CN116915377B - Unauthorized access pilot frequency distribution method based on hybrid automatic request mechanism - Google Patents
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Abstract
The invention relates to the technical field of wireless communication, in particular to an unauthorized access pilot frequency distribution method based on a hybrid automatic request mechanism, which comprises the following steps: establishing a model of unauthorized random access of a mass machine type communication system under a hybrid automatic repeat request mechanism; constructing an analytic type of the number of users using the special pilot pool; utilizing Monte Carlo simulation data, and adopting least square fitting to use analytic type of special pilot pool user quantity probability; and obtaining the minimum failure probability of a single user when the massive machine type communication system uses a hybrid automatic repeat request mechanism to perform unauthorized random access through an optimizing algorithm, calculating the pilot frequency number of the shared pilot frequency pool and the pilot frequency number of the special pilot frequency pool at the moment, and guiding the massive machine type communication system to perform pilot frequency distribution. The pilot frequency distribution method can meet the requirements of mass machine communication environments on the reliability of the system, and the probability of user conflict is obviously reduced.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to an unauthorized access pilot frequency distribution method based on a hybrid automatic request mechanism.
Background
The mass machine type communication (MASSIVE MACHINE-type communication, mMTC) is taken as one of typical application scenes of the Internet of things, and a user of the mass machine type communication has the characteristics of high connection density, sporadic burst, low data rate, high connection density and the like. Grant-Based (GB) access technology specified by long term evolution (Long Term Evolution, LTE) causes excessive delay and energy consumption due to cumbersome scheduling Grant steps and high signaling overhead, and is not suitable for users in mMTC environments. In unlicensed (GF) access, a User Equipment (UE) transmits a message consisting of pilot and data in a contention-based manner, without waiting for explicit Grant by a base station, is a more potential access mechanism.
Unlicensed Access generally employs a Random Access (RA) mechanism: when the user equipment data packet arrives, it randomly selects one pilot from the available pilot pool, composes a message with the data, and then transmits the message on the randomly selected channel. The base station performs channel estimation based on the received pilot to decode the message of the user equipment. Collision occurs when two or more ues select the same channel and the same pilot frequency during a certain transmission. The base station cannot successfully decode the conflicting messages, resulting in failure of these users to access.
One mechanism to effectively reduce collision probability is the hybrid automatic repeat request (Hybrid Automatic Repeat request, HARQ) scheme. The hybrid automatic repeat request scheme allows users to reduce failure probability by repeating transmission a plurality of times and prepares separate pilots for users who have failed to transmit all the time to ensure low failure probability for a single user. Specifically, the hybrid automatic repeat request scheme divides the pilot pool into a shared pilot pool (Shared Preamble Pool, SPP) and a dedicated pilot pool (DEDICATED PREAMBLE POOL, DPP), and the user selects a pilot in the shared pilot pool first and repeatedly initiates transmissions, each of which occupies one time frame containing a plurality of selectable channels. The channels selected by the users using the shared pilot pool and the dedicated pilot pool may overlap, and the base station needs to allocate different pilots for the shared pilot pool and the dedicated pilot pool in order to avoid additional collision and collision of the users.
The total number of available pilots of a system is a fixed value, the size of a dedicated pilot pool is usually set as a constant in the traditional scheme, but in theory, the probability of access failure of user equipment is the lowest due to the existence of an optimal pilot allocation method for sharing the pilot pool and the dedicated pilot pool, and no strict pilot allocation guiding theory exists at present, and the main difficulty is presented in the following steps: since the number of users using the dedicated pilot pool is an indefinite value, it becomes very difficult to analyze the performance of the dedicated pilot pool, and the expression of the probability of access failure of the user equipment is too complex and has insufficient accuracy.
Disclosure of Invention
Therefore, the invention aims to solve the technical problem that the shared pilot pool and the special pilot pool are not reasonably distributed in the prior art.
In order to solve the technical problem, the invention provides an unauthorized access pilot frequency distribution method based on a hybrid automatic request mechanism, which is characterized by comprising the following steps:
s1, representing a model of unauthorized random access of a mass machine type communication system under a hybrid automatic repeat request mechanism by utilizing a relation between a single user access failure probability and a pilot frequency number distributed by a base station for a shared pilot frequency pool, wherein the hybrid automatic repeat request mechanism comprises the shared pilot frequency pool and a special pilot frequency pool, and the process for establishing the model specifically comprises the following steps: calculating the probability of success of all users accessing the shared pilot pool once in a certain time frame by adopting a probability theory and a random geometry method, deducing the probability of success of single user accessing the shared pilot pool once and the probability of failure of accessing once, and further solving the probability of failure of single user accessing the shared pilot pool for preset times K times; if the user still fails after the shared pilot frequency pool is accessed for K times, the special pilot frequency pool is used for transmission, the probability of the access failure of the single user in the special pilot frequency pool is obtained, and finally the access failure probability of the single user is obtained;
S2, constructing an analytic type of the number of users using the special pilot pool; utilizing Monte Carlo simulation data and adopting least square fitting to use analytic type of special pilot pool user quantity probability;
S3, obtaining a closed analytic expression of the single user access failure probability in S1 under different shared pilot frequency configuration pilot frequency numbers according to the analytic expression of the user quantity probability of the special pilot frequency pool in S2; and obtaining the minimum failure probability of a single user when the massive machine type communication system uses a hybrid automatic repeat request mechanism to perform unauthorized random access through an optimizing algorithm, calculating the pilot frequency number of the shared pilot frequency pool and the pilot frequency number of the special pilot frequency pool at the moment, and guiding the massive machine type communication system to perform pilot frequency distribution.
In one embodiment of the present invention, the calculating the probability P that all users access once in the shared pilot pool for a certain time frame is:
Wherein N 0＝CNS, for ease of analysis, takes the strict lower bound of the formula:
Wherein C is the number of channels of the shared pilot pool, N S is the number of pilots allocated by the base station for the shared pilot pool, and M is the number of active users in the current time frame.
In one embodiment of the present invention, the probability ρ of the single user accessing the shared pilot pool once is: the probability v of the single user failing to access the shared pilot pool once is as follows:
In one embodiment of the present invention, the probability v S that the single user fails to access the shared pilot pool for a preset number of times K is:
since the last time frame will join the current time frame when the failed paired user repeatedly accesses, the number of active users in the current time frame increases from M to m+2.
In one embodiment of the present invention, the probability v D of the single user failing to access the dedicated pilot pool is:
Where u is the number of users using the dedicated pilot pool, equal to the number of users still failed to access for K times using the shared pilot pool, u e {1,2, …, M }; p (u) is the probability of u using the dedicated pilot pool, denoted as p (u) =f (M, N S);ND is the pilot number allocated by the base station for the dedicated pilot pool.
In one embodiment of the present invention, the single user access failure probability v ind is:
Where u is the number of users using the dedicated pilot pool, equal to the number of users still failed to access for K times using the shared pilot pool, u e {1,2, …, M }; p (u) is the probability of u being used by the dedicated pilot pool, denoted as p (u) =f (M, N S);NS is the number of pilots allocated by the base station for the shared pilot pool, N D is the number of pilots allocated by the base station for the dedicated pilot pool, M is the number of active users in the current time frame, and C is the number of channels of the shared pilot pool.
In one embodiment of the present invention, the analytical formula p (u) of using the number probability of dedicated pilot pool users is:
Wherein a, b, c, d, e is a coefficient, and g is a constant term according to the value of u; the application range of the analytical formula p (u) =f (M, N S) using the number probability of the dedicated pilot pool users is M e {6,7,8, …,20}.
In one embodiment of the invention, a damping Newton method-based optimizing algorithm is adopted to obtain the minimum failure probability of a single user when a hybrid automatic repeat request mechanism is used for unauthorized random access in a mass machine type communication system, and the damping Newton method is based on the following principle: constructing a function g (x) =v ind,x＝NS, selecting an initial point of the function g (x), approximating the function g (x) by using a first derivative and a second derivative at the initial point, then taking a minimum point of the approximated function as a new iteration point, and continuously repeating the process until the minimum point x 0,g(x0 meeting the error requirement is found, namely the minimum failure probability.
In one embodiment of the invention, a line search algorithm is adopted to determine the step length of the damping Newton method during iteration, so that the iteration times are reduced.
In one embodiment of the invention, the minimum failure probability of the single user access and the pilot frequency number N 0＝x0 of the shared pilot frequency pool are obtained by rounding upwardsRounding downwards to obtainCalculation ofAndIndividual user access failure probabilityAndAnd compare ifThen selectThe pilot frequency number as the shared pilot frequency pool is selected otherwiseThe pilot number as a shared pilot pool; the number of pilots in the dedicated pilot pool, N D＝N-NS, where N is the total number of pilots.
Compared with the prior art, the technical scheme of the invention has the following advantages:
The unauthorized access pilot frequency distribution method based on the hybrid automatic request mechanism obtains the statistical characteristics of unauthorized random access of the mass machine type communication system through analysis, deduces the analysis type of single user access failure probability based on the hybrid automatic request mechanism, obtains the lowest single user failure probability and the optimal pilot frequency distribution scheme by using the optimizing algorithm based on the damping Newton method, can meet the requirement of the mass machine type communication environment on the system reliability, and can obviously reduce the probability of user conflict compared with the traditional pilot frequency distribution method.
The analytic expression of the number probability of the users using the special pilot pool provided by the invention expands the value range of the active users in the time slot while keeping fitting accuracy and not improving analytic complexity, has a wider application range and accords with the actual environment conditions of the number of the active users in the time slot and mass machine type communication.
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In order that the invention may be more readily understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings, in which
FIG. 1 is a system model diagram of the present invention;
FIG. 2 is a flow chart of an optimizing algorithm based on a damping Newton method;
FIG. 3 is a graph of failure probability for a user based on a hybrid automatic request mechanism in an embodiment of the present invention;
FIG. 4 is a diagram of an optimization algorithm in accordance with an embodiment of the present invention;
Fig. 5 is a graph showing the comparison of the success probability of the allocation method of the present invention and the conventional allocation method.
Detailed Description
The present invention will be further described with reference to the accompanying drawings and specific examples, which are not intended to be limiting, so that those skilled in the art will better understand the invention and practice it.
Referring to fig. 1, the present invention provides a method for allocating unlicensed access pilot frequencies based on a hybrid automatic request mechanism, which is characterized in that the method includes the following steps:
S1, establishing a model of unauthorized random access of a mass machine type communication system under a hybrid automatic repeat request mechanism, and analyzing the performance of the unauthorized random access model.
The invention uses the probability of failure of access as an evaluation index, and deduces a closed expression of the probability of failure of single user access under a hybrid automatic repeat request mechanism based on the mathematical framework of the model. The specific deduction process is as follows:
In this embodiment, a general mass machine communication scenario is adopted, that is, users are deployed in a cellular network, where the user location distribution is described as a poisson point process, and the number of active users in each time frame is M. Unlicensed random access employs contention access, i.e., a user randomly selects a pilot on a channel and transmits with data transmission.
Assuming that there are N pilots in the communication system, the base station allocates N S pilots for the shared pilot pool and N D pilots for the dedicated pilot pool.
The probability P that all users are accessed once in the shared pilot pool in a certain time frame is as follows:
where N 0＝CNS, C is the number of channels sharing the pilot pool. For each active user, it can randomly select one transmission pilot and data from the C channels when using the shared pilot pool, so the number of pilots actually available to the user is increased from N S to CN S.
Since the above mathematical expression of probability P that all users access once in a shared pilot pool for a certain time frame is not easy to perform mathematical analysis, the present invention uses the strict lower bound of the expression for analysis in subsequent calculations, namely:
The reason for the failure of the user transmission for a certain time frame is that the same channel and pilot are selected as other users, and thus the colliding users always appear in pairs. Assuming that the communication system comprises M/2 pairs of independent users, the probability rho of one-time success of single user access in the shared pilot frequency pool can be deduced as follows:
Accordingly, the probability v of a single user failing to access the shared pilot pool once is:
Hybrid automatic request mechanisms allow users to repeat transmissions using a shared pilot pool, but they typically specify a maximum number of repeat transmissions K times that users use the shared pilot pool, given that repeated transmissions by users for long periods of time can increase the latency and load of the network. If the user still fails to access, the special pilot frequency pool is used for transmission, and the special pilot frequency pool has 1 channel.
Therefore, the probability v S that a single user fails to access the shared pilot pool for a preset number of times K is:
since the last time frame will join the current time frame when the failed paired user repeatedly accesses, the number of active users in the current time frame increases from M to m+2.
If the user still fails after the shared pilot pool is accessed for a preset number of times of K, the special pilot pool is used for transmission, and the probability v D of the single user failing to access the special pilot pool is as follows:
Where u is the number of users using the dedicated pilot pool, i.e. users still failed to access for K times using the shared pilot pool, u e {1,2, …, M }. p (u) is the probability of u using the dedicated pilot pool user, denoted p (u) =f (M, N S).
It has been proved by studies that even if the user uses the shared pilot pool to repeat transmission only once, that is, the probability of k=1, u.ltoreq.4 exceeds 93.98%, and the probability increases continuously with the maximum number of repeated transmissions K allowed by the shared pilot pool and the number of active users M in the current time frame, so the invention only considers the case of u.ltoreq.4. When u=1, since contention for resources with other users is not considered, access must be successful, and therefore only u=2, 3,4 needs to be considered. The probability v D of a single user failing to access the dedicated pilot pool can be reduced to:
from the analysis, it can be obtained that in the unlicensed access scheme based on the hybrid automatic request mechanism, the access failure probability v ind of a single user is:
S2, constructing an analytic type of the number of users using the special pilot pool; the invention utilizes Monte Carlo simulation data and adopts least square fitting to use the analytic type of the user quantity probability of the special pilot pool.
The invention considers the case of u=2, 3,4, so the expression of 3 u should be more complex, thus giving a general analytical expression, and the analytical expression p (u) of using the number probability of the dedicated pilot pool user is:
Wherein a, b, c, d, e is a coefficient, and g is a constant term according to the value of u. The application range of the analysis type p (u) =f (M, N S) of the number probability of the users using the special pilot pool is M epsilon {6,7,8, …,20}, the analysis type p (u) =f (M, N S) maintains the accuracy, the analysis type complexity is not improved, and the wider value range of M is maintained, so that the method meets the environment conditions of the active user number and mass machine type communication in the actual time slot.
Of the different values of u, the most important is the accuracy of the fit when u=2, since the value of p (u=2) is much larger than the other values. The accuracy of the final model depends largely on the accuracy of p (u=2).
And S3, obtaining a closed analytic expression of the single user access failure probability under different shared pilot frequency configuration pilot frequency numbers in S1 according to the analytic expression of the user number probability of the special pilot frequency pool in S2, wherein the closed analytic expression is marked as g (x) =v ind,x＝NS, and when M is determined, v ind is a continuous concave function of the pilot frequency number N S distributed by the shared pilot frequency pool.
The minimum value of g (x) and the current x can be obtained through an optimizing algorithm based on a damping Newton method, namely the minimum failure probability of a single user when a massive machine type communication system uses a hybrid automatic repeat request mechanism to perform unauthorized random access and the current shared pilot frequency pool pilot frequency number N 0.
Since the value of the function v ind is small, the whole function is enlarged by 10 6 times on the premise of not influencing the optimizing result, and the whole function is marked as g (x) =10 6vind.
The damping Newton method adopts a line search algorithm to determine the step length, increases the convergence range, has higher tolerance to the selection of an initial point, and specifically comprises the following steps as described with reference to fig. 2:
Inputting a function g (x) and an initial point x;
setting a termination error epsilon, solving preset values delta and sigma of step length, and obtaining the cycle times k=0 of the damping Newton method, wherein epsilon is generally 0-1, delta epsilon (0, 1) and sigma epsilon (0, 0.5);
Calculating e k =g' (x), and if |e k |ε is not less than epsilon, determining a step size by using a line search method; and otherwise, outputting x 0 =x, and ending the cycle.
The line search method includes the steps of:
Calculating E k＝g"(x),dk＝-ek/Ek, and setting the cycle times m=0 of the line search method;
If g (x+δ mdk)<g(x)+σδmekdk), x=x+δ mdk is updated, and if the number of cycles of the damped newton method is k=k+1, m=m+1 is set to be m+1, and the magnitudes of g (x+δ mdk) and g (x) +σδ mekdk are compared again.
Wherein g' (x) and g "(x) represent the first derivative and the second derivative, respectively.
The line search algorithm can find the most suitable step delta mdk in self iteration, and can reduce the iteration times k of Newton's method.
Obtaining the minimum failure probability of single user access and the pilot frequency number N 0＝x0 of the shared pilot frequency pool at the moment, and rounding upwards to obtainRounding downwards to obtainCalculation ofAndIndividual user access failure probabilityAndAnd compare ifThen selectThe pilot frequency number as the shared pilot frequency pool is selected otherwiseAs the number of pilots in the shared pilot pool.
The number of pilots in the dedicated pilot pool, N D＝N-NS, where N is the total number of pilots.
The method comprises the steps of obtaining the pilot frequency number of a shared pilot frequency pool and the pilot frequency number of a special pilot frequency pool when a massive machine communication system uses a hybrid automatic repeat request mechanism to perform unauthorized random access, and guiding the massive machine communication system to perform pilot frequency distribution according to the pilot frequency number of the shared pilot frequency pool and the pilot frequency number of the special pilot frequency pool.
The invention will be further illustrated with reference to specific examples.
Embodiment one:
Assuming a cell site area of 0.86km 2, a connection density of 10 6 users per square kilometer, where each user is active on average every two hours, 120 transmissions per second are received by the base station, each time frame lasting 80ms. Then there are 9.6 users per time frame, i.e. m≡10; each time frame contains 8 channels, i.e., c=8; the available number of pilots is 64, i.e. n=64.
The probability v of a single user failing to access the shared pilot pool once is:
Assuming that the maximum number of repeated transmissions k=2 of the shared pilot pool is used by the user, the probability v S that a single user fails to access the shared pilot pool for a preset number of times K is:
When m=10, k=2, c=8, the probability v S that a single user fails to access the shared pilot pool a preset number of times K decreases with an increase in the number of pilots N S of the shared pilot pool, because the increase in available pilots decreases the probability of collision of the user.
Considering only the case of u=2, 3,4, the probability v D of a single user failing to access the dedicated pilot pool is:
The single user access failure probability v ind is:
Where N D＝64-NS, p (u) is a function of M and N S, denoted p (u) =f (M, N S).
In the present embodiment, a polynomial function is used Fitting is performed, and the obtained formula parameters are shown in table 2, so that a closed analytical formula of the single user access failure probability v ind under the condition of u=2, 3 and 4 can be obtained, wherein R represents the fitting goodness.
Tables 1, f (M, N S) parameter Table
Referring to fig. 3, when m=10, k=2, c=8, the single user access failure probability v ind decreases and increases with the increase of the pilot number N S of the shared pilot pool, because when the pilot number N S of the shared pilot pool increases, the probability v S that a single user fails to access the shared pilot pool for a preset number K times increases, and because the total pilot number N is unchanged, the pilot number N D of the dedicated pilot pool decreases, and thus the probability v D that a single user fails to access the dedicated pilot pool decreases, and vice versa.
Because v ind＝vS·vD, there is a single user access minimum failure probability theoretically, and the accuracy of the theory of the present invention is verified by the data in this embodiment.
Referring to fig. 4, the closed-loop analysis of the single-user access failure probability v ind in the present embodiment uses the damping newton method-based optimization algorithm, and the termination error epsilon=1×10 -5, delta=0.55, and sigma=0.4 is given. When the number of active users m=10, the optimizing algorithm reaches a set termination error value after 4 iterations, and N 0 = 45.3559 is output, and the integer is N 0 =45. The failure rate of the user at this time is the lowest, i.e. v ind =0.000005.
In practical applications, in order to avoid excessive iteration times, the number of loops m of the line search algorithm needs to be set to a maximum loop value, and is generally set to be m is less than or equal to 20.
The best pilot number N S of the shared pilot pool and its corresponding reliability at different values of M are obtained by the optimization algorithm, as shown in table 2. The reliability is indicated by 1-v ind.
TABLE 2 shared Pilot Chi Daopin assignment and reliability analysis in this embodiment
As can be seen from table 2, the proposed unlicensed random access scheme can meet the reliability requirements of a massive machine-type communication environment. When M is less than or equal to 12, the reliability of the system can reach 0.99999, and the ultra-reliability requirements of some limit environments are met.
Fig. 5 is a reliability comparison between the pilot frequency allocation method proposed by the present invention and the conventional pilot frequency allocation method when the number M of active users in a certain time frame is different. Although as M increases, more and more users are in the time slot, the network becomes more and more crowded, and the probability of successful user access is lower, 1-v ind, the hybrid automatic request mechanism effectively suppresses the increase of failure probability. Compared with the pilot frequency distribution method in the traditional scheme, the pilot frequency distribution method provided by the invention can obviously reduce the collision probability of users.
In the embodiment, at least 10 8 Monte Carlo simulation experiments are carried out on each numerical simulation result, and the experimental results prove that the accuracy of the model construction is high, and the matching degree of the numerical simulation results and the analysis results is high.
In summary, the pilot frequency distribution method provided by the invention can meet the reliability requirement of a mass machine type communication environment on users, namely, the access success rate is more than or equal to 99.9 percent (the failure probability is less than 0.1 percent). The analysis principle used by the invention can be used for the same hybrid automatic request mechanism class scheme. The pilot frequency distribution method provided by the invention can provide pilot frequency distribution reference for the access mechanism of the hybrid automatic request mechanism.
Embodiments of the present invention have been described in detail so far. In order to avoid obscuring the concepts of the invention, some details known in the art have not been described. How to implement the technical solutions disclosed herein for deploying unlicensed access schemes in cellular networks will be fully apparent to those skilled in the art from the above description.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations and modifications of the present invention will be apparent to those of ordinary skill in the art in light of the foregoing description. It is not necessary here nor is it exhaustive of all embodiments. And obvious variations or modifications thereof are contemplated as falling within the scope of the present invention.
Claims (10)
1. An unlicensed access pilot allocation method based on a hybrid automatic request mechanism is characterized by comprising the following steps:
s1, representing a model of unauthorized random access of a mass machine type communication system under a hybrid automatic repeat request mechanism by utilizing a relation between a single user access failure probability and a pilot frequency number distributed by a base station for a shared pilot frequency pool, wherein the hybrid automatic repeat request mechanism comprises the shared pilot frequency pool and a special pilot frequency pool, and the process for establishing the model specifically comprises the following steps: calculating the probability of success of all users accessing the shared pilot pool once in a certain time frame by adopting a probability theory and a random geometry method, deducing the probability of success of single user accessing the shared pilot pool once and the probability of failure of accessing once, and further solving the probability of failure of single user accessing the shared pilot pool for preset times K times; if the user still fails after the shared pilot frequency pool is accessed for K times, the special pilot frequency pool is used for transmission, the probability of the access failure of the single user in the special pilot frequency pool is obtained, and finally the access failure probability of the single user is obtained;
S2, constructing an analytic type of the number of users using the special pilot pool; utilizing Monte Carlo simulation data and adopting least square fitting to use analytic type of special pilot pool user quantity probability;
S3, obtaining a closed analytic expression of the single user access failure probability in S1 under the pilot frequency number distributed by different base stations for the shared pilot frequency pool according to the analytic expression of the user number probability of the special pilot frequency pool in S2; and obtaining the minimum failure probability of a single user when the massive machine type communication system uses a hybrid automatic repeat request mechanism to perform unauthorized random access through an optimizing algorithm, calculating the pilot frequency number of the shared pilot frequency pool and the pilot frequency number of the special pilot frequency pool at the moment, and guiding the massive machine type communication system to perform pilot frequency distribution.
2. The method for allocating unlicensed access pilots based on the hybrid automatic request mechanism according to claim 1, wherein the calculating the probability P that all users access once in the shared pilot pool for a certain time frame is:
Wherein N 0＝CNS, for ease of analysis, takes the strict lower bound of the formula:
Wherein C is the number of channels of the shared pilot pool, N S is the number of pilots allocated by the base station for the shared pilot pool, and M is the number of active users in the current time frame.
3. The method for allocating unlicensed access pilots based on the hybrid automatic request mechanism according to claim 2, wherein the probability ρ of a single user accessing the shared pilot pool once is: the probability v of the single user failing to access the shared pilot frequency pool once is:
4. The method for allocating unlicensed access pilots based on the hybrid automatic request mechanism according to claim 3, wherein the probability v S of the single user failing to access the shared pilot pool for a preset number of times K is:
since the last time frame will join the current time frame when the failed paired user repeatedly accesses, the number of active users in the current time frame increases from M to m+2.
5. The method for assigning unlicensed access pilots based on a hybrid automatic request mechanism according to claim 4, wherein the probability of failure of access of the single user in the dedicated pilot pool v D is:
where u is the number of users using the dedicated pilot pool, equal to the number of users still failed to access for K times using the shared pilot pool, u e {1,2, …, M }; p (u)
The probability of u for the user using the dedicated pilot pool is denoted as p (u) =f (M, N S);ND is the number of pilot frequencies allocated by the base station for the dedicated pilot pool.
6. The method for assigning unlicensed access pilots based on a hybrid automatic request mechanism according to claim 5, wherein the single user access failure probability v ind is:
where u is the number of users using the dedicated pilot pool, equal to the number of users still failed to access for K times using the shared pilot pool, u e {1,2, …, M }; p (u)
For the probability of u using the dedicated pilot pool, p (u) =f (M, N S);NS is the number of pilots allocated by the base station for the shared pilot pool, N D is the number of pilots allocated by the base station for the dedicated pilot pool, M is the number of active users in the current time frame, and C is the number of channels in the shared pilot pool.
7. The method for assigning unlicensed access pilots based on the hybrid automatic request mechanism according to claim 6, wherein the analytical formula p (u) of the number probability of users using the dedicated pilot pool is:
Wherein a, b, c, d, e is a coefficient, and g is a constant term according to the value of the number u of users using the special pilot pool; the application range of the analytical formula p (u) =f (M, N S) using the number probability of the dedicated pilot pool users is M e {6,7,8, …,20}.
8. The method for allocating the unauthorized access pilot frequency based on the hybrid automatic request mechanism according to claim 7, wherein the method is characterized in that a damping newton method-based optimizing algorithm is adopted to obtain the minimum failure probability of a single user when the hybrid automatic repeat request mechanism is used by a mass machine type communication system for unauthorized random access, and the damping newton method is based on the principle that: constructing a function g (x) =v ind,x＝NS, selecting an initial point of the function g (x), approximating the function g (x) by using a first derivative and a second derivative at the initial point, then taking a minimum point of the approximated function as a new iteration point, and continuously repeating the process until the minimum point x 0,g(x0 meeting the error requirement is found, namely the minimum failure probability.
9. The method for assigning unlicensed access pilots based on a hybrid automatic request mechanism according to claim 8, wherein a line search algorithm is used to determine a step size when damping newton's method is iterated, thereby reducing the number of iterations.
10. The method for assigning unlicensed access pilots based on a hybrid automatic request mechanism according to claim 8, wherein the minimum probability of failure of single-user access and the number of shared pilot pool pilots at that time N 0＝x0 are obtained by rounding upRounding downwards to obtainCalculation ofAndIndividual user access failure probabilityAndAnd compare ifThen selectThe pilot frequency number as the shared pilot frequency pool is selected otherwiseThe pilot number as a shared pilot pool; the number of pilots in the dedicated pilot pool, N D＝N-NS, where N is the total number of pilots.
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| CN109195228A (en) * | 2018-11-01 | 2019-01-11 | 国网重庆市电力公司电力科学研究院 | A kind of leading code distributing method of machine type communication random access procedure |
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| CN109195228A (en) * | 2018-11-01 | 2019-01-11 | 国网重庆市电力公司电力科学研究院 | A kind of leading code distributing method of machine type communication random access procedure |
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