CDMA-based Unauthorized Diversity Competitive Random Access Method

Abstract

CDMA-based license-free diversity competition random access method, comprising the following steps; S1: constructing a large-scale user CDMA uplink access scenario; S2: in the access scenario, each user randomly selects two spreading sequences from the orthogonal spreading codebook provided by the system for spreading communication, and then records the selected spreading sequences in the data frame sent by the user; S3: after the user's transmission is successful and can be correctly decoded, find the two spreading sequences it has selected, and then subtract the output of this user corresponding to the two spreading sequences from the information received at the base station receiver to eliminate the conflict of this user for other users; S4: continue to decode the information of the remaining users from the remaining output at the receiver; S5: when any user's information cannot be decoded in a certain iteration, the iteration ends. The present invention adopts the method that active users randomly select two orthogonal spreading sequences for access, and the users transmit their own data in diversity on the two orthogonal sequences, greatly expanding the capacity of the system.

Description

Technical Field

[0001] The present invention belongs to the field of communication technologies, and particularly relates to a grant-free diversity competition random access method based on CDMA. Background Art

[0002] Currently, most cellular Internet of Things devices are connected to an access point (AP) or a base station (BS) through an authorized connection method, and their wireless devices need to obtain authorization from the access point through a handshake and allocate resources to achieve access. This is because from 1G to 4G, human-dominated communication has relatively few devices, long duration, and large data volume, and authorized access has advantages in implementation. However, with the development of society, wireless communication has started to be mainly device- or machine-based, the number of devices has increased rapidly, and the service traffic is small. This makes the authorized access method have many drawbacks. Therefore, the grant-free uplink access (GFA) method has become a key research issue at present.

[0003] Based on the above problems, traditional grant-free schemes based on orthogonal multiple access have begun to be proposed to reduce signaling interaction during access, reduce access latency, and improve access efficiency. Among them, the direct spread spectrum code division multiple access (DS-CDMA) communication system has the advantages of high system capacity, strong anti-interference ability, and good confidentiality because it uses an orthogonal spreading codebook. However, during traditional CDMA uplink access, the user and the base station will first go through a four-step handshake process for access, and the user sends its own data according to the scheduling of the base station. There are many signaling interaction processes during this period, which increases the access latency. Moreover, when the data packet is small, the signaling occupies most of the resources; during large-scale user access, the authorized uplink access process will cause the access latency to increase and the transmission efficiency to decrease due to more signaling interaction.

[0004] Moreover, the current grant-free access process generally needs to allocate a unique sequence to all users for user detection at the base station end, which will cause great limitations on the user scale due to the limited number of orthogonal sequences in CDMA. Summary of the Invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a grant-free diversity competition random access method based on CDMA, which uses the method of randomly selecting two orthogonal spreading sequences by active users for access, and the users transmit their own data in a diversity manner on the two orthogonal spreading sequences, greatly expanding the system capacity.

[0006] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0007] CDMA-based license-free diversity competition random access method, including the following steps;

[0008] S1: Construct a large-scale user CDMA uplink access scenario;

[0009] S2: In the access scenario, each user randomly selects two orthogonal spreading sequences from the orthogonal spreading codebook provided by the system for spreading communication, and then records the selected spreading sequences in the data frame sent by the user. As long as the user transmits successfully without conflict on one spreading sequence;

[0010] S3: If the user can correctly decode after successful transmission, find the two spreading sequences it selected, and then subtract the output of this user corresponding to the two spreading sequences from the information received at the base station receiver, so as to eliminate the conflict of this user for other users; The information remaining after subtracting the output corresponding to the two spreading sequences of this user from the information received at the base station receiver is called the remaining output;

[0011] S4: After eliminating the conflict of this user, continue to decode the information of the corresponding user in the remaining output (in the remaining output). Because the users who cause conflicts for the users who correctly decode the data can be correctly decoded in this round, and iterate in turn;

[0012] S5: When no user information can be decoded in a certain iteration, the iteration ends. The users who have decoded all the correct information are the users who have successfully transmitted. The base station sends a response to these users indicating that the information sent has been correctly received. The users who have not received a response will re-send the information when the next time slot arrives.

[0013] The specific content of S1 is as follows:

[0014] In the scenario, a base station serves M user devices. The user devices include a large number of devices such as mobile phones and sensors. Each device is only configured with one antenna. The characteristic of this scenario is a large user scale, that is, the number M is very large, but only a small number of users need to send data. The users who send data are in an active state, called active users, and the rest of the users belong to inactive users. At the same time, the number of active users does not exceed 5% of the total number of users, that is, it has the characteristic of sporadic communication, and the characteristic of active users is that the transmitted data packets are small, and they randomly access and leave the system.

[0015] The specific content of S2 is as follows:

[0016] In the access scenario, when K users are in an active state and need to send data, define the transmission information of the kth user as x k , define the orthogonal spreading codebook S and the ith sequence in the codebook as s i , and then each active user selects from the orthogonal spreading codebook S with a total of N = [s1, s2,..., s NRandomly select two spreading sequence codes from (N > k). After modulating its own data bits, communicate on these two orthogonal codewords respectively. They respectively represent that the k-th user selects the i-th and j-th sequences in the codebook S, and each user will record the selected spreading sequence in its own data frame structure after selection. The labels i and j, and at the base station side, an exactly the same local codebook S will be generated synchronously for demodulating the received signal.

[0017] The specific content of S3 is as follows:

[0018] The information x of user k k Will be transmitted on two spreading sequences. As long as there is no data information of other users on one of the spreading sequences, that is, no other user selects it, conflict-free transmission can be achieved, that is, the transmission is successful. Then, after decoding on the successfully transmitted spreading sequence, the correct x can be obtained. k , verify its correctness through code verification, and then analyze its data frame structure to find the corresponding other codeword in its record.

[0019] The received signal at the base station side is y:

[0020]

[0021] Where h k Is the wireless channel gain of user k, w represents that the channel is additive white Gaussian noise, and it follows the distribution N(0, σ 2 ), assuming that the channel gains of all users are the same at the same time and normalizing processing is performed, the received signal y is simplified to:

[0022]

[0023] Define y k As the output y corresponding to user k k Is:

[0024]

[0025] At the base station side, use the synchronized local codebook S to perform autocorrelation demodulation on the received signal y;

[0026] Define u = S T y as the process of autocorrelation demodulation. Each element in u is the user data demodulated corresponding to each sequence in the codebook S. After autocorrelation demodulation, the users using each orthogonal spreading sequence are demodulated. Define the user data demodulated on the n-th sequence in the codebook as:

[0027] x n = s n y

[0028] After self-correlation demodulation, the user information on each spreading sequence is obtained. Since the spreading sequences of users are randomly selected, there may be multiple users on one spreading sequence. After code verification at the base station, the information of multiple users is decoded into a scrambled sequence, and when there is only one user sending information on the spreading sequence, it is correctly decoded data.

[0029] Specifically, S4 is as follows:

[0030] Using the correctly decoded user data in S3, parse its data frame to obtain the data information of the user and the two selected spreading sequences, further obtain the correct output corresponding to the user, and then subtract the output corresponding to the user whose correct data is demodulated from the received signal, so as to eliminate the interference of these users to other users;

[0031] After defining and subtracting the output corresponding to the user whose correct data is decoded, the remaining received signal is defined as y':

[0032]

[0033] where y k represents the correct output of the kth user, and k represents the correct data of k users demodulated in total.

[0034] Specifically, S5 is as follows:

[0035] For the remaining received signal y' after eliminating interference, the base station continues to demodulate y' using the local codebook, repeating the above S3 and S4. When no correct information of any user can be decoded at the base station, the iteration terminates, and all the correctly demodulated data is used as the data sent by the active users detected in the license-free access process.

[0036] Advantages of the present invention:

[0037] Compared with the traditional DS-CDMA system, the present invention first adopts a license-free uplink access method, which simplifies the signaling process and reduces the access delay. Secondly, because the users sending information are random, in the present invention, each user randomly selects two different orthogonal sequences for spreading transmission in the uplink transmission to achieve diversity transmission. Only when multiple users select exactly the same two orthogonal sequences will there be interference, greatly reducing the probability of interference, increasing the access rate of the system, and having a certain ability to eliminate interference when users interfere. In the case of very few active users, the active user detection performance is better. Brief Description of the Drawings

[0038] Figure 1 is the uplink access scenario diagram of the present invention.

[0039] Figure 2It is the DS-CDMA unlicensed uplink random access spreading selection diagram of the present invention.

[0040] Figure 3 It is the specific process of the user information detection algorithm of the present invention.

[0041] Figure 4 It is the data frame structure sent by the user of the present invention. Specific implementation manners

[0042] The present invention will be further described in detail below with reference to the accompanying drawings.

[0043] Refer to Figure 3 , the specific operation steps of this embodiment are as follows:

[0044] Step 1: Construct a large-scale user uplink access scenario

[0045] The system scenario of the present invention is as Figure 1 shown. In this scenario, a base station serves M user devices, which may include a large number of devices such as mobile phones and sensors, and each device is only configured with one antenna. The feature of this scenario is that the user scale is large, that is, the number M is very large, but only a small number of users need to send data. The users who send data are in an active state and are called active users, and the rest of the users belong to inactive users. At the same time, the number of active users does not exceed 5% of the total number of users, that is, it has the characteristic of sporadic communication. Moreover, the characteristics of active users are that the transmitted data packets are small, with random access and leaving the system.

[0046] Step 2: Users select spreading sequences

[0047] In Figure 1 the corresponding uplink access scenario, when K users are in an active state and need to send data, define the transmission information of the kth user as x k , x k 's frame structure is as Figure 4 shown. Define the orthogonal spreading codebook S, and the ith sequence in the codebook as s i . Then each active user randomly selects two spreading sequence codes from the total N orthogonal spreading codebook S = [s1, s2,..., s N (N>k), modulates its own data bits, and then communicates on these two orthogonal codewords respectively. respectively represent that the kth user selects the ith and jth sequences in the codebook S, and each user will record the labels i, j of the spreading sequences it selects in its own data frame structure after selection. Moreover, at the base station side, an exactly the same local codebook S will be generated synchronously for demodulating the received signal.

[0048]

[0048] Step 3: Decode and successfully transmit the user information

[0049] The information x of user k k will be transmitted on two spreading sequences. As long as there is no data information of other users on one of the spreading sequences, that is, no other users select it, conflict-free transmission can be achieved, that is, the transmission is successful. Then, the correct x can be obtained after decoding on the successfully transmitted spreading sequence k , verify its correctness through code verification, and then analyze its data frame structure to find the corresponding another codeword in its record

[0050] Define the received signal at the base station as y:

[0051]

[0052] where h k is the wireless channel gain of user k. Assuming that the channel is stable, the gain of the wireless channel for each user is the same at the same time. For the convenience of calculation, after normalization processing, w represents that the channel is additive white Gaussian noise and follows the distribution N(0,σ 2 ). After normalizing the wireless channel gain, the received signal y is simplified to:

[0053]

[0054] Define y k as the output y corresponding to user k k as:

[0055]

[0056] At the base station, use the synchronized local codebook S to perform autocorrelation demodulation on the received signal y. Define u = S T y as the process of autocorrelation demodulation. Each element in u is the user data demodulated corresponding to each sequence in the codebook S. Because the spreading codes selected by users are mutually orthogonal, after autocorrelation demodulation, the users using each orthogonal spreading sequence are demodulated

[0057] Define the user data demodulated on the nth sequence in the codebook as:

[0058] x n = s n y

[0059] After autocorrelation demodulation, the user information on each spreading sequence is obtained. Because the spreading sequences of users are randomly selected, there may be multiple users on one spreading sequence. After code verification at the base station, the information of multiple users is decoded into a scrambled sequence. When only one user sends information on the spreading sequence, the data can be correctly decoded

[0060] Step 4: Conflict Resolution

[0061] Using the correctly decoded user data in Step 3, parsing its data frame, the data information of the user and the two selected spreading sequences can be obtained, and further the correct output corresponding to the user can be obtained. Then, subtract the output corresponding to the user whose correct data has been demodulated from the received signal, and the conflicts of these users with other users can be eliminated. Since a user can be correctly decoded if the transmission is successful on one sequence, and the other sequence may conflict with other users, the conflict on the other sequence with other users can be eliminated through conflict resolution, that is, conflict resolution.

[0062] After defining and subtracting the output corresponding to the user whose correct data has been decoded, the remaining received signal is y':

[0063]

[0064] where y k represents the correct output of the k-th user, and k represents the total number of users whose correct data has been demodulated.

[0065] Step 5: Iterative Decoding

[0066] For the remaining received signal y' after eliminating conflicts, the base station continues to demodulate y' using the local codebook, repeating the above Step 3 and Step 4. When no correct information of any user can be decoded at the base station, the iteration terminates. All the correctly demodulated data is used as the data sent by the active users detected during the license-free access process.

[0067] Step 6: Algorithm Example

[0068] As Figure 2 shown: User 1 selects spreading sequences s1 and s2, User 2 selects spreading sequences s2 and s4, and User 3 selects spreading sequences s3 and s4. There is a conflict between User 1 and User 2 on the s2 sequence, but the data of User 1 can be correctly decoded on the s1 code sequence. Then, by subtracting the modulation result of User 1's data and s2 from the signal received on the s2 code sequence, the conflict between User 2 and User 1 can be resolved, and both User 1 and User 2 can correctly transmit their own data, while User 3 can directly and correctly transmit on the s3 codeword.

[0069] In the above example, the received signal at the receiving end is:

[0070]

[0071] Demodulating using the locally generated synchronization codebook gives:

[0072] S T y = [s1y, s2y, …, sN y] = [x1, x1 + x2, x3, x2 + x3]

[0073] In the above formula, first, x1 and x3 can be correctly decoded on the s1 and s3 sequences. After decoding x1, it can be obtained from its data information that the sequences selected by User 1 and User 3 are s1, s2 and s3, s4 respectively, and the corresponding outputs of User 1 and User 3 can be further obtained:

[0074] y1 + y3 = s1x1 + s2x1 + s3x3 + s4x3

[0075] At the receiving end, subtracting y1 and y3 from the received signal gives:

[0076]

[0077] At this time, the formula x n = s n can be used on the s2 and s4 chips to demodulate the correct data of User 2. It should be noted here that if there are still users that have not been correctly detected, when subtracting the data information of User 2 from the remaining received signal, only one operation should be performed on its corresponding sequence, that is, User 2 can demodulate the correct data information on both s2 and s4, but only one correct data can be used to obtain the two chips it selected, and then subtract it from the received signal. It should be noted here to avoid repeated subtraction of the same user causing detection errors.

[0078] The above description is only a specific example of the present invention and does not constitute any limitation to the present invention. Obviously, for professionals in this field, after understanding the content and principle of the present invention, various modifications and changes in form and details may be made without departing from the principle and structure of the present invention. However, these corrections and changes based on the idea of the present invention are still within the protection scope of the claims of the present invention.

Claims

1. A license-free diversity competition random access method based on CDMA, characterized in that It includes the following steps; S1: Construct a large-scale user CDMA uplink access scenario; S2: In the said access scenario, each user randomly selects two orthogonal spreading sequences from the orthogonal spreading codebook provided by the system for spreading communication, and then records the selected spreading sequences in the data frame sent by the user. As long as there is no conflict in the transmission on one spreading sequence, the transmission is successful; S3: If the user can correctly decode after successful transmission, find the two spreading sequences it selects, and then subtract the output of this user corresponding to the two spreading sequences from the information received at the base station receiver, so as to eliminate the conflict of this user for other users; The information remaining after subtracting the output corresponding to the two spreading sequences of this user from the information received at the base station receiver is called the remaining output; S4: After eliminating the conflict of this user, continue to decode the information of the corresponding user from the remaining output at the receiver, and iterate in turn; S5: When it is impossible to decode the information of any user in a certain iteration, the iteration ends. The users who have decoded all the correct information are the users with successful transmission. The base station sends a response to these users indicating that the information sent has been correctly received. The users who have not received the response will resend the information when the next time slot arrives.

2. The unlicensed diversity contention random access method based on CDMA according to claim 1, wherein The specific content of S1 is as follows: In the scenario, a base station serves M user devices, and each device is only configured with one antenna. The user sending data is in an active state and is called an active user, and the rest of the users belong to inactive users. At the same time, the number of active users does not exceed 5% of the total number of users, that is, it has the characteristics of sporadic communication, and the characteristics of active users are small transmission data packets, random access to and departure from the system.

3. The license-free diversity competition random access method based on CDMA according to claim 1, characterized in that The specific content of S2 is as follows: In the access scenario, when K users are active and need to send data, the transmission information of the k-th user is defined as x k , the orthogonal spreading codebook S and the i-th sequence in the codebook are defined as s i , and then each active user randomly selects two spreading sequences from the orthogonal spreading codebook S of total length N = [s1, s2, …, s N (N > K) to modulate its own data bits and then communicate on these two orthogonal codewords respectively. Let it be denoted that the k-th user selects the i-th and j-th sequences from the codebook S, and after each user makes a selection, it records the labels i, j of the selected spreading sequences in its own data frame structure. Moreover, the base station will synchronously generate an exactly identical local codebook S for demodulating the received signals. ​ 4. The license-free diversity competition random access method based on CDMA according to claim 1, wherein The specific content of S3 is as follows: The information x of user k k will be transmitted on two spreading sequences. As long as there is no data information of other users on one of the spreading sequences, that is, no other users select it, conflict-free transmission can be achieved, that is, the transmission is successful. Then, after decoding on the successfully transmitted spreading sequence, the correct x can be obtained k , verify its correctness through code verification, and then analyze its data frame structure to find the corresponding another codeword in its record 5. The license-free diversity competition random access method based on CDMA according to claim 1, wherein The received signal at the base station end is y: where h k is the wireless channel gain of user k, w represents the channel as additive white Gaussian noise, which follows the distribution N(0, σ 2 ), and the received signal y is simplified as: Define y k as the output y corresponding to user k k is: At the base station end, use the synchronized local codebook S to perform autocorrelation demodulation on the received signal y; Define \(u = S\) T Let \(y\) be the process of autocorrelation demodulation. Each element in \(u\) is the demodulated user data corresponding to each sequence in the codebook \(S\). After autocorrelation demodulation, the user using each orthogonal spreading sequence is demodulated. Define the user data demodulated on the \(n\)th sequence in the codebook as follows: x n = s n y After autocorrelation demodulation, the user information on each spreading sequence is obtained. Because the spreading sequences of users are randomly selected, there may be multiple users on one spreading sequence. After code verification at the base station, the information of multiple users is decoded into a scrambled sequence, and when there is only one user sending information on the spreading sequence, it is correctly decoded data.

6. The unlicensed diversity contention random access method based on CDMA according to claim 1, wherein The specific content of S4 is as follows: Use the correctly decoded user data in S3 to parse its data frame to obtain the data information of this user and the two selected spreading sequences, and further obtain the correct output corresponding to the user. Then subtract the output corresponding to the user with correctly demodulated data from the received signal, so as to eliminate the conflict of these users for other users; Define that after subtracting the output corresponding to the user with correctly decoded data, the remaining received signal is y': where y k represents the correct output of the k-th user, and k represents the total number of correct data of k users demodulated.

7. The unlicensed diversity contention random access method based on CDMA according to claim 1, wherein The specific content of S5 is as follows: For the remaining received signal y' after eliminating the conflict, the base station continues to use the local codebook to demodulate y', and repeats the above S3 and S4. When it is impossible to decode the correct information of any user at the base station end, the iteration terminates, and all the correctly demodulated data is used as the data sent by the active users detected in the license-free access process.

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