CN116260563A - Decoding sequence judging method in non-orthogonal multi-point cooperation system - Google Patents

Decoding sequence judging method in non-orthogonal multi-point cooperation system Download PDF

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CN116260563A
CN116260563A CN202310244413.3A CN202310244413A CN116260563A CN 116260563 A CN116260563 A CN 116260563A CN 202310244413 A CN202310244413 A CN 202310244413A CN 116260563 A CN116260563 A CN 116260563A
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decoding order
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base station
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吕玲
戴燕鹏
孙世煊
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Dalian Maritime University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0032—Distributed allocation, i.e. involving a plurality of allocating devices, each making partial allocation
    • H04L5/0035—Resource allocation in a cooperative multipoint environment
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0002—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
    • H04L1/0036—Systems modifying transmission characteristics according to link quality, e.g. power backoff arrangements specific to the receiver
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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Abstract

The invention relates to a decoding sequence judging method in a non-orthogonal multi-point cooperation system, which belongs to the technical field of wireless communication and comprises the following steps: based on the non-orthogonal coordinated multi-point system, two different decoding sequences of the user pair are constructed: a first decoding order and a second decoding order, and gives the achievable rate of the user; obtaining optimal transmitting power and transmission rate of the base station based on the first decoding sequence by a monotonic optimization method, and giving a closed solution of the optimal transmitting power and the transmission rate; obtaining optimal transmitting power and transmission rate of the base station based on the second decoding sequence through a monotone optimization method and a built low-complexity algorithm; based on the optimal transmission rate, a decision criterion for an optimal decoding order is determined. The method realizes different optimal decoding sequences of different user pairs and effectively improves the transmission rate of the user.

Description

Decoding sequence judging method in non-orthogonal multi-point cooperation system
Technical Field
The invention belongs to the technical field of wireless communication, and relates to a decoding sequence judging method in a non-orthogonal multipoint cooperation system.
Background
Non-orthogonal multiple access techniques have recently been integrated into coordinated multipoint systems to improve spectral efficiency while mitigating severe interference in future ultra-dense networks. In a NOMA-CoMP system (non-orthogonal coordinated multi-point system), a cluster of base stations performs joint transmission for one user, while each coordinated base station in the cluster can use NOMA to associate with other users that are within the same coverage of spectrum resources. In addition, the decoding order of users has a significant impact on the transmission efficiency of the NOMA-CoMP system. Typically, the decoding order is determined by the channel gain between the base station and its associated users. However, since joint transmission extends user association from a single base station to multiple base stations, conventional decoding order based on single base station channel conditions would not be applicable to NOMA-CoMP systems. Thus, exploring the proper decoding order is critical to the NOMA-CoMP system.
In recent years, there have been a great deal of research into the decoding order and scheduling of NOMA-CoMP systems. Hou et al propose a power control algorithm for a NOMA-CoMP system in a conventional decoding order (i.e., user channel gain ascending order) in downlink NOMA. This indicates that the decoding order has a great impact on a given power control for a given user pair. Kilzi et al studied the optimization of decoding order, and found that the optimization of decoding order had a significant impact on the transmission efficiency of NOMA-CoMP systems, with the complexity increasing exponentially with the number of users. Rezvani et al jointly optimize user pairing and decoding order in a NOMA-CoMP system and indicate that user pairing and decoding order interact.
In summary, the problems of the prior art are: how to clarify the interaction between decoding order and user pairing.
Disclosure of Invention
In order to solve the problem of how to definitely decode the interaction between sequence and user pairing, the invention provides the technical scheme adopted by the invention as follows: a decoding order judging method in a non-orthogonal coordinated multi-point system comprises the following steps:
s1, constructing two different decoding sequences of a user pair based on a non-orthogonal multi-point cooperation system: a first decoding order and a second decoding order, and gives the achievable rate of the user;
s2, obtaining optimal transmitting power and transmission rate of the base station based on the first decoding sequence through a monotonic optimization method, and giving a closed solution of the optimal transmitting power and the transmission rate; obtaining optimal transmitting power and transmission rate of the base station based on the second decoding sequence through a monotone optimization method and a built low-complexity algorithm;
s3, determining a decision criterion of the optimal decoding sequence based on the optimal transmission rate.
Further, the non-orthogonal coordinated multi-point system is a NOMA user pair for users m and n to reuse the same spectrum bandwidth and is associated with a base station i, the base stations i and j are adjacent and clustered together to perform coordinated multi-point joint transmission for the user n at the cell edge,
let h be k,l Representing the channel gain between base station k and user l, P k,l Representing the transmit power between base station k and user l, N 0 Representing additive white gaussian noise at user i, without loss of generality, it is assumed that user m is closer to base station i than user n is to base station j, i.e.:
|h i,m | 2 >|h i,n | 2 ，|h j,n | 2 >|h j,m | 2 ， |h i,m | 2 >|h j,m | 2 (1)
in practical application, a base station obtains channel gain through channel estimation feedback information of a user;
user n receives the wanted signal from base stations i and j through coordinated multi-point joint transmission, while user m receives the wanted signal from base station i only; in addition, because of the frequency spectrum reuse, two users can be interfered by the same channel, NOMA utilizes SIC decoding to detect user signals, and the residual error of eliminating part of the same channel interference and the same channel interference is related to the decoding sequence of the users; thus, there are two cases for the considered non-orthogonal coordinated multi-point system.
Further, the non-orthogonal coordinated multi-point system constructs two different decoding orders of the user pair: the procedure for the first decoding order and the second decoding order, and giving the achievable rate of the user is as follows:
the order of the two different decodes includes: a first decoding order and a second decoding order;
s11, determining a first decoding sequence, namely decoding signals of a user n firstly, wherein the decoding sequence follows the ascending sequence of the power gain of a user channel, and the descending NOMA system standard, according to the SIC decoding principle, the user m firstly decodes and subtracts the signals of the user n, then decodes the signals wanted by the user n, the user n directly decodes the needed signals, the SIC decoding condition of the signals of the user n at the user m is R m→n ≥R min The method comprises the following steps:
Figure BDA0004125596710000031
the second decoding order is determined by first decoding the signal of user m, the decoding order of the downstream NOMA system is different from the standard decoding order, user m directly decodes the desired signal, suffers co-channel interference, user eliminates co-channel interference, then decodes the desired signal, and must ensure R n→m ≥R min Wherein:
Figure BDA0004125596710000032
s12, let α be a binary variable of the decoding order, if the decoding order is consistent with the first decoding order, α=1, otherwise α=0, so the achievable rates of user m and user n are respectively expressed as:
Figure BDA0004125596710000033
Figure BDA0004125596710000034
further, the decoding order and power controlSum rate maximization problem P 0 Expressed as:
Figure BDA0004125596710000035
wherein P= [ P ] i,m ,p i,n ,p j,n ]C1 is the minimum rate constraint of the user, C2 is the SIC decoding condition, and C3 and C4 pass through respectively
Figure BDA0004125596710000036
And->
Figure BDA0004125596710000037
To limit the maximum transmit power of base station i and base station j,
further, the optimal transmit power and transmission rate solving process of the base station is as follows;
problem P 0 Before solving, a lemma 1 is given, lemma 1 is problem P 0 A requirement for an optimal solution; the quotation 1 is as follows:
optimal solution of transmit power
Figure BDA0004125596710000041
Must meet->
Figure BDA0004125596710000042
Discussion of the cases:
s21, a closed solution of the optimal transmitting power and the optimal transmitting rate of the first decoding sequence is as follows:
theorem 1: given α=1, if the following condition is satisfied
Figure BDA0004125596710000043
Problem P 0 Is possible in which
Figure BDA0004125596710000044
Then, the optimal transmit power in the first decoding order is given/>
Figure BDA0004125596710000045
When α=1, problem P 0 The rewriting is as follows:
Figure BDA0004125596710000046
by constraint C 1 And C 2.1 It can be seen that p i,m The feasible range of (2) is expressed as
Figure BDA0004125596710000047
If it is
Figure BDA0004125596710000048
Problem P 1 Is not feasible and the objective function R c1 Regarding p i,m Is monotonically increasing due to
Figure BDA0004125596710000049
The following expression may be written: />
Figure BDA00041255967100000410
Thus, p i,m Is the optimum value of (2)
Figure BDA00041255967100000411
I.e. if problem P 1 Feasible (i.e. easy to get up)>
Figure BDA00041255967100000412
As can be seen from the quotation mark 1,
Figure BDA0004125596710000051
it was observed that R c1 Regarding p j,n Is monotonically increasing, so that +.>
Figure BDA0004125596710000052
Thus, problem P 1 The optimal values of (2) are:
Figure BDA0004125596710000053
s22, solving the optimal transmitting power and the optimal transmitting rate of the second decoding sequence as follows:
given α=0, problem P 0 Equivalently rewritten as follows,
Figure BDA0004125596710000054
according to R n→m And R is m Expression, giving:
Figure BDA0004125596710000055
wherein: (z) follow |h j,n | 2 >|h j,m | 2 And |h i,m | 2 >|h i,n | 2 ；
Therefore, the minimum rate constraint for user m is ignored in the second decoding order; problem P 2 Problem P0 equivalent to when α=0;
and R is c2 Are respectively related to p i,m And p j,n Is monotonically increasing because
Figure BDA0004125596710000056
And->
Figure BDA0004125596710000057
They are expressed as: />
Figure BDA0004125596710000061
Wherein:
A＝N 0 +(P i max -p i,m )|h i,n | 2 +p j,n |h j,n | 2 ，B＝N 0 +(P i max -p i,m )|h i,m | 2 +p j,n |h j,m | 2 ；
the following theorem is then obtained by a monotonic optimization method:
s221, theorem 2: let the
Figure BDA0004125596710000062
Substitution problem P 2 According to>
Figure BDA0004125596710000063
The feasibility of (2) can be given by:
Figure BDA0004125596710000064
Figure BDA0004125596710000065
Figure BDA0004125596710000066
in the constraint of
Figure BDA0004125596710000067
Under the condition of only->
Figure BDA0004125596710000068
Problem P 2 Is feasible under constraint of
Figure BDA0004125596710000069
Under the condition of only->
Figure BDA00041255967100000610
Problem P 2 It is possible.
Further, the method also comprises the steps of constructing a low-complexity algorithm and obtaining the optimal transmitting power of the second decoding sequence under the condition that two constraint conditions are not met, wherein the process is as follows:
Figure BDA0004125596710000071
is a problem P 2 Is indicated as +.>
Figure BDA0004125596710000072
Constraint C when 1.2 And C 2.2 Are all violated if the problem P 2 At->
Figure BDA0004125596710000073
Down-going, then must get +.>
Figure BDA0004125596710000074
and
Figure BDA0004125596710000075
Then, there is the following reasoning: />
S222, deducing 1: if the problem P 2 At the position of
Figure BDA0004125596710000076
Down-going, constraint C when taking optimal value 2.2 The left side and the right side are equal, and the two sides are:
Figure BDA0004125596710000077
according to inference 1 and constraint C 1.2 And C 2.2 The expression for the optimal transmit power is obtained as follows:
Figure BDA0004125596710000078
then, a low-complexity algorithm is designed by utilizing binary search to find a problem P 2 At the position of
Figure BDA0004125596710000079
The following optimum transmit power:
the main idea of low complexity algorithms is to find p j,n To the maximum value of R c2 Maximum:
first, the problem P is verified 2 Feasibility of (2); if u is>v, the problem is not viable, at the same time, because
Figure BDA00041255967100000710
And
Figure BDA00041255967100000711
by P i max -p i,m And p i,m Substitution p j,n After that, p j,n The increase will violate constraint C 2.2 Thus, if P (0) is not a viable point, the problem is also not viable;
the goal of the low complexity algorithm is then to find the largest and feasible p in an iterative manner j,n Let R be c2 Maximum until convergence conditions are met;
thus, problem P is found by theorem 2 and low complexity algorithms 2 Is the optimum value R of (2) c2,* And P * Since a binary search is applied, the linear complexity of the low complexity algorithm is O (t max ) Wherein t is max Is the maximum number of iterations.
Further, the criterion for determining the optimal decoding order based on the optimal transmission rate is specifically:
r is obtained by theorem 1, theorem 2 and low complexity algorithm c1,* And R is c2,* Then, the criteria for the optimal decoding order in the considered case are determined:
i.e. if R c1,* ≥R c2,* α=1, otherwise α=0; if R is c1,* Or R is c2 And α=0; the optimal decoding order is different for different pairs of users, and implemented separately,
in a NOMA-CoMP system, decoding order is not a necessary precondition for user pairing, and in a NOMA-CoMP joint transmission, user pairing can be efficiently performed preferentially even without explicit decoding order.
The decoding sequence judging method in the non-orthogonal multipoint cooperation system provided by the invention can find the optimal decoding sequence of the maximum user and the maximum rate, and explore the influence of the non-orthogonal multipoint cooperation system on the pairing of the users; has the following advantages: different optimal decoding sequences of different user pairs are realized, the transmission rate of the user is effectively improved, and technical guidance is provided for optimization of a NOMA-CoMP system in the future, so that the scheduling efficiency of the NOMA-CoMP system is improved.
For the reasons, the invention can be widely popularized in the fields of wireless communication and the like.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to the drawings without inventive effort to a person skilled in the art.
FIG. 1 is a flow chart of the method of the present invention;
fig. 2 is a flowchart of an optimal transmit power algorithm for a second decoding order according to an embodiment of the present invention;
FIG. 3 is a graph showing a distance relationship between a sum of transmission rates of base stations and users m and n according to an embodiment of the present invention;
FIG. 4 is a graph of the relationship between the achievable rates of users m and n and the distances between users m and n according to an embodiment of the present invention;
fig. 5 is a graph showing a comparison analysis of the sum of the transmission rates of the base stations under different schemes according to the embodiment of the present invention.
Reference numerals:
Detailed Description
It should be noted that, without conflict, the embodiments of the present invention and features in the embodiments may be combined with each other, and the present invention will be described in detail below with reference to the drawings and the embodiments.
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present invention. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
The relative arrangement of the components and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless it is specifically stated otherwise. Meanwhile, it should be clear that the dimensions of the respective parts shown in the drawings are not drawn in actual scale for convenience of description. Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail, but are intended to be part of the specification where appropriate. In all examples shown and discussed herein, any specific values should be construed as merely illustrative, and not a limitation. Thus, other examples of the exemplary embodiments may have different values. It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further discussion thereof is necessary in subsequent figures.
In the description of the present invention, it should be understood that the azimuth or positional relationships indicated by the azimuth terms such as "front, rear, upper, lower, left, right", "lateral, vertical, horizontal", and "top, bottom", etc., are generally based on the azimuth or positional relationships shown in the drawings, merely to facilitate description of the present invention and simplify the description, and these azimuth terms do not indicate and imply that the apparatus or elements referred to must have a specific azimuth or be constructed and operated in a specific azimuth, and thus should not be construed as limiting the scope of protection of the present invention: the orientation word "inner and outer" refers to inner and outer relative to the contour of the respective component itself.
Spatially relative terms, such as "above … …," "above … …," "upper surface at … …," "above," and the like, may be used herein for ease of description to describe one device or feature's spatial location relative to another device or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "above" or "over" other devices or structures would then be oriented "below" or "beneath" the other devices or structures. Thus, the exemplary term "above … …" may include both orientations of "above … …" and "below … …". The device may also be positioned in other different ways (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
In addition, the terms "first", "second", etc. are used to define the components, and are only for convenience of distinguishing the corresponding components, and the terms have no special meaning unless otherwise stated, and therefore should not be construed as limiting the scope of the present invention.
FIG. 1 is a flow chart of the method of the present invention;
a decoding order judging method in a non-orthogonal coordinated multi-point system comprises the following steps:
s1, constructing two different decoding sequences of a user pair based on a non-orthogonal multi-point cooperation system: a first decoding order and a second decoding order, and gives the achievable rate of the user;
s2, obtaining optimal transmitting power and transmission rate of the base station based on the first decoding sequence through a monotonic optimization method, and giving a closed solution of the optimal transmitting power and the transmission rate; obtaining optimal transmitting power and transmission rate of the base station based on the second decoding sequence through a monotone optimization method and a built low-complexity algorithm;
s3, determining a decision criterion of the optimal decoding sequence based on the optimal transmission rate.
The steps S1/S2/S3 are sequentially executed;
further, the non-orthogonal coordinated multi-point system is a NOMA user pair for users m and n to reuse the same spectrum bandwidth and is associated with a base station i, the base stations i and j are adjacent and clustered together to perform coordinated multi-point joint transmission for the user n at the cell edge,
let h be k,l Representing the channel gain between base station k and user l, P k,l Representing the transmit power between base station k and user l, N 0 Representing additive white gaussian noise at user i, without loss of generality, it is assumed that user m is closer to base station i than user n is to base station j, i.e.:
|h i,m | 2 >|h i,n | 2 ，|h j,n | 2 >|h j,m | 2 ，|h i,m | 2 >|h j,m | 2 (1)
in practical application, a base station obtains channel gain through channel estimation feedback information of a user;
user n receives the wanted signal from base stations i and j through coordinated multi-point joint transmission, while user m receives the wanted signal from base station i only; in addition, because of the frequency spectrum reuse, two users can be interfered by the same channel, NOMA utilizes SIC decoding to detect user signals, and the residual error of eliminating part of the same channel interference and the same channel interference is related to the decoding sequence of the users; thus, there are two cases for the considered non-orthogonal coordinated multi-point system.
Further, the first, based on the non-orthogonal coordinated multi-point system, constructs two different decoding orders of the user pair: the procedure for the first decoding order and the second decoding order, and giving the achievable rate of the user is as follows:
s11, determining a first decoding sequence, namely decoding signals of a user n firstly, wherein the decoding sequence follows the ascending sequence of the power gain of a user channel, and the descending NOMA system standard, according to the SIC decoding principle, the user m firstly decodes and subtracts the signals of the user n, then decodes the signals wanted by the user n, the user n directly decodes the needed signals, the SIC decoding condition of the signals of the user n at the user m is R m→n ≥R min The method comprises the following steps:
Figure BDA0004125596710000111
the second decoding order is determined by first decoding the signal of user m, the decoding order of the downstream NOMA system is different from the standard decoding order, user m directly decodes the desired signal, suffers co-channel interference, user eliminates co-channel interference, then decodes the desired signal, and must ensure R n→m ≥R min Wherein:
Figure BDA0004125596710000112
s12, let α be a binary variable of the decoding order, if the decoding order is consistent with the first decoding order, α=1, otherwise α=0, so the achievable rates of user m and user n are respectively expressed as:
Figure BDA0004125596710000113
Figure BDA0004125596710000121
further, the sum rate maximization problem P of decoding order and power control 0 Expressed as:
Figure BDA0004125596710000122
wherein P= [ P ] i,m ,p i,n ,p j,n ]C1 is the minimum rate constraint of the user, C2 is the SIC decoding condition, and C3 and C4 pass through respectively
Figure BDA0004125596710000123
And->
Figure BDA0004125596710000124
To limit the maximum transmit power of base station i and base station j,
by solving problem P 0 The optimal decoding order and the transmitting power of the user pairs in the NOMA-CoMP of the non-orthogonal coordinated multi-point system are obtained, and the optimal solution of the decoding order under the conditions of different user pairing and power control is determined, so that how the decoding order affects the single rate and the sum rate of the user pairs in the NOMA-CoMP can be displayed.
Further, the optimal transmit power and transmission rate solving process of the base station is as follows;
problem P 0 Before solving, a lemma 1 is given, lemma 1 is problem P 0 A requirement for an optimal solution; the quotation 1 is as follows:
optimal solution of transmit power
Figure BDA0004125596710000125
Must meet->
Figure BDA0004125596710000126
Discussion of the cases:
s21, a closed solution of the optimal transmitting power and the optimal transmitting rate of the first decoding sequence is as follows:
theorem 1: given α=1, if the following condition is satisfied
Figure BDA0004125596710000127
Problem P 0 Is possible in which
Figure BDA0004125596710000128
Then, the optimal transmit power in the first decoding order is given +.>
Figure BDA0004125596710000131
When α=1, problem P 0 The rewriting is as follows:
Figure BDA0004125596710000132
by constraint C 1 And C 2.1 It can be seen that p i,m The feasible range of (2) is expressed as
Figure BDA0004125596710000133
If it is
Figure BDA0004125596710000134
Problem P 1 Is not feasible and the objective function R c1 Regarding p i,m Is monotonically increasing due to
Figure BDA0004125596710000135
The following expression may be written:
Figure BDA0004125596710000136
thus, p i,m Is the optimum value of (2)
Figure BDA0004125596710000137
I.e. if problem P 1 Feasible (i.e. easy to get up)>
Figure BDA0004125596710000138
As can be seen from the quotation mark 1,
Figure BDA0004125596710000139
it was observed that R c1 Regarding p j,n Is monotonically increasing, so that +.>
Figure BDA00041255967100001310
Therefore, the optimal value of the problem P1 is:
Figure BDA00041255967100001311
s22, solving the optimal transmitting power and the optimal transmitting rate of the second decoding sequence as follows:
given α=0, problem P 0 Equivalently rewritten as follows,
Figure BDA00041255967100001312
according to R n→m And R is m Expression, giving:
Figure BDA0004125596710000141
wherein: (z) follow |h j,n | 2 >|h j,m | 2 And |h i,m | 2 >|h i,n | 2 ；
Therefore, the minimum rate constraint for user m is ignored in the second decoding order; problem P 2 Problem P equivalent to α=0 0 ；
And R is c2 Are respectively related to p i,m And p j,n Is monotonically increasing because
Figure BDA0004125596710000142
And->
Figure BDA0004125596710000143
They are expressed as:
Figure BDA0004125596710000144
wherein:
A＝N 0 +(P i max -pi,m)|h i,n | 2 +p j,n |h j,n | 2 ，B＝N 0 +(P i max -p i,m )|h i,m | 2 +p j,n |h j,m | 2 ；
the following theorem is then obtained by a monotonic optimization method:
s221, theorem 2: let the
Figure BDA0004125596710000145
Substitution problem P 2 According to>
Figure BDA0004125596710000146
The feasibility of (2) can be given by: />
Figure BDA0004125596710000147
Figure BDA0004125596710000151
Figure BDA0004125596710000152
In the constraint of
Figure BDA0004125596710000153
Under the condition of only->
Figure BDA0004125596710000154
Problem P 2 Is feasible under constraint of
Figure BDA0004125596710000155
Under the condition of only->
Figure BDA0004125596710000156
Problem P 2 It is possible.
Fig. 2 is a flowchart of an optimal transmit power algorithm for a second decoding order according to an embodiment of the present invention;
further: meanwhile, a low-complexity algorithm is constructed, and the process of obtaining the optimal transmitting power of the second decoding sequence under the condition that two constraint conditions are not met is as follows:
Figure BDA0004125596710000157
is a problem P 2 Is indicated as +.>
Figure BDA0004125596710000158
Constraint C when 1.2 And C 2.2 Are all violated if the problem P 2 At->
Figure BDA0004125596710000159
Down-going, then must get +.>
Figure BDA00041255967100001510
and
Figure BDA00041255967100001511
Then, there is the following reasoning:
s222, deducing 1: if the problem P 2 At the position of
Figure BDA00041255967100001512
Down-going, constraint C when taking optimal value 2.2 The left side and the right side are equal, and the two sides are:
Figure BDA00041255967100001513
the following was demonstrated: when problem P 2 If feasible, assume that at the optimal solution
Figure BDA00041255967100001514
R n→m >R min Then there is necessarily Δp j,n And->
Figure BDA00041255967100001515
Satisfy->
Figure BDA00041255967100001516
And
Figure BDA00041255967100001517
in addition, in the case of the optical fiber,
according to
Figure BDA00041255967100001518
Obtain->
Figure BDA00041255967100001519
This is in accordance with P * Contradiction of initial assumptions of optimality, and completion of the proving;
according to inference 1 and constraint C 1.2 And C 2.2 The expression for the optimal transmit power is obtained as follows:
Figure BDA0004125596710000161
then, a low-complexity algorithm is designed by utilizing binary search to find a problem P 2 At the position of
Figure BDA0004125596710000162
The following optimum transmit power:
the main idea of low complexity algorithms is to find p j,n To the maximum value of R c2 Maximum:
first, verifyProblem P 2 Feasibility of (2); if u is>v, the problem is not viable, at the same time, because
Figure BDA0004125596710000163
And
Figure BDA0004125596710000164
by P i max -p i,m And p i,m Substitution p j,n After that, p j,n The increase will violate constraint C 2.2 Thus, if P (0) is not a viable point, the problem is also not viable;
the goal of the low complexity algorithm is then to find the largest and feasible p in an iterative manner j,n Let R be c2 Maximum until convergence conditions are met;
thus, problem P is found by theorem 2 and low complexity algorithms 2 Is the optimum value R of (2) c2,* And P * Since a binary search is applied, the linear complexity of the low complexity algorithm is O (t max ) Wherein t is max Is the maximum number of iterations.
Further, based on the optimal transmission rate, the criteria for determining the optimal decoding order are specifically:
r is obtained by theorem 1, theorem 2 and low complexity algorithm c1,* And R is c2,* Then, the criteria for the optimal decoding order in the considered case are determined:
i.e. if R c1,* ≥R c2,* α=1, otherwise α=0; if R is c1,* Or R is c2 And α=0; the optimal decoding order is different for different pairs of users, and implemented separately,
in a NOMA-CoMP system, decoding order is not a necessary precondition for user pairing, and in a NOMA-CoMP joint transmission, user pairing can be efficiently performed preferentially even without explicit decoding order.
In order to verify the effectiveness of the method of the present invention, the effect of the application of the present invention will be described in detail with reference to simulation.
Simulation conditions
In the simulation scenario, the base stations i and j and the user m and user n coordinates are (-100, 0), (-50, 0) and (0, 0) [ m ] in order]. The spectrum bandwidth is 180kHz, P 1 max ，
Figure BDA0004125596710000171
Are all 27dBm and xi min (R min ) 8dB (2.87 bits/s/Hz), N 0 Is-144 dBm/Hz multiplied by 180kHz, and the path loss is 37.6log 2 (d[km]) +128.1dB, multipath fading follows an exponential distribution of unit mean.
Simulation content and result analysis
The maximum value of the exhaustive search problem P0 is adopted as a reference algorithm by using a Global Search (GS) algorithm, and the effectiveness of the method is verified by comparing with the following three transmission methods.
Comparison method 1: orthogonal multiple access (orthogonal multiple access, OMA), coordinated multi-point joint transmission is disabled. Base station i and base station j are associated with user m and user n using different and non-overlapping spectrum bandwidths, respectively according to nearest neighbor association principles.
Comparison method 2: non-orthogonal multiple access, coordinated multipoint joint transmission is also disabled. The user pairs are associated with only base station i and reuse the same spectrum bandwidth through non-orthogonal multiple access.
Comparison method 3: based on orthogonal multiple access coordinated multipoint (OMA-CoMP), the base station adopts coordinated multipoint joint transmission to serve two users by using different and non-overlapping spectrum bandwidths. The user association is the same as the scenario considered herein.
Simulation 1: distance diagram between sum of transmission rates of base station and users m and n
As shown in fig. 3, the relationship of the sum of the base station transmission rates to the ratio of the distances of base station i and base station j to user n is shown, where the x-coordinate of user n varies between-40 and 60. It can be seen that the proposed solution can achieve the same performance as a global search solution. This verifies the optimality of the proposed solution and verifies theorem 1, 2 and inference 1. It can further be seen that case 1 gradually changes from lower than case 2 to higher than the sum rate of case 2 as user n moves away from base station i and approaches base station j. The results show that the decoding order has a significant impact on the sum rate of the user pairs, and the position of user n determines the decoding order of the NOMA-CoMP joint transmission. In particular, when user n is not very close to base station j, decoding user m's signal first is the best choice for the NOMA user pair.
Simulation 2: graph of the achievable rates for user m and user n versus the distance between user m and n
As shown in fig. 4, the achievable rates for user m and user n are shown versus the base station i and base station j to user n distance ratio under the proposed scheme. It follows that the proposed solution is able to effectively guarantee a minimum value of the sum of the transmission rates of the users. Furthermore, in NOMA-CoMP joint transmission, the location of user n significantly affects the achievable rate of an individual user. If it is desired to increase the achievable rate of user m, user m should be paired with a user located at the edge of the cell and closer to base station j than base station i. Therefore, it is necessary to optimize the decoding order according to the channel gain difference between the user n and the base station (depending on the location of the user n).
Simulation 3: comparison analysis chart of sum of base station transmission rates under different schemes
As shown in fig. 5, a comparison of the performance of different schemes when the x-coordinate of base station j is in the range of 30-160 is shown. It can be seen that NOMA-CoMP always achieves higher sum rates than other schemes. As the channel power gain gap between the user and the coordinating base station increases, the performance gap between NOMA-CoMP and other schemes also increases.
Although embodiments of the present invention have been described in connection with the accompanying drawings, various modifications and variations may be made by those skilled in the art without departing from the spirit and scope of the invention, and such modifications and variations fall within the scope of the invention as defined by the appended claims.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims (7)

1. A decoding order judging method in a non-orthogonal coordinated multi-point system is characterized in that: the method comprises the following steps:
s1, constructing two different decoding sequences of a user pair based on a non-orthogonal multi-point cooperation system: a first decoding order and a second decoding order, and gives the achievable rate of the user;
s2, obtaining optimal transmitting power and transmission rate of the base station based on the first decoding sequence through a monotonic optimization method, and giving a closed solution of the optimal transmitting power and the transmission rate; obtaining optimal transmitting power and transmission rate of the base station based on the second decoding sequence through a monotone optimization method and a built low-complexity algorithm;
s3, determining a decision criterion of the optimal decoding sequence based on the optimal transmission rate.
2. The decoding order decision method in a non-orthogonal coordinated multi-point system according to claim 1, wherein the non-orthogonal coordinated multi-point system is a NOMA user pair for users m and n to reuse the same spectrum bandwidth and is associated with a base station i, the base stations i and j are adjacent and clustered together to perform coordinated multi-point joint transmission for user n located at the cell edge,
let h be k,l Representing the channel gain between base station k and user l, P k,l Representing the transmit power between base station k and user l, N 0 Representing additive white gaussian noise at user i, without loss of generality, it is assumed that user m is closer to base station i than user n is to base station j, i.e.:
|h i,m | 2 >|h i,n | 2 ，|h j,n | 2 >|h j,m | 2 ，|h i,m | 2 >|h j,m | 2 (1)
in practical application, a base station obtains channel gain through channel estimation feedback information of a user;
user n receives the wanted signal from base stations i and j through coordinated multi-point joint transmission, while user m receives the wanted signal from base station i only; in addition, because of the frequency spectrum reuse, two users can be interfered by the same channel, NOMA utilizes SIC decoding to detect user signals, and the residual error of eliminating part of the same channel interference and the same channel interference is related to the decoding sequence of the users; thus, there are two cases for the considered non-orthogonal coordinated multi-point system.
3. The decoding order deciding method in a non-orthogonal coordinated multi-point system according to claim 1, wherein the order of two different decoding of the user pair is constructed based on the non-orthogonal coordinated multi-point system: the procedure for the first decoding order and the second decoding order, and giving the achievable rate of the user is as follows:
s11, determining a first decoding sequence, namely decoding signals of a user n firstly, wherein the decoding sequence follows the ascending sequence of the power gain of a user channel, and the descending NOMA system standard, according to the SIC decoding principle, the user m firstly decodes and subtracts the signals of the user n, then decodes the signals wanted by the user n, the user n directly decodes the needed signals, the SIC decoding condition of the signals of the user n at the user m is R m→n ≥R min The method comprises the following steps:
Figure QLYQS_1
the second decoding order is determined by first decoding the signal of user m, the decoding order of the downstream NOMA system is different from the standard decoding order, user m directly decodes the desired signal, suffers co-channel interference, user eliminates co-channel interference, then decodes the desired signal, and must ensure R n→m ≥R min Wherein:
Figure QLYQS_2
s12, let α be a binary variable of the decoding order, if the decoding order is consistent with the first decoding order, α=1, otherwise α=0, so the achievable rates of user m and user n are respectively expressed as:
Figure QLYQS_3
Figure QLYQS_4
4. the decoding order decision method in a non-orthogonal coordinated multi-point system according to claim 1, wherein the sum rate of decoding order and power control maximizes a problem P 0 Expressed as:
Figure QLYQS_5
wherein P= [ P ] i,m ,p i,n ,p j,n ]C1 is the minimum rate constraint of the user, C2 is the SIC decoding condition, and C3 and C4 pass through respectively
Figure QLYQS_6
And->
Figure QLYQS_7
To limit the maximum transmit power of base station i and base station j.
5. The decoding order decision method in a non-orthogonal coordinated multi-point system according to claim 1, wherein the optimal transmit power and transmission rate solving process of the base station is as follows;
problem P 0 Prior to solving, give lemma 1Lemma 1 is problem P 0 A requirement for an optimal solution; the quotation 1 is as follows:
optimal solution of transmit power
Figure QLYQS_8
Must meet->
Figure QLYQS_9
Discussion of the cases:
s21, a closed solution of the optimal transmitting power and the optimal transmitting rate of the first decoding sequence is as follows:
theorem 1: given α=1, if the following condition is satisfied
Figure QLYQS_10
Problem P 0 Is possible in which
Figure QLYQS_11
Then, the optimal transmit power in the first decoding order is given +.>
Figure QLYQS_12
When α=1, problem P 0 The rewriting is as follows:
Figure QLYQS_13
by constraint C 1 And C 2.1 It can be seen that p i,m The feasible range of (2) is expressed as
Figure QLYQS_14
If it is
Figure QLYQS_15
Problem P 1 Is not feasible and the objective function R c1 Regarding p i,m Is monotonically increasing due to
Figure QLYQS_16
The following expression may be written:
Figure QLYQS_17
thus, p i,m Is the optimum value of (2)
Figure QLYQS_18
I.e. if problem P 1 Feasible (i.e. easy to get up)>
Figure QLYQS_19
As can be seen from the quotation mark 1,
Figure QLYQS_20
it was observed that R c1 Regarding p j,n Is monotonically increasing, so that +.>
Figure QLYQS_21
Thus, problem P 1 The optimal values of (2) are:
Figure QLYQS_22
s22, solving the optimal transmitting power and the optimal transmitting rate of the second decoding sequence as follows:
given α=0, problem P 0 Equivalently rewritten as follows,
Figure QLYQS_23
according to R n→m And R is m Expression, giving:
Figure QLYQS_24
wherein: (z) follow |h j,n | 2 >|h j,m | 2 And |h i,m | 2 >|h i,n | 2 ；
Therefore, the minimum rate constraint for user m is ignored in the second decoding order; problem P 2 Problem P0 equivalent to when α=0;
and R is c2 Are respectively related to p i,m And p j,n Is monotonically increasing because
Figure QLYQS_25
And->
Figure QLYQS_26
They are expressed as:
Figure QLYQS_27
Figure QLYQS_28
wherein:
A＝N 0 +(P i max -p i,m )|h i,n | 2 +p j,n |h j,n | 2 ，B＝N 0 +(P i max -p i,m )|h i,m | 2 +p j,n |h j,m | 2 ；
the following theorem is then obtained by a monotonic optimization method:
s221, theorem 2: let the
Figure QLYQS_29
Substitution problem P 2 According to>
Figure QLYQS_30
The feasibility of (2) can be given by:
Figure QLYQS_31
Figure QLYQS_32
Figure QLYQS_33
in the constraint of
Figure QLYQS_34
Under the condition of only->
Figure QLYQS_35
Problem P 2 Is possible in the constraint +.>
Figure QLYQS_36
Under the condition of only->
Figure QLYQS_37
Problem P 2 It is possible.
6. The decoding order decision method in a non-orthogonal coordinated multi-point system according to claim 1, wherein: the method also comprises the following process of constructing a low-complexity algorithm to obtain the optimal transmitting power of the second decoding sequence under the condition that two constraint conditions are not met:
Figure QLYQS_38
is a problem P 2 Is indicated as +.>
Figure QLYQS_39
Constraint C when 1.2 And C 2.2 Are all violated if the problem P 2 At->
Figure QLYQS_40
Down-going, then must get +.>
Figure QLYQS_41
And +.>
Figure QLYQS_42
Then, there is the following reasoning:
s222, deducing 1: if the problem P 2 At the position of
Figure QLYQS_43
Down-going, constraint C when taking optimal value 2.2 The left side and the right side are equal, and the two sides are:
Figure QLYQS_44
according to inference 1 and constraint C 1.2 And C 2.2 The expression for the optimal transmit power is obtained as follows:
Figure QLYQS_45
then, a low-complexity algorithm is designed by utilizing binary search to find a problem P 2 At the position of
Figure QLYQS_46
The following optimum transmit power:
the main idea of low complexity algorithms is to find p j,n To the maximum value of R c2 Maximum:
first, the problem P is verified 2 Feasibility of (2); if u is>v, the problem is not viable, at the same time, because
Figure QLYQS_47
And
Figure QLYQS_48
by P i max -p i,m And p i,m Substitution p j,n After that, p j,n The increase will violate constraint C 2.2 Thus, if P (0) is not a viable point, the problem is also not viable;
the goal of the low complexity algorithm is then to find the largest and feasible p in an iterative manner j,n Let R be c2 Maximum until convergence conditions are met;
thus, problem P is found by theorem 2 and low complexity algorithms 2 Is the optimum value R of (2) c2,* And P * Since a binary search is applied, the linear complexity of the low complexity algorithm is O (t max ) Wherein t is max Is the maximum number of iterations.
7. The decoding order deciding method in a non-orthogonal coordinated multi-point system according to claim 1, wherein the criterion for determining the optimal decoding order based on the optimal transmission rate is specifically:
r is obtained by theorem 1, theorem 2 and low complexity algorithm c1,* And R is c2,* Then, the criteria for the optimal decoding order in the considered case are determined:
i.e. if R c1,* ≥R c2,* α=1, otherwise α=0; if R is c1,* Or R is c2 And α=0; the optimal decoding order is different for different pairs of users, and implemented separately,
in a NOMA-CoMP system, decoding order is not a necessary precondition for user pairing, and in a NOMA-CoMP joint transmission, user pairing can be efficiently performed preferentially even without explicit decoding order.
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