CN101383796A - OFDM system and channel estimation method thereof - Google Patents

Abstract

The invention discloses an OFDM system and the channel estimating method thereof, and belongs to the field of wireless communication. In the method of the invention, a sending end inserts shared control information in the setting position of a data stream and then sends the data stream to a receiving end, after the receiving end receives the data stream and acquires the shared control information through a first time of traffic channel estimation, the receiving end cooperates with a public pilot frequency to conduct channel estimation again. The invention also provides the OFDM system which comprises a transmitter and a receiver, wherein the transmitter inserts shared control information in the setting position of a data stream to be sent and then sends the data stream to a receiver, after the receiver receives the data stream and acquires the shared control information through a first time of traffic channel estimation, the receiver cooperates with the received public pilot frequency to conduct channel estimation again. By rationally designing and utilizing the existing resources, the invention can improve the demodulation performance of the system without increasing system spending.

Description

A kind of ofdm system and channel estimation methods thereof

Technical field

The invention belongs to field of wireless communication, relate in particular to a kind of orthogonal frequency division multiplex OFDM system and channel estimation methods thereof.

Background technology

In present communication technical field, ofdm system receives much concern, and will realize the technical advantage of OFDM fully, needs to realize earlier relevant key technology, and channel estimation technique is exactly one of them, and the quality of its performance directly has influence on the communication quality of whole system.Channel estimation technique is mainly used in wireless communication field and obtains the frequency response of transmitting antenna to wireless channel between the reception antenna.

Based on the wireless communication system of OFDM, to having relatively high expectations of transmission rate, the while receiving terminal need carry out coherent detection and could obtain systematic function preferably.Therefore, in the research to ofdm system, more lay particular emphasis on the channel estimation method of employing based on pilot tone at present, it can follow the tracks of the variation of channel well, promotes the performance of receiver.In the channel estimation technique research based on pilot tone, except the pilot channel estimation algorithm performance, the transmitting terminal pilot design also directly influences the performance of system to a great extent.

In multicarrier system, adopt in the channel estimation method based on pilot tone, transmitter is determined the pilot tone pattern of insertion earlier, fixed pilot tone pattern is inserted in design in the data flow that will send then, behind the receiver receiving data stream, obtain the channel information on the pilot frequency locations, utilize channel estimation method then, realize estimation whole channel.Wherein pilot design is very crucial, considers from the reliability angle, and it is many more to insert pilot tone, estimates just accurately more, but the speed of the overstocked effective transmission of pilot design is just low more, and pilot design is crossed to dredge and can be influenced system's demodulation performance.Therefore, need a kind of ofdm system at present, and in this system, do not increase overhead, just can improve the channel estimation methods of system's demodulation performance.

Summary of the invention

Technical problem to be solved by this invention is a kind of ofdm system and channel estimation methods thereof to be provided, thereby under the prerequisite that does not increase overhead, to improve the demodulation performance of channel estimating performance and system.

In order to address the above problem, the invention provides, the method of channel estimating in a kind of ofdm system, at first transmitting terminal sends to receiving terminal after the desired location of data flow inserts shared control information, after receiving terminal receives described data flow, after Traffic Channel estimates to obtain shared control information first,, carry out channel estimating once more in conjunction with public guide frequency.

This method specifically may further comprise the steps:

A: transmitting terminal sends to receiving terminal after the desired location of want data flow transmitted inserts shared control information;

B: after receiving terminal receives described data flow, carry out first to the shared control channel decoding, obtaining to share control information after Traffic Channel estimates according to public guide frequency;

C: the shared control information that receiving terminal will obtain is as the auxiliary reference pilot tone, in conjunction with public guide frequency, carries out once more obtaining the whole service channel after Traffic Channel estimates.

Above-mentioned shared control information is continuous shared control information or discrete shared control information.

Wherein Li San shared control information, its insertion position and public guide frequency insertion position constant duration, equifrequent are at interval.

If when adopting time division multiplexing mode to insert described continuous shared control information, share control information insertion position and public guide frequency insertion position constant duration, perhaps shared control information and public guide frequency are positioned at same OFDM symbol.

Realize the ofdm system that said method relied on, comprise transmitter and receiver, wherein transmitter is after the desired location of the data flow that will send inserts shared control information, send data and flow to receiver, after receiver is received data flow, obtain shared control information by channel estimating first, the public guide frequency in conjunction with receiving carries out channel estimating once more.

The shared control information that above-mentioned transmitter inserts is continuous shared control information or discrete shared control information.

When if transmitter inserts discrete shared control information, its insertion position and public guide frequency insertion position constant duration, equifrequent interval.

If when transmitter adopts the time division multiplexing inserted mode to insert continuous shared control information, share control information insertion position and public guide frequency insertion position constant duration, perhaps shared control information and public guide frequency are positioned at same OFDM symbol.

The present invention under the prerequisite that does not increase overhead, has improved the demodulation performance of system by to existing reasonable resources design and utilization.

Description of drawings

Fig. 1 inserts schematic diagram for public guide frequency;

Fig. 2 is the schematic diagram that uniformly-spaced inserts discrete shared control information;

Fig. 3 is for inserting the schematic diagram of continuous shared control information;

Fig. 4 inserts the schematic diagram of sharing control information at the high speed pilot design.

Embodiment

Main design of the present invention is, adopt the high characteristics of low-order-modulated reliability requirement at shared control channel, rationally insert shared control channel at transmitting terminal, receiving terminal elder generation demodulation shared control channel, utilize demodulated shared control channel then, and, estimate channel response once more in conjunction with public guide frequency, with other channel of this demodulation.

Below in conjunction with accompanying drawing the technical solution used in the present invention is described in further detail.

Embodiment, the method for control information assisted channel estimation is shared in a kind of ofdm system and utilization thereof.

Ofdm system comprises transmitter and receiver in the present embodiment, wherein the difference of transmitter and existing transmitter is, insert shared control information at desired location in the data flow that will send, promptly the framing module of transmitter will be shared the position that setting is inserted in control information according to the shared control channel of design.And receiver is different from existing receiver part and is, after the public guide frequency that the channel estimation module utilization of receiver receives carries out first channel estimating, with the shared control information that obtains as the auxiliary reference pilot tone, in conjunction with public guide frequency, carry out channel estimating once more, thereby obtain channel frequency response more accurately.

Wherein, transmitter can insert continuous or discrete shared control information in data flow.When transmitter inserts discrete shared control information in data flow, as shown in Figure 2, share the insertion position and public guide frequency insertion position constant duration, equifrequent interval of control information C.

When transmitter when data flow is inserted continuous shared control information, can adopt time-multiplexed inserted mode at continuous shared control information, as shown in Figure 3, the control information of sharing continuously of inserting is positioned at the 1st and the 5th OFDM symbol, promptly with public guide frequency in same OFDM symbol, and be covered with whole frequency band, can guarantee the decoding performance that receiver is good to shared control channel this moment, when shared control information during, also can improve the performance of receiver to the shared data channel demodulation as the auxiliary reference pilot tone.

Be illustrated in figure 4 as, the another kind of time division multiplexing that transmitter adopts is inserted the mode of continuous shared control information, the continuous shared control information of inserting is covered with whole frequency band, and the insertion position constant duration of the insertion position of continuous shared control information and public guide frequency, at this kind situation, receiver extract to share control information as the auxiliary reference pilot tone after, then can when high-speed mobile, improve decoding performance to the shared data channel.

In addition, for flat fading channel, transmitter also can adopt the inserted mode of frequency division multiplexing, inserts continuous shared control information.

The inserted mode of the shared control information that transmitter adopts except above-mentioned three kinds of optimal way, also can adopt any alternate manner.

Above-mentioned ofdm system utilizes the method for sharing the control information assisted channel estimation, may further comprise the steps:

The first step: transmitting terminal inserts public guide frequency and shares control information in want data flow transmitted;

In this step, the public guide frequency that inserts and to share control information be continuous or discrete, be public guide frequency and the inserted mode of sharing control information, can adopt existing inserted modes such as time division multiplexing inserted mode, frequency division multiplexing inserted mode, discrete inserted mode.

In the present embodiment, adopt discrete public guide frequency inserted mode, as shown in Figure 1, each subframe is uniformly-spaced inserted public guide frequency at frequency domain, wherein T1 is the public guide frequency on the antenna 1, and T2 is the public guide frequency on the antenna 2, and T1, T2 are positioned at the 1st and the 5th OFDM symbol on time domain.

In the present embodiment, adopt discrete shared control information inserted mode, as shown in Figure 2, the insertion position of shared control information C and public guide frequency insertion position constant duration, equifrequent are at interval.Can certainly adopt continuous shared control information, can adopt time-multiplexed inserted mode at continuous shared control information, as shown in Figure 3, the control information of sharing continuously of inserting is positioned at the 1st and the 5th OFDM symbol, promptly with public guide frequency in same OFDM symbol, and be covered with whole frequency band, can guarantee the decoding performance that shared control channel is good this moment, when shared control information during, also can improve performance to the shared data channel demodulation as the auxiliary reference pilot tone.

Be illustrated in figure 4 as the another kind of inserted mode of continuous shared control information, its inserted mode has also adopted time-multiplexed inserted mode, be that continuous shared control information is covered with whole frequency band, and the insertion position constant duration of the insertion position of continuous shared control information and public guide frequency, this kind situation receiving terminal extract to share control information as the auxiliary reference pilot tone after, then can when high-speed mobile, improve decoding performance to the shared data channel.

In addition, when continuous shared control information place shared control channel is a quasi-static channel opens, promptly during the low speed mobile subscriber, can also adopt the mode of frequency division multiplexing to insert shared control information.

At public guide frequency and shared control information, except the inserted mode of above-mentioned three kinds of optimizations, also can adopt any alternate manner.

Second step: receiving terminal obtains public guide frequency position channel information, estimates thereby carry out Traffic Channel;

In this step, channel estimating can adopt prior art to carry out, and such as adopting channel estimation methods such as LS, LMMSE, present embodiment adopts LS frequency domain algorithm for estimating, because this estimation is only carried out on frequency domain, computation complexity is lower.

The subcarrier that wherein inserts common pilot symbols is called pilot sub-carrier, and HPji represents the frequency response of the channel between i transmitting antenna, the j reception antenna, and then the ofdm signal after the demodulation can be expressed as form on j reception antenna:

$\begin{array}{cc}{Y}_j=\underset{i=1}{\overset{2}{\mathrm{\Σ}}}{H}_{\mathrm{Pji}}{X}_i+W_j& i=\mathrm{1,2};j=\mathrm{1,2}\end{array}$

The LS channel estimating is exactly under the condition of not considering noise, estimates the impulse response vector of channel, makes the cost function minimum as giving a definition:

$J={(Y_j-\underset{i=1}{\overset{2}{\mathrm{\Σ}}}{H}_{\mathrm{Pji}}{X}_i)}^H(Y_j-\underset{i=1}{\overset{2}{\mathrm{\Σ}}}{H}_{\mathrm{Pji}}{X}_i)$

Can obtain thus, the channel frequency response LS estimator of pilot frequency locations is between i transmitting antenna, the j reception antenna:

${\hat{H}}_{\mathrm{Pji}}={\left[\mathrm{diag}\left(X_i\right)\right]}^{-1}{Y}_j,i=\mathrm{1,2};j=\mathrm{1,2}$

The channel frequency response that following formula is estimated to the public guide frequency position

Carry out interpolation, obtain the response H of whole channel _Ji(j=1,2; I=1,2).

Described interpolation can adopt first-order linear interpolation, second-order linearity interpolation, spline interpolation, FFT interpolation method and based on interpolation method of transform domain etc.Adopt the method for first-order linear interpolation in the present embodiment, the response that obtains whole channel as shown in the formula:

H(k)＝(H _Pji(k _P+1)-H _Pji(k _P))d/D _f+H _Pji(k _P) 0≤d<D _f

The 3rd step: receiving terminal is decoded to shared control channel, obtains shared control information;

This step can adopt any existing coding/decoding method to realize, because shared control channel adopts existing SFBC coding, then correspondingly adopts the SFBC decoding in the present embodiment, and its process is as follows:

According to the response of the second whole channel that obtain of step, it is as follows to obtain channel matrix:

$H=\left(\begin{array}{cc}{h}_{11}& h_{12}\\ h_{21}& h_{22}\end{array}\right)$

H wherein _IjThe channel gain of expression from i transmitting antenna to j reception antenna.Use r ₁, r ₃Represent the receiving symbol of the 1st emission mark space reception antenna, use r ₂, r ₄Represent the received signal of the 2nd emission mark space reception antenna, obtain following equation group:

r ₁＝h ₁₁x ₁+h ₁₂x ₂+n ₁

$r_2=-h_{11}{x}_2^{*}+h_{12}{x}_1^{*}+n_2$

r ₃＝h ₂₁x ₁+h ₂₂x ₂+n ₃

$r_4=-h_{21}{x}_2^{*}+h_{22}{x}_1^{*}+n_4$

Work as x ₁, x ₂Power be 1 o'clock, the energy sum of received signal is | h ₁₁| ²+ | h ₁₂| ²+ | h ₂₁| ²+ | h ₂₂| ², the noise energy sum is 2 σ ²N wherein ₁, n ₂, n ₃, n ₄Be that variance is σ ²Answer Gaussian random variable, represent the interference and the noise of receiver.

Optimum thus maximum likelihood decoding can be characterized by following formula:

${\tilde{r}}_1=h_{11}^{*}{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="A200710145616E00132.png"\; state="\{\{state\}\}">r</figure-callout>}}_1+h_{12}{r}_2^{*}+h_{21}^{*}{r}_3+h_{22}{r}_4^{*}$

${\tilde{r}}_2=h_{12}^{*}{r}_1-h_{11}{r}_2^{*}+h_{22}^{*}{r}_3-h_{21}{r}_4^{*}$

Because the extremely low code check of the general employing of shared control channel, and multiple means such as employing diversity guarantee that shared control channel has extremely low code check, so shared control channel generally can be correctly decoded, promptly obtain sharing control information, can be expressed as the time-frequency two-dimensional pattern, as shown in Figure 2.

In the 4th step, receiving terminal carries out channel estimating once more according to the shared control information and the public guide frequency that have obtained;

In this step, think the shared control information and the public guide frequency that have obtained known, and will share control information as the auxiliary reference pilot tone, just can think that pilot density increases this moment, carry out channel estimating once more, promptly can adopt channel estimation methods such as existing LS, LMMSE, estimate the channel frequency response of public guide frequency position and shared control information position, then interpolation is carried out in this frequency response, thereby obtain the frequency response of whole channel.

Wherein interpolation can adopt first-order linear interpolation, second-order linearity interpolation, spline interpolation, FFT interpolation method, based on the existing interpolation methods such as interpolation method of transform domain.

In the 5th step, detect Traffic Channel according to the public guide frequency of estimating;

This step can adopt any detection method of the prior art to realize, adopt the LMMSE detection algorithm in the present embodiment: find a concrete weighting matrix W according to the received signal r of receiving terminal and known channel matrix response H, thereby utilize weighting matrix and received signal to obtain sending the estimation of signal

That is:

$\hat{x}=\mathrm{Wr}$

The LMMSE algorithm will make ε reach minimum, that is:

$\mathrm{\&epsiv;}=E\left[{(x-\hat{x})}^H(x-\hat{x})\right]=E\left[{(x-\mathrm{Wr})}^H(x-\mathrm{Wr})\right]$

Calculate: $W={(H^{H}H+{\mathrm{\&sigma;}}_n^2/{\mathrm{\&sigma;}}_s^2\&CenterDot;I)}^{-1}{H}^H$

It is the weighting matrix in the LMMSE algorithm.

The detection step of LMMSE algorithm is as follows:

Step a: initialization, i=1, $W_i={({H_i}^H{H}_i+{\mathrm{\&sigma;}}_n^2/{\mathrm{\&sigma;}}_s^2.I)}^{-1}{H_i}^H,$ H in the formula ^HThe conjugate transpose of expression channel matrix H;

Step b: the signal to noise ratio according to following formula calculating received signal, sort by its signal to noise ratio is descending, and detect according to the order of sequence,

k _i＝arg?min‖(W _i)‖‖ ²，k _i≤M

M represents number of transmit antennas in the formula, (W) _iThe i that W is got in expression is capable, k _iThe little pairing row of row of expression weighting matrix norm number, the big reception antenna of promptly corresponding receiving terminal signal to noise ratio.；

Step c: be calculated as follows weight vectors

$W_{k_i}={\left(W_i\right)}_{k_i};$

Steps d: be calculated as follows the judgement vector

$y_{k_i}=W_{k_i}{r}_i$

Step e: adjudicate, be calculated as follows and obtain estimated value,

${\hat{x}}_{k_i}=Q\left(y_{k_i}\right);$

Step f: be calculated as follows pseudo inverse matrix,

$W_{i+1}={({H_{i+1}}^H{H}_{i+1}+{\mathrm{\&sigma;}}_n^2/{\mathrm{\&sigma;}}_s^2\&CenterDot;I)}^{-1}{H_{i+1}}^H;$

Step g: according to that signal of following formula selection signal to noise ratio maximum,

$k_{i+1}=\arg \min {\left|\right|{\left(W_{i+1}\right)}_j\left|\right|}^2;$

Step h:i=i+1;

Step I: whether judge i greater than the antenna sum, if, the detection of end flow process, otherwise return step b.

The foregoing description after receiving terminal carries out the channel estimating decoding control information, is estimated channel at transmitting terminal appropriate design shared control channel once more, thereby has improved the correctness of channel estimation accuracy and channel-decoding.

Certainly, above-mentioned specific embodiment is not the further qualification to technical solution of the present invention, and any those of ordinary skill in the art replaced or corresponding improvement the technology of the present invention feature being equal to of being done, still within protection scope of the present invention.

Claims (9)

1, the method for channel estimating in a kind of orthogonal frequency division multiplex OFDM system, it is characterized in that, transmitting terminal sends to receiving terminal after the desired location of data flow inserts shared control information, after receiving terminal receives described data flow, after Traffic Channel estimates to obtain shared control information first, in conjunction with public guide frequency, carry out channel estimating once more.

2, the method for claim 1 is characterized in that, this method may further comprise the steps:

A: transmitting terminal sends to receiving terminal after the desired location of want data flow transmitted inserts shared control information;

B: after receiving terminal receives described data flow, carry out first to the shared control channel decoding, obtaining to share control information after Traffic Channel estimates according to public guide frequency;

C: the shared control information that receiving terminal will obtain is as the auxiliary reference pilot tone, in conjunction with public guide frequency, carries out once more obtaining the whole service channel after Traffic Channel estimates.

As claim 1 or 2 described methods, it is characterized in that 3, described shared control information is continuous shared control information or discrete shared control information.

4, method as claimed in claim 3 is characterized in that, described discrete shared control information, and its insertion position and public guide frequency insertion position constant duration, equifrequent are at interval.

5, method as claimed in claim 3, it is characterized in that, when adopting time division multiplexing mode to insert described continuous shared control information, share control information insertion position and public guide frequency insertion position constant duration, perhaps shared control information and public guide frequency are positioned at same OFDM symbol.

6, the ofdm system that relied on of the described method of claim 1, comprise transmitter and receiver, it is characterized in that, transmitter is after the desired location of the data flow that will send inserts shared control information, send data and flow to receiver, after receiver is received data flow, obtain shared control information by channel estimating first, public guide frequency in conjunction with receiving carries out channel estimating once more.

7, system as claimed in claim 6 is characterized in that, the shared control information that described transmitter inserts is continuous shared control information or discrete shared control information.

8, system as claimed in claim 7 is characterized in that, when described transmitter inserts discrete shared control information, and its insertion position and public guide frequency insertion position constant duration, equifrequent interval.

9, system as claimed in claim 7, it is characterized in that, when described transmitter adopts the time division multiplexing inserted mode to insert continuous shared control information, share control information insertion position and public guide frequency insertion position constant duration, perhaps share control information and public guide frequency and be positioned at same OFDM symbol.

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