Distributed random access method combined with space pilot frequency

Abstract

The invention provides a distributed random access method combined with space pilot frequency, relates to the technical field of pilot frequency random access, and aims to solve the defect that a large number of space pilot frequency resources often appear in the random access process, comprising the following steps: each user side randomly selects and sends a pilot frequency sequence to a base station based on an orthogonal pilot frequency set, the pilot frequency sequence received by the base station is Y; the base station generates and broadcasts precoding random access response (PRAR) information, null pilot frequency information and ACB parameters according to the pilot frequency sequence Y; each user side judges whether the user side is the strongest user side or not, and sends a corresponding pilot frequency sequence and an uplink message to the base station according to a judgment result; and the base station estimates channel information of the user side according to the pilot frequency sequence, demodulates an uplink message sent by the user side, and allocates a special data pilot frequency sequence for the user side according to a demodulation result. The method has the advantage of effectively improving the utilization rate of pilot frequency resources.

Description

Technical Field

[0001] The present invention relates to the technical field of pilot random access, and in particular to a distributed random access method in conjunction with a null pilot. Background Art

[0002] Pilot Random Access (PRA) technology allows the user end to randomly select a pilot sequence from the available pilot set, thereby solving the pilot shortage problem and supporting more user ends to access the network.

[0003] However, pilot random access will inevitably introduce pilot collision problems, resulting in the base station being unable to obtain the channel state information of the user end. During the PRA process, each user end randomly selects a pilot from the available pilot set and sends it to the base station. According to the number of user ends that access the pilot, the pilots can be divided into the following three categories: (1) non-collision pilots: pilots selected by only one user end; (2) collision pilots: pilots selected by multiple user ends at the same time; (3) empty pilots: pilots not selected by any user end. In M2M application scenarios, user ends usually have a low activation probability, which results in a large number of empty pilot resources in the PRA process.

[0004] In order to improve the utilization rate of the empty pilot, it is necessary to optimize the distributed random access method of the joint empty pilot to effectively improve the access success rate of M2M. Summary of the invention

[0005] The object of the present invention is to provide a distributed random access method in conjunction with a null pilot, which can effectively improve the access success rate of M2M.

[0006] The present invention is achieved through the following technical solutions:

[0007] A distributed random access method with a joint null pilot comprises the following steps:

[0008] Step S1: Each user terminal randomly selects and sends a pilot sequence to the base station based on the orthogonal pilot set, and the pilot sequence received by the base station is Y;

[0009] Step S2: The base station generates and broadcasts precoding random access response information PRAR, null pilot information and ACB parameters according to the pilot sequence Y;

[0010] Step S3: Each user terminal determines whether it is the strongest user terminal according to the received precoding random access response information PRAR, and sends a corresponding pilot sequence and an uplink message to the base station according to the determination result;

[0011] Step S4: the base station estimates the channel information of the user terminal according to the pilot sequence, demodulates the uplink message sent by the user terminal, and allocates a dedicated data pilot sequence to the user terminal according to the demodulation result.

[0012] Preferably, the method in which each user terminal randomly selects and sends a pilot sequence to the base station is:

[0013] Each activated M2M user terminal transmits a signal in the orthogonal pilot set P o A pilot sequence is randomly selected and sent to the base station. The orthogonal pilot set P o for The orthogonal pilot set P o The elements in represent different orthogonal pilots;

[0014] The pilot sequence Y received by the base station is:

[0015]

[0016] Among them, ψ k is the pilot sequence selected by user terminal k, Z i represents the total number of clients, ρ k is the uplink transmission power of user terminal k, h k represents the channel information between the user terminal k and the base station, Z is a Gaussian white noise matrix and each element has a mean of 0 and a variance of σ 2 Circularly symmetric complex Gaussian distribution.

[0017] Preferably, the method by which the base station generates the precoded random access response information PRAR is:

[0018] The base station performs correlation operations on the pilot sequence Y from the user end and each pilot sequence in the cell:

[0019]

[0020] Among them, y i is the sum of Y and the i-th pilot sequence s in the cell i The result of the correlation operation and includes a vector of M elements, where M is the number of antennas, (·) * represents the conjugation operation;

[0021] The base station obtains the precoding random access response information PRAR:

[0022]

[0023] Wherein, V represents the precoded random access response information PRAR, q represents the downlink transmission power, φ trepresents the downlink pilot sequence corresponding to the tth uplink pilot sequence in the orthogonal pilot set, τ p is the total number of uplink pilot sequences.

[0024] Preferably, the method for the base station to generate the null pilot information is:

[0025] Get the reference value b when M approaches infinity:

[0026]

[0027] Among them, α i is the channel gain of all users who select the same pilot sequence. If y i If the calculated reference value b is less than a preset threshold, the corresponding i-th pilot sequence is judged as a null pilot;

[0028] Get all empty pilots and obtain the number G of the empty pilots i , and assign indexes to them respectively

[0029] Preferably, the base station generates the ABC parameters The method is:

[0030] Obtain the number F of user terminals estimated by the base station that do not send the pilot sequence in step S3:

[0031]

[0032] Among them, F u represents the expected value of the number of user terminals that do not send the pilot sequence in step S3 among the u user terminals that select the same pilot sequence in step S1, represents the expected value of the number of pilot sequences selected by u UEs, represents the event that u UEs select the same pilot sequence in step S1 and d (0≤d≤u) UEs send pilot sequences in step S3, P r (.) represents the probability of an event occurring;

[0033] Get the ABC parameters

[0034]

[0035] Among them, G i is the number of null pilots.

[0036] Preferably, the method by which the base station broadcasts the precoding random access response information PRAR, the null pilot information and the ACB parameter is:

[0037] The base station broadcasts the precoding random access response information PRAR, the null pilot information and the ACB parameter through a downlink broadcast channel.

[0038] Preferably, the method in which each of the user terminals sends the corresponding pilot sequence to the base station according to the judgment result is:

[0039] If the result of the determination is that it is the strongest user terminal, the user terminal resends the pilot sequence selected in step S1 to the base station;

[0040] If the judgment result is that the client is not the strongest client, the client randomly generates a value that obeys a uniform distribution of [0, 1], and compares the value with the ACB parameter;

[0041] If it is less than the ACB parameter, the user terminal i A pilot sequence is randomly selected from the empty pilot resources and sent to the base station;

[0042] If it is not less than the ACB parameter, the user terminal fails to access the current access time slot.

[0043] Preferably, the uplink message includes a user terminal identification code.

[0044] Preferably, the method of allocating a dedicated data pilot sequence to the user terminal according to the demodulation result is:

[0045] If the user terminal demodulates successfully, the base station temporarily allocates a dedicated data pilot sequence to the user terminal;

[0046] If the demodulation of the user terminal is unsuccessful, determining whether the user terminal has reached a maximum number of retransmissions;

[0047] If the user terminal has not reached the maximum number of retransmissions, then in [1,2,3...,W BO ] Randomly select an integer B, W from the set BO is an integer. After waiting for B, the user terminal will re-access in the nearest random access time slot.

[0048] The technical solution of the present invention has at least the following advantages and beneficial effects:

[0049] The present invention makes full use of the empty pilot resources, improves the utilization rate of the empty pilots, and effectively solves the defect of the prior art that a large number of empty pilot resources often appear during the random access process;

[0050] The present invention allows the non-strongest user terminals that select the same pilot sequence to randomly select a pilot sequence from the empty pilot resources and send it to the base station, which can effectively improve the pilot resource utilization rate while ensuring fairness between user terminals;

[0051] The present invention has reasonable design, strong adaptability, high cost performance of computing power, and is easy to promote and implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A schematic diagram of the flow of a distributed random access method with a joint null pilot provided in Embodiment 1 of the present invention;

[0053] Figure 2 A schematic diagram of the principle of a multi-slot access system model provided in Embodiment 1 of the present invention;

[0054] Figure 3 The curve of the number of successfully accessed users changing with the number of antennas in each time slot block provided in Embodiment 1 of the present invention. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0056] Example 1

[0057] This embodiment provides a distributed random access method with a joint null pilot. Figure 1 , including the following steps:

[0058] Step S1: Send pilot sequence:

[0059] Each user terminal randomly selects and sends a pilot sequence to the base station based on the orthogonal pilot set, and the pilot sequence received by the base station is Y;

[0060] Step S2: Obtain precoding random access response information, null pilot information and ACB parameters:

[0061] The base station generates and broadcasts precoding random access response information PRAR, null pilot information and ACB parameters according to the pilot sequence Y;

[0062] Step S3: Decision on the strongest user terminal and competition for empty pilot resources:

[0063] Each user terminal determines whether it is the strongest user terminal according to the received precoding random access response information PRAR, and sends a corresponding pilot sequence and an uplink message to the base station according to the determination result;

[0064] Step S4: Allocate dedicated data pilot:

[0065] The base station estimates the channel information of the user terminal according to the pilot sequence, demodulates the uplink message sent by the user terminal, and allocates a dedicated data pilot sequence to the user terminal according to the demodulation result.

[0066] A time-frequency block in the system is divided into two parts, one for transmitting data and the other for transmitting random access pilot sequences. The multi-slot access system model is as follows: Figure 2 As shown, δ is the duration of each time slot block, and D is the observed time. This embodiment mainly focuses on the PRA block, and the data information transmission process is consistent with the process in the traditional MIMO system. During the access process, the empty pilot often always exists, and the specific analysis is as follows:

[0067] Considering that the activation probability of a user terminal is 0.1%, the number of activated users is Z i =173. In addition, the number of users who select the same pilot sequence is subject to the parameter Z i =173 and τ p Bernoulli distribution, τ p is the total number of pilot sequences in the orthogonal pilot set. Therefore, in the i-th random access time slot, the expected value of the number of empty pilots is for:

[0068]

[0069] Z i =173 Substituting into the above formula, we can get that is, for the considered micro-cell urban dense environment, as long as the number of pilots in the cell is greater than 30, the empty pilot always exists, that is, In addition, in M2M communication, the user terminal's mobility rate is very low and the channel coherence time is relatively long, so it is easy to meet the requirement that the number of pilots in the cell is greater than 30.

[0070] The main idea of ​​this embodiment is to allow non-strongest user terminals (user terminals with poor channel quality) that select the same pilot sequence in the scheme to randomly select a pilot sequence from empty pilot resources and send it to the base station, thereby effectively improving the pilot resource utilization while ensuring fairness between user terminals.

[0071] In this embodiment, the method in which each user terminal randomly selects and sends a pilot sequence to the base station is:

[0072] Each activated M2M user terminal transmits a signal in the orthogonal pilot set P o A pilot sequence is randomly selected and sent to the base station. The orthogonal pilot set P o for The orthogonal pilot set P o The elements in represent different orthogonal pilots;

[0073] The pilot sequence Y received by the base station is:

[0074]

[0075] Among them, ψ k is the pilot sequence selected by user terminal k, Z i represents the total number of clients, ρ k is the uplink transmission power of user terminal k, h k Indicates the channel information between user terminal k and base station, for example:

[0076]

[0077] Z is a Gaussian white noise matrix, and each element has a mean of 0 and a variance of σ. 2 Circular symmetric complex Gaussian distribution, that is, CN(0,σ 2 ), Z∈C M×L That is, the matrix dimension of Z is M×L, where M is the number of antennas.

[0078] As a preferred solution, the method in which the base station generates the precoded random access response information PRAR is:

[0079] The base station performs correlation operations on the pilot sequence Y from the user end and each pilot sequence in the cell:

[0080]

[0081] Among them, y i is the sum of Y and the i-th pilot sequence s in the cell i The result of the correlation operation and includes a vector of M elements, where M is the number of antennas, (·) * represents the conjugation operation;

[0082] The method for the base station to obtain the precoding random access response information PRAR is:

[0083]

[0084] Wherein, V represents the precoded random access response information PRAR, q represents the downlink transmission power, φ t represents the downlink pilot sequence corresponding to the tth uplink pilot sequence in the orthogonal pilot set, τ p is the total number of uplink pilot sequences.

[0085] At the same time, based on the above, the method for the base station to generate the empty pilot information is:

[0086] According to the asymptotically optimal propagation characteristics of the MIMO system channel, when the number of antennas M tends to infinity, we can obtain:

[0087]

[0088] It can be seen from the above formula that for an empty pilot sequence, i.e., a pilot sequence not selected by any user end, b is only the variance of Gaussian white noise; while for a pilot sequence selected by a user end, b is equal to the channel gain α of all users who select the same pilot sequence. i The sum of the variance of the Gaussian white noise is much larger than the b value corresponding to the empty pilot. Therefore, the base station sets the threshold according to the b value corresponding to each pilot, and can easily determine the number of empty pilots and the index of each empty pilot, which are represented by G i and

[0089] Furthermore, the base station generates the ABC parameters The method is:

[0090] Obtain the number F of user terminals estimated by the base station that do not send the pilot sequence in step S3:

[0091]

[0092] Among them, F u represents the expected value of the number of user terminals that do not send the pilot sequence in step S3 among the u user terminals that select the same pilot sequence in step S1, represents the expected value of the number of pilot sequences selected by u UEs, represents the event that u UEs select the same pilot sequence in step S1 and d (0≤d≤u) UEs send pilot sequences in step S3, P r (.) represents the probability of an event occurring.

[0093] Get the ABC parameters

[0094]

[0095] Among them, G i is the number of null pilots.

[0096] Then, the method in which the base station broadcasts the precoding random access response information PRAR, the null pilot information, and the ACB parameter is preferably:

[0097] The base station broadcasts the precoding random access response information PRAR, the null pilot information and the ACB parameter through a downlink broadcast channel.

[0098] Next, the method in which each of the user terminals sends the corresponding pilot sequence to the base station according to the judgment result is preferably:

[0099] If the result of the determination is that it is the strongest user terminal, the user terminal resends the pilot sequence selected in step S1 to the base station;

[0100] If the judgment result is that the client is not the strongest client, the client randomly generates a value that obeys a uniform distribution of [0, 1], and compares the value with the ACB parameter;

[0101] If it is less than the ACB parameter, the user terminal i A pilot sequence is randomly selected from the empty pilot resources and sent to the base station;

[0102] If it is not less than the ACB parameter, the user terminal fails to access the current access time slot.

[0103] As a further optimization solution, the uplink message includes a user terminal identification code so that the base station can perform collision detection in step S4.

[0104] Finally, the method for allocating a dedicated data pilot sequence to the user terminal according to the demodulation result is:

[0105] If the user terminal demodulates successfully, the base station temporarily allocates a dedicated data pilot sequence to the user terminal;

[0106] If the demodulation of the user terminal is unsuccessful, determining whether the user terminal has reached a maximum number of retransmissions;

[0107] If the user terminal has not reached the maximum number of retransmissions, then in [1,2,3...,W BO ] Randomly select an integer B, W from the set BO is an integer. After waiting for B, the user terminal will re-access in the nearest random access time slot.

[0108] The following is a performance analysis of the solution in this embodiment:

[0109] If the user terminal can obtain the dedicated data pilot sequence, it indicates that the user terminal has successfully accessed the network. According to the distributed random access scheme with joint empty pilot of this embodiment, the user terminal can obtain the dedicated data pilot sequence in the following two cases: (a) among all the user terminals that select the same pilot sequence, only one user terminal considers itself to be the strongest user terminal in step S3; (b) in step S3, the user terminal considers itself not to be the strongest user terminal, but the user terminal does not have a pilot collision with other user terminals when selecting empty pilot resources. Therefore, the total number of successfully accessed user terminals obtained by this scheme is It can be calculated as:

[0110]

[0111] in, and are the number of successfully connected users obtained from cases (a) and (b), respectively, and The method to obtain is:

[0112]

[0113] in, represents the probability that a pilot sequence is selected by u UEs in step S1, represents the probability that in step S1 a pilot sequence is selected by u user terminals and only one user terminal believes that it is the strongest user terminal. According to random theory, u is subject to the parameter Z i and Bernoulli distribution of ;

[0114] It can be calculated as:

[0115]

[0116] This embodiment uses represents the event that u UEs select the same pilot sequence in step S1 and d (0≤d≤u) UEs send the pilot sequence in step S3. For the event that d UEs among the u UEs that select the same pilot sequence in step S1 send the pilot sequence in step S3, there are a total of Different situations, for the In this case, use represents the index of the d user terminals that sent the pilot sequence in step S3, and the index of the remaining ud user terminals is recorded as Event Probability It can be calculated as:

[0117]

[0118] Among them, R k represents the event that user terminal k sends a pilot sequence in step S3, and J k Indicates that user terminal k did not send the pilot sequence in step S3. The probability value that only one competitor sends a pilot sequence in step S3 is obtained by setting d to 1. For any d, It can be calculated as:

[0119]

[0120] in, are mutually independent events. Since the channel considered in this embodiment is an uncorrelated Rayleigh fading channel, the channel information of the user terminal obeys a cyclic symmetric complex Gaussian distribution with a mean of 0. Therefore, the channel information of the user terminal is an independent and identically distributed random variable. Each user terminal independently determines whether to send a pilot sequence in step S3.

[0121] In the above calculation, Pr(R k )for:

[0122]

[0123] in, is the intermediate parameter, For z k The real part of the broadcast information received by the user end With pilot sequence s n After doing the correlation operation, the received signal obtained by user end k is z k , Γ(.) is the gamma function.

[0124] in addition, for:

[0125]

[0126] in, represents the probability that an empty pilot sequence is selected by e UEs in step S3, where e follows the Bernoulli distribution.

[0127] In summary, the number of successfully connected users can be rewritten as:

[0128]

[0129] See also Figure 3 , Figure 3 A distributed uplink random access scheme with joint null pilot and a distributed uplink multi-user random access scheme are proposed in the random access time slot RS. i Number of successful access users The curve changes with the number of antennas M. Set the access time slot RS i The number of activated user terminals is 21. In this scenario, one pilot is selected by one user terminal on average, which belongs to the basic overload scenario. When the number of antennas is less than 20, the number of successfully accessed user terminals of the two schemes increases sharply; when the number of antennas continues to increase, the number of successfully accessed user terminals increases relatively slowly. In addition, it can be seen from the figure that since the distributed random access scheme of the joint empty pilot of this embodiment makes full use of the empty pilot resources, the number of successfully accessed user terminals of the distributed random access scheme of the joint empty pilot of this embodiment is significantly greater than that of the distributed uplink multi-user random access scheme, which demonstrates the effectiveness of the technical scheme of this embodiment.

[0130] In summary, the overall resource utilization efficiency of the system is effectively improved, the possibility of pilot idleness is reduced, and the fairness of resource competition and the further improvement of pilot resource utilization are taken into account.

[0131] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A distributed random access method with a joint null pilot, characterized in that: The following steps are involved: Step S1: Each user terminal randomly selects and sends a pilot sequence to the base station based on the orthogonal pilot set, and the pilot sequence received by the base station is Y; Step S2: The base station generates and broadcasts precoding random access response information PRAR, null pilot information and ACB parameters according to the pilot sequence Y; Step S3: Each user terminal determines whether it is the strongest user terminal according to the received precoding random access response information PRAR, and sends a corresponding pilot sequence and an uplink message to the base station according to the determination result; Step S4: the base station estimates the channel information of the user terminal according to the pilot sequence, demodulates the uplink message sent by the user terminal, and allocates a dedicated data pilot sequence to the user terminal according to the demodulation result.

2. The distributed random access method with joint null pilot according to claim 1, characterized in that: The method in which each user terminal randomly selects and sends a pilot sequence to the base station is: Each activated M2M user terminal transmits a signal in the orthogonal pilot set P o A pilot sequence is randomly selected and sent to the base station. The orthogonal pilot set P o for The orthogonal pilot set P o The elements in represent different orthogonal pilots; The pilot sequence Y received by the base station is: Among them, ψ k is the pilot sequence selected by user terminal k, Z i represents the total number of clients, ρ k is the uplink transmission power of user terminal k, h k represents the channel information between the user terminal k and the base station, Z is a Gaussian white noise matrix and each element has a mean of 0 and a variance of σ 2 Circularly symmetric complex Gaussian distribution.

3. The distributed random access method with joint null pilot according to claim 2, characterized in that: The method for the base station to generate the precoded random access response information PRAR is: The base station performs correlation operations on the pilot sequence Y from the user end and each pilot sequence in the cell: Among them, y i is the sum of Y and the i-th pilot sequence s in the cell i The result of the correlation operation and includes a vector of M elements, where M is the number of antennas, (·) * represents the conjugation operation; The base station obtains the precoding random access response information PRAR: Wherein, V represents the precoded random access response information PRAR, q represents the downlink transmission power, φ t represents the downlink pilot sequence corresponding to the tth uplink pilot sequence in the orthogonal pilot set, τ p is the total number of uplink pilot sequences.

4. The distributed random access method with joint null pilot according to claim 3, characterized in that: The method for the base station to generate the empty pilot information is: Get the reference value b when M approaches infinity: Among them, α i is the channel gain of all users who select the same pilot sequence. If y i If the calculated reference value b is less than a preset threshold, the corresponding i-th pilot sequence is judged as a null pilot; Get all empty pilots and obtain the number G of the empty pilots i , and assign indexes to them respectively 5. The distributed random access method with joint null pilot according to claim 4, characterized in that: The base station generates the ABC parameters The method is: Obtain the number F of user terminals estimated by the base station that do not send the pilot sequence in step S3: Among them, F u represents the expected value of the number of user terminals that do not send the pilot sequence in step S3 among the u user terminals that select the same pilot sequence in step S1, represents the expected value of the number of pilot sequences selected by u UEs, represents the event that u UEs select the same pilot sequence in step S1 and d (0≤d≤u) UEs send pilot sequences in step S3, P r (.) represents the probability of an event occurring; Get the ABC parameters Among them, G i is the number of null pilots.

6. The distributed random access method with joint null pilot according to claim 5, characterized in that: The method for the base station to broadcast the precoding random access response information PRAR, the null pilot information and the ACB parameter is: The base station broadcasts the precoding random access response information PRAR, the null pilot information and the ACB parameter through a downlink broadcast channel.

7. The distributed random access method with joint null pilot according to claim 1, characterized in that: The method for each of the user terminals to send the corresponding pilot sequence to the base station according to the judgment result is: If the result of the determination is that it is the strongest user terminal, the user terminal resends the pilot sequence selected in step S1 to the base station; If the judgment result is that the client is not the strongest client, the client randomly generates a value that obeys a uniform distribution of [0, 1], and compares the value with the ACB parameter; If it is less than the ACB parameter, the user terminal i A pilot sequence is randomly selected from the empty pilot resources and sent to the base station; If it is not less than the ACB parameter, the user terminal fails to access the current access time slot.

8. The distributed random access method with joint null pilot according to claim 7, characterized in that: The uplink message includes a user terminal identification code.

9. The distributed random access method with joint null pilot according to claim 1, characterized in that: The method for allocating a dedicated data pilot sequence to the user terminal according to the demodulation result is: If the user terminal demodulates successfully, the base station temporarily allocates a dedicated data pilot sequence to the user terminal; If the demodulation of the user terminal is unsuccessful, determining whether the user terminal has reached a maximum number of retransmissions; If the user terminal has not reached the maximum number of retransmissions, then in [1,2,3...,W BO ] Randomly select an integer B, W from the set BO is an integer. After waiting for B, the user terminal will re-access in the nearest random access time slot.

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