CN113891489B - Frequency hopping-based contention random access method and device - Google Patents
Frequency hopping-based contention random access method and device Download PDFInfo
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- CN113891489B CN113891489B CN202111205401.7A CN202111205401A CN113891489B CN 113891489 B CN113891489 B CN 113891489B CN 202111205401 A CN202111205401 A CN 202111205401A CN 113891489 B CN113891489 B CN 113891489B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access, e.g. scheduled or random access
- H04W74/08—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access]
- H04W74/0833—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using a random access procedure
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/713—Spread spectrum techniques using frequency hopping
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access, e.g. scheduled or random access
- H04W74/002—Transmission of channel access control information
- H04W74/004—Transmission of channel access control information in the uplink, i.e. towards network
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
Abstract
The invention discloses a contention random access method and a device based on frequency hopping, which combine the time hopping based on synchronous frequency hopping with a random access preamble in a random access time slot, and construct a two-dimensional random access preamble set based on synchronous frequency hopping in a time domain and a code domain for transmitting Msg1 messages in the contention random access process; dividing the generated two-dimensional random access preamble set into different subsets according to the difference of the number of frequency points occupied in the time hopping process, wherein the different subsets are used for supporting competing random access with different priorities. The invention solves the problems of larger probability of multiuser random access conflict, larger influence of power control and far-near effect on the performance of the competitive random access, weaker capability of supporting multi-priority competitive random access and the like caused by the limitation of random access resources of the competitive random access in a frequency hopping system.
Description
Technical Field
The present invention relates to the technical field of contention random access communication based on four-way handshake, and in particular, to a contention random access method and apparatus based on frequency hopping.
Background
Contention random access based on four-way handshake has been widely used in mobile communication networks and in self-organizing networks with centers, and its specific flow is shown in fig. 1, which is also called "four-step" access method.
(1) Msg1: mobile user sends random access preamble to base station/control node
The message is uplink information, which is sent by the mobile user, and received by the base station/control node. The mobile user selects a preamble sequence to be transmitted, and transmits a random access preamble code to the base station using a designated transmission power on a random access channel resource indicated by a higher layer.
The mobile user selects a preamble to transmit using the preamble sequence index set. When triggering random access, a mobile user firstly determines a preamble set according to the priority to be sent and the path loss size, and supposedly set B is applied to a scene with low priority service and smaller path loss, and set A is applied to a scene with high priority service or larger path loss. After determining the preamble set, the mobile user randomly selects one preamble from the set.
The transmission power setting of the initial preamble sequence is based on open loop estimation, ensuring that the received power of the preamble sequence is independent of the path loss; for transmission of retransmission preamble sequences, the base station may configure the preamble sequence power ramp up such that the transmission power of each retransmission sequence is increased by a fixed step size.
(2) Msg2: base station/control node sends random access response message to mobile user
After receiving the random access preamble sent by the mobile user, the base station/control node sends a random access response grant to the mobile user on the downlink channel, where the random access response grant must be sent within a specified random access response window. Msg2 may carry information such as a backoff (backoff) delay parameter, a preamble sequence identifier detected by a base station/control node, a mobile user uplink transmission timing alignment instruction, and an initial uplink resource to which Msg3 grants transmission.
After the mobile user has sent the random access preamble, the mobile user will monitor the downlink channel in the specified random access response window (the start and end of the random access response window are set by the base station/control node and broadcast as part of the system information), and receive the Msg2 sent by the base station/control node.
After the mobile user sends the preamble, different operations are performed according to different base station/control node response results, and an example of a processing strategy is given below:
-if an Msg2 message is detected at time frame n and parsed into a corresponding transmitted preamble sequence, transmitting an Msg3 message at a time slot specified by Msg2 of time frame n or time frame n+1 according to this corresponding information.
If an Msg2 message is detected at time frame n, but the parsing finds that it does not contain a transmitted preamble sequence, the mobile user will retransmit the preamble sequence no later than n +5 time frames before if required by higher layers.
If no Msg2 message is detected on time frame n, the mobile user will retransmit the preamble sequence no later than n+4 time frames before if required by higher layers.
-if no Msg2 message is detected on time frame n and the random access procedure is triggered by data arrival, if required by higher layers, the mobile user initiates a random access within time frame n or time frame n+1.
(3) Msg3: mobile user sends Msg3 message to base station/control node
After receiving the random access response Msg2 of the base station/control node, the mobile user sends an Msg3 message on an uplink channel and carries or sends an L2/L3 message. The L2/L3 message contains the purpose of the exact random access procedure and related information such as connection establishment request, tracking area update, scheduling request.
If multiple mobile users send the same preamble sequence, the conflicting mobile users will receive the same uplink resource grant from the random access response grant, and the L2/L3 message is sent on the same time-frequency resource, and interference exists among the multiple mobile users, so that the message sent by the conflicting mobile users cannot be decoded. The Msg3 message sent by the mobile user can be retransmitted but the collision still exists. For this reason, contention resolution is required.
(4) Msg4: base station/control node sends competition decision message to mobile user
If the base station/control node correctly decodes the Msg3 message sent by a certain mobile user, the mobile user is considered to be successfully accessed, and a competition judgment message is sent to the mobile user. The contention resolution message Msg4 may include information such as a contention resolution identifier, a successful access user ID, a random access result, and parameters sent by the mobile user in the Msg3 message.
And when the mobile user successfully receives the Msg4 message containing the own competition resolution identification during the starting of the competition decision timer, the random access is considered to be successful, otherwise, the random access is considered to be failed. The base station/control node will allocate time-frequency resources required for data transmission for the mobile users that successfully access the contention resolution.
The carrier frequency needs to be changed frequently as the name implies, the carrier frequency is hopped in a similar way of 'beating a gun to change a place', a rule of changing the carrier frequency in the frequency hopping communication is called a frequency hopping pattern, and the frequency hopping pattern is determined in a pseudo-random mode. The two parties to communication can communicate only after knowing the frequency hopping pattern of each other and synchronizing with each other. Therefore, the frequency hopping system is a strictly synchronous system, has the capabilities of resisting interference and interception, can share spectrum resources, and is widely applied to the current modern military communication. In addition, the frequency hopping communication can also be applied to civil communication, and can resist fading, multipath and inter-network interference, and the spectrum utilization efficiency is improved.
As shown in fig. 2, a schematic diagram of a time frame structure of a simple frequency hopping system is given. In the frequency hopping system, a time frame is composed of N_D downlink time slots and N_U uplink time slots, and a time slot with a length of t_s contains n_hop_f frequency hopping points (n_hop_f > 1), and each frequency hopping point is selected in a determined frequency hopping set containing N_F frequencies in a pseudo-random mode. The minimum unit of system resource scheduling and use is a time slot, and the time slot can be further divided into a synchronous time slot for synchronization, a broadcast time slot for broadcasting information, a control time slot for transmitting control information, a service time slot for transmitting service and a random access time slot for transmitting random access message Msg1 according to different purposes of transmitting the message.
Assuming that the single-shot frequency hopping system uses the general time frame structure and adopts a competition random access mechanism based on four-way handshake to complete corresponding network access operation, the competition random access has the following defects:
(1) Because the frequency hopping system needs to comprehensively consider the system overhead, the time slots available for random access are less, and meanwhile, the processing capacity limit of equipment is considered, the number of random access preambles available for competing for random access is not large, so that the collision probability is larger under the condition that a plurality of users are accessed simultaneously, namely the capability of supporting the simultaneous access of a plurality of users is not strong.
(2) If there is no power control or power control is not ideal when the contention random access transmits the random access preamble, the existing contention random access mechanism is greatly affected by the 'near-far effect', which is easy to cause the decrease of the detection performance of the random access preamble and affect the random access capability of the system.
(3) The existing competitive random access mechanism can distinguish the priority of random access through different random access preamble groups, the priority level which can be supported is limited, and the number of the random access preamble codes is required to be larger, which is not beneficial to the detection of the random access preamble codes.
The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person of ordinary skill in the art.
Disclosure of Invention
The invention aims to provide a contention random access method and a device based on frequency hopping, which can combine the time hopping based on synchronous frequency hopping with a random access preamble in a random access time slot, and construct a two-dimensional random access preamble set based on synchronous frequency hopping in a time domain and a code domain for transmitting Msg1 messages in the contention random access process; meanwhile, the two-dimensional random access preamble set is divided into different subsets according to the difference of the number of frequency points occupied in the time hopping process, and the different subsets are used for supporting the competitive random access with different priorities, in short, the subset with more occupied frequency points is used for supporting the higher priority of the competitive random access; in addition, the transmission time (frequency point) occupied by any two sequences of the same subset is not identical, and even if the influence of the far-near effect is obvious, the probability of correctly detecting the two-dimensional random access preamble can be obviously increased.
It is assumed that the single-shot synchronous frequency hopping system uses a general time frame structure as shown in fig. 3, wherein the number of downlink time slots n_d=10, the number of uplink time slots n_u=10, the time slot length t_s=10 ms, any one time slot is formed by n_hop_f=10 frequency hopping points, each frequency hopping point is selected in a determined frequency hopping set containing n_f=1024 frequencies in a pseudo-random manner, 2 random access time slots are configured in each time frame, and network operations of initial access, network synchronization, resource application, auxiliary positioning and the like are completed by adopting a contention random access mechanism based on four-way handshake.
In order to achieve the above object, the present invention provides a contention random access method based on frequency hopping, including:
step 1, a mobile user sends an Msg1 message, the mobile user needing to perform competition random access constructs a two-dimensional random access lead code, then selects an available random access time slot or a designated random access time slot to send the random access Msg1 message containing the two-dimensional random access lead code, monitors a downlink channel in a designated random access response window after the mobile user sends the random access lead code, receives an Msg2 message sent by a base station/a control node, and the beginning and the end of the random access response window are set by the base station/the control node and are used as partial system information broadcast;
step 2, the base station/control node sends Msg2 information, the base station/control node continuously detects each random access time slot in a time frame, records the detected random access lead code and the transmission time of the random lead code, recovers the time hopping pattern corresponding to each random access lead code according to the information, then determines the received two-dimensional random access lead code according to the time hopping pattern and the random access lead code, and sends random access response Msg2 information in the following downlink time slot, wherein the received two-dimensional random access lead code identification and the uplink resource authorization of Msg3 information corresponding to the two-dimensional random access lead code are included;
step 3, the mobile user sends Msg3 information, after receiving the random access response Msg2 of the base station/control node, the mobile user sends Msg3 information on the uplink channel and carries or sends related control information, the related control information comprises the purpose of the definite random access process and related information such as connection establishment request, tracking area update and scheduling request, and after sending the Msg3 information, the mobile user waits for competition judgment Msg4 information sent by the base station/control node;
and 4, the base station/control node transmits an Msg4 message, the base station/control node correctly decodes the Msg3 message transmitted by the mobile user, the mobile user is successfully accessed, the competition judgment Msg4 message is transmitted to the mobile user, the competition judgment Msg4 message comprises a competition resolution identification transmitted by the mobile user in the Msg3 message, a successfully accessed user ID, a random access result and parameter information, and the base station/control node allocates time-frequency resources required by data transmission for the mobile user successfully accessed by the competition judgment.
Further, in the contention random access process, the time length available for transmitting one random access preamble is t_p, the minimum time unit available for transmitting valid data is t_min, the t_min includes the necessary isolation time between different minimum time units for transmitting valid data, and the two-dimensional random access preamble is constructed as follows:
determining the number n_hop_t=t_p/(t_min×n) of available time hopping moments for transmitting the two-dimensional random access preamble according to the time length t_p and the minimum time unit t_min, wherein n is an integer greater than or equal to 1, and ensuring that n_hop_t is an integer;
determining a maximum time hopping pattern set s_tmap according to the number n_hop_t of time hopping moments, and further dividing the time hopping pattern into n_s time hopping pattern subsets s_tmap_sub according to the number of time hopping moments in the time hopping pattern, wherein the n_s time hopping pattern subsets s_tmap_sub are used for supporting n_s levels of competing random access priorities, and the higher the access priorities are represented by the subsets with the larger number of time hopping moments in the frequency hopping pattern;
according to the size of a time unit t_min multiplied by n, constructing a pseudo-random sequence set s_seq which has good autocorrelation characteristics and cross correlation characteristics and can effectively distinguish different code words, setting the number of pseudo-random sequences in the set meeting the requirement as n_seq, and dividing the pseudo-random sequence set into m_s pseudo-random sequence subsets s_seq_sub, wherein m_s is less than or equal to n_seq;
the user selects a time hopping pattern subset s_tmap_sub (i) according to the requirement of the competition random access priority, selects a time hopping pattern tmap (j) in the subset, then selects a pseudo random sequence in a pseudo random sequence set s_seq as a random access preamble seq (k), and calls the code word as a basic code word of a two-dimensional random access preamble;
the determined time hopping pattern tmap (j) is combined with the random access preamble seq (k), i.e. the random access preamble seq (k) is transmitted at the transmission moment determined by the time hopping pattern tmap (j), forming a two-dimensional random access preamble seq_dim (tmap (j), seq (k)) for the user to initiate the contention random access.
Further, the user selects a time hopping pattern subset s_tmap_sub (i) according to the requirement of the contention random access priority, selects a time hopping pattern tmap (j) in the subset, then determines a corresponding pseudo random sequence subset s_seq_sub (f (s_tmap_sub (i)) according to the selected time hopping pattern subset s_tmap_sub (i) according to the determined mapping rule, and selects a pseudo random sequence in the subset as a random access preamble seq (k), namely a basic codeword of the two-dimensional random access preamble.
Further, the set of pseudo-random sequences s_seq is constructed using a Zadoff-Chu sequence to determine the random access preamble seq (k) of the mobile user, for the generation of the set of time hopping patterns s_tmap, when n_hop_t is small, all possible time hopping patterns are listed by way of enumeration, and when n_hop_t is large, the set of time hopping patterns meeting the requirements is generated using the pseudo-random sequences.
Further, in the step 3 and the step 4, when the plurality of mobile users send the same preamble sequence, the conflicting mobile users receive the same uplink resource grant from the random access response Msg2 message, the Msg3 message is sent on the same time-frequency resource, and at this time, interference exists among the plurality of mobile users, so that the message sent by the conflicting mobile users cannot be decoded; and the mobile user also comprises a competition judgment timer, when the mobile user successfully receives the Msg4 message containing the own competition resolution identification during the starting period of the competition judgment timer, the random access is considered to be successful, otherwise, the random access is considered to be failed.
The invention also provides a contention random access device based on frequency hopping, which is applied to a base station/a control node and comprises the following components:
a receiving module, configured to receive an Msg1 message sent by a mobile user, where the mobile user needs to perform contention random access constructs a two-dimensional random access preamble, then select an available random access time slot or a designated random access time slot to send a random access Msg1 message containing the two-dimensional random access preamble, after the mobile user sends the random access preamble, monitor a downlink channel in a designated random access response window, receive an Msg2 message sent by a base station/control node, where the start and end of the random access response window are set by the base station/control node and broadcast as part of system information;
the processing module is used for continuously detecting each random access time slot in a time frame by the base station/the control node, recording the detected random access lead codes and the transmission time of the random lead codes, recovering the time hopping pattern corresponding to each random access lead code according to the information, and determining the received two-dimensional random access lead codes according to the time hopping pattern and the random access lead codes;
the sending module is used for sending a random access response Msg2 message at the subsequent downlink time slot, and the base station/control node comprises a received two-dimensional random access preamble identifier and uplink resource authorization of an Msg3 message corresponding to the two-dimensional random access preamble;
the receiving module is further configured to receive an Msg3 message sent by a mobile user, send the Msg3 message on an uplink channel after the mobile user receives a random access response Msg2 of a base station/a control node, and carry or send a related control message, where the related control message includes a specific purpose of a random access process and related information, such as a connection establishment request, a tracking area update, and a scheduling request, and wait for a contention decision Msg4 message sent by the base station/the control node after the mobile user sends the Msg3 message;
the processing module is further used for correctly decoding the Msg3 message sent by the mobile user by the base station/control node, so that the mobile user is successfully accessed, the sending module is further used for sending a competition judgment Msg4 message to the mobile user, the competition judgment Msg4 message comprises a competition resolution identification sent by the mobile user in the Msg3 message, a successfully accessed user ID, a random access result and parameter information, and the base station/control node allocates time-frequency resources required by data transmission for the mobile user successfully accessed by the competition judgment.
Further, in the contention random access process, the time length available for transmitting one random access preamble is t_p, the minimum time unit available for transmitting valid data is t_min, the t_min includes the necessary isolation time between different minimum time units for transmitting valid data, and the processing module constructs a two-dimensional random access preamble as follows:
determining the number n_hop_t=t_p/(t_min×n) of available time hopping moments for transmitting the two-dimensional random access preamble according to the time length t_p and the minimum time unit t_min, wherein n is an integer greater than or equal to 1, and ensuring that n_hop_t is an integer;
determining a maximum time hopping pattern set s_tmap according to the number n_hop_t of time hopping moments, and further dividing the time hopping pattern into n_s time hopping pattern subsets s_tmap_sub according to the number of time hopping moments in the time hopping pattern, wherein the n_s time hopping pattern subsets s_tmap_sub are used for supporting n_s levels of competing random access priorities, and the higher the access priorities are represented by the subsets with the larger number of time hopping moments in the frequency hopping pattern;
according to the size of a time unit t_min multiplied by n, constructing a pseudo-random sequence set s_seq which has good autocorrelation characteristics and cross correlation characteristics and can effectively distinguish different code words, setting the number of pseudo-random sequences in the set meeting the requirement as n_seq, and dividing the pseudo-random sequence set into m_s pseudo-random sequence subsets s_seq_sub, wherein m_s is less than or equal to n_seq;
the user selects a time hopping pattern subset s_tmap_sub (i) according to the requirement of the competition random access priority, selects a time hopping pattern tmap (j) in the subset, then selects a pseudo random sequence in a pseudo random sequence set s_seq as a random access preamble seq (k), and calls the code word as a basic code word of a two-dimensional random access preamble;
the determined time hopping pattern tmap (j) is combined with the random access preamble seq (k), i.e. the random access preamble seq (k) is transmitted at the transmission moment determined by the time hopping pattern tmap (j), forming a two-dimensional random access preamble seq_dim (tmap (j), seq (k)) for the user to initiate the contention random access.
Further, the user selects a time hopping pattern subset s_tmap_sub (i) according to the requirement of the contention random access priority, selects a time hopping pattern tmap (j) in the subset, then determines a corresponding pseudo random sequence subset s_seq_sub (f (s_tmap_sub (i)) according to the selected time hopping pattern subset s_tmap_sub (i) according to the determined mapping rule, and selects a pseudo random sequence in the subset as a random access preamble seq (k), namely a basic codeword of the two-dimensional random access preamble.
Further, the set of pseudo-random sequences s_seq is constructed using a Zadoff-Chu sequence to determine the random access preamble seq (k) of the mobile user, for the generation of the set of time hopping patterns s_tmap, when n_hop_t is small, all possible time hopping patterns are listed by way of enumeration, and when n_hop_t is large, the set of time hopping patterns meeting the requirements is generated using the pseudo-random sequences.
Further, if multiple mobile users send the same preamble sequence, the conflicting mobile users receive the same uplink resource grant from the random access response Msg2 message, the Msg3 message is sent on the same time-frequency resource, and at this time, interference exists among the multiple mobile users, so that the message sent by the conflicting mobile users cannot be decoded; and the mobile user also comprises a competition judgment timer, when the mobile user successfully receives the Msg4 message containing the own competition resolution identification during the starting period of the competition judgment timer, the random access is considered to be successful, otherwise, the random access is considered to be failed.
Compared with the prior art, the following technical points are provided:
(1) In the random access time slot, combining the time hopping based on synchronous frequency hopping with the random access preamble, and constructing a two-dimensional random access preamble set based on synchronous frequency hopping in a time domain and a code domain for transmitting the Msg1 message in the competition random access process.
(2) Dividing the generated two-dimensional random access preamble set into different subsets according to the difference of the number of frequency points occupied in the time hopping process, wherein the different subsets are used for supporting competing random access with different priorities.
The invention has the following beneficial effects:
the contention random access method based on frequency hopping effectively reduces the conflict probability of multi-user random access and improves the performance of random access under the condition that the number of random access lead codes and the number of time-frequency resources available for random access are limited; reducing the influence of near-far effect on the detection capability of the random access preamble under the condition that the random access preamble is transmitted without power control or the power control is not ideal; in addition, the support of multi-user multi-priority contention random access is increased by the selection of available code domain-time domain resources, i.e., the combination of codes and hops.
Drawings
FIG. 1 is a flow chart of a prior art competitive random access "four step" access method;
fig. 2 is a schematic diagram of a time frame structure of a prior art frequency hopping system;
FIG. 3 is a diagram of a general time frame structure of a single-shot synchronous frequency hopping system;
fig. 4 is a flow chart of contention random access based on frequency hopping according to the present invention;
fig. 5 is a diagram of a two-dimensional random access preamble example of an embodiment of the invention;
FIG. 6 is an autocorrelation property diagram of a Zadoff-Chu sequence;
FIG. 7 is a graph of cross-correlation properties of Zadoff-Chu sequences.
Detailed Description
The following detailed description of embodiments of the invention is, therefore, to be taken in conjunction with the accompanying drawings, and it is to be understood that the scope of the invention is not limited to the specific embodiments.
Throughout the specification and claims, unless explicitly stated otherwise, the term "comprise" or variations thereof such as "comprises" or "comprising", etc. will be understood to include the stated element or component without excluding other elements or components.
As shown in fig. 4, the main steps of the contention random access method based on frequency hopping are as follows:
(1) Mobile user sends Msg1 message
The mobile subscriber who needs to perform the contention random access constructs a two-dimensional random access preamble according to the method given in this patent, and then selects an available random access time slot (when there are a plurality of random access time slots in a time frame, the random access time slots are selected according to a predetermined rule, and may be selected randomly or may be selected according to a certain order), and transmits a random access Msg1 message containing the two-dimensional random access preamble.
After the mobile user has sent the random access preamble, the mobile user will monitor the downlink channel in the specified random access response window (the start and end of the random access response window are set by the base station/control node and broadcast as part of the system information), and receive the Msg2 message sent by the base station/control node.
(2) Base station/control node transmitting Msg2 message
The base station/control node continuously detects each random access time slot in the time frame, records the detected random access lead code and the transmission time of the random lead code, recovers the time hopping pattern corresponding to each random access lead code according to the information, and then determines the received two-dimensional random access lead code according to the time hopping pattern and the random access lead code.
In the subsequent downlink time slot, the base station/control node transmits a random access response Msg2 message including, but not limited to, the received two-dimensional random access preamble identity, the uplink resource grant of the Msg3 message corresponding to the two-dimensional random access preamble.
(3) Mobile user sends Msg3 message
After receiving the random access response Msg2 of the base station/control node, the mobile user sends an Msg3 message on an uplink channel and carries or sends a related control message. The relevant control message contains the purpose of the exact random access procedure and relevant information such as connection establishment request, tracking area update, scheduling request, etc.
If multiple mobile users send the same preamble sequence, the conflicting mobile users receive the same uplink resource grant from the random access response Msg2 message, the Msg3 message is sent on the same time-frequency resource, and at this time, interference exists among the multiple mobile users, so that the message sent by the conflicting mobile users cannot be decoded. After the mobile user sends the Msg3 message, waiting for the contention resolution Msg4 message sent by the base station/control node.
And when the mobile user successfully receives the Msg4 message containing the own competition resolution identification during the starting of the competition decision timer, the random access is considered to be successful, otherwise, the random access is considered to be failed.
(4) Base station/control node sends Msg4 message
If the base station/control node correctly decodes the Msg3 message sent by a certain mobile user, the mobile user is considered to be successfully accessed, and a competition judgment Msg4 message is sent to the mobile user.
The contention resolution Msg4 message may include information such as a contention resolution identifier, a user ID of a successful access, a random access result, parameters, etc., sent by the mobile user in the Msg3 message, and may allocate time-frequency resources required for data transmission to the mobile user of which the contention resolution is successful.
In the contention random access procedure based on the four-way handshake, assuming that the time length available for transmitting one random access preamble is t_p and the minimum time unit available for transmitting valid data is t_min (the time t_min includes a necessary isolation time between different minimum time units for transmitting valid data), the two-dimensional random access preamble may be constructed as follows:
(1) And determining the number n_hop_t=t_p/(t_min×n) of available time hopping moments of transmitting the two-dimensional random access preamble according to the time length t_p and the minimum time unit t_min, wherein n is an integer greater than or equal to 1, and ensuring that n_hop_t is an integer.
(2) The maximum time hopping pattern set s_tmap is determined according to the number n_hop_t of time hopping times, and the time hopping patterns are further divided into n_s time hopping pattern subsets s_tmap_sub according to the number of time hopping times in the time hopping patterns, so that the n_s time hopping pattern subsets s_tmap_sub can be used for supporting n_s levels of competing random access priorities, and the subset with the larger number of time hopping times contained in the frequency hopping patterns indicates the higher access priority.
(3) According to the size of the time unit t_min×n, a pseudo-random sequence set s_seq with good autocorrelation characteristics and cross correlation characteristics and capable of effectively distinguishing different codewords is constructed, the number of pseudo-random sequences in the set meeting the requirement is set as n_seq, and the pseudo-random sequence set can be divided into m_s pseudo-random sequence subsets s_seq_sub, wherein m_s is less than or equal to n_seq.
(4) The user selects a time hopping pattern subset s_tmap_sub (i) according to the requirement of the competition random access priority, selects a time hopping pattern tmap (j) in the subset, and then selects a pseudo random sequence in the pseudo random sequence set s_seq as a random access preamble seq (k), and the code word is called as a basic code word of the two-dimensional random access preamble.
(5) Or, the user selects a time hopping pattern subset s_tmap_sub (i) according to the requirement of the contention random access priority, and selects a time hopping pattern tmap (j) in the subset, then determines a corresponding pseudo random sequence subset s_seq_sub (f (s_tmap_sub (i)) according to the selected time hopping pattern subset s_tmap_sub (i) according to the determined mapping rule, and selects a pseudo random sequence in the subset as a random access preamble seq (k), namely, a basic codeword of the two-dimensional random access preamble.
(6) The determined time hopping pattern tmap (j) is combined with the random access preamble seq (k), i.e. the random access preamble seq (k) is transmitted at the transmission moment determined by the time hopping pattern tmap (j), forming a two-dimensional random access preamble seq_dim (tmap (j), seq (k)) for the user to initiate the contention random access.
In the time frame structure of the synchronous frequency hopping system as shown in fig. 2, assuming that a two-dimensional random access preamble constructed by a mobile user uses a time hopping pattern tmap10 (j) = 0100101000 of length 10 and a base codeword seq128 (k) of length 128, the form of the two-dimensional random access preamble is as shown in fig. 5, wherein NULL represents not transmitting in the time-frequency resource, and seq128 (k) represents transmitting the base codeword seq128 (k) in the time-frequency resource.
Zadoff-Chu sequences meet the constant modulus zero auto-correlation characteristic and have the following characteristics, and have been paid attention in recent years and have been applied to 4G and 5G systems. The generator polynomial is as follows, wherein q is a sequence root index, the value {1, …, (NZC-1) }, NZC is the length of the ZC sequence, n=0, 1, …, (NZC-1):
(1) The Zadoff-Chu sequence has a constant amplitude value, and the NZC point discrete Fourier transform of the Zadoff-Chu sequence also has a constant amplitude value, so that the Zadoff-Chu sequence has a very good peak-to-average power ratio;
(2) Zadoff-Chu sequences of arbitrary length have ideal periodic autocorrelation functions, that is, the autocorrelation functions exhibit delta function distribution;
(3) Therefore, a plurality of sequences can be expanded from one Zadoff-Chu sequence, and the expansibility is strong;
(4) The cross-correlation value between Zadoff-Chu sequences is a fixed value of 1/≡zc.
As shown in fig. 6 and 7, zadoff-Chu sequences have good auto-correlation and cross-correlation properties and can be used to construct a set of pseudo-random sequences s_seq to determine the random access preamble seq (k) of a mobile user. For the generation of the time hopping pattern set s_tmap, when n_hop_t is small, all possible time hopping patterns can be listed in an enumerated manner; and when n_hop_t is large, a pseudo-random sequence may be used to generate a satisfactory set of time-hopping patterns.
The invention provides a frequency hopping-based contention random access method, which solves the problems of larger multi-user random access collision probability, larger influence of power control and far-near effect on the performance of contention random access, weaker capability of supporting multi-priority contention random access and the like caused by limited random access resources of contention random access in a frequency hopping system, can be used for the aspects of initial access, network synchronization, resource application, auxiliary positioning and the like of a central civil frequency hopping communication system, and can also be used for the corresponding aspects of a central special frequency hopping communication system.
The foregoing descriptions of specific exemplary embodiments of the present invention are presented for purposes of illustration and description. It is not intended to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application to thereby enable one skilled in the art to make and utilize the invention in various exemplary embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims and their equivalents.
Claims (10)
1. A contention random access method based on frequency hopping, comprising:
step 1, a mobile user sends an Msg1 message, the mobile user needing to perform competition random access constructs a two-dimensional random access lead code, then selects an available random access time slot or a designated random access time slot to send the random access Msg1 message containing the two-dimensional random access lead code, monitors a downlink channel in a designated random access response window after the mobile user sends the random access lead code, receives an Msg2 message sent by a base station/a control node, and the beginning and the end of the random access response window are set by the base station/the control node and are used as partial system information broadcast;
step 2, the base station/control node sends Msg2 information, the base station/control node continuously detects each random access time slot in a time frame, records the detected random access lead code and the transmission time of the random lead code, recovers the time hopping pattern corresponding to each random access lead code according to the information, then determines the received two-dimensional random access lead code according to the time hopping pattern and the random access lead code, and sends random access response Msg2 information in the following downlink time slot, wherein the received two-dimensional random access lead code identification and the uplink resource authorization of Msg3 information corresponding to the two-dimensional random access lead code are included;
step 3, after the mobile user sends the Msg3 message and receives the random access response Msg2 of the base station/the control node, the mobile user sends the Msg3 message on the uplink channel and carries or sends the related control message, wherein the related control message contains the purpose of the exact random access process and related information, and the method comprises the following steps: a connection establishment request, a tracking area update and a scheduling request, and after a mobile user sends an Msg3 message, waiting for a competition judgment Msg4 message sent by a base station/a control node;
and 4, the base station/control node transmits an Msg4 message, the base station/control node correctly decodes the Msg3 message transmitted by the mobile user, the mobile user is successfully accessed, the competition judgment Msg4 message is transmitted to the mobile user, the competition judgment Msg4 message comprises a competition resolution identification transmitted by the mobile user in the Msg3 message, a successfully accessed user ID, a random access result and parameter information, and the base station/control node allocates time-frequency resources required by data transmission for the mobile user successfully accessed by the competition judgment.
2. The contention random access method based on frequency hopping according to claim 1, wherein in the contention random access procedure, a time length available for transmitting one random access preamble is t_p, a minimum time unit available for transmitting effective data is t_min, and the t_min includes a necessary isolation time between different minimum time units for transmitting effective data, and the two-dimensional random access preamble is constructed as follows:
determining the number n_hop_t=t_p/(t_min×n) of available time hopping moments for transmitting the two-dimensional random access preamble according to the time length t_p and the minimum time unit t_min, wherein n is an integer greater than or equal to 1, and ensuring that n_hop_t is an integer;
determining a maximum time hopping pattern set s_tmap according to the number n_hop_t of time hopping moments, and further dividing the time hopping pattern into n_s time hopping pattern subsets s_tmap_sub according to the number of time hopping moments in the time hopping pattern, wherein the n_s time hopping pattern subsets s_tmap_sub are used for supporting n_s levels of competing random access priorities, and the higher the access priorities are represented by the subsets with the larger number of time hopping moments in the frequency hopping pattern;
according to the size of a time unit t_min multiplied by n, constructing a pseudo-random sequence set s_seq which has good autocorrelation characteristics and cross correlation characteristics and can effectively distinguish different code words, setting the number of pseudo-random sequences in the set meeting the requirement as n_seq, and dividing the pseudo-random sequence set into m_s pseudo-random sequence subsets s_seq_sub, wherein m_s is less than or equal to n_seq;
the user selects a time hopping pattern subset s_tmap_sub (i) according to the requirement of the competition random access priority, selects a time hopping pattern tmap (j) in the subset, then selects a pseudo random sequence in a pseudo random sequence set s_seq as a random access preamble seq (k), and calls the code word as a basic code word of a two-dimensional random access preamble;
the determined time hopping pattern tmap (j) is combined with the random access preamble seq (k), i.e. the random access preamble seq (k) is transmitted at the transmission moment determined by the time hopping pattern tmap (j), forming a two-dimensional random access preamble seq_dim (tmap (j), seq (k)) for the user to initiate the contention random access.
3. The contention random access method according to claim 2, wherein the user selects a time hopping pattern subset s_tmap_sub (i) according to the requirement of contention random access priority, and selects a time hopping pattern tmap (j) in the subset, and then determines a corresponding pseudo random sequence subset s_seq_sub (f (s_tmap_sub (i)) according to the selected time hopping pattern subset s_tmap_sub (i) according to a determined mapping rule, and selects a pseudo random sequence in the subset as a base codeword of a random access preamble seq (k), i.e., a two-dimensional random access preamble.
4. A contention random access method based on frequency hopping according to claim 3, characterized in that the set of pseudo random sequences s_seq is constructed with Zadoff-Chu sequences to determine the random access preamble seq (k) of the mobile user, for the generation of the set of time hopping patterns s_tmap, all possible time hopping patterns are listed by means of enumeration when n_hop_t is small, and when n_hop_t is large, the set of time hopping patterns meeting the requirements is generated using pseudo random sequences.
5. The contention random access method according to any one of claims 1-4, wherein in the step 3 and the step 4, a plurality of mobile users transmit the same preamble sequence, so that the conflicted mobile users receive the same uplink resource grant from the random access response Msg2 message, the Msg3 message is transmitted on the same time-frequency resource, and at this time, interference exists among the plurality of mobile users, so that the message transmitted by the conflicted mobile users cannot be decoded; and the mobile user also comprises a competition judgment timer, when the mobile user successfully receives the Msg4 message containing the own competition resolution identification during the starting period of the competition judgment timer, the random access is considered to be successful, otherwise, the random access is considered to be failed.
6. A contention random access device based on frequency hopping, applied to a base station/a control node, comprising:
a receiving module, configured to receive an Msg1 message sent by a mobile user, where the mobile user needs to perform contention random access constructs a two-dimensional random access preamble, then select an available random access time slot or a designated random access time slot to send a random access Msg1 message containing the two-dimensional random access preamble, after the mobile user sends the random access preamble, monitor a downlink channel in a designated random access response window, receive an Msg2 message sent by a base station/control node, where the start and end of the random access response window are set by the base station/control node and broadcast as part of system information;
the processing module is used for continuously detecting each random access time slot in a time frame by the base station/the control node, recording the detected random access lead codes and the transmission time of the random lead codes, recovering the time hopping pattern corresponding to each random access lead code according to the information, and determining the received two-dimensional random access lead codes according to the time hopping pattern and the random access lead codes;
the sending module is used for sending a random access response Msg2 message at the subsequent downlink time slot, and the base station/control node comprises a received two-dimensional random access preamble identifier and uplink resource authorization of an Msg3 message corresponding to the two-dimensional random access preamble;
the receiving module is further configured to receive an Msg3 message sent by a mobile user, and after receiving a random access response Msg2 of a base station/a control node, the mobile user sends the Msg3 message on an uplink channel and carries or sends a related control message, where the related control message includes an exact purpose of a random access process and related information, and the method includes: a connection establishment request, a tracking area update and a scheduling request, and after a mobile user sends an Msg3 message, waiting for a competition judgment Msg4 message sent by a base station/a control node;
the processing module is further used for correctly decoding the Msg3 message sent by the mobile user by the base station/control node, so that the mobile user is successfully accessed, the sending module is further used for sending a competition judgment Msg4 message to the mobile user, the competition judgment Msg4 message comprises a competition resolution identification sent by the mobile user in the Msg3 message, a successfully accessed user ID, a random access result and parameter information, and the base station/control node allocates time-frequency resources required by data transmission for the mobile user successfully accessed by the competition judgment.
7. The contention random access apparatus based on frequency hopping according to claim 6, wherein in the contention random access procedure, a time length available for transmitting one random access preamble is t_p, a minimum time unit available for transmitting valid data is t_min, and the t_min includes a necessary isolation time between different minimum time units for transmitting valid data, and the processing module constructs the two-dimensional random access preamble as follows:
determining the number n_hop_t=t_p/(t_min×n) of available time hopping moments for transmitting the two-dimensional random access preamble according to the time length t_p and the minimum time unit t_min, wherein n is an integer greater than or equal to 1, and ensuring that n_hop_t is an integer;
determining a maximum time hopping pattern set s_tmap according to the number n_hop_t of time hopping moments, and further dividing the time hopping pattern into n_s time hopping pattern subsets s_tmap_sub according to the number of time hopping moments in the time hopping pattern, wherein the n_s time hopping pattern subsets s_tmap_sub are used for supporting n_s levels of competing random access priorities, and the higher the access priorities are represented by the subsets with the larger number of time hopping moments in the frequency hopping pattern;
according to the size of a time unit t_min multiplied by n, constructing a pseudo-random sequence set s_seq which has good autocorrelation characteristics and cross correlation characteristics and can effectively distinguish different code words, setting the number of pseudo-random sequences in the set meeting the requirement as n_seq, and dividing the pseudo-random sequence set into m_s pseudo-random sequence subsets s_seq_sub, wherein m_s is less than or equal to n_seq;
the user selects a time hopping pattern subset s_tmap_sub (i) according to the requirement of the competition random access priority, selects a time hopping pattern tmap (j) in the subset, then selects a pseudo random sequence in a pseudo random sequence set s_seq as a random access preamble seq (k), and calls the code word as a basic code word of a two-dimensional random access preamble;
the determined time hopping pattern tmap (j) is combined with the random access preamble seq (k), i.e. the random access preamble seq (k) is transmitted at the transmission moment determined by the time hopping pattern tmap (j), forming a two-dimensional random access preamble seq_dim (tmap (j), seq (k)) for the user to initiate the contention random access.
8. The contention random access apparatus according to claim 7, wherein the user selects a subset of time hopping patterns s_tmap_sub (i) according to the requirement of contention random access priority, selects a time hopping pattern tmap (j) among the subset, then determines a corresponding subset of pseudo random sequences s_seq_sub (f (s_tmap_sub (i)) according to the selected subset of time hopping patterns s_tmap_sub (i) according to a determined mapping rule, and selects a pseudo random sequence among the subset as a base codeword of a random access preamble seq (k), i.e., a two-dimensional random access preamble.
9. The contention random access apparatus based on frequency hopping according to claim 8, wherein the set of pseudo random sequences s_seq is constructed using Zadoff-Chu sequences to determine the random access preamble seq (k) of the mobile user, and for generation of the set of time hopping patterns s_tmap, all possible time hopping patterns are listed by enumeration when n_hop_t is small, and when n_hop_t is large, the set of time hopping patterns meeting requirements is generated using pseudo random sequences.
10. A contention random access device based on frequency hopping according to any of claims 6-9, wherein a plurality of mobile users send the same preamble sequence, and if a conflicted mobile user receives the same grant of uplink resources from a random access response Msg2 message, the Msg3 message is sent on the same time-frequency resource, and interference exists among the plurality of mobile users, so that the message sent by the conflicted mobile user cannot be decoded; and the mobile user also comprises a competition judgment timer, when the mobile user successfully receives the Msg4 message containing the own competition resolution identification during the starting period of the competition judgment timer, the random access is considered to be successful, otherwise, the random access is considered to be failed.
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