CN107872900A - A satellite channel S-ALOHA access system and method supporting differentiated services - Google Patents

Abstract

The present invention relates to a kind of satellite channel S ALOHA access systems and method for supporting Differentiated Services, and on S ALOHA protocol basis, employing repetition sending strategy reduces the access delay of high-priority users, realizes Differentiated Services；The present invention have studied user under the conditions of the satellite channel using S ALOHA dynamic access time delay with the basis of total business arrival rate relation, improve the validation testing of user's access request, propose repetition sending strategy, i.e. user can continuously transmit multiple requests in the case of not receiving access request and confirming, Differentiated Services are realized by the control that different terminals are repeated to send with the factor.This method can simply and effectively lift Differentiated Services ability of the satellite communication system in user's access phase, provide the quantitative predication of user's access delay, be supported to ensure that the QoS of user provides aid decision.

Description

A satellite channel S-ALOHA access system and method supporting differentiated services

technical field

The invention relates to a satellite channel S-ALOHA access system and method supporting differentiated services, belonging to the technical field of communication.

Background technique

The existing satellite channel S-ALOHA access has the following problems:

(1) Under normal circumstances, the S-ALOHA protocol parameters of all users are fixed configurations, which cannot be adjusted according to the status of the entire satellite communication system, resulting in users being unable to obtain consistent access service quality and predictable access at different times and locations input delay.

(2) The S-ALOHA protocol itself does not support differentiated service features among different users, and cannot meet the priority service requirements of high-priority users in the access phase.

(3) Under normal circumstances, the satellite communication system that adopts the S-ALOHA protocol for access does not control the total service arrival rate of the system. When the number of users increases, the system may enter the unstable area of the S-ALOHA protocol, aggravating Channel conflict is caused, which seriously affects the user access efficiency.

According to the above analysis, the traditional S-ALOHA protocol has shortcomings in terms of flexibility, stability, and ability to support differentiated services. In a satellite communication system with wide-area The development trend of increased quantity, increased business types, and enhanced access service quality requirements.

Contents of the invention

The purpose of the present invention is to: overcome the deficiencies in the prior art, provide a satellite channel S-ALOHA access method that supports differentiated services, utilize this method to satisfy the distinction of users of different levels under the premise of ensuring the stability of the S-ALOHA protocol Service access requirements.

The above object of the present invention is achieved by the following technical solutions: a satellite channel S-ALOHA access system that supports differentiated services, including: a user total service arrival rate calculation unit, a user priority division unit, and a time slot collision probability calculation unit , user access delay estimation unit, S-ALOHA protocol stability evaluation unit and iterative calculation unit;

Total user service arrival rate calculation unit: calculate the user's total service arrival rate according to the new service arrival rate of the user (ground user) and the collision probability of the current single time slot transmission. Assuming that the new service arrival rate of the user is λ _i , the collision probability of the current single time slot is 1-p(0), where p(0) is the successful transmission probability of the time slot, then the average number of attempts required by the user for successful transmission is

Therefore, the total service arrival rate of users is

The successful transmission of a time slot means that the signals sent by users in the current time slot do not collide. Collision means that different users send signals in the same time slot, that is, a collision occurs, otherwise the time slot transmission fails.

The time axis is divided into several time periods with equal intervals, each time period is a time slot, and each user can send a message (group) in each time slot.

The first information (packet) is sent by a user for the first time and becomes the user's new service. If the new service is not successfully transmitted, the user resends the information in a later time slot, which is called a retransmission service. The total business includes new business and retransmission business.

User priority division unit: divide the set composed of all users, divide different users into different priority sets, number the divided priority sets sequentially, and the priority corresponding to the set with the larger number value The higher the value is, the different retransmission factors are set for different priority sets, and the retransmission factor of the priority set is set as the number value of the set. Assuming that the value range of the repeated transmission factor in the system is [1, N], the total service arrival rate of the system after user priority division is

The system total service arrival rate is sent to the time slot collision probability calculation unit.

The value of the repeated sending factor is the number of repeated sendings.

The arrival rate refers to the traffic volume arriving per unit time, and the unit time includes one or more time slots.

Time slot collision probability calculation unit: calculate according to the Poisson process of system service arrival, and the collision probability p(0)=e ^-ΛT of a single time slot can be obtained according to the total service arrival rate Λ of the system, and then according to the total service arrival rate of users The relationship between Λ and the collision probability of a single time slot is calculated by the simultaneous equations p(0), and sent to the user access delay estimation unit. T is the duration of a single time slot.

The equation set is as follows:

User access delay estimation unit: estimate the user access delay, assuming that the repeated transmission factor of the current user is K _i , and the collision probability of the current time slot is 1-p(0), then a single access signal (packet) The probability of successful transmission is The average number of successful transmission attempts of the access signal (packet) corresponding to the current user is Since the average access delay of the user is proportional to the average number of successful transmission attempts of the access packet, the average access delay T _i of the user is calculated as Send the user's average access delay T _i to the iterative calculation unit;

S-ALOHA protocol stability evaluation unit: evaluate the stability of the S-ALOHA protocol adopted by the user access after priority division, if ΛT>1, then the S-ALOHA protocol is unstable, if ΛT≤1, then S- The ALOHA protocol is stable.

Iterative calculation unit: according to the user's average access delay T _i and the requirements for access delay, adjust the user priority division, and gradually increase the priority and repeated transmission factor of users who do not meet the access delay requirements; After the level division is adjusted, when the access delays of all users meet the requirements or reach the set maximum number of adjustments, the last adjusted user priority is determined as the final user priority. As shown in Figure 3, the steps of iterative calculation are as follows

First, all users are divided into a priority set numbered 1. In this case, the repeated transmission factor of all users is 1. The collision probability p(0) of a single time slot is calculated by the equation group, and the average access delay of the users is respectively And determine the stability of the protocol.

The average access delay T _i of user access is calculated by the collision probability p(0) of a single time slot and the user's repeated transmission factor, and compared with the average access delay requirement T _i ′ of the user, if T _i ≤ T′ _i indicates that the user's access delay requirement is met.

Calculate the total service arrival rate λ′ i of each user through the relationship between the new service arrival rate λ _{i of} each user and the collision probability p(0) of a single time slot, and further calculate the total service arrival rate Λ of all users in the system , whether the protocol is stable can be judged by whether the product of the total service arrival rate Λ of all users and the time slot length T is less than or equal to 1.

If the access delay requirements of all users are satisfied and the protocol is stable, the iterative algorithm ends successfully, and the user's priority division method is taken as the output result of the iterative calculation unit; if the protocol is unstable, it means that the iterative calculation unit cannot calculate Feasible solution, it is necessary to consider adjusting the user service arrival rate or access delay requirements to re-calculate iteratively; if the access delay of some users cannot be satisfied, then these users are divided into duplicates corresponding to the current priority set in turn In the priority set whose sending factor is greater than 1, re-calculate iteratively.

The advantage of the present invention compared with prior art is:

(1) The present invention allows users with high requirements on access delay to adopt a repeated sending strategy, that is, multiple access request packets can be continuously sent on the premise of not receiving an access response packet. There are K access request packets, and the success probability of independent transmission of each packet is P(0), then the probability of the user's successful access this time is 1-(1-P(0)) ^K , the larger K is, the single success The higher the access probability, the shorter the user access delay. The number K of consecutively sent access request packets is related to the user's priority to implement differentiated services among users.

(2) The present invention provides a satellite channel S-ALOHA access system and method supporting differentiated services, establishes a mathematical model of user service arrival rate, and provides an estimation method for user access delay. On this basis, the user set is divided to form multiple priority sets, and the mapping relationship between the priority set and the retransmission factor is given, and different retransmission factors are used to realize differentiated services for different users.

(3) The present invention provides the iterative algorithm of user priority division, and the stability of S-ALOHA agreement is incorporated in the criterion of iterative algorithm, and the result of iterative calculation needs to guarantee the stability of S-ALOHA agreement, in practical application It ensures that the access system using the S-ALOHA protocol is in a stable state.

Description of drawings

Fig. 1 is the schematic diagram of each unit relation involved in the present invention;

Fig. 2 is the execution flow chart of iterative calculation unit algorithm;

FIG. 3 is a schematic diagram of the retransmission of the S-ALOHA access protocol using the repeated sending strategy.

Detailed ways

The present invention will be further introduced below in conjunction with the accompanying drawings and specific examples.

The invention relates to a satellite channel S-ALOHA (slotted ALOHA) access system and method supporting differentiated services. On the basis of the S-ALOHA protocol, a repeated transmission strategy is used to reduce the access delay of high-priority users, and realize Differentiated services; the present invention studies the relationship between the time delay and the total service arrival rate of users using S-ALOHA dynamic access under satellite channel conditions, improves the confirmation mode of user access requests, and proposes a repeated sending strategy, namely The user can continuously send multiple requests without receiving the confirmation of the access request, and realize differentiated services by controlling the repeated sending factors of different terminals. This method can simply and effectively improve the differentiated service capability of the satellite communication system during the user access phase, provide a quantitative estimate of the user access delay, and provide auxiliary decision support for ensuring the user's QoS.

The satellite channel S-ALOHA access system supporting differentiated services in the present invention includes: a user total service arrival rate calculation unit, a user priority division unit, a time slot collision probability calculation unit, a user access delay estimation unit, and a stable S-ALOHA protocol A performance evaluation unit and an iterative calculation unit, as shown in Figure 1;

Total user service arrival rate calculation unit: calculate the user's total service arrival rate according to the new service arrival rate of the user (ground user) and the collision probability of signal transmission in a single time slot. Assuming that the new service arrival rate of the user is λ _i , p(0) is the probability of successful signal transmission in a single time slot, so the collision probability of signal transmission in a single time slot is 1-p(0), then the signal arrives at time The average number of attempts of the user until the slot is successfully transmitted is

Therefore, the total service arrival rate of users is

Signal collision means that two or more users transmit in the same time slot, and signal collision will cause related user signal transmission failure. The successful transmission of signals in a time slot means that the signals sent by users in the current time slot do not collide.

Divide the time axis into several equal time periods, each time period is called a time slot, and each user can send at most one message (packet) in any time slot.

The signal (packet) sent by the user for the first time is called the user's new service. If the signal (packet) is not successfully transmitted, the user will resend the signal (packet) in a certain time slot later, and these retransmissions Signals (packets) are called retransmission traffic. The user's total business includes new business and retransmission business.

User priority division unit: divide the set composed of all users, divide different users into different priority sets, number the divided priority sets sequentially, and the priority corresponding to the set with the larger number value The higher the value is, the repeated sending factor of the priority set is set to the number value of the set at the same time. Assuming that the value range of the repeated transmission factor in the system is [1, N], the total service arrival rate of the system after user priority division is

The system total service arrival rate is sent to the time slot collision probability calculation unit.

The value of the repeated sending factor is the number of repeated sendings.

The arrival rate refers to the traffic volume arriving per unit time, and the unit time includes one or more time slots.

Time slot collision probability calculation unit: calculate according to the Poisson process of system service arrival, and the collision probability p(0)=e ^-ΛT of a single time slot can be obtained according to the total service arrival rate Λ of the system, and then according to the total service arrival rate of users The relationship between Λ and the collision probability of a single time slot is calculated by the simultaneous equations p(0), and sent to the user access delay estimation unit. T is the duration of a single time slot.

The equation set is as follows:

User access delay estimation unit: estimate the user access delay, assuming that the repeated transmission factor of the current user is K _i , and the collision probability of the current time slot is 1-p(0), then a single access signal (packet) The probability of successful transmission is The average number of successful transmission attempts of the access signal (packet) corresponding to the current user is Since the average access delay of the user is proportional to the average number of successful transmission attempts of the access packet, the average access delay T _i of the user is calculated as

Send the user's average access delay T _i to the iterative calculation unit;

S-ALOHA protocol stability evaluation unit: evaluate the stability of the S-ALOHA protocol adopted by the user access after priority division, if ΛT>1, then the S-ALOHA protocol is unstable, if ΛT≤1, then S - ALOHA protocol is stable.

Iterative calculation unit: according to the user's average access delay T _i and the requirements for access delay, adjust the user priority division, and gradually increase the priority and repeated transmission factor of users who do not meet the access delay requirements; After the level division is adjusted, when the access delays of all users meet the requirements or reach the set maximum number of adjustments, the last adjusted user priority is determined as the final user priority.

The satellite channel S-ALOHA access system that supports DiffServ satisfies its access delay requirements by allowing some users to use repeated transmission strategies. The repeated sending strategy means that when the user uses the S-ALOHA protocol to send a signal (packet), several identical signals (packets) can be sent repeatedly before the response is received or the feedback times out, as shown in Figure 3, as long as any one of the signals ( The successful transmission of the packet) means the successful transmission of the user signal (packet). Under the premise that the time slot collision probability remains unchanged, the repeated transmission strategy can significantly increase the probability of successful signal (packet) transmission. Considering that in the satellite communication system, the round-trip propagation delay of the communication signal between the user and the satellite is relatively large, because the retransmission of the signal (packet) after collision will significantly increase the user's access delay, and the repeated transmission strategy can improve the user's access delay. The successful transmission probability of the signal (packet), thereby reducing the user's access delay. The greater the user's repeated transmission factor, the more significant the improvement effect and the shorter the access delay. Therefore, different repeated transmission factors can be configured for different levels of users to achieve differentiated services. The system adopts an iterative calculation unit based on the stability of the protocol and whether the user access delay is satisfied, so as to ensure that the access system can meet the access delay requirements of each user under the premise of stability.

According to the requirements of all users on the access delay and the stability requirements of the S-ALOHA protocol, there are two possible results for the user priority division method obtained by the iterative calculation unit. One is that the priority division method can not only meet the user's demand for access delay but also meet the stability requirements of the S-ALOHA protocol, which is the expected result of the satellite channel S-ALOHA access system supporting differentiated services; the other The first is that the priority division method cannot meet the requirements of access delay or the stability requirements of the protocol, indicating that a reasonable user priority division method cannot be found under the current input conditions, and the input conditions of the system need to be adjusted and reset. Perform iterative calculations. As shown in Figure 3, the specific adjustment strategy is as follows

(1) Reduce some users' demand for access delay, so that the iterative calculation unit does not need to configure a larger repeated transmission factor for these users, thereby reducing the total system service arrival rate, improving the system stability margin, and it is also easier to meet the user's requirements access delay requirements;

(2) Reducing the arrival rate of new services of some users or increasing the retransmission interval of users is equivalent to reducing the contribution of these users to the total service arrival rate of the system, thereby reducing the total service arrival rate of the system and improving the system stability margin.

As shown in Figures 2 and 3, the steps of iterative calculation in the iterative calculation unit are as follows

First, all users are divided into a priority set numbered 1. In this case, the repeated transmission factor of all users is 1. The collision probability p(0) of a single time slot is calculated by the equation group, and the average access delay of the users is respectively And determine the stability of the protocol.

The average access delay T _i of user access is calculated by the collision probability p(0) of a single time slot and the user's repeated transmission factor, and compared with the average access delay requirement T′ _i of the user, if T _i ≤ T′ _i indicates that the user's access delay requirement is met.

Calculate the total service arrival rate λ′ i of each user through the relationship between the new service arrival rate λ _{i of} each user and the collision probability p(0) of a single time slot, and further calculate the total service arrival rate Λ of all users in the system , whether the protocol is stable can be judged by whether the product of the total service arrival rate Λ of all users and the time slot length T is less than or equal to 1.

If the access delay requirements of all users are satisfied and the protocol is stable, the iterative algorithm ends successfully, and the user's priority division method is taken as the output result of the iterative calculation unit; if the protocol is unstable, it means that the iterative calculation unit cannot calculate Feasible solution, it is necessary to consider adjusting the user service arrival rate or access delay requirements to re-calculate iteratively; if the access delay of some users cannot be satisfied, then these users are divided into duplicates corresponding to the current priority set in turn In the priority set whose sending factor is greater than 1, re-calculate iteratively.

There are preferably 10 users in the system, each user has the same new service arrival rate, and all belong to priority set 1, the normalized new service arrival rate λT=0.03, then the new service arrival rate of all users in the system is 10λT=0.3 , using p(0) to represent the successful transmission probability of a single time slot, then the total service arrival rate of all users in the system is According to the total service arrival rate of all users in the system, the successful transmission probability of a single time slot can be calculated By solving the equation p(0)lnp(0)=0.3, p(0)=0.613 can be solved, so it can be further calculated that the average number of attempts required for the successful transmission of each user's access packet is The total business arrival rate of all users in the system is 0.489, and the S-ALOHA protocol is stable at this time.

Assuming that the average number of attempts required by one of the users for the successful transmission of the access packet does not exceed 1.2, run the iterative algorithm to divide the user into the priority set 2, then the normalized new service arrival rate of the system at this time is 11λT = 0.33, use the equation p(0)lnp(0)=0.33 to solve the successful transmission probability p(0)=0.547 of a single time slot, and can further calculate the average Attempts are The average number of attempts required for the successful transmission of user access packets belonging to priority set 2 is If the user's needs cannot be met, the user is assigned to priority set 3 according to the algorithm flow. At this time, the normalized new service arrival rate of the system is 12λT=0.36, using the equation p(0)lnp(0)=0.36 to solve the probability of successful transmission of a single time slot p(0)=0.447, which can be further calculated to belong to the priority The average number of attempts required for the successful transmission of user access packets in set 1 is The average number of attempts required for the successful transmission of user access packets belonging to priority set 3 is If the user requirement is met, the iterative algorithm exits normally.

From the above example, it can be seen that the satellite channel S-ALOHA access system supporting differentiated services reduces the average number of attempts required for the successful transmission of one user's access packet to 1.2, because the average access delay of the user is different from the average number of attempts The number of times is proportional, so compared with the traditional S-ALOHA access system, the satellite channel S-ALOHA access system supporting differentiated services reduces the average access delay of the user by 36%, which meets the user's requirements for access Latency requirements. At the same time, the average access delay of this user is reduced by 46% compared with other users, realizing differentiated services for this user.

The content that is not described in detail in the specification of the present invention belongs to the well-known technology of those skilled in the art.

Claims (10)

1. A kind of 1. satellite channel S-ALOHA access systems for supporting Differentiated Services, it is characterised in that including：User's total business reaches Rate computing unit, User Priority division unit, time slot collision probability calculation unit, user's access delay estimation unit, S- ALOHA agreement stability assessment units and iterative calculation unit；

   User's total business arrival rate computing unit, the collision transmitted according to the new business arrival rate of user and signal in single time slot Probability, the average number of attempt of user when obtaining signal untill time slot Successful transmissions, and user's total business arrival rate；

   User Priority division unit, the set to all users composition are divided, different users are divided into different In priority set, the repetition of setting priority set sends the factor, and the repetition of priority set is sent into the factor is set as this The number value of set, then obtain the system total business arrival rate after User Priority divides；System total business arrival rate Give time slot collision probability calculation unit；

   Time slot collision probability calculation unit, reach obedience Poisson process according to system business and calculated, according to total industry of system Business arrival rate Λ can obtain the collision probability of single time slot, further according to the collision of user total business arrival rate Λ and single time slot The relation Simultaneous Equations of probability calculate the collision probability of single time slot, deliver to user's access delay estimation unit；

   User's access delay estimation unit, estimates the access delay of user, according to the collision probability of current time slots, obtains Single accesses the probability of signal Successful transmissions, the average number of attempt of access signal Successful transmissions corresponding to active user, user's Average access delay T_i；By the average access delay T of user_iDeliver to iterative calculation unit；

   S-ALOHA agreement stability assessment units：User after being divided to priority accesses the stabilization of the S-ALOHA agreements used Property assessed, if the duration T of the total business arrival rate Λ of system and single time slot meet require, S-ALOHA agreements Unstable, otherwise S-ALOHA agreements are stable；

   Unit is iterated to calculate, according to the average access delay T of user_iRequirement with to access delay, is partitioned into User Priority Row adjustment, it is stepped up being unsatisfactory for the priority of access delay requirement user and repeats to send the factor；User Priority is divided After being adjusted, when all users access delay meet demand or reach setting adjustment maximum times when, will last time The User Priority of adjustment is defined as final User Priority.
2. 2. a kind of satellite channel S-ALOHA access systems for supporting Differentiated Services according to claim 1, its feature exist In：Signal collision refers to that two or more users are transmitted in identical time slot, and signal collision can cause related use Family signal bust this.
3. 3. a kind of satellite channel S-ALOHA access systems for supporting Differentiated Services according to claim 1, its feature exist In：Untill time slot Successful transmissions, the average number of attempt M of user is signal

   <mrow> <mi>M</mi> <mo>=</mo> <msubsup> <mo>&amp;Sigma;</mo> <mrow> <mi>k</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>&amp;infin;</mi> </msubsup> <mi>k</mi> <msup> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>p</mi> <mo>(</mo> <mn>0</mn> <mo>)</mo> <mo>)</mo> </mrow> <mrow> <mi>k</mi> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mi>p</mi> <mrow> <mo>(</mo> <mn>0</mn> <mo>)</mo> </mrow> <mo>=</mo> <mfrac> <mn>1</mn> <mrow> <mi>p</mi> <mrow> <mo>(</mo> <mn>0</mn> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>;</mo> </mrow>

   In formula, k is summation variable.
4. 4. a kind of satellite channel S-ALOHA access systems for supporting Differentiated Services according to claim 1, its feature exist In：The λ ' of user's total business arrival rate_iFor：

   <mrow> <msubsup> <mi>&amp;lambda;</mi> <mi>i</mi> <mo>&amp;prime;</mo> </msubsup> <mo>=</mo> <mfrac> <msub> <mi>&amp;lambda;</mi> <mi>i</mi> </msub> <mrow> <mi>p</mi> <mrow> <mo>(</mo> <mn>0</mn> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>.</mo> </mrow>
5. 5. a kind of satellite channel S-ALOHA access systems for supporting Differentiated Services according to claim 1, its feature exist In：Signal refers to that the signal that current time slots user sends does not collide in time slot Successful transmissions, the total business arrival rate of system The requirement that the duration T of Λ and single time slot meets is Λ T ＞ 1.
6. 6. a kind of satellite channel S-ALOHA access systems for supporting Differentiated Services according to claim 1, its feature exist In：Time shaft is divided into several identicals period, each period can be with office as a time slot, each user An at most message is sent in what time slot, message is to be grouped.
7. 7. a kind of satellite channel S-ALOHA access systems for supporting Differentiated Services according to claim 1, its feature exist In：The signal that user sends for the first time is referred to as the new business of the user, if the signal transmits not successfully, user is by afterwards Some time slot resends the signal, and these re-transmission signals are referred to as into re-transmission business, and the total business of user includes new business and again Biography business.
8. 8. a kind of satellite channel S-ALOHA access systems for supporting Differentiated Services according to claim 1, its feature exist In：Assuming that the span for repeating to send the factor in system is [1, N], then the system obtained after User Priority divides is total Business arrival rate is

   <mrow> <mi>&amp;Lambda;</mi> <mo>=</mo> <msubsup> <mo>&amp;Sigma;</mo> <mrow> <mi>k</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>N</mi> </msubsup> <mi>k</mi> <msub> <mo>&amp;Sigma;</mo> <mrow> <mi>i</mi> <mo>&amp;Element;</mo> <msub> <mi>U</mi> <mi>i</mi> </msub> </mrow> </msub> <msubsup> <mi>&amp;lambda;</mi> <mi>i</mi> <mo>&amp;prime;</mo> </msubsup> <mo>,</mo> </mrow>

   In formula,λ_iFor the new business arrival rate of user.
9. 9. a kind of satellite channel S-ALOHA access systems for supporting Differentiated Services according to claim 1, its feature exist In：The value for repeating to send the factor is attached most importance to the number that send of recurrence；Arrival rate refers to the portfolio reached in the unit interval, unit interval Including one or more time slots.
10. 10. a kind of satellite channel S-ALOHA cut-in methods for supporting Differentiated Services, it is characterised in that step is as follows：

    (1) collision probability transmitted according to the new business arrival rate of user and current single time slot, total industry of the user is calculated Business reaches, it is assumed that the new business arrival rate of user is λ_i, the collision probability of current single time slot is 1-p (0), when wherein p (0) is Gap Successful transmissions probability, then the average number of attempt M required for user's Successful transmissions be

    <mrow> <mi>M</mi> <mo>=</mo> <msubsup> <mi>&amp;Sigma;</mi> <mrow> <mi>k</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>&amp;infin;</mi> </msubsup> <mi>k</mi> <msup> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>p</mi> <mo>(</mo> <mn>0</mn> <mo>)</mo> <mo>)</mo> </mrow> <mrow> <mi>k</mi> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mi>p</mi> <mrow> <mo>(</mo> <mn>0</mn> <mo>)</mo> </mrow> <mo>=</mo> <mfrac> <mn>1</mn> <mrow> <mi>p</mi> <mrow> <mo>(</mo> <mn>0</mn> <mo>)</mo> </mrow> </mrow> </mfrac> </mrow>

    Then, user's total business arrival rate is

    Time slot Successful transmissions refer to that the signal that current time slots user sends does not collide, and collision refers to different user in identical Time slot sends signal, that is, regards as colliding, otherwise time slot failed transmission；

    The period of several same intervals is divided into time shaft, each period is a time slot, every in each time slot Individual user can send a message；

    First information is sent by some user for the first time, turns into the new business of this user, if the new business is transmitted not successfully, User resends the information in some time slot afterwards, referred to as retransmits business, and total business includes new business and retransmits business；

    (2) according to the total business arrival rate of the user of step (1), the set to all users composition divides, will be different User is divided into different priority set, and the priority set after division is carried out into serial number, the bigger collection of number value Close that corresponding priority is higher, setting different repetitions for different priority set sends the factor, while by priority set The repetition of conjunction sends the number value that the factor is set as the set, it is assumed that and the span for repeating to send the factor in system is [1, N], Then the system total business arrival rate after User Priority divides is

    <mrow> <mi>&amp;Lambda;</mi> <mo>=</mo> <msubsup> <mo>&amp;Sigma;</mo> <mrow> <mi>k</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>N</mi> </msubsup> <mi>k</mi> <munder> <mo>&amp;Sigma;</mo> <mrow> <mi>i</mi> <mo>&amp;Element;</mo> <msub> <mi>U</mi> <mi>i</mi> </msub> </mrow> </munder> <msubsup> <mi>&amp;lambda;</mi> <mi>i</mi> <mo>&amp;prime;</mo> </msubsup> </mrow>

    Time slot collision probability calculation unit is given system total business arrival rate；Repeat send the factor value attach most importance to recurrence send time Number；Arrival rate refers to the portfolio reached in the unit interval, and the unit interval includes a multiple time slots；

    (3) user after being divided to priority accesses the S-ALOHA agreement stability used and assessed, if Λ T ＞ 1, S- ALOHA agreements are unstable, carry out step (7), if Λ T≤1, S-ALOHA agreement are stable, carry out step (4)；

    (4) reach obedience Poisson process according to system business to be calculated, can be obtained according to the total business arrival rate Λ of system Collision probability p (0)=e of single time slot^-ΛT, further according to user total business arrival rate Λ and the pass of the collision probability of single time slot It is that Simultaneous Equations calculate p (0), T is the duration of single time slot；

    (5) access delay of user is estimated, it is assumed that it is K that the repetition of active user, which sends the factor,_i, the collision of current time slots Probability is 1-p (0), then the probability of single access signal Successful transmissions isConnect corresponding to active user Entering the average number of attempt of signal Successful transmissions isBecause the average access delay of user is grouped successfully with access The average number of attempt of transmission is directly proportional, therefore the average access delay T of user_iIt is calculated as

    (6) by the average access delay T of user_iWith the contrast of the requirement of access delay, as the average access delay T of all users_i Respectively less than it is equal to the requirement of access delay, then exports step (3) User Priority division result, otherwise, return to step (3) is right User Priority division is adjusted；Deliver to iterative calculation unit；

    (7) according to the average access delay T of user_iWith the requirement to access delay, step (3) User Priority is divided and carried out Adjustment, it is stepped up being unsatisfactory for the priority of access delay requirement user and repeats to send the factor；User Priority is partitioned into Row adjustment after, when all users access delay meet demand or reach setting adjustment maximum times when, will last time adjust Whole User Priority is defined as final User Priority output.