CN115038192A - Improved non-time slot CSMA/CA optimization method and evaluation method - Google Patents

Improved non-time slot CSMA/CA optimization method and evaluation method Download PDF

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CN115038192A
CN115038192A CN202210958171.XA CN202210958171A CN115038192A CN 115038192 A CN115038192 A CN 115038192A CN 202210958171 A CN202210958171 A CN 202210958171A CN 115038192 A CN115038192 A CN 115038192A
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probability
backoff
medical data
data packet
retransmission
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CN115038192B (en
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侯睿
王涵
张成俊
田微
张俊敏
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Wuhan Textile University
South Central Minzu University
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South Central University for Nationalities
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    • H04W74/08—Non-scheduled access, e.g. ALOHA
    • H04W74/0808—Non-scheduled access, e.g. ALOHA using carrier sensing, e.g. carrier sense multiple access [CSMA]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
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Abstract

The invention discloses an improved non-time slot CSMA/CA optimization method, which is used for grading medical data; setting the size of an initial backoff window; setting a back-off window and a back-off time slot; carrying out channel detection, adjusting the length of a contention window, and accessing an end node to a channel; and performing backoff according to the setting of the backoff times, and performing retransmission according to the setting of the retransmission times. The invention also discloses an improved non-time slot CSMA/CA optimization evaluation method.

Description

Improved non-time slot CSMA/CA optimization method and evaluation method
Technical Field
The invention belongs to the technical field of wireless sensor networks, and particularly relates to an improved non-time slot CSMA/CA optimization method, and an improved non-time slot CSMA/CA optimization evaluation method, which is suitable for improving the transmission performance of a ZigBee network system.
Background
In a low-speed wireless personal area network, there may be a separation into a beacon-enabled network and a non-beacon-enabled network according to whether a coordinator node among the networks generates a network beacon. In the beacon-enabled network, a common device first needs to listen to a beacon frame in a receiving network, and if the beacon frame is received, the common device synchronizes with a node of a superframe which starts to transmit a beacon, and uses a time slot CSMA/CA algorithm to compete for a channel after synchronization. In the non-beacon-enabled network, when a common node sends data to a coordinator node, a non-slotted CSMA/CA algorithm is used for competing a channel to transmit data packets.
In the MAC protocol based on the non-time slot CSMA/CA algorithm, the purpose of the back-off algorithm is to give a moderate back-off time to the nodes so as to correctly reflect the channel competition situation near the nodes. Most wireless communication protocols adopt binary exponential backoff, and the process of the algorithm is mainly determined by three variables, namely backoff times NB (number of backoffs), contention Window length CW (content Window length), and backoff index BE (backoff exponents). BE has a minimum value of 3, a maximum value of 8, and a backoff counter of [0,2 ] at the standard setting BE -1]By default, CW value of 2.
With the rapid development of wireless sensor networks, the flow rate of network communication is also getting larger and larger, and the situation of serious packet loss rate, high delay and the like due to too large flow rate cannot be tolerated by the medical industry, so stable transmission of data, especially important data, is required to be ensured, most programs require high reliability and low delay, and even some programs require high reliability and low delay at the same time.
Disclosure of Invention
The invention aims to provide an improved non-time slot CSMA/CA optimization method and an improved non-time slot CSMA/CA optimization evaluation method aiming at the problems of the non-time slot CSMA/CA algorithm of the IEEE 802.15.4 network.
In order to achieve the purpose, the invention adopts the following technical scheme:
an improved non-slotted CSMA/CA optimization method, comprising the steps of:
step 1, classifying medical data by a terminal node;
step 2, the terminal node sets the size of an initial backoff window according to the priority of the medical data packet to be transmitted
Figure 606671DEST_PATH_IMAGE001
；
Step 3, setting a backoff window corresponding to the ith backoff
Figure 179603DEST_PATH_IMAGE002
Setting back-off time slots corresponding to medical data packets with different priorities;
step 4, after the terminal node retreats, the terminal node performs channel detection, when the detection channel is idle, the step 5 is skipped, and when the detection channel is busy, the step 6 is skipped;
step 5, when the length CW of a contention window corresponding to the terminal node is reduced by 1 and CW =0, successfully contending the channel, allowing the terminal node to access the channel, and going to step 7;
step 6, adding 1 to the backoff number NB, if the backoff number NB is greater than the maximum backoff number value macmaxCSABackofs, discarding the medical data packet, and turning to the step 2 to transmit the next medical data packet, and if the backoff number NB is not greater than the maximum backoff number value macmaxCSABackofs, turning to the step 3;
step 7, the terminal node starts to transmit the medical data packet to the coordinator node, if the transmission is successful, the step 8 is switched to, and if the transmission is failed, the step 9 is switched to;
step 8, after the coordinator node successfully receives the medical data packet sent by the terminal node, an ACK (acknowledgement) frame is returned to the terminal node, and the step 2 is switched to for the next transmission of the medical data packet;
step 9, adding 1 to the retransmission times FR, discarding the medical data packet if the retransmission times FR is greater than the maximum retransmission times macMaxFrameRetries, returning the error to the upper network, and turning to the step 2 to transmit the next medical data packet; and (4) the retransmission times FR is not more than the maximum value macMaxFrameRetries of the retransmission times, and the step 2 is carried out to continue retransmitting the medical data packet.
Initial backoff window size in step 2 as described above
Figure 428182DEST_PATH_IMAGE003
The macMinBE is the minimum value of the backoff index, and the backoff number initial value is set to 0 as the minimum value macMinBE of the backoff index corresponding to the medical data packet with higher priority is smaller.
As described above, the backoff window corresponding to the ith backoff in step 3
Figure 682446DEST_PATH_IMAGE004
，
Figure 965660DEST_PATH_IMAGE001
For the initial back-off window size,
Figure 883062DEST_PATH_IMAGE005
wherein
Figure 618937DEST_PATH_IMAGE006
is the maximum value of the backoff index macMaxBE,
Figure 411313DEST_PATH_IMAGE007
is the minimum value of the backoff index, macMinBE,
the back-off time slots corresponding to the medical data packets with different priorities are set as
Figure 814612DEST_PATH_IMAGE008
，
Figure 276817DEST_PATH_IMAGE009
Cache team in ZigBee gateway for medical data packetThe cache occupancy of a column is determined,
Figure 624622DEST_PATH_IMAGE010
is a priority factor, X is
Figure 830476DEST_PATH_IMAGE011
An integer within the interval.
An improved non-slotted CSMA/CA optimized evaluation method, comprising the steps of:
step 1, constructing a three-dimensional Markov chain model
Figure 212915DEST_PATH_IMAGE012
；
Wherein,
Figure 111601DEST_PATH_IMAGE013
indicates the number of back-offs at time t,
Figure 451097DEST_PATH_IMAGE014
indicates the state of the backoff counter at time t, the backoff counter having a value of
Figure 195062DEST_PATH_IMAGE011
A random value in between, and a random value,
Figure 432008DEST_PATH_IMAGE015
representing the retransmission times at the time t, defining m to represent the maximum backoff times, and r to represent the maximum retransmission times;
step 2, constructing a formula:
Figure 501595DEST_PATH_IMAGE016
wherein,
Figure 699358DEST_PATH_IMAGE017
denoted as backoff i, backoff window j, probability at retransmission k,
Figure 371648DEST_PATH_IMAGE018
expressed as the i-th backoff, the probability of CCA occurring at the k-th retransmission,
Figure 604046DEST_PATH_IMAGE019
expressed as the probability of successful receipt of the medical data packet,
Figure 969169DEST_PATH_IMAGE020
indicating the probability that the terminal node does not receive the ACK acknowledgement frame after successfully sending the medical data packet,
Figure 388649DEST_PATH_IMAGE021
representing the probability of discarding the medical data packet as a transmission failure of the medical data packet;
Figure 366094DEST_PATH_IMAGE022
Figure 187420DEST_PATH_IMAGE023
Figure 723443DEST_PATH_IMAGE024
Figure 895799DEST_PATH_IMAGE025
Figure 785257DEST_PATH_IMAGE026
wherein,
Figure 851302DEST_PATH_IMAGE027
probability of random backoff being completed for the first time by the terminal node,
Figure 433593DEST_PATH_IMAGE028
a probability is generated for the medical data packet,
Figure 217878DEST_PATH_IMAGE029
as is the probability of a CCA failure,
Figure 911028DEST_PATH_IMAGE030
in order to be the probability of retransmission,
Figure 64535DEST_PATH_IMAGE031
,
Figure 817728DEST_PATH_IMAGE032
，
Figure 964675DEST_PATH_IMAGE033
indicating the time slot length corresponding to the length of the medical data packet,
Figure 586149DEST_PATH_IMAGE034
indicating the ACK acknowledgement frame latency time,
Figure 236574DEST_PATH_IMAGE035
indicating the length of the time slot corresponding to the length of the ACK acknowledgment frame,
Figure 285301DEST_PATH_IMAGE036
indicating the length of the time slot corresponding to the interval of the medical data packet,
Figure 653966DEST_PATH_IMAGE037
indicating ACK timeout time, parameter
Figure 813551DEST_PATH_IMAGE038
，
Figure 584061DEST_PATH_IMAGE039
，
Step 3, defining the generation rate of the medical data packet of the terminal node as
Figure 39576DEST_PATH_IMAGE040
，T 0 Is the unit cycle time of each time slot, T is the interval cycle;
step 4, defining terminal node execution nullProbability of idle channel estimation
Figure 161115DEST_PATH_IMAGE041
Comprises the following steps:
Figure 999758DEST_PATH_IMAGE042
step 5, defining retransmission probability
Figure 483829DEST_PATH_IMAGE043
Comprises the following steps:
Figure 749726DEST_PATH_IMAGE044
wherein,
Figure 217616DEST_PATH_IMAGE045
n represents the number of terminal nodes for the probability of transmission errors;
step 6, defining CCA failure probability
Figure 859950DEST_PATH_IMAGE029
Comprises the following steps:
Figure 464107DEST_PATH_IMAGE046
step 7, solving according to the formula constructed in the steps 2-6 and according to Markov chain normalization
Figure 900904DEST_PATH_IMAGE047
To calculate the probability
Figure 731457DEST_PATH_IMAGE048
Retransmission probability
Figure 529212DEST_PATH_IMAGE043
And probability of CCA failure
Figure 863242DEST_PATH_IMAGE029
The value of (c).
Step 8, calculating the probability of channel access failure
Figure 861153DEST_PATH_IMAGE049
Comprises the following steps:
Figure 913423DEST_PATH_IMAGE050
；
step 9, calculating the probability of packet loss caused by exceeding retransmission limit during transmission
Figure 756614DEST_PATH_IMAGE051
Comprises the following steps:
Figure 210729DEST_PATH_IMAGE052
；
step 10, calculating reliability
Figure 254909DEST_PATH_IMAGE053
The probability of (c) is:
Figure 919108DEST_PATH_IMAGE054
；
step 11, calculating the total delay
Figure 441356DEST_PATH_IMAGE055
Comprises the following steps:
Figure 641656DEST_PATH_IMAGE055
= delay of backoff stage
Figure 591157DEST_PATH_IMAGE056
+ delay of successful transmission of data packet
Figure 477074DEST_PATH_IMAGE057
+ delay of retransmission procedure
Figure 803013DEST_PATH_IMAGE058
；
Figure 231720DEST_PATH_IMAGE059
；
Figure 476757DEST_PATH_IMAGE060
；
Figure 990915DEST_PATH_IMAGE061
；
Wherein,
Figure 979599DEST_PATH_IMAGE062
is a unit time of a time slot,
Figure 262813DEST_PATH_IMAGE063
in order to initiate the back-off window,
Figure 442865DEST_PATH_IMAGE064
a delay indicating a failure in transmission of the medical data packet at the k-th retransmission,
Figure 178740DEST_PATH_IMAGE065
。
compared with the prior art, the invention has the following beneficial effects:
1. the hardware transmission module selected by the invention is a ZigBee module chip CC2530, the ZigBee module adopts a default CSMA/CA algorithm to avoid collision, important data can not be transmitted in time, even serious packet loss occurs, according to the non-time slot CSMA/CA optimization method provided by the invention, the MAC layer protocol in the ZigBee protocol stack is changed, and the medical data packet can be transmitted more stably.
2. Due to the particularity of the medical system, the priority of the medical data packets is set through the priority factor and the cache proportion, so that the transmission proportion of the high-priority data packets is increased in the transmission process, and the transmission of the high-priority data packets is in line with the actual situation.
Drawings
Figure 1 is a diagram of a three-dimensional markov chain model;
FIG. 2 is a graph of the impact of retransmission times on reliability versus comparison;
FIG. 3 is a graph of the effect of maximum backoff number on reliability versus comparison;
FIG. 4 is a graph of the effect of backoff index minimum values on reliability versus comparison;
FIG. 5 is a graph of the effect of retransmission times on delay versus comparison;
fig. 6 is a graph of the effect of maximum backoff number on delay versus comparison;
figure 7 is a graph of the effect of backoff index minimum values on delay versus comparison;
FIG. 8 is a graph of different priority data channel access probabilities;
fig. 9 is a graph of different priority packet throughput.
Detailed Description
The present invention will be further described in detail below with reference to examples in order to facilitate understanding and practice of the invention by those of ordinary skill in the art, and it should be understood that the examples described herein are for illustration and explanation only and are not intended to limit the invention.
In the non-beacon-enabled network, when the terminal node transmits the medical data to the coordinator node, the non-slotted CSMA/CA algorithm is used for competing the channel to transmit the medical data packet. The default CSMA/CA algorithm can not meet the condition that high reliability and low delay are required to be met under the medical condition, and the existing CSMA/CA algorithms only can meet the high reliability and only can meet the low delay, so that the invention optimizes the prior art and provides an improved non-time slot CSMA/CA optimization method, which comprises the following steps:
the medical data is classified by a terminal node, the judgment of the medical data grade mainly depends on the importance of each body index in the treatment process, the main medical data in the medical field comprises physical sign data of a human body, such as heart rate, blood pressure, blood oxygen and the like, alarm signals of emergency situations, distress signals sent by patients and the like, and low-priority medical data, such as environmental temperature, humidity and the like. According to the above medical treatment numberBased on the importance level, the high priority data priority factor
Figure 971116DEST_PATH_IMAGE010
Set to 0.7, low priority data priority factor
Figure 108836DEST_PATH_IMAGE010
And setting the value to be 0.3, and packaging the medical data into a medical data packet by the terminal node for transmission.
Step 2, the terminal node sets the size of an initial backoff window according to the priority of the medical data packet to be transmitted
Figure 836620DEST_PATH_IMAGE001
，
Figure 184425DEST_PATH_IMAGE066
In this embodiment, the minimum value macMinBE of the backoff index of the high-priority medical packet is set to 2, and the minimum value macMinBE of the backoff index of the low-priority medical packet is set to 3. The backoff Number (NB) initial values are all set to 0.
Step 3, setting a back-off window
Figure 655858DEST_PATH_IMAGE067
I is the number of the backoff times,
Figure 772718DEST_PATH_IMAGE001
for the initial back-off window size,
Figure 671404DEST_PATH_IMAGE066
wherein
Figure 742391DEST_PATH_IMAGE006
Is macmaxBE, the maximum value of the backoff index (BE),
Figure 17514DEST_PATH_IMAGE007
is macMinBE, the minimum value of the backoff index (BE).
Scanning slot boundaries in
Figure 129827DEST_PATH_IMAGE011
Randomly selecting an integer within the intervalXAnd then according to the cache occupancy rate of the medical data packets with different priorities in the cache queue of the ZigBee gateway
Figure 58468DEST_PATH_IMAGE009
And a priority factor corresponding to the priority of the medical data packet
Figure 521811DEST_PATH_IMAGE010
To determine the back-off time slot, and to set the back-off time slots corresponding to the medical data packets with different priorities as
Figure 194101DEST_PATH_IMAGE008
. (e.g., a total buffer queue size of 200, where 150 gives high priority data and 50 gives low priority data, then the buffer occupancy for high priority is high priority medical data packets/150 in the queue, and likewise, the buffer occupancy for low priority data is low priority medical data packets/50 in the queue).
And 4, after the terminal node finishes the backoff, the terminal node performs channel detection, and jumps to the step 5 when the detection channel is idle, and jumps to the step 6 when the detection channel is busy.
Step 5, subtracting 1 from the contention window length (CW) corresponding to the terminal node, in this embodiment, it is default that the initial value of the contention window lengths corresponding to all the terminal nodes is 1, when CW =0, the contention channel succeeds, the terminal node is allowed to access the channel, and the process goes to step 7.
And 6, because the channel is busy, the terminal node needs to perform the next backoff, the backoff Number (NB) is added with 1, whether the backoff number NB is greater than the maximum backoff number macmaxCSABackofs or not is judged, if so, the channel competition fails, the medical data packet is discarded, the step 2 is switched to transmit the next medical data packet, and if not, the step 3 is switched to.
And 7, the terminal node is successfully accessed into the channel, the terminal node starts to transmit the medical data packet to the coordinator node, if the transmission is successful, the step 8 is switched, and if the transmission is failed, the medical data packet is retransmitted, and the step 9 is switched.
And 8, after the coordinator node successfully receives the medical data packet sent by the terminal node, returning an ACK (acknowledgement) frame to the terminal node, completing the transmission, and turning to the step 2 to transmit the medical data packet for the next time.
And 9, adding 1 to the retransmission times (FR), judging whether the retransmission times FR is greater than the maximum retransmission times macMaxFrameRetries, if so, discarding the medical data packet, returning the error to an upper network, and turning to the step 2 to transmit the next medical data packet. If the retransmission times are not more than the maximum value macMaxFrameRetries, the step 2 is switched to continue retransmitting the medical data packet.
Example 2:
embodiment 1 describes an improved evaluation method for non-slotted CSMA/CA optimization, comprising the steps of:
establishing a three-dimensional Markov chain model, as shown in FIG. 1
Figure 160920DEST_PATH_IMAGE012
Indicating the state of the terminal node at time t, wherein
Figure 260463DEST_PATH_IMAGE013
Indicates the number of back-offs at time t,
Figure 211101DEST_PATH_IMAGE014
indicates the state of the backoff counter at time t, the backoff counter having a value of
Figure 562448DEST_PATH_IMAGE011
A random value in between, and a random value,
Figure 12802DEST_PATH_IMAGE015
representing the number of retransmissions at time t, for convenient notation, defining m to represent the maximum number of backoff, r to represent the maximum number of retransmissions, and a backoff window
Figure 424192DEST_PATH_IMAGE068
Is shown as
Figure 721181DEST_PATH_IMAGE004
I is the number of the backoff times,
Figure 610639DEST_PATH_IMAGE001
for the initial back-off window size,
Figure 676684DEST_PATH_IMAGE066
wherein
Figure 258975DEST_PATH_IMAGE006
Is macmaxBE, the maximum value of the backoff index (BE),
Figure 653048DEST_PATH_IMAGE069
is macMinBE, the minimum value of the backoff index (BE). The embodiment adopts a single-hop star network topology, wherein the topology comprises a coordinator node and 12 terminal nodes, and the interception ranges of all the nodes are large enough, so that the problem of hidden nodes is not considered.
In order to ensure the reliable transmission of the data frame, a retransmission mechanism is added for the non-time slot CSMA/CA algorithm, after the terminal node sends the data frame to the coordinator node, if the ACK confirmation frame sent by the coordinator node is not received within the specified time, the terminal node accesses the channel again and sends the data frame, the retransmission time (FR) is added with 1, and when the retransmission time reaches the maximum time macMaxFrameReties, the transmission fails.
Suppose the terminal node is at [ nT, (n +1) T]In the time interval of (1), T is an interval period, the nth medical data packet is randomly and uniformly generated every time, and the unit cycle time of each time slot is T 0 Value of 320us, terminal nodeThe medical data packet generation rate of the points is
Figure 470831DEST_PATH_IMAGE070
The time period T is, during the time interval T,
Figure 266749DEST_PATH_IMAGE070
can be calculated as:
Figure 911619DEST_PATH_IMAGE071
the non-time slot CSMA/CA algorithm process can be divided into different stages, namely backoff decrement, CCA, successful data packet reception, non-reception of ACK acknowledgement frame by the terminal node and data packet discarding, according to the rule of Markov chain, the probability sum of all stages is 1, and the following equation is given:
Figure 792987DEST_PATH_IMAGE016
wherein,
Figure 148882DEST_PATH_IMAGE017
denoted as backoff i, backoff window j, probability at retransmission k,
Figure 799306DEST_PATH_IMAGE072
expressed as the i-th backoff, the probability of CCA on the k-th retransmission,
Figure 988979DEST_PATH_IMAGE073
expressed as the probability of successful receipt of the medical data packet,
Figure 482277DEST_PATH_IMAGE020
indicating the probability that the terminal node does not receive the ACK acknowledgement frame after successfully sending the medical data packet,
Figure 517230DEST_PATH_IMAGE021
the probability of discarding the medical data packet is indicated as a transmission failure of the medical data packet.
The probability sum expression for each stage is as follows:
Figure 146794DEST_PATH_IMAGE022
Figure 507368DEST_PATH_IMAGE023
Figure 986498DEST_PATH_IMAGE074
Figure 559561DEST_PATH_IMAGE025
Figure 309212DEST_PATH_IMAGE075
wherein
Figure 840687DEST_PATH_IMAGE076
Probability of random backoff being completed for the first time by the terminal node,
Figure 918365DEST_PATH_IMAGE070
a probability is generated for the medical data packet,
Figure 685332DEST_PATH_IMAGE029
as is the probability of a CCA failure,
Figure 164855DEST_PATH_IMAGE077
in order to be the probability of retransmission,
Figure 726287DEST_PATH_IMAGE031
,
Figure 556839DEST_PATH_IMAGE032
. Here, the
Figure 97804DEST_PATH_IMAGE033
Indicating the time slot length corresponding to the length of the medical data packet,
Figure 697413DEST_PATH_IMAGE078
indicating the ACK acknowledgement frame latency time,
Figure 570691DEST_PATH_IMAGE079
indicating the length of the time slot corresponding to the length of the ACK acknowledgment frame,
Figure 747594DEST_PATH_IMAGE036
indicating the length of the time slot corresponding to the interval of the medical data packet,
Figure 466152DEST_PATH_IMAGE037
indicating an ACK timeout time. To simplify the whole formula, let
Figure 44901DEST_PATH_IMAGE038
，
Figure 89080DEST_PATH_IMAGE039
。
Defining the probability of the terminal node performing Clear Channel Assessment (CCA) in a random time period as
Figure 753280DEST_PATH_IMAGE048
Comprises the following steps:
Figure 275528DEST_PATH_IMAGE081
definition of
Figure 849729DEST_PATH_IMAGE030
If a medical data packet collides with other transmitted medical data packets on the way of transmission or a transmission error is caused by a channel error, the terminal node will try to retransmit the medical data packet until the maximum retransmission number is reached. So there are two reasons for packet lossThe method comprises the following steps: 1) packet loss due to collision, 2) transmission error. Is provided with
Figure 439977DEST_PATH_IMAGE045
Is the probability of transmission error, and therefore retransmission probability
Figure 201260DEST_PATH_IMAGE030
Is defined as:
Figure 651833DEST_PATH_IMAGE082
wherein
Figure 814961DEST_PATH_IMAGE083
And N represents the number of terminal nodes. Similarly, to determine the probability of CCA failure
Figure 59997DEST_PATH_IMAGE029
I.e. the probability of detecting that the channel discovery channel is occupied, the CCA failure probability may be defined as
Figure 839734DEST_PATH_IMAGE029
Divided into two parts, namely the probability of CCA failure during the transmission of medical data packet
Figure 828419DEST_PATH_IMAGE084
And probability of CCA failure at ACK acknowledgement frame transmission
Figure 846054DEST_PATH_IMAGE085
Hence probability of CCA failure
Figure 668516DEST_PATH_IMAGE029
Is defined as:
Figure 30490DEST_PATH_IMAGE086
will be provided with
Figure 432652DEST_PATH_IMAGE084
And
Figure 695006DEST_PATH_IMAGE085
are respectively represented as
Figure 422791DEST_PATH_IMAGE087
Figure 770595DEST_PATH_IMAGE088
Wherein
Figure 242028DEST_PATH_IMAGE035
In order to ACK the frame length is acknowledged,Nthe number of terminal nodes is obtained, so that the CCA failure probability can be deduced
Figure 358889DEST_PATH_IMAGE029
Comprises the following steps:
Figure 991995DEST_PATH_IMAGE046
by combining the above formulas, the normalization of the Markov chain can be obtained
Figure 968041DEST_PATH_IMAGE027
Using numerical solution to calculate the probability of performing the idle channel assessment
Figure 600755DEST_PATH_IMAGE048
Retransmission probability
Figure 447488DEST_PATH_IMAGE043
And probability of CCA failure
Figure 641709DEST_PATH_IMAGE029
The value of (c).
In order to analyze the performance of the algorithm, the reliability and delay of the algorithm are calculated, wherein the reliability is defined as the probability that the coordinator node successfully receives the data packet after the terminal node sends the medical data packet. In non-time slot CSMA/CA, the reason for packet loss is mainlyThere are two: 1) channel access failure, 2) retransmission limit exceeded at transmission. When the backoff times reach the maximum backoff time, the terminal node still cannot sense the idle channel, and the channel access fails, or the medical data packet still cannot sense the idle channel and is discarded when the maximum retransmission times are reached. Probability of channel access failure
Figure 839472DEST_PATH_IMAGE049
Comprises the following steps:
Figure 777341DEST_PATH_IMAGE089
wherein
Figure 744160DEST_PATH_IMAGE090
Expressed as the probability of experiencing the maximum number of back-offs, the probability of packet loss beyond the retransmission limit at transmission
Figure 843703DEST_PATH_IMAGE091
Comprises the following steps:
Figure 794342DEST_PATH_IMAGE092
thus, the reliability can be derived from the above formula
Figure 145689DEST_PATH_IMAGE093
Has a probability of
Figure 593113DEST_PATH_IMAGE094
The delay is defined as the time interval from the generation of a medical data packet by the end node to the reception of an ACK acknowledgement frame by the end node, the discarded medical data packet being without regard to the delay problem. Dividing the total delay into three parts, 1) the delay of the backoff stage
Figure 4502DEST_PATH_IMAGE056
，2)
Figure 35912DEST_PATH_IMAGE095
Figure 190950DEST_PATH_IMAGE057
And 3) delay of retransmission process when terminal node does not receive ACK acknowledgement frame
Figure 991416DEST_PATH_IMAGE096
And thus, the total delay
Figure 839286DEST_PATH_IMAGE055
The expression of (c) is:
Figure 233358DEST_PATH_IMAGE097
when the terminal node performs CCA, if the channel is found to be busy, the terminal node enters a backoff state, and the delay of the backoff stage
Figure 51142DEST_PATH_IMAGE098
The expression is as follows:
Figure 847059DEST_PATH_IMAGE099
wherein,
Figure 229280DEST_PATH_IMAGE062
is a unit time of a time slot,
Figure 845069DEST_PATH_IMAGE063
is the initial backoff window. Since the successfully transmitted data packet length is
Figure 466543DEST_PATH_IMAGE100
It is easy to derive the delay of successful transmission of the data packet
Figure 382547DEST_PATH_IMAGE101
. When the medical data packet is sent to the channel, the sending terminal node cannot receive the medical data packet due to collision or transmission errorWhen ACK frame is received, it enters into retransmission state, and the retransmission process is delayed
Figure 431274DEST_PATH_IMAGE102
The expression of (a) is:
Figure 799939DEST_PATH_IMAGE104
wherein,
Figure 959525DEST_PATH_IMAGE105
indicates a delay of failure in transmission of the medical data packet at the k-th retransmission, an
Figure 464455DEST_PATH_IMAGE106
Due to the fact that
Figure 185549DEST_PATH_IMAGE107
In this embodiment, then,
Figure 775930DEST_PATH_IMAGE065
。
according to the technical scheme provided by the invention, an OMNET + + 5.6.2 platform is used for simulation, and the simulation scene is as follows: the simulation topological structure is a star topology, 1 coordinator node and 12 terminal nodes, and the terminal nodes regularly send medical data packets to the coordinator nodes. To compare the effects of MAC parameters on reliability and delay, three key parameters were chosen, respectively the maximum of the number of retransmissions
Figure 739207DEST_PATH_IMAGE108
Maximum value of backoff number
Figure 629803DEST_PATH_IMAGE109
Minimum value of the backoff index
Figure 895699DEST_PATH_IMAGE110
And (5) performing variable analysis. Experimental setup
Figure 98010DEST_PATH_IMAGE108
Has a value range of [1,7 ]]，
Figure 474765DEST_PATH_IMAGE109
Has a value range of [3,6],
Figure 344501DEST_PATH_IMAGE111
Has a value range of [1,6 ]]Setting transmission error probability
Figure 781298DEST_PATH_IMAGE045
The values of (A) are respectively 0.05, 0.1 and 0.2, the probability of transmission error of each node is the same, and the simulation parameter table is shown in table 1.
TABLE 1 simulation parameter Table
Figure 969441DEST_PATH_IMAGE112
(one), reliability analysis and comparison
And selecting a Biswas model for comparison, wherein the Biswas model is a non-time slot IEEE 802.15.4 network two-dimensional Markov chain analysis model, considers the probability of transmission errors, has no retransmission mechanism, and only analyzes and compares the reliability of the retransmission mechanism. As shown in figure 2 of the drawings, in which,
Figure 149886DEST_PATH_IMAGE110
the setting is 3, and the setting is,
Figure 15074DEST_PATH_IMAGE109
set to 4, it is clear that reliability follows
Figure 747407DEST_PATH_IMAGE108
Becomes larger and larger, and the transmission error probability
Figure 534097DEST_PATH_IMAGE045
Has different values and different reliabilities, when
Figure 49392DEST_PATH_IMAGE045
Relatively small, reliabilityWith following
Figure 34666DEST_PATH_IMAGE108
Become significantly larger when
Figure 265796DEST_PATH_IMAGE108
When the number is more than 5, the reliability becomes larger, because too many retransmissions will cause the probability of collision to become larger, and the packet loss rate becomes larger. Therefore, the number of the first and second electrodes is increased,
Figure 539782DEST_PATH_IMAGE108
not the larger the better, but the more network overhead increases. As shown in figure 3 of the drawings,
Figure 327610DEST_PATH_IMAGE069
the setting is 3, and the setting is,
Figure 262330DEST_PATH_IMAGE108
is set to 3, it can be seen that
Figure 211831DEST_PATH_IMAGE109
The value of (a) has no significant effect on reliability, as shown in figure 4,
Figure 363327DEST_PATH_IMAGE109
the setting is 4, and the setting is,
Figure 689266DEST_PATH_IMAGE108
the setting is 3, and the setting is,
Figure 242607DEST_PATH_IMAGE110
reliability can be improved because
Figure 363010DEST_PATH_IMAGE110
The initial backoff window size is determined to reduce the number of collisions, and the analysis above shows that the main factor affecting reliability is
Figure 877168DEST_PATH_IMAGE108
。
(II) delay analysis and comparison
Also, the effect of three key parameters on delay was analyzed, as shown in FIG. 5, when
Figure 865853DEST_PATH_IMAGE045
When the comparison is small, the comparison result is that,
Figure 149066DEST_PATH_IMAGE108
the effect on the delay is not significant, however when
Figure 57680DEST_PATH_IMAGE113
When larger, the delay follows
Figure 258034DEST_PATH_IMAGE108
Becomes larger because when the pressure is higher than the pressure of the gas
Figure 520388DEST_PATH_IMAGE045
When smaller, most end nodes can transmit successfully without retransmission. As shown in fig. 6, again, only if
Figure 982594DEST_PATH_IMAGE045
When larger, the delay will follow
Figure 330398DEST_PATH_IMAGE109
Becomes larger and becomes larger. As shown in fig. 7, with
Figure 67410DEST_PATH_IMAGE111
Becomes larger, the delay becomes significantly larger because
Figure 59637DEST_PATH_IMAGE110
The initial back-off window is decided upon,
Figure 817377DEST_PATH_IMAGE110
the larger the latency before accessing the channel, the longer, and therefore the main parameter affecting the delay is
Figure 527844DEST_PATH_IMAGE110
。
Because of the CSMA/CA algorithm under the medical system, in order to ensure that important data can be transmitted preferentially, the optimization algorithm can grade the data, the judgment of the data grade mainly depends on the importance of each body index in the treatment process, and the main data in the medical field are divided into the first priority data, the first priority data are physical sign data of a human body, such as heart rate, blood pressure, blood oxygen and the like, the second priority data are environmental temperature, such as temperature, humidity and the like, and the third priority data are other signals, such as an alarm signal in an emergency situation, a distress signal sent by a patient and the like. According to the importance degree of the data, the physical sign data and other signals of the human body are divided into high-priority data, and the environment temperature is divided into low-priority data. As can be seen in the above analysis,
Figure 163487DEST_PATH_IMAGE110
is a main parameter affecting the delay, in order to ensure that high priority data is transmitted first, and therefore given
Figure 275800DEST_PATH_IMAGE110
With initial value set to 2, low priority data
Figure 470021DEST_PATH_IMAGE110
The initial value is set to 3, thereby allowing high priority data to access the channel preferentially, and through simulation experiments, as shown in fig. 8, the high priority data has a higher probability of accessing the channel than the low priority data.
In order to further ensure the prior transmission of high-priority data, the method sets twice priority screening, namely the cache occupancy rate of the cache queue of the ZigBee gateway for the first time
Figure 402205DEST_PATH_IMAGE009
(e.g., a total buffer queue size of 200, where 150 gives high priority data and 50 gives low priority data, then the buffer occupancy of high priority is high priority medical data packets/150 in the queue, and likewise, the buffer occupancy of low priority data is low priority medical data packets in the queue50) of priority data, the second time being a priority factor of the priority data
Figure 340074DEST_PATH_IMAGE010
To determine the back-off time slot, the high priority data priority factor is 0.7, the low priority data priority factor is 0.3, and the back-off time slot is
Figure 41314DEST_PATH_IMAGE011
Random value in betweenXAfter prioritization, the backoff time slot is
Figure 547381DEST_PATH_IMAGE008
Through simulation experiments, as shown in fig. 9, the throughput of high priority packets is higher than that of low priority packets.
In summary, the non-time slot CSMA/CA algorithm and the three-dimensional markov chain model thereof are provided, the expression of reliability and delay is deduced, the influence of three key parameters on the reliability and the delay is verified through simulation experiments, the effectiveness of the provided algorithm is proved, the reliability is increased, the reliable transmission of the whole network is ensured, and the performance of the network is optimized.

Claims (9)

1. An improved non-slotted CSMA/CA optimization method, comprising the steps of:
step 1, classifying medical data by a terminal node;
step 2, the terminal node sets the size of an initial backoff window according to the priority of the medical data packet to be transmitted
Figure 311212DEST_PATH_IMAGE001
；
Step 3, setting a backoff window corresponding to the ith backoff
Figure 723739DEST_PATH_IMAGE002
Setting back-off time slots corresponding to medical data packets with different priorities;
step 4, after the terminal node retreats, the terminal node performs channel detection, when the detection channel is idle, the step 5 is skipped, and when the detection channel is busy, the step 6 is skipped;
step 5, when the length CW of a contention window corresponding to the terminal node is reduced by 1 and the CW =0, successfully contending a channel, allowing the terminal node to access the channel, and going to step 7;
step 6, adding 1 to the backoff number NB, if the backoff number NB is greater than the maximum backoff number value macmaxCSABackofs, discarding the medical data packet, and turning to the step 2 to transmit the next medical data packet, and if the backoff number NB is not greater than the maximum backoff number value macmaxCSABackofs, turning to the step 3;
7, the terminal node starts to transmit the medical data packet to the coordinator node, if the transmission is successful, the step 8 is switched to, and if the transmission is failed, the step 9 is switched to;
step 8, after the coordinator node successfully receives the medical data packet sent by the terminal node, an ACK (acknowledgement) frame is returned to the terminal node, and the step 2 is switched to for the next transmission of the medical data packet;
step 9, adding 1 to the retransmission times FR, discarding the medical data packet if the retransmission times FR is greater than the maximum retransmission times macMaxFrameRetries, returning the error to the upper network, and turning to the step 2 to transmit the next medical data packet; and (4) the retransmission times FR is not more than the maximum value macMaxFrameRetries of the retransmission times, and the step 2 is carried out to continue retransmitting the medical data packet.
2. The improved non-slotted CSMA/CA optimization method of claim 1, wherein the initial back-off window size in step 2 is
Figure 220579DEST_PATH_IMAGE003
The macMinBE is the minimum value of the backoff index, and the backoff number initial value is set to 0 as the minimum value macMinBE of the backoff index corresponding to the medical data packet with higher priority is smaller.
3. An improved non-slotted CSMA/CA optimization as in claim 2The method is characterized in that the backoff window corresponding to the ith backoff in the step 3
Figure 402162DEST_PATH_IMAGE004
，
Figure 591835DEST_PATH_IMAGE001
For the initial back-off window size,
Figure 209767DEST_PATH_IMAGE005
wherein
Figure 775877DEST_PATH_IMAGE006
is the maximum value of the backoff index macMaxBE,
Figure 77546DEST_PATH_IMAGE007
is the minimum value of the backoff index, macMinBE,
the back-off time slots corresponding to the medical data packets with different priorities are set as
Figure 906962DEST_PATH_IMAGE008
，
Figure 294081DEST_PATH_IMAGE009
For the cache occupancy rate of the medical data packet in the cache queue of the ZigBee gateway,
Figure 663882DEST_PATH_IMAGE010
is a priority factor, X is
Figure 23319DEST_PATH_IMAGE011
An integer within the interval.
4. An improved non-slotted CSMA/CA optimized evaluation method as recited in claim 3, comprising the steps of:
step 1, constructing a three-dimensional Markov chain model;
step 2, constructing a formula:
Figure 820374DEST_PATH_IMAGE012
wherein,
Figure 429210DEST_PATH_IMAGE013
denoted as backoff i, backoff window j, probability at retransmission k,
Figure 71544DEST_PATH_IMAGE014
expressed as the i-th backoff, the probability of CCA occurring at the k-th retransmission,
Figure 82225DEST_PATH_IMAGE015
expressed as the probability of successful receipt of the medical data packet,
Figure 50181DEST_PATH_IMAGE016
indicating the probability that the terminal node does not receive the ACK acknowledgement frame after successfully sending the medical data packet,
Figure 864422DEST_PATH_IMAGE017
representing the probability of discarding the medical data packet as a transmission failure of the medical data packet;
step 3, defining the generation rate of the medical data packet of the terminal node as
Figure 576026DEST_PATH_IMAGE018
，T 0 Is the unit cycle time of each time slot, T is the interval cycle;
step 4, establishing the probability of the terminal node for executing the idle channel evaluation
Figure 910056DEST_PATH_IMAGE019
The formula (2);
step 5, constructing retransmission probability
Figure 48913DEST_PATH_IMAGE020
The formula (2);
step 6, constructing CCA failure probability
Figure 632341DEST_PATH_IMAGE021
The formula (2);
step 7, solving according to the formula constructed in the step 2-6 and the Markov chain normalization
Figure 350898DEST_PATH_IMAGE022
To calculate the probability
Figure 336172DEST_PATH_IMAGE023
Probability of retransmission
Figure 645930DEST_PATH_IMAGE020
And probability of CCA failure
Figure 716655DEST_PATH_IMAGE021
The value of (a) is,
step 8, calculating the probability of channel access failure
Figure 238903DEST_PATH_IMAGE024
；
Step 9, calculating the probability of packet loss caused by exceeding retransmission limit during transmission
Figure 78683DEST_PATH_IMAGE025
；
Step 10, calculating reliability
Figure 559343DEST_PATH_IMAGE026
The probability of (d);
step 11, calculating the total delay
Figure 581612DEST_PATH_IMAGE027
= delay of backoff stage
Figure 438709DEST_PATH_IMAGE028
+ delay of successful transmission of data packet
Figure 132996DEST_PATH_IMAGE029
+ delay of retransmission procedure
Figure 253399DEST_PATH_IMAGE030
。
5. The method of claim 4, wherein the evaluation of non-slotted CSMA/CA optimization is performed by: the three-dimensional Markov chain model in the step 1 is
Figure 298715DEST_PATH_IMAGE031
；
Wherein,
Figure 693924DEST_PATH_IMAGE032
indicates the number of back-offs at time t,
Figure 711559DEST_PATH_IMAGE033
indicates the state of the backoff counter at time t, the backoff counter having a value of
Figure 799600DEST_PATH_IMAGE011
A random value in between, and a random value,
Figure 535475DEST_PATH_IMAGE034
denotes the number of retransmissions at time t, and defines that m denotes the maximum number of backoff and r denotes the maximum number of retransmissions.
6. The improved non-slotted CSMA/CA optimized evaluation method of claim 5, wherein: in the step 2:
Figure 734375DEST_PATH_IMAGE035
Figure 137675DEST_PATH_IMAGE036
Figure 114727DEST_PATH_IMAGE037
Figure 869057DEST_PATH_IMAGE038
Figure 606068DEST_PATH_IMAGE039
wherein,
Figure 598295DEST_PATH_IMAGE040
probability of random backoff being completed for the first time by the terminal node,
Figure 28139DEST_PATH_IMAGE041
a probability is generated for the medical data packet,
Figure 4186DEST_PATH_IMAGE021
as is the probability of a CCA failure,
Figure 13730DEST_PATH_IMAGE042
in order to be the probability of retransmission,
Figure 657201DEST_PATH_IMAGE043
,
Figure 992367DEST_PATH_IMAGE044
，
Figure 721289DEST_PATH_IMAGE045
indicating the time slot length corresponding to the length of the medical data packet,
Figure 268945DEST_PATH_IMAGE046
indicating the ACK acknowledgement frame latency time and,
Figure 766922DEST_PATH_IMAGE047
indicating the length of the time slot corresponding to the length of the ACK acknowledgment frame,
Figure 272990DEST_PATH_IMAGE048
indicating the length of the time slot corresponding to the interval of the medical data packet,
Figure 207317DEST_PATH_IMAGE049
indicating ACK timeout time, parameter
Figure 89822DEST_PATH_IMAGE050
，
Figure 442306DEST_PATH_IMAGE051
。
7. The improved non-slotted CSMA/CA optimized evaluation method of claim 6, wherein: the probability of the terminal node performing the idle channel assessment in the step 4
Figure 853696DEST_PATH_IMAGE019
Comprises the following steps:
Figure 291631DEST_PATH_IMAGE052
retransmission probability in said step 5
Figure 712248DEST_PATH_IMAGE020
Comprises the following steps:
Figure 653659DEST_PATH_IMAGE053
wherein,
Figure 501529DEST_PATH_IMAGE054
n represents the number of terminal nodes for the probability of transmission errors;
the CCA failure probability in step 6
Figure 426760DEST_PATH_IMAGE021
Comprises the following steps:
Figure 119909DEST_PATH_IMAGE055
。
8. the improved non-slotted CSMA/CA optimized evaluation method of claim 7, wherein: probability of channel access failure in the step 8
Figure 446985DEST_PATH_IMAGE024
Comprises the following steps:
Figure 731336DEST_PATH_IMAGE056
；
probability of packet loss exceeding retransmission limit during transmission in the step 9
Figure 861972DEST_PATH_IMAGE025
Comprises the following steps:
Figure 624392DEST_PATH_IMAGE057
；
reliability in said step 10
Figure 805974DEST_PATH_IMAGE026
The probability of (c) is:
Figure 730068DEST_PATH_IMAGE058
。
9. the improved non-slotted CSMA/CA optimized evaluation method of claim 7, wherein: in the step 11, the process is carried out,
Figure 629891DEST_PATH_IMAGE059
；
Figure 196002DEST_PATH_IMAGE060
；
Figure 232091DEST_PATH_IMAGE061
；
wherein,
Figure 327086DEST_PATH_IMAGE062
is a unit time of a time slot,
Figure 714205DEST_PATH_IMAGE063
in order to initiate the back-off window,
Figure 818427DEST_PATH_IMAGE064
a delay indicating a failure in transmission of the medical data packet at the k-th retransmission,
Figure 443443DEST_PATH_IMAGE065
。
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