CN108599881B - Radio dynamic spectrum access method for multi-user and multi-channel - Google Patents

Radio dynamic spectrum access method for multi-user and multi-channel Download PDF

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CN108599881B
CN108599881B CN201810191313.8A CN201810191313A CN108599881B CN 108599881 B CN108599881 B CN 108599881B CN 201810191313 A CN201810191313 A CN 201810191313A CN 108599881 B CN108599881 B CN 108599881B
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黄新林
唐小伟
高煜
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Tongji University
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Abstract

The invention relates to a radio dynamic spectrum access method for multi-user and multi-channel, which comprises the following steps: s1: based on a Dirichlet process, acquiring a subcarrier loading strategy and a data packet arrival rate of each virtual user according to an ACK/NACK message broadcasted by a cluster head in a cognitive radio network in unit time; s2: defining the collision probability of the target secondary user data packet; s3: obtaining a probability density function obeyed by the data packet transmission delay of a target secondary user; s4: establishing a relation between the data packet transmission delay and the queue delay of a target secondary user data packet, and acquiring the total delay characteristic of multimedia transmission; s5: combining the retransmission times of the data packet to obtain the channel capacity characteristic of multimedia transmission; and S6, constructing a service quality evaluation system by combining the capacity characteristic and the time delay characteristic, and establishing an optimal data packet loading mode for the target secondary user by maximizing the service quality. Compared with the prior art, the method has the advantages of low cost, high practicability and the like.

Description

Radio dynamic spectrum access method for multi-user and multi-channel
Technical Field
The invention relates to the technical field of cognitive radio spectrum access, in particular to a radio dynamic spectrum access method for multiple users and multiple channels.
Background
The spectrum sensing is a core technology in cognitive radio, and needs to monitor surrounding wireless environment in real time, provide available spectrum resources for unauthorized users, and simultaneously ensure that the occupation of the authorized users on the current frequency band is found in time, so as to avoid causing interference. Therefore, the accuracy of spectrum sensing plays a very critical role for cognitive radio networks. A great deal of research work on spectrum sensing technology provides a plurality of detection methods based on signal processing, and the detection methods can be mainly divided into two categories of uncooperative spectrum sensing and cooperative spectrum sensing.
With the development of wireless communication technology, the demand of people for wireless communication services is rapidly increasing, so that wireless spectrum becomes a more and more tense resource. In wireless communications, spectrum resources are very limited and expensive, and wireless spectrum can only be legally used if authorized. However, studies have shown that some wireless bands are heavily loaded and some bands are almost free. Therefore, a new wireless access mode is urgently needed to utilize the idle frequency bands, so that the problem that the wireless spectrum is increasingly tense can be relieved, and the cognitive radio technology is taken as a hot research technology in the field of future wireless communication, so that the spectrum utilization efficiency of wireless resources can be effectively improved.
The Federal Communications Commission (FCC) published a spectrum report in 2003 that has a milestone significance, which confirms the low utilization of licensed bands and emphasizes that cognitive radio technology plays an important role in future FCC policies. According to reports, the probability that the authorized frequency bands below 3GHz are not fully used is up to 70%, and the traditional spectrum allocation mode causes the waste of the spectrum resources in time and space. The cognitive radio technology is proposed under the condition that the spectrum resources are seriously tensed, and makes a great contribution to improving the utilization efficiency of the spectrum resources. The cognitive radio technology has unique advantages, can realize dynamic spectrum allocation, and effectively relieves the situation of spectrum resource shortage. Although most of the cognitive radio technologies are still under research state and the technologies are not mature enough, the cognitive radio technologies can certainly have strong development prospects in the field of wireless communication by virtue of flexible radio characteristics and dynamic spectrum allocation characteristics.
With the development of cognitive radio technology, research and application of the cognitive radio technology are no longer the initial category, and different researchers have elaborated more deeply on cognitive radio from different angles. The concept of cognitive Radio was originally proposed by Joseph Mitola III, a doctor of royal technical college, sweden, and is an intelligent extension of Software Defined Radio (SDR) technology. Doctor Mitola has proposed a concept of "Radio Knowledge Representation Language (RKRL)" and Spectrum pool (Spectrum pool) describing the internal structural modules, devices and radio environment of a radio network. Doctor Mitola thinks that the cognitive radio technology is based on software radio, but there are essential differences from software radio, which are mainly reflected in: the cognitive radio can recognize the use model of radio frequency environment, air interface, communication protocol and frequency spectrum through the reasoning ability of the radio module and intelligently communicate with the network through the RKRL language, thereby greatly improving the flexibility of communication and realizing a more personalized communication mode.
From the perspective of spectrum management, the FCC calls any radio with adaptive spectrum sensing capability as a cognitive radio, and therefore, the FCC has proposed a narrow definition of cognitive radio. To overcome the current inefficient utilization of radio spectrum resources, the federal communications commission in the united states has proposed a "secondary usage" radio spectrum system to open authorized bands, in which authorized users have priority for using radio spectrum resources, while unauthorized users must opportunistically access when the authorized users do not occupy the radio spectrum resources and exit in time when the authorized users are re-occupied. According to the definition of the FCC, a cognitive radio is a radio whose transmitting end adjusts transmission parameters according to the interaction with the working environment in which it is located, and is therefore also called an "opportunistic spectrum access radio".
In the conventional cooperative spectrum access scheme, when an authorized user in the system successfully sends a data packet, another unauthorized user receives the data packet and then sends the data packet back for confirmation, while the number of users in the whole radio network is large, and great expense is caused by frequent information exchange of sending and receiving.
Disclosure of Invention
The present invention is directed to overcoming the above-mentioned drawbacks of the prior art and providing a dynamic spectrum access method for multi-user multi-channel radio.
The purpose of the invention can be realized by the following technical scheme:
a radio dynamic spectrum access method for multi-user multi-channel, comprising the steps of:
s1: the on-line learning method based on the Dirichlet process acquires a subcarrier loading strategy and a data packet arrival rate of each virtual user according to an ACK/NACK message broadcast by a cluster head in a cognitive radio network in unit time;
s2: defining the conflict probability of a target secondary user data packet according to the data packet arrival rate of the virtual user;
s3: acquiring a probability density function obeyed by the data packet transmission delay of the target secondary user and the data packet loss probability according to the collision probability of the data packet of the target secondary user and a deferral retransmission mechanism when the data packet in the S-ALOHA system collides;
s4: establishing a relation between the data packet transmission delay and the queue delay of a target secondary user data packet, and acquiring the total delay characteristic of multimedia transmission;
s5: acquiring the capacity characteristic and the channel characteristic of multimedia transmission by combining the retransmission times of the data packet according to the data packet loss probability acquired in the step S3;
s6: and (4) constructing a service quality evaluation standard by combining the capacity characteristic, the channel characteristic and the total time delay characteristic obtained in the step (S4), and establishing an optimal data packet loading mode for the target secondary user to complete dynamic spectrum access.
Preferably, the step S1 specifically includes the following steps:
101) regarding other secondary users except the target secondary user in the cognitive radio network as a virtual user;
102) when the virtual user successfully receives or sends a data packet, the cluster head broadcasts an ACK/NACK message;
103) according to the number of ACK/NACK messages broadcast by the cluster head in unit time, obtaining a subcarrier loading strategy of the virtual user, and calculating the data packet arrival rate of other virtual users except the target secondary user
Figure GDA0002723760810000036
The calculation formula is as follows:
Figure GDA0002723760810000031
wherein, E { mu }jThe loading ratio of the virtual user on the sub-carrier j is multiplied, K is the number of ACK/NACK messages broadcast by the cluster head,
Figure GDA0002723760810000032
as an authorized userProbability of occupying the channel.
Preferably, in step S2, the defining process of the collision probability of the target secondary user data packet is as follows:
assuming that the arrival rate and the retransmission rate of the virtual user data packets obey poisson distribution, the probability that a data packet is not received in the channel within the time t is equal to the probability that a target secondary user generates a new data packet every time t, and the probability F that the target secondary user generates a new data packet every time t is equal to the probability that the target secondary user generates a new data packet every time tij(T is more than or equal to T,0) is as follows:
Figure GDA0002723760810000033
wherein T is the inter-packet arrival time and compliance parameter is
Figure GDA0002723760810000035
Is then the probability p that the target secondary user data packet is not subject to collisionijThe expression of (a) is:
Figure GDA0002723760810000034
where τ is the minimum unit of time required for a packet to succeed from transmission to reception.
Preferably, the step S3 specifically includes the following steps:
301) retransmitting the data packet after collision or conflict, and acquiring the data packet loss probability and probability density function of the target secondary user on the subcarrier j under different transmission time delays according to the conflict probability of the target secondary user data packet;
302) and acquiring the mixed exponential distribution obeyed by the total transmission delay according to the data packet loss probability and the probability density function.
Preferably, the specific content of step 301) is:
suppose that the retransmission time of each time is T respectively1,T2,T3,…,TkTarget secondary user SUiThe probability of packet loss on subcarrier j is ωj(k-1)Then, there are:
when transmission delay Tpτ, target secondary user SUiThe probability of packet loss on subcarrier j is ωj1＝pijThe probability density function is:
f1(Tp)＝δ(Tp-τ)
when transmission delay Tp＝τ+T1Then, the target secondary user SUiThe probability of packet loss on subcarrier j is ωj2＝(1-pij)·pijThe probability density function is:
Figure GDA0002723760810000041
when transmission delay Tp＝τ+T1+T2Then, the target secondary user SUiThe probability of packet loss on subcarrier j is ωj3＝(1-pij)2·pijThe probability density function is:
Figure GDA0002723760810000042
when the transmission delay is Tp＝τ+T1+T2+T3+…+TkThen, the target secondary user SUiThe probability of packet loss on subcarrier j is ωjk＝(1-pij)k-1·pijThe probability density function is:
Figure GDA0002723760810000043
when the transmission delay is TpInfinity indicates that the packet is dropped and the targeted secondary user SUiThe probability of packet loss on subcarrier j is
Figure GDA0002723760810000044
The probability density function is:
f∞(Tp)＝δ(Tp-τ)
where δ (.) is an impulse function.
Preferably, in the step 302), the expression of the mixed exponential distribution obeyed by the total transmission delay is as follows:
Figure GDA0002723760810000045
preferably, the step S4 specifically includes the following steps:
401) obtaining queue time delay according to Blackcut-Qinzi formula
Figure GDA0002723760810000051
Figure GDA0002723760810000052
In the formula, X is
Figure GDA0002723760810000053
Targeted secondary users SU during timeiThe number of data packets waiting to be transmitted on the subcarrier j is r, and the r is the residual transmission time of the data packets transmitted on the subcarrier by the virtual user at the current moment; using the mean value of r
Figure GDA0002723760810000054
To represent r, wherein,
Figure GDA0002723760810000055
for a targeted secondary user SUiThe time of the data packet transmitted on the subcarrier j is the second order distance, the queue delay
Figure GDA0002723760810000056
Becomes:
Figure GDA0002723760810000057
wherein λ isi·For a targeted secondary user SUiData packet arrival rate of sijIs SUiThe loading ratio on subcarrier j;
402) queue delay based on data packets
Figure GDA0002723760810000058
And transmission delay
Figure GDA0002723760810000059
Obtaining total time delay d in data packet transmission processij：
Figure GDA00027237608100000510
403) Suppose a target secondary user SUiHas a maximum tolerated delay of DiAccording to the total delay d in the transmission of the data packetijThen the target secondary user SUiThe queue time delay loaded on the subcarrier j is less than DiThe probability of (c) is:
Figure GDA00027237608100000511
in the formula:
Figure GDA00027237608100000512
where ψ is the maximum number of retransmissions allowed by the system, T0Is TpThe expression of the upper limit value of (2) is:
Figure GDA00027237608100000513
preferably, the step S5 specifically includes the following steps:
501) obtaining the capacity characteristic of the multimedia transmission, namely the target secondary user SU according to the data packet loss probability obtained in the step S3iPacket transmission rate of (PDR)i：
Figure GDA0002723760810000061
Wherein M is the total number of channels.
502) And acquiring the channel characteristics of multimedia transmission, namely the transmitting power corresponding to different modulation modes according to different modulation modes.
Preferably, the step S6 specifically includes the following steps:
601) defining a service quality evaluation standard U according to the time delay of multimedia transmission and the spectrum utilization efficiency performance of the subcarrieri(S, L) is:
Figure GDA0002723760810000062
in the formula, thetaiThe weight coefficient is the preference degree of the user to the capacity characteristic and the time delay characteristic in the system; l isjThe number of bits per symbol;
602) setting a power limiting condition, a channel capacity limiting condition and a subcarrier loading strategy limiting condition of a service quality evaluation standard;
603) and according to the limiting conditions, maximizing the service quality standard, acquiring the optimal data packet loading mode of the target secondary user, and completing dynamic spectrum access.
Preferably, the specific content of step 602) is:
the power limiting condition is as follows:
Figure GDA0002723760810000063
wherein the content of the first and second substances,
Figure GDA0002723760810000065
power, P, of data packets transmitted for a time useriThe limiting condition requires that the sum of the powers of the users for transmitting data packets simultaneously within a certain time cannot exceed the transmitting power of the users;
channel capacity limiting conditions:
Figure GDA0002723760810000064
wherein, B is the bit capacity of the channel per second, L is the length of each data packet, and the limitation condition requires that the capacity of the data packet loaded on the subcarrier j by the virtual user and the target user in unit time cannot exceed the available capacity of the subcarrier;
subcarrier loading strategy constraints:
Figure GDA0002723760810000071
the constraint condition requires that the subcarrier loading strategy constraint requires that the sum of the subcarrier loading strategies of the target secondary users is less than or equal to 1.
Compared with the prior art, the invention has the following advantages:
firstly, reducing the overhead: the invention divides the whole radio network system into a plurality of mutually independent cluster structures, each cluster structure has a cluster head, when the member in the cluster needs to send a data packet, the data packet is sent to the cluster head, the cluster head is responsible for collecting the data packet and transmitting the data packet, the cluster head broadcasts an ACK message to the member in the cluster when successfully receiving the data packet, and when the transmission is wrong or the collision happens, the cluster head broadcasts a NACK message, the ACK messages can be used for estimating the data packet arrival rate of each secondary user, namely, the invention only needs to send and receive the ACK/NACK message to judge whether the data packet is successfully received, thereby effectively avoiding the overhead caused by frequent information exchange in the traditional cooperative spectrum access scheme;
secondly, the practicability is strong: the service evaluation system defined in the invention can enable users to set different weight coefficients according to the preference degree of the users on the time delay characteristics and the capacity characteristics, and has certain flexibility in the aspects of time delay and spectrum utilization efficiency.
Drawings
Fig. 1 is a schematic diagram of dynamic spectrum access in a cognitive radio network;
FIG. 2 is a diagram illustrating queue delays for a packet transmitted over a channel;
fig. 3 is a flow chart of a radio dynamic spectrum access method for multi-user multi-channel;
fig. 4 is a graph of an influence relationship of the maximum tolerable delay to the transmission delay distribution function under different collision probabilities in the embodiment of the present invention;
fig. 5 is a diagram illustrating an influence relationship of a target secondary user loading policy on a transmission delay distribution function under different collision probabilities in the embodiment of the present invention;
FIG. 6 is a diagram illustrating the impact of transmit power on a target secondary user loading policy in an embodiment of the present invention;
FIG. 7 is a graph illustrating the impact of channel availability on packet loss probability according to an embodiment of the present invention;
FIG. 8 is a diagram illustrating the effect of maximum tolerable delay on the probability of packet loss according to an embodiment of the present invention;
FIG. 9 is a graph illustrating the effect of transmit power on latency and throughput in an embodiment of the present invention;
fig. 10 is a comparison graph of the influence relationship of the weight coefficient of a certain channel on the service quality when different authorized users do not occupy the channel probability under the method and the uniform loading method provided in the embodiment of the present invention;
fig. 11 is a comparison graph of the influence relationship between the weight coefficient of a certain channel and the service quality under different maximum tolerable delays in the method and the uniform loading method according to the embodiment of the present invention;
FIG. 12 is a diagram illustrating the effect of the maximum tolerable delay on the delay and the throughput in the embodiment of the present invention;
FIG. 13 is a diagram illustrating the effect of an original video frame according to an embodiment of the present invention;
FIG. 14 is a diagram illustrating the effect of a video frame demodulated by an intelligent cross-layer method according to an embodiment of the present invention;
FIG. 15 is a diagram illustrating the effect of video frames demodulated by the dynamic learning method according to the embodiment of the present invention;
FIG. 16 is a diagram illustrating the effect of a video frame demodulated by the dynamic minimum interference method according to an embodiment of the present invention;
fig. 17 is a diagram illustrating the effect of the video frame demodulated by the method of the present invention in the embodiment of the present invention.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
Examples
As shown in fig. 1, fig. 2, and fig. 3, the present invention relates to a radio dynamic spectrum access method for multi-user and multi-channel, comprising the following steps:
step one, an online learning process:
11) the other secondary users than the target secondary user are treated as a virtual user.
12) Whenever a packet is successfully received or transmitted, the cluster head broadcasts an ACK/NACK message, where ACK (acknowledgement) indicates an acknowledgement signal and NACK (negative acknowledgement) indicates a non-acknowledgement signal.
13) The subcarrier loading strategy of the virtual user is obtained by observing the number of K ACK/NACK messages sent by the virtual user in unit time, and the data packet arrival rate of the virtual user is calculated by the following specific formula:
Figure GDA0002723760810000081
wherein the content of the first and second substances,
Figure GDA0002723760810000083
packet arrival rate for users other than the target secondary user, E { mu }jThe loading ratio of the virtual user on the subcarrier j is multiplied, and K is the cluster headThe number of ACK/NACK messages that are broadcast,
Figure GDA0002723760810000082
to authorize the probability that a user does not occupy the channel, the subcarrier loading policy of the virtual user is a set of loading proportions of each user on subcarrier j.
Step two, defining the collision probability of the target secondary user data packet:
21) assuming that the arrival rate and retransmission rate of the virtual users obey the poisson distribution, the probability that no data packet is received in the channel at time t is equal to the probability that a secondary user generates a new data packet at every time t, and the probability is:
Figure GDA0002723760810000091
wherein, Fij(T is more than or equal to T,0) represents the probability that the secondary user generates a new data packet at every T moments;
22) the inter-arrival time T of the data packet obeys a parameter of
Figure GDA0002723760810000098
Is then the probability p that the target secondary user data packet is not subject to collisionijThe expression of (a) is:
Figure GDA0002723760810000092
wherein p isijIndicating the probability that the data packet of the target secondary user is not subject to collision, τ is the length of one slot in TDMA technique and is the minimum unit of time required for the data packet to succeed from transmission to reception.
Step three, obtaining a transmission delay distribution probability density function and a data packet loss probability:
31) after the data packets collide or collide, the maximum retransmission times is 3 times, and it is assumed that the retransmission time per time is T1、T2And T3Time delay of transmission of data packetAnd the packet loss probability is shown in table 1:
table 1 transmission time and corresponding probability of data packet when maximum retransmission times is 3
Figure GDA0002723760810000093
32) Since the time interval t obeys a parameter of
Figure GDA0002723760810000099
So that it can be deduced that the data packet transmission time delay is tau, tau + T1、τ+T1+T2、τ+T1+T2+T3The probability density function at ∞ is shown as follows:
f1(Tp)＝δ(Tp-τ),Tp＝τ
Figure GDA0002723760810000094
Figure GDA0002723760810000095
Figure GDA0002723760810000096
f5(Tp)＝δ(Tp-τ),Tp＝∞
wherein, Tpδ () is an impulse function for the transmission delay of a data packet. Thus, the overall propagation delay obeys a mixed exponential distribution that can be expressed as:
Figure GDA0002723760810000097
step four, acquiring the total time delay characteristic:
41) assume team of the data packetFor column delay
Figure GDA0002723760810000101
Expressed, the queue time delay is according to a Blake-Qinzi formula (P-K formula)
Figure GDA0002723760810000102
Can be expressed as:
Figure GDA0002723760810000103
wherein X represents
Figure GDA0002723760810000104
Targeted secondary users SU during timeiThe number of data packets waiting to be transmitted on subcarrier j,
Figure GDA0002723760810000105
the transmission time of the data packet on the subcarrier follows the mixing index distribution which is obtained in the previous step, and r represents the residual transmission time of the data packet transmitted on the subcarrier by the user at the current moment.
42) Because r is less than or equal to X.TpFor simple calculation, the mean value of r is used in the embodiment
Figure GDA0002723760810000106
Represents a unit of a structure represented by r, wherein,
Figure GDA0002723760810000107
for a user SUiIs transmitted on subcarrier j. Thus, the queue delay
Figure GDA0002723760810000108
The expression of (c) can be expressed as:
Figure GDA0002723760810000109
wherein λ isi·Representing a target secondary user SUiData packet arrival rate of sijRepresents SUiThe loading ratio on subcarrier j.
43) Because the time delay of the data packet comprises queue time delay and transmission time delay, the transmission time delay of the newly loaded data packet is considered, and therefore the total time delay d in the data packet transmission process can be obtainedijComprises the following steps:
Figure GDA00027237608100001010
44) suppose a user SUiHas a maximum tolerated delay of DiThen its queue delay loaded on subcarrier j is less than DiThe probability of (d) can be expressed as:
Figure GDA00027237608100001011
in the formula:
Figure GDA00027237608100001012
where ψ is the maximum number of retransmissions allowed by the system, T0Is TpThe expression of the upper limit value of (2) is:
Figure GDA00027237608100001013
step five, acquiring capacity characteristics:
51) suppose that the probability of packet loss has been given in table 1 as
Figure GDA0002723760810000111
Then the target secondary user SUiThe packet transmission rate of (a) is:
Figure GDA0002723760810000112
where M is the total number of channels.
52) In an actual communication process, the fading characteristics between channels are different, which causes differences between channels, so that the wireless channel characteristics between users in a cluster and a cluster are different, and it is assumed that the time-domain CIR of an ISI channel between a secondary user and the cluster is h ═ 0.80.6]The transmission power required for transmitting the data packets according to different modulation modes is also different, and the bit error rate p of the data packets in the transmission process is assumed0If the modulation scheme is constant, the transmission power of each modulation scheme is fixed, and the transmission power corresponding to each modulation scheme is shown in table 2.
TABLE 2 modulation scheme and Transmission Power
Figure GDA0002723760810000113
In table 2, q (x) is a mathematical common integral expressed by:
Figure GDA0002723760810000114
wherein HjIs the frequency domain CIR on subcarrier j.
Step six, establishing a service quality evaluation standard, and obtaining an optimal data packet loading mode of a target secondary user:
61) considering the time delay of multimedia transmission and the spectrum utilization efficiency performance of subcarriers, defining the service quality evaluation standard as follows:
Figure GDA0002723760810000115
wherein, thetaiAs a weight factor, this parameter reflects the preference of the user data packet for the time delay or the spectrum utilization efficiency, LjFor the number of bits per symbol,
62) setting a limiting condition for service quality evaluation;
setting power limiting conditions, channel capacity limiting conditions and subcarrier loading strategy limiting conditions, wherein the expressions are as follows:
the power limiting condition is as follows:
Figure GDA0002723760810000121
wherein the content of the first and second substances,
Figure GDA0002723760810000126
power, P, of data packets transmitted for a time useriThe transmit power of the user, the limitation condition describes that the sum of the power of the users transmitting data packets simultaneously in a certain time cannot exceed the transmit power of the users;
channel capacity limiting conditions:
Figure GDA0002723760810000122
the limiting condition indicates that the capacity of the data packets loaded on the subcarrier j by the virtual user and the target user in unit time cannot exceed the available capacity of the subcarrier;
subcarrier loading strategy constraints:
Figure GDA0002723760810000123
the constraint requires that the sum of the subcarrier loading strategies for the target secondary user is less than or equal to 1.
63) And under the limiting condition provided by the step 62), maximizing the service quality in the step 61), thereby obtaining the optimal data packet loading mode of the target secondary user and completing the access of the dynamic spectrum.
In order to verify the effectiveness of the spectrum access method of the present invention, the present embodiment performs a multi-user multi-channel multimedia transmission scene simulation experiment.
Assume that a cognitive wireless point network is divided intoA plurality of mutually independent cluster structures, and each cluster is composed of a cluster head and four cluster members. Consider a scenario with four channels, four secondary users SU and one primary user PU. According to the condition limitations of channel capacity and the like in the system, the transmission bit rate of the data packets of four secondary users in a cluster is 0.4Mbps, the size L of each data packet is 1000 bits, the bandwidth B of a channel is 1MHz, the length tau of each time slot is 1ms, and the probability that a primary user PU does not occupy the channel
Figure GDA0002723760810000124
The threshold of the error rate is set to be 10 < -5 > when the multimedia is transmitted, which is 0.85.
The embodiment firstly simulates the performance of a transmission delay function, and changes the maximum tolerance delay D of the systemiAnd the loading ratio s of the target secondary userijAnd observing the distribution situation of the transmission delay. The distribution performance of the transmission delay is shown in fig. 4 and 5. Abscissa is packet collision probability
Figure GDA0002723760810000125
Is a value of 0-1, and the ordinate is that the transmission delay is less than the threshold value T0The distribution probability of (2). In fig. 4, the maximum tolerable delays are set to 6ms, 8ms, 10ms and 12ms, respectively. As can be seen from fig. 4, under the same maximum tolerable delay value, as the collision probability increases, the probability that the transmission delay is smaller than the threshold value also gradually decreases; under the same collision probability, the probability that the transmission delay is smaller than the threshold value is increased along with the increase of the maximum endurance delay. In fig. 5, the target secondary user SUiThe packet loading rates on channel j are set to 0.1, 0.3, 0.5 and 0.7, respectively. As can be seen from fig. 5, under the same data packet loading ratio, as the collision probability increases, the probability that the transmission delay is smaller than the threshold value gradually decreases; under the condition of the same collision probability, the probability that the transmission delay is smaller than the threshold value is reduced along with the increase of the loading proportion.
The throughput characteristics of the inventive method are verified below. According to the method, the data packet loss can be caused by four reasons. The first is that the data packet still fails after three times of collision retransmission; the second is to ensure the delay characteristic of the system, a part of the data packets will be actively discarded; the third is due to the limited power of the target secondary user; the fourth is due to the limited channel capacity. In this simulation, it is assumed that the noise in the channel is white gaussian noise and the noise power is 1, and the transmission power of the target secondary user is 5, 10, 20 and 30dB, respectively. Specific throughput characteristics are shown in fig. 6 to 9. Fig. 6 shows the data packet loading manner of the target secondary user at different transmission powers, and because the channel quality of the third channel is the worst due to the fading characteristics of the channel transmitted by the data packet, when the transmission power is low, the proportion of the data packet loaded on the third channel by the target secondary user is the lowest; fig. 7 shows the packet loss probability corresponding to different maximum tolerable delays under different transmission powers, and it can be seen that the packet loss probability decreases with the increase of the maximum tolerable delay. Fig. 8 shows the data packet loss probability corresponding to the idle probability of different primary users under different transmission powers, and it can be seen that the data packet loss probability also decreases as the idle probability increases. Fig. 9 shows the delay characteristic and throughput characteristic in the present application at different transmission powers, and in this case, the selected optimal modulation scheme, and it can be seen from the figure that as the power increases, the optimal modulation scheme is sequentially changed to BPSK, QPSK, 16QAM, and 64 QAM.
The performance of the method of the invention under different preference factors was then analyzed. When the transmission delay of the data packets in the system is high, some data packets need to be discarded to meet the delay requirement, and at the same time, the throughput performance in the system may not be met, so that the transmission delay and the throughput have to be balanced. The specific performance simulation is shown in FIGS. 10-12. Fig. 10 and fig. 11 show performance comparison between the spectrum dynamic access method and the uniform loading method provided by the present invention when the preference coefficients are different, that is, when the weight coefficients are different. As can be seen from fig. 10, the performance of the method of the present invention is better than that of the uniform loading method, and in the method, as the idle probability of the primary user increases, the performance also increases. As can be seen from fig. 11, the performance of the method of the present invention is generally better than that of the method of uniform loading under different maximum endurance delay conditions, and the performance is also improved as the maximum endurance delay increases. Fig. 12 shows the delay characteristic and throughput characteristic in the present application at different transmission powers, and in this case, the selected optimal modulation scheme, and it can be seen from the figure that the optimal modulation scheme is sequentially changed to BPSK, QPSK, 16QAM, and 64QAM as the maximum tolerable delay increases.
To further prove the effectiveness of the method of the present invention, the present embodiment verifies through a standard video sequence, and compares the method of the present invention with several other existing methods, including an intelligent cross-layer algorithm, a dynamic learning algorithm, and a dynamic minimum interference algorithm. The simulation results are shown in fig. 13 to 17, fig. 13 shows an original video frame, fig. 14 shows a demodulation effect diagram after an intelligent cross-layer algorithm is adopted, fig. 15 shows a demodulation effect diagram after a dynamic learning method is adopted, fig. 16 shows a demodulation effect diagram after a dynamic minimum interference algorithm is adopted, and fig. 16 shows a demodulation effect diagram after a dynamic access method proposed by the present invention is adopted. From fig. 13 to 17, it can be found that the video frames demodulated by the method of the present invention have the best visual effect.
While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and those skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope of the invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (8)

1. A radio dynamic spectrum access method for multi-user multi-channel is used for optimizing a dynamic spectrum access process in a cognitive radio network, and is characterized by comprising the following steps:
s1: the on-line learning method based on the Dirichlet process acquires a subcarrier loading strategy and a data packet arrival rate of each virtual user according to an ACK/NACK message broadcast by a cluster head in a cognitive radio network in unit time;
s2: defining the conflict probability of a target secondary user data packet according to the data packet arrival rate of the virtual user;
s3: acquiring a probability density function obeyed by the transmission delay of the data packet of the target secondary user according to the collision probability of the data packet of the target secondary user and a deferral retransmission mechanism when the data packet in the S-ALOHA system collides;
s4: establishing a relation between the data packet transmission delay and the queue delay of a target secondary user data packet, and acquiring the total delay characteristic of multimedia transmission;
s5: acquiring the capacity characteristic and the channel characteristic of multimedia transmission by combining the retransmission times of the data packet according to the data packet loss probability acquired in the step S3;
s6, combining the capacity characteristic, the channel characteristic and the total time delay characteristic obtained in the step S4, constructing a service quality evaluation standard, and establishing an optimal data packet loading mode for a target secondary user to complete dynamic spectrum access;
step S1 specifically includes the following steps:
101) regarding other secondary users except the target secondary user in the cognitive radio network as a virtual user;
102) when the virtual user successfully receives or sends a data packet, the cluster head broadcasts an ACK/NACK message;
103) according to the number of ACK/NACK messages broadcast by the cluster head in unit time, obtaining a subcarrier loading strategy of the virtual user, and calculating the data packet arrival rate of other virtual users except the target secondary user
Figure FDA0002723760800000014
The calculation formula is as follows:
Figure FDA0002723760800000012
wherein, E { mu }jThe loading proportion of the virtual user on the sub-carrier j is multiplied, and K is the ACK/NACK cancellation broadcast by the cluster headThe number of the messages is counted,
Figure FDA0002723760800000013
probability of not occupying a channel for an authorized user;
in step S2, the specific content of the collision probability of the target secondary user data packet is defined as:
assuming that the arrival rate and the retransmission rate of the virtual user data packets obey poisson distribution, the probability that a data packet is not received in the channel within the time t is equal to the probability that a target secondary user generates a new data packet every time t, and the probability F that the target secondary user generates a new data packet every time t is equal to the probability that the target secondary user generates a new data packet every time tij(T is more than or equal to T,0) is as follows:
Figure FDA0002723760800000021
wherein T is the inter-packet arrival time and compliance parameter is
Figure FDA0002723760800000022
Is then the probability p that the target secondary user data packet is not subject to collisionijThe expression of (a) is:
Figure FDA0002723760800000023
where τ is the minimum unit of time required for a packet to succeed from transmission to reception.
2. The method according to claim 1, wherein the step S3 specifically includes the following steps:
301) retransmitting the data packet after collision or conflict, and acquiring the data packet loss probability and probability density function of the target secondary user on the subcarrier j under different transmission time delays according to the conflict probability of the target secondary user data packet;
302) and acquiring the mixed exponential distribution obeyed by the total transmission delay according to the data packet loss probability and the probability density function.
3. The method according to claim 2, wherein the specific content of step 301) is:
suppose that the retransmission time of each time is T respectively1，T2，T3，…，TkTarget secondary user SUiThe probability of packet loss on subcarrier j is ωj(k-1)Then, there are:
when transmission delay Tpτ, target secondary user SUiThe probability of packet loss on subcarrier j is ωj1＝pijThe probability density function is:
f1(Tp)＝δ(Tp-τ)
when transmission delay Tp＝τ+T1Then, the target secondary user SUiThe probability of packet loss on subcarrier j is ωj2＝(1-pij)·pijThe probability density function is:
Figure FDA0002723760800000024
when transmission delay Tp＝τ+T1+T2Then, the target secondary user SUiThe probability of packet loss on subcarrier j is ωj3＝(1-pij)2·pijThe probability density function is:
Figure FDA0002723760800000025
when the transmission delay is Tp＝τ+T1+T2+T3+…+TkThen, the target secondary user SUiThe probability of packet loss on subcarrier j is ωjk＝(1-pij)k-1·pijThe probability density function is:
Figure FDA0002723760800000031
when the transmission delay is TpInfinity indicates that the packet is dropped and the targeted secondary user SUiThe probability of packet loss on subcarrier j is
Figure FDA0002723760800000032
The probability density function is:
f∞(Tp)＝δ(Tp-τ)
where δ (.) is an impulse function.
4. The method as claimed in claim 3, wherein the expression of the mixing exponential distribution obeyed by the total transmission delay in step 302) is:
Figure FDA0002723760800000033
。
5. the method according to claim 4, wherein the step S4 specifically comprises the following steps:
401) obtaining queue time delay according to Blackcut-Qinzi formula
Figure FDA0002723760800000034
Figure FDA0002723760800000035
In the formula, X is
Figure FDA0002723760800000036
Targeted secondary users SU during timeiThe number of data packets waiting to be transmitted on the subcarrier j is r, and the r is the residual transmission time of the data packets transmitted on the subcarrier by the virtual user at the current moment; using the mean value of r
Figure FDA0002723760800000037
To represent r, wherein,
Figure FDA0002723760800000038
for a targeted secondary user SUiThe time of the data packet transmitted on the subcarrier j is the second order distance, the queue delay
Figure FDA00027237608000000314
Becomes:
Figure FDA0002723760800000039
wherein λ isi·For a targeted secondary user SUiData packet arrival rate of sijIs SUiThe loading ratio on subcarrier j;
402) queue delay based on data packets
Figure FDA00027237608000000310
And transmission delay
Figure FDA00027237608000000311
Obtaining total time delay d in data packet transmission processij：
Figure FDA00027237608000000312
403) Suppose a target secondary user SUiHas a maximum tolerated delay of DiAccording to the total delay d in the transmission of the data packetijThen the target secondary user SUiThe queue time delay loaded on the subcarrier j is less than DiThe probability of (c) is:
Figure FDA00027237608000000313
in the formula:
Figure FDA0002723760800000041
where ψ is the maximum number of retransmissions allowed by the system, T0Is TpThe expression of the upper limit value of (2) is:
Figure FDA0002723760800000042
。
6. the method as claimed in claim 5, wherein the step S5 specifically includes the following steps:
501) obtaining the capacity characteristic of the multimedia transmission, namely the target secondary user SU according to the data packet loss probability obtained in the step S3iPacket transmission rate of (PDR)i：
Figure FDA0002723760800000043
Wherein M is the total number of channels;
502) and acquiring the channel characteristics of multimedia transmission, namely the transmitting power corresponding to different modulation modes according to different modulation modes.
7. The method according to claim 6, wherein the step S6 specifically includes the following steps:
601) defining a service quality evaluation standard U according to the time delay of multimedia transmission and the spectrum utilization efficiency performance of the subcarrieri(S, L) is:
Figure FDA0002723760800000044
where M is the total number of channels, θiThe weight coefficient is the preference degree of the user to the capacity characteristic and the time delay characteristic in the system; l isjThe number of bits per symbol;
602) setting a power limiting condition, a channel capacity limiting condition and a subcarrier loading strategy limiting condition of a service quality evaluation standard;
603) according to the three limiting conditions set in the step 602), the service quality standard is maximized, the optimal data packet loading mode of the target secondary user is obtained, and the dynamic spectrum access is completed.
8. The method according to claim 7, wherein in step 602), the specific contents of the power limitation condition, the channel capacity limitation condition and the subcarrier loading policy limitation condition for setting the qos criteria are as follows:
the power limiting condition is as follows:
Figure FDA0002723760800000051
wherein, M is the total channel number,
Figure FDA0002723760800000052
power, P, of data packets transmitted for a time useriThe limiting condition requires that the sum of the powers of the users for transmitting data packets simultaneously within a certain time cannot exceed the transmitting power of the users;
channel capacity limiting conditions:
Figure FDA0002723760800000053
wherein, B is the bit capacity of the channel per second, L is the length of each data packet, and the limitation condition requires that the capacity of the data packet loaded on the subcarrier j by the virtual user and the target user in unit time cannot exceed the available capacity of the subcarrier;
subcarrier loading strategy constraints:
Figure FDA0002723760800000054
the constraint condition requires that the subcarrier loading strategy constraint requires that the sum of the subcarrier loading strategies of the target secondary users is less than or equal to 1.
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