CN106412931B - A kind of LTE-U clear channel assessment based on multi-slot syncretizing mechanism - Google Patents
A kind of LTE-U clear channel assessment based on multi-slot syncretizing mechanism Download PDFInfo
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Abstract
The present invention relates to a kind of LTE-U clear channel assessments based on multi-slot syncretizing mechanism, belong to LTE-U in mobile communication technology (LTE in unlicensed spectrum) technical field.LTE-U system works in unauthorized frequency range, and system generally requires carry out clear channel assessment (CCA) before accessing channel.Firstly, entire CCA window is divided into multiple time slots by LTE-U system；Secondly, sampling matrix is generated using the sampled data of multiple time slots, it calculates its covariance matrix and obtains characteristic value, unequal weighting is carried out to each corresponding time slot using the characteristic value of ascending order arrangement, assess performance to improve channel status when CCA window is not exclusively aligned with data packet.Clear channel assessment based on multi-slot Weighted Fusion mechanism can effectively improve the accuracy rate of channel status judgement, different inter-system data packet collision probabilities are reduced, and then promote LTE-U system and the WIFI system spectrum efficiency that cochannel coexists in unauthorized frequency range.
Description
Technical field
LTE-U (LTE in the invention belongs to wireless communication technology field, in especially unauthorized frequency range
Unlicensed spectrum) clear channel assessment (CCA) technical field of the system when accessing channel, it is related to a kind of based on multi-slot
The LTE-U clear channel assessment of syncretizing mechanism.
Background technique
LTE-U is the emerging technology that 3GPP proposes for alleviating authorized spectrum band communication load pressure in recent years, it can allow
LTE system is deployed in unauthorized frequency range (common frequency band) by operator.Using the technical advantage of LTE, unauthorized frequency can be improved
The spectrum efficiency of Duan Pin reaches simultaneously also by flow is transferred to unauthorized frequency range from authorized spectrum band and alleviates existing authorization frequency
The purpose of communication pressure in section.Due to the regional open policy of unauthorized frequency range and the limitation of spectral characteristic, LTE-U technology will
Applied to the unauthorized frequency range near 5GHz.The frequency range mainly has WIFI (IEEE 802.11a) system using at present, therefore
It is mainly concentrated in both at home and abroad about the research of LTE-U and allows LTE-U and WIFI system harmonious coexistence in the frequency range.
It is to allow LTE-U using LBT (Listen Before currently based on the co-existence schemes that fairness (contention access) considers
Talk) the Channel Access Mechanism of mode, i.e. LTE-U equipment first carry out clear channel assessment (CCA) (Clear before accessing channel
Channel Assessment, CCA).If LTE-U equipment does not find WIFI signal during CCA, then visual channel is sky
Spare time busy channel and can transmit data；Conversely, cannot then access channel.Meanwhile in order to make other systems also have an opportunity to access
Channel, LTE-U equipment will reserve one section of free timeslot after the data transfer is complete, so that other systems use channel spectrum.LBT
Under CCA generally use single node energy measuring (Energy Detection, ED) method, can be described as ED-CCA.ED-CCA is first
To time domain signal sampling modulus, required modulus value is squared, the summation that then adds up is averaged again, will finally be averaged and system
Preset detection threshold value is compared, and judges that (or other reside in unauthorized frequency range and are WIFI system according to comparison result
System) transmission state.
What if the sampling window (carrying out the time interval of data acquisition to destination channel) of ED-CCA was sent with WIFI
When data packet is perfectly aligned or is staggered, there can be preferable judgement to channel status.However, in the actual environment, by
It is asynchronous between the long uncertainty of WIFI data packet packet and LTE-U device request access channel time point and WIFI timing
Property, prevent practical CCA sampling window often with WIFI data packet from perfectly aligned, therefore, causes to receive in sampling window
WIFI signal it is less and cause the erroneous judgement to channel status.In addition, the structure design of CCA is relatively fixed, can only generally pass through
The width of sampling window is set to adapt to coexisted environment, cannot neatly apply data fusion and judgement side according to current demand
Method.Accordingly, the present invention ED-CCA there are aiming at the problem that, propose a kind of based on multi-slot (Multi-Slot) syncretizing mechanism
CCA method.
Summary of the invention
In view of this, for ED-CCA sampling window is not exclusively aligned with WIFI data packet under practical circumstances when to channel
The problem of state judgement shortcoming accuracy, the purpose of the present invention is to provide a kind of, and the LTE-U based on multi-slot syncretizing mechanism is empty
CCA sampling window is divided into multiple time slots in LTE-U equipment by channel assessment method, utilizes the characteristic value for receiving signal
Information carries out the weighting of uneven equal weight to the reception data of each time slot, then weighted fusion algorithm is generated global detection statistic
(Global Test Statistic, GTS), and make final threshold value judgement.Theory analysis and the results show: this hair
The MS-CCA algorithm of bright proposition than existing ED-CCA in the case where data packet is not exclusively aligned with CCA sampling window, to letter
The occupancy situation in road can more accurately judge, number occurs when cochannel coexists so as to reduce LTE-U and WIFI system
According to the probability of packet collision, and then lifting system coexistence efficiency.
In order to achieve the above objectives, the invention provides the following technical scheme:
A kind of LTE-U clear channel assessment based on multi-slot syncretizing mechanism, in the method, LTE-U terminal exists
The CCA that at least 20 μ s are first carried out before access channel, is divided into multiple time slots for original CCA window, using in multiple time slots
Data form signal sampling matrix Y, according to sampling matrix obtain sampled signal covariance matrix Ry, calculate covariance matrix Ry
Characteristic value and composition characteristic value matrix Λ；Unequal weighting is carried out to each time slot using Λ, is finally merged by weighted gain
Mode generates global detection statistic GTS, and carries out destination channel and whether there is the conclusive judgement of WIFI signal.
Further, described that original CCA window is divided into multiple time slots, divide the standard of time slot specifically:
A length of 4 μ s when OFDM symbol specified in WIFI802.11a standard, a length of minimum unit, MS-CCA when with single OFDM symbol
Window width is not less than 20 μ s and should be the integral multiple of OFDM symbol duration, and timeslot number is CCA sampling window duration TCCADivided by
OFDM symbol duration T0FDM。
Further, the acquisition eigenvalue matrix specifically: sampling matrix is formed according to the sampled data in multi-slot
Y, the hits in each time slot is N ', timeslot number S, acquires its covariance matrix R using Yy, calculate characteristic value then to collect
The form of conjunction indicates are as follows: λ={ λ1, λ2..., λs, ordered set λ '={ λ is obtained in ascending orderj1, λj2..., λjS}；Sequence
The element in set meets { λ laterj1≤λj2≤…≤λjS, wherein { j1, j2 ..., jS } is the row again to { 1,2 ..., S }
Sequence；λ ' is write as diagonal matrix form and obtains Λ.
Further, the method for weighting specifically: the characteristic value obtained by sampling matrix Y and through multi-slot signal processing
MatrixIt is weighted gain merging, is enabled:
Z (n)=ΛTY (n), according to formulaWeighted gain combined value is calculated as GTS.
Further, by T and according to desired false-alarm probability PFA,DESThe decision threshold γ of calculating is compared, and is made final
Judgement:Work as TMS-CCAMore than or equal to γ2When, it adjudicates as H1, indicate that judgement PU signal exists；
Conversely, judgement is H0, indicate that judgement PU signal is not present.
The beneficial effects of the present invention are:
1) effectively improve WIFI data packet and CCA sampling window it is unjustified when, LTE-U terminal to channel status just
True judgement.By the unequal weighting to different time-gap, the specific gravity of several time slots below is aggravated, to not before being sampled as
(referring to Fig. 5 scene 1) when perfectly aligned, since MS-CCA method gives the rear higher weight of several time slots, so that receiving signal
In WIFI signal component amplified and enhanced, to reduce false dismissal probability.After being sampled as to when incomplete alignment (referring to
Fig. 5 scene 2), the specific gravity that MS-CCA weakens the WIFI signal component in reception signal avoids to reduce false-alarm probability
Because be judged to it is busy due to need to wait for wasting channel resource to next CCA period.
2) structure of MS-CCA makes it more flexible and changeable compared to tradition CCA in the use of data fusion mode,
Excellent soft data blending algorithm can be cooperated to bring more preferable judgement performance.
3) from the point of view of data processing, the judgement lower hard decision fusion side of complexity is can be used in the structure of MS-CCA
Method, i.e., each time slot individually make judgement, and the court verdict of each time slot is then carried out fusion and makes conclusive judgement.Hard decision melts
Conjunction can select fusion criterion as needed, if you need to maximize protect WIFI user from LTE-U user due to missing inspection caused by do
When disturbing, OR fusion criterion can be used.If pursuing the maximization of frequency spectrum resource utilization rate, AND fusion criterion can be used.
Detailed description of the invention
In order to keep the purpose of the present invention, technical scheme and beneficial effects clearer, the present invention provides following attached drawing and carries out
Illustrate:
Fig. 1 is LTE-U channel estimating access system model；
Fig. 2 is the LBT mechanism and its parameter that ETSI is formulated；
Fig. 3 is that CCA desired alignment samples schematic diagram；
Fig. 4 is that CCA is not exclusively aligned sampling schematic diagram；
Fig. 5 is MS-CCA structural schematic diagram；
Fig. 6 is MS-CCA method flow diagram；
Fig. 7 is MS-CCA weighting and Performance Evaluation flow chart；
Fig. 8 is preceding to incomplete aligned condition lower channel status assessment performance comparison；
Fig. 9 be after to incomplete aligned condition lower channel status assessment performance comparison；
Figure 10 is that collision probability compares under algorithms of different.
Specific embodiment
The present invention proposes a kind of MS-CCA clear channel assessment based on multi-slot syncretizing mechanism, comprising: LTE-U is whole
End or base station first carry out CCA before the channel that request accesses unauthorized frequency range, carry out data to destination channel in CCA window
Sampling.CCA window under LBT mechanism is divided into the time slot for the durations such as S (S > 1) is a by the present invention, utilizes the N ' in each time slot
A sampled data constructs signal sampling matrix Y (S × N ')；Its covariance matrix R is calculated according to sampling matrix Yy, then calculate association
Variance matrix RyCharacteristic value, by S characteristic value by ascending order arrange, and as diagonal element construct diagonal matrix Λ, utilize Λ
Unequal weighting is carried out to signal sampling matrix Y according to the mode of Weighted Fusion and generates global detection statistic TMS-CCA, last benefit
Use TMS-CCACarry out conclusive judgement.
Wherein, timeslot number divides specifically: CCA window width cannot be less than 20 μ s under LBT mechanism, and WIFI
(IEEE802.11a) a length of 4 μ s when OFDM symbol, occupied bandwidth 20Mhz, the ofdm signal of transmitting include that 64 sons carry
Wave, each OFDM symbol are made of 64 signals after QPSK or QAM modulation, operate by IFFT and add circulation
It include 80 time domain samples in each OFDM symbol after prefix.It is construction sampling matrix Y in the mentioned method of the present invention, it is desirable that every
Sample points in a time slot are identical, a length of minimum unit when with single OFDM symbol, and MS-CCA window width is not less than 20 μ s
And should be the integral multiple of OFDM symbol duration, timeslot number is CCA sampling window duration TCCADivided by OFDM symbol duration TOFDM。
Signal accumulation matrix Y is received using the reception signal construction in multi-slot, including, when n-th in i-th of time slot
The sampled data at quarter is yi(n), wherein i=1,2 ..., S, n=0,1 ..., N ' -1, then Y are as follows:
Calculate the covariance matrix R of receipt signal matrix Yy, utilize RyEigenvalue cluster at diagonal matrix to each time slot
Data carry out unequal weighting, merge mode using weighted gain and generate global detection statistic TMS-CCA(i.e. GTS)；According to public affairs
Formula z (n)=ΛTY (n) will receive the signal sampling square of eigenvalue matrix and receiver based on multi-slot of signal covariance matrix
Battle array merges；According to formulaThe weighted gain for calculating MS-CCA algorithm merges statistics
Value, and as global detection statistic TMS-CCA.Here, | | | | it is -2 norm of vector.
Decision threshold γ is determined according to desired false-alarm probability, by the global detection statistic T of generationMS-CCA(i.e. GTS)
It is compared with decision threshold, and according to formulaConclusive judgement is made, that is, works as TMS-CCAGreater than etc.
When γ, adjudicate as H1, indicate that there are WIFI signals in destination channel；Conversely, working as TMS-CCAWhen less than γ, adjudicate as H0, target
WIFI signal is not present in channel.
Below in conjunction with attached drawing, a preferred embodiment of the present invention will be described in detail.
In actual LTE-U system and WIFI coexistence of systems environment, due to the uncertain and LTE-U of WIFI long data packet
Device request accesses existing asynchronous relationship between the time point and WIFI timing of channel, so that using the LTE-U of LBT mechanism
The relative position during CCA that terminal is carried out before request is linked into channel, between sampling window and WIFI data packet
It is general uncertain.Especially when the data of WIFI are continuous short packages, sampling window occurs and WIFI data packet is not exclusively right
Neat probability is bigger.To when incomplete alignment before occurring, only a small amount of WIFI signal appears in the CCA window second half section, so that
The noise section that CCA window front half section obtains dilutes WIFI signal part included in the data of second half section acquisition, causes
The probability that missing inspection occurs increases.And when being not exclusively aligned backward, WIFI signal mainly appears on the front half section of CCA window, this portion
Point WIFI signal improves the equivalent power of noise section, causes channel status to be judged to the free time on demand, so that using LBT
The LTE-U equipment of mechanism has to wait until that next CCA window carries out access attempts again, to cause the wave of frequency spectrum resource
Take.In addition, CCA structure is usually very fixed, coexisted environment can only be adapted to by setting sampling window width, it cannot be according to existing
Real demand neatly applies other assessment algorithms.
The present invention can solve to a certain extent CCA of the tradition based on ED mode occur under practical circumstances WIFI data packet with
When the incomplete alignment condition of LTE-U equipment sampling window, the problem of to the accuracy Shortcomings of channel status judgement.
Traditional ED-CCA is first to time domain signal sampling modulus, after being squared to required modulus value, then adds up and sums and calculate flat
Mean value will finally be averaged and is compared with systemic presupposition threshold value, judge WIFI in destination channel according to comparison result
Transmission state.Sampled signal in the ED-CCA period in the time domain is represented by and (sets hits as N):
yCCA=[y (O), y (1) ..., y (N-1)]T
Therefore the detection statistic of ED-CCA are as follows:
Wherein | | indicate modulus operation.
By TED-CCAWith according to desired false-alarm probability PFA, DESPre-set decision threshold γ1It is compared, makes final
Judgement:Work as TED-CCAMore than or equal to γ1When, it adjudicates as H1, indicate that judgement destination channel has
WIFI signal exists；Conversely, judgement is H0, indicate that judgement destination channel WIFI signal is not present.
In view of in actual conditions, ED method is when sampling window is not exclusively aligned with WIFI data packet to channel status
Not accurate enough problem is adjudicated, it is prior to observe that the sample at rear several moment of sampling window has whole judgement
Effect, sampling window is divided into S time slot by the present invention, and establishes receipt signal matrix Y according to the sampled data of each time slot,
And calculate its covariance matrix Ry, then calculate RyS characteristic value, by this S characteristic value by ascending order arrangement after, according to weighting
Gain merges mode and generates GTS participation conclusive judgement.
After the CCA period is divided into S impartial time slot, relative to ED-CCA, the hits in each time slot be N '=
The sampled signal at n-th moment of N/S, the LTE-U terminal in i-th of time slot may be expressed as:
Wherein xi(n) signal from WIFI equipment that n-th of reception of i-th of time slot arrives, η are indicatedi(n) it is
White Gaussian noise meetsThe corresponding reception signal covariance matrix in this S time slot are as follows:
Ry=E [y (n) yH(n)]
=E [x (n) xH(n)]+E[η(n)ηH(n)]
=Rx+Rη
R in above formulax=E [x (n) xH(n)] autocorrelation matrix of signal is received for WIFI,Table
Show noise autocorrelation matrix, ISIndicate S rank unit matrix.Have again:
Y (n)=[y1(n), y2(n) ..., yS(n)]T
X (n)=[x1(n), x2(n) ..., xS(n)]T
η (n)=[η1(n), η2(n) ..., ηS(n)]T
R is calculated according to YyAfterwards, R is calculatedyCharacteristic value and be λ={ λ with set expression1, λ2..., λS, it will be in λ
Characteristic value is arranged to obtain λ '={ λ by ascending orderj1, λj2..., λjS, wherein serial number { j1, j2 ..., jS } is to { 1,2 ..., S }
Rearrangement.Using the element in λ ' as diagonal element structural matrix Λ are as follows:
Above-mentioned Λ is generated to the global detection statistic T of MS-CCA algorithm as weighting matrixMS-CCA:
Wherein, z (n)=ΛTY (n), y (n) are the column vector of the sampling matrix Y under MS-CCA algorithm, and N ' is sampling time
Number.
By TMS-CCAWith according to desired false-alarm probability PFA, DESThe decision threshold γ of calculating2It is compared, makes and finally sentencing
Certainly:Work as TMS-CCAMore than or equal to γ2When, it adjudicates as H1, indicate that there are WIFI letters on judgement channel
Number；Conversely, judgement is H0, indicate that WIFI signal is not present in judgement destination channel.
Fig. 1 show LTE-U terminal CCA illustraton of model when LTE-U coexists with WIFI cochannel.LTE-U and WIFI Coexisting Field
Clear channel assessment (CCA) under scape is that LTE-U user detects the WIFI signal (i.e. ofdm signal) received to judge channel
Whether occupied, i.e., need to only adjudicate whether there is or not WIFI signal by WIFI terminal, does not need to demodulate original signal.In order to guarantee LTE-U
With WIFI in the harmonious coexistence of cochannel and the widespread deployment of LTE-U technology, LTE-U terminal is using as shown in Figure 2 based on competing
The LBT Channel Access Mechanism for striving access, first carries out the CCA based on energy measuring before accessing channel, i.e., minimum 20 μ s when
Interior progress limited times sampling, is calculated sampled energy value.Mesh is thought if received signal energy value is greater than preset threshold
It marks on channel there are WIFI signal, the CCA window that LTE-U continues waiting for next cycle arrives；It is on the contrary, then it is assumed that channel is empty
Spare time, LTE-U can be directly accessed channel and send data.
The alignment analysis of CCA window
Traditional CCA is relatively preferable to the status assessment performance of channel when facing two kinds of situations of Fig. 3, i.e., in sampling window
It always exists WIFI signal or is completely absent WIFI data, but when two class situation as shown in Figure 4 occurs for sampling, and
The occupied state of channel cannot be judged well.Under Fig. 4 situation 1, when data appear in the CCA window second half section, due to connecing
The WIFI signal received is less, and channel is very likely judged to idle and transmits data by ED-CCA, and actually CCA window it
There are WIFI data to transmit in destination channel afterwards, if at this moment LTE-U transmission data will cause the collision of data packet.Work as generation
When appearing in CCA window first half such as 2 data packet of Fig. 4 situation, channel is very likely judged as busy again by ED-CCA, and practical
On channel after CCA window be it is idle, will cause in this way because be judged to it is busy due to need to wait for arriving to next CCA window
Come, channel resource is caused to waste.As seen from Figure 4, the aft section when incomplete alignment condition occurs, in CCA window
Have to whole judgement and more importantly acts on, for this feature, free time based on multi-slot Weighted Fusion that the present invention designs
Channel evaluation method is as shown in figure 5, be divided into multiple time slots for CCA window, according to the reception data configuration in each time slot
Then receiving matrix calculates its covariance matrix, carry out unequal weighting to each time slot using the characteristic value of covariance matrix,
The specific gravity for increasing several time slots below carries out conclusive judgement using the data after Weighted Fusion.The invention is when perfectly aligned
There is similar performance with ED-CCA, and traditional side ED-CCA is compared to the judgement of channel status under incomplete aligned condition
Case is more accurate.
MS-CCA algorithm
Fig. 6 is MS-CCA algorithm flow chart, is included the following steps:
(1) when LTE-U terminal uses LBT Channel Access Mechanism, its CCA window is divided into S time slot, it is desirable that CCA window
Mouth is the integral multiple of WIFI OFDM symbol duration, and timeslot number is CCA window duration divided by OFDM symbol duration, i.e. S=TCCA/
TOFDM.A sampled value of the N ' that LTE-U terminal obtains in i-th of time slot are as follows: yi=[yi(0), yi(1) ..., yi(N′-1)]T,
Middle i=1,2 ..., S.
(2) sampling matrix Y is generated using the sampled data of all time slots(S×N′), the covariance matrix R of Y is calculatedy, so
S characteristic value for sampling anti-variance matrix is calculated afterwards, is indicated with aggregate form are as follows: λ={ λ1, λ2..., λS, it will be in λ
Characteristic value obtains ordered set λ '={ λ in ascending orderj1, λj2..., λjS}.Element after sequence in set meets { λj1≤
λj2≤…≤λjS, wherein { j1, j2 ..., jS } is the rearrangement to { 1,2 ..., S }.λ ' is write as diagonal matrix form and is obtained
Λ, Λ be according to receive signal be calculated, diagonal element be sized after diagonal matrix, be used as time slot weight.
Weighted energy merges mode
Fig. 7 be weighting and Performance Evaluation flow chart, include the following steps: by receiver sampled signal y (n) and it is divided when
The eigenvalue matrix Λ that gap is calculated merges to obtain ΛTY (n) enables z (n)=ΛTy(n)；According to formulaWeighted gain combining energy value is calculated as GTS；By TMS-CCAWith it is general according to desired false-alarm
Rate PFA, DESThe decision threshold γ of calculating2It is compared, makes conclusive judgement:Work as TMS-CCAIt is greater than
Equal to γ2When, it adjudicates as H1, indicate that judgement destination channel WIFI signal exists, LTE-U is not linked into channel；Conversely, judgement is
H0, indicate that judgement destination channel WIFI signal is not present, LTE-U is linked into channel.
The present invention believes in actual environment since the uncertainty and LTE-U terminal request of WIFI long data packet access
Sampling window caused by the uncertainty at road time point, there is a situation where being not exclusively aligned, considers CCA with WIFI data packet
Window is divided into multiple small time slots, aggravates the weight of relatively important time slot, and then proposes a kind of based on multi-slot syncretizing mechanism
Clear channel assessment.This method does not need any prior information in a practical situation, and data packet and CCA window not
Relatively traditional ED-CCA has more accurate decision-making ability when perfectly aligned, and the CCA for solving traditional LBT to a certain extent exists
Data packet is unable to the problem of accurate judgement channel status when being not exclusively aligned with CCA window.
Fig. 8, Fig. 9 and Figure 10 compared the correlated performance of two kinds of assessment algorithms of ED-CCA and MS-CCA, using detection probability,
Accuracy rate and false-alarm probability are as measuring alignment standard.The Monte Carlo that 5000 iteration are carried out under Matlab environment is imitative
Very, a length of 20 μ s, MS-CCA timeslot number is 5 when setting CCA.WIFI is modulated using OFDM, when occupied bandwidth 20Mhz, OFDM
It is expected a length of 4 μ s, WIFI system sends data every time and occupies whole bandwidth, sets false-alarm probability in addition as 10%, emulation signal-to-noise ratio
Range is [- 8dB 8dB].
Emulation 1: to incomplete alignment (LTE-U equipment need to detect the presence of WIFI data), CCA window before investigation Fig. 4 situation 1
In the case that mouth is aligned 20%, 40% and 80% respectively with WIFI data packet, MS-CCA and ED-CCA based on multi-slot are to letter
The judgement of road state.From Fig. 8 (a) as can be seen that when in sampling window comprising less WIFI data (alignment 20%),
MS-CCA expands the specific gravity of WIFI signal effectively to there is relatively good detectability.Include in CCA window
When more WIFI data (alignment 80%), the detection performance of MS-CCA and ED-CCA are close.To sum up, MS-CCA is incomplete in forward direction
Good detection performance is suffered from each situation of alignment.From Fig. 8 (b) as can be seen that the false alarm rate of the two algorithm is kept at this time
Within the scope of a relatively steady acceptable level.
Emulation 2: to (data packet appears in CCA window front half section, and LTE-U is set when incomplete alignment after investigation Fig. 4 situation 2
It is standby channel status to be judged to the free time), the accurate judgement ability of MS-CCA and ED-CCA based on multi-slot to channel status.From
As can be seen that when in CCA window including less WIFI data (being aligned 20%), what MS-CCA was effectively expanded makes an uproar Fig. 9 (a)
Acoustical power specific gravity, so that it is more accurate with respect to ED-CCA to the judgement of channel status.It is worth noting that the accuracy rate in figure
To when incomplete alignment after referring to, need for channel status to be accurately judged to idle probability.With the increase of signal-to-noise ratio, CCA weeks
The specific gravity of WIFI signal power in phase can increase with it, so that channel is judged to idle probability by each algorithm to be reduced.This
When each algorithm false-alarm probability situation of change such as Fig. 9 (b) shown in.
To sum up, MS-CCA is due to giving rear several time slots more Gao Quanchong, so that it is when forward and backward is not exclusively aligned
It is all more accurate to the judgement of channel status, and MS-CCA and ED-CCA have similar performance under perfectly aligned state.Therefore
MS-CCA algorithm is facing in destination channel there are the continuous short packages of WIFI, i.e. CCA window and data packet is endless frequent occurrence
There is better channel status assessment performance when the case where full alignment.
Emulation 3: when investigation LTE-U and WIFI cochannel coexist, WIFI portfolio is under high, medium and low three kinds of states,
When ED-CCA and the MS-CCA fusion detection algorithm random access based on multi-slot is respectively adopted to channel in LTE-U with WIFI generation
The probability size of data packet collision.
From Figure 10 (a) as can be seen that WIFI is sent in the case that signal is mostly long data packet, i.e. CCA window and data packet
There is a situation where when not exclusively alignment is less, MS-CCA and ED-CCA based on multi-slot to the judgement of channel status very
It is close.Figure 10 (b) illustrates WIFI and sends signal when being continuous short packages, the probability that LTE-U and WIFI collide.It can be with
Find out when not exclusively alignment probability of happening increases, MS-CCA promotes the judgment of channel status with respect to ED-CCA more bright
It is aobvious, effectively reduce the probability of data packet collision.
Finally, it is stated that preferred embodiment above is only used to illustrate the technical scheme of the present invention and not to limit it, although logical
It crosses above preferred embodiment the present invention is described in detail, however, those skilled in the art should understand that, can be
Various changes are made to it in form and in details, without departing from claims of the present invention limited range.
Claims (2)
1. a kind of LTE-U clear channel assessment based on multi-slot syncretizing mechanism, it is characterised in that: in the method,
LTE-U terminal first carries out the CCA of at least 20 μ s before accessing channel, and original CCA window is divided into multiple time slots, utilizes
Data in multiple time slots form signal sampling matrix Y, obtain sampled signal covariance matrix R according to sampling matrixy, calculate association
Variance matrix RyCharacteristic value and composition characteristic value matrix Λ；Unequal weighting is carried out to each time slot using Λ, finally by adding
Power gain merges mode and generates global detection statistic GTS, and carries out destination channel and whether there is the conclusive judgement of WIFI signal；
Described is divided into multiple time slots for original CCA window, divides the standard of time slot specifically: WIFI802.11a standard
Specified in OFDM symbol when a length of 4 μ s, a length of minimum unit when with single OFDM symbol, MS-CCA window width is not less than 20
μ s and the integral multiple that should be OFDM symbol duration, timeslot number are CCA sampling window duration TCCADivided by OFDM symbol duration
TOFDM；
The acquisition eigenvalue matrix specifically: sampling matrix Y is formed according to the sampled data in multi-slot, in each time slot
Hits be N ', timeslot number S, acquire its covariance matrix R using Yy, then calculate characteristic value indicates in the form gathered
Are as follows: λ={ λ1, λ2..., λS, ordered set λ '={ λ is obtained in ascending orderj1, jλ2..., λjS}；After sequence in set
Element meets { λj1≤λj2≤…≤λjSWherein { j1, j2 ..., jS } be the rearrangement to { 1,2 ..., S }；λ ' is write as diagonally
Matrix form obtains Λ；
The method of weighting specifically: carry out sampling matrix Y with the eigenvalue matrix Λ obtained through multi-slot signal processing
Weighted gain merges, and enables:
Z (n)=ΛTY (n) hates according to formulaWeighted gain combined value is calculated as GTS
Wherein y (n) is the data that S time slot is arrived in n-th of reception, and n=0,1 ..., N'-1, N' is moment number, that is, is sampled
Number.
2. a kind of LTE-U clear channel assessment based on multi-slot syncretizing mechanism according to claim 1, feature
It is: by global detection statistic TMS-CCAWith the decision threshold γ calculated according to desired false-alarm probability PFA, DES2Compared
Compared with making conclusive judgement:Work as TMS-CCAMore than or equal to γ2When, it adjudicates as H1, table
Show that judgement WIFI signal exists；Conversely, judgement is H0, indicate that judgement WIFI signal is not present.
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