the situation of poor neighbor cell interference always.

Description of drawings

Fig. 1 is typical ofdm system structure chart;

Fig. 2 is the communication means schematic flow sheet based on OFDM of the better embodiment according to the present invention;

Fig. 3 is that the search optimum of the better embodiment according to the present invention blocks the schematic flow sheet of length;

Fig. 4 is the distribution situation of typical OFDM symbol sub-carriers;

Fig. 5 is the simulation result comparison diagram of the present invention and prior art.

Embodiment

For making the purpose, technical solutions and advantages of the present invention clearer, the present invention is described in further detail below in conjunction with accompanying drawing.

In the present invention, propose a very building method of the CAZAC sequence of broad sense, just the complete unit root sequence structure of the normalization of Mow method comprises Frank, and Chu and GCL sequence and their sideband invariant converted version all have been considered.Reduce the PAPR value of these sequences by technology of blocking and sideband invariant switch technology.Also can obtain simultaneously a arrangement set by technology of blocking and cyclically shifted sequences with fine time domain cross-correlation mean square.For every the sequence that is assigned to different districts, a pseudorandom linear phase is moved in addition then, thus the suffered neighbor cell interference of randomization user.

In better embodiment of the present invention, the CAZAC sequence of the modification with low PAPR is used for system based on OFDM, as efficient channel detection sequence and header.These length are N _sSequence s _Optimal(n) can provide by following equation (1).

s _optimal(n)＝s ₁(mod[(δ ₂+n)，N _s])exp(i2πnθ/N) (1)

Wherein, s ₁(n)=s (mod[(δ ₁+ n), (N _s+ l)]), 0＜=n＜N _s, θ is a pseudo-random phase, N is the size of discrete Fourier transform (DFT), δ ₁And δ ₂Be cyclic shift or offset parameter, l blocks length, and s (n) is that length is sm ²=(N _s+ l) CAZAC sequence can be obtained by following normalizing PRUS structured approach.

$s\left(n\right)=\exp \left(\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="A20061017130500221.png"\; state="\{\{state\}\}">i</figure-callout>}2\mathrm{\&pi;}\frac{\mathrm{mc}\left(s\right)\mathrm{\&alpha;}\left(p\right){\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="A20061017130500221.png"\; state="\{\{state\}\}">k</figure-callout>}}^2+\mathrm{\&beta;}\left(p\right)k+f_p\left(0\right)}{\mathrm{sm}}\right)---\left(2\right)$

$n\&Element;{\mathrm{<figure-callout\; id="2"\; label="Z\; sm"\; filenames="A20061017130500221.png"\; state="\{\{state\}\}">Z</figure-callout>}}_{{\mathrm{sm}}^{}},$ p＝mod(n，m)，k＝floor(n/m)

Wherein, α (p) ∈ Z _sBe arbitrary function, satisfy $\gcd (\mathrm{\&alpha;}\left(p\right),s)=1,\&ForAll;p\&Element;Z_m$

β (p) ∈ Z _SmArbitrary function, (β (p) m) is Z to satisfy mod _mAn arrangement

$f_p\left(0\right),\&ForAll;p\&Element;Z_m,$ It is any rational

The particular content of PRUS structured approach can be referring to document (Wai Ho Mow, " A New UnifiedConstruction of Perfect Root-or-Unity Sequences ", Proc.IEEE 4th InternationalSymposium on Spread Spectrum Techniques and Applications (ISSSTA ' 96), Germany, September 1996, pp.955-959).

Article one, length is N _s=sm ²The PRUS sequence can obtain by equation (2).By selection appropriate C AZAC sequence from structured approach, and to the parameter δ in the equation (1) ₁, δ ₂Give suitable value with l, we can obtain having the CAZAC sequence of the modification of low PAPR value.One of them method of optimizing these parameter values is by the computer program search.Here δ 1, and δ 2 is exactly the skew of cyclic shift in fact, and l then is the appropriate length of blocking.

To explain the CAZAC sequence that how to obtain these modifications with low PAPR value in detail below, dependence diagram as shown in Figure 2.

In step 201, choose initial CAZAC sequence.Initial CAZAC sequence is chosen from complete unit root sequence (Perfect Root of Unity Sequences is called for short " the PRUS ") set with optimum cross-correlation.For example, can from Chu sequence, Frank sequence or their sideband invariant transformation results (as the FFT transformation results), choose initial CAZAC sequence.The length of initiation sequence can be identical or different in the set.The interval of initiation sequence length will be obtained enough greatly in the set, makes the peak value of time domain cross-correlation in acceptable level; While also will be obtained enough little, and the most bad PAPR value is little of the acceptable level in the feasible set.

After this enter step 202, revise initial CAZAC sequence.The present invention does not limit in principle to the mode of revising, and in better embodiment of the present invention, can revise initial CAZAC sequence in the following manner:

A blocks initial CAZAC sequence or sideband invariant conversion (as the FFT conversion) result, obtains a shorter sequence;

B carries out the conversion of sideband invariant, for example cyclic shift to the sequence after blocking.

For aforesaid operations A, one is had than practical application and need (Ns) longer sequence block to reduce its PAPR.Optimum, also, depend on the used sequence and the length of former sequence promptly corresponding to the length of blocking of minimum PAPR, rather than the minimum possible value of prior art suggestion.Two key factors are arranged in break-in operation: one is to block length l; Another is the skew δ of the subsequence of blocking ₁The optimum of estimating blocks length can be from hypothesis δ ₂Be to obtain in the PAPR of observation in 0 o'clock and the relation of blocking length.The present invention finds, all is no more than subduplicate 4 times of former sequence length usually corresponding to the length of blocking of hanging down PAPR.Near this estimates optimum point upper and lower to search decide the required adjustment of blocking length.Amount of calculation when this helps to reduce the hunting zone and is reduced in search.And sequence can at first be recycled displacement to obtain different PAPR values before being blocked.Therefore, in the superincumbent search procedure, block all cyclic shift versions of being applied to sequence PAPR value with further reduction sequence.Have (N altogether _s+ l) the selection of individual cyclic shift.Optimum cyclic shift δ ₁With block length l and in search, be recorded.Search procedure as shown in Figure 3.

For aforesaid operations B, the conversion that some do not change the sideband invariant of sequence autocorrelation performance can be applied in the sequence with further reduction PAPR value.The conversion example of present embodiment comprises the cyclic shift in FFT and the frequency domain.Can further reduce the PAPR value to the suitable cyclic shift δ 2 that blocks sequence.Operation A and B can combine in search and carry out.

Block and the cyclic shift version for any CAZAC sequence or its, the amplitude of its frequency domain is constant, and its time domain auto-correlation is a delta function.Pass through Parseval ' s theorem, equal its energy at frequency domain in the time domain cross-correlation function average energy of two sequences.This means that as long as the amplitude and the length of sequential element are fixed, any modification of sequence and conversion do not change its time domain cross-correlation energy.

After this enter step 203, obtain the PAPR value of modified sequence by emulation.Computational methods are as follows.

In an OFDM symbol, usually the subcarrier of the right and left all can be established and do zero, and with as protection at interval, simultaneously, DC also can be made as zero.In addition, also can insert zero between the adjacent data subcarrier.For extracting factor M, have (M-1) individual zero carrier between two adjacent data subcarriers.A typical OFDM symbol as shown in Figure 4.Required sequence length Ns can be obtained by following,

N _s＝floor[(N-Ng _l-Ng _r)/M] (3)

Wherein N is the length of FFT, and Ngl and Ngr are respectively the protection number of sub carrier wave of the right and left, and M extracts the factor, and floor (x) then represents to be no more than the maximum integer of x.

In the ofdm system that uses FFT 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:

$\mathrm{PAPR}=10\log \left[\underset{k\&Element;[0,\mathrm{DN}-1]}{\max }\frac{{\left|\left(\underset{n=0}{\overset{\mathrm{DN}-1}{\mathrm{\&Sigma;}}}{s}^{\&prime;}\left(n\right)\exp \right[-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20061017130500221.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;nk}/\left(\mathrm{DN}\right)\left]\right)\right|}^2}{\frac{1}{\mathrm{DN}}\underset{k=0}{\overset{\mathrm{DN}-1}{\mathrm{\&Sigma;}}}{\left|\left(\underset{n=0}{\overset{\mathrm{DN}-1}{\mathrm{\&Sigma;}}}{s}^{\&prime;}\left(n\right)\exp \right[-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20061017130500221.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&pi;nk}/\left(\mathrm{DN}\right)\left]\right)\right|}^2}\right]---\left(4\right)$

Wherein, N is the size of FFT, and D is oversample factor and is chosen as 4 at least.OFDM symbol s ' (n), n=0,1 ..., N-1 can be that the sequence of Ns obtains with a length, and is as follows,

Use above-mentioned formula 4, just can calculate the PAPR value of modified sequence with simulation means.

After this enter step 204, it is pre-conditioned whether the PAPR value of judging modified sequence satisfies, if then enter step 205, keeps this sequence and survey as detection sequence and distribute or carry out channel estimating as header, otherwise enter step 206, abandon this sequence.

The pre-conditioned PAPR value that can be the PAPR value of the sequence that is retained less than initiation sequence; The PAPR value of the sequence that perhaps, is retained is less than default thresholding.

After step 205 and step 206, get back to step 202, initial CAZAC sequence is proceeded to revise.After initial CAZAC sequence attempted predefined some kinds of alter modes, can obtain the set of a sequence that is retained, the PAPR value of the sequence in this set can satisfy pre-conditioned.

Though for the CAZAC sequence of any two unit amplitudes, the average energy of the cross-correlation function of its time domain equals the big or small N of FFT, the shape of cross-correlation can be controlled by the length difference before blocking of adjusting them.This provides in the big collection size, low PAPR value and hang down other of maximum cross correlation level and take all factors into consideration.Suppose that it is l that the optimum with minimum PAPR blocks length.Value l utilizes the previously described truncated process decision of this document.When selecting the Chu sequence in set, first sequence of set is to obtain to length N s by the length (Ns+l) of blocking the Chu sequence.More sequence can be by the Chu sequence of search length in [Ns+1-Δ/2, Ns+1+ Δ/2] scope, is truncated to then that Ns obtains, and here Δ is that search is that maximum stage is poor.The PAPR of these sequences is near minimum value.Simultaneously, increase when blocking length difference, the maximum time domain cross-correlation of two sequences can be lowered.When selecting the Frank sequence to set, all sequences are blocked identical length l.But, in the set sequence block the starting position and block after cyclic shift be different.The sequence that only has low PAPR value is chosen set.

Obtain by above method after the set of a sequence that is retained, each sequence that is assigned to different districts is used the pseudorandom linear phase, also be equal to the pseudorandom cyclic shift on the time domain cross-correlation function, its objective is suffered neighbor cell interference for each user of randomization.According to Parseval ' s theorem, the average energy of time domain cross-correlation function is constant.By the position that the randomization maximum cross correlation occurs, avoided occurring certain user and be subjected to the situation of poor neighbor cell interference always.It should be noted that linear phase on frequency domain is equivalent to the cyclic shift in time domain.Therefore, this operation does not change its PAPR value.

The pseudo-random phase displacement can be the function of a sub-district or sector index and/or user index and/or packets of information number.

In the prior art, during sequence in the set from selecting single the CAZAC sequence type, such as the Chu sequence.And, satisfy the arrangement set of cross-correlation feature, sequence is used differently extracted factor structures, rather than obtain by blocking with cyclic shift technique.

How explaining with simple example below can be by carrying out suitable blocking and cyclic shift to an initial Frank sequence, obtaining the CAZAC sequence that a length is the modification of 32 low PAPR,

1. structure length is 36,49 and 64 Frank sequence.Usually the optimum length l of blocking can be not 64 so we can limit maximum original series length above subduplicate 4 times of former sequence length.

2. (correspond respectively to and block length 4 for above every Frank sequence, 17 and 32) carry out all possible cyclic shift and (correspond respectively to cyclic shift parameter δ 1 [0,35], [0,48] and [0,63] choose in these scopes), and the rear section of sequence after the displacement blocked, to obtain the sequence of length 32.

3. carry out 32 possible cyclic shifts (in the scope of [0,31], choosing) again for the sequence of resulting every the length 32 of step 2, and calculate the PAPR value of these sequence correspondences corresponding to δ 2.These PAPR values and their corresponding parameters value δ 1, δ 2 and 1 record get up.

4. the PAPR value that step 3 is obtained is arranged, thereby determines the sequence corresponding to minimum PAPR value.

From above this simple case, we can obtain the sequence of a length 32, and its PAPR value is 2.07dB.Corresponding parameters value δ 1=15, δ 2=4,1=4, and institute's calling sequence is [1,1 ,-1,1 ,-1,1 ,-0.5000-0.8660i ,-0.5000+0.8660i, 1,-0.5000-0.8660i ,-0.5000+0.8660i, 1,0.5000-0.8660i ,-0.5000-0.8660i ,-1,-0.5000+0.8660i, 0.5000+0.8660i, 1,1,1,1,1,1,1,0.5000+0.8660i ,-0.5000+0.8660i ,-1,-0.5000-0.8660i, 1 ,-0.5000+0.8660i ,-0.5000-0.8660i, 1].

Provide some simulation results below.

Equation (1) has provided the CAZAC sequence of the modification of low PAPR value of the present invention.We will enumerate may selecting of parameter value in some equations and corresponding PAPR value.Below in the example, we have adopted the setting of IEEE802.22 the inside, and the size that also is FFT is 2048, about 160 and 159 zero subcarriers are respectively arranged respectively, the DC carrier wave is also established does zero.The PAPR value of wall scroll sequence and their corresponding parameters value δ ₁, δ ₂Be listed in table 1 li with l.PAPR value as the PN sequence of header in the IEEE802.22 is also listed, as a comparison.

The improvement and the suitable parameters value of table 1PAPR value

FFT size=2,048 zero subcarriers [160, DC, 159]

The PN sequence of IEEE 802.22

δ 1

δ 2

l

Modification of the present invention

					The CAZAC sequence
						Extract the short header (Frame Short Preamble) of the factor=4 frames	8.62dB	158	0	51	1.94dB
Extract the factor=2 frame length headers (Frame Long Preamble)	10.78dB	33	0	35	1.75dB
						Extract the short header (Superframe Short Preamble) of the factor=4 super frame	7.86dB	0	0	21	1.85dB
Extract the super frame length headers in the factor=2 (Superframe Long Preamble)	9.42dB	28	0	27	1.83dB

At disclosed technological document (IEEE 802.16e-2005, " IEEE Standard for Local and Metropolitan AreaNetworks-Part 16:Air Interface for Fixed Broadband Wireless Access Systems ", IEEE Standard, 28Feb 2006) lining, 114 PN sequences are used as header (Preamble).Their PAPR value exceeds 4dB.These numerical value also have the PAPR value of the CAZAC sequence of modification of the present invention, and the PAPR value of traditional Chu arrangement set as shown in Figure 5.Three data wires are arranged among Fig. 5, press order from the top down, article one is the PN sequence in 802.16, and second is the Chu sequence, and the 3rd is the CAZAC sequence of revising according to the present invention program.Can see that compare with the PN sequence, the PAPR of sequence of the present invention has reduced 3dB.We notice that the CAZAC arrangement set of this modification also can be used as the channel detection sequence simultaneously.

Technical scheme of the present invention can be applicable in the various communication systems based on OFDM, for example WLAN, DVB, WiMAX, WRAN or the like.Below for an example that technical scheme of the present invention is applied in the detection sequence of WRAN system.

WRAN is a kind of network that uses the fixing point of the UHF/VHF TV frequency range between 54 to 862MHz to multiple spot.In the WRAN standard, OFDM inserts (Orthogonal FrequencyMultiple Access is called for short " OFDMA ") and is adopted to support the multi-user.Because the output of FFT is separate subcarrier sum, cause amplitude to fluctuate in very big scope.Therefore big peak value will appear at the consistent addition of all subcarriers.Have high PAPR, power amplifier is required to be operated in the also exigent dynamic range of the very wide range of linearity and D/A and A/D converter, has improved the expense that realizes like this.When signal is used the wave absorption technology, the distortion that causes will make the PER performance degradation of system.The present invention is applicable to the detection sequence of WRAN system.Some reason is as follows:

Because WRAN uses the OFDM technology, so need to consider PAPR.Use technical scheme of the present invention and can reduce the PAPR value, thereby reduced the expense of system and improved the performance of system.

The detection sequence that needs some different lengths in WRAN satisfies certain auto-correlation and their cross correlation, and technical scheme of the present invention has solved this problem.

The modified CAZAC sequence that technical scheme of the present invention proposes also can be used for designing the header (Preamble) in the ofdm system, is used to lower PAPR value and neighbor cell interference.

In sum, in embodiments of the present invention, initial CAZAC sequence is made amendment, obtain the PAPR value of amended sequence by means such as emulation, keep PAPR sequence preferably, survey distribution or carry out channel estimating as header as detection sequence.Because be not limited to known arrays such as Golay, GCL, but search in the larger context, increase greatly so obtain the possibility of the better sequence of PAPR value, the result of emulation has also proved and can find the PAPR value than the better sequence of prior art.Because in ofdm system, used the better sequence of PAPR value, so can improve the performance of ofdm system effectively.

Use is blocked and sideband invariant conversion (as cyclic shift etc.), initial CAZAC sequence is made amendment, the cross correlation that can keep sequence, and can go out a sequences of sets from an initial CAZAC sequence transformation, thus can satisfy the needs of surveying distribution and channel estimating.

When determining to block length, can be earlier according to simulation result from PAPR with block the relation of length and obtain optimum estimated value of blocking length, search near the preset range this estimated value again, obtain making the minimum optimum of PAPR to block length.So to estimate the result who finally obtains generally better because have, because only near estimated value, search for, so the workload of search is less.

Each sequence that is assigned to different districts is used the displacement of pseudorandom linear phase on frequency domain, or be equivalent in time domain application pseudorandom cyclic shift.Thereby the neighbor cell interference that each user is suffered has been carried out randomization, avoided occurring certain user and be subjected to the situation of poor neighbor cell interference always.

Though pass through with reference to some of the preferred embodiment of the invention, the present invention is illustrated and describes, but those of ordinary skill in the art should be understood that and can do various changes to it in the form and details, and without departing from the spirit and scope of the present invention.

Claims (16)

1. the communication means based on orthogonal frequency division multiplex OFDM is characterized in that, comprises following steps:

Choose initial constant amplitude zero auto-correlation CAZAC sequence;

Revise described initial CAZAC sequence, from each sequence of revising gained, keep peak-to-average power ratio PAPR value and satisfy pre-conditioned sequence;

Use the described sequence that is retained to survey distribution or carry out channel estimating as header as detection sequence.

2. the communication means based on OFDM according to claim 1 is characterized in that, described initial CAZAC sequence is chosen from the complete unit root sequence PRUS set with optimum cross-correlation.

3. the communication means based on OFDM according to claim 2 is characterized in that, described initial CAZAC sequence is chosen from following sequence or its sideband invariant transformation results:

The Chu sequence, the Frank sequence.

4. the communication means based on OFDM according to claim 2 is characterized in that, described initiation sequence is chosen from the identical or different PRUS set of length.

5. the communication means based on OFDM according to claim 4 is characterized in that, the following requirement satisfied at the interval of initiation sequence length in the described PRUS set:

The peak value of time domain cross-correlation is in acceptable level;

The most bad PAPR value is little of acceptable level in the described set.

6. the communication means based on OFDM according to claim 1 is characterized in that, describedly pre-conditionedly is:

The PAPR value of the described sequence that is retained is less than the PAPR value of described initiation sequence; Or

The PAPR value of the described sequence that is retained is less than default thresholding.

7. according to each described communication means in the claim 1 to 6, it is characterized in that, revise described initial CAZAC sequence by following steps based on OFDM:

Carry out the conversion of sideband invariant after described initial CAZAC sequence blocked again.

8. the communication means based on OFDM according to claim 7 is characterized in that, described length of blocking obtains in the following manner:

According to simulation result from PAPR with block and obtain optimum estimated value of blocking length the relation of length;

Search near described estimated value the preset range, obtain making the minimum optimum of PAPR to block length.

9. the communication means based on OFDM according to claim 7 is characterized in that, described sideband invariant conversion comprises cyclic shift or fast Fourier transform.

10. according to each described communication means in the claim 1 to 6, it is characterized in that, also comprise following steps based on OFDM:

Each sequence that is assigned to different districts is used the displacement of pseudorandom linear phase on frequency domain, or be equivalent in time domain application pseudorandom cyclic shift.

11. the communication means based on OFDM according to claim 10 is characterized in that, the displacement of described pseudo-random phase is at least one a function in a sub-district or sector index, user index, the packets of information number.

12., it is characterized in that the PAPR value of each described sequence obtains by emulation according to each described communication means in the claim 1 to 6 based on OFDM.

13. the communication means based on OFDM is characterized in that,

When surveying distribution or channel estimating, be N with the length that satisfies following feature _sSequence s _Optimal(n) sequence is as detection sequence or header:

s _optimal(n)＝s ₁(mod[(δ ₂+n)，N _s])exp(i2πnθ/N)

Wherein, s ₁(n)=s (mod[(δ ₁+ n), (N _s+ l)]), 0＜=n＜N _s, θ is a pseudo-random phase, N is the size of discrete Fourier transform (DFT), δ ₁And δ ₂Be cyclic shift or offset parameter, l blocks length, and s (n) is that length is sm ²=(N _s+ l) CAZAC sequence.

14. the communication means based on OFDM according to claim 13 is characterized in that, described CAZAC sequence obtains by following PRUS structured approach:

$s\left(n\right)=\exp \left(i2\mathrm{\&pi;}\frac{\mathrm{mc}\left(s\right)\mathrm{\&alpha;}\left(p\right)k^2+\mathrm{\&beta;}\left(p\right)k+f_p\left(0\right)}{\mathrm{sm}}\right)$

n∈Z _sm ²，p＝mod(n，m)，k＝floor(n/m)

Wherein, α (p) ∈ Z _sBe arbitrary function, satisfy gcd (α (p), s)=1, $\&ForAll;p\&Element;Z_m$

β (p) ∈ Z _SmArbitrary function, (β (p) m) is Z to satisfy mod _mAn arrangement

$f_p\left(0\right),\&ForAll;p\&Element;Z_m,$ It is any rational.

15. the communication system based on OFDM is characterized in that, comprising the length that will satisfy following feature is N _sSequence s _Optimal(n) equipment that sends as detection sequence or header of sequence:

s _optimal(n)＝s ₁(mod[(δ ₂+n)，N _s])exp(i2πnθ/N)

Wherein, s ₁(n)=s (mod[(δ ₁+ n), (N _s+ l)]), 0＜=n＜N _s, θ is a pseudo-random phase, N is the size of discrete Fourier transform (DFT), δ ₁And δ ₂Be cyclic shift or offset parameter, l blocks length, and s (n) is that length is sm ²=(N _s+ l) CAZAC sequence.

16. the communication system based on OFDM according to claim 15 is characterized in that,

Described communication system comprises WLAN (wireless local area network), digital video broadcasting, micro-wave access to global intercommunication or radio area network.

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