CN117377122A - Load self-adaptive NOMA-IRSA dynamic random access method - Google Patents
Load self-adaptive NOMA-IRSA dynamic random access method Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access, e.g. scheduled or random access
- H04W74/08—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access]
- H04W74/0833—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using a random access procedure
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access, e.g. scheduled or random access
- H04W74/08—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access]
- H04W74/0833—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using a random access procedure
- H04W74/0841—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using a random access procedure with collision treatment
- H04W74/0858—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using a random access procedure with collision treatment collision detection
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- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
Abstract
The invention belongs to the technical field of wireless communication, discloses a load self-adaptive NOMA-IRSA dynamic random access method, solves the overload access problem of an mMTC system, is suitable for the scene of burst transmission of a large number of small data packets scattered by machine type equipment, and specifically comprises the following steps: firstly, designing a large-scale random access scheme based on power diversity and irregular repeated time slot ALOHA; then, jointly optimizing the power level selection probability distribution and the transmission replica degree distribution; finally, a load-adaptive NOMA-IRSA protocol is designed to support large-scale equipment overload access transmission. The invention can utilize the capture effect, and can jointly detect more data packets through the continuous interference elimination technology and the orthogonal characteristic of the preamble, thereby improving the access success probability of users and improving the throughput of the system.
Description
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a load self-adaptive NOMA-IRSA dynamic random access scheme.
Background
With the explosive development of wireless communication technology, the global mobile internet and the internet of things industry enter an explosive development stage, and the number of wireless terminal devices is rapidly increasing. The large-scale machine type communication (Massive Machine Type Communication, mMTC) is widely applied to the fields of medical care, smart home, smart grid, smart city and the like as one of three scenes of 5G, and the main purpose of the large-scale machine type communication is to solve a core technical problem of everything interconnection, namely to support mass terminal equipment connection communication with small-scale data transmission.
However, the traditional authorized multiple access technology has large signaling overhead and is difficult to be applied to a large-scale terminal access scene; random Access (RA) signaling overhead is small, and becomes an alternative scheme for mctc. In view of the short-time packet transmission characteristics of mctc terminals, a classical RA scheme, a contention resolution diversity slot ALOHA (Contention Resolution Diversity Slotted ALOHA, CRDSA) technique, has attracted a lot of academic attention again. The CRDSA scheme resolves RA collisions using replica diversity and SIC techniques by retransmitting multiple data replicas in multiple slots of a frame; however, in the existing CRDSA scheme, the number of copies of the user transmission data and the copy transmission power are generally fixed, which will bring a huge system load to the mctc scenario, and the user collision rate is difficult to reduce. How to fully exploit the potential of replica diversity to support random access for large-scale terminals becomes an important issue to be addressed in current wireless communications.
The irregular repeated slot ALOHA (Irregular Repetition Slotted ALOHA, IRSA) protocol explores the advantages of replica diversity, improving CRDSA performance to some extent. However, randomly determining the number of transmitted copies without any optimization may lead to overload of the system, which exacerbates congestion of the wireless spectrum. Non-orthogonal multiple access (Non-Orthogonal Multiple Access, NOMA) fully utilizes power diversity to improve spectral efficiency and can improve CRDSA system throughput without expanding bandwidth. Therefore, the NOMA technology and the IRSA protocol are fused, and the access probability of the large-scale terminal is expected to be greatly improved.
However, the work of combining NOMA and IRSA is less at present, and how to design a dynamic optimization strategy of replica diversity and a power level selection strategy to solve the random access of a large-scale terminal in a high load state is still a current difficult problem.
Disclosure of Invention
In order to solve the problems in the prior art, the invention fully excavates the diversity gain of the replica and the power level diversity, and provides a load self-adaptive NOMA-IRSA dynamic random access method. The main content of the invention comprises: firstly, designing a large-scale random access scheme based on power diversity and irregular repeated time slot ALOHA; then, jointly optimizing the power level selection probability distribution and the transmission replica degree distribution; finally, a load-adaptive NOMA-IRSA protocol is designed to support large-scale equipment overload access transmission. The invention can utilize the capture effect, and can jointly detect more data packets through the continuous interference elimination technology and the orthogonal characteristic of the preamble, thereby improving the access success probability of users and improving the throughput of the system.
In order to achieve the above purpose, the invention is realized by the following technical scheme:
the invention relates to a load self-adaptive NOMA-IRSA dynamic random access method, which comprises the following specific steps:
step 1, aiming at the problem that the terminal collision is obvious under the large-scale random access of the traditional IRSA protocol, a random multiple access protocol combining time diversity and power diversity, namely NOMA-IRSA protocol, is provided to support the overload access of the large-scale mMTC terminal;
step 2, constructing a joint optimization problem of power level selection and duplicate degree distribution transmission, and solving the problem to obtain duplicate degree distribution and power level selection probability distribution which enable throughput to be maximum under the current system load;
and step 3, designing a load self-adaptive NOMA-IRSA dynamic access scheme, allowing the terminal to self-adaptively adjust the number of copies of the transmitted data packet according to the current system load condition, optimizing and selecting the power level, and improving the access success rate of the terminal.
Further, the NOMA-IRSA protocol described in step 1 is described as follows:
in step 1-1, the terminal performs uplink access contention by using IRSA, allowing the terminal to adaptively adjust the number of copies of the transmitted data packet and optimally select a power level. Each terminal independently and randomly selects K time slots from N time slots of a frame according to the current system load condition to transmit K copies of preamble-data of the terminal, wherein K is more than or equal to 1 and less than or equal to K and less than or equal to N, and the number K of transmitted copies obeys the degree distribution; the transmit power level of each replica is selected according to certain criteria.
Step 1-2, the base station receives multi-path uplink data from a plurality of terminals, and the multi-user uplink signal is detected by combining the SIC technology and the orthogonal characteristic of the preamble in two steps: the first step, adopting SIC technology to iteratively detect the signal carried by each power level; and a second step of detecting the transmission signal by correlation operation using the orthogonal characteristic of the preamble. And feeding back a response signal to the successfully detected terminal to finish uplink access transmission.
Further, the problem of joint optimization of the selection of the constructed power level and the number of transmitted replicas in step 2 is specifically described as follows:
m machine type terminals in a single-cell mMTC system simultaneously compete for access to a base station, and the terminals and the base station are respectively provided with a single antenna; each terminal randomly selects one preamble from J orthogonal preambles, combines the preamble with a data symbol into a data packet, and transmits k copies of the data packet in k randomly selected time slots, thereby forming transmission time diversity; each terminal transmits K copies at most, namely K is more than or equal to 1 and less than or equal to K and less than or equal to N; the transmit power of each replica of the same terminal may be different and different terminals may transmit replicas using the NOMA technique occupying the same time slot.
Step 2-1: and establishing a terminal sending duplicate degree distribution function and defining a normalized system load.
The transmission duplicate degree distribution is defined as the probability distribution of the number of copies transmitted by the terminal in one frame, and is defined by the set { phi } k Represented by phi k Representing the probability of a terminal transmitting K copies, 1.ltoreq.k.ltoreq.n, K representing the maximum number of copies allowed to be transmitted. The degree distribution function of the sent replica is defined as follows:
where x represents the variable of the duplicate degree distribution function.
The system load G is defined as the ratio of the total number of the average terminal replications carried to the number of time slots of a frame, namely:
step 2-2: and designing a terminal transmission power level selection scheme, and establishing an uplink transmission signal model.
Different terminals may transmit copies of data at different powers on selected time slots. Let the power level set detected by the base station by adopting SIC technology be P= { P 1 ,P 2 ...,P l ,...,P L }, wherein P l Represents the first target detection power level, L is more than or equal to 1 and less than or equal to L, and P 1 ＜P 2 ＜...＜P l ＜P L 。
If terminal U m M epsilon {1, 2., a certain replica of M has a target received power at the base station of P m,l ＝P l L e {1,2,., L }, terminal U m Is set to the transmission power of (a)The calculation is as follows:
wherein alpha is m For terminal U m An uplink channel attenuation coefficient to the base station; it is considered herein that the uplink channel of each terminal is unchanged for one frame time.
According to (3), terminal U m Transmit power level set PT of (1) m The method comprises the following steps:
assuming the uplink channel attenuation coefficient alpha from terminal to base station in each frame time m The transmit power level selection criteria for a terminal per frame time are known as follows:
terminal U m As each preamble-data replica is transmitted, with probability η l L e {1,2,., L } select set PT m The first power level of (2)Probability of power level selection η l Obeys [0,1 ]]Randomly distributed and satisfy->
Thus, terminal U m Transmitting signals in the nth time slot of a frameExpressed as:
wherein X is m ＝[V m ,D m ]Indicating terminal U m Data transmitted in the current frame, V m Representing the preamble, D m The data vector is represented by a vector of data, X m || 2 ＝1；Is a double indication function, and represents a terminal U m Whether or not to use the set PT on time slot n of the current frame m A first power level transmission replica of (a); if it is (I)>Otherwise, go (L)>And have->
Step 2-3: and establishing an uplink received signal model and calculating the single terminal replica detection probability.
Uplink signal received by base station on certain frame time slot nModeling is as follows:
wherein,indicating a power level q in slot n l Is provided.
The base station detects the received uplink signal in two steps: first, iteratively detecting each power level P by SIC technique l Carried signal Y n,l The method comprises the steps of carrying out a first treatment on the surface of the Second, the correlation operation is adopted from Y n,l Detecting a transmission signalNext, the probability of success of detection of the data copy transmitted by the terminal is analyzed.
First, the power level detection probability is analyzed. For the first power level P on time slot n l When the preamble L-L levels P L ,P L-1 ,...,P l+1 Signal to noise ratio gamma of current power level carrying signal n,l Above a certain threshold value gamma th At the time P l Carried signal Y n,l The accurate detection can be realized; conversely, signal Y n,l And cannot be detected correctly. Thus, signal Y n,l Probability of success of detectionThe calculation is as follows:
wherein, gamma n,i Representing the ith power level P at time slot n i The signal-to-noise ratio of the carrier signal is calculated as:
wherein,indicating terminal U m Whether or not to use the set PT on time slot n m I power level of (a), if yes, < ->Otherwise, go (L)>Representing the power level P at time slot n i Number of user copies carried; />Representing the power level P at time slot n l Number of user copies carried.
Next, the probability of detecting the terminal replica from the power level signal, i.e., the replica detection probability, is analyzed. Let power level P on slot n l Carried signal Y n,l The detection value of (2) isIt is L n，l Superimposed signals of the individual user copies. If->Comprises a terminal U m If and only if terminal U m When the selected preamble is different from the preambles of other users, terminal U m Can be detected correctly. Thus, terminal U m Can be derived from the signal->Probability of detection->The calculation is as follows:
where J represents the number of orthogonal preambles.
Equation (9) is also expressed in power level P l Load bearing L n,l Terminal U under the condition of user copy m Probability Pr (U) that copies of (1) can be detected m |L n,l )。
Then, the successful terminal U is detected in view of both stages m Can be restored, thus computing terminal U m At power level P on time slot n l Probability of successful detection p of transmitted replicas n,l The method comprises the following steps:
computing terminal U m Successful detection probability p of transmitting duplicate on time slot n n ；
Finally, consider terminal U m The probability q of transmitting a replica in slot n is:
while terminal U m Selecting power level P at time slot n l Is eta (eta) l Thus terminal U m At power level P on time slot n l The probability of transmitting duplicates is v l ＝qη l 。
Since all terminals obey the same power level selection probability distribution, the power level P on slot n l The bearer comprises a user U m L of (2) n,l Probability Pr of each replica (L n,l ,q l ) The calculation is as follows:
for power level P l And the number of user copies carried by it L n,l Traversing and summing to obtain a terminal U m Successful detection probability p of transmitting duplicate on time slot n n The method comprises the following steps:
correspondingly, terminal U m Probability of detection error for transmitting copies on time slot nThe method comprises the following steps:
if a copy of a terminal is decoded at the base station, the interference caused by the terminal can be removed from the remaining time slots. For received signals over all N time slotsThe two-step detection and interference de-duplication are repeated until all user duplicates are detected.
Step 2-4: and calculating the throughput of the system and establishing a throughput optimization model.
The system throughput R is defined as the number of successfully processed terminals in each frame unit time slot, namely the number of the terminals in the unit time slot and the probability p of successfully detecting the terminals m Is a product of (a) and (b).
Terminal U m The success probability p of (2) m The calculation is as follows:
wherein,is the probability of a terminal detecting an error.
Thus, the system throughput R is calculated as:
wherein, the success detection probability p of the terminal m See formula (15).
With the goal of maximizing system throughput, the following optimization problem is established:
wherein the first constraint defines a sum of power level selection probabilities of 1; the second constraint specifies a power level selection probability between 0-1; the third constraint defines the sum of the transmit duplicate distributions to be 1; the fourth constraint specifies that the probability of transmitting k copies is between 0-1.
Step 2-5: and solving the throughput optimization model to obtain the optimal duplicate degree distribution and the power level selection probability distribution.
Solving the throughput optimization problem of equation (17) by using a differential evolution algorithm, wherein the specific steps are shown in Table 1, and finally obtaining the optimal probability distribution of the power level for maximizing RAnd optimal duplicate distribution->
TABLE 1 differential evolutionary algorithm
Further, the load adaptive NOMA-IRSA dynamic access scheme in step 3 is specifically described as follows:
step 3-1: the base station broadcasts an optimal replica level distribution and a power level selection probability distribution.
The base station divides the time slots into idle time slots, successful time slots and collision time slots according to the occupied state. An idle slot refers to a slot where no data is transmitted. The base station calculates the number N of uplink idle time slots in the previous frame time idle The method comprises the following steps:
wherein,indicating the number of copies of the data packet that the terminal is transmitting on average.
Based on (18), the base station estimates the number of terminals to be accessed in the present frame timeThe method comprises the following steps:
accordingly, the system load is estimated as:
the base station willAs an input value in the differential evolution algorithm of Table 1, the optimal duplicate degree distribution under the current system load is solved>And power level selection probability distribution +.>And broadcast to the terminals.
Step 3-2: the terminal adaptively adjusts the number of copies of the transmitted data packet according to the current system load condition and optimally selects the power level.
Terminal U m After receiving the broadcast information, the broadcast information is distributed according to the duplicate degreeDetermining the number of transmitted replicas, selecting the probability distribution according to the power level>Determining terminal U m The power level selected in transmitting each preamble-data replica is as follows:
terminal U m Randomly generate a [0,1 ]]A uniformly distributed random number beta; when (when)Terminal U m Transmitting 1 copy; when->Terminal U m Transmitting 2 copies; by analogy, when->Terminal U m K copies are sent.
Terminal U m Randomly generate a [0,1 ]]A uniformly distributed random number alpha; when (when)When selecting the set PT m 1 st power level of->When->When selecting the set PT m 2 nd power level of->By analogy, whenWhen selecting the set PT m The first power level of +.>
Step 3-3: the base station receives and detects multiple paths of uplink data from the terminal.
The base station receives the multi-channel uplink data from a plurality of terminals and detects multi-user uplink signals in two steps. The first step, adopting SIC technology to iteratively detect the signal carried by each power level; and a second step of detecting the transmission signal by correlation operation using the orthogonal characteristic of the preamble. Each replica of a terminal contains the slot position index of the remaining replicas, and if one replica of the terminal is decoded at the base station, the interference caused by the terminal can be removed from the remaining slots, thereby eliminating access collisions on these slots. And feeding back a response signal to the successfully detected terminal to finish uplink access transmission.
The beneficial effects of the invention are as follows:
the invention adopts an irregular repeated time slot ALOHA random access protocol based on power diversity, a receiving end utilizes SIC technology and orthogonal characteristic of a preamble to jointly detect multi-user uplink signals, the traditional NOMA-IRSA protocol does not consider the orthogonal characteristic of the preamble, each power level is only possible to be successfully transmitted when one user selects, and the scheme adopted by the invention reduces the collision probability of the user.
The invention provides a joint optimization problem of constructing power level selection and transmitting duplicate degree distribution, solves the problem to obtain duplicate degree distribution and power level selection probability distribution which enable throughput to be maximum under the current system load, and improves system throughput. The conventional NOMA-IRSA protocol does not consider the impact of duplicate size distribution and power level selection probability distribution on system performance in combination. The scheme adopted by the invention improves the throughput of the system.
The invention designs a load self-adaptive NOMA-IRSA dynamic access scheme. The terminal is allowed to adaptively adjust the number of copies of the transmitted data packet according to the current system load condition and optimize and select the power level, so that the success rate of terminal access is improved.
Drawings
Fig. 1 is a network model diagram in an embodiment of the invention.
Fig. 2 is a schematic diagram of a transmission protocol according to an embodiment of the present invention.
FIG. 3 is a block diagram of a method implementation in an embodiment of the invention.
Fig. 4 is a graph of simulation results of system throughput in an embodiment of the invention.
Detailed Description
Embodiments of the invention are disclosed in the drawings, and for purposes of explanation, numerous practical details are set forth in the following description. However, it should be understood that these practical details are not to be taken as limiting the invention. That is, in some embodiments of the invention, these practical details are unnecessary.
Setting a system scene:
m machine type terminals in a single-cell mMTC system simultaneously compete for access to a base station, and the terminals and the base station are respectively provided with a single antenna; each terminal randomly selects one preamble from J orthogonal preambles, combines the preamble with a data symbol into a data packet, and transmits k copies of the data packet in k randomly selected time slots, thereby forming transmission time diversity; each terminal transmits K copies at most, namely K is more than or equal to 1 and less than or equal to K and less than or equal to N; the transmit power of each replica of the same terminal may be different and different terminals may transmit replicas using the NOMA technique occupying the same time slot.
As shown in fig. 1-3, the invention is a load-adaptive NOMA-IRSA dynamic random access method, which specifically includes the following steps:
step 1, aiming at the problem that the terminal collision is obvious under the large-scale random access of the traditional IRSA protocol, a random multiple access protocol combining time diversity and power diversity, namely NOMA-IRSA protocol, is provided to support the overload access of the large-scale mMTC terminal.
Step 1-1, in order to fully explore the random access of the duplicate diversity potential support large-scale terminals, a dynamic time diversity scheme of an irregular repeated time slot ALOHA (IRSA) protocol is mainly explored, the change gain of the number of transmitted duplicates is obtained, and meanwhile, the duplicate power diversity gain is fully explored by combining a non-orthogonal multiple access technology. The influence of the duplicate diversity dynamic optimization strategy and the power level selection strategy on the system performance is jointly considered, so that the random access of a large-scale terminal in a high load state is solved, and the successful access probability of the mMTC terminal equipment is improved.
And step 1-2, the terminal performs uplink access competition by adopting IRSA, and allows the terminal to adaptively adjust the number of copies of the transmitted data packet and optimally select the power level. Each terminal independently and randomly selects K time slots from N time slots of a frame according to the current system load condition to transmit K copies of preamble-data of the terminal, wherein K is more than or equal to 1 and less than or equal to K and less than or equal to N, and the number K of transmitted copies obeys the degree distribution; the transmit power level of each replica is selected in accordance with the transmit power level selection criteria of the terminal at each frame time.
Step 1-3, the base station receives multi-path uplink data from a plurality of terminals, and the multi-user uplink signal is detected by combining the SIC technology and the orthogonal characteristic of the preamble in two steps: the first step, adopting SIC technology to iteratively detect the signal carried by each power level; and a second step of detecting the transmission signal by correlation operation using the orthogonal characteristic of the preamble. And feeding back a response signal to the successfully detected terminal to finish uplink access transmission.
And 2, constructing a joint optimization problem of power level selection and transmission duplicate degree distribution, and solving the problem to obtain duplicate degree distribution and power level selection probability distribution which maximize throughput under the current system load.
Step 2-1: and establishing a terminal sending duplicate degree distribution function and defining a normalized system load.
The transmission duplicate degree distribution is defined as the probability distribution of the number of copies transmitted by the terminal in one frame, and is defined by the set { phi } k Represented by phi k Representing the probability of a terminal transmitting K copies, 1.ltoreq.k.ltoreq.n, K representing the maximum number of copies allowed to be transmitted. The degree distribution function of the sent replica is defined as follows:
where x represents the variable of the duplicate degree distribution function.
The system load G is defined as the ratio of the total number of the average terminal replications carried to the number of time slots of a frame, namely:
step 2-2: and designing a terminal transmission power level selection scheme, and establishing an uplink transmission signal model.
Different terminals may transmit copies of data at different powers on selected time slots. Let the power level set detected by the base station by adopting SIC technology be P= { P 1 ,P 2 ...,P l ,...,P L }, wherein P l Represents the first target detection power level, L is more than or equal to 1 and less than or equal to L, and P 1 ＜P 2 ＜...＜P l ＜P L 。
If terminal U m M epsilon {1, 2., a certain replica of M has a target received power at the base station of P m,l ＝P l L e {1,2,., L }, terminal U m Is set to the transmission power of (a)The calculation is as follows:
wherein alpha is m For terminal U m To the base stationA line channel attenuation coefficient; it is considered herein that the uplink channel of each terminal is unchanged for one frame time.
According to (3), terminal U m Transmit power level set PT of (1) m The method comprises the following steps:
assuming the uplink channel attenuation coefficient alpha from terminal to base station in each frame time m The transmit power level selection criteria for a terminal per frame time are known as follows:
terminal U m As each preamble-data replica is transmitted, with probability η l L e {1,2,., L } select set PT m The first power level of (2)Probability of power level selection η l Obeys [0,1 ]]Randomly distributed and satisfy->
Thus, terminal U m Transmitting signals in the nth time slot of a frameExpressed as:
wherein X is m ＝[V m ,D m ]Indicating terminal U m Data transmitted in the current frame, V m Representing the preamble, D m The data vector is represented by a vector of data, X m || 2 ＝1；Is a double indication function, and represents a terminal U m Whether or not to use the set PT on time slot n of the current frame m The first of (3)Transmitting copies of l power levels; if it is (I)>Otherwise, go (L)>And have->
Step 2-3: and establishing an uplink received signal model and calculating the single terminal replica detection probability.
Uplink signal received by base station on certain frame time slot nModeling is as follows:
wherein,indicating a power level q in slot n l Is provided.
The base station detects the received uplink signal in two steps: first, iteratively detecting each power level P by SIC technique l Carried signal Y n,l The method comprises the steps of carrying out a first treatment on the surface of the Second, the correlation operation is adopted from Y n,l Detecting a transmission signalNext, the probability of success of detection of the data copy transmitted by the terminal is analyzed.
First, the power level detection probability is analyzed. For the first power level P on time slot n l When the preamble L-L levels P L ,P L-1 ,...,P l+1 Signal to noise ratio gamma of current power level carrying signal n,l Above a certain threshold value gamma th At the time P l Carried signal Y n,l The accurate detection can be realized; conversely, signal Y n,l And cannot be detected correctly. Thus, signal Y n,l Probability of success of detectionThe calculation is as follows:
wherein, gamma n,i Representing the ith power level P at time slot n i The signal-to-noise ratio of the carrier signal is calculated as:
wherein,indicating terminal U m Whether or not to use the set PT on time slot n m And, if so,otherwise, go (L)>Representing the power level P at time slot n i Number of user copies carried; />Representing the power level P at time slot n l Number of user copies carried.
Next, the probability of detecting the terminal replica from the power level signal, i.e., the replica detection probability, is analyzed. Let power level P on slot n l Carried signal Y n,l The detection value of (2) isIt is L n,l Superimposed signals of the individual user copies. If->Comprises a terminal U m If and only if terminal U m When the selected preamble is different from the preambles of other users, terminal U m Can be detected correctly. Thus, terminal U m Can be derived from the signal->Probability of detection->The calculation is as follows:
where J represents the number of orthogonal preambles.
Equation (9) is also expressed in power level P l Load bearing L n,l Terminal U under the condition of user copy m Probability Pr (U) that copies of (1) can be detected m |L n,l )。
Then, the successful terminal U is detected in view of both stages m Can be restored, therefore terminal U m At power level P on time slot n l Probability of successful detection p of transmitted replicas n,l The calculation is as follows:
computing terminal U m Successful detection probability p of transmitting duplicate on time slot n n ；
Finally, consider terminal U m The probability q of transmitting a replica in slot n is:
while terminal U m Selecting power level P at time slot n l Is eta (eta) l Thus terminal U m At power level P on time slot n l The probability of transmitting duplicates is v l ＝qη l 。
Since all terminals obey the same power level selection probability distribution, the power level P on slot n l The bearer comprises a user U m L of (2) n,l Probability Pr of each replica (L n,l ,q l ) The calculation is as follows:
for power level P l And the number of user copies carried by it L n,l Traversing and summing to obtain a terminal U m Successful detection probability p of transmitting duplicate on time slot n n The method comprises the following steps:
correspondingly, terminal U m Probability of detection error for transmitting copies on time slot nThe method comprises the following steps:
if a copy of a terminal is decoded at the base station, the interference caused by the terminal can be removed from the remaining time slots. For received signals over all N time slotsThe two-step detection and interference de-duplication are repeated until all user duplicates are detected.
Step 2-4: and calculating the throughput of the system and establishing a throughput optimization model.
Defining a system throughput R as perThe number of successfully processed terminals in a frame unit time slot, namely the number of the terminals in the unit time slot and the probability p of successfully detecting the terminals m Is a product of (a) and (b).
Terminal U m The success probability p of (2) m The calculation is as follows:
wherein,is the probability of a terminal detecting an error.
Thus, the system throughput R is calculated as:
with the goal of maximizing system throughput, the following optimization problem is established:
wherein,defines the sum of the power level selection probabilities as 1, 0.ltoreq.eta l ≤1，1≤l≤L，l∈N + Providing a power level selection probability between 0 and 1, ">Defines the sum of the distribution of the transmitted copies to be 1, 0.ltoreq.phi k ≤1，1≤k≤K，k∈N + The probability of transmitting k copies is specified to be between 0-1.
Step 2-5: and solving the throughput optimization model to obtain the optimal duplicate degree distribution and the power level selection probability distribution.
Solving the throughput optimization problem of (17) by utilizing a differential evolution algorithm, wherein the specific steps are as followsTABLE 1 optimal probability distribution of power level to maximize RAnd optimal duplicate distribution->
TABLE 1 differential evolutionary algorithm
And step 3, designing a load self-adaptive NOMA-IRSA dynamic access scheme, allowing the terminal to self-adaptively adjust the number of copies of the transmitted data packet according to the current system load condition, optimizing and selecting the power level, and improving the access success rate of the terminal.
Step 3-1: the base station broadcasts an optimal replica level distribution and a power level selection probability distribution.
The base station divides the time slots into idle time slots, successful time slots and collision time slots according to the occupied state. An idle slot refers to a slot where no data is transmitted. The base station calculates the number N of uplink idle time slots in the previous frame time idle The method comprises the following steps:
wherein,indicating the number of copies of the data packet that the terminal is transmitting on average.
Based on (18), the base station estimates the number of terminals to be accessed in the present frame timeThe method comprises the following steps: />
Accordingly, the system load is estimated as:
the base station willAs an input value in the differential evolution algorithm of Table 1, the optimal duplicate degree distribution under the current system load is solved>And power level selection probability distribution +.>And broadcast to the terminals.
Step 3-2: the terminal adaptively adjusts the number of copies of the transmitted data packet according to the current system load condition and optimally selects the power level.
Terminal U m After receiving the broadcast information, the broadcast information is distributed according to the duplicate degreeDetermining the number of transmitted replicas, selecting the probability distribution according to the power level>Determining terminal U m The power level selected in transmitting each preamble-data replica is as follows:
terminal U m Randomly generate a [0,1 ]]A uniformly distributed random number beta; when (when)Terminal U m Transmitting 1 copy; when->Terminal U m Send 2A copy; by analogy, when->Terminal U m K copies are sent.
Terminal U m Randomly generate a [0,1 ]]A uniformly distributed random number alpha; when (when)When selecting the set PT m 1 st power level of->When->When selecting the set PT m 2 nd power level of->By analogy, whenWhen selecting the set PT m The first power level of +.>
Step 3-3: the base station receives and detects multiple paths of uplink data from the terminal.
The base station receives the multi-channel uplink data from a plurality of terminals and detects multi-user uplink signals in two steps. The first step, adopting SIC technology to iteratively detect the signal carried by each power level; and a second step of detecting the transmission signal by correlation operation using the orthogonal characteristic of the preamble. Each replica of a terminal contains the slot position index of the remaining replicas, and if one replica of the terminal is decoded at the base station, the interference caused by the terminal can be removed from the remaining slots, thereby eliminating access collisions on these slots. And feeding back a response signal to the successfully detected terminal to finish uplink access transmission.
The effect of the present invention was further verified by the following simulation.
1. Experimental scenario:
there is a base station in a cell, a frame has 30 slots, the number of selectable power levels is 2, the number of preambles is 2, and each terminal can generate up to 8 copies. The signal-to-noise threshold is 3dB.
2. Experimental content and results:
fig. 4 is a simulation result, the abscissa is the number of terminals per unit time slot of a frame, and the ordinate is the system throughput. IRSA is a conventional irregular repeat slot ALOHA scheme. NOMA-IRSA is a traditional power diversity based irregular repeated slot ALOHA scheme, where the degree distribution to which each terminal transmits copies is unchanged, each terminal equiprobability selects a power level, and each power level only has one user to select and is likely to be successfully transmitted. These schemes all degrade system performance at high loads.
The above description is merely of preferred embodiments of the present invention, and the scope of the present invention is not limited to the above embodiments, but all equivalent modifications or variations according to the present disclosure will be within the scope of the claims.
Claims (10)
1. A load self-adaptive NOMA-IRSA dynamic random access method is characterized in that: by adopting the irregular repeated time slot ALOHA and the power domain non-orthogonal multiple access technology in a combined way, the uplink unlicensed random access self-adapting to the service load is realized by optimizing the selection probability of the power level and the degree distribution of the user transmission copies, the random access collision probability of the terminal is effectively reduced, the overload access capacity and the system throughput of an mMTC system are improved, and the NOMA-IRSA dynamic random access method specifically comprises the following steps:
step 1, providing a random multiple access protocol combining time diversity and power diversity, namely NOMA-IRSA protocol, and supporting overload access of a large-scale mMTC terminal;
step 2, constructing a joint optimization problem of power level selection and duplicate degree distribution transmission, and solving the problem to obtain duplicate degree distribution and power level selection probability distribution which enable throughput to be maximum under the current system load;
and step 3, designing a load self-adaptive NOMA-IRSA dynamic access scheme, allowing the terminal to self-adaptively adjust the number of copies of the transmitted data packet according to the current system load condition, optimizing and selecting the power level, and improving the access success rate of the terminal.
2. The load-adaptive NOMA-IRSA dynamic random access method according to claim 1, wherein: the NOMA-IRSA in the step 1 specifically comprises the following steps:
step 1-1, a terminal executes uplink access competition by adopting IRSA, the terminal is allowed to adaptively adjust the number of copies of a transmitted data packet and optimally select power level, each terminal independently and randomly selects K time slots from N time slots of a frame to transmit K copies of preamble-data according to the current system load condition, K is more than or equal to 1 and less than or equal to K and less than or equal to N, the number K of transmitted copies obeys degree distribution, and the transmission power level of each copy is selected according to a criterion;
step 1-2, the base station receives multi-channel uplink data from a plurality of terminals, and the multi-user uplink signal is detected by combining the SIC technology and the orthogonal characteristic of the preamble in two steps.
3. The load-adaptive NOMA-IRSA dynamic random access method according to claim 2, wherein: in the step 1-2, the multi-user uplink signal is jointly detected by using the SIC technology and the orthogonal characteristic of the preamble in two steps, specifically:
step 1-2-1, iteratively detecting signals carried by each power level by adopting SIC technology;
and step 1-2-2, detecting a transmission signal by using the orthogonal characteristic of the preamble and adopting correlation operation, and feeding back a response signal to a successfully detected terminal to finish uplink access transmission.
4. The load-adaptive NOMA-IRSA dynamic random access method according to claim 1, wherein: in step 2, M machine type terminals in a single cell mtc system compete for access to a base station simultaneously, each terminal and the base station is configured with a single antenna, each terminal randomly selects a preamble from J orthogonal preambles, combines the preamble with a data symbol to form a data packet, and transmits K copies of the data packet in K time slots randomly selected, thereby forming a transmit time diversity, each terminal transmits K copies at most, that is, K is greater than or equal to 1 and less than or equal to K and less than or equal to N, the transmit power of each copy of the same terminal may be different, and different terminals occupy the same time slot to transmit copies through NOMA technology, and step 2 specifically includes the following steps:
step 2-1, establishing a terminal sending duplicate degree distribution function and defining a normalized system load;
step 2-2, designing a terminal transmission power level selection scheme, and establishing an uplink transmission signal model;
step 2-3, establishing an uplink received signal model and calculating single terminal duplicate detection probability, which specifically comprises the following steps:
step 2-3-1, the base station receives the uplink signal Y on a certain frame time slot n n Modeling is as follows:
wherein,indicating a power level q in slot n l Is a signal received by the base station;
step 2-3-2, the base station detects the received uplink signal in two steps: first, each power level P is iteratively detected using SIC techniques l Carried signal Y n,l Next, a correlation operation is used from Y n,l Detecting a transmission signalAnalyzing the successful detection probability of the single terminal copy based on the two-step detection;
step 2-4, calculating the throughput of the system and establishing a throughput optimization model;
and 2-5, solving a throughput optimization model by utilizing a differential evolution algorithm to obtain the optimal duplicate distribution and the power level selection probability distribution.
5. The load-adaptive NOMA-IRSA dynamic random access method according to claim 4, wherein: the step 2-1 establishes a terminal sending duplicate degree distribution function and defines a normalized system load specifically as follows:
the transmission duplicate degree distribution is defined as the probability distribution of the number of copies transmitted by the terminal in one frame, and is defined by the set { phi } k Represented by phi k Representing the probability of a terminal transmitting K copies, wherein K is equal to or more than 1 and equal to or less than K is equal to or less than N, K represents the maximum number of copies allowed to be transmitted, and the degree distribution function of the transmitted copies is defined as follows:
wherein x represents a variable of the duplicate degree distribution function;
the system load G is defined as the ratio of the total number of the average terminal replications carried to the number of time slots of a frame, namely:
6. the load-adaptive NOMA-IRSA dynamic random access method according to claim 4, wherein: step 2-2 designs a terminal transmitting power level selection scheme, and establishes an uplink transmitting signal model, which specifically comprises the following steps:
step 2-2-1, let the power level set detected by the base station using the SIC technology be p= { P 1 ,P 2 ...,P l ,...,P L }, wherein P l Represents the first target detection power level, L is more than or equal to 1 and less than or equal to L, and P 1 ＜P 2 ＜...＜P l ＜P L If terminal U m ，m∈{1,2,...,M}Target received power at base station of a certain replica of (a) is P m,l ＝P l L e {1,2,., L }, terminal U m Is set to the transmission power of (a)The calculation is as follows:
wherein alpha is m For terminal U m An uplink channel attenuation coefficient to the base station;
step 2-2-2, according to the transmission power in step 2-2-1Formula of (1), terminal U m Transmit power level set PT of (1) m The method comprises the following steps:
7. the load-adaptive NOMA-IRSA dynamic random access method of claim 6, wherein: in said step 2-2-2, the uplink channel of each terminal is considered to be unchanged in one frame time, assuming that the uplink channel attenuation coefficient alpha from the terminal to the base station in each frame time m The transmit power level selection criteria for a terminal per frame time are known as follows:
terminal U m As each preamble-data replica is transmitted, with probability η l L e {1,2,., selects a set of transmit power levels PT m The first power level of (2)Probability of power level selection η l Obeys [0,1 ]]Randomly distributed and satisfy->Terminal U m Transmitting signal +.>Expressed as:
wherein X is m ＝[V m ,D m ]Indicating terminal U m Data transmitted in the current frame, V m Representing the preamble, D m The data vector is represented by a vector of data, X m || 2 ＝1，Is a double indication function, and represents a terminal U m Whether to use the set of transmit power levels PT on time slot n of the current frame m The first power level of (a) transmits copies, if yes, ">Otherwise, go (L)>And have->
8. The load-adaptive NOMA-IRSA dynamic random access method according to claim 4, wherein: step 2-3-2, the base station detects the received uplink signal and analyzes the successful detection probability of the single terminal copy specifically includes the following steps:
step 2-3-2-1, analyzing the power level detection probability: for the first power level P on time slot n l When the preamble L-L levels P L ,P L-1 ,...,P l+1 Signal to noise ratio gamma of current power level carrying signal n,l Above a certain threshold value gamma th At the time P l Carried signal Y n,l Can correctly detect, otherwise, signal Y n,l Can not be correctly detected, signal Y n,l Probability of success of detectionThe calculation is as follows:
wherein, gamma n,i Representing the ith power level P at time slot n i The signal-to-noise ratio of the carrier signal is calculated as:
wherein,indicating terminal U m Whether or not to use the set PT on time slot n m I power level of (a), if yes, < ->Otherwise, go (L)> Representing the power level P at time slot n i Number of user copies carried,/>Representing the power level P at time slot n l Number of user copies carried;
step 2-3-2-2, analyzing the probability of detecting the terminal replica from the power level signal, namely, the replica detection probability: let power level P on slot n l Carried signal Y n,l The detection value of (2) is Is L n,l Superimposed signal of individual user copies, if->Comprises a terminal U m If and only if terminal U m When the selected preamble is different from the preambles of other users, terminal U m Can correctly detect copies of (a) terminal U m Can be derived from the signal->Probability of detection->The calculation is as follows:
wherein J represents the number of orthogonal preambles;
probability ofThe calculation is also shown at power level P l Load bearing L n,l Terminal U under the condition of user copy m Probability Pr (U) that copies of (1) can be detected m |L n,l )；
Step 2-3-2-3, computing terminal U m At power level P on time slot n l Probability of successful detection of transmitted copiesp n,l The method comprises the following steps:
step 2-3-2-4, computing terminal U m Successful detection probability p of transmitting duplicate on time slot n n ；
Considering the terminal U m The probability q of transmitting a replica in slot n is:
while terminal U m Selecting power level P at time slot n l Is eta (eta) l Thus terminal U m At power level P on time slot n l The probability of transmitting duplicates is v l ＝qη l Since all terminals obey the same power level selection probability distribution, the power level P on slot n l The bearer comprises a user U m L of (2) n,l Probability Pr of each replica (L n,l ,q l ) The calculation is as follows:
for power level P l And the number of user copies carried by it L n,l Traversing and summing to obtain a terminal U m Successful detection probability p of transmitting duplicate on time slot n n The method comprises the following steps:
terminal U m Probability of detection error for transmitting copies on time slot nThe method comprises the following steps:
if a replica of a terminal is decoded at the base station, the interference caused by the terminal is removed from the remaining time slots for the received signals over all N time slotsThe two-step detection and interference de-duplication are repeated until all user duplicates are detected.
9. The load-adaptive NOMA-IRSA dynamic random access method according to claim 4, wherein: the step 2-4 calculates the throughput of the system and establishes a throughput optimization model, and specifically comprises the following steps:
the system throughput R is defined as the number of successfully processed terminals in each frame unit time slot, namely the number of the terminals in the unit time slot and the probability p of successfully detecting the terminals m Is a product of (a) and (b),
terminal U m The success probability p of (2) m The calculation is as follows:
wherein,the probability of error detection of the terminal;
the system throughput R is calculated as:
with the goal of maximizing system throughput, the following optimization problem is established:
0≤η l ≤1,1≤l≤L,l∈N + ,
0≤φ k ≤1,1≤k≤K,k∈N +
wherein,defines the sum of the power level selection probabilities as 1, 0.ltoreq.eta l ≤1，1≤l≤L，l∈N + Providing a power level selection probability between 0 and 1, ">Defines the sum of the distribution of the transmitted copies to be 1, 0.ltoreq.phi k ≤1，1≤k≤K，k∈N + The probability of transmitting k copies is specified to be between 0-1.
10. The load-adaptive NOMA-IRSA dynamic random access method according to claim 1, wherein: in step 3, the load adaptive NOMA-IRSA dynamic access scheme includes the following steps:
step 3-1, the base station broadcasts the optimal duplicate degree distribution and the power level selection probability distribution:
the base station divides the time slot into an idle time slot, a successful time slot and a collision time slot according to the occupied state, wherein the idle time slot refers to a time slot without data transmission, and the base station calculates the number N of uplink idle time slots in the previous frame time idle The method comprises the following steps:
wherein,representing the number of copies of the data packet transmitted by the terminal on average;
based on the number N of uplink idle time slots idle The base station estimates the number of terminals to be accessed in the frame timeThe method comprises the following steps:
accordingly, the system load is estimated as:
the base station willAs an input value in the differential evolution algorithm, solving the optimal duplicate degree distribution under the current system load>And power level selection probability distribution +.>And broadcast to the terminal;
step 3-2, terminal U m After receiving the broadcast information, the broadcast information is distributed according to the duplicate degreeDetermining the number of transmitted replicas, selecting according to power levelProbability distribution->Determining terminal U m The power level selected in transmitting each preamble-data replica is as follows:
terminal U m Randomly generate a [0,1 ]]Uniformly distributed random number beta, whenTerminal U m Send 1 copy ofTerminal U m Send 2 copies, and so on, when +.>Terminal U m Transmitting k copies;
terminal U m Randomly generate a [0,1 ]]Uniformly distributed random number alpha, whenWhen selecting the set PT m 1 st power level of->When->When selecting the set PT m 2 nd power level of->By analogy, whenWhen selecting the set PT m The first power level of +.>Step 3-3, the base station receives and detects multiple paths of uplink data from the terminal: the base station receives multi-channel uplink data from a plurality of terminals and detects multi-user uplink signals in two steps: firstly, iteratively detecting signals carried by each power level by adopting SIC technology, secondly, detecting a transmitted signal by adopting correlation operation by utilizing the orthogonal characteristic of a preamble, wherein each replica of a terminal comprises time slot position indexes of other replicas, if one replica of the terminal is decoded at a base station, interference caused by the terminal can be eliminated from other time slots, further, access conflicts on the time slots are eliminated, and a response signal is fed back to the successfully detected terminal to finish uplink access transmission. />
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