CN1909534A - Reconstructional OFDM system and its operation method for transmitting and receiving - Google Patents

Abstract

The invention relates to an OFDM system which can be rebuilt, wherein in said system, using received pilot signal, estimating the maximum time delay extending mean square root and Doppler frequency shift of said signal channel, based on which, fixing the upper and lower limits of time period of OFDM mark and finding the period; the CP controllers of sender and receiver, based on the signal channel band width, the OFDM mark period and the band width efficiency factor, fixing the modulate carrier wave number of OFDM mark, the total sub carrier wave number and the sub carrier wave number occupied by the cycle prefix; using obtained OFDM parameter, controlling the operations of sender and receiver. The inventive system can self-adaptive adjust the cycle prefix and sub carrier wave, to improve the system frequency efficiency.

Description

Restructural ofdm system and transmission thereof and reception method of operation

Technical field

The present invention relates to a kind of reconfigurable OFDM (OFDM) system, particularly adopt the information transmission system and the transmission and the reception method of operation of the WLAN (wireless local area network), mobile communication, ground digital television broadcast etc. of OFDM.

Background technology

Along with the fusion gradually of wireless network, multimedia technology and internet, people are more and more higher to the requirement of the type of radio communication service and quality.For satisfying the requirement of radio multimedium and high speed data transfers, need the Development of New Generation wireless communication system.In the new generation of wireless system, to network layer, will extensively adopt some new technologies from physical layer, media access control layer, for example OFDM (OFDM) etc.

OFDM is divided into many orthogonal sub-channels to channel at frequency domain; whole wideband frequency selective channel is divided into the subchannel of relatively flat; simultaneously, insert Cyclic Prefix (CP) as protection interval (GI), greatly reduce intersymbol interference (ISI) at each OFDM intersymbol.Because OFDM has advantages such as ability of anti-multipath is strong, its application of in systems such as ADSL, VDSL, DVB, DAB and WLAN, having succeeded, and generally believe that it is the key technology of new generation of wireless transmission link.

In ofdm system, important characteristic is to introduce Cyclic Prefix to reduce the multipath channel time delay and expand caused ISI influence.General ofdm system greater than the principle of channel maximum delay expansion (be generally time delay expansion root mean square RMS value 2～4 times), comes the CP of designs fix according to CP length.Actual test shows, in indoor office environments, the RMS value is about 35ns, and at environment such as factories, the RMS value reaches 300ns.If according to indoor office environments design CP, can be subjected to serious ISI when entering environment such as factories and miness when portable terminal; If according to Environment Design CP such as factories and miness, when portable terminal entered indoor office environments, the length of CP existed the increasing surplus, had expended defectives such as excess power resource.

Fig. 5 is the operational flowchart according to the ofdm system of prior art.At step S501, receiving terminal estimates channel condition information according to the signal that receives; At step S502, calculate the length of the minimum protection time slot (Cyclic Prefix) of eliminating symbol delay; And, adjust OFDM symbol protection slot length at step S503.In the disclosed prior art of some documents, solve this problem by CP length reasonable in design.For example, U.S. Pat 6535550 has disclosed according to the sample of signal of receiving terminal output and has regulated circulating prefix-length.In the European patent EP 1439679,, proposed to change and protected time slot (CP) length, carrier cycle to wait and distinguish different carrier transmitting the ofdm system of TV signal.Japan Patent JP2003152670 has proposed to decide the length of protecting time slot by the correlation between N the sample of N sample of protection time slot end and significant character end.The minimum protection slot length that European patent EP 1014639 has proposed to utilize channel quality to calculate eliminates delayed symbol.In existing these patents, only go out to send design CP length from static channel mostly, and do not redesign the carrier wave that transmits data when changing CP length, based on this, the present invention proposes a kind of ofdm system and transmission and reception method of operation with scalable characteristic.

The list of references tabulation:

[1] Hyunsoo cheon, Daesik Hong are published in IEEE communicationletters, in May, 2002, the 6th volume, the article that is entitled as " Effectof channel estimation error in OFDM-based WLAN " on No. 3, the 190th～192 page.

[2] Osval do Simeone, Yeheskel Bar-Ness, Umberto Spagnolini are published in IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, in January, 2004, the 3rd volume, the article that is entitled as " Pilot-Based Channel Estimation forOFDM Systems by Tracking the Delay-Subspace " on No. 1.

[3] R.Negi and J.Cioffi are published in IEEE Trans.ConsumerElectron., in August, 1998, the 44th volume, the article that is entitled as " Pilottone selection for channel estimation in a mobile OFDM system " on the 1122nd～1128 page.

Summary of the invention

The object of the present invention is to provide a kind of ofdm system and method for operation thereof of adaptive channel environmental change, be used for overcoming the shortcoming of traditional ofdm system fixation of C P.

According to a first aspect of the invention, a kind of restructural ofdm system has been proposed, comprise transmitting terminal and receiving terminal, it is characterized in that: described transmitting terminal comprises the Cyclic Prefix control device, described receiving terminal comprises channel delay and Doppler's estimation unit, and Cyclic Prefix control device, the pilot signal that described channel delay and the utilization of Doppler's estimation unit receive, estimate the maximum delay expansion root-mean-square value and the Doppler frequency shift of channel, maximum delay expansion root-mean-square value and Doppler frequency shift according to channel, determine OFDM symbol time cycle on, lower bound, and determine its cycle; And these estimated informations are input to the Cyclic Prefix control device of receiving terminal, and the control information foldback is given the Cyclic Prefix control device of transmitting terminal by feedback channel; The Cyclic Prefix control device of described receiving terminal and transmitting terminal is determined the sub-carrier number that the modulated carrier number of OFDM symbol, total sub-carrier number and Cyclic Prefix take according to channel width, OFDM symbol time cycle and bandwidth efficiency coefficient; And utilize the OFDM parameter that is obtained, the operation of described transmitting terminal and receiving terminal is controlled.

Preferably, described channel delay and Doppler's estimation unit are determined the upper bound of OFDM symbol time cycle according to the peak carrier deviation of system requirements and the ratio of channel maximum doppler frequency.

Preferably, described channel delay and Doppler's estimation unit are at first determined the Cyclic Prefix duration according to the maximum delay expansion root-mean-square value of multipath channel, and then the lower bound of the time cycle of definite OFDM symbol.

Preferably, the described Cyclic Prefix duration of described channel delay and Doppler's estimation unit is set to more than or equal to 2 times of maximum delay expansion root-mean-square value and less than its 4 times.

Preferably, described channel delay and Doppler's estimation unit are determined the lower bound of the time cycle of OFDM symbol according to the ratio in cyclic prefix period and OFDM symbol cycle.

In addition, in restructural ofdm system according to the present invention, described transmitting terminal also comprises: contrary discrete fourier transform device is used for input signal is modulated into OFDM symbol; Add the Cyclic Prefix device, be used for control, before each OFDM symbol, insert Cyclic Prefix according to described transmitting terminal Cyclic Prefix control device; The emission rf chain is used for the orthogonal frequency-division multiplex base tape symbol is modulated; Transmitting antenna is used for the orthogonal frequency-division multiplex base tape symbol after the modulation is transmitted into channel; And described receiving terminal also comprises: reception antenna is used for the signal that receiving end/sending end is launched; The received RF chain is used for the signal that reception antenna is received and down-converts to baseband signal; Shift out the Cyclic Prefix device, according to the control of described receiving terminal Cyclic Prefix control device, the signed Cyclic Prefix of deletion orthogonal frequency-division multiplex base; The discrete fourier transform device carries out demodulation to OFDM symbol, and the OFDM symbol after the output demodulation.

According to a second aspect of the invention, propose a kind of transmission of restructural ofdm system and received method of operating, it is characterized in that may further comprise the steps: utilize the pilot frequency sequence that sends, estimate the maximum delay expansion root-mean-square value of multipath channel and the maximum doppler frequency of channel; According to the maximum delay expansion root-mean-square value of multipath channel, determine the lower bound of the time cycle of OFDM symbol; According to the channel maximum doppler frequency, determine the upper bound of the time cycle of OFDM symbol; Upper and lower boundary according to time cycle of OFDM symbol determines its cycle; According to the time cycle and the bandwidth efficiency coefficient of channel width, OFDM symbol, determine the sub-carrier number that the modulated carrier number of OFDM symbol, total sub-carrier number and Cyclic Prefix take; Utilize the OFDM parameter that is obtained, the transmitting terminal of described restructural ofdm system and the transmission and the reception operation of receiving terminal are controlled.

Preferably, according to the peak carrier deviation of system requirements and the ratio of channel maximum doppler frequency, determine the upper bound of the time cycle of OFDM symbol.

Preferably,, at first determine the Cyclic Prefix duration according to the maximum delay expansion root-mean-square value of multipath channel, and then the lower bound of the time cycle of definite OFDM symbol.

Preferably, the described Cyclic Prefix duration is set to more than or equal to 2 times of maximum delay expansion root-mean-square value and less than its 4 times.

Preferably, according to the ratio in cyclic prefix period and OFDM symbol cycle, determine the lower bound of the time cycle of OFDM symbol.

Description of drawings

Below with reference to accompanying drawings, the preferred embodiments of the present invention are described in detail, wherein:

Fig. 1 shows the example of OFDM symbol;

Fig. 2 shows the block diagram of restructural ofdm system according to an embodiment of the invention;

Fig. 3 shows the OFDM symbolic construction that is used in according in the restructural ofdm system of the embodiment of the invention;

Fig. 4 shows the flow chart according to the method for operation of the restructural ofdm system of the embodiment of the invention; And

Fig. 5 is the operational flowchart according to the ofdm system of prior art.

Embodiment

Below in conjunction with accompanying drawing the present invention is specified.Be noted that described embodiment only is for illustrative purposes, rather than limitation of the scope of the invention.Described various numerical value is not to be used to limit the present invention, and these numerical value can carry out any suitable modification according to those of ordinary skills' needs.

In traditional ofdm system, the base-band information bit stream is delivered to respectively behind the serial to parallel conversion on a plurality of subcarriers through coding, modulation, respectively each subcarrier data is carried out amplifying the back against discrete fourier transform (IDFT), radio frequency and sends.For eliminating intersymbol interference (ISI), insert Cyclic Prefix (CP) at interval as protection at the OFDM intersymbol.At receiving terminal, behind the deletion CP, utilize discrete fourier transform (DFT) that each subcarrier data stream is carried out demodulation, and after also string was converted to serial data stream, last demodulation, decoding recovered the transmission signal.In traditional ofdm system, be the opposing multipath fading, at the CP of OFDM intersymbol insertion regular length, shown in Fig. 1 (a).When motion of mobile terminals, the continuous change of its channel circumstance, time delay expansion root mean square (RMS) value of channel also becomes thereupon.Suppose to exist two kinds of channel circumstances, the maximum RMS value of the time delay of channel 1 is τ _Max1, the maximum RMS value of the time delay of channel 2 is τ _Max2, and τ _Max2＜＜τ _Max1If according to τ _Max1Design CP, it is long to be l ₁, if according to τ _Max2Design CP, it is long to be l ₂, and l ₁＞l ₂, as Fig. 1 (b).At this moment, can see, if design the long l of being of CP regularly ₁, then for channel 2, the time domain samples number that expends is l ₁-l ₂On the contrary,, adjust CP adaptively,, the length of CP is changed into l as for channel 2 if with the channel environment change ₂, then can increase (l ₁-l ₂) individual OFDM subcarrier, like this, both avoided the wasting of resources, also can improve system's speed.

Specifically, in order to overcome the shortcoming of inserting fixation of C P, the present invention proposes a kind of restructural ofdm system, as shown in Figure 2.Fig. 2 shows the block diagram according to the restructural ofdm system of the embodiment of the invention.At the base station transmitting terminal, input information is flowed through after IDFT unit 201 is modulated into the OFDM symbol, add CP unit 202 and before each OFDM symbol, insert Cyclic Prefix (CP), RF chain 203 the modulation of OFDM baseband signalling after antenna 204 be transmitted on the channel.At user's receiving terminal, RF chain 207 down-converts to baseband signal to the signal that receives from antenna 206, shifts out CP unit 208 the deletion of the Cyclic Prefix of OFDM baseband signalling, and the 209 pairs of OFDM symbols in DFT unit carry out exporting after the demodulation; The channel delay of user side and Doppler's estimation unit 210 utilize the pilot signal that receives to estimate the RMS scope of channel and speed, the Doppler frequency shift of user terminal, and these estimated informations are input to CP control unit 211, this unit 211 is input to the CP control information and shifts out CP unit 208, and control information being returned to the CP control unit 205 of base station end by feedback channel, CP control unit 205 is in order to adjust the length of CP.

According to description to above system, if under the static channel environment, utilize the RMS value of estimating to obtain channel earlier, design CP length again.How to design the transmission system of spectral efficient below from the discussion of ofdm system parameter.

Define following parameter: channel width B earlier; System subcarrier is counted N; (I) the FFT modulated carrier is counted N _Mod(may need the zero padding operation during because of (I) FFT computing, so N _Mod≤ N); The long N of CP _CPModulation constellation exponent number C; The subcarrier period T.Then obtain: OFDM symbol period (duration) T _s=NT; Frequency interval Δ f between subcarrier _c=l/T _sThe CP duration T _CP=N _CPT.System spectral efficiency can be represented by formula (1).

$\mathrm{\η}=\frac{N_{\mathrm{mod}}}{N+N_{\mathrm{CP}}}\·\frac{{\log }_{2}C}{\mathrm{BT}}---\left(1\right)$

The transmission rate of its OFDM symbolic blocks of expression (comprising CP).Introduce bandwidth efficiency α=N _ModΔ f _c/ B, then spectrum efficiency can be expressed as with formula (2).

$\mathrm{\η}=\frac{\mathrm{\α}}{1+N_{\mathrm{CP}}/N}\·{\log }_{2}C$

$=\frac{\mathrm{\α}}{1+T_{\mathrm{CP}}/T_s}\·{\log }_{2}C---\left(2\right)$

If definition ζ=T _CP/ T _s, then formula (2) further can be rewritten as following formula (3).

$\mathrm{\η}=\frac{\mathrm{\α}}{1+\mathrm{\ζ}}\·{\log }_{2}C---\left(3\right)$

After the bandwidth efficiency factor alpha is fixing,, need make ζ as far as possible little for obtaining highest spectral efficiency.Therefore, when portable terminal is low from entering than the long time delay extended channel, during delay extended channel, shorten the CP duration adaptively, simultaneously, under constant situation of OFDM symbolic blocks duration, prolong OFDM data symbol time T _s, ζ is corresponding to diminish, and the spectrum efficiency of system improves.If make T _CP=(2～4) τ _Max, then can design the OFDM symbol period as shown in Equation (4)

T _s＝(2～4)τ _max/ζ (4)

Usually, for reducing the expense of CP, generally set ζ≤1/4, as in the IEEE802.11a standard, the CP duration is 800ns, accounts for 1/5 of OFDM symbol duration 4 μ s, i.e. ζ=1/5.

More than analyze the parameter designing under the static multipath channel, become the parameter adjustment under (dynamically) channel condition when discussing below.At this moment, need consider that the upper bound of ICI power is by formula (5) expression (referring to list of references [1]) owing to terminal moves the inter-carrier interference (ICI) that the carrier wave frequency deviation ε that causes causes

$P_{\mathrm{ICI}}<\frac{{\mathrm{\&pi;}}^2}{3}\&CenterDot;{\mathrm{\&epsiv;}}^2---\left(5\right)$

Hence one can see that, and ε is more little for carrier wave frequency deviation, and inter-carrier interference (ICI) is also low more.If maximum doppler frequency is f _d, then peak carrier deviation is ε=f _d/ Δ f _c, promptly as shown in Equation (6)

ε＝f _dT _s (6)

So can get T _s=ε/f _d, because of ε is more little, the OFDM performance is good more, so T _sOn be limited to T _s=ε/f _d, can be expressed as formula (7)

T _s≤ε/f _d (7)

Simultaneous formula (4) and (7), the OFDM symbol period that obtains under time-variant multipath channel should satisfy the condition of being represented by following formula (8):

(2～4)τ _max/ζ≤T _s≤ε/f _d (8)

Above-mentioned condition combined channel parameter and system parameters feature are determined the OFDM data symbol duration, have the advantage of spectrum efficiency height, strong robustness.

Fig. 3 shows the OFDM symbolic construction that is used in the restructural ofdm system shown in Figure 2.In Fig. 3, the OFDM symbol period remains unchanged, but the modulated sub-carriers number of CP length and transmission data becomes with the channel condition.

Fig. 4 shows the flow chart according to the method for operation of the restructural ofdm system of the embodiment of the invention.

At first, at step S401, the pilot frequency sequence that the receiving terminal utilization sends, according to prior art, the method that list of references for example above-mentioned [2], [3] are proposed estimates the maximum delay expansion root mean square RMS value of multipath channel.At step S402, choose the Cyclic Prefix duration more than or equal to 2 times of maximum delay expansion root-mean-square value and less than its 4 times.At step S403,, determine the lower bound (equation (4)) in OFDM symbol time cycle according to the ratio of cyclic prefix period and OFDM symbol period.Meanwhile, at step S404, the pilot frequency sequence that the receiving terminal utilization sends estimates the maximum doppler frequency of channel.At step S405,, determine the upper bound (equation (7)) in OFDM symbol time cycle according to the peak carrier deviation of system requirements and the ratio of channel maximum doppler frequency.At step S406, the upper and lower boundary according to the OFDM symbol time cycle determines its cycle.At step S407, according to channel width, OFDM symbol time cycle and bandwidth efficiency coefficient, calculate the modulated carrier number of OFDM symbol, the sub-carrier number that total sub-carrier number and Cyclic Prefix take.At last, at step S408, the OFDM parameter that obtains is sent into the Cyclic Prefix control unit, this unit outputs to corresponding unit to each parameter control information, and adjusts parameter.

Compare with the conventional method (see figure 5), it is maximum delay expansion root-mean-square value and maximum doppler frequency that the present invention need to have pointed out estimated channel information clearly, and readjusts the carrier number of Cyclic Prefix and transmission data according to these channel conditions.In conventional method, only utilized the maximum delay expansion root-mean-square value information of static channel to design CP length, the carrier wave that transmits data is not carried out any readjusting yet.

Below provided the instantiation of using according to restructural ofdm system of the present invention and method of operation thereof.The RMS that supposes certain channel is τ _Max=200ns, work carrier wave frequency range f _c=5GHz, moving velocity of terminal v=30m/s, maximum doppler frequency f _d=v/ λ=vf _c/ c=30 * 5 * 10 ⁹/ 3 * 10 ⁸=500Hz, channel width B=15MHz, QPSK modulation.If select ζ=0.2, bandwidth efficiency factor alpha=0.8, frequency deviation ε≤0.005 then can obtain:

The CP period T _CP=4 τ _Max=800ns;

The scope of OFDM symbol duration is:

4 τ _Max/ ζ≤T _s≤ ε/f _d=800ns/0.2≤T _s≤ 0.005/500=4 μ s≤T _s≤ 10 μ s select T _s=4 μ s, at this moment the OFDM data carrier part duration is 4-0.8=3.2 μ s;

Modulated carrier is counted N _Mod=α T _sB=0.8 * 4 * 10 ^-6* 15 * 10 ⁶=48;

Sub-carrier number N=N _Mod/ α=48/0.8=60 realizes for being easy to FFT, inserts 4 zero subcarriers (not transmitting data), selects N=64;

CP length is $N_{\mathrm{CP}}=\frac{T_{\mathrm{CP}}}{T_s}\&CenterDot;N=\frac{0.8}{4}\&CenterDot;64=12.8,$ Be taken as 12;

System spectral efficiency $\mathrm{\&eta;}=\frac{48}{64+12}\&CenterDot;\frac{{\log }_{2}2}{15\&times;{10}^6\&times;4\&times;{10}^{-6}/64}=0.67\mathrm{bps}/\mathrm{Hz}.$

If portable terminal enters in another environment, the RMS of this channel is τ _Max=50ns, if utilize this RMS value redesign, then relevant system parameters is:

The CP period T _CP=4 τ _Max=200ns;

OFDM symbol duration scope is:

4 τ _Max/ ζ=200ns/0.2≤T _s=1 μ s≤T _s,, select the T identical with afore-mentioned for reducing complexity _s=4 μ s, at this moment the OFDM data carrier part duration is 4-0.2=3.8 μ s, compares with afore-mentioned, this duration has increased by 0.6 μ s.This part time can be used for increasing the carrier number that transmits data, so can select bigger bandwidth efficiency factor alpha=0.95;

Modulated carrier is counted N _Mod=α T _sB=0.95 * 4 * 10 ^-6* 15 * 10 ⁶=57;

Sub-carrier number N=N _Mod/ α=57/0.95=60 realizes for being easy to FFT, inserts 4 zero subcarriers (not transmitting data), selects N=64;

CP length is $N_{\mathrm{CP}}=\frac{T_{\mathrm{CP}}}{T_s}\&CenterDot;N=\frac{0.2}{4}\&CenterDot;64=3.2,$ Be taken as 4;

System spectral efficiency $\mathrm{\&eta;}=\frac{57}{64+4}\&CenterDot;\frac{{\log }_{2}2}{15\&times;{10}^6\&times;4\&times;{10}^{-6}/64}=0.89\mathrm{bps}/\mathrm{Hz}.$

As seen, in difference according to channel circumstance, adjust CP and modulated carrier parameter adaptively after, system spectral efficiency has improved 0.89-0.67=0.22bps/Hz, correspondingly, transmission speed can improve 0.22 * 15 * 10 ⁶=3.3Mbps, and satisfy anti-ISI condition simultaneously.

Although illustrated and described the present invention at exemplary embodiments, will be understood by those skilled in the art that, under the situation that does not break away from the spirit and scope of the present invention, can carry out various other change, replacement and interpolations.Therefore, the present invention should not be understood that to be limited to above-mentioned particular instance, and should be limited by claims.

Claims (11)

1, a kind of restructural ofdm system comprises transmitting terminal and receiving terminal, it is characterized in that:

Described transmitting terminal comprises the Cyclic Prefix control device, and described receiving terminal comprises channel delay and Doppler's estimation unit and Cyclic Prefix control device,

The pilot signal that described channel delay and the utilization of Doppler's estimation unit receive, estimate the maximum delay expansion root-mean-square value and the Doppler frequency shift of channel, maximum delay expansion root-mean-square value and Doppler frequency shift according to channel, determine the upper and lower boundary of the time cycle of OFDM symbol, and determine its cycle; And these estimated informations are input to the Cyclic Prefix control device of receiving terminal, and the control information foldback is given the Cyclic Prefix control device of transmitting terminal by feedback channel;

The Cyclic Prefix control device of described receiving terminal and transmitting terminal is determined the sub-carrier number that the modulated carrier number of OFDM symbol, total sub-carrier number and Cyclic Prefix take according to channel width, OFDM symbol time cycle and bandwidth efficiency coefficient; And utilize the OFDM parameter that is obtained, the operation of described transmitting terminal and receiving terminal is controlled.

2, restructural ofdm system according to claim 1, it is characterized in that described channel delay and Doppler's estimation unit according to the peak carrier deviation of system requirements and the ratio of channel maximum doppler frequency, determine the upper bound of OFDM symbol time cycle.

3, restructural ofdm system according to claim 1, it is characterized in that described channel delay and Doppler's estimation unit maximum delay expansion root-mean-square value according to multipath channel, at first determine the Cyclic Prefix duration, and then the lower bound of definite OFDM symbol time cycle.

4, restructural ofdm system according to claim 3 is characterized in that the described Cyclic Prefix duration of described channel delay and Doppler's estimation unit is set to more than or equal to 2 times of maximum delay expansion root-mean-square value and less than its 4 times.

5, restructural ofdm system according to claim 3, it is characterized in that described channel delay and Doppler's estimation unit according to the ratio in cyclic prefix period and OFDM symbol cycle, determine the lower bound of OFDM symbol time cycle.

6, according to any one the described restructural ofdm system in the aforementioned claim, it is characterized in that:

Described transmitting terminal also comprises: contrary discrete fourier transform device is used for input signal is modulated into OFDM symbol; Add the Cyclic Prefix device, be used for control, before each OFDM symbol, insert Cyclic Prefix according to described transmitting terminal Cyclic Prefix control device; The emission rf chain is used for the orthogonal frequency-division multiplex base tape symbol is modulated; Transmitting antenna is transmitted into the orthogonal frequency-division multiplex base tape symbol after the modulation on the channel; And

Described receiving terminal also comprises: reception antenna is used for the signal that receiving end/sending end is launched; The received RF chain is used for the signal that reception antenna is received and down-converts to baseband signal; Shift out the Cyclic Prefix device, according to the control of described receiving terminal Cyclic Prefix control device, the signed Cyclic Prefix of deletion orthogonal frequency-division multiplex base; The discrete fourier transform device carries out demodulation to OFDM symbol, and the OFDM symbol after the output demodulation.

7, a kind of transmission and reception method of operating of controlling the restructural ofdm system adaptively is characterized in that may further comprise the steps:

Utilize the pilot frequency sequence that sends, estimate the maximum delay expansion root-mean-square value of multipath channel and the maximum doppler frequency of channel;

According to the maximum delay expansion root-mean-square value of multipath channel, determine the lower bound of the time cycle of OFDM symbol;

According to the channel maximum doppler frequency, determine the upper bound of the time cycle of OFDM symbol;

Upper and lower boundary according to time cycle of OFDM symbol determines its cycle;

According to the time cycle and the bandwidth efficiency coefficient of channel width, OFDM symbol, determine the sub-carrier number that the modulated carrier number of OFDM symbol, total sub-carrier number and Cyclic Prefix take;

Utilize the OFDM parameter that is obtained, the transmitting terminal of described restructural ofdm system and the transmission and the reception operation of receiving terminal are controlled.

8, method according to claim 7 is characterized in that determining the upper bound of the time cycle of OFDM symbol according to the peak carrier deviation of system requirements and the ratio of channel maximum doppler frequency.

9, method according to claim 7 is characterized in that the maximum delay expansion root-mean-square value according to multipath channel, at first determines the Cyclic Prefix duration, and then the lower bound of the time cycle of definite OFDM symbol.

10, method according to claim 9 is characterized in that the described Cyclic Prefix duration is set to more than or equal to 2 times of maximum delay expansion root-mean-square value and less than its 4 times.

11, method according to claim 9 is characterized in that the ratio according to cyclic prefix period and OFDM symbol cycle, determines the lower bound of OFDM symbol time cycle.

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