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CN110234129B - Terminal retransmission frequency optimization method in NB-IoT network - Google Patents

Terminal retransmission frequency optimization method in NB-IoT network Download PDF

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CN110234129B
CN110234129B CN201910507454.0A CN201910507454A CN110234129B CN 110234129 B CN110234129 B CN 110234129B CN 201910507454 A CN201910507454 A CN 201910507454A CN 110234129 B CN110234129 B CN 110234129B
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user terminal
resource block
user
channel
matching
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CN110234129A (en
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贾杰
刘瑶
陈剑
王兴伟
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Northeastern University China
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
    • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
    • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W24/00—Supervisory, monitoring or testing arrangements
    • H04W24/02—Arrangements for optimising operational condition
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/53—Allocation or scheduling criteria for wireless resources based on regulatory allocation policies
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/70—Services for machine-to-machine communication [M2M] or machine type communication [MTC]

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Abstract

The embodiment of the disclosure relates to a method for optimizing terminal retransmission times in an NB-IoT network, which comprises the following steps: dividing channel resources in an NB-IoT network into a plurality of resource blocks and serializing the resource blocks according to time to obtain a serialized resource block set; matching a user with a serialized resource block set, and calculating to obtain an efficacy function of the resource block according to a selected channel and retransmission times of the user; and combining an efficacy function based on the resource block with a greedy matching algorithm to realize the mapping relation between the resource block and the user, and combining a matching pair cross algorithm to stably optimize the mapping relation between the resource block and the user, and determining the initial time and the retransmission times of the channel selected by the specific user in the NB-IoT network. The method provided by the disclosure can simultaneously determine the channels used by each NB-IoT user, the initial time and the times of repeatedly sending messages, thereby effectively improving the probability of the NB-IoT user accessing the network and improving the utilization efficiency of resources.

Description

Terminal retransmission frequency optimization method in NB-IoT network
Technical Field
The present disclosure relates to the field of communications technologies, and in particular, to a method for optimizing retransmission times of a terminal in an NB-IoT network.
Background
Narrow-Band Internet of Things (Narrow Band Internet of Things, NB-IoT for short) defined by 3GPP as a Narrow-Band Internet of Things technology based on cellular network can support massive Internet of Things connection with low power consumption requirement, and can be widely applied to the fields of intelligent meter reading, intelligent parking, vehicle tracking, logistics monitoring, intelligent agriculture, forestry, animal husbandry, intelligent wearing, intelligent families, intelligent communities and the like.
The NB-IoT network originates from the mobile Long Term Evolution (LTE), but unlike LTE, the NB-IoT system has only a bandwidth of 180KHz for coverage enhancement, and uses two signaling, namely, a NarrowBand Physical Random Access Channel (NPRACH) and a NarrowBand Physical Uplink Shared Channel (NPUSCH), for resource application and data transmission, where NPRACH is a Channel used for prefix transmission in a Random Access procedure, that is, RACH. In order to meet the wide area coverage (such as 10-30 km coverage radius) and deep coverage (such as 20dB penetration loss) capabilities required by massive Internet of things equipment, a time diversity gain method based on data retransmission is introduced in a random access process (RACH) in an NB-IoT system. In addition, the number of retransmissions can be freely selected for the modulation scheme and the intensity of the coverage used by each terminal. Further, according to the maximum coupling loss, 3GPP defines three coverage strengths of normal coverage, extended coverage and extreme coverage, and in a poor channel environment, the terminal may increase the number of retransmissions to improve the network access rate.
It should be noted that when there are many types of terminals in the network, in order to improve the success probability of the self RACH, the terminal user may frequently increase the number of self retransmissions, and such an increase in the number of non-ordered retransmissions may result in too many resource blocks RB being used for contention, resulting in reduction of RBs used for data transmission, and causing a severe burden on the NB-IoT system.
Based on the above, the existing solutions still have the above problems to be solved.
Disclosure of Invention
Technical problem to be solved
In order to solve the above problems in the prior art, the present disclosure provides a method for optimizing retransmission times of a terminal in an NB-IoT network, which solves the problem that the increase of the disordered retransmission times in the prior art causes a severe burden on an NB-IoT system.
(II) technical scheme
In order to achieve the above purpose, the present disclosure adopts a main technical solution including:
an embodiment of the present disclosure provides a method for optimizing retransmission times of a terminal in an NB-IoT network, including:
dividing channel resources in an NB-IoT network into a plurality of resource blocks and serializing the resource blocks according to time to obtain a serialized resource block set;
matching a user terminal with the serialized resource block set, and calculating to obtain an efficacy function of the resource block according to the selected channel and retransmission times of the user terminal;
and based on the efficacy function of the resource block, combining with a greedy matching algorithm to realize the mapping relation between the resource block and the user terminal, and combining with a matching pair cross algorithm to stably optimize the mapping relation between the resource block and the user terminal, and determining the starting time and the retransmission times of the channel selected by the specific user in the NB-IoT network on the channel.
In an embodiment of the present disclosure, the dividing channel resources in the NB-IoT network into a plurality of resource blocks and performing serialization according to time to obtain a serialized resource block set includes:
serializing a selected channel in the NB-IoT network according to an initial time to obtain a first serialized resource block set;
aggregating the first serialized resource block sets of the selected channel at all times to obtain a second serialized resource block set of the channel;
and aggregating the second serialized resource block sets of all channels in the NB-IoT network to obtain the serialized resource block set of the network.
In an embodiment of the present disclosure, after obtaining the serialized resource block set, the method further includes:
aiming at the user terminal, when the user terminal is matched with the plurality of resource blocks, the corresponding relation between the mapping table of the resource blocks and the channel, the initial time and the retransmission times is searched, and the efficacy function of the user terminal is calculated
Figure GDA0003054433320000031
Wherein UFn(l) As a function of the power when the user terminal n is matched to the resource block l,
Figure GDA0003054433320000032
probability of success of random access process RACH for user terminal n once, t is starting time, n is user terminal, m is channel, n isτIs the number of retransmissions.
In an embodiment of the present disclosure, before calculating the power function of the user terminal, the method further includes:
calculating the SINR value of the transmitted single symbol of the user terminal n at the time t '(t ≦ n ≦ t')τ+ t) the probability of successful transmission of one prefix symbol when channel m is used;
calculating the time t '(t is less than or equal to t' and less than or equal to n) of the user terminal nτ+ t) the probability of successful transmission of a prefix symbol group when channel m is used, wherein the prefix symbol group comprises 4 prefix symbols;
calculating the retransmission n of the prefix symbol group retransmitted by the user terminal nτThe probability of secondary success;
the probability of success of the RACH of the user terminal n once is calculated.
In an embodiment of the present disclosure, the obtaining the power function of the resource block by matching the user terminal with the serialized resource block set and calculating for the selected channel and the number of retransmissions of the user terminal includes:
aiming at the selected resource block, combining the mapping relation between the pre-established resource block and the user terminal to obtain a user terminal set formed by the user terminal corresponding to the selected resource block;
summing the user terminal efficacy functions of the user terminal concentrated user terminals to obtain the efficacy function of the resource block, wherein the formula is as follows:
Figure GDA0003054433320000033
and S is the user terminal set.
In one embodiment of the disclosure, the user terminal n is at time t '(t ≦ n ≦ t' ≦ nτ+ t) the probability of successful transmission of a prefix symbol using channel m is calculated as
Figure GDA0003054433320000034
Wherein
Figure GDA0003054433320000035
For transmitting a signal to interference plus noise ratio SINR value for a single symbol, the formula is:
Figure GDA0003054433320000041
wherein
Figure GDA0003054433320000042
Is an indicative function and if the user terminal n occupies the sub-channel m at time t', then
Figure GDA0003054433320000043
Otherwise
Figure GDA0003054433320000044
σ2Is Gaussian white noise, gammathThe lowest SINR value at which the signal can be recovered is initially set.
In one embodiment of the disclosure, the user terminal n is at time t '(t ≦ t' ≦ n) when the transmission channel is subject to Rayleigh distributionτ+ t) the probability of successful transmission of a prefix symbol when channel m is used is calculated as:
Figure GDA0003054433320000045
wherein
Figure GDA0003054433320000046
In an embodiment of the present disclosure, the greedy matching algorithm is:
creating a first preference list according to the preference value of the user terminal to the resource block;
creating a second preference list according to the preference value of the resource block to the user terminal;
obtaining a user list which is not matched with the resource block according to the first preference list of the user terminal and the second preference list of the resource block;
deleting the resource block with the highest preference value for the user terminal according to a first preference list of the user terminal for the resource block;
and deleting the accepted user terminal from the user list which is not matched with the resource block in an auxiliary way according to the matching state of the current user terminal and the resource block.
In an embodiment of the present disclosure, the matching pair crossing algorithm exchanges resource blocks matched with each other for an exchange pair formed by two user terminals, and it is ensured that a matching relationship between the other user terminals and the resource blocks is not changed.
In one embodiment of the present disclosure, the essential conditions of the exchange pair are: after the two user terminals participating in the exchange the respectively matched resource blocks, the numerical values of the efficacy functions of the two user terminals are not reduced; and after the switching, at least one power function value in the two user terminals is increased.
(III) advantageous effects
The beneficial effects of this disclosure are: the method for optimizing the retransmission times of the terminal in the NB-IoT network provided by the embodiment of the disclosure provides a user channel selection and optimal retransmission times optimization method based on a matching method, and the matching mechanism can simultaneously determine the channel used by each NB-IoT user, the initial time and the times of repeatedly sending messages, thereby effectively improving the probability of accessing the NB-IoT user to the network and improving the utilization efficiency of resources.
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Fig. 1 is a flowchart of a method for optimizing retransmission times of a terminal in an NB-IoT network according to an embodiment of the present disclosure;
FIG. 2 is a flowchart illustrating step S110 in FIG. 1 according to an embodiment of the present disclosure;
FIG. 3 is a flowchart illustrating the calculation of retransmission n in step S120 according to an embodiment of the present disclosureτA flow chart of the probability of secondary RACH success;
fig. 4 is a comparison diagram of the number of switching times for different numbers of ues in an embodiment of the present disclosure;
FIG. 5 is a graph comparing power functions when the number of user terminals is 5 to 60 according to an embodiment of the present disclosure.
Detailed Description
For the purpose of better explaining the present disclosure, and to facilitate understanding thereof, the present disclosure will be described in detail below by way of specific embodiments with reference to the accompanying drawings.
All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein in the description of the disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
In the embodiment related to the present disclosure, when the number of out-of-order retransmissions of a large number of terminals in the network increases, the success probability of the RACH of other users is reduced, and finally, the network performance is drastically reduced. When multi-type terminals with different coverage strengths simultaneously apply for resources, how to match the most appropriate network resources for each terminal and determine the optimal application times of each terminal, the current NB-IoT system is still lack of a relatively clear processing method. Therefore, the present disclosure provides a probability evaluation method for RACH based on retransmission times for a case where multiple heterogeneous terminals simultaneously apply for resources in an NB-IoT system. On the basis, a user channel selection and optimal retransmission time optimization method based on a matching method is provided, and the matching mechanism can simultaneously determine the channels used by the NB-IoT users and the times of repeatedly sending messages, so that the probability of the NB-IoT users accessing the network is effectively improved, and the utilization efficiency of resources is improved.
Fig. 1 is a flowchart of a method for optimizing retransmission times of a terminal in an NB-IoT network according to an embodiment of the present disclosure, and as shown in fig. 1, the method includes the following steps:
as shown in fig. 1, in step S110, dividing channel resources in the NB-IoT network into a plurality of resource blocks and performing serialization according to time to obtain a serialized resource block set;
as shown in fig. 1, in step S120, a power function of the resource block is obtained by matching a user terminal with the serialized resource block set and calculating for a selected channel and retransmission times of the user terminal;
as shown in fig. 1, in step S130, based on the power function of the resource block, a greedy matching algorithm is combined to implement a mapping relationship between the resource block and the user terminal, and a cross matching pair algorithm is combined to perform stable optimization on the mapping relationship between the resource block and the user terminal, so as to determine a channel selected by the specific user in the NB-IoT network, a starting time and a retransmission number on the channel.
In the technical solution provided by the embodiment of the present disclosure shown in fig. 1, a method for optimizing the number of terminal retransmissions in an NB-IoT network based on target detection is provided, which aims to determine channels used by NB-IoT users and the number of times of repeatedly sending messages simultaneously based on a resource allocation mechanism of a matching method.
The specific implementation of the steps of the embodiment shown in fig. 1 is described in detail below:
in step S110, the channel resources in the NB-IoT network are divided into a plurality of resource blocks and are serialized according to time, so as to obtain a serialized resource block set.
In one embodiment of the present disclosure, the base stations in the NB-IoT network are subject to a uniform distribution, and the user terminals UE within each base station coverage are subject to a random distribution. For any base station, the set of terminal devices in that base station is defined as {1,2, … N }. For any user terminal n belonging to the same group, defining the resource repeated application times of the user terminal as nτ. According to the NB-IoT network requirement, the frequency of initiating the resource application by each terminal N is NτAny value of {1,2,4,8,16,32,64,128}, i.e., nτ∈Nτ. Sub-channel set of user terminal based on NPRACH signaling
Figure GDA0003054433320000071
When the bandwidth of each sub-channel is 3.75KHz, M is 48.
In order to construct the one-to-one correspondence relationship between the users and the resource blocks, in the step, a resource sequence method is firstly adopted to serialize the continuous resource blocks on each channel, so that a two-dimensional resource allocation table is mapped into a one-dimensional resource table.
Fig. 2 is a flowchart of step S110 in fig. 1 according to an embodiment of the disclosure, which specifically includes the following steps:
as shown in fig. 2, in step S201, a selected channel in the NB-IoT network is serialized according to a starting time to obtain a first serialized resource block set. For example, for an arbitrary channel m, the serialized resource block set (i.e., the first serialized resource block set) is R according to the difference of the starting time tm,t＝{t+i|t+i＜128,1＜t＜128,i∈Nτ}。
As shown in fig. 2, in step S202, the first serialized resource block set of the selected channel at all time instances is aggregated to obtain a second serialized resource block set of the channel. For example, the serialized resource block R of channel m at all time instants tm,tPerforming aggregation to form a serialized resource block set (i.e., a second serialized resource block set) R of the channel mm＝{Rm,t|1≤t≤127}。
As shown in fig. 2, in step S203, the second serialized resource block sets of all channels in the NB-IoT network are aggregated to obtain the serialized resource block set of the network. For example, set R of serialized resource blocks for all channels mmAggregating to form a set of serialized resource blocks R ═ { R ] for the entire networkm|1≤t≤128}。
In step S120, a power function of the resource block is obtained by matching the user terminal with the serialized resource block set and calculating for the selected channel and the number of retransmissions of the user terminal.
In an embodiment of the present disclosure, after obtaining the serialized resource block set, the method further includes:
for a user terminal (e.g., for a user terminal UEn), when the user terminal is matched with the plurality of resource blocks RBl, calculating a user terminal power function by searching a mapping table of resource blocks and channels, a corresponding relation of a starting time and a retransmission time
Figure GDA0003054433320000081
Wherein UFn(l) As a function of the power when the user terminal n is matched to the resource block l,
Figure GDA0003054433320000082
probability of success of random access process RACH for user terminal n once, t is starting time, n is user terminal, m is channel, n isτIs the number of retransmissions.
In an embodiment of the present disclosure, before calculating the power function of the user terminal, the method further includes:
for any user terminal n, calculating its retransmission nτProbability of secondary RACH success.
FIG. 3 is a flowchart illustrating the calculation of retransmission n in step S120 according to an embodiment of the present disclosureτThe flowchart of the probability of secondary RACH success specifically includes the following steps:
as shown in FIG. 3, in step S301, a user terminal n is calculated at time t '(t ≦ t' ≦ n) based on the SINR value of the transmitted single symbolτ+ t) the probability of successful transmission of one prefix symbol when channel m is used. In one embodiment of the disclosure, the user terminal n is at time t '(t ≦ n ≦ t' ≦ nτ+ t) the probability of successful transmission of a prefix symbol using channel m is calculated as
Figure GDA0003054433320000083
Wherein
Figure GDA0003054433320000084
For transmitting a signal to interference plus noise ratio SINR value for a single symbol, the formula is:
Figure GDA0003054433320000085
wherein
Figure GDA0003054433320000086
Is an indicative function and if the user terminal n occupies the sub-channel m at time t', then
Figure GDA0003054433320000087
Otherwise
Figure GDA0003054433320000088
σ2Is Gaussian white noise, gammathThe lowest SINR value for which signals can be recovered, i.e., the SINR threshold, is initially set.
It should be noted that, when the transmission channel is subject to rayleigh distribution, the user terminal n is at time t '(t ≦ t' ≦ n)τ+ t) the probability of successful transmission of a prefix symbol when channel m is used is calculated as:
Figure GDA0003054433320000089
wherein
Figure GDA0003054433320000091
As shown in FIG. 3, in step S302, the user terminal n is calculated at time t '(t ≦ t' ≦ n)τ+ t) probability of successful transmission of a prefix symbol group comprising 4 prefix symbols when channel m is used.
In one embodiment of the present disclosure, since each symbol group is composed of 4 symbols, and each symbol is transmitted independently, the probability of transmitting one prefix symbol group is:
Figure GDA0003054433320000092
as shown in fig. 3, in step S303, it is calculated that the user terminal n retransmits the prefix symbol group retransmission nτThe probability of secondary success is given by the formula:
Figure GDA0003054433320000093
as shown in fig. 3, in step S304, the probability of success of RACH of user terminal n once is calculated, and the formula is:
Figure GDA0003054433320000094
based on the above formula, the probability of the NB-IoT user accessing the network has a close relationship with the selected channel and the number of retransmissions. Therefore, how to allocate the optimal access channel and retransmission times to each user in this step needs to consider that the matching method can provide a simple and feasible processing method and a resource allocation mechanism based on the matching method for this complex resource optimization problem.
In an embodiment of the present disclosure, the obtaining the power function of the resource block by matching the user terminal with the serialized resource block set and calculating for the selected channel and the number of retransmissions of the user terminal includes:
firstly, aiming at a selected resource block, combining a mapping relation between a pre-established resource block and a user terminal to obtain a user terminal set formed by the user terminal corresponding to the selected resource block; secondly, the power functions of the UEs in the set of UEs are summed to obtain the power function of the resource block, that is, for resource block RBl, the power function depends on the matched UE, the UE set selected by resource block RBl is defined as S, then the power function of RBl is equal to the sum of the power functions of the S UEs, that is, the power function of resource block RBl is:
Figure GDA0003054433320000101
in step S130, based on the power function of the resource block, a greedy matching algorithm is combined to realize a mapping relationship between the resource block and the user, and a cross-matching algorithm is combined to perform stable optimization on the mapping relationship between the resource block and the user, so as to determine a channel selected by the specific user in the NB-IoT network, an initial time and a retransmission frequency on the channel.
In an embodiment of the present disclosure, the greedy matching algorithm in this step is:
creating a first preference list according to the preference value of the user terminal to the resource block;
creating a second preference list according to the preference value of the resource block to the user terminal;
obtaining a user list which is not matched with the resource block according to the first preference list of the user terminal and the second preference list of the resource block;
deleting the resource block with the highest preference value for the user terminal according to a first preference list of the user terminal for the resource block;
and deleting the accepted user terminal from the user list which is not matched with the resource block in an auxiliary way according to the matching state of the current user terminal and the resource block.
The following examples illustrate specific implementations of the above steps and associated code:
Figure GDA0003054433320000102
Figure GDA0003054433320000111
based on the above, it can be seen that when the matching states are different, the corresponding operations are different, for example, when the matching states are satisfied
Figure GDA0003054433320000112
When the conditions are met, the resource block RB accepts all the user terminals which make preference requests, and deletes the accepted user terminals from the unmatched list; when the matching state is not satisfied
Figure GDA0003054433320000113
When the condition is met, the resource block RB accepts q with good preference valuemaxUser terminal ofAnd deleting the accepted user terminal from the unmatched list and continuously keeping the rejected user terminal in the unmatched list.
In an embodiment of the present disclosure, the matching pair crossing algorithm exchanges resource blocks matched with each other for an exchange pair formed by two user terminals, and it is ensured that a matching relationship between the other user terminals and the resource blocks is not changed.
After completing the initialization mapping based on the greedy matching algorithm, in this embodiment, different ue is allowed to exchange resource blocks matched by itself, and swap matching operation (swap matching) is defined as
Figure GDA0003054433320000121
Based on the exchange matching operation, the exchange pair formed by the user terminal n and the user terminal n' exchanges the matched resource block, while keeping the matching between other user terminals and the resource block unchanged.
In one embodiment of the present disclosure, the essential conditions for (n, n') forming an exchange pair are:
(1)
Figure GDA0003054433320000122
(2)
Figure GDA0003054433320000123
wherein the condition (1) indicates that the power function values of two user terminals participating in the exchange are not reduced after the exchange formed by the two user terminals exchanges resource blocks matched with each other; and the condition (2) indicates that at least one of the two ues has an increased power function value after the handover, so that an equivalent cycle can be avoided. Based on the concept of a switching pair, i.e. when a user terminal device wants to switch the matched resource blocks (a single user device wants to complete the switching operation with "hole"), then (n, n ') or (n-k') must be guaranteed
Figure GDA0003054433320000124
Is a switching pair, wherein
Figure GDA0003054433320000125
As empty locations in the RB. For this reason, the matching pair interaction method is defined as follows:
Figure GDA0003054433320000126
based on the above, the matching relationship between the resource block and the user terminal is stabilized through switching.
After initializing and exchanging the matching relationship between the user terminal and the resource block, calculating by combining the efficacy function of the user terminal and the efficacy function of the resource block, and determining the channel and the retransmission times.
If the channel is 3, the maximum retransmission number is 4, and the maximum access user of each RB is 2, the convergence achieved by the algorithm of this embodiment is verified when the number of ues is 10 and 30, and fig. 4 is a comparison graph of the number of switching times for different numbers of ues in an embodiment of the present disclosure. As can be seen from fig. 4, the optimization mechanism designed in this embodiment can better converge, and when the number of users increases, more interactions are required.
Fig. 5 is a comparison graph of power functions when the number of ues is 5 to 60 in an embodiment of the disclosure, and as shown in fig. 5, as the number of network ues increases, the average value of the power functions of resource blocks in the network increases continuously. But since resources are limited, the trend of curve growth tends to be smooth. Meanwhile, it can be found that network performance can be improved by about 15% to 20% on the basis of a greedy matching (GS) algorithm through matching pair interaction operation (SWAP).
In summary, by adopting the embodiments of the present disclosure, a probability evaluation method for RACH based on retransmission times is provided for a situation that multiple heterogeneous terminals simultaneously apply for resources in an NB-IoT system. On the basis, a user channel selection and optimal retransmission time optimization method based on a matching method is provided, and the matching mechanism can simultaneously determine the channels used by the NB-IoT users, the initial time and the times of repeatedly sending messages, so that the probability of accessing the NB-IoT users to the network is effectively improved, and the utilization efficiency of resources is improved.
It should be noted that although in the above detailed description several modules or units of the device for action execution are mentioned, such a division is not mandatory. Indeed, the features and functionality of two or more modules or units described above may be embodied in one module or unit, according to embodiments of the present disclosure. Conversely, the features and functions of one module or unit described above may be further divided into embodiments by a plurality of modules or units.
Through the above description of the embodiments, those skilled in the art will readily understand that the exemplary embodiments described herein may be implemented by software, or by software in combination with necessary hardware. Therefore, the technical solution according to the embodiments of the present disclosure may be embodied in the form of a software product, which may be stored in a non-volatile storage medium (which may be a CD-ROM, a usb disk, a removable hard disk, etc.) or on a network, and includes several instructions to enable a computing device (which may be a personal computer, a server, a touch terminal, or a network device, etc.) to execute the method according to the embodiments of the present disclosure.
Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. This application is intended to cover any variations, uses, or adaptations of the disclosure following, in general, the principles of the disclosure and including such departures from the present disclosure as come within known or customary practice within the art to which the disclosure pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.
It will be understood that the present disclosure is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims (5)

1. A method for optimizing retransmission times of a terminal in an NB-IoT network is characterized by comprising the following steps:
dividing channel resources in an NB-IoT network into a plurality of resource blocks and serializing the resource blocks according to time to obtain a serialized resource block set;
matching a user terminal with the serialized resource block set, and calculating to obtain an efficacy function of the resource block according to the selected channel and retransmission times of the user terminal;
based on the efficacy function of the resource block, combining a greedy matching algorithm to realize the mapping relation between the resource block and the user terminal, and combining a matching pair cross algorithm to stably optimize the mapping relation between the resource block and the user terminal, and determining the initial time and the retransmission times of a channel selected by a specific user in the NB-IoT network on the channel;
the greedy matching algorithm is as follows:
creating a first preference list according to the preference value of the user terminal to the resource block;
creating a second preference list according to the preference value of the resource block to the user terminal;
obtaining a user list which is not matched with the resource block according to the first preference list of the user terminal and the second preference list of the resource block;
deleting the resource block with the highest preference value for the user terminal according to a first preference list of the user terminal for the resource block;
deleting the accepted user terminal from the user list which is not matched with the resource block in an auxiliary way according to the matching state of the current user terminal and the resource block;
the matching pair crossing algorithm is used for exchanging the resource blocks matched with each other for the exchange pair formed by the two user terminals, and the matching relation between other user terminals and the resource blocks is ensured to be unchanged;
the essential conditions of the exchange pair are as follows: after the two user terminals participating in the exchange the respectively matched resource blocks, the numerical values of the efficacy functions of the two user terminals are not reduced; and after the switching, at least one power function value in the two user terminals is increased.
2. The method of claim 1, wherein the dividing channel resources in the NB-IoT network into a plurality of resource blocks and sequencing the resource blocks according to time to obtain a set of sequenced resource blocks comprises:
serializing a selected channel in the NB-IoT network according to an initial time to obtain a first serialized resource block set;
aggregating the first serialized resource block sets of the selected channel at all times to obtain a second serialized resource block set of the channel;
and aggregating the second serialized resource block sets of all channels in the NB-IoT network to obtain the serialized resource block set of the network.
3. The method for optimizing retransmission times for terminals in NB-IoT network according to claim 1, wherein after obtaining the set of sequenced resource blocks, the method further comprises:
aiming at the user terminal, when the user terminal is matched with the plurality of resource blocks, the corresponding relation between the mapping table of the resource blocks and the channel, the initial time and the retransmission times is searched, and the efficacy function of the user terminal is calculated
Figure FDA0003122162880000021
Wherein UFn(l) As a function of the power when the user terminal n is matched to the resource block l,
Figure FDA0003122162880000022
probability of success of random access process RACH for user terminal n once, t is starting time, n is user terminal, m is channel, n isτIs the number of retransmissions.
4. The method for optimizing retransmission times for terminals in NB-IoT network according to claim 3, wherein before calculating the power function of the ue, the method further comprises:
calculating the SINR value of the transmitted single symbol of the user terminal n at the time t '(t ≦ n ≦ t')τ+ t) the probability of successful transmission of one prefix symbol when channel m is used;
calculating the time t '(t is less than or equal to t' and less than or equal to n) of the user terminal nτ+ t) the probability of successful transmission of a prefix symbol group when channel m is used, wherein the prefix symbol group comprises 4 prefix symbols;
calculating the retransmission n of the prefix symbol group retransmitted by the user terminal nτThe probability of secondary success;
the probability of success of the RACH of the user terminal n once is calculated.
5. The method of claim 3, wherein the calculating the power function of the resource block by matching the user terminal with the set of serialized resource blocks and for the selected channel and the number of retransmissions for the user terminal comprises:
aiming at the selected resource block, combining the mapping relation between the pre-established resource block and the user terminal to obtain a user terminal set formed by the user terminal corresponding to the selected resource block;
summing the user terminal efficacy functions of the user terminal concentrated user terminals to obtain the efficacy function of the resource block, wherein the formula is as follows:
Figure FDA0003122162880000031
and S is the user terminal set.
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