CN102055708A - Timing synchronization scheme of multi-band orthogonal frequency division multiplexing (OFDM) ultra wide-band system - Google Patents

Abstract

Aiming at an IEEE 802.15.3a proposal and a multi-band orthogonal frequency division multiplexing (OFDM) ultra wide-band system adopted by the ECMA-368 standard, the invention designs an integral method applied to timing synchronization of the system. Frame detection and rough timing are performed by a leader sequence first frequency band information-based maximal self-correlation method and fine timing is performed by full three-frequency band information-based least energy ratio method. The timing position is corrected for two times, so the performance of algorithm is guaranteed. By the timing synchronization method, the residual timing deviation can be controlled in a relatively small range, so the residual timing deviation can be estimated by a frequency domain channel and absorbed uniformly. The scheme has relatively low complexity at the same time.

Description

The regular synchronization scheme of multi-band OFDM radio ultra wide band system

Technical field

The present invention relates to a kind of regular synchronization scheme of multi-band OFDM radio ultra wide band system, multi-band OFDM radio ultra wide band system at IEEE 802.15.3a motion and the employing of ECMA-368 standard, design the frame that is applicable to this system and detected, slightly regularly reached thin complete scheme regularly, thereby find the symbol start bit, carry out correct demodulation.

Background technology

Ultra broadband (UWB) wireless communication technology has characteristics such as power spectral density is low, transmission rate is high, the anti-multipath interference performance is strong, will be applied to the short distance high-speed radiocommunication, penetrate aspects such as imaging and measurement.The system of realization UWB has multiple, and wherein Mb-ofdm (MB-OFDM) technology is proposed the physical layer standard as indoor personal communication IEEE 802.15.3a, and is adopted by European ECMA-368 standard.OFDM (OFDM) is a kind of data transmission technology efficiently, the transmission data that it walks abreast by mutually orthogonal subcarrier, and the band efficiency height, the anti-multipath interference performance is strong.The OFDM technology is widely used in fields such as communications, for example European standard DAB, DVB, ADSL, IEEE802.11a and HIPERLAN II etc.In the traditional narrow ofdm system, be no more than protection at interval if timing offset is leading, then only bring and disturb (ICI) between subcarrier; need to use the method for channel estimating at frequency domain compensation; then also can bring intersymbol interference (ISI) if lag behind, cause the snr loss, systematic function seriously descends.

The MB-OFDM radio ultra wide band system is different with traditional single band ofdm system, and have following characteristics: different frequency bands has different channel responses and carrier wave frequency deviation; For the UWB system of power limited, adopt zero suffix (ZP) rather than Cyclic Prefix (CP) to avoid power loss; Employing is by the frequency hopping mechanism of time-frequency code control, thus the dehop that wrong timing position can make the mistake, and systematic function has deterioration.For the ZP-OFDM system of UWB, less timing offset compensates when can carry out frequency domain channel equalization by overlap-add (OLA) method.If the protection gap length is N _g, the multipath number is L, then the OLA method can be described as the last N with the OFDM symbol after the timing _gNumber and beginning N _gNumber phase adduction places beginning, makes the ZP-OFDM symbol become the CP-OFDM symbol of equivalence.When remaining timing offset d belongs to [(N _g-L), 0] time, being equivalent to the cyclic shift of OFDM symbol after the overlap-add operation in time domain, thus can compensate with pilot tone at frequency domain, otherwise will introduce ISI, systematic function is descended.

The ECMA-368 standard code a kind of MB-OFDM system of ultra broadband, this system transmissions speed can be up to 480Mbps, frequency band uses unallocated 3.1G-10.6GHz, and it is divided into 14 sub-frequency bands, each subband bandwidth is 528MHz, three subbands are one group, and the frequency hopping mechanism of time-frequency code control realizes the conversion of radio frequency part centre carrier frequency.FFT length is 128, comprising 100 information subcarriers, 12 pilot sub-carriers, 10 protections subcarrier, a direct current subcarrier and 5 gap carrier waves.Add length behind the transmitting terminal IFFT and be 37 ZP at interval, form length and be 165 OFDM symbol as protection.Every frame begins to be targeting sequencing, is made up of 24 synchronizing symbols and 6 channel estimation symbol.Synchronizing sequence in the structure of time-frequency domain as shown in Figure 1, its time-frequency code is 1,2,3,1,2,3.This system's brief block diagram as shown in Figure 2.

The UWB channel impulse response that IEEE 802.15.3a working group is recommended can be expressed as:

$h\left(t\right)=X\underset{n=1}{\overset{N}{\mathrm{\Σ}}}\underset{k=1}{\overset{K\left(n\right)}{\mathrm{\Σ}}}{\mathrm{\α}}_{\mathrm{nk}}\mathrm{\δ}(t-T_n-{\mathrm{\τ}}_{\mathrm{nk}})$

Wherein X is the lognormal stochastic variable, represents the amplitude gain of channel; N be observe bunch number, K (n) is the multipath number of receiving in n bunch, α=p _Nkβ _Nk, p _NkBe the discrete random variable of equiprobability+1 and-1, β _NkIt is the channel coefficients of the obeys logarithm normal distribution of k paths in n bunch.T _nBe the n bunch of time of advent, T _NkBe the time delay of k paths in n bunch, the two all obeys Poisson distribution.In addition, the multipath average power becomes two exponential decay models

$E\left[{\left|h_{k,l}\right|}^2\right]={\mathrm{\Ω}}_0{e}^{-\frac{T_n}{\mathrm{\Γ}}}{e}^{-\frac{{\mathrm{\τ}}_{\mathrm{nk}}}{\mathrm{\γ}}}$

E[. wherein] expression statistical average, Ω ₀Headed by reach the footpath average power,

Be a bunch arrival rate, γ is the footpath arrival rate.IEEE802.15.3a working group has determined four kinds of standard UWB channel model CM1～CM4, the distributed constant difference of the above-mentioned variable of four kinds of models, and wherein the CM4 channel is the most abominable.

Summary of the invention

The present invention seeks to multi-band OFDM radio ultra wide band system at IEEE 802.15.3a motion and the employing of ECMA-368 standard, design is applicable to the synchronous complete scheme of timing of this system, be intended to remaining timing offset control within the specific limits, thereby can be estimated by frequency domain channel and balanced the absorption by suitable timing algorithm.

Technical scheme of the present invention:

Use maximum correlation method to carry out frame detection and regularly thick, use least energy ratio method to carry out thin timing based on whole three band informations based on targeting sequencing first band information.Timing position is revised for twice, remaining timing offset is controlled at [(N _g-L), and 0] in the scope, guaranteed the performance of algorithm, this scheme has lower complexity simultaneously.

Beneficial effect of the present invention:

The present invention has designed a kind of regular synchronization scheme of multi-band OFDM radio ultra wide band system, this scheme has been taken into account regularly net synchronization capability and system's implementation complexity, realize effective correction with the lower algorithm of complexity to timing offset, promptly guaranteed the demodulation performance of receiver, make correct recovery initial data, reduced the realization cost again, hardware has been realized that the ultra-wideband communications receiver has actual directive significance.

Description of drawings

Fig. 1 is preamble synchronization sequential structure figure

Fig. 2 is the simple block diagram of MB-OFDM-UWB system

Fig. 3 (a) is the auto-correlation peak of auto-correlation window long 128

Fig. 3 (b) is the auto-correlation peak of auto-correlation window long 132

False-alarm and alarm dismissal probability under the different thresholdings of Fig. 4

Thick timing offset probability under Fig. 5 different channels model

Thin timing root-mean-square error under Fig. 6 different-energy window length

Thin timing root-mean-square error under Fig. 7 distinct symbols number

Thin timing offset probability line under Fig. 8 different channels model

Embodiment

Below in conjunction with accompanying drawing with by embodiment the specific embodiment of the present invention is described further:

The present invention has designed a kind of regular synchronization scheme of multi-band OFDM radio ultra wide band system, it is characterized in that: this programme may further comprise the steps:

A. receiver is before carrying out timing synchronously, and the local oscillator of down-conversion is initiated on first mid-band frequency;

B. frame detects preceding two training symbols that utilize first sub-band, asks the mould C of its autocorrelation value _i, and with this as judgement amount, set a threshold value G, work as C _i, C _I+1, C _I+2During all greater than G, confirm as and detected frame, order corresponding i=μ this moment, wherein i is the sample value sequence number, μ is the position that detects frame;

C. carry out thick timing, look for C more than or equal to μ and in smaller or equal to μ+M scope at i _iMaximum, and with the sample value sequence number i of this maximum correspondence _CtBe decided to be thick timing sync bit, M is the length of an OFDM symbol;

D. thick timing sync bit is done correction, revised thick timing sync bit i _Ct' deduct δ before equaling to revise _Ct, δ wherein _CtBe the thick maximum length of lag regularly;

E. start dehop according to revised thick timing position, with the previous window energy of three band informations and divided by adjacent back one window energy with, and its ratio is designated as D _i, in i belongs to certain limit, look for D _iMinimum value, the sample value sequence number i of this minimum value correspondence then _FtBe decided to be thin timing sync bit;

F. thin timing sync bit is done correction, revised thin timing sync bit i _Ft' deduct δ before equaling to revise _Ft, δ _FtBe the thin maximum length of lag regularly.

When doing auto-correlation computation, the auto-correlation length of window is got N among the step b, and wherein N is the subcarrier number of each frequency band.

The maximum length of lag of the thick timing described in the steps d refers to the maximum in the thick definite time delay deviation of four maximums under four kinds of ultra-wideband channel models.

The length of window of asking energy ratio among the step e is smaller or equal to N _g-L, wherein N _gBe the protection gap length, the maximum multipath number of L for rule of thumb choosing.

I described in the step e belongs to certain limit and refers to i more than or equal to i _Ct' and smaller or equal to i _Ct'+δ _Ct-γ, wherein i _Ct' be the described revised thick timing sync bit of steps d in the claim 1, δ _CtBe the maximum length of lag of the described thick timing of steps d in the claim 1, γ is the maximum in the thick timing advance deviation of four maximums under four kinds of ultra-wideband channel models.

Three band informations described in the step e can be the 3rd symbols of each frequency band in the targeting sequencing, also can be a plurality of symbols of each frequency band.

The maximum length of lag of the thin timing described in the step f refers to the maximum in the thin definite time delay deviation of four maximums under four kinds of ultra-wideband channel models.

Embodiment

The present invention is applied in the multi-band OFDM radio ultra wide band system of ECMA-368 standard this UWB system be carried out emulation, is illustrated in figure 3 as that frame detects and thick autocorrelation value C in synchronously _i, can see that correlation window length is that the relevant peaks of 128 correspondences is very sharp-pointed, 132 can make relevant peaks flat site occur, the thick regularly performance of influence.Fig. 4 is for signal to noise ratio is under 0dB, the CM4 channel, correlation window length was got 128 o'clock, the false-alarm of different threshold value G correspondences and alarm dismissal probability, and G gets 0.35～0.5 o'clock performance the best as can be seen.

Fig. 5 is that signal to noise ratio is that 0dB, correlation window length get 128, G gets 0.425 o'clock thick timing offset probability graph under AWGN, CM1～CM4 channel.Regularly performance is the poorest down for the CM4 channel as can be seen, the deviation maximum.Its maximum leading deviation is 2, and maximum hysteresis deviation is 32, then correction value δ _Ct=32.Find out easily under several channel models and all can not satisfy for all d _i' all belong to [(N _g-L _i), 0].For example, under the CM4 channel, d ₄∈ [9,32], after the correction, d ₄' ∈ [23,0].L ₄＝26，[-(N _g-L ₄)，0]＝[-11，0]。[23,0] do not belong to [11,0], so the OLA method can't be corrected; Under the CM1 channel, d ₁∈ [1,8], after the correction, d ₁' ∈ [33 ,-24], L ₁=8, [(N _g-L ₁), 0]=[29,0].[33 ,-24] do not belong to [29,0], and the OLA method can't be corrected equally.So need thin timing, thin regularly comparison range is [i _Ct', i _Ct'+34].For keeping lower complexity, do not estimate the channel multi-path number, but rule of thumb select bigger multipath several 26 that then energy window length is smaller or equal to 11.Fig. 6 is under the CM4 channel, and energy window length H is 5,6,8,10 and root-mean-square error (MSRE) curve of 11 o'clock thin timing offset.As can be seen, the MSRE of different windows length and is not that the big more effect of window is just good more all less than 2 during 12dB, and the different length window performance is close, so consider complexity, selects for use the window of smaller length can reach preferable performance.Fig. 7 under the CM4 channel, length of window is 5 o'clock, utilizes single symbol and a plurality of symbol to ask the MSRE curve of energy ratio, it is respectively the 3rd symbol, the 3rd to the 6th symbol and the 3rd to the 8th symbol that adopts targeting sequencing.Can see that symbolic number many timings performance more is good more, because utilize a plurality of symbols can play the effect of smooth noise.

By above-mentioned emulation, take all factors into consideration implementation complexity, we determine that finally energy window length is 5, utilize targeting sequencing the 3rd to the 8th totally six synchronizing symbols carry out thin timing.Fig. 8 is the thin timing offset probability graph when signal to noise ratio is 0dB under AWGN, CM1～CM4 channel.Can see that thin maximum hysteresis deviation regularly is 3, then revises δ _Ft=3, find out easily can guarantee like this under all channel model CM1～CM4 that the revised thin timing offset of secondary all drops on [(N _g-L _i), 0] in.So far we have reached re-set target, and remaining timing offset can be absorbed by frequency domain channel equalization.

Claims (7)

1. the regular synchronization scheme of a multi-band OFDM radio ultra wide band system, it is characterized in that: this programme may further comprise the steps:

A. receiver is before carrying out timing synchronously, and the local oscillator of down-conversion is initiated on first mid-band frequency;

B. frame detects preceding two training symbols that utilize first sub-band, asks the mould C of its autocorrelation value _i, and with this as judgement amount, set a threshold value G, work as C _i, C _I+1, C _I+2During all greater than G, confirm as and detected frame, order corresponding i=μ this moment, wherein i is the sample value sequence number, μ is the position that detects frame;

C. carry out thick timing, look for C more than or equal to μ and in smaller or equal to μ+M scope at i _iMaximum, and with the sample value sequence number i of this maximum correspondence _CtBe decided to be thick timing sync bit, M is the length of an OFDM symbol;

D. thick timing sync bit is done correction, revised thick timing sync bit i _Ct' deduct δ before equaling to revise _Ct, δ wherein _CtBe the thick maximum length of lag regularly;

E. start dehop according to revised thick timing position, with the previous window energy of three band informations and divided by adjacent back one window energy with, and its ratio is designated as D _i, in i belongs to certain limit, look for D _iMinimum value, the sample value sequence number i of this minimum value correspondence then _FtBe decided to be thin timing sync bit;

F. thin timing sync bit is done correction, revised thin timing sync bit i _Ft' deduct δ before equaling to revise _Ft, δ _FtBe the thin maximum length of lag regularly.

2. the regular synchronization scheme of a kind of multi-band OFDM radio ultra wide band system according to claim 1 is characterized in that: when doing auto-correlation computation, the auto-correlation length of window is got N among the step b, and wherein N is the subcarrier number of each frequency band.

3. the efficient implementation method of a kind of Digita Correlator (JP) according to claim 1 is characterized in that: the maximum length of lag of the thick timing described in the steps d refers to the maximum in the thick definite time delay deviation of four maximums under four kinds of ultra-wideband channel models.

4. the regular synchronization scheme of a kind of multi-band OFDM radio ultra wide band system according to claim 1 is characterized in that: the length of window of asking energy ratio among the step e is smaller or equal to N _g-L, wherein N _gBe the protection gap length, the maximum multipath number of L for rule of thumb choosing.

5. the efficient implementation method of a kind of Digita Correlator (JP) according to claim 1 is characterized in that: the maximum length of lag of the thin timing described in the step f refers to the maximum in the thin definite time delay deviation of four maximums under four kinds of ultra-wideband channel models.

6. the regular synchronization scheme of a kind of multi-band OFDM radio ultra wide band system according to claim 1 is characterized in that: the i described in the step e belongs to certain limit and refers to i more than or equal to i _Ct' and smaller or equal to i _Ct'+δ _Ct-γ, wherein i _Ct' be the described revised thick timing sync bit of steps d in the claim 1, δ _CtBe the maximum length of lag of the described thick timing of steps d in the claim 1, γ is the maximum in the thick timing advance deviation of four maximums under four kinds of ultra-wideband channel models.

7. the efficient implementation method of a kind of Digita Correlator (JP) according to claim 1, it is characterized in that: three band informations described in the step e can be the 3rd symbols of each frequency band in the targeting sequencing, also can be a plurality of symbols of each frequency band.

Images