CN106412931A - LTE-U idle channel evaluation method based on multi-slot fusion mechanism - Google Patents
LTE-U idle channel evaluation method based on multi-slot fusion mechanism Download PDFInfo
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Abstract
The invention relates to an LTE-U idle channel evaluation method based on a multi-slot fusion mechanism, and belongs to the technical field of LTE-U (LTE in unlicensed spectrum) in mobile communication. An LTE-U system works in an unauthorized frequency range, and before the system access a channel, idle channel evaluation is needed generally. The LTE-U system divides the whole CCA window into multiple slots; sampling data of the multiples slots is used to generate a sampling matrix, a covariance matrix of the sampling data is calculated to obtain characteristic values, the characteristic values in ascending order are used to carry out unequal weighting on the corresponding slots, and the channel state evaluation performance when the CCA window is not completely aligned with a data packet is improved. The idle channel evaluation method can be used to improve the accuracy of channel state determination effectively, reduce the possibility of data packet collision among different systems, and the improves the spectral efficiency that the LTE-U system and a WIFI system coexist in the same channel in the unauthorized frequency range.
Description
Technical field
The invention belongs to wireless communication technology field, LTE-U (the LTE in particularly unauthorized frequency range
Unlicensed spectrum) the clear channel assessment (CCA) technical field when accessing channel for the system, it is related to one kind and be based on multi-slot
The LTE-U clear channel assessment of syncretizing mechanism.
Background technology
LTE-U is that 3GPP proposes for alleviating the emerging technology authorizing band communication load pressure in recent years, and 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, is transferred to unauthorized frequency range and reaches alleviation existing mandate frequency from mandate frequency range simultaneously also by by flow
The purpose of the communication pressure in section.Due to the regional open policy of unauthorized frequency range and the restriction of spectral characteristic, LTE-U technology will
It is applied to the unauthorized frequency range near 5GHz.This frequency range mainly has WIFI (IEEE 802.11a) system using, therefore at present
The research with regard to LTE-U both at home and abroad is mainly concentrated in allowing LTE-U and WIFI system harmonious coexistence in this frequency range.
Being currently based on the co-existence schemes that fairness (contention access) considers is to allow LTE-U adopt LBT (Listen Before
Talk) the Channel Access Mechanism of mode, that is, LTE-U equipment access channel before first carry out clear channel assessment (CCA) (Clear
Channel Assessment, CCA).If LTE-U equipment does not find WIFI signal during CCA, then visual channel is sky
Not busy, you can busy channel transmission data；Conversely, channel then can not be accessed.Meanwhile, in order that other system also has an opportunity to access
Channel, LTE-U equipment will reserve one section of free timeslot after the data transfer is complete, so that other system uses channel spectrum.LBT
Under CCA typically adopt single node energy measuring (Energy Detection, ED) method, can be described as ED-CCA.ED-CCA is first
Time-domain signal is sampled modulus, squared to required modulus value, the summation that then adds up is averaged again, finally will be averaged and system
Default detection threshold value is compared, and judges that (or other reside in and in unauthorized frequency range are WIFI system according to comparison result
System) transmission state.
If the sampling window of ED-CCA (destination channel is carried out with the time interval of data acquisition) is sent with WIFI
When packet is perfectly aligned or staggers, can have preferable judgement to channel status.However, in actual environment, by
Asynchronous between the uncertainty and LTE-U device request access channel time point and WIFI sequential of WIFI packet bag length
Property, so that actual CCA sampling window often can not be perfectly aligned with WIFI packet, therefore, leads to receive in sampling window
WIFI signal less and cause the erroneous judgement to channel status.Additionally, the structure design of CCA is more fixing, typically can only pass through
Setting sampling window width come to adapt to coexisted environment it is impossible to according to current demand neatly application data merge and judgement side
Method.Accordingly, the present invention is directed to the problem that ED-CCA exists, and proposes one kind based on multi-slot (Multi-Slot) syncretizing mechanism
CCA method.
Content of the invention
In view of this, for ED-CCA sampling window is not exclusively alignd with WIFI packet under practical circumstances when to channel
Condition adjudgement is short of the problem of the degree of accuracy, it is an object of the invention to provide a kind of LTE-U based on multi-slot syncretizing mechanism is empty
Channel assessment method, in LTE-U equipment, CCA sampling window is divided into multiple time slots, using the characteristic value of receipt signal
Information carries out the weighting of uneven equal weight to the receiving 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
The MS-CCA algorithm of bright proposition than existing ED-CCA in the case that packet is not exclusively alignd with CCA sampling window, to letter
The occupancy situation in road can more accurately judge such that it is able to reduce LTE-U, with WIFI system, number occurs when cochannel coexists
According to the probability of bag collision, and then lift system coexistence efficiency.
For reaching above-mentioned purpose, the present invention provides following technical scheme：
A kind of LTE-U clear channel assessment based on multi-slot syncretizing mechanism, in the method, LTE-U terminal exists
First carry out the CCA of at least 20 μ s before accessing channel, original CCA window is divided into multiple time slots, using in multiple time slots
Data composition 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；Using Λ, unequal weighting is carried out to each time slot, finally merged by weighted gain
Mode generates global detection statistic GTS, and carries out the conclusive judgement that destination channel whether there is WIFI signal.
Further, described original CCA window is divided into multiple time slots, the standard dividing time slot is specially：
A length of 4 μ s during OFDM symbol specified in WIFI802.11a standard, with least unit a length of during single OFDM symbol, MS-CCA
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, described acquisition eigenvalue matrix is specially：According to the sampled data composition sampling matrix in multi-slot
Y, the hits in each time slot is N ', and timeslot number is S, tries to achieve its covariance matrix R using Yy, then calculate characteristic value to collect
The form closed is expressed as：λ={ λ1, λ2..., λs, obtain ordered set λ '={ λ in ascending orderj1, λj2..., λjS}；Sequence
Element in gathering afterwards meets { λj1≤λj2≤…≤λjS, wherein { j1, j2 ..., jS } is the row again to { 1,2 ..., S }
Sequence；λ ' is write as diagonal matrix form and is obtained Λ.
Further, described method of weighting is specially：By sampling matrix Y and the characteristic value obtaining through multi-slot signal transacting
MatrixIt is weighted gain to merge, order：
Z (n)=ΛTY (n), according to formulaCalculate weighted gain combined value as GTS.
Further, by T and according to desired false-alarm probability PFA,DESThe decision threshold γ calculating is compared, and makes final
Judgement：Work as TMS-CCAMore than or equal to γ2When, adjudicate as H1, represent that judgement PU signal exists；
Conversely, adjudicating as H0, represent that judgement PU signal does not exist.
The beneficial effects of the present invention is：
1) effectively improve when WIFI packet and CCA sampling window are unjustified, LTE-U terminal-pair channel status is just
Really judgement.By the unequal weighting to different time-gap, increase the proportion of several time slots below, to not before being sampled as
When perfectly aligned (referring to Fig. 5 scene 1), after being given due to MS-CCA method, the higher weight of several time slots is so that receipt signal
In WIFI signal component be amplified and strengthen, thus reducing false dismissal probability.When being sampled as not exclusively aliging backward (referring to
Fig. 5 scene 2), MS-CCA weakens the proportion of the WIFI signal component in receipt signal, thus reducing false-alarm probability, it is to avoid
Need to wait for the next CCA cycle wasting channel resource because being judged to busy.
2) to make it compare traditional CCA in the use of data fusion mode more flexible and changeable for the structure of MS-CCA,
Excellent soft data blending algorithm can be coordinated to bring more preferable judgement performance.
3) from the point of view of data processing, the structure of MS-CCA can be using the lower hard decision fusion side of judgement complexity
Method, that is, each time slot individually make judgement, then the court verdict of each time slot is carried out fusion and makes conclusive judgement.Hard decision melts
Conjunction can select fusion criterion as needed, such as need to maximize and protect WIFI user from doing that LTE-U user causes because of missing inspection
When disturbing, OR fusion criterion can be adopted.If pursuing the maximization of frequency spectrum resource utilization rate, AND fusion criterion can be adopted.
Brief description
In order that the purpose of the present invention, technical scheme and beneficial effect are clearer, the present invention provides drawings described below to carry out
Explanation：
Fig. 1 is LTE-U channel estimating access system model；
LBT mechanism and its parameter that Fig. 2 formulates for ETSI；
Fig. 3 is CCA desired alignment sampling schematic diagram；
Fig. 4 not exclusively aligns sampling schematic diagram for CCA；
Fig. 5 is MS-CCA structural representation；
Fig. 6 is MS-CCA method flow diagram；
Fig. 7 is MS-CCA weighting and Performance Evaluation flow chart；
Fig. 8 is front to incomplete aligned condition lower channel state estimation performance comparison；
Fig. 9 is incomplete aligned condition lower channel state estimation performance comparison backward；
Figure 10 is collision probability contrast under algorithms of different.
Specific embodiment
The present invention proposes a kind of MS-CCA clear channel assessment based on multi-slot syncretizing mechanism, including：LTE-U is eventually
End or base station first carried out CCA before request accesses the channel of unauthorized frequency range, carried out data to destination channel in CCA window
Sampling.CCA window under LBT mechanism is divided into S (S by the present invention>1) the individual time slot waiting duration, using the N ' in each time slot
Individual sampled data construction signal sampling matrix Y (S × N ')；Its covariance matrix R is calculated according to sampling matrix Yy, subsequently calculate association
Variance matrix RyCharacteristic value, by S characteristic value press ascending order arrange, and as diagonal element construct diagonal matrix Λ, using Λ
Mode according to Weighted Fusion carries out unequal weighting and generates global detection statistic T to signal sampling matrix YMS-CCA, finally profit
Use TMS-CCACarry out conclusive judgement.
Wherein, timeslot number divides and is specially：Under LBT mechanism, CCA window width cannot be less than 20 μ s, and WIFI
(IEEE802.11a) a length of 4 μ s during OFDM symbol, occupied bandwidth is 20Mhz, and the ofdm signal of transmitting comprises 64 sons and carries
Ripple, each OFDM symbol is made up of 64 signals after QPSK or QAM modulation, operates through IFFT and adds circulation
80 time domain samples are included in each OFDM symbol after prefix.It is construction sampling matrix Y in institute of the present invention extracting method it is desirable to every
Sample points in individual time slot are identical, and with least unit a length of during single OFDM symbol, 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.
Using the receipt signal construction receipt signal cumulant matrix Y in multi-slot, including during in i-th time slot n-th
The sampled data carved is yi(n), wherein i=1,2 ..., S, n=0,1 ..., N ' -1, then Y be：
Calculate the covariance matrix R of receipt signal matrix Yy, using RyCharacteristic value composition diagonal matrix to each time slot
Data carries out unequal weighting, merges mode using weighted gain and generates global detection statistic TMS-CCA(i.e. GTS)；According to public affairs
Formula z (n)=ΛTY (n) is by the eigenvalue matrix of receipt signal covariance matrix and the signal sampling square based on multi-slot for the receiver
Battle array merges；According to formulaThe weighted gain calculating MS-CCA algorithm merges statistics
Value, and as global detection statistic TMS-CCA.Here, | | | | for vectorial -2 norms.
Determine decision threshold γ according to desired false-alarm probability, the global detection statistic T that will generateMS-CCA(i.e. GTS)
It is compared with decision threshold, and according to formulaMake conclusive judgement, that is, work as TMS-CCAMore than etc.
When γ, adjudicate as H1, represent in destination channel there is WIFI signal；Conversely, working as TMS-CCADuring less than γ, adjudicate as H0, target
There is not WIFI signal in channel.
Below in conjunction with accompanying drawing, the preferred embodiments of the present invention are described in detail.
In actual LTE-U system with WIFI coexistence of systems environment, due to the uncertain of WIFI long data packet and LTE-U
Device request accesses the asynchronous relationship existing between the time point of channel and WIFI sequential so that employing the LTE-U of LBT mechanism
Relative position during the CCA that terminal was carried out before request is linked into channel, between sampling window and WIFI packet
Typically uncertain.Especially when the data of WIFI is continuous short packages, occur sampling window not exclusively right with WIFI packet
Neat probability is bigger.When before occurring to incomplete alignment, only a small amount of WIFI signal occur in the CCA window second half section so that
The noise section that CCA window front half section obtains dilutes the WIFI signal part included in the data of second half section acquisition, leads to
The probability that missing inspection occurs increases.And when not exclusively aliging 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, leads on demand channel status can not be judged to the free time so that adopting LBT
The LTE-U equipment of mechanism has to wait until that next CCA window carries out access attempts again, thus causing the wave of frequency spectrum resource
Take.Additionally, CCA structure is generally very fixing, coexisted environment can only be adapted to by arranging sampling window width it is impossible to according to existing
Real demand neatly applies other assessment algorithms.
The present invention can solve to a certain extent the CCA based on ED mode for the tradition occur under practical circumstances WIFI packet with
Problem during the incomplete alignment condition of LTE-U equipment sampling window, to the accuracy Shortcomings that channel status judges.
Traditional ED-CCA first samples to time-domain signal modulus, squared to required modulus value after, more cumulative sue for peace and calculate flat
Average, is finally compared averaging with systemic presupposition threshold value, judges WIFI in destination channel according to comparison result
Transmission state.In the ED-CCA cycle, the sampled signal in time domain is represented by (setting hits as N)：
yCCA=[y (O), y (1) ..., y (N-1)]T
Therefore the detection statistic of ED-CCA is：
Wherein | | represent modulus computing.
By TED-CCAWith according to expectation false-alarm probability PFA, DESThe decision threshold γ pre-setting1It is compared, make final
Judgement：Work as TED-CCAMore than or equal to γ1When, adjudicate as H1, represent that judgement destination channel has
WIFI signal exists；Conversely, adjudicating as H0, represent that judgement destination channel WIFI signal does not exist.
In view of in actual conditions, ED method is when sampling window is not exclusively alignd with WIFI packet to channel status
Adjudicate not accurate enough problem it was observed that the sample in rear several moment of sampling window overall judgement is had prior
Effect, sampling window is divided into S time slot by the present invention, and sets up 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 press ascending order arrangement after, according to weighting
Gain merges mode and generates GTS participation conclusive judgement.
After the CCA cycle is divided into S impartial time slot, with respect to ED-CCA, the hits in each time slot be N '=
The sampled signal in n-th moment in i-th time slot for N/S, the LTE-U terminal is represented by：
Wherein xi(n) represent i-th time slot n-th reception to the signal coming from WIFI equipment, ηiN () is
White Gaussian noise, meetsIn this S time slot, corresponding receipt signal covariance matrix is：
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)] for WIFI receipt signal autocorrelation matrix,Table
Show noise autocorrelation matrix, ISRepresent 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, calculate RyCharacteristic value and with set expression as λ={ λ1, λ2..., λS, by λ
Characteristic value obtains λ '={ λ by ascending order arrangementj1, λj2..., λjS, wherein sequence number { j1, j2 ..., jS } is to { 1,2 ..., S }
Rearrangement.Element with λ ' for diagonal element structural matrix Λ is：
Using above-mentioned Λ as weighting matrix to generate the global detection statistic T of MS-CCA algorithmMS-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 calculating2It is compared, make and finally sentencing
Certainly：Work as TMS-CCAMore than or equal to γ2When, adjudicate as H1, represent that WIFI letter is existed on judgement channel
Number；Conversely, adjudicating as H0, represent that in judgement destination channel, WIFI signal does not exist.
Fig. 1 show LTE-U terminal CCA illustraton of model when LTE-U is coexisted with WIFI cochannel.LTE-U and WIFI Coexisting Field
Clear channel assessment (CCA) under scape is that LTE-U user carries out detection to judge channel to the WIFI signal (i.e. ofdm signal) receiving
Whether taken by WIFI terminal, only need to adjudicate and have or not WIFI signal, do not need to demodulate original signal.In order to ensure LTE-U
With the widespread deployment of the harmonious coexistence in cochannel for the WIFI and LTE-U technology, LTE-U terminal adopt as shown in Figure 2 based on competing
Strive the LBT Channel Access Mechanism of access, first carry out CCA based on energy measuring before accessing channel, that is, minimum 20 μ s when
Interior carry out limited number of time sampling, be calculated sampled energy value.If the signal energy value receiving is more than predetermined threshold value, think mesh
There is WIFI signal, the CCA window that LTE-U continues waiting for next cycle arrives on mark channel；Otherwise then it is assumed that channel is empty
In the 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 state estimation performance of channel when facing two kinds of situations of Fig. 3, that is, in sampling window
There is WIFI signal always or be completely absent WIFI data, but when sampling occurs two class situation as shown in Figure 4, and
The seizure condition of channel can not be judged well.Under Fig. 4 situation 1, when data occurs in CCA window second half section, due to connecing
The WIFI signal receiving is less, and channel is very likely judged to the free time and transmission data by ED-CCA, and actually CCA window it
WIFI data is had to transmit in destination channel afterwards, if at this moment LTE-U sends the collision that data can cause packet.Work as generation
When occurring in CCA window first half as Fig. 4 situation 2 packet, channel very likely is judged as hurrying by ED-CCA again, and actual
On channel after CCA window be idle, so can cause to need to wait for arriving to next CCA window because being judged to busy
Come, cause channel resource to waste.As seen from Figure 4, when there is incomplete alignment condition, the aft section in CCA window
Overall judgement is had and more importantly acts on, for this feature, the free time based on multi-slot Weighted Fusion of present invention design
Channel evaluation method, as shown in figure 5, multiple time slots will be divided into CCA window, constructs according to the receiving data in each time slot
Receiving matrix, then calculates its covariance matrix, and the characteristic value using covariance matrix carries out unequal weighting to each time slot,
Increase the proportion of several time slots below, carry out conclusive judgement using the data after Weighted Fusion.This invention is when perfectly aligned
There is close performance with ED-CCA, and traditional ED-CCA side is compared in the judgement to channel status under incomplete aligned condition
Case is more accurate.
MS-CCA algorithm
Fig. 6 is MS-CCA algorithm flow chart, comprises the steps：
(1), when LTE-U terminal adopts LBT Channel Access Mechanism, its CCA window is divided into S time slot it is desirable to 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.The individual sampled value of N ' that LTE-U terminal obtains in i-th time slot is：yi=[yi(0), yi(1) ..., yi(N′-1)]T, its
Middle i=1,2 ..., S.
(2) sampled data utilizing all time slots generates sampling matrix Y(S×N′), it is calculated the covariance matrix R of Yy, so
It is calculated S characteristic value of anti-variance matrix of sampling afterwards, be expressed as with aggregate form：λ={ λ1, λ2..., λS, by λ
Characteristic value obtains ordered set λ '={ λ in ascending orderj1, λj2..., λjS}.Element in gathering after sequence 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 are calculated according to receipt signal, diagonal element be sized after diagonal matrix, as time slot weighting.
Weighted energy merges mode
Fig. 7 is weighting and Performance Evaluation flow chart, comprises the steps：By receiver sampled signal y (n) with divided when
Calculated eigenvalue matrix Λ of gap merges and obtains ΛTY (n), makes z (n)=ΛTy(n)；According to formulaCalculate weighted gain combining energy value as GTS；By TMS-CCAGeneral with according to desired false-alarm
Rate PFA, DESThe decision threshold γ calculating2It is compared, make conclusive judgement：Work as TMS-CCAIt is more than
Equal to γ2When, adjudicate as H1, represent that judgement destination channel WIFI signal exists, LTE-U is not linked into channel；Conversely, adjudicate being
H0, represent that judgement destination channel WIFI signal does not exist, LTE-U is linked into channel.
The present invention is directed in actual environment because the uncertainty of WIFI long data packet and LTE-U terminal request access letter
There is situation about not exclusively aliging it is considered to by CCA in the sampling window caused by the uncertainty of road time point and WIFI packet
Window is divided into multiple small time slots, increases the weight of relatively important time slot, and then proposes one kind based on multi-slot syncretizing mechanism
Clear channel assessment.The method does not need any prior information in a practical situation, and in packet with CCA window not
When perfectly aligned, relatively conventional ED-CCA has more accurate decision-making ability, and the CCA solving traditional LBT to a certain extent exists
The problem of channel status can not accurately be judged with CCA window when packet is not exclusively alignd.
Fig. 8, Fig. 9 and Figure 10 compared for 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 carrying out 5000 iteration under Matlab environment imitates
Very, a length of 20 μ s when setting CCA, MS-CCA timeslot number is 5.WIFI adopts OFDM to modulate, and occupied bandwidth is 20Mhz, during OFDM
A length of 4 μ s, WIFI system sends data every time and takies whole bandwidth, in addition sets expectation false-alarm probability as 10%, emulates signal to noise ratio
Scope is [- 8dB 8dB].
Emulation 1：To incomplete alignment (LTE-U equipment need to detect WIFI data to be existed), CCA window before investigating Fig. 4 situation 1
Mouthful align in the case of 20%, 40% and 80% respectively with WIFI packet, MS-CCA and ED-CCA based on multi-slot is to letter
The judgement of road state.From Fig. 8 (a) as can be seen that when comprising less WIFI data (alignment 20%) in sampling window,
MS-CCA all effectively expands the proportion of WIFI signal thus there being relatively good detectability.Comprise in CCA window
During more WIFI data (alignment 80%), the detection similar nature of MS-CCA and ED-CCA.To sum up, MS-CCA is incomplete in forward direction
Alignment each in the case of suffer from good detection performance.From Fig. 8 (b) as can be seen that the false alarm rate of algorithm both now keeps
In the range of a relatively steady acceptable level.
Emulation 2：When investigation Fig. 4 situation 2 is not exclusively alignd backward, (packet occurs in CCA window front half section, and LTE-U sets
Standby channel status need to be judged to the free time), the accurate judgement to channel status for MS-CCA and ED-CCA based on multi-slot.From
Fig. 9 (a) is as can be seen that when comprising less WIFI data (i.e. alignment 20%) in CCA window, what MS-CCA effectively expanded makes an uproar
Acoustical power proportion is so that it is more accurate relative to ED-CCA to the judgement of channel status.What deserves to be explained is, the accuracy rate of in figure
When referring to not exclusively align backward, need channel status is accurately judged to the probability of free time.With the increase of signal to noise ratio, CCA week
The proportion of the WIFI signal power in the phase can increase therewith, and then the probability that channel is judged to the free time is reduced by each algorithm.This
When each algorithm false-alarm probability situation of change such as Fig. 9 (b) shown in.
To sum up, MS-CCA is because the higher weight of time slots several after giving is so that it is when forward and backward is not exclusively alignd
Judgement to channel status is all more accurate, and under perfectly aligned state, MS-CCA and ED-CCA has close performance.Therefore
There are the continuous short packages of WIFI in MS-CCA algorithm in destination channel, that is, CCA window and packet often cannot occur completely
There is more preferable channel status assessment performance during the situation of full alignment.
Emulation 3：When investigation LTE-U is coexisted with WIFI cochannel, WIFI portfolio is under high, medium and low three kinds of states,
LTE-U is respectively adopted ED-CCA and the MS-CCA fusion detection algorithm Stochastic accessing based on multi-slot and is occurred with WIFI to during channel
The probability size of data packet collision.
In the case that Figure 10 (a) can be seen that WIFI sending signal mostly long packet, i.e. CCA window and packet
When occurring the situation of not exclusively alignment less, the MS-CCA based on multi-slot and ED-CCA is to the judgement of channel status very
Close.When Figure 10 (b) illustrates WIFI sending signal for continuous short packages, the probability that LTE-U and WIFI collides.Permissible
Find out that, when incomplete alignment probability of happening increases, MS-CCA is lifted more bright to the judgment of channel status relative to ED-CCA
Aobvious, effectively reduce the probability of data packet collision.
Finally illustrate, preferred embodiment above only in order to technical scheme to be described and unrestricted, although logical
Cross above preferred embodiment the present invention to be described in detail, it is to be understood by those skilled in the art that can be
In form and various changes are made to it, without departing from claims of the present invention limited range in details.
Claims (5)
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 carried out the CCA of at least 20 μ s before accessing channel, and original CCA window is divided into multiple time slots, utilized
Data composition signal sampling matrix Y in multiple time slots, obtains sampled signal covariance matrix R according to sampling matrixy, calculate association
Variance matrix RyCharacteristic value and composition characteristic value matrix Λ；Using Λ, unequal weighting is carried out to each time slot, finally by plus
Power gain merges mode and generates global detection statistic GTS, and carries out the conclusive judgement that destination channel whether there is WIFI signal.
2. a kind of LTE-U clear channel assessment based on multi-slot syncretizing mechanism according to claim 1, its feature
It is：Described is divided into multiple time slots by original CCA window, and the standard dividing time slot is specially：WIFI 802.11a marks
A length of 4 μ s during OFDM symbol specified in standard, with least unit a length of during single OFDM symbol, 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.
3. a kind of LTE-U clear channel assessment based on multi-slot syncretizing mechanism according to claim 1, its feature
It is：Described acquisition eigenvalue matrix is specially：According to the sampled data composition sampling matrix Y in multi-slot, each time slot
Interior hits is N ', and timeslot number is S, tries to achieve its covariance matrix R using Yy, then calculate characteristic value table in the form of gathering
It is shown as：λ={ λ1, λ2..., λS, obtain ordered set λ '={ λ in ascending orderj1, λj2..., λjS}；In gathering after sequence
Element meet { λj1≤λj2≤…≤λjS, wherein { j1, j2 ... .jS } be to (1,2 ..., S } rearrangement；λ ' is write as
Diagonal matrix form obtains Λ.
4. a kind of LTE-U clear channel assessment based on multi-slot syncretizing mechanism according to claim 1, its feature
It is：Described method of weighting is specially：By sampling matrix Y and the eigenvalue matrix obtaining through multi-slot signal transactingCarry out
Weighted gain merges, order：
Z (n)=ΛTY (n), according to formulaCalculate weighted gain combined value as GTS.
5. a kind of LTE-U clear channel assessment based on multi-slot syncretizing mechanism according to claim 1, its feature
It is：By T and according to desired false-alarm probability PFA, DESThe decision threshold γ calculating is compared, and makes conclusive judgement：Work as TMS-CCADuring more than or equal to γ 2, adjudicate as H1, represent that judgement PU signal exists；Conversely,
Adjudicate as H0, represent that judgement PU signal does not exist.
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