CN111328052B - Channel resource allocation method in high-density wireless network - Google Patents
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Abstract
The invention relates to the field of wireless network communication, in particular to a channel resource allocation method in a high-density wireless network; the method divides a channel into a plurality of sub-channels, namely resource units; dividing the channel into a plurality of stages including an uplink random access stage and an uplink resource allocation stage; in the uplink random access stage, the invention reduces the number of competition stations in the network, namely reduces the network density so as to reduce the conflict, and adjusts the optimal competition window value by maximizing the RU throughput in the uplink random access process so as to improve the MAC efficiency. In the uplink resource allocation stage, the uplink resource allocation efficiency is greatly improved by constructing the maximum independent set, so that the RU resources are multiplexed by the D2D link pairs as many as possible, and the channel resource multiplexing rate is greatly improved. During the uplink data transmission phase, the station and D2D link pair can achieve collision-free data transmission on its allocated RU resources, thereby improving channel utilization and system throughput.
Description
Technical Field
The invention relates to the field of wireless network communication, in particular to a channel resource allocation method in a high-density wireless network.
Background
Nowadays, wireless communication technology has penetrated into the aspects of people's life and work, and plays an increasingly important role. With the rapid development of wireless communication technology, wireless local area networks have been widely used in the fields of residential, commercial, and public services. Therefore, how to reduce the network load, improve the channel utilization rate, and reduce the power consumption of the ue becomes a major challenge for the wireless network. Recently, the concept of D2D communication has become a potential solution to the problem of spectral efficiency in 5G. Thus, two users in close proximity can communicate directly in a simple and fast manner without relying on a network infrastructure entity such as an AP or base station. Especially in a high-density scene, the D2D communication can greatly reduce the influence of data service on the network, alleviate the problem of wireless resource constraint, and improve the spectrum efficiency of the system by multiplexing the resources of cellular users.
IEEE 802.11ax is the first Wi-Fi standard that mirrors Orthogonal Frequency Division Multiple Access (OFDMA) technology employed by cellular networks. OFDMA divides the subcarriers of all the bandwidth in the WLAN into several subchannels or RUs. Among them, Wi-Fi channels of 20MHz, 40MHz, 80MHz, and 160MHz can be divided into 9, 18, 37, and 74 RU resources, respectively. Based on this, multiple stations can access different RUs at the same time to realize multi-user parallel transmission. IEEE 802.11ax channel access includes both scheduled access and random access mechanisms. In the scheduling access mode, after receiving a Buffer Status Report (BSR) frame from a station through a random access mechanism, the AP centrally allocates RUs to users in a predefined manner. In the scheduled access mode, data of the scheduling station can be transmitted without collision. However, since the conventional random access mechanism is adopted, collision in the network is inevitable. Especially in high density networks, the contention for the channel by a large number of sites results in higher collisions, which significantly reduces network performance.
Disclosure of Invention
Based on the problems in the prior art, the invention is inspired by D2D communication in the traditional cellular network, and the introduction of the D2D concept into the Wi-Fi network can greatly improve the network performance. In Wi-Fi networks, the use of D2D communication techniques may improve spectral efficiency and reduce the load on the AP when certain devices are located in close spatial proximity and the quality of the communication signal with the AP is poor. Therefore, it is of great interest to use and improve the D2D communication resource allocation algorithm that is suitable for the 802.11ax cellular network model.
The technical scheme adopted by the invention for solving the technical problems comprises the following steps:
in a first aspect of the present invention, a method for allocating channel resources in a high-density wireless network includes:
dividing a channel into a plurality of sub-channels, namely resource units; dividing a channel into a plurality of stages including an uplink random access stage and an uplink resource allocation stage; the sites are divided into D2D sites and non-D2D sites, namely Wi-Fi sites;
in an uplink random access stage, a non-D2D station, namely a Wi-Fi station, randomly accesses a resource unit by adopting a backoff mechanism and sends a BSR frame to compete for channel resources; when the number of stations successfully contending for the resource unit is greater than or equal to the number of RUs, or when the uplink period is reached,
entering an uplink resource allocation stage, modeling an interference relationship between D2D link pairs into an interference graph by the AP according to pre-established D2D link pair information, and generating a plurality of maximum independent set MIS information containing all D2D link pairs and an interference relationship matrix LRSD between the Wi-Fi station and all D2D link pairs; and the AP allocates RU resources to the Wi-Fi stations which successfully compete to the channel in sequence, and allocates interference-free D2D link pairs for each RU according to the maximum independent set information and the interference relation matrix information.
In a second aspect of the present invention, the present invention further provides a method for allocating channel resources in a high-density wireless network suitable for data transmission, including:
dividing a channel into a plurality of resource units RU; dividing a channel into a plurality of stages including an uplink random access stage, an uplink resource allocation stage and an uplink data transmission stage;
in an uplink random access stage, a non-D2D station randomly accesses a resource unit by adopting a backoff mechanism and sends a BSR frame to compete for channel resources; when the number of stations successfully contending for the resource unit is greater than or equal to the number of RUs, or when the uplink period is reached,
entering an uplink resource allocation stage, abstracting an interference relationship between D2D link pairs into an interference graph by the AP according to pre-established D2D link pair information, and generating a maximum independent set information MIS containing all D2D link pairs and an interference relationship matrix LRSD between the station and all D2D link pairs; the AP allocates RU resources (channel resources) to stations which successfully compete to the channel in sequence, and allocates a non-interference D2D link pair to each RU according to the maximum independent set information and the interference relation matrix information;
in the uplink data transmission phase, the station and the D2D link perform collision-free data transmission according to the resource allocation result in the TF frame.
The invention has the beneficial effects that:
the present invention reduces collisions by reducing the number of contention sites in the network, i.e., reducing the network density, in the uplink random access phase, and in addition, adjusts the optimal contention window value by maximizing the RU (subchannel) throughput in the uplink random access process, thereby improving MAC efficiency. In the uplink resource allocation stage, by referring to the concept and characteristics of the maximum independent set, the uplink resource allocation efficiency is greatly improved, so that as many D2D link pairs as possible multiplex RU (sub-channel) resources, and the channel resource multiplexing rate is greatly improved. During the uplink data transmission phase, the station and D2D link pair can achieve collision-free data transmission on its allocated RU resources, thereby improving channel utilization and system throughput.
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FIG. 1 is an example of a network topology provided by an embodiment of the present invention;
FIG. 2 is a general block diagram of the present invention;
fig. 3 is an example of an uplink access mechanism of the present invention;
FIG. 4 is a channel state illustration in the time domain for an embodiment of the present invention;
fig. 5 is a diagram of an interference graph modeling process of a D2D communication pair provided by an embodiment of the present invention;
FIG. 5(a) is a diagram of a network topology provided by the present invention; FIG. 5(b) is a schematic diagram of interference provided by the present invention; FIG. 5(c) is an interference graph provided by the present invention;
FIG. 6 is a resource allocation flow diagram of the present invention;
fig. 7 is an exemplary diagram of D2D link pair allocation RU resources of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more clearly and completely apparent, the technical solutions in the embodiments of the present invention are described below with reference to the accompanying drawings, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.
The invention provides a channel resource allocation method in a high-density wireless network, which mainly comprises the following contents: two phases of uplink random access and uplink resource allocation, and modeling of an interference graph and generation of a maximum independent set and an updating process thereof by a D2D link.
Fig. 1 shows a network architecture diagram of an embodiment of the present invention, in which a wireless access point AP is deployed in the geometric center of a basic service set BSS, and all stations (Wi-Fi stations and D2D link pairs, i.e., D2D stations) are randomly distributed in the coverage area of the AP. Suppose there are m Wi-Fi station and n D2D link pairs in the network under study, where Am denotes stations communicating over the Wi-Fi infrastructure, m is 1,2, …, m; dn represents a D2D link satisfying the direct communication link condition, and n is 1,2, …, n. Therefore, the present invention represents the Wi-Fi site set and the D2D link pair set by a ═ { a1, a2, …, Am } and D ═ D1, D2, …, Dn } respectively. Furthermore, IEEE 802.11ax employs OFDMA in uplink transmission, dividing the entire channel into r RUs (resource units or subchannels), and supporting simultaneous transmission by multiple users at low data rates. Thus, the channel resources may be denoted as R ═ RU1, RU2, …, RUr, each RU consisting of a certain number of subcarriers, where each RU contains at least 26 subcarriers.
Based on the network architecture diagram, the main idea of the invention design is as follows:
i) the AP establishes a D2D link pair for the station meeting the link establishment condition according to the information of each station in the network, and resets the power of the D2D link pair to minimize the interference.
ii) abstract the D2D link pair as an interference graph.
iii) further generating and updating a series of maximum independent sets based on the generated interference graph.
iv) the AP may schedule D2D link pairs belonging to the same MIS to multiplex the same RU, avoiding interference between D2D link pairs while ensuring higher resource reuse.
It is understood that, in the present invention, if not explicitly referred to, a station generally refers to a Wi-Fi station, and a station refers to all stations including a Wi-Fi station and a D2D station only when a D2D station is not selected.
In one embodiment, a channel resource allocation method in a high-density wireless network comprises an uplink random access phase and an uplink resource allocation phase.
In another embodiment, the present invention further provides a channel resource allocation method in a high density wireless network suitable for data transmission, including an uplink random access phase, an uplink resource allocation phase, and an uplink data transmission phase.
Fig. 2 shows that the overall architecture of the invention mainly comprises three phases: an uplink random access phase, an uplink resource allocation phase and an uplink data transmission phase.
Prior to the uplink random access stage, preferentially dividing the whole channel into a plurality of RUs; the uplink random access phase consists of a plurality of backoff phases. To improve spectrum utilization, stations perform dual back-off in both time and frequency domains to participate in medium contention. In addition, in combination with the centralized control characteristic of the IEEE 802.11ax MAC layer, the embodiment of the present invention optimizes the efficiency of the MAC layer by adjusting the optimal contention window by maximizing the throughput of RUs in the uplink random access process, i.e., calculating the optimal contention window CW value by taking the maximized throughput of RU as an objective function.
Fig. 3 shows a backoff mechanism of a station in the uplink random access process, which includes the following detailed processes:
step 1: the AP publishes an optimal contention window value CW and the number of available RUs R in its Random Access Trigger (TF-R) Frame.
And 2, step: if a Wi-Fi station has data to send, it will randomly choose a value from [0, CW ] as its OFDMA Backoff count (OFDMA Backoff, OBO).
And step 3: the Wi-Fi station executes a backoff stage, judges whether a backoff count OBO in the backoff stage is greater than 0, and reduces the backoff count OBO of the backoff stage by r if the backoff count OBO is greater than 0; otherwise, executing step 4;
and 4, step 4: the Wi-Fi station randomly selects one RU from r available RU resources and sends a BSR frame of the RU to the AP; resetting the OBO value of the Wi-Fi site to CW; namely, the Wi-Fi station does not participate in medium competition any more in the random access stage of the current round;
and 5: if the AP successfully receives the BSR frame from the Wi-Fi sites, recording the information of the Wi-Fi sites; and when the number of the Wi-Fi stations successfully contending to the RU is larger than or equal to the number of the RUs, the AP sends a TF frame to inform the end of the uplink random access phase, otherwise, the AP enters the next backoff phase, and the step 3 is executed.
Therefore, in the uplink random access phase, the present embodiment accesses the channel by dual back-off in time and frequency domains, and optimizes MAC efficiency for an objective function based on maximizing Resource Unit (RU) throughput. The back-off mechanism proposed by the present invention not only can reduce collisions by offloading nodes in the network to the D2D communication mode, but also can improve MAC efficiency by optimizing the Contention Window (CW) value of each random access phase.
The related literature indicates that higher throughput can be obtained by optimizing the period of the uplink random access phase, that is, the maximum throughput can be achieved in the uplink random access phase by setting the optimal MAC parameter. Therefore, in the embodiment of the present invention, the optimal CW value is obtained by establishing the target of maximizing the RU throughput, and the theoretical model is as follows:
let τ be the probability that a Wi-Fi station will attempt to transmit a packet in a randomly selected RU at a random slot time, which can be expressed as equation (1).
Where CW is the contention window of the uplink random access phase. CW also denotes an uplink random access period and a backoff value of the AP, and r is the number of available RU resources. Ptr denotes the probability of transmission on a random RU of a random slot, i.e. the probability of at least one station transmitting data in the RU under consideration, then Ptr is:
Ptr＝1-(1-τ)n (2)
pi is used to indicate the probability when no station in the RU under consideration is transmitting data, i.e. the idle probability, then Pi is:
Pi＝(1-τ)n (3)
ps is used to indicate the success probability of selecting a random RU to transmit data on a random time slot, i.e., only one station transmits data on the RU in the same time domain. The successful transmission probability Ps can be calculated by equation (4).
Similarly, the collision probability Pc ═ Ptr-P on randomly selected RUs over random time slotsS. Therefore, the throughput S on each RURUThe calculation can be performed by equation (5).
Wherein, E [ p ]]Indicating the average length of the transmitted data packets. Ts and Tc are the average times of successful transmission and collision, respectively. T is a unit ofiThe time the channel is idle. Assuming that Ts is equal to Tc, the expression is as in equation (6).
Tc＝Ts＝TBSR+2*TSIFS (6)
Wherein, TBSRIndicating the average time to successfully transmit a BSR frame. T isSIFSIs a short inter-frame time. Therefore, substituting the above formula into formula (5) can be SRUThe rewrite is:
to maximize RU throughput in equation (7), and since E [ P ] is a constant, it is only necessary to maximize equation (8).
For a given n, there is an optimal CW to maximize the throughput of the RU. To find CW, the partial derivative of equation (8) with respect to τ is calculated, where τ is a function of CW. The formula (9) gives the corresponding expression.
Wherein k is Tc/Ti. Equation (10) approximately derives an expression for τ using the associated simplified rule.
Therefore, by substituting the τ value of equation (10) into equation (1), an approximate relationship between the optimal CW value and the number of stations can be obtained:
the present invention allows for multi-user parallel transmission, where the number of available RUs is r. Thus, the system throughput can be calculated from CW derived from equation (11), then S is:
where Ps 'and Pi' are the successful transmission probability and the idle probability, respectively. The station adopts a double back-off mechanism in the frequency domain and the time domain, and adopts a traditional back-off mechanism in the time domain, so that Ps 'and Pi' are respectively:
finally, substituting the above-mentioned correlation equation into equation (7) and rewriting equation (12), the system throughput expression is shown as equation (15).
For ease of understanding, fig. 4 is used to further illustrate three channel states in the time domain, namely idle, successful transmission and collision situations.
In the uplink resource allocation stage, to avoid wasting the channel utilization, the AP may schedule downlink transmission at the same time. The goal of uplink resource allocation is to make the resource allocation algorithm simple and efficient. The implementation of the invention mainly divides a resource allocation model into three stages: modeling of the D2D interference graph, generating the maximum independent set and resource allocation decision, as shown in fig. 5.
A first sub-stage: modeling of D2D interference patterns
The first sub-phase of the uplink resource allocation phase is to construct an interference map according to the interference relationship of the D2D link pair. Fig. 5 shows the network topology of a D2D link pair in a network and modeled as a corresponding interference graph, denoted by G ═ V, E >. As shown in fig. 5(a), the network structure is centered by the AP, and is covered with a plurality of D2D link pairs around it; respectively denoted D1, D2, …, D12; the vertices in set V represent pairs of D2D communication links, and thus are represented by D1, D2, …, D12, while the elements in edge set E represent interference relationships between pairs of D2D. The interference relationship is defined by SINR values at the receiving ends of the two links. Fig. 5(b) shows a case where interference is generated when D2D1 and D2D2 use the same RU for data transmission. Fig. 5(c) shows an interference graph after modeling the interference relationship of the D2D link pair; therein, the communication links of S1 (sender 1) to R1 (receiver 1) and S2 (sender 2) to R2 (receiver 2) will cause two interfering links from S2 to R1 and S1 to R2, respectively. And if the SINR of the receiving end of any link is smaller than the SINR threshold, considering that an interference relationship exists between the two communication links. The instantaneous SINR at the receiving end is shown in equation (16).
In the formula, PDBeta is the SINR threshold, alpha is the transmission power of the D2D communication deviceN→DThe path loss for the D2D communication link from the sender to the destination can be represented by equation (17).
Where ρ is the distance of the D2D communication link pair and λ is the wavelength of visible light in the ideal free space transmission model.
In addition, once the D2D link establishment is complete, the transmit power of the D2D communication link is adjusted according to the maximum interference distance of the D2D communication pair to further reduce interference between the D2D link pair, and between the D2D link pair and the STA.
A second sub-stage: generating a maximum independent set
The goal in view of the present implementation is to find the optimal RU multiplexing scheme for the D2D link pair to maximize network performance. Therefore, the present invention is implemented by using the concept and characteristics of MIS in graph theory, that is, there is no neighbor relationship between any two nodes in the same MIS, which means that nodes in the same MIS can transmit data simultaneously without being interfered by each other. Therefore, the temperature of the molten metal is controlled,according to the D2D interference graph G<V，E>The D2D link pairs are classified into different MIS's according to their interference relationships. With S ═ S1, S2, S3, …, Sk]K maximum independent sets representing updated interference maps, where k is variable, with different interference maps corresponding to different k. Sk stores the ID of the D2D link pair in the kth MIS. Further, by using NR (n × n) ═ NRi，j]To represent the interference relationship, nr, between the D2D link pairsi,jThe value of (i, j ∈ n) is expressed as:
a third sub-stage: resource allocation
When the uplink random access phase is finished. The AP will assign RUs to the station and D2D link pair according to the generated maximum independent set and the interference relationship of the station and D2D link pair. Similarly, let LRSD ═ lri,j]Representing the interference relationship of the STA and the D2D link pair, where i e m, j e n. Therefore, lri,jCan be expressed as
The main contribution of the embodiment of the invention is to realize efficient RU resource allocation, and the core idea is to ensure that stations competing to RUs can successfully transmit data, and simultaneously schedule the interference-free D2D link pair multiplexing non-interference RU resources to realize parallel transmission on the same RU resource. Therefore, based on the MIS and LRSD information, not only the goal of resource reuse can be achieved, but also the resource allocation efficiency can be improved.
Fig. 6 shows a flowchart of uplink resource allocation, which describes a process flow of resource allocation by an AP according to station information of successful contention for channel resources, generated maximum independent set information, and an interference relationship between a station and a D2D link pair, where the method includes:
step 1: the AP acquires interference relationship matrix information of Wi-Fi stations competing to RU resources;
step 2: the AP sequentially allocates RU resources to Wi-Fi stations competing to a channel, and initializes RU indexes i to 1;
and step 3: matching the interference relation matrix of the Wi-Fi site competing to the ith RU resource with the maximum independent set with the most elements;
and 4, step 4: judging whether interference does not exist between the D2D link and the site in the current maximum independent set, and if the interference does not exist, performing step 5; otherwise, performing step 6;
and 5: assigning the ith RU to a non-interfering D2D link, removing the D2D link that has been assigned to the RU from the maximum independent set, and updating the maximum independent set;
step 6: matching the interference relation matrix of the Wi-Fi site with the maximum independent set with the most elements in the remaining maximum independent sets;
and 7: and judging whether all RU allocation is completed or all the maximum independent sets are empty, if so, making i equal to i +1, returning to the step 2, and otherwise, ending the flow.
In the present embodiment, the D2D link pairs belonging to the same MIS can reuse the same RU resource or subchannel, but there is no interference between these D2D link pairs and the Wi-Fi site occupying the RU. The uplink resource allocation phase ends when the AP allocates a D2D link pair for each RU or there is no D2D link pair with no allocated RU.
Fig. 7 shows an example in resource allocation. In each resource allocation sub-phase, the AP will allocate a reusable D2D link pair for each RU based on the S _ STA (storing Wi-Fi sites that successfully contend to RU resources) and the LRSD information. For example, when i equals 1, the AP allocates channel resource RU1 to S _ STA (i), assuming that the Wi-Fi station is STA 1. Thus, the AP obtains the maximum independent set information from S (1) and the interference relationship matrix between STA1 and D2D link pairs, LRSD (STA1) [1, 1, 0, 0, 1, 1, 0, 1], where the number of elements in LRSD is equal to the number of D2D link pairs. Then, the AP matches the LRSD (STA1) and S (1), and finally stores the result in dr (i), and updates S.
In one embodiment, the uplink data transmission stage performs operations including:
in the uplink data transmission stage, the AP sends a TF frame, the Wi-F station and the D2D link that receive the TF frame perform collision-free data transmission on its allocated RU according to the resource allocation information included in the frame, and when the AP successfully receives the data sent by the station, the AP replies a multi-user block ACK (MBA) frame.
It may also include the station and D2D link pair performing collision-free data transmission on its available RUs based on information in the TF frame sent by the AP. Assuming that the uplink data transmission period is TXOP, these station and D2D link pairs may transmit data during a given TXOP. After receiving the packet from the station, the AP will reply to the station using a multi-block acknowledgement mechanism.
Those skilled in the art will appreciate that all or part of the steps in the methods of the above embodiments may be implemented by associated hardware instructed by a program, which may be stored in a computer-readable storage medium, and the storage medium may include: ROM, RAM, magnetic or optical disks, etc.; in addition, the channel resource allocation algorithm of the present invention is not limited to allocating RU resources but also applies to allocating subchannel resources.
The above-mentioned embodiments, which are further detailed for the purpose of illustrating the invention, technical solutions and advantages, should be understood that the above-mentioned embodiments are only preferred embodiments of the present invention, and should not be construed as limiting the present invention, and any modifications, equivalents, improvements, etc. made to the present invention within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. A method for allocating channel resources in a high-density wireless network is characterized by comprising the following steps:
dividing a channel into a plurality of subchannels, namely resource units; dividing the channel into a plurality of stages including an uplink random access stage and an uplink resource allocation stage;
in an uplink random access stage, a non-D2D station, namely a Wi-Fi station, randomly accesses a resource unit by adopting a backoff mechanism and sends a BSR frame to compete for channel resources; when the number of Wi-Fi stations successfully contending for the resource unit is greater than or equal to the number of RUs, or when an uplink period is reached,
entering an uplink resource allocation stage, modeling an interference relationship between D2D link pairs, namely D2D stations, as an interference graph by the AP according to pre-established D2D link pair information, and generating a plurality of maximum independent set MIS information containing all D2D link pairs and an interference relationship matrix LRSD between the Wi-Fi stations and all D2D link pairs; the AP allocates RU resources to the Wi-Fi stations which successfully compete to the channel in sequence, and allocates an interference-free D2D link pair to each RU according to the maximum independent set information and the interference relationship matrix information;
the modeling process of the interference graph comprises that a network topology structure is formed by taking an AP as a center and covering a plurality of D2D link pairs around the AP; representing the D2D link pairs by a vertex set V and representing the interference relationship between the D2D link pairs by an edge set E to form an interference graph G < V, E >; the interference relationship is defined by SINR values of receiving ends of two links; if the SINR of the receiving end of any link is smaller than the SINR threshold, the interference relationship between the two communication links is considered to exist;
the process of generating multiple maximum independent sets MIS information containing all D2D link pairs includes generating a maximum independent set MIS information from an interference graph G<V，E>Dividing the D2D link pair into different MIS according to the interference relation; with S ═ S1, S2, S3, …, Sk]K most independent sets representing updated interference maps, where k is variable, different interference maps corresponding to different k; sk stores the ID of the D2D link pair in the kth MIS; by NR (nxn) ═ NRi，j]To represent the interference relationship between the D2D link pair, when there is an interference relationship between the D2D link pair i and the D2D link pair j, nr is the interference relationship between the link pair i and the link pair ji,j1, otherwise nri,j＝0；
The process that the AP allocates RU resources to the Wi-Fi stations which successfully compete to the channel in sequence comprises the step that when the uplink random access stage is finished; the AP will assign RUs to station and D2D link pair, let LRSD ═ l, according to the generated maximum independent set and interference relationship of station and D2D link pairri,j]Representing a STA and D2D link pairWhen there is an interference relationship between site i and D2D link pair j, then lri,j1, otherwise lri,j＝0；
The process of allocating a non-interfering D2D link pair to each RU according to the maximum independent set information and the interference relationship matrix information includes:
step 1: the AP acquires interference relationship matrix information of Wi-Fi stations competing to RU resources;
step 2: the AP sequentially allocates RU resources to Wi-Fi stations competing to a channel, and initializes RU indexes i to 1;
and step 3: matching the interference relation matrix of the Wi-Fi site competing to the ith RU resource with the maximum independent set with the most elements;
and 4, step 4: judging whether interference does not exist between the D2D link and the site in the current maximum independent set, and if interference does not exist, performing step 5; otherwise, performing step 6;
and 5: assigning the ith RU to a non-interfering D2D link, removing the D2D link that has been assigned to the RU from the maximum independent set, and updating the maximum independent set;
step 6: matching the interference relation matrix of the Wi-Fi site with the maximum independent set with the most elements in the remaining maximum independent sets;
and 7: and (3) judging whether all RU allocation is completed or all the maximum independent sets are empty, if so, making i equal to i +1, returning to the step (2), otherwise, ending the flow.
2. The method of claim 1, wherein the back-off mechanism comprises:
step 1: the AP publishes an optimal contention window value CW and an available RU number R in a random access trigger TF-R frame;
step 2: if the Wi-Fi station needs to send data, a value is randomly selected from a contention window [0, CW ] to serve as a backoff count OBO of the Wi-Fi station;
and step 3: the Wi-Fi station executes a backoff stage, judges whether a backoff count OBO in the backoff stage is greater than 0, and reduces the backoff count OBO of the backoff stage by r if the backoff count OBO is greater than 0; otherwise, executing step 4;
and 4, step 4: the Wi-Fi station randomly selects one RU from r available RU resources and sends a BSR frame of the RU to the AP; resetting the OBO value of the Wi-Fi station to CW; namely, the Wi-Fi station does not participate in medium competition any more in the current round of uplink random access stage;
and 5: if the AP successfully receives the BSR frame from the Wi-Fi sites, recording the information of the Wi-Fi sites; and when the number of the Wi-Fi stations successfully contending to the RU is larger than or equal to the number of the RUs, the AP sends a TF frame to inform the end of the uplink random access phase, otherwise, the AP enters the next backoff phase, and the step 3 is executed.
3. The method of claim 2, wherein the contention window value is calculated by maximizing the throughput of the RUs as an objective function to calculate an optimal contention window value, such that the throughput S per RU is the maximumRUExpressed as:
wherein, TiIndicating the average time of occurrence of the collision; t is a unit ofcRepresents the average time that the channel is idle; e [ P ]]Is the average packet length; n represents the number of Wi-Fi sites; tau represents the probability of sending data packets in randomly selected RUs at random time slot of the Wi-Fi station; CW denotes a contention window value.
4. A method for allocating channel resources in a high-density wireless network according to claim 3, wherein τ is calculated by calculating a partial derivative of throughput in each RU with respect to τ, and extracting τ in an approximately derived manner; the calculation formula is expressed as:
wherein k is Tc/Ti.
5. The method of claim 1, wherein the interference relationship matrix between the station and all D2D link pairs is generated by constructing an interference graph according to D2D link pairs and their interference relationships; judging whether the SINR between any Wi-Fi station and the D2D link to the receiving end is smaller than an SINR threshold value, if so, determining that an interference relationship exists between the two links; forming interference relation matrix information LRSD (lrr) between the Wi-Fi station and the D2D link pair according to the interference relationi,j]Wherein, lri,jRepresents the interference relationship between Wi-Fi station i and D2D link pair j, lri,j1 represents that an interference relationship exists between the Wi-Fi station i and the D2D link pair j; lr ofi,j0 means that there is no interference relationship between Wi-Fi station i and D2D link pair j.
6. The method as claimed in claim 1, wherein the channel is further divided into an uplink data transmission phase, and in the uplink data transmission phase, the station and the D2D link perform collision-free data transmission according to the resource allocation result in the TF frame.
7. The method as claimed in claim 6, wherein the operation performed in the uplink data transmission phase includes the AP sending a TF frame, the Wi-Fi station and the D2D link receiving the TF frame performing collision-free data transmission on its allocated RU according to the resource allocation information contained in the frame, and the AP replying a multi-user block acknowledgement MBA after the AP successfully receives the data sent by the station.
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