CN109963319B - Graded access method for mass power distribution and utilization data - Google Patents
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- H04L5/00—Arrangements affording multiple use of the transmission path
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Abstract
The invention relates to a hierarchical access method of massive power distribution and utilization data, which adopts 2 continuous access subframes as the conflict judgment basis of random access, each subframe selects a leader sequence according to a leader sequence resource pool of base station broadcast information, thereby increasing an adoptable leader sequence set, effectively reducing the probability of random access collision of massive power distribution and utilization services and improving the concurrent access rate of the massive services; the problems that the concurrency access rate which can be supported by the traditional LTE random access method is low, and delay, blockage, packet loss and the like can be caused in a massive concurrency access scene of power distribution and consumption services of the smart power grid are solved. The base station allocates the existing leader sequence resource pool to the services of different grades according to the access requirements of the services of different grades, thereby avoiding access conflict among the services of different priorities and effectively protecting the access rate of the services of high priority. The invention provides a leader sequence resource pool configuration and transmission mechanism, which is simple and feasible and has strong operability.
Description
Technical Field
The invention relates to the technical field of data access, in particular to a hierarchical access method for mass power distribution and utilization data.
Background
At present, in a smart grid, service terminals capable of transmitting through a wireless broadband private network of electric power include a distribution network automation terminal, a metering automation terminal, an electric vehicle charging pile, a new energy access terminal and the like. The types of terminals are various, and the data transmission is characterized in that: the single transmission data volume is small, the access is very frequent, and the number of the access terminals is huge. Therefore, such a power-dedicated terminal is collectively referred to as an M2M (Machine-to-Machine) device.
The random access process of the uplink of the LTE system adopts an asynchronous access mode, namely when a terminal does not obtain uplink time synchronization or loses synchronization, the random access process is used for the eNodeB to estimate and adjust the uplink transmission clock of the UE, and the process is also used for the UE to request resource allocation to the eNodeB. The eNodeB responds to the UE's non-synchronized random access attempt by transmitting time information to the UE to adjust uplink transmission timing and allocate uplink resources for transmitted data or control signaling, and the timing information and uplink data resource allocation may also be transmitted to the UE in combination. The random access procedure has two modes: firstly, based on the random access of competition, all equipment access the base station competitively, collision is inevitable, so the mode is suitable for the access request which can tolerate time delay; and secondly, random access without competition, wherein the base station reserves a part of resources for scenes which have high access rate, such as handover. The primary step of the M2M device attempting to upload data through the power wireless private network is to initiate a random access request, and data transmission can be performed after the base station agrees with the base station and obtains wireless resources, and the random access mode of the M2M device is contention access. In the LTE system, there are 64 available preamble sequences in each cell, and for the contention-based random access procedure, the UE randomly selects one preamble sequence to initiate the random access procedure to the network side, so if multiple UEs use the same preamble sequence to initiate the random access procedure at the same time, a collision occurs, which may result in access failure. The contention-free random access uses the leader sequence allocated by the eNodeB to initiate the random access process, so the access success rate is higher. However, considering that the eNodeB can know in advance that the UE needs to initiate the random access process only in two scenarios, i.e., handover or downlink data transmission, the eNodeB can use contention-free random access only in the two scenarios, and can only use contention-based random access for other application scenarios.
Before discussing the LTE system random access in detail, it is necessary to introduce the following random access channel. The base station continuously broadcasts the access channel parameters, and the M2M device to be accessed can acquire the frequency and time period of the random access channel from the broadcast channel. Generally speaking, the random access channel occupies 1.08MHz spectrum, corresponding to 6 resource blocks, which is also the lowest LTE bandwidth configuration; in the time domain, the random access channel is a periodic subframe, and the LTE specifies 64 kinds of periodic distributions, which are specified by "physical layer random access configuration index" in broadcasted system information. Since the random access channel occupies the uplink bandwidth, it is necessary to configure the index parameter according to the current transmission load condition to balance the mutual constraints of access and transmission.
The competitive random access procedure includes four information handshakes of the base station and the terminal, as shown in fig. 1. The access request is successfully completed only if the four-way handshake is completed. The following is a brief explanation of the four-way handshake:
MSG 1: and transmitting the leader sequence. The base station informs all terminals of the random access channel parameters and the leader sequence set which can be used for competitive access through broadcasting system information. After the M2M device to be accessed determines an access channel, a sequence transmission is randomly selected from the preamble sequence set. The LTE protocol specifies that a total of 64-clock preamble sequences are available, with a portion of the sequence reserved for non-contention access. The preamble sequences are orthogonal to each other, and the base station can distinguish different sequence accesses at the uplink receiving end, so that a plurality of M2M devices select different preamble sequences in the same access channel time slot and no conflict exists. The time domain length of the preamble sequence can be adjusted (1-3ms) according to the size of the cell coverage radius. The 3GPP protocol specifies that M2M device waits 3 sub-frame (3ms) time windows after transmitting MSG1 for the base station to reply to MSG2, the time window parameters being obtained from the system information broadcast by the base station, ranging from 2-10 ms.
MSG 2: and (4) random access feedback. And after the base station completes the decoding of the preamble sequence, calculating a network temporary identity (RA-RNTI) according to the time slot transmitted by the sequence. The random access feedback information is transmitted through a physical downlink shared channel and comprises the following data:
1. an acknowledgement ACK signal decoded for the preamble sequence;
2. an uplink channel time synchronization adjustment instruction;
3. an uplink radio resource allocation for MSG3 transmissions;
4. network temporary identifiers (RA-RNTIs), wherein different sequences and time slots correspond to different RA-RNTIs;
5. and the back-off time parameter is used for selecting the back-off time after the access failure.
At this stage, two M2M devices select the same preamble sequence to transmit the request in the same time slot, and the base station can find the collision according to the difference of the arrival time and abandon the transmission of MSG 2. When the distance difference between the two devices and the base station is not large, the time delay difference is small, the two signals are superposed at the receiving end of the base station, and the collision cannot be detected, which can cause the collision of the MSG 3.
MSG 3: and (6) connection request. The M2M device sends a connection request using an automatic hybrid retransmission mechanism over the divided resources in MSG 2. The request signal includes a unique identifier (C-RNTI) for each M2M device. Multiple devices occupying the same channel necessarily cause collisions and correct reception of MSG3 can only be accomplished through multiple retransmissions.
MSG 4: and (5) conflict resolution. The M2M receives the correct conflict resolution signaling to identify the successful access, otherwise, the access fails, and the MSG1 request is reinitiated after the backoff period. When the number of access failures reaches a certain number (the base station broadcasts signaling to configure the parameters), the cellular network is not available and the information is sent to the upper layer application.
The random access specified by the LTE protocol is of a slotted ALOHA type, namely, a terminal starts an access request when data is sent, a plurality of terminals access simultaneously to generate collision so as to cause frame damage, each terminal judges whether the access is successful according to feedback signaling, and if the access is failed, the frame can be retransmitted after waiting for a period of random time. The 3GPP organization has carried out a study on the random access limitations [1] [2], and the system model assumes that the period of random access is 5ms, that is, 200 accesses can be started within 1s, of 64 preamble sequences, 10 are reserved for non-contention access, and the remaining 54 are used for contention access. Under this assumption, 10,800 preamble sequence accesses can be allowed within 1s, which is fully satisfied for the current power M2M service deployment situation, but this number is the maximum capacity without collision. Due to the collision caused by the same leader sequence and the adopted evading delayed retransmission, the actual access capacity is far lower than the maximum capacity.
In the actual scene of the power wireless private network, there are many situations, and the access performance is adversely affected by the LTE random access procedure. For example, after the power failure is recovered, all devices start to access the network after being electrified; the metering terminal uploads the electricity consumption data at regular time (for example, in a period of 5 minutes). If the number of access terminals is known, an optimal queuing access mode can be preset, but in practical situations, services with uncertain number can only be accessed through a random access process. Therefore, in a specific application scenario of the smart grid, massive concurrent access brings problems of blocking, time delay, power consumption and the like.
Disclosure of Invention
The invention provides a method for grading access of mass power distribution and utilization data to solve one or more of the defects.
In order to solve the technical problems, the invention adopts the technical scheme that: a hierarchical access method for mass power distribution and utilization data is provided, and the random access process of the hierarchical access method comprises the following steps: performing system information and leader sequence resource pool allocation information handshake and four-time information handshake between the base station and the terminal;
the four-way information handshake is as follows:
MSG 1: transmitting a leader sequence; the base station informs all terminals of random access channel parameters, a leader sequence set which can be used for competitive access and leader sequence resource pools of different grades of services through broadcasting system information; after determining an access channel, the M2M device to be accessed randomly selects 2 sequences (2 access subframes) in a preamble sequence set for transmission; according to the size of the cell coverage radius, the time domain length of the leader sequence can be adjusted (1-3 ms; 3GPP protocol stipulates that M2M equipment waits for the base station to reply to MSG2 in a time window of 3 subframes (3ms) after transmitting MSG1, and the time window parameter is obtained by the system information broadcast by the base station and has a range of 2-10 ms;
MSG 2: random access feedback; after finishing the decoding of the leader sequence, the base station calculates the network temporary identifier (RA-RNTI) according to the time slot transmitted by the sequence, and the random access feedback information is transmitted by a physical downlink shared channel and comprises the following data:
1. an acknowledgement ACK signal decoded for the preamble sequence;
2. an uplink channel time synchronization adjustment instruction;
3. an uplink radio resource allocation for MSG3 transmissions;
4. different sequences and slots of network temporary identities (RA-RNTIs) correspond to different RA-RNTIs;
5. the back-off time parameter is used for selecting the back-off time after the access failure;
at this stage, two M2M devices select the same preamble sequence to send a request in the same time slot, and the base station may find a collision according to the difference of arrival times and abandon the sending of MSG 2; when the distance difference between the two devices and the base station is not large, the time delay difference is small, the two signals are superposed at the receiving end of the base station, the collision cannot be detected, and the MSG3 is caused to collide;
MSG 3: a connection request; the M2M equipment adopts an automatic hybrid retransmission mechanism to send a connection request through the frequency-divided resources in the MSG 2; the request signal contains a unique identifier (C-RNTI) for each M2M device; multiple devices occupying the same channel necessarily bring about collision, and correct receiving of the MSG3 can be completed only through multiple retransmissions;
MSG 4: conflict resolution; M2M receives the correct conflict resolution signaling identification, if the access is successful, the access is failed, and after a certain backoff time, the MSG1 request is reinitiated; when the number of access failures reaches a certain number (the base station broadcasts signaling to configure the parameters), the cellular network is not available and the information is sent to the upper layer application.
In the scheme, 2 continuous access subframes are used as a conflict judgment basis for random access, and each subframe selects a leader sequence according to a leader sequence resource pool of base station broadcast information, so that an adoptable leader sequence set is increased, the probability of random access collision of mass power distribution and utilization services is effectively reduced, and the concurrent access rate of the mass services is improved; the problems that the concurrency access rate which can be supported by the traditional LTE random access method is low, and delay, blockage, packet loss and the like can be caused in a massive concurrency access scene of power distribution and consumption services of the smart power grid are solved.
The base station allocates the existing leader sequence resource pool to the services of different grades according to the access requirements of the services of different grades, thereby avoiding access conflict among the services of different priorities and effectively protecting the access rate of the services of high priority. The invention provides a leader sequence resource pool configuration and transmission mechanism, which is simple and feasible and has strong operability.
Preferably, the handshake between the base station and the terminal for performing the system information and the preamble sequence resource pool allocation information is as follows:
the preamble resource pool is set as follows:
the number of leader sequences which can be used for competitive access is N (N is less than or equal to 64), and the number of leader sequence resource pools selected by two continuous access subframes is N multiplied by N, namely the access number of M2M terminals which are simultaneously concurrent; the preamble sequence resource pool for two consecutive access subframe choices is represented as:
Ω＝{(i,j)|0≤i,j<N} (1)
wherein the leader sequence index is i, j, and satisfies that i is more than or equal to 0 and j is less than N;
the power wireless private network base station classifies the existing services in advance, and the power distribution automation service and the metering automation service are considered here, namely, the service is divided into two classes: the distribution automation service is level 1, and the metering automation service is level 2; the leader sequence resource pools selectable by level 1 and level 2 are respectively omega1And Ω2Wherein Ω is1And Ω2Are all subsets of Ω;
D. if the service accesses of different levels are independent, different leader sequence resource pools are used to avoid the conflict of the random accesses of the two services; then it needs to satisfy:
generally, level 1 has a higher priority, and this configuration can ensure effective access of level 1M 2M terminals and avoid access collision between level 1 terminals and level 2 terminals when the number of level 2M 2M terminals is very large;
E. resource pools Ω 1 and Ω 2 are containment relationships; the independent setting can make the leader sequence resource pool of two classes of levels reduce relative to the original resource pool omega, if there are many users of level 2, the increase of the conflict caused by the reduction of the set caused by the splitting of the leader sequence pool needs to be avoided, the alternative setting is:
it should be noted that in this case, the two types of service access conflict;
f, (2) and (3) are two typical settings, and the leader sequence resource pools of the respective levels are adjusted according to specific application scenarios;
the preamble resource pool configuration and transmission specifically include the following:
leader sequence resource pool omega1And Ω2The M2M terminal does not have the configuration information, and needs to be sent to each terminal by the base station ENodeB through broadcast information, determined by the user, i.e. the application server; after analyzing the broadcast information, the terminal randomly selects a leader sequence according to configuration;
the base station transmits the configuration in a plurality of modes, and the base station can send out the resource pool data of each level;
the resource pool omega is divided into M parts, M is an integer, and the serial number of each part is 0, 1. Leader sequence resource pool omega1And Ω2The corresponding serial numbers are respectively lambada 1 ═ i |0 ≦ i<M and Λ 2 ═ i |0 ≦ i<M }; the broadcast information of the base station only needs to contain M, Lambda 1 and Lambda 2 information, thereby greatly reducing the transmitted data volume;
the M2M terminal randomly selects 2 preamble sequences according to the received configuration information M, Lambda 1 and Lambda 2; the preamble resource pool can be expressed as:
wherein,% represents the operation of dividing the integer and taking the remainder; the M2M terminal comprises the following specific operation steps:
3) randomly selecting a first leader sequence i from 0, 1.., M-1;
4) for a level 1M 2M terminal, a second preamble sequence i is randomly selected from 0,1,.. multidot.m-1 based on the first preamble sequence i such that (i + j)% M k k ∈ Λ is satisfied1(ii) a For a level 2M 2M terminal, a second preamble sequence j is randomly selected from 0, 1.. multidot.M-1 based on the first preamble sequence i such that (i + j)% M＝＝k k∈Λ2。
Preferably, the hierarchical access method adopts a mode of 2 access subframes, the maximum number of concurrent users at the same time is 2016, an alternative leader sequence candidate pool is increased, the probability of collision is effectively reduced, and the access rate of the system is improved.
Preferably, the method for calculating the number of concurrent users is as follows:
comprises 2 parts:
1) if two access subframes select the same leader sequence, 64 conditions are totally existed;
2) if two access subframes select different preamble sequences, there are 2016 cases.
Preferably, the method for accessing the mass power distribution and utilization data in a grading manner is used for wireless transmission of power distribution and utilization services of the smart grid.
Preferably, the hierarchical access method is TD-LTE based on a technical system.
Compared with the prior art, the invention has the beneficial effects that: in the scheme, 2 continuous access subframes are used as a conflict judgment basis for random access, and each subframe selects a leader sequence according to a leader sequence resource pool of base station broadcast information, so that an adoptable leader sequence set is increased, the probability of random access collision of mass power distribution and utilization services is effectively reduced, and the concurrent access rate of the mass services is improved; the problems that the concurrency access rate which can be supported by the traditional LTE random access method is low, and delay, blockage, packet loss and the like can be caused in a massive concurrency access scene of power distribution and consumption services of the smart power grid are solved.
The base station allocates the existing leader sequence resource pool to the services of different grades according to the access requirements of the services of different grades, thereby avoiding access conflict among the services of different priorities and effectively protecting the access rate of the services of high priority. The invention provides a leader sequence resource pool configuration and transmission mechanism, which is simple and feasible and has strong operability.
Drawings
Fig. 1 is a flowchart of a hierarchical access method for mass power distribution and utilization data according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be described in detail below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
A hierarchical access method for mass power distribution and utilization data is disclosed, and a flow chart is shown in figure 1:
the random access process of the hierarchical access method comprises the following steps: performing system information and leader sequence resource pool allocation information handshake and four-time information handshake between the base station and the terminal;
the four-way information handshake is as follows:
MSG 1: transmitting a leader sequence; the base station informs all terminals of random access channel parameters, a leader sequence set which can be used for competitive access and leader sequence resource pools of different grades of services through broadcasting system information; after determining an access channel, the M2M device to be accessed randomly selects 2 sequences (2 access subframes) in a preamble sequence set for transmission; according to the size of the cell coverage radius, the time domain length of the leader sequence can be adjusted (1-3 ms; 3GPP protocol stipulates that M2M equipment waits for the base station to reply to MSG2 in a time window of 3 subframes (3ms) after transmitting MSG1, and the time window parameter is obtained by the system information broadcast by the base station and has a range of 2-10 ms;
MSG 2: random access feedback; after finishing the decoding of the leader sequence, the base station calculates the network temporary identifier (RA-RNTI) according to the time slot transmitted by the sequence, and the random access feedback information is transmitted by a physical downlink shared channel and comprises the following data:
1. an acknowledgement ACK signal decoded for the preamble sequence;
2. an uplink channel time synchronization adjustment instruction;
3. an uplink radio resource allocation for MSG3 transmissions;
4. different sequences and slots of network temporary identities (RA-RNTIs) correspond to different RA-RNTIs;
5. the back-off time parameter is used for selecting the back-off time after the access failure;
at this stage, two M2M devices select the same preamble sequence to send a request in the same time slot, and the base station may find a collision according to the difference of arrival times and abandon the sending of MSG 2; when the distance difference between the two devices and the base station is not large, the time delay difference is small, the two signals are superposed at the receiving end of the base station, the collision cannot be detected, and the MSG3 is caused to collide;
MSG 3: a connection request; the M2M equipment adopts an automatic hybrid retransmission mechanism to send a connection request through the frequency-divided resources in the MSG 2; the request signal contains the unique identifier (C-RNTI) of each M2M device, and the conflict is necessarily caused when a plurality of devices occupy the same channel, and the correct receiving of the MSG3 can be completed only through a plurality of retransmissions;
MSG 4: conflict resolution; M2M receives the correct conflict resolution signaling identification, if the access is successful, the access is failed, and after a certain backoff time, the MSG1 request is reinitiated; when the number of access failures reaches a certain number (the base station broadcasts signaling to configure the parameters), the cellular network is not available and the information is sent to the upper layer application.
In the scheme, 2 continuous access subframes are used as a conflict judgment basis for random access, and each subframe selects a leader sequence according to a leader sequence resource pool of base station broadcast information, so that an adoptable leader sequence set is increased, the probability of random access collision of mass power distribution and utilization services is effectively reduced, and the concurrent access rate of the mass services is improved; the problems that the concurrency access rate which can be supported by the traditional LTE random access method is low, and delay, blockage, packet loss and the like can be caused in a massive concurrency access scene of power distribution and consumption services of the smart power grid are solved.
The base station allocates the existing leader sequence resource pool to the services of different grades according to the access requirements of the services of different grades, thereby avoiding access conflict among the services of different priorities and effectively protecting the access rate of the services of high priority. The invention provides a leader sequence resource pool configuration and transmission mechanism, which is simple and feasible and has strong operability.
In this embodiment, the M2M terminal establishes a connection with an eNodeB through a random access procedure (random access procedure) and acquires uplink synchronization. Only when uplink synchronization is obtained, the M2M terminal can perform uplink transmission. Random access is a basic and important process in LTE systems, and its main purpose is as follows:
1) establishing uplink synchronization; 2) and establishing a unique terminal identifier C-RNTI to request the network to allocate uplink resources to the terminal. Therefore, the random access is not only used for initiating access, but also used for new cell access in a switching process, access after radio link failure, uplink synchronization recovery when uplink/downlink data are transmitted, UL-SCH resource request and the like.
In this embodiment, the handshake between the base station and the terminal for performing the system information and the preamble sequence resource pool allocation information is specifically as follows:
the preamble resource pool is set as follows:
the number of leader sequences which can be used for competitive access is N (N is less than or equal to 64), and the number of leader sequence resource pools selected by two continuous access subframes is N multiplied by N, namely the access number of M2M terminals which are simultaneously concurrent; the preamble sequence resource pool for two consecutive access subframe choices is represented as:
Ω＝{(i,j)|0≤i,j<N} (1)
wherein the leader sequence index is i, j, and satisfies that i is more than or equal to 0 and j is less than N;
the power wireless private network base station classifies the existing services in advance, and the power distribution automation service and the metering automation service are considered here, namely, the service is divided into two classes: the distribution automation service is level 1, and the metering automation service is level 2; the leader sequence resource pools selectable by level 1 and level 2 are respectively omega1And Ω2Wherein Ω is1And Ω2Are all subsets of Ω;
G. if the service accesses of different levels are independent, different leader sequence resource pools are used to avoid the conflict of the random accesses of the two services; then it needs to satisfy:
generally, level 1 has a higher priority, and this configuration can ensure effective access of level 1M 2M terminals and avoid access collision between level 1 terminals and level 2 terminals when the number of level 2M 2M terminals is very large;
H. resource pools Ω 1 and Ω 2 are containment relationships; the independent setting can make the leader sequence resource pool of two classes of levels reduce relative to the original resource pool omega, if there are many users of level 2, the increase of the conflict caused by the reduction of the set caused by the splitting of the leader sequence pool needs to be avoided, the alternative setting is:
it should be noted that in this case, the two types of service access conflict;
i, (2) and (3) are two typical settings, and the leader sequence resource pools of the respective levels are adjusted according to specific application scenarios;
the preamble resource pool configuration and transmission specifically include the following:
leader sequence resource pool omega1And Ω2The M2M terminal does not have the configuration information, and needs to be sent to each terminal by the base station ENodeB through broadcast information, determined by the user, i.e. the application server; after analyzing the broadcast information, the terminal randomly selects a leader sequence according to configuration;
the base station transmits the configuration in a plurality of modes, and the base station can send out the resource pool data of each level;
the resource pool omega is divided into M parts, M is an integer, and the serial number of each part is 0, 1. Leader sequence resource pool omega1And Ω2The corresponding serial numbers are respectively lambada 1 ═ i |0 ≦ i<M and Λ 2 ═ i |0 ≦ i<M }; the broadcast information of the base station only needs to contain M, Lambda 1 and Lambda 2 information, thereby greatly reducing the transmitted data volume;
the M2M terminal randomly selects 2 preamble sequences according to the received configuration information M, Lambda 1 and Lambda 2; the preamble resource pool can be expressed as:
wherein,% represents the operation of dividing the integer and taking the remainder; the M2M terminal comprises the following specific operation steps:
5) randomly selecting a first leader sequence i from 0, 1.., M-1;
6) for a level 1M 2M terminal, a second preamble sequence i is randomly selected from 0,1,.., M-1 based on the first preamble sequence i such that (i + j)% M ═ k k ∈ Λ is satisfied1(ii) a For a level 2M 2M terminal, a second preamble sequence j is randomly selected from 0,1,.. times.m-1 based on the first preamble sequence i such that (i + j)% M ═ k k ∈ Λ is satisfied2。
In this embodiment, the hierarchical access method selects a mode of 2 access subframes, and the maximum number of concurrent users at the same time is 2070, so that the selectable leader sequence candidate pool is increased, the probability of collision is effectively reduced, and the access rate of the system is improved.
In this embodiment, the method for calculating the number of concurrent users is as follows:
comprises 2 parts:
1) if two access subframes select the same leader sequence, 64 conditions are totally existed;
2) if two access subframes select different preamble sequences, there are 2016 cases.
In this embodiment, the method for accessing the mass power distribution and utilization data in a grading manner is used for wireless transmission of power distribution and utilization services of the smart grid.
In this embodiment, the hierarchical access method is TD-LTE based on a technical system.
It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.
Claims (5)
1. A hierarchical access method for mass power distribution and utilization data is characterized by comprising the following steps: the random access process of the hierarchical access method comprises the following steps: performing system information and leader sequence resource pool allocation information handshake and four-time information handshake between the base station and the terminal;
the four-way information handshake is as follows:
MSG 1: transmitting a leader sequence; the base station informs all terminals of random access channel parameters, a leader sequence set which can be used for competitive access and leader sequence resource pools of different grades of services through broadcasting system information; after the M2M device to be accessed determines an access channel, randomly selecting 2 sequences in a preamble sequence set, that is, 2 access subframes for transmission; adjusting the time domain length of the leader sequence to 1-3ms according to the size of the cell coverage radius; 3GPP protocol stipulates that M2M equipment waits for a base station to reply to MSG2 in 3-ms subframe time windows after transmitting MSG1, and the time window parameters are acquired through system information broadcasted by the base station and range from 2 ms to 10 ms;
MSG 2: random access feedback; after finishing decoding the leader sequence, the base station calculates a network temporary identifier RA-RNTI according to the time slot transmitted by the sequence; the random access feedback information is transmitted through a physical downlink shared channel and comprises the following data:
s1, an acknowledgement ACK signal for decoding a leader sequence;
s2, an uplink channel time synchronization adjustment instruction is received;
s3, allocating uplink wireless resources for MSG3 transmission;
s4, network temporary identifiers RA-RNTIs, wherein different sequences and time slots correspond to different RA-RNTIs;
s5, selecting backoff time after access failure according to the backoff time parameter;
at this stage, two M2M devices select the same preamble sequence to send a request in the same time slot, the base station finds a collision according to the difference of arrival times, and abandons the sending of MSG 2; when the distance difference between the two devices and the base station is not large, the time delay difference is small, the two signals are superposed at the receiving end of the base station, the collision cannot be detected, and the MSG3 is caused to collide;
MSG 3: a connection request; the M2M equipment adopts an automatic hybrid retransmission mechanism to send a connection request through the frequency-divided resources in the MSG 2; the unique identifier C-RNTI of each M2M device is included in the request signal; multiple devices occupying the same channel necessarily bring about collision, and correct receiving of the MSG3 can be completed only through multiple retransmissions;
MSG 4: conflict resolution; M2M receives the correct conflict resolution signaling identification, if the access is successful, the access is failed, and after a certain backoff time, the MSG1 request is reinitiated; when the access failure times reach a certain number, the times are configured by broadcasting signaling through a base station, a cellular network is unavailable, and the information is sent to an upper layer application;
the handshake for carrying out system information and leader sequence resource pool allocation information between the base station and the terminal is as follows:
the preamble resource pool is set as follows:
making the number of the leader sequences which can be used for competitive access be N, wherein N is less than or equal to 64, and the number of the leader sequence resource pools selected by two continuous access subframes is NxN, namely the access number of the M2M terminals which are simultaneously concurrent; the preamble sequence resource pool for two consecutive access subframe choices is represented as:
Ω＝{(i，j)|0≤i，j<N} (1)
wherein the leader sequence index is i, j, and satisfies that i is more than or equal to 0 and j is less than N;
the power wireless private network base station classifies the existing services in advance, and the power distribution automation service and the metering automation service are considered here, namely, the service is divided into two classes: the distribution automation service is level 1, and the metering automation service is level 2; the leader sequence resource pools selectable by level 1 and level 2 are respectively omega1And Ω2Wherein Ω is1And Ω2All are omega childrenCollecting;
A. if the service accesses of different levels are independent, different leader sequence resource pools are used to avoid the conflict of the random accesses of the two services; then it needs to satisfy:
level 1 has higher priority, and the configuration can ensure the effective access of the M2M terminal of level 1 under the condition that the number of the M2M terminals of level 2 is very large, thereby avoiding the access conflict between the terminal of level 1 and the terminal of level 2;
B. resource pools Ω 1 and Ω 2 are containment relationships; the independent setting can make the leader sequence resource pool of two classes of levels reduce relative to the original resource pool omega, if there are many users of level 2, the increase of the conflict caused by the reduction of the set caused by the splitting of the leader sequence pool needs to be avoided, the alternative setting is:
it should be noted that in this case, the two types of service access conflict;
c, (2) and (3) are two typical settings, and the leader sequence resource pools of the respective levels are adjusted according to specific application scenarios;
the preamble resource pool configuration and transmission specifically include the following:
leader sequence resource pool omega1And Ω2The M2M terminal does not have the configuration information, and needs to be sent to each terminal by the base station ENodeB through broadcast information, determined by the user, i.e. the application server; after analyzing the broadcast information, the terminal randomly selects a leader sequence according to configuration;
the base station transmits the configuration in various modes, and the base station sends out the resource pool data of each level;
the resource pool omega is divided into M parts, M is an integer, and the number of each part is 01, 1.., M-1; leader sequence resource pool omega1And Ω2The corresponding serial numbers are respectively Lambda1I |0 ≦ i < M, and Λ2I |0 ≦ i < M }; the broadcast information of the base station only needs to contain M and Lambda1And Λ2The information is enough, so that the transmitted data volume is greatly reduced;
the M2M terminal receives the configuration information M, Lambda1And Λ2To randomly select 2 preamble sequences; the preamble resource pool can be expressed as:
wherein,% represents the operation of dividing the integer and taking the remainder; the M2M terminal comprises the following specific operation steps:
1) randomly selecting a first leader sequence i from 0, 1.., M-1;
2) for a level 1M 2M terminal, a second preamble sequence i is randomly selected from 0,1,.., M-1 based on the first preamble sequence i such that (i + j)% M ═ k k ∈ Λ is satisfied1(ii) a For a level 2M 2M terminal, a second preamble sequence j is randomly selected from 0,1,.. multidot.m-1 based on the first preamble sequence i, such that (i + j)% M k k ∈ Λ is satisfied2。
2. The hierarchical access method for mass power distribution and utilization data according to claim 1, characterized in that: the hierarchical access method adopts a mode of 2 access subframes, and the maximum number of concurrent users at the same time is 2016.
3. The hierarchical access method for mass power distribution and utilization data according to claim 2, characterized in that: the method for calculating the number of the concurrent users comprises the following steps:
comprises 2 parts:
1) if two access subframes select the same leader sequence, 64 conditions are totally existed;
2) if two access subframes select different preamble sequences, there are 2016 cases.
4. The hierarchical access method for mass power distribution and utilization data according to claim 1, characterized in that: the grading access method of the mass power distribution and utilization data is used for wireless transmission of power distribution and utilization services of the smart grid.
5. The hierarchical access method for mass power distribution and utilization data according to claim 1, characterized in that: the hierarchical access method is TD-LTE based on a technical system.
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