CN108768903A - Low-orbit satellite random access system multi-user test method based on CRDSA class agreements - Google Patents
Low-orbit satellite random access system multi-user test method based on CRDSA class agreements Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
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- H04W74/0833—Random access procedures, e.g. with 4-step access
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- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
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Abstract
The invention belongs to technical field of satellite communication, a kind of low-orbit satellite random access system multi-user test method based on CRDSA class agreements is disclosed, multiple accessing users are according to CRDSA classes agreement to satellite launch user grouping；Satellite reception end according to multiple superpositions on each time slot in orderly one frame of processing of CRDSA class agreements user grouping；Satellite reception end is in K superposition user grouping on handling some time slot, using the channel of each user on basis expansion model modeling time slot；The base system number of each user is solved by maximum likelihood method joint；Each subscriber channel is fitted using the base system number of solution；All interference user groupings are reconstructed using the preceding K-1 subscriber channel for having detected the preceding K-1 user data of decoding when handling other time slots and having fitted and carry out interference elimination；Residual signal after detection decoding interference elimination；It is iterated channel estimation using decoding bit and interference is eliminated.Precision of channel estimation of the present invention is high, and it is accurate that interference is eliminated, and Packet Error Ratio is low.
Description
Technical field
The invention belongs to technical field of satellite communication more particularly to a kind of low-orbit satellite based on CRDSA class agreements with
Machine access system multi-user test method.
Background technology
Currently, the prior art commonly used in the trade is such：Internet of Things has been increasingly becoming domestic and international emphasis and has ground since proposition
One of the problem of studying carefully.Internet of Things is widely used in environmental monitoring, hazard prediction and oil-gas exploration.In this kind of scene, object
Networked devices are typically distributed on wide or remote region, and ground network is difficult to provide number to a wide range of in this way or specific region
According to acquisition and transmission service, and satellite network can be fine make up defect of the ground network in covering power.In satellite object
It, can be to avoid excessively high access delay and raising handling capacity using accidental access method in networking.In traditional random access side
It is thus caused if the collision probability of Aloha and Slot-aloha, user grouping are constantly promoted as number of users increases in method
Re-transmission will cause the data transmission of whole system larger delay occur.In satellite network, in order to avoid due to frequently weighing
Big access delay caused by biography, some new accidental access methods are suggested in succession, such as CRDSA (contention resolved diversity time slots
Aloha), IRSA (irregularly repeating Slot-aloha) and MuSCA (multi-slot encodes Aloha).CRDSA class accidental access methods
Basic principle be that each user sends the packet of multiple repetitions, receiver detects the grouping not collided one by one, and
All copies for having detected grouping are further eliminated, to achieve the purpose that interference is eliminated, improve the detection probability of grouping.Dry
During disturbing elimination, in order to accurately eliminate decoding grouping, receiver needs effective channel estimation to obtain accurate letter
Channel state information.Otherwise, the channel state information of mistake can cause decoding grouping that cannot accurately eliminate, and remainder error is superimposed upon not
In decoding grouping, to influence the performance of system interference elimination, interblock interference probability is reduced.Currently, about new in satellite network
Multiuser Detection under accidental access method has part document and has carried out research.Based on CRDSA class random access protocols, carry
A kind of channel estimation method being based on EM (greatest hope) algorithm is gone out, and interblock interference decoding is realized by interfering to eliminate.Needle
To Deadlock existing for CRDSA class random access protocols, by located in connection packet positions, then correction parameter is utilized to merge
It is grouped and decodes.However, the prior art all only considered simple channel model.It is passed in view of LEO (low orbit) satellite has
Sowing time prolongs the short feature low with path loss, and has been widely used for the little satellite communication field of portfolio.Therefore, LEO
Satellite has the inherent advantage being combined with low rate, low time delay, the Internet of Things that extensively covers.But since LEO satellite near-earth flies
Capable angular speed is very big, and the maximum doppler frequency that high-speed mobile is brought can lead to the quick of channel up to tens KHz up to a hundred
Time-varying problem, and the quasi-static channel model in above-mentioned document can not describe such channel.Make under LEO satellite scene
The Packet Error Ratio of system can be caused to be promoted in aforementioned manners.
In conclusion problem of the existing technology is：Since the angular speed of LEO satellite near-earth flight is very big, high speed is moved
The dynamic maximum doppler frequency brought leads to the quick time-varying problem of channel up to tens KHz up to a hundred.
Solve the difficulty and meaning of above-mentioned technical problem：It is quick that the maximum Doppler frequency shift characteristic of LEO satellite results in channel
Time-varying.In such a scenario, the Multiuser Detection based on CRDSA class random access protocols needs to carry out the connection of multi-user on time slot
Close channel estimation.Estimate in this difficult accurate channel of acquisition of varying Channels estimation there are under multi-user interference and noise situations
Count precision.
The LEO satellite high-precision channel estimation based on CRDSA class random access protocols is designed, to accurately eliminate interference
And successfully detect user.Realize the physical layer solution under the LEO satellite of high-throughput random access protocol and matching Internet of Things demand
Certainly scheme.
Invention content
In view of the problems of the existing technology, the present invention provides a kind of low-orbit satellite based on CRDSA class agreements with
Machine access system multi-user test method.
The invention is realized in this way a kind of low-orbit satellite random access system multi-user based on CRDSA class agreements
Detection method, the low-orbit satellite random access system multi-user test method based on CRDSA class agreements include：It is multiple to connect
Access customer is according to CRDSA classes agreement to satellite launch user grouping；Satellite reception end is according to the orderly processing one of CRDSA class agreements
In frame on each time slot multiple superpositions user grouping；It is adopted in K superposition user grouping on handling some time slot at satellite reception end
With the channel of each user on basis expansion model modeling time slot；The base system number of each user is solved by maximum likelihood method joint；It utilizes
The base system number of solution fits each subscriber channel；Using handle other time slots when detected decoding preceding K-1 user data and
The preceding K-1 subscriber channel fitted reconstructs all interference user groupings and carries out interference elimination；After detection decoding interference is eliminated
Residual signal；It is iterated channel estimation using decoding bit and interference is eliminated.
Further, the low-orbit satellite random access system multi-user test method based on CRDSA class agreements includes
Following steps：
Step 1, multiple accessing users are according to CRDSA classes agreement to satellite launch user grouping；
Step 2, satellite reception end according to multiple superpositions on each time slot in orderly one frame of processing of CRDSA class agreements use
Family is grouped；
The time slot is skipped at step 3, satellite reception end, when the time slot is the last one time slot in a frame, and is this time traversed
In, satellite reception end does not process any one time slot, and satellite reception end stops detection, and otherwise, satellite reception end jumps to
First time slot in one frame executes satellite reception end and receives the signal that user is emitted as unit of frame, and it is all to cache present frame
Signal on time slot, when the time slot is not the last one time slot in a frame, satellite reception end continues to detect next time slot, when some
On time slot there is no do not detect on user grouping or some time slot there are it is multiple do not detect user grouping when, execute step 3,
When not detecting user grouping there are one on some time slot, step 4 is executed；
The time slot for not detecting user grouping there are one is done at channel estimation and interference elimination at step 4, satellite reception end
Reason；
Step 5, satellite reception end utilize the residual signal after the k-th user time varying channel and interference elimination fitted
Detection decodes out k-th bits of user data；
Step 6, satellite reception end reconstruct k-th by coded modulation using the k-th bits of user data decoded out and use
User data symbol, and combine the leading of preceding K-1 user data and K user for having detected decoding, pilot tone, after lead and be iterated
Channel estimation and interference are eliminated, and after meeting iterations, execute step 3.
Further, the step 1 specifically includes：
(1) all customer data bit passes through the corresponding user data symbol of coded modulation generation respectively, and respectively from this
One group of ZC sequence is randomly selected in ground ZC arrangement sets, as leading, pilot tone, after lead be inserted into user data symbol in, constitute use
Family is grouped；
(2) all users randomly select two or more slot transmission user groupings in anchor-frame.
Further, the local ZC arrangement sets in described (2) are generated by ZC root sequence cyclic shifts, ZC root sequence expression formulas
For：
N=0,1 ... NZC-1(NZCIt is odd number)；
N=0,1 ... NZC-1(NZCIt is even number)；
Wherein NZCIt is the length of sequence, μ and NZCRelatively prime, q is arbitrary integer；
All users in (2) randomly select two or more slot transmission user groupings in anchor-frame, according to
The difference for taking agreement, in CRDSA agreements, user randomly selects two copies of two slot transmissions grouping, is assisted in IRSA
In view, user randomly selects multiple copies of multiple slot transmission groupings.
Further, the step 2 specifically includes：
(1) satellite reception end receives the signal that user is emitted as unit of frame, and caches the letter on all time slots of present frame
Number；
(2) each time slot in one frame of satellite reception end searching loop, using local ZC arrangement sets respectively on time slot
It is related to receive training signal, detects user grouping number on output time slot；
(3) when there is no do not detect not detecting user point there are multiple on user grouping or some time slot on some time slot
When group, step 3 is executed, when not detecting user grouping there are one on some time slot, executes step 4.
Further, related to the reception training signal on time slot respectively using local ZC arrangement sets in described (2), detection
User grouping number on output time slot, satellite reception end set corresponding thresholding, when the reception in local ZC sequences and time slot is trained
When the correlation of signal is more than the thresholding of setting, then it is assumed that the corresponding user grouping of local ZC sequences is launched.
Further, the step 4 specifically includes：
(1) satellite reception end models the time varying channel of K user on time slot using basis expansion model；
(2) satellite reception end according to K user leading, pilot tone, after lead and base system number, basic function and receive signal between
Relationship builds maximum likelihood function, and combines solution and obtain the base system number estimated value of each user
(3) satellite reception end utilizes the base system number estimated value of each userAnd basic function μqFit each user's time-varying letter
Road；
(4) satellite reception end is using having detected the preceding K-1 user data of decoding when handling other time slots and fitted
Preceding K-1 user time varying channel reconstructs all interference user groupings, and interference is eliminated in receiving signal.
Further, believed using the time-varying of K user on basis expansion model modeling time slot at the satellite reception end in described (1)
Road, expression formula are：
Wherein bqkFor q-th of base system number of k-th of user, Q is basic function number, and T is channel coefficients length, μq=[μq
(0) … μq(T-1)]TIndicate q-th of basic function vector；
Structure maximum likelihood function in (2), and combine solution and obtain the base system number estimated value of each userIt calculates
Formula is：
WhereinIndicate the training block vector of k-th of user transmitting, μtqIndicate the basic function vector engraved when training block, Ut
=[μt1…μtQ], Bk=[b1k…bQk]T, ForRepeat Q
It is secondary,Indicate Hadamard products, YtIndicate that block vector is trained in the superposition received；
Satellite reception end in (3) utilizes the base system number estimated value of each userAnd basic function μqFit each user
Time varying channel, expression formula are：
Satellite reception end in (4) using the preceding K-1 user data for having detected decoding when handling other time slots and
The preceding K-1 user time varying channel fitted reconstructs all interference user groupings, and interference, expression formula are eliminated in receiving signal
For：
WhereinIndicate that the residual signal at n moment, Y (n) indicate the reception signal at n moment, sk(n) k-th of use is indicated
Transmitting of the family at the n moment is grouped.
Another object of the present invention is to provide the low-orbit satellites based on CRDSA class agreements described in a kind of application to connect at random
Enter the satellite communication system of system multi-user detection method.
In conclusion advantages of the present invention and good effect are：Multi-user's letter is modeled using BEM (basis expansion model)
Road, and combine the base system number for solving multi-user by ML (maximum likelihood) algorithm, the time-varying of each user is fitted by base system number
Channel finally reconstructs all interference user groupings and carries out interference elimination, to interfering the residual signal after eliminating into row decoding；
Block is trained using decoding bit and each user and has detected user data and repeats above-mentioned channel estimation and interference cancellation process, with this
Improve the detection probability of grouping.The present invention is since satellite reception end carries out based on channel estimation current system and interferes elimination
When Multiuser Detection, multi-user's time varying channel is modeled using basis expansion model, basis expansion model is made full use of to model time varying channel
Validity, basis expansion model can accurately model multi-user in unknown in entire user grouping with a small amount of unknown parameter
Become channel coefficients, compared with prior art, under LEO satellite scene, the present invention can more accurately estimate multi-user's time-varying letter
Road is eliminated to carry out more accurately interference, significantly reduces system Packet Error Ratio and lifting system handling capacity.
Description of the drawings
Fig. 1 is the low-orbit satellite random access system multi-user provided in an embodiment of the present invention based on CRDSA class agreements
Detection method flow chart.
Fig. 2 is applicable CRDSA random access schematic diagrames provided in an embodiment of the present invention.
Fig. 3 is user grouping structure chart provided in an embodiment of the present invention.
Fig. 4 is multi-user system illustraton of model provided in an embodiment of the present invention.
Fig. 5 is provided in an embodiment of the present invention and the prior art Packet Error Ratio performance simulation comparison diagram.
Fig. 6 is provided in an embodiment of the present invention and the prior art channel estimation mean square error performance simulation comparison diagram.
Fig. 7 is provided in an embodiment of the present invention and the prior art throughput performance simulation comparison figure.
Specific implementation mode
In order to make the purpose , technical scheme and advantage of the present invention be clearer, with reference to embodiments, to the present invention
It is further elaborated.It should be appreciated that the specific embodiments described herein are merely illustrative of the present invention, it is not used to
Limit the present invention.
The multiuser detection algorithm that the present invention carries out channel estimation to low-orbit satellite random access system and interference is eliminated,
It can be used for the random access system of satellite Internet of Things, it is intended to solve the system existing in the prior art under LEO satellite scene and miss
The higher technical problem of packet rate.
As shown in Figure 1, the low-orbit satellite random access system provided in an embodiment of the present invention based on CRDSA class agreements is more
Detection method includes the following steps by user：
S101：Multiple accessing users are according to CRDSA classes agreement to satellite launch user grouping；Satellite reception end according to
In orderly one frame of processing of CRDSA class agreements on each time slot multiple superpositions user grouping；
S102：Satellite reception end is modeled in the user grouping of K superposition on handling some time slot using basis expansion model
The channel of each user on time slot；The base system number of each user is solved by maximum likelihood method joint；
S103：Each subscriber channel is fitted using the base system number of solution；Decoding has been detected using when handling other time slots
Preceding K-1 user data and the preceding K-1 subscriber channel fitted reconstruct all interference user groupings and carry out interference elimination；
S104：Residual signal after detection decoding interference elimination；It is iterated channel estimation and interference using decoding bit
It eliminates.
The application principle of the present invention is further described below in conjunction with the accompanying drawings.
As shown in Fig. 2, user 1, user 2 and user 3 send same grouping on two different time-gaps in a frame respectively
Two copies.There was only some copy 1b that user 1 is grouped on time slot 3, it is assumed that receiver detects grouping 1b and decoding success first.
Then it reconstructs the grouping 1a on output time slot 1 using the decoding result of grouping 1b and carries out interference elimination, the then grouping on time slot 1
2a is grouped as collisionless, and receiver detects grouping 2a and decoding success again.Consider the LEO with tens KHz Doppler frequency shifts
Satellite channel, channel parameter difference of each user on different time-gap are apparent.Therefore, receiver needs accurately to estimate each use
Channel parameter of the family on each time slot.Receiver needs first accurately estimate channel parameter of the user 1 on time slot 3,
Then successfully detect and decode grouping 1b.And wanting the grouping 1a on accurately reconstruct output time slot 1, decoding success grouping 1b is the
One step additionally needs accurately to estimate the channel parameter of user 1 on timeslot 1.Assuming that when receiver accurately reconstructs
Grouping 1a in gap 1 simultaneously carries out interference elimination, and receiver then needs that grouping 2a is detected and decoded using accurate channel parameter,
So far user 1 and user 2 are grouped decoding success.It can be seen that, it is desirable to decoding success goes out grouping, and receiver must improve channel as far as possible
The precision of estimation.Otherwise, the channel estimation of mistake can cause to introduce larger residual interference when reconstruct interference grouping, to deteriorate
Interblock interference performance.In order to fully show the present invention, in conjunction with existing literature, the present embodiment uses CRDSA random access protocols, ginseng
Examine ITU-RM.1225 Satellite channel models, Rice factor 7dB, Doppler frequency shift 35KHz.
As shown in figure 3, user grouping structure uses single carrier, be inserted into respectively before and after packet configuration it is leading and after lead, be grouped
Pilot tone is uniformly inserted into structured data.The leading of the present embodiment, pilot tone, after lead using length be respectively 40,12,12 ZC sequences
Row, pilot tone number are 7.
As shown in figure 4, more in the low-orbit satellite random access system provided in an embodiment of the present invention based on CRDSA agreements
User's detection algorithm includes the following steps：
The multiple accessing users of step 1), to satellite launch user grouping, realize that step is according to CRDSA agreements：
Step 1a) all customer data bit passes through coded modulation and generates corresponding user data symbol respectively, and distinguishes
One group of ZC sequence is randomly selected from local ZC arrangement sets, as leading, pilot tone, after lead be inserted into user data symbol in, structure
At user grouping；
Wherein, the Turbo codings in the present embodiment using 1/2 and QPSK modulation, user data symbol length are 456.
Step 1b) all users randomly select two slot transmission user groupings in anchor-frame；
Wherein, in the present embodiment in a frame include 100 time slots.
Step 2) satellite reception end is divided according to the user of multiple superpositions on each time slot in orderly one frame of processing of CRDSA agreements
Group realizes that step is:
Step 2a) satellite reception end receives the signal that user is emitted as unit of frame, and caches on all time slots of present frame
Signal；
Step 2b) each time slot in frame of satellite reception end searching loop one, using local ZC arrangement sets respectively with time slot
On reception training signal it is related, detect user grouping number on output time slot；
Step 2c) when there is no do not detect not detect use there are multiple on user grouping or some time slot on some time slot
When family is grouped, step (3) is executed, when not detecting user grouping there are one on some time slot, executes step (4)；
The time slot is skipped at step 3) satellite reception end, when the time slot is the last one time slot in a frame, and is this time traversed
In, satellite reception end does not process any one time slot, and satellite reception end stops detection, and otherwise, satellite reception end jumps to
First time slot in one frame executes step (2b), and when the time slot is not the last one time slot in a frame, satellite reception end continues to examine
Next time slot is surveyed, step (2b) is executed；
The time slot for not detecting user grouping there are one is done at channel estimation and interference elimination at step 4) satellite reception end
Reason realizes that step is：
Step 4a) using the time varying channel of K user on basis expansion model modeling time slot, expression formula is at satellite reception end：
Wherein, basis expansion model uses DPS-BEM (discrete ellipsoid basis expansion model) in the present embodiment, and the value of Q is 11,
The value of T is 592；
Step 4b) satellite reception end according to K user leading, pilot tone, after lead and base system number, basic function with receive signal it
Between relationship, build maximum likelihood function, and combine solution obtain the base system number estimated value of each userCalculation formula is：
Step 4c) satellite reception end utilize each user base system number estimated valueAnd basic function μqFit each user's time-varying
Channel, expression formula are：
Step 4d) satellite reception end utilizes the when of handling other time slots to detect preceding K-1 user data and the fitting of decoding
The preceding K-1 user time varying channel gone out reconstructs all interference user groupings, and interference is eliminated in receiving signal, and expression formula is：
Residual signal after step 5) satellite reception end is eliminated using the k-th user time varying channel and interference fitted is examined
Survey decodes out k-th bits of user data；
Step 6) satellite reception end reconstructs k-th by coded modulation using the k-th bits of user data decoded out and uses
User data symbol, and combine the leading of preceding K-1 user data and K user for having detected decoding, pilot tone, after lead and be iterated
Channel estimation and interference are eliminated, and after meeting certain iterations, execute step (3)；
Wherein, iterations are twice in the present embodiment.
The application effect of the present invention is explained in detail with reference to emulation.
1, simulated conditions：
The system that the present invention is applicable in is satellite Internet of Things random access system, CRDSA random access protocols is based on, in emulation
Using ITU-R M.1225 Satellite channel models, Rice factor 7dB, user use code check for 1/2 Turbo code and QPSK
Modulation.Be grouped leading, pilot tone, after to lead length be respectively 40,12,12,7 pieces are uniformly inserted into the data comprising 456 symbols
Pilot tone, basis expansion model use DPS-BEM.Simulation software environment is Intel (R) Core (TM) i7-4790CPU@3.60GHz,
MATLAB R2015b under Windows 764bit operating systems.
The present invention come the performance of evaluation system multi-user test method, is detected in emulation translate every time using Packet Error Ratio (PER)
Code k-th user grouping, it is assumed that simulation times N, successfully detection decoding k-th user grouping number is M, then Packet Error Ratio is
The present invention is using channel estimation mean square error (MSE) come the performance of evaluation system channel estimation methods, it is assumed that emulation
Number is N, and n moment subscriber channel coefficient actual values and estimated value are respectively h in ith emulationi(n) andThen channel is estimated
Counting mean square error is
2, analysis of simulation result：
As shown in figure 5, abscissa expression is signal-to-noise ratio, what ordinate indicated is Packet Error Ratio.It can be seen from the figure that
Under the same terms, algorithm is significantly better than that algorithm in the prior art in the present invention.Also, either algorithm is still existing in the present invention
Have algorithm in technology, using data after decoding as the iterative algorithm of pilot tone both with respect to using only training block noniterative algorithm
It has a distinct increment.As number of users increases, algorithm performance slightly decreases in the present invention, and algorithm performance declines in the prior art
Obviously, algorithm can more tolerate multi-user in the present invention.As signal-to-noise ratio increases, algorithm performance is promoted more rapid in the present invention.
Algorithm can preferably work in the multi-user scene with high s/n ratio in the present invention.
As shown in fig. 6, abscissa expression is signal-to-noise ratio, what ordinate indicated is channel estimation mean square error.Fig. 6 gets the bid
The Cramér-Rao lower bound that initial channel estimation is carried out using training block is remembered.It can be seen from the figure that number of users do not influence two kinds it is non-
The channel estimation mean square error performance of iterative algorithm, and in the present invention algorithm compared with the prior art in algorithm have significantly it is excellent
Gesture.
As shown in fig. 7, abscissa expression is normalized load, what ordinate indicated is handling capacity.Handling capacity is defined as
The ratio between decoding success number of users and timeslot number, normalized load is defined as the ratio between number of users and timeslot number.Signal-to-noise ratio is in Fig. 7
10dB, it can be seen from the figure that under the same conditions, algorithm is superior to algorithm in the prior art in the present invention.Since CRDSA is assisted
The limitation of theoretical throughput is discussed, the performance difference between the present invention and in the prior art algorithm is more bright in non-iterative
It is aobvious.
The foregoing is merely illustrative of the preferred embodiments of the present invention, is not intended to limit the invention, all essences in the present invention
All any modification, equivalent and improvement etc., should all be included in the protection scope of the present invention made by within refreshing and principle.
Claims (9)
1. a kind of low-orbit satellite random access system multi-user test method based on CRDSA class agreements, which is characterized in that institute
Stating the low-orbit satellite random access system multi-user test method based on CRDSA class agreements includes：Multiple accessing users according to
CRDSA classes agreement is to satellite launch user grouping；Satellite reception end is according to each time slot in orderly one frame of processing of CRDSA class agreements
The user grouping of upper multiple superpositions；Satellite reception end is in K superposition user grouping on handling some time slot, using base expanded mode
Type models the channel of each user on time slot；The base system number of each user is solved by maximum likelihood method joint；Utilize the base system of solution
Number fits each subscriber channel；Before having detected the preceding K-1 user data of decoding when handling other time slots and having fitted
K-1 subscriber channel reconstructs all interference user groupings and carries out interference elimination；Residual signal after detection decoding interference elimination；
It is iterated channel estimation using decoding bit and interference is eliminated.
2. the low-orbit satellite random access system multi-user test method described in claim 1 based on CRDSA class agreements,
It is characterized in that, the low-orbit satellite random access system multi-user test method based on CRDSA class agreements includes following step
Suddenly：
Step 1, multiple accessing users are according to CRDSA classes agreement to satellite launch user grouping；
Step 2, satellite reception end are divided according to the user of multiple superpositions on each time slot in orderly one frame of processing of CRDSA class agreements
Group；
The time slot is skipped at step 3, satellite reception end, in the time slot is the last one time slot in a frame, and this is traversed,
Satellite reception end does not process any one time slot, and satellite reception end stops detection, and otherwise, satellite reception end jumps to a frame
In first time slot, execute satellite reception end and receive the signal that user is emitted as unit of frame, and cache all time slots of present frame
On signal, when the time slot is not the last one time slot in a frame, satellite reception end continues to detect next time slot, when some time slot
It is upper there is no do not detect on user grouping or some time slot there are it is multiple do not detect user grouping when, step 3 is executed, when certain
When not detecting user grouping there are one on a time slot, step 4 is executed；
Channel estimation and interference elimination treatment are done in step 4, satellite reception end to the time slot for not detecting user grouping there are one；
Step 5, the residual signal after satellite reception end is eliminated using the k-th user time varying channel and interference fitted detect
Decode out k-th bits of user data；
Step 6, satellite reception end reconstruct k-th number of users using the k-th bits of user data decoded out by coded modulation
According to symbol, and combine the preceding K-1 user data for having detected decoding and the leading of K user, pilot tone, after lead and be iterated channel
Estimation and interference are eliminated, and after meeting iterations, execute step 3.
3. the low-orbit satellite random access system multi-user test method based on CRDSA class agreements described in claim 2,
It is characterized in that, the step 1 specifically includes：
(1) all customer data bit passes through the corresponding user data symbol of coded modulation generation respectively, and respectively from local ZC
One group of ZC sequence is randomly selected in arrangement set, as leading, pilot tone, after lead and be inserted into user data symbol, constitute user point
Group；
(2) all users randomly select two or more slot transmission user groupings in anchor-frame.
4. the low-orbit satellite random access system multi-user test method based on CRDSA class agreements described in claim 3,
It is characterized in that, the local ZC arrangement sets in (2) are generated by ZC root sequence cyclic shifts, and ZC root sequence expression formulas are：
Wherein NZCIt is the length of sequence, μ and NZCRelatively prime, q is arbitrary integer；
All users in (2) randomly select two or more slot transmission user groupings in anchor-frame, according to taking
The difference of agreement, in CRDSA agreements, user randomly selects two copies of two slot transmissions grouping, in IRSA agreements,
User randomly selects multiple copies of multiple slot transmission groupings.
5. the low-orbit satellite random access system multi-user test method based on CRDSA class agreements described in claim 2,
It is characterized in that, the step 2 specifically includes：
(1) satellite reception end receives the signal that user is emitted as unit of frame, and caches the signal on all time slots of present frame；
(2) each time slot in one frame of satellite reception end searching loop, using local ZC arrangement sets respectively with the reception on time slot
Training signal is related, detects user grouping number on output time slot；
(3) when there is no do not detect not detect user grouping there are multiple on user grouping or some time slot on some time slot
When, step 3 is executed, when not detecting user grouping there are one on some time slot, executes step 4.
6. the low-orbit satellite random access system multi-user test method based on CRDSA class agreements described in claim 5,
It is characterized in that, it is related to the reception training signal on time slot respectively using local ZC arrangement sets in (2), detect output time slot
Upper user grouping number, satellite reception end set corresponding thresholding, when the reception training signal in local ZC sequences and time slot
When correlation is more than the thresholding of setting, then it is assumed that the corresponding user grouping of local ZC sequences is launched.
7. the low-orbit satellite random access system multi-user test method based on CRDSA class agreements described in claim 2,
It is characterized in that, the step 4 specifically includes：
(1) satellite reception end models the time varying channel of K user on time slot using basis expansion model；
(2) satellite reception end according to K user leading, pilot tone, after lead and base system number, basic function and receive signal between pass
System builds maximum likelihood function, and combines solution and obtain the base system number estimated value of each user
(3) satellite reception end utilizes the base system number estimated value of each userAnd basic function μqFit each user's time varying channel；
(4) satellite reception end utilizes the preceding K-1 for having detected the preceding K-1 user data of decoding when handling other time slots and having fitted
A user's time varying channel reconstructs all interference user groupings, and interference is eliminated in receiving signal.
8. the low-orbit satellite random access system multi-user test method based on CRDSA class agreements described in claim 7,
It is characterized in that, the satellite reception end in (1) is using the time varying channel of K user on basis expansion model modeling time slot, expression
Formula is：
Wherein bqkFor q-th of base system number of k-th of user, Q is basic function number, and T is channel coefficients length, μq=[μq(0) …
μq(T-1)]TIndicate q-th of basic function vector；
Structure maximum likelihood function in (2), and combine solution and obtain the base system number estimated value of each userCalculation formula
For：
WhereinIndicate the training block vector of k-th of user transmitting, μtqIndicate the basic function vector engraved when training block, Ut=
[μt1 … μtQ], Bk=[b1k … bQk]T, ForRepeat Q
It is secondary,Indicate Hadamard products, YtIndicate that block vector is trained in the superposition received；
Satellite reception end in (3) utilizes the base system number estimated value of each userAnd basic function μqFit each user's time-varying
Channel, expression formula are：
Satellite reception end in (4) utilizes preceding K-1 user data and the fitting that decoding has been detected when handling other time slots
The preceding K-1 user time varying channel gone out reconstructs all interference user groupings, and interference is eliminated in receiving signal, and expression formula is：
WhereinIndicate that the residual signal at n moment, Y (n) indicate the reception signal at n moment, sk(n) indicate k-th of user in n
The transmitting at moment is grouped.
9. a kind of low-orbit satellite random access system using based on CRDSA class agreements described in claim 1~8 any one
The satellite communication system of multi-user test method.
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