CN107484255B - Method for determining optimal channel number in multi-channel CSMA protocol based on frequency grouping - Google Patents
Method for determining optimal channel number in multi-channel CSMA protocol based on frequency grouping Download PDFInfo
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- CN107484255B CN107484255B CN201710677528.6A CN201710677528A CN107484255B CN 107484255 B CN107484255 B CN 107484255B CN 201710677528 A CN201710677528 A CN 201710677528A CN 107484255 B CN107484255 B CN 107484255B
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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]
- H04W74/0808—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using carrier sensing, e.g. as in CSMA
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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
Abstract
The invention discloses a method for determining the optimal channel number in a multi-channel CSMA protocol based on frequency grouping, which is characterized in that a base station determines the node access load condition of the current base station by detecting the frequency of the random access of nodes in a cell, each node communicates with the base station by using a multi-channel non-continuous carrier sense multiple access mode based on frequency grouping, and in order to ensure the low-delay communication between the nodes and the base station, the base station predicts the average load of a next period of time according to the load change condition, thereby determining the optimal channel number.
Description
Technical Field
The invention relates to a method for determining an optimal channel number in a multi-channel non-continuous carrier sense multiple access protocol based on frequency grouping, belonging to the technical field of random access of the Internet of things.
Background
Machine communication is the most basic communication mode in the era of the internet of things, and is mainly characterized in that seamless data exchange is independently carried out among a large number of equipment nodes without human interference. The application fields of machine communication include aspects of life, such as smart homes, smart health, smart power grids, industrial automation and the like. The biggest characteristic of these applications is the huge number of nodes, for example, in the field of smart meters, in a circular cell with a radius of 2km, the number of meters can be as high as 35760, and in such an environment, how to ensure that a large number of nodes can be successfully accessed in a short time is a crucial issue.
At present, there are many packet access modes aiming at reducing access delay or reducing collision probability, which mainly include grouping according to time, grouping according to space and grouping according to frequency. The most common of the time-grouped methods is time division multiple access, in which each node is assigned the full bandwidth and part of the time. In contrast to this, a common frequency-grouped approach, i.e., frequency division multiple access, where each node is allocated the full time and part of the bandwidth. In the paper by k.s.ko et al, a method based on spatial grouping is introduced, which is characterized in that the position of different judgment nodes is judged according to distance parameter values by using the characteristic that the distance parameter values of the nodes having different distances from a base station are also different, thereby performing grouping. However, the above methods have some disadvantages, and in time division multiple access and frequency division multiple access, the resource allocation method is fixed and cannot adapt to the situation that the number of active nodes in machine communication changes all the time. The position of the node is required to be fixed according to the spatial grouping mode, which greatly limits the application range, and as is well known, a large number of mobile nodes exist in the internet of things, so that the mode cannot be applied to machine communication.
Disclosure of Invention
The invention aims to provide a method for determining the optimal channel number in a multi-channel non-continuous carrier sense multiple access protocol based on frequency grouping, the multi-channel non-continuous carrier sense multiple access protocol based on the frequency grouping can reduce the time delay of node access when the load is large in machine communication, and the method can change the number of transmission channels according to the load so as to enable the protocol to be in the optimal working state all the time.
The invention provides a method for determining the optimal channel number in multi-channel non-continuous carrier sense multiple access based on frequency grouping, which has the technical scheme that: the base station determines the node access load condition of the current base station by detecting the frequency of the random access of the nodes in the cell, each node communicates with the base station by using a multi-channel non-continuous carrier sense multiple access mode based on frequency grouping, in order to ensure the low-delay communication between the nodes and the base station, the base station predicts the average load of a period of time according to the load change condition, determines the optimal channel number and ensures the low delay of the communication. The method comprises the following steps:
(1) the base station determines the initial optimal channel number according to the number of nodes in the cell and the data packet transmission frequency of each node, and broadcasts the optimal channel number n through a downlink broadcast channelopt。
(2) The node which needs to send data monitors the downlink broadcast channel, obtains the value of the optimal channel number, calculates the channel where the node is located and the frequency band which is allowed, and utilizes the non-continuous carrier sense multiple access protocol to carry out data transmission.
(3) And (3) the base station estimates the average load of the next time period according to the instantaneous load in a time period, calculates the optimal channel number of the next time period by using the average load, and repeats the steps (2) and (3) until convergence.
In the step (1), the specific method for calculating the optimal number of channels is as follows:
wherein the content of the first and second substances,
represents the value of an independent variable n when the function obtains the minimum value, wherein n represents the number of channels, D represents the size of a data packet and the unit is kbit, omegamAnd SNR respectively represent the total bandwidth and the receiving-end signal-to-noise ratio when n is 1. p is a radical ofsuccThe probability of successful transmission of a data packet is represented, two conditions are required for successful transmission of the data packet, namely that the channel state is idle when the data packet is transmitted, and no other node can transmit data in the whole cell within a period of time after the data start to be transmitted, and if another node fails to monitor that the channel is busy and starts to transmit data, collision is generated with the currently transmitted data packet, so that access failure is caused. Let p beiAnd psRespectively representing the probability that the channel is idle at the time of transmission and no other node transmits data for a period of transmission,
and
psucc＝pi*ps，gnrepresenting the load in each channel by a calculation method of
M represents the number of nodes in a cell, r represents the frequency of each node applying for access, and n represents the number of channels. T ═ τp+d+，τpWhich indicates the time of transmission of the data packet,dthe interception delay represents that other nodes can intercept the busy channel, and the propagation delay represents the propagation delay of the data packet from the node to the base station. ThetabAnd thetafRespectively indicating that the channel is busy and that there are other nodes within a period of time after the transmissionSending data results in wasted time when it fails.
In step (2), the node determines the channel according to the following method: each node randomly generates a random number within the range of 0 to 1, if the generated random number is within the range, the random number is in a first channel, if the generated random number is within the range, the random number is in a second channel, and so on. The method for calculating the permitted frequency band comprises the following steps:
fiindicating the permitted transmission frequency range of the node in the ith channel, f1And f2Each represents the start-stop frequency of the entire band, and n represents the number of channels.
In step (3), the formula used by the base station to estimate the load in the next period of time is:
wherein g (t) represents the function of the time variation of the times of successful access requests of the base station end, t1And t2Respectively representing the starting and stopping time points of the access number of the statistical data packet of the base station, (t)2-t1) For statistical time duration, t may be set at base station initialization1Is set to 0, t2Set to the length of the statistical time period, then
For counting the access requests, p, successfully received by the base station every second within a time periodsuccThe ratio of the two is the number of access attempts of all nodes per second in the statistical time period.
Advantageous effects
1. The invention can divide the whole frequency band into n sub-channels, reduce the number of nodes participating in competition in each sub-band, improve the probability of successful access, reduce time delay and improve energy efficiency and spectrum efficiency.
2. The invention can continuously adjust the number n of the channels, so that the performance of the whole system is always in the optimal state, and the life cycle of the whole network is further prolonged.
Drawings
Fig. 1 is a diagram of a machine communication network model used in an example of the present invention.
Fig. 2 is a flowchart illustrating a method for determining an optimal number of channels in a non-persistent carrier sense multiple access protocol based on frequency grouping according to an embodiment of the present invention.
Fig. 3 is a flowchart illustrating an uplink random access performed by a detecting node according to an embodiment of the present invention.
Detailed Description
An example of a method for determining an optimal channel number in a non-persistent carrier sense multiple access protocol based on frequency grouping according to the present invention is described in detail below with reference to the accompanying drawings.
Fig. 1 is a model diagram of a machine communication network applicable to an embodiment of the present invention, and as shown in fig. 1, the present invention is applicable to a machine communication network scenario of "base station node + detection node", where the type of machine communication network scenario has features including:
1. and the monitoring node is responsible for acquiring surrounding environment data and uploading the data to the base station node.
2. The monitoring nodes are randomly distributed in the machine communication network, and can directly communicate with the base station node when exchanging data without a relay node.
3. The single-time data uploading amount of the monitoring nodes is small, and the data acquisition time of the nodes is regular.
4. The monitoring node is a battery type device, the energy of the node is limited, and the base station has no limit requirement on energy supply.
5. The monitoring nodes have a dormancy feature, that is, the number of active nodes in the network is changed.
In the embodiment of the invention, the method for determining the optimal channel number in the frequency grouping-based non-persistent carrier sense multiple access protocol applicable to machine communication needs a plurality of steps. As shown in fig. 2, a specific implementation process of a method for determining an optimal channel number in a non-persistent carrier sense multiple access protocol based on frequency grouping includes the following steps:
the method comprises the following steps: the base station estimates the channel load and calculates the initial optimal channel number n according to a formulaopt。
Step two: and the node calculates the channel and the licensed band according to the received channel information.
Step three: and each node performs uplink random access by using a non-continuous carrier sense multiple access protocol according to the allocated uplink resources.
Step four: and the base station counts the successful access times in real time.
Step five: the base station calculates the optimal n according to the average load at intervalsopt。
Step six: and repeating the second, third, fourth and fifth steps.
In the first step, the method for calculating the optimal number of channels in machine communication according to the present invention comprises:
wherein the content of the first and second substances,
represents the value of an independent variable n when the function obtains the minimum value, wherein n represents the number of channels, D represents the size of a data packet and the unit is kbit, omegamAnd SNR respectively represent the total bandwidth and the receiving-end signal-to-noise ratio when n is 1. p is a radical ofsuccThe probability of successful transmission of a data packet is represented, two conditions are required for successful transmission of the data packet, namely that the channel state is idle when the data packet is transmitted, and no other node can transmit data in the whole cell within a period of time after the data start to be transmitted, and if another node fails to monitor that the channel is busy and starts to transmit data, collision is generated with the currently transmitted data packet, so that access failure is caused. Let p beiAnd psRespectively representing the probability that the channel is idle at the time of transmission and no other node transmits data for a period of transmission,
and
psucc＝pi*ps，gnrepresenting the load in each channel by a calculation method of
M represents the number of nodes in a cell, r represents the frequency of each node applying for access, and n represents the number of channels. T ═ τp+d+，τpWhich indicates the time of transmission of the data packet,dthe interception delay represents that other nodes can intercept the busy channel, and the propagation delay represents the propagation delay of the data packet from the node to the base station. ThetabAnd thetafRespectively, indicate the time wasted when a failure occurs due to the channel being busy and other nodes transmitting data for a period of time after transmission.
In step two, the node determines the channel according to the following method: each node randomly generates a random number within the range of 0 to 1, if the generated random number is within the range of [0,1/n), the node is in the first channel, if the generated random number is within the range of [1/n,2/n), the node is in the second channel, and so on. The method for calculating the permitted frequency band comprises the following steps:
fiindicating the permitted transmission frequency range of the node in the ith channel, f1And f2Respectively, the start-stop frequency of the whole channel, and n represents the number of channels.
In the third step, when there is data to be sent, each node uses the corresponding frequency band to perform uplink random access by using the non-persistent carrier sense multiple access method according to the channel where the node is located. The method comprises the following steps that when data needs to be sent, a node monitors whether other nodes transmit the data in an allocated frequency band, if other nodes transmit the data, the node randomly waits for a period of time to monitor the busy and idle state of a channel again, if the node monitors that the channel is idle, the node immediately sends the data, and if the channel is still busy, the node continues to wait for a period of time and then monitors until the channel is idle and immediately sends the data.
In steps four and five, the formula used by the base station to estimate the load for the next period of time is:
wherein g (t) represents the function of the time variation of the times of successful access requests of the base station end, t1And t2Respectively representing the starting and stopping time points of the access number of the statistical data packet of the base station, (t)2-t1) For statistical time duration, t may be set at base station initialization1Is set to 0, t2Set to the length of the statistical time period, then
For counting the access requests, p, successfully received by the base station every second within a time periodsuccThe ratio of the two is the number of access attempts of all nodes per second in the statistical time period.
In step six, the estimated average load of the next time period is used to calculate the optimal number of channels n again according to the method in step oneoptAnd repeating the steps two to five.
Fig. 3 is a timing diagram of a random access application of a monitoring node according to an embodiment of the present invention, where as shown in the figure, a certain node determines whether there is data to be transmitted after starting to operate, and if not, continues to monitor. And if data needs to be transmitted, receiving information about channels, frequencies and the like contained in the downlink control channel. And after the receiving is finished, the channel is intercepted, if the channel is busy, the channel is intercepted again after waiting for a period of time, the data is transmitted immediately after the channel is intercepted to be idle, after the transmission is finished, whether the data needs to be transmitted or not is judged again, if so, the process is continued, and if not, the monitoring is continued.
Claims (4)
1. A method for determining the optimal channel number in a multi-channel CSMA protocol based on frequency grouping is characterized in that: the base station determines the node access load condition of the current base station by detecting the frequency of the random access of the nodes in the cell, each node uses a multi-channel non-continuous carrier sense multiple access mode based on frequency grouping to communicate with the base station, in order to ensure the low-delay communication between the nodes and the base station, the base station predicts the average load of a period of time according to the load change condition and determines the optimal channel number to ensure the low-delay of the communication, and the method comprises the following steps:
(1) the base station determines the initial optimal channel number according to the number of nodes in the cell and the data packet transmission frequency of each node, and broadcasts the optimal channel number n through a downlink broadcast channelopt；
(2) A node needing to send data monitors a downlink broadcast channel, obtains the value of the optimal channel number, calculates the channel where the node is located and the allowed frequency band, and utilizes a non-continuous carrier sense multiple access protocol to carry out data transmission;
(3) and (3) the base station estimates the average load of the next time period according to the instantaneous load in a time period, calculates the optimal channel number of the next time period by using the average load, and repeats the steps (2) and (3) until convergence.
2. The method of claim 1, wherein: in the step (1), the specific method for calculating the initial optimal channel number is as follows:
wherein the content of the first and second substances,
represents the value of an independent variable n when the function obtains the minimum value, wherein n represents the number of channels, D represents the size of a data packet and the unit is kbit, omegamAnd SNR respectively represents a total bandwidth and a receiving-end signal-to-noise ratio when n is 1; p is a radical ofsuccThe probability of successful transmission of the data packet is represented, two conditions are required for successful transmission of the data packet, namely the channel state is required to be idle when the data packet is transmitted, and the number of times that other nodes cannot be transmitted in the whole cell within a period of time after the data transmission is started is respectively representedAccordingly, if another node fails to monitor that the channel is busy and starts to transmit data, the another node collides with the currently transmitted data packet to cause access failure; let p beiAnd psRespectively representing the probability that the channel is idle at the time of transmission and no other node transmits data for a period of transmission,
and
psucc＝pi*ps，gnrepresenting the load in each channel by a calculation method of
M represents the number of nodes in a cell, r represents the frequency of each node applying for access, and n represents the number of channels; t ═ τp+d+，τpWhich indicates the time of transmission of the data packet,dan interception delay indicating that other nodes can intercept the busy channel, a propagation delay indicating that a data packet is transmitted from a node to a base station, thetabAnd thetafRespectively, indicate the time wasted when a failure occurs due to the channel being busy and other nodes transmitting data for a period of time after transmission.
3. The method of claim 1, wherein: in step (2), the node determines the channel according to the following method: each node randomly generates a random number within the range of 0 to 1, if the generated random number is within the range of [0,1/n), the random number is in a first channel, and if the generated random number is within the range of [1/n,2/n), the random number is in a second channel, and so on; the method for calculating the permitted frequency band comprises the following steps:
fiindicating the permitted transmission frequency range of the node in the ith channel, f1And f2Are respectively provided withDenotes the start-stop frequency of the entire band, and n denotes the number of channels.
4. The method of claim 1, wherein: in step (3), the formula used by the base station to estimate the load in the next period of time is:
wherein g (t) represents the function of the time variation of the times of successful access requests of the base station end, t1And t2Respectively representing the starting and stopping time points of the access number of the statistical data packet of the base station, (t)2-t1) For statistical time length, at the initialization of the base station, t is set1Is set to 0, t2Set to the length of the statistical time period, then
For counting the access requests, p, successfully received by the base station every second within a time periodsuccThe ratio of the two is the number of access attempts of all nodes per second in the statistical time period.
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| CN102300257A (en) * | 2011-07-21 | 2011-12-28 | 西北工业大学 | Channel booking mechanism-based multi-channel multi-address access method in wireless ad hoc network |
| CN102781115A (en) * | 2012-08-03 | 2012-11-14 | 西安电子科技大学 | Automatic channel selection method based on channel order in dense wireless fidelity (WiFi) |
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