CN105392201A - 802.11-n-based bandwidth determination method and apparatus - Google Patents

Abstract

The invention discloses an 802.11-n-based bandwidth determination method and apparatus. The method comprises: received 40-MHz bandwidth signals are divided into 20-MHz signals at a main channel and 20-MHz signals at an auxiliary channel; sampling is carried out on the main channel signals and the auxiliary channel signals according to a certain sampling mode, energy detection and OFDM autocorrelation detection are carried out on the main channel sampling signals and the auxiliary channel sampling signals, sampling rate conversion is carried out on the main channel signals, and then DSSS cross-correlation detection is carried out on the sampled signals; if the main channel and the auxiliary channel are determined to receive the OFDM signals simultaneously after the energy detection and OFDM autocorrelation detection, channel response energy detection is carried out on the main channel sampling signals and the auxiliary channel sampling signals; and according to a detection result, determination on the signal bandwidth is carried out. According to the invention, when the energy detection and OFDM autocorrelation detection display that main channel and the auxiliary channel receive the OFDM signals simultaneously, channel response energy detection is carried out on the main channel sampling signals and the auxiliary channel sampling signals, thereby improving reliability of 802.11-n signal bandwidth determination.

Description

A kind of bandwidth decision method based on 802.11n and device

Technical field

The present invention relates to communication technical field, be specifically related to a kind of bandwidth decision method based on 802.11n and device.

Background technology

802.11n agreement allows the network equipment to use two adjacent 20MHz channels and 40MHz channel to send data, meanwhile, in order to compatible legacy equipment, when 802.11n equipment is operated in 40MHz channel, needs to possess the ability sending and receive 20MHz bandwidth signal.When equipment is in 40MHz mode of operation, first correctly must judge the bandwidth of 802.11 signals, just can carry out reception process.

Prior art based on the bandwidth decision method of 802.11n for little energy signal, the signal of major-minor channel is obtained by shift frequency and low pass filter, respectively carrier sense is carried out to 40MHz signal, main channel signal and auxiliary channel signal, finally judge the bandwidth of useful signal according to result; For macro-energy signal, then carry out signal bandwidth detection again after carrying out an AGC adjustment and preamble detecting.

The shortcoming of prior art decision method is, if signal is 20MHz and there is the interference identical with the ofdm signal short training sequence cycle at auxiliary channel, so bandwidth decision logic can produce erroneous judgement, once erroneous judgement, just cannot carry out correct demodulation to signal.

Summary of the invention

The technical problem to be solved in the present invention is, for the deficiencies in the prior art, provides a kind of bandwidth decision method based on 802.11n and device, overcomes prior art 802.11n signal bandwidth decision method and easily produce the not high defect of erroneous judgement, reliability.

The present invention for solving the problems of the technologies described above adopted technical scheme is:

Based on a bandwidth decision method of 802.11n, comprise step:

A1, the 40MHz bandwidth signal received is divided into the 20MHz signal being positioned at main channel and the 20MHz signal being positioned at auxiliary channel;

A2, according to certain sampling configuration, main channel signal and auxiliary channel signal to be sampled, energy measuring and OFDM Autocorrelation Detection are carried out to main channel sampled signal and auxiliary channel sample signal, sample rate conversion is carried out to main channel signal, then DSSS cross-correlation test is carried out to sampled signal;

If A3 is through energy measuring and OFDM Autocorrelation Detection, determine that main channel and auxiliary channel receive ofdm signal simultaneously, then channel response energy measuring is carried out to main channel sampled signal and auxiliary channel sample signal;

A4, according to testing result, signal bandwidth to be judged.

According to embodiments of the invention, this steps A 4 comprises step: if through energy measuring and OFDM Autocorrelation Detection, determine only to receive ofdm signal in main channel, then decision signal is ofdm signal, and bandwidth is 20MHz, and is positioned at main channel.

According to embodiments of the invention, this steps A 4 comprises step: if through energy measuring and OFDM Autocorrelation Detection, and determine only to receive ofdm signal at auxiliary channel, then decision signal is ofdm signal, and bandwidth is 20MHz, and is positioned at auxiliary channel.

According to embodiments of the invention, this steps A 4 comprises step: if be 40M through channel response energy measuring determination bandwidth, then decision signal is ofdm signal, and bandwidth is 40MHz.

According to embodiments of the invention, this steps A 4 comprises step: if be 20M through channel response energy measuring determination bandwidth, then decision signal is ofdm signal, and bandwidth is 20MHz, and is positioned at main channel.

According to embodiments of the invention, this steps A 4 comprises step: if determine to receive DSSS signal through DSSS cross-correlation test, then decision signal is DSSS signal, and is positioned at main channel.

According to embodiments of the invention, this steps A 1 comprises step: by frequency conversion and low-pass filtering, the 40MHz bandwidth signal received is divided into the 20MHz signal being positioned at main channel and the 20MHz signal being positioned at auxiliary channel.

According to embodiments of the invention, this sampling configuration is set to down-sampled.

A kind of bandwidth decision maker based on 802.11n, comprise frequency conversion and filtration module, sampling module, signal detection module and bandwidth judge module, this frequency conversion and filtration module, this sampling module, this signal detection module is connected successively with this bandwidth judge module, this frequency conversion and filtration module are used for, by frequency conversion and low-pass filtering, the 40MHz bandwidth signal received is divided into the 20MHz signal being positioned at main channel and the 20MHz signal being positioned at auxiliary channel, this sampling module is used for sampling to main channel signal and auxiliary channel signal according to certain sampling configuration, this signal detection module is used for carrying out energy measuring and OFDM Autocorrelation Detection to main channel sampled signal and auxiliary channel sample signal, sample rate conversion is carried out to main channel signal, then DSSS cross-correlation test is carried out to sampled signal, if through energy measuring and OFDM Autocorrelation Detection, determine that main channel and auxiliary channel receive ofdm signal simultaneously, then channel response energy measuring is carried out to main channel sampled signal and auxiliary channel sample signal, this bandwidth judge module is used for judging signal bandwidth according to sampled signal testing result.

According to embodiments of the invention, this signal detection module comprises channel response energy detection module.

Implement technical scheme of the present invention, there is following beneficial effect: the present invention is when energy measuring and OFDM Autocorrelation Detection show main channel and auxiliary channel receives ofdm signal simultaneously, channel response energy measuring is carried out to main channel sampled signal and auxiliary channel sample signal, improves the reliability that 802.11n signal bandwidth judges.

Accompanying drawing explanation

Below by with reference to accompanying drawing describe the present invention particularly in conjunction with example, advantage of the present invention and implementation will be more obvious, wherein content shown in accompanying drawing is only for explanation of the present invention, and does not form restriction of going up in all senses of the present invention, in the accompanying drawings:

Fig. 1 is 802.11n signal frame structure schematic diagram;

Fig. 2 is flow chart of the present invention;

Fig. 3 is signal bandwidth decision flow chart of the present invention;

Fig. 4 is upconversion operation schematic diagram of the present invention;

Fig. 5 is channel response energy measuring schematic diagram of the present invention;

Fig. 6 is bandwidth decision maker module map of the present invention;

Fig. 7 is bandwidth decision maker embodiment schematic diagram of the present invention.

Embodiment

As shown in Figure 2, the present invention is based on the bandwidth decision method of 802.11n, comprise step:

S101, the 40MHz bandwidth signal received is divided into the 20MHz signal being positioned at main channel and the 20MHz signal being positioned at auxiliary channel;

S102, according to certain sampling configuration, main channel signal and auxiliary channel signal to be sampled, energy measuring and OFDM Autocorrelation Detection are carried out to main channel sampled signal and auxiliary channel sample signal, sample rate conversion is carried out to main channel signal, then DSSS cross-correlation test is carried out to sampled signal;

If S103 is through energy measuring and OFDM Autocorrelation Detection, determine that main channel and auxiliary channel receive ofdm signal simultaneously, then channel response energy measuring is carried out to main channel sampled signal and auxiliary channel sample signal;

S104, according to testing result, signal bandwidth to be judged.

As shown in Figure 3, according to embodiments of the invention, if through energy measuring and OFDM Autocorrelation Detection when judging signal bandwidth according to testing result, determine only to receive ofdm signal in main channel, then decision signal is ofdm signal, and bandwidth is 20MHz, and is positioned at main channel.If through energy measuring and OFDM Autocorrelation Detection, determine only to receive ofdm signal at auxiliary channel, then decision signal is ofdm signal, and bandwidth is 20MHz, and is positioned at auxiliary channel.If be 40M through channel response energy measuring determination bandwidth, then decision signal is ofdm signal, and bandwidth is 40MHz.If be 20M through channel response energy measuring determination bandwidth, then decision signal is ofdm signal, and bandwidth is 20MHz, and is positioned at main channel.If determine to receive DSSS signal through DSSS cross-correlation test, then decision signal is DSSS signal, and is positioned at main channel.According to embodiments of the invention, by frequency conversion and low-pass filtering, the 40MHz bandwidth signal received is divided into the 20MHz signal being positioned at main channel and the 20MHz signal being positioned at auxiliary channel.Sampling configuration can be set to down-sampled.

As shown in Figure 6 and Figure 7, the present invention is based on the bandwidth decision maker of 802.11n, comprise frequency conversion and filtration module, sampling module, signal detection module and bandwidth judge module, frequency conversion and filtration module, sampling module, signal detection module is connected successively with bandwidth judge module, frequency conversion and filtration module are used for, by frequency conversion and low-pass filtering, the 40MHz bandwidth signal received is divided into the 20MHz signal being positioned at main channel and the 20MHz signal being positioned at auxiliary channel, sampling module is used for sampling to main channel signal and auxiliary channel signal according to certain sampling configuration, signal detection module is used for carrying out energy measuring and OFDM Autocorrelation Detection to main channel sampled signal and auxiliary channel sample signal, sample rate conversion is carried out to main channel signal, then DSSS cross-correlation test is carried out to sampled signal, if through energy measuring and OFDM Autocorrelation Detection, determine that main channel and auxiliary channel receive ofdm signal simultaneously, then channel response energy measuring is carried out to main channel sampled signal and auxiliary channel sample signal, bandwidth judge module is used for judging signal bandwidth according to sampled signal testing result.According to embodiments of the invention, signal detection module comprises channel response energy detection module.

As shown in Figure 1,802.11n agreement is based on OFDM physical layer, the network equipment is allowed to use two adjacent 20MHz channels and 40MHz channel to send data, simultaneously, in order to compatible legacy equipment, when 802.11n equipment is operated in 40MHz channel, need to possess the ability sending and receive 20MHz bandwidth signal.When using 40MHz channel, the example of 20MHz bandwidth signal and 40MHz bandwidth signal as shown in Figure 1 (main channel is positioned at top).

As shown in Figure 4, radiofrequency signal is after down-conversion and analog-to-digital conversion, obtain complex baseband signal x (n) that sampling rate is 40MHz=I (n)+jQ (n), x (n) and represent the sampled value obtained in the n-th moment (i.e. n/40000000 second).

As shown in Figure 6, complex baseband signal x (n) is input to up-conversion and the down-conversion that main channel frequency-variable module and auxiliary channel frequency-variable module carry out 10MHz.If main channel is positioned at the top of center frequency point, main channel frequency-variable module carries out down-conversion operation, and auxiliary channel frequency-variable module carries out frequency up-conversion operation, and the signal indication after frequency conversion is:

$y_1\left(n\right)=x\left(n\right)*e^{-\frac{j2\mathrm{\π}\left(10e6\right)n}{40e6}}=x\left(n\right)*e^{-\frac{j\mathrm{\π}n}{2}}$

$y_2\left(n\right)=x\left(n\right)*e^{\frac{j2\mathrm{\π}\left(10e6\right)n}{40e6}}=x\left(n\right)*e^{\frac{j\mathrm{\π}n}{2}}$

Otherwise main channel frequency-variable module carries out frequency up-conversion operation, auxiliary channel frequency-variable module carries out down-conversion operation, and the signal indication after frequency conversion is:

$y_1\left(n\right)=x\left(n\right)*e^{\frac{j2\mathrm{\π}\left(10e6\right)n}{40e6}}=x\left(n\right)*e^{\frac{j\mathrm{\π}n}{2}}$

$y_2\left(n\right)=x\left(n\right)*e^{-\frac{j2\mathrm{\π}\left(10e6\right)n}{40e6}}=x\left(n\right)*e^{-\frac{j\mathrm{\π}n}{2}}$

By the two paths of signals through frequency conversion respectively through low pass filter, only retain the signal of 20MHz bandwidth, then down-sampled is 20MHz sample rate.Wherein, the coefficient of filter is: h (n)={-4,0,12,0 ,-18,0,28,0 ,-52,0,162,256,162,0 ,-52,0,28,0 ,-18,0,12,0 ,-4}

The output signal of filter is expressed as:

$z_1\left(n\right)=y_1\left(n\right)\⊗h\left(n\right)$

$z_2\left(n\right)=y_2\left(n\right)\⊗h\left(n\right)$

Output signal after down-sampled is expressed as:

z′ ₁(k)＝z ₁(2k)

z′ ₂(k)＝z ₂(2k)

Energy measuring is carried out to the signal after down-sampled.Energy measuring is obtained by the average power of the sampling point in calculating time window, and this time window is traditionally arranged to be the ofdm signal short training sequence cycle, i.e. 16 sampling points.At a kth sampling point, average power is expressed as:

$E_1\left(k\right)=\frac{1}{16}\underset{n=0}{\overset{15}{\Σ}}\left|\right|z_1^{\′}(k-n)|{|}^2$

$E_2\left(k\right)=\frac{1}{16}\underset{n=0}{\overset{15}{\Σ}}\left|\right|z_2^{\′}(k-n)|{|}^2$

Signal after down-sampled carries out auto-correlation computation (wherein conj represents conjugate operation):

${\mathrm{\Λ}}_1\left(k\right)=\frac{1}{16}\underset{n=0}{\overset{15}{\Σ}}\left(z_1^{\′}\right(k-n)*conj(z_1^{\′}\left(k-n-16\right)\left)\right)$

${\mathrm{\Λ}}_2\left(k\right)=\frac{1}{16}\underset{n=0}{\overset{15}{\Σ}}\left(z_2^{\′}\right(k-n)*conj(z_2^{\′}\left(k-n-16\right)\left)\right)$

At a kth sampling point, for m=-15 ,-14 ..., 0: if normalized autocorrelation coefficient be greater than the number of times of 0.75 more than 8 times, so think and main channel detects ofdm signal; If normalized autocorrelation coefficient number of times more than 8 times, so think and auxiliary channel detect ofdm signal.When main channel and auxiliary channel detect ofdm signal simultaneously, start channel response energy detection module, and be calculated as follows metric as reference energy:

$E_{1,ref}=\frac{1}{16}\underset{m=0}{\overset{15}{\Σ}}{E}_2(k-m)$

First main channel 20MHz signal and auxiliary channel 20MHz signal are carried out cross-correlation with local sequence by channel response energy detection module respectively.Local sequence LTF _tby the inverse Fourier transform (IFFT) of one sequence and cyclic shift 32 sampling points obtain, length is 64:[0,1 ,-1 ,-1,1,1 ,-1,1 ,-1,1,-1 ,-1 ,-1 ,-1 ,-1,1,1 ,-1 ,-1,1 ,-1,1 ,-1,1,1,1,1,0,0,0,0,0,0,0,0,0,0,0,1,1 ,-1 ,-1,1,1 ,-1,1 ,-1,1,1,1,1,1,1 ,-1,-1,1,1 ,-1,1 ,-1,1,1,1,1]

The cross-correlation calculation of main channel and auxiliary channel, output signal is expressed as:

$X_1\left(k\right)=\underset{m=0}{\overset{63}{\Σ}}\left(z_1^{\′}\right(k-63+m)*conj({\mathrm{LTF}}_t\left(m\right)\left)\right)$

$X_2\left(k\right)=\underset{m=0}{\overset{63}{\Σ}}\left(z_2^{\′}\right(k-63+m)*conj({\mathrm{LTF}}_t\left(m\right)\left)\right)$

Calculate the energy value of a time window (16 sampling points) interior cross-correlation:

$E_{chan,1}\left(k\right)=\underset{n=0}{\overset{15}{\Σ}}\left(\right|\left|X_1\right(k-n)\left|{|}^2\right)$

$E_{chan,2}\left(k\right)=\underset{n=0}{\overset{15}{\Σ}}\left(\right|\left|X_2\right(k-n)\left|{|}^2\right)$

Meanwhile, main channel and the energy value of auxiliary channel on 64 sampling points is calculated:

$P_1\left(k\right)=\underset{m=0}{\overset{63}{\Σ}}\left(z_1^{\′}\right(k-63+m)*conj(z_1^{\′}\left(k-63+m\right)\left)\right)$

$P_2\left(k\right)=\underset{m=0}{\overset{63}{\Σ}}\left(z_2^{\′}\right(k-63+m)*conj(z_2^{\′}\left(k-63+m\right)\left)\right)$

If at p sampling point, E _{chan, 1}(p) >32*E _{1, ref}, so from sampling point p, find E _{chan, 1}(p), E _{chan, 1}(p+1) ..., E _{chan, 1}(p+16) maximum, the index q that record maximum is corresponding.As shown in Figure 5.

If current demand signal is 40MHzOFDM signal, so there is following relation:

E _chan,1(q)≈P ₁(q)

E _chan,2(q)≈P ₂(q)

That is:

E _chan,1(q)/E _chan,2(q)≈P ₁(q)/P ₂(q)

Therefore, compare as follows:

E _chan,1(q)/E _chan,2(q)≥0.5*P ₁(q)/P ₂(q)

E _chan,1(q)/E _chan,2(q)≤2*P ₁(q)/P ₂(q)

If above-mentioned two conditions meet simultaneously, so, think that signal bandwidth is 40MHz.Otherwise, think that signal bandwidth is 20MHz.

While above-mentioned module work, the signal of (but without down-sampled) after main channel after filtering device is carried out sample rate conversion, the input signal of 40MHz sample rate through first through 11 times of over-sampling filtering interpolations, then carry out 10 times down-sampled, become 44MHz sample rate.

Signal indication after 11 times of over-samplings is:

Signal indication after filtering interpolation is:

$z_{DSSS}\left(n\right)=y_1^{\′}\left(n\right)\⊗h_{DSSS}\left(n\right)$

Wherein, filter coefficient is:

h _DSSS(n)＝{1,2,4,6,8,10,11,11,9,5,-1,-9,-19,-31,-42,-53,-61,-64,-61,-50,-30,1,41,90,147,209,273,336,393,442,480,503,511,503,480,442,393,336,273,209,147,90,41,1,-30,-50,-61,-64,-61,-53,-42,-31,-19,-9,-1,5,9,11,11,10,8,6,4,2,1}

Carry out again 10 times down-sampled after signal indication be:

z′ _DSSS(k)＝z _DSSS(10k)

Signal z ' after sample rate conversion _dSSSk () is input to DSSS coherent detection module, carry out cross-correlation with local sequence, and wherein, local sequence is:

Barker＝[+1,0,0,0,-1,0,0,0,+1,0,0,0,+1,0,0,0,-1,0,0,0,+1,0,0,0,+1,0,0,0,+1,0,0,0,-1,0,0,0,-1,0,0,0,-1,0,0,0]

Signal indication after cross-correlation is:

$X_{DSSS}\left(k\right)=\underset{m=0}{\overset{43}{\Σ}}\left(z_{DSSS}^{\′}\right(k-43+m)*Bar\ker (m\left)\right)$

Calculate the average energy of signal simultaneously:

$E_{DSSS}\left(k\right)>0.5*\underset{m=0}{\overset{43}{\Σ}}\left|\right|z_{DSSS}^{\′}(k-43+m)|{|}^2/44$

If sometime, || X _dSSS(k)/11|| ²>0.5*E _dSSSk (), then think and DSSS signal detected.

Bandwidth judge module is according to the bandwidth information of the output information judgement Received signal strength of OFDM Autocorrelation Detection, DSSS cross-correlation test and channel response energy measuring.

If the OFDM Autocorrelation Detection module of main channel and auxiliary channel detects ofdm signal simultaneously:

1) if channel response energy measuring bandwidth is 40M, then decision signal is ofdm signal, and bandwidth is 40MHz;

2) if channel response energy measuring bandwidth is 20M, then decision signal is ofdm signal, and bandwidth is 20MHz, and is positioned at main channel.

If only ofdm signal detected in main channel Autocorrelation Detection module, then decision signal is ofdm signal, and bandwidth is 20MHz, and is positioned at main channel.

If only ofdm signal detected in auxiliary channel Autocorrelation Detection module, then decision signal is ofdm signal, and bandwidth is 20MHz, and is positioned at auxiliary channel.

If DSSS cross-correlation test module detects DSSS signal, then decision signal is DSSS signal, and is positioned at main channel.

Otherwise, judge do not have signal to be detected.

Those skilled in the art do not depart from essence of the present invention and spirit, various deformation scheme can be had to realize the present invention, the foregoing is only the better feasible embodiment of the present invention, not thereby interest field of the present invention is limited to, the equivalent structure change that all utilizations specification of the present invention and accompanying drawing content are done, is all contained within interest field of the present invention.

Claims (10)

1., based on a bandwidth decision method of 802.11n, it is characterized in that, comprise step:

A1, the 40MHz bandwidth signal received is divided into the 20MHz signal being positioned at main channel and the 20MHz signal being positioned at auxiliary channel;

A2, according to certain sampling configuration, main channel signal and auxiliary channel signal to be sampled, energy measuring and OFDM Autocorrelation Detection are carried out to main channel sampled signal and auxiliary channel sample signal, sample rate conversion is carried out to main channel signal, then DSSS cross-correlation test is carried out to sampled signal;

If A3 is through energy measuring and OFDM Autocorrelation Detection, determine that main channel and auxiliary channel receive ofdm signal simultaneously, then channel response energy measuring is carried out to main channel sampled signal and auxiliary channel sample signal;

A4, according to testing result, signal bandwidth to be judged.

2. the bandwidth decision method based on 802.11n according to claim 1, it is characterized in that, described steps A 4 comprises step: if through energy measuring and OFDM Autocorrelation Detection, determine only to receive ofdm signal in main channel, then decision signal is ofdm signal, bandwidth is 20MHz, and is positioned at main channel.

3. the bandwidth decision method based on 802.11n according to claim 2, it is characterized in that, described steps A 4 comprises step: if through energy measuring and OFDM Autocorrelation Detection, determine only to receive ofdm signal at auxiliary channel, then decision signal is ofdm signal, bandwidth is 20MHz, and is positioned at auxiliary channel.

4. the bandwidth decision method based on 802.11n according to claim 3, is characterized in that, described steps A 4 comprises step: if be 40M through channel response energy measuring determination bandwidth, then decision signal is ofdm signal, and bandwidth is 40MHz.

5. the bandwidth decision method based on 802.11n according to claim 4, it is characterized in that, described steps A 4 comprises step: if be 20M through channel response energy measuring determination bandwidth, then decision signal is ofdm signal, bandwidth is 20MHz, and is positioned at main channel.

6. the bandwidth decision method based on 802.11n according to claim 5, is characterized in that, described steps A 4 comprises step: if determine to receive DSSS signal through DSSS cross-correlation test, then decision signal is DSSS signal, and is positioned at main channel.

7. the bandwidth decision method based on 802.11n according to claim 6, it is characterized in that, described steps A 1 comprises step: by frequency conversion and low-pass filtering, the 40MHz bandwidth signal received is divided into the 20MHz signal being positioned at main channel and the 20MHz signal being positioned at auxiliary channel.

8. the bandwidth decision method based on 802.11n according to claim 7, is characterized in that: described sampling configuration is set to down-sampled.

9. the bandwidth decision maker based on 802.11n, it is characterized in that: comprise frequency conversion and filtration module, sampling module, signal detection module and bandwidth judge module, described frequency conversion and filtration module, described sampling module, described signal detection module is connected successively with described bandwidth judge module, described frequency conversion and filtration module are used for, by frequency conversion and low-pass filtering, the 40MHz bandwidth signal received is divided into the 20MHz signal being positioned at main channel and the 20MHz signal being positioned at auxiliary channel, described sampling module is used for sampling to main channel signal and auxiliary channel signal according to certain sampling configuration, described signal detection module is used for carrying out energy measuring and OFDM Autocorrelation Detection to main channel sampled signal and auxiliary channel sample signal, sample rate conversion is carried out to main channel signal, then DSSS cross-correlation test is carried out to sampled signal, if through energy measuring and OFDM Autocorrelation Detection, determine that main channel and auxiliary channel receive ofdm signal simultaneously, then channel response energy measuring is carried out to main channel sampled signal and auxiliary channel sample signal, described bandwidth judge module is used for judging signal bandwidth according to sampled signal testing result.

10. the bandwidth decision maker based on 802.11n according to claim 9, is characterized in that: described signal detection module comprises channel response energy detection module.