A method for random access to low-orbit satellite Internet of Things without authorization

Abstract

The present invention relates to the field of wireless communication technology, and specifically discloses a method for random access of low-orbit satellite Internet of Things without authorization. The method comprises the following steps: Step S01: the terminal generates a BPSK-modulated SC-IFDMA symbol, adds a cyclic prefix to the SC-IFDMA symbol, and generates a data signal; Step S02: the terminal selects multiple pilot sequences from a pilot sequence set to form a pilot signal, uses the pilot signal and the data signal to form a data packet, and sends the data packet to the satellite; Step S03: the satellite performs pilot detection on the received data packet, compares it with the detection threshold, identifies the pilot sequence selected by the active user, and removes the cyclic prefix from the received data packet to obtain a data packet with the cyclic prefix removed; Step S04: the satellite uses the received pilot signal and the detected pilot sequence set to perform parameter estimation on the active user, completes ML detection decoding of the active user data signal, and obtains a decoded signal.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a method for random access of a low-orbit satellite Internet of Things without authorization. Background Art

[0002] With the surge in the number of IoT users and the significant increase in latency, the authorization-based access protocol commonly used in ground systems will result in a large amount of signaling overhead and timing confusion, making it unsuitable for satellite communication scenarios. At the same time, unauthorized random access that does not require signal interaction between users and base stations has become an important direction for the development of the Internet of Things. In unauthorized access, the user sends a pilot signal to the access point, and then immediately sends its own data signal. Due to its simple process, unauthorized access effectively reduces access latency and signal overhead.

[0003] However, the conflict between the limited number of pilots and a large number of IoT devices often restricts access efficiency. In addition, if the pilot signal of the ground communication network is used, the transmission delay in satellite communication is too large, resulting in a significant increase in the length and number of pilot sequences, and at the same time causing the sequence to be highly sensitive to carrier frequency deviation. Therefore, it is necessary to design a new pilot sequence to meet the access requirements of low-orbit satellite IoT scenarios. Summary of the invention

[0004] In view of the above problems, the purpose of the present invention is to provide a method for unauthorized random access of low-orbit satellite Internet of Things. A scheme in which a user selects multiple short sequences to form a pilot signal is adopted. The pilot is composed of multiple short sequences, and the complexity of pilot detection is low. Moreover, since the types of permutations and combinations of multiple sequences are increased, the probability of pilot conflicts occurring when there are many active users in the Internet of Things scenario can be effectively reduced when the number of pilots is limited. A mode in which multiple satellite nodes are jointly used for parameter estimation and data decoding is adopted to achieve simultaneous access of multiple users, improve user access efficiency, and reduce the average user access delay. The method of alternating the estimation of two parameters at the same time can reduce the complexity of estimation.

[0005] The technical solution adopted by the present invention is: a method for random access of low-orbit satellite Internet of Things without authorization, comprising the following steps: a method for random access of low-orbit satellite Internet of Things without authorization, comprising the following steps:

[0006] Step S01: The terminal generates a BPSK-modulated SC-IFDMA symbol, adds a cyclic prefix to the SC-IFDMA symbol, and generates a data signal;

[0007] Step S02: the terminal selects a plurality of pilot sequences from a pilot sequence set to form a pilot signal, uses the pilot signal and the data signal to form a data packet, and sends the data packet to a satellite;

[0008] Step S03: the satellite performs pilot detection on the received data packet, compares it with the detection threshold, identifies the pilot sequence selected by the active user, and removes the cyclic prefix of the received data packet to obtain a data packet with the cyclic prefix removed;

[0009] Step S04: the satellite uses the received pilot signal and the detected pilot sequence set to perform parameter estimation on the active user, completes ML detection and decoding of the active user data signal, and obtains a decoded signal.

[0010] Preferably, the data signal in step S01 is represented as:

[0011] ;

[0012] ;

[0013] in, is the data signal, is the cyclic prefix length, Transform the time domain for the mapped signal, is the number of subcarriers.

[0014] Preferably, the data packet in step S02 is represented as:

[0015] ;

[0016] ;

[0017] in, For data packets, is the pilot signal, For data signal.

[0018] Preferably, the pilot signal in step S02 is represented as:

[0019] ;

[0020] in, is the pilot sequence after adding the cyclic prefix, is the pilot sequence.

[0021] Preferably, the satellite includes a plurality of satellites within communication range.

[0022] Preferably, the pilot detection method in step S03 is: performing correlation operation on the pilot signal in the received data packet and all pilot sequences, and the correlation result is expressed as:

[0023] , ;

[0024] ;

[0025] in, is the correlation result, is the starting search position in the pilot signal, is the maximum search position, is the pilot signal, is the set detection threshold.

[0026] Preferably, when the correlation result is greater than the detection threshold, the corresponding pilot sequence is a pilot sequence selected by the active user.

[0027] Preferably, the data packet from which the cyclic prefix is ​​removed in step S03 is represented as follows:

[0028] ;

[0029] in, is the phase shift matrix caused by CFO, is the channel parameter, is the phase shift parameter, is the transmission delay, is noise, and K represents the number of active users.

[0030] Preferably, the method for performing parameter estimation in step S04 includes: performing parameter estimation on multiple satellites within the communication range by using a linear minimum mean square error method and a Newton method alternately;

[0031] The parameters include channel parameters and phase parameters:

[0032] The linear minimum mean square error method is used to estimate channel parameters;

[0033] The Newton method is used to estimate the phase parameters.

[0034] Preferably, the decoded signal in step S04 is:

[0035] ;

[0036] ;

[0037] in, The estimated users The mth symbol of is the frequency domain phase shift parameter estimation matrix after demapping, is the frequency domain channel parameter estimation matrix after demapping, For all The satellite receives the mth frequency domain symbol.

[0038] Beneficial effects of the above technical solution:

[0039] The method for unauthorized access of low-orbit satellite Internet of Things provided by the present invention adopts a scheme in which a user selects multiple short sequences to form a pilot signal. The pilot is composed of multiple short sequences, and the complexity of pilot detection is low. Moreover, since the types of permutations and combinations of multiple sequences are increased, the probability of pilot conflicts occurring when there are many active users in the Internet of Things scenario can be effectively reduced when the number of pilots is limited.

[0040] The mode of using multiple satellite nodes to jointly perform parameter estimation and data decoding enables simultaneous access of multiple users, improves user access efficiency, and reduces the average user access delay. The method of alternately estimating two parameters can reduce the complexity of estimation. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A flow chart of a method for unauthorized access to a low-orbit satellite Internet of Things provided by one embodiment of the present invention;

[0042] Figure 2 A schematic diagram of a low-orbit satellite Internet of Things provided by an embodiment of the present invention;

[0043] Figure 3 A relationship diagram between the pilot collision probability and the number of pilots in a method for unlicensed access to low-orbit satellite Internet of Things provided by one embodiment of the present invention;

[0044] Figure 4 A graph showing the relationship between the pilot collision probability and the number of users of a method for unlicensed access to low-orbit satellite Internet of Things provided by one embodiment of the present invention;

[0045] Figure 5 A graph showing the relationship between the pilot collision probability and the number of pilots selected by the user in a method for unlicensed access to a low-orbit satellite Internet of Things provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0046] The following is a further detailed description of the implementation methods of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than an exhaustive list of all the embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict.

[0047] The terms "first", "second", etc. (if any) in the specification and claims are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way are interchangeable where appropriate so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products, or devices.

[0048] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0049] Embodiment 1

[0050] An embodiment of the present invention provides a method for random access of a low-orbit satellite Internet of Things without authorization, such as Figure 1 As shown, the following steps are included:

[0051] Step S01: The terminal generates a BPSK-modulated SC-IFDMA symbol, adds a cyclic prefix to the SC-IFDMA symbol, and generates a data signal.

[0052] Step S02: the terminal selects a plurality of pilot sequences from a pilot sequence set to form a pilot signal, uses the pilot signal and the data signal to form a data packet, and sends the data packet to a satellite.

[0053] The method for unauthorized access of low-orbit satellite Internet of Things provided by the present invention adopts a scheme in which a user selects multiple short sequences to form a pilot signal. The pilot is composed of multiple short sequences, and the complexity of pilot detection is low. Moreover, since the types of permutations and combinations of multiple sequences are increased, the probability of pilot conflicts occurring when there are many active users in the Internet of Things scenario can be effectively reduced when the number of pilots is limited.

[0054] Step S03: the satellite performs pilot detection on the received data packet, compares it with the detection threshold, identifies the pilot sequence selected by the active user, and removes the cyclic prefix of the received data packet to obtain a data packet with the cyclic prefix removed.

[0055] Step S04: the satellite uses the received pilot signal and the detected pilot sequence set to perform parameter estimation on the active user, completes ML detection and decoding of the active user data signal, and obtains a decoded signal.

[0056] The mode of using multiple satellite nodes to jointly perform parameter estimation and data decoding enables simultaneous access of multiple users, improves user access efficiency, and reduces the average user access delay. The method of alternately estimating two parameters can reduce the complexity of estimation.

[0057] Step 1: Data signal generation

[0058] like Figure 2 The figure shows a schematic diagram of the low-orbit satellite Internet of Things, where the terminal UE follows a Poisson distribution and is distributed in a circular area with a radius of R. Satellite nodes. A i is the i-th LEO satellite node, (i∈[1,] ); U j is the signal of the jth active user accessed by LEO.

[0059] Assume that the channel between the terminal and the satellite is a Rician channel, one frame has n time slots, and each terminal transmits a message in a randomly selected time slot.

[0060] The terminal uses BPSK modulated single carrier interleaved frequency division multiple access (SC-IFDMA) symbols to carry data. U j The signal is represented as , a total of L symbols. m SC-IFDMA symbols are represented as , M is the modulation data length of each symbol. s j ( m ) to perform a discrete Fourier transform (DFT) and then map it to N From the subcarriers we can get:

[0061] ;

[0062] ;

[0063] ;

[0064] .

[0065] in,S j ( m )for s j ( m )’s frequency domain signal, F M is the M-point DFT matrix, s j ( m ) for users U j No. m SC-IFDMA symbols, is the mapped signal, P is the mapping matrix with dimension N×M, F M(a,b) F M The element in the ath row and bth column, a is the row number and b is the column number. M The modulated data length of each symbol.

[0066] If P If the bit element is 1, it means The data on the subcarriers are mapped to the on the subcarrier.

[0067] Then By converting back to the time domain through the inverse DFT transform, we get:

[0068] ;

[0069] ;

[0070] ;

[0071] in, is the inverse DFT matrix of N points, is the element in the cth row and dth column, where c is the row number and d is the column number.

[0072] Finally, a cyclic prefix (CP) is added to obtain the transmitted data signal, which is expressed as:

[0073] ;

[0074] in, is the data signal, is the cyclic prefix length.

[0075] Step 2: Generate a pilot signal and combine it with the data signal to form a data packet

[0076] The ZC sequence with good periodic correlation characteristics and low peak-to-average power ratio is used as the pilot sequence. The value of the nth bit in the sequence is expressed as:

[0077] ;

[0078] in, is the root number, is the sequence length.

[0079] Due to the uncertainty of time, the duration of the sequence usually satisfies , is the maximum transmission delay difference of the ground terminal. And because the distance between the satellite and the ground is far, the propagation delay of the satellite communication system is larger than that of the ground communication system. The duration and length of the sequence need to be larger, and the pilot detection is more complicated. The pilot frequency deviation can reach half of the subcarrier spacing, and the subcarrier spacing is With sequence duration It is inversely proportional to the carrier frequency offset (CFO), and will decrease significantly with the increase of sequence length, resulting in a low tolerance of the sequence to carrier frequency offset (CFO). It is not feasible to simply apply the general preamble sequence to satellite communication scenarios. During the initial synchronization process, when the CFO is less than half of the subcarrier spacing, the preamble sequence is easily detected. Therefore, in order to eliminate the influence of CFO in advance, the subcarrier spacing is set to more than twice the CFO, that is, , is the maximum Doppler shift. Much smaller than the maximum propagation delay difference , the user's smooth access cannot be guaranteed.

[0080] The solution of the present invention is to allow each terminal to select multiple short ZC sequences to form its own pilot signal.

[0081] Active users from ZC sequence set Random selection P Add CP to The forward vector of transmission is obtained :

[0082] ;

[0083] Then, the pilot signal and the data signal form a data packet, which is represented as:

[0084] ;

[0085] Step 3: Identification of active user pilot signals

[0086] Satellite Node A i In time slot s Received Symbols, represented by:

[0087] ;

[0088] ;

[0089] ;

[0090] in, is the pilot signal, is the phase shift caused by CFO, is the channel parameter, is the phase shift parameter, is the transmission delay, For noise, N is the number of subcarriers, L cp is the cyclic prefix length.

[0091] By using the strong correlation of ZC sequence, the received pilot signal and The sequence set is correlated to detect the pilot signal selected by the active user:

[0092] ;

[0093] ;

[0094] in, is the starting search position in the pilot signal, is the maximum search position, is the pilot signal, is the set detection threshold.

[0095] when When is active, and the set of all active pilots is recorded as .

[0096] The CP can be removed by pilot detection, and the pilot signal received after the CP is removed can be used for parameter estimation.

[0097] After removing the CP, the signal received by the satellite is expressed as:

[0098] ;

[0099] Where K is the number of active users.

[0100] Convert the mth symbol received by the satellite after removing the CP to the frequency domain:

[0101] ;

[0102] in, is the frequency domain representation of the phase shift matrix caused by CFO, is the frequency domain representation of the channel parameter matrix, is the frequency domain representation of the data signal, is the frequency domain representation of the noise.

[0103] Will Demapping to M subcarriers yields:

[0104] ;

[0105] in, represents the demapped signal, is the frequency domain channel parameter matrix after demapping, is the frequency domain phase shift parameter matrix after demapping, is the noise after demapping. Same as the previous F N 、F M are the DFT matrices of N points and M points respectively, and P is the mapping matrix.

[0106] Step 4: ML detection decoding of active user data signals

[0107] Using the detected active pilot sequence set and the received pilot signal Estimated parameters and .

[0108] Assumptions and Remain unchanged within the same time slot, and Simplified to and .

[0109] Defining unknown parameters , represents the channel parameters of K active users, represents the phase shift parameter of K active users.

[0110] According to the maximum likelihood (ML) estimation principle, the estimated value Make the conditional probability The maximum, conditional probability is expressed as:

[0111] ;

[0112] in, is the noise variance, For the The estimated value, For users The pilot sequence.

[0113] Joint estimation of channel impulse response and When, due to by The impact of uncertainty is small. It can be assumed that Known, estimate first , get the estimated value Estimate later .

[0114] First, the linear minimum mean square error (LMMSE) is used to obtain , expressed as:

[0115] ;

[0116] in, for The autocorrelation matrix of is the least squares (LS) estimation result, It is the channel modulation type parameter.

[0117] Newton's method Make an estimate.

[0118] ;

[0119] in, is the estimation result of the linear minimum mean square error.

[0120] Assume that there are K users transmitting signals in the same time slot. In order to successfully decode these signals, all satellite nodes must perform parameter estimation and then convert the estimated parameters to the frequency domain for demapping:

[0121] ;

[0122] in, is the frequency domain phase shift parameter estimation matrix after demapping, is the frequency domain channel parameter estimation matrix after demapping, F N , M are the DFT matrices of N points and M points respectively, and P is the mapping matrix.

[0123] Multi-satellite joint detection can be approximately equivalent to the MIMO signal model, so the maximum relief estimation principle ML detection is used to decode the data packet.

[0124] The mth symbol received by all nodes is expressed as:

[0125] ;

[0126] The decoded signal is:

[0127] ;

[0128] in, The estimated users The mth symbol of .

[0129] Evaluation of unauthorized random access methods for low-orbit satellite Internet of Things

[0130] Assume that there is a L available pilots, from which each user selects m The sequence is combined into its own pilot signal. N When there are active users, the probability of pilot conflict among users is:

[0131] .

[0132] Figure 3 and Figure 4 The relationship between the pilot collision probability and the number of pilots, the number of pilot selections, and the number of users is shown. It can be seen that the more selectable pilots there are, the smaller the user's collision probability is, and the more users there are, the greater the user's collision probability will be. When the number of users and pilots is constant, each user can effectively reduce the pilot collision probability by selecting two pilots to form his or her own pilot signal, because there are more combinations when the user selects two pilots. At the same time, when the user selects a two-pilot solution to serve more users or has fewer selectable pilots, it can still have a lower collision probability than selecting a single pilot, which further proves the effectiveness of this strategy.

[0133] Figure 5 It shows the relationship between the number of pilots selected by the user and the collision probability when the total number of pilots is 100 and the number of users is 10. It can be seen that when the number of selected pilots increases from one to two, the pilot collision probability will be greatly reduced and has reached a very small value. Continuing to increase the number of selected pilots will bring about a smaller change. Therefore, considering the collision probability and computational complexity, the user's benefit of selecting two pilots is the best.

[0134] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A method for random access of low-orbit satellite Internet of Things without authorization, characterized in that: The steps include: Step S01: The terminal generates a BPSK-modulated SC-IFDMA symbol, adds a cyclic prefix to the SC-IFDMA symbol, and generates a data signal; Step S02: the terminal selects a plurality of pilot sequences from a pilot sequence set to form a pilot signal, uses the pilot signal and the data signal to form a data packet, and sends the data packet to a satellite; Step S03: the satellite performs pilot detection on the received data packet, compares it with the detection threshold, identifies the pilot sequence selected by the active user, and removes the cyclic prefix of the received data packet to obtain a data packet with the cyclic prefix removed; Step S04: the satellite uses the received pilot signal and the detected pilot sequence set to perform parameter estimation on the active user, completes ML detection and decoding of the active user data signal, and obtains a decoded signal; In step S02, each terminal randomly selects a plurality of pilot sequences from the pilot sequence set to form a pilot signal; The method for performing parameter estimation in step S04 includes: performing parameter estimation on multiple satellites within the communication range by using a linear minimum mean square error method and a Newton method alternately; The parameters include channel parameters and phase parameters: The linear minimum mean square error method is used to estimate channel parameters; The Newton method is used to estimate the phase parameters.

2. The method for random access to low-orbit satellite Internet of Things without authorization according to claim 1, characterized in that: The data signal in step S01 is represented as: Φ j (m)=[x j (m,N-L CP ),x j (m,N-L CP +1),...,x j (m,N-1),x j (m,0),x j (m,1),…,x j (m,N-1)] T ; m=0,1,...,L; Among them, Φ j (m) is the data signal, L CP is the cyclic prefix length, x j is the time domain of the signal transformation after mapping, and N is the number of subcarriers.

3. The method for random access to low-orbit satellite Internet of Things without authorization according to claim 1, characterized in that: The data packet in step S02 is represented as: m=0,1,...,L; in, For data packets, is the pilot signal, Φ j (m) is the data signal.

4. The method for random access to low-orbit satellite Internet of Things without authorization according to claim 1, characterized in that: The pilot signal in step S02 is expressed as: c p =[c v (N-L CP ),c v (N-L CP +1),…,c v (N-1),c v (0),c v (1),…,c v (N-1)] T ; Among them, c p is the pilot sequence after adding the cyclic prefix, c v is the pilot sequence.

5. The method for random access to low-orbit satellite Internet of Things without authorization according to claim 1, characterized in that: The satellites include a plurality of satellites within a communication range.

6. The method for random access to low-orbit satellite Internet of Things without authorization according to claim 1, characterized in that: The pilot detection method in step S03 is: performing correlation operation on the pilot signal in the received data packet and all pilot sequences, and the correlation result is expressed as: Among them, I v,s,i,p is the correlation result, τ is the starting search position in the pilot signal, τ s is the maximum search position, is the pilot signal, and γ is the set detection threshold.

7. The method for random access to low-orbit satellite Internet of Things without authorization according to claim 6, characterized in that: When the correlation result is greater than the detection threshold, the corresponding pilot sequence is the pilot sequence selected by the active user.

8. The method for random access to low-orbit satellite Internet of Things without authorization according to claim 1, characterized in that: The data packet with the cyclic prefix removed in step S03 is represented as: in, is the phase shift matrix caused by CFO, is the channel parameter, is the phase shift parameter, τ j, i is the transmission delay, is noise, and K represents the number of active users.

9. The method for random access to low-orbit satellite Internet of Things without authorization according to claim 1, characterized in that: The decoded signal in step S04 is: in, are estimated users u1,u2,...,u K The mth symbol of is the frequency domain phase shift parameter estimation matrix after demapping, is the frequency domain channel parameter estimation matrix after demapping, Y m For all N SA The satellite receives the mth frequency domain symbol.

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