CN108901073B - Reliable channel allocation method of task-oriented low-power wireless network - Google Patents

Reliable channel allocation method of task-oriented low-power wireless network Download PDF

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CN108901073B
CN108901073B CN201810508771.XA CN201810508771A CN108901073B CN 108901073 B CN108901073 B CN 108901073B CN 201810508771 A CN201810508771 A CN 201810508771A CN 108901073 B CN108901073 B CN 108901073B
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link
retransmission
links
path
link quality
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CN108901073A (en
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赵志为
闵革勇
高伟峰
杨轩
杨明航
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University of Electronic Science and Technology of China
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
    • H04W72/542—Allocation or scheduling criteria for wireless resources based on quality criteria using measured or perceived quality
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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Abstract

The invention provides a reliable channel allocation method of a task-oriented low-power wireless network. With "two-stage" channel allocation, in the first stage, the present invention proposes a mechanism that takes the link quality, deadline and network topology into consideration jointly to prioritize the most appropriate links and paths. In the second stage, the present invention considers the retransmission probability and assigns the unassigned slots to the most appropriate link to accommodate more retransmissions in one cycle. And the retransmission slot will only be used for lossy links and no additional overhead will occur on good links with no packet loss. Compared with the prior art, the invention can obviously improve the data packet transmission rate before the cut-off time without generating additional energy consumption.

Description

Reliable channel allocation method of task-oriented low-power wireless network
Technical Field
The invention relates to the technical field of wireless communication, in particular to a reliable channel allocation method of a task-oriented low-power wireless network.
Background
In the field of communications, multi-channel communications are widely used to improve the reliability of Low Power Wireless Networks (LPWN). For task-oriented LPWN, data transfers typically need to be delivered before a given deadline, making deadline-driven channel allocation an important task. The prior art on multi-channel allocation often fails to establish a channel allocation scheme that can meet the deadline requirements.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a reliable channel allocation method of a task-oriented low-power wireless network. The method considers the requirements of the deadline time, the link quality, the correlation of the network topology structure and the interference of the adjacent links at the same time, can obviously improve the receiving rate of the data packet, and has no extra energy loss.
The invention is realized by the following technical scheme:
a method for reliable channel allocation for a task-oriented low power wireless network, the method comprising:
step 1: a two-stage channel allocation scheme is adopted;
step 2: first-stage distribution: obtaining a statistical relationship between byte error rates of different RSSI distances through byte-level RSSI values in the packet, thereby calculating link quality through the byte error rates;
and step 3: determining path priority according to the link length and the interference condition;
and 4, step 4: given a path and its link quality in different time slots and channels, allocating time slots and channels to the links in the path using a penalty function method;
and 5: second-stage distribution: and enabling retransmission in the same transmission period, and allocating the first-level unallocated channel/time slot to the link needing retransmission.
Preferably, in step 2, the statistical relationship between the byte error rates of different RSSI distances is obtained by specifically using the byte-level RSSI values in the packet, so as to calculate the link quality by using the byte error rate, as shown in the following formula:
Figure BDA0001672304850000011
where q is the link quality, biIndicating the byte error rate of the ith byte.
Preferably, the step 3 determines the path priority by specifically following formula:
mi＝αli+(1-α)ciin the formula, miAs the priority of path i,/iIndicates the length of path i, ciIndicates the number of collisions for path i and α is a weight parameter.
Preferably, the step 4 of allocating time slots and channels to the links in the path by using a penalty function method specifically includes:
the distribution problem is converted into a nonlinear programming problem and solved through a penalty function method, and cutoff time, interference of adjacent links and link quality are comprehensively considered, so that time slots and channels with the highest link quality are preferentially distributed for the links with the most urgent and the most complex interference.
Preferably, the step 5 of allocating the unallocated channels/timeslots to the links requiring retransmission specifically includes:
5.1, adding the links meeting the link dependency relationship and the conflict constraint into a retransmission link set of the corresponding time slot/channel;
5.2, sequencing the links in the retransmission link set based on the link quality benefit and the retransmission opportunity, wherein the link quality benefit is calculated according to the following formula:
pri＝(1-(1-qb)(1-qn))-qbin the formula, priFor link quality gain, q, of link ibIndicates the link quality before the retransmission, qnIndicating the quality of the link after the retransmission;
dividing the retransmission link set into a series of subsets, the links in the subsets being non-conflicting, the link quality benefit pr for a subsetgExpressed as:
Figure BDA0001672304850000021
wherein G represents the number of links in the subset;
5.3, determining the priority mr of the retransmission link subsetgThe following formula:
Figure BDA0001672304850000022
in the formula, AiRepresenting the number of retransmission slots/channels available to link i in the subset, and α is a weight parameter.
The invention has the following advantages and beneficial effects:
the invention adopts a two-stage channel allocation method, before channel allocation, the statistical relationship between byte error probabilities of different RSSI distances is obtained through byte-level RSSI values in a packet, so that the link quality q is calculated through the byte error rate, and then the link quality q is calculated according to the length l of a pathiAnd the number of collision paths ciTo calculate the path priority miFor a given path and its link quality in different time slots and channels, we solve the assignment problem as a non-linear programming problem using a penalty function method and then select the appropriate time slot and channel for this pathAnd (4) carrying out the following steps. In the second stage, we consider the retransmission probability and allocate the unassigned slots in the second stage to the most suitable link to accommodate more retransmissions in one cycle.
The retransmission time slot of the present invention is only used for lossy links and no additional overhead will occur on good links without packet loss. Compared with the prior art, the invention can obviously improve the data packet transmission rate before the cut-off time without generating additional energy consumption.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not used as limitations of the present invention.
The embodiment provides a channel allocation method of the invention, which mainly comprises the following steps: dividing the channel allocation scheme into two stages, the first stage allocating time slots with appropriate priority according to link quality and deadline requirements, and the second stage reallocating unused time slots for future retransmissions; in the first stage, the statistical relationship between the byte error probabilities of different RSSI distances is obtained through the byte-level RSSI values in the packets, so that the link quality is calculated through the byte error rate; determining path priority according to the link length and the interference condition; given a path and the link quality thereof in different time slots and channels, the present embodiment reduces the assignment problem to a nonlinear programming problem and solves it using a penalty function method, and then selects a suitable time slot and channel for the path; in the second stage, retransmission is enabled in the same transmission cycle and the extra channel or slot pairs not allocated by the first stage are allocated to the lossy links that may be retransmitted. Wherein,
A. the link quality is briefly evaluated by using the byte-level RSSI value in the packet:
1) specifically, the present embodiment uses a 32KHz timer to measure the byte level RSSI values within the packet. From the intra-packet RSSI values, statistical relationships between byte error probabilities for different RSSI distances can be obtained. The present embodiment may also infer that the error rate increases as the RSSI distance becomes larger. From the byte error rate, the link quality can be further calculated
Figure BDA0001672304850000031
Where q is the link quality, biIndicating the byte error rate of the ith byte.
B. After determining the link quality, since the present embodiment is based on the channel allocation scheme of the path, the priority of the path is determined to determine to allocate the link with higher quality to the path with higher priority:
1) a path priority. The method of the present embodiment iteratively allocates time slots and channels for paths in the network until all paths are allocated. The present embodiment proposes a new path priority metric in which the path length and interference are taken into account
mi＝αli+(1-α)ci，
In the formula, miAs the priority of path i,/iIndicates the length of path i, ciIndicates the number of collisions for path i and α is a weight parameter.
1) Channel assignment based on link quality. The allocation of the present embodiment aims to maximize the packet transfer ratio before the deadline, which is affected by the link quality, and is also limited by the link allocation order and interference. The present embodiment comprehensively considers the above factors, and proposes the following formula:
Figure BDA0001672304850000041
s.t.
Figure BDA0001672304850000042
Figure BDA0001672304850000043
Figure BDA0001672304850000044
Figure BDA00016723048500000410
(symbol)
Figure BDA0001672304850000045
reflecting whether the link l transmits data in time slot t and channel c: (
Figure BDA0001672304850000046
The representation is not present at all,
Figure BDA0001672304850000047
represented in) c; piFor the link set in the path i, T is the number of assignable time slots, and C is the number of assignable channels; t is tlDenotes the allocation time, t, of the link ll+1The distribution time of the next hop of the link l is represented, and d is the deadline; as is the assigned link set.
The first constraint is: link l must be allocated time before its next hop link;
the second constraint is: link l must be allocated more than 0 less than the cutoff time;
the third constraint is: if the receiver (receiver) of link m can listen to the signal of link l in time slot t and channel c, link m cannot be allocated to time slot t and channel c, i.e. link m is not allocated to time slot t and channel c
Figure BDA0001672304850000048
The fourth constraint is: if link m and link l are adjacent (have a common node), then they cannot transmit data at the same time, i.e., they do not transmit data at the same time
Figure BDA0001672304850000049
Given a path and its link quality in different time slots and channels, the present embodiment reduces the assignment problem to a non-linear programming problem and solves it using a penalty function method, and then selects the appropriate time slot and channel for this path.
C. To further increase the packet transmission rate before the deadline, the present embodiment utilizes unused slots and channels for retransmissions. First, the present embodiment finds an available retransmission link for each slot and channel. If the link meets the sequence and collision requirements, it is added to the retransmission link set for this slot/channel. In the second step, the upper links are divided into collision-free ordered subsets. The best subset is then selected for retransmission allocation. The ordering process is based on two factors, namely link quality gains and forwarding opportunities:
1) for the links in the retransmission set, the present embodiment may obtain the following link quality gains for retransmission:
pri＝(1-(1-qb)(1-qn))-qb，
in the formula, priFor link quality gain, q, of link ibIndicates the link quality before the retransmission, qnIndicating the link quality after the retransmission.
2) Dividing the retransmission link set into a series of subsets, the links within a subset being non-interfering (colliding), the link quality benefit pr for a subsetgExpressed as:
Figure BDA0001672304850000051
in the formula, G represents the number of links in the subset.
D. In this embodiment, a specific metric is proposed to determine the priority mr of the retransmission link subsetgThe following formula:
Figure BDA0001672304850000052
in the formula, AiIndicating retransmission time slots/channels available for link i in the subsetThe number, α, is a weight parameter. With this metric, a subset of better quality margins and fewer retransmission opportunities can be served ahead of time.
E. In addition, the present embodiment extends this reliable channel allocation method for task-oriented low-power wireless networks to a distributed algorithm, where each node only needs information from its single-hop neighbors until the model is complete. First, each node records the link quality of the next hop in all available channels by periodically exchanging beacons. If a node has a packet to send, it will preferentially select the channel with the highest link quality and compare its own priority with the priorities of the neighboring nodes on that channel. If its priority is maximum, it immediately transmits the packet. Otherwise, it will switch to another channel and compare the new priorities. If all channels are not available, it may refrain from transmitting until the next slot. Furthermore, if a transmission failure occurs, the node will update its priority taking into account the retransmission cost.
The embodiment provides a new priority channel allocation scheme for different paths and channels, and comprehensively considers the requirements of deadline time, link quality and network topology.
The allocation in this embodiment aims to maximize the data transmission rate before the deadline. Due to the varying link quality, data packets cannot always reach the sink node. In order to further increase the data transmission rate before the deadline, the present embodiment uses unused slots and channels for retransmission, using TOSSIM simulation, which shows that 71% of the nodes retransmit twice or more, and therefore it is necessary to consider the retransmission. Available retransmission links are found for each slot and channel, the retransmission links are ordered based on link quality gains and retransmission opportunities, and a subset of higher link quality gains and fewer retransmission opportunities is then selected for preferential retransmission. The embodiment enables retransmission in the same transmission period, and allocates an additional channel/slot pair to a lossy link that may be retransmitted without generating additional energy consumption.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (4)

1. A method for reliable channel allocation for a task-oriented low power wireless network, the method comprising:
step 1: a two-stage channel allocation scheme is adopted;
step 2: first-stage distribution: obtaining a statistical relationship between byte error rates of different RSSI distances through byte-level RSSI values in the packet, thereby calculating link quality through the byte error rates;
and step 3: determining the path priority according to the path length and the interference condition;
and 4, step 4: given a path and its link quality in different time slots and channels, allocating time slots and channels to the links in the path using a penalty function method;
and 5: second-stage distribution: enabling retransmission in the same transmission period, and allocating the first-level unallocated channel/time slot to a link needing retransmission;
the step 5 of allocating the unallocated channel/timeslot to the link requiring retransmission specifically includes:
5.1, adding the links meeting the link dependency relationship and the conflict constraint into a retransmission link set of the corresponding time slot/channel;
5.2, sequencing the links in the retransmission link set based on the link quality benefit and the retransmission opportunity, wherein the link quality benefit is calculated according to the following formula:
pri＝(1-(1-qb)(1-qn))-qbin the formula, priFor link quality gain, q, of link ibIndicates the link quality before the retransmission, qnIndicating the quality of the link after the retransmission;
dividing the retransmission link set into a series of subsets, wherein the links in the subsets do not conflict with each other, and the pairLink quality benefit pr over a subsetgExpressed as:
Figure FDA0003123570840000011
wherein G represents the number of links in the subset;
5.3, determining the priority mr of the retransmission link subsetgThe following formula:
Figure FDA0003123570840000012
in the formula, AiRepresenting the set of retransmission slots/channels available to link i in the subset, and α is the weight parameter.
2. The method as claimed in claim 1, wherein the step 2 obtains statistical relationship between byte error rates of different RSSI distances by using the RSSI values at byte level in the packet, so as to calculate link quality by the byte error rate, as shown in the following formula:
Figure FDA0003123570840000013
where q is the link quality, biIndicating the byte error rate of the ith byte.
3. The method according to claim 1, wherein the step 3 determines the path priority by specifically using the following formula:
mi＝αli+(1-α)ciin the formula, miAs the priority of path i,/iIndicates the length of path i, ciIndicates the number of collisions for path i and α is a weight parameter.
4. The method for reliably allocating channels of a task-oriented low-power wireless network according to claim 1, wherein the step 4 of allocating time slots and channels to links in the path by using a penalty function method specifically comprises:
the distribution problem is converted into a nonlinear programming problem and solved through a penalty function method, and cutoff time, interference of adjacent links and link quality are comprehensively considered, so that time slots and channels with the highest link quality are preferentially distributed for the links with the most urgent and the most complex interference.
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