CN111246578B - NOMA downlink communication method under directional antenna scene - Google Patents

NOMA downlink communication method under directional antenna scene Download PDF

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CN111246578B
CN111246578B CN202010022841.8A CN202010022841A CN111246578B CN 111246578 B CN111246578 B CN 111246578B CN 202010022841 A CN202010022841 A CN 202010022841A CN 111246578 B CN111246578 B CN 111246578B
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far
user
users
antenna
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CN111246578A (en
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张昌明
郑华荣
彭建鑫
黄腾
罗喜伶
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Hangzhou Innovation Research Institute of Beihang University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/04—Wireless resource allocation
    • H04W72/044—Wireless resource allocation based on the type of the allocated resource
    • H04W72/0473—Wireless resource allocation based on the type of the allocated resource the resource being transmission power
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H04W52/18—TPC being performed according to specific parameters
    • H04W52/26—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service]
    • H04W52/267—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service] taking into account the information rate
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H04W52/30—TPC using constraints in the total amount of available transmission power
    • H04W52/34—TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading
    • H04W52/346—TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading distributing total power among users or channels
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H04W52/38—TPC being performed in particular situations
    • H04W52/42—TPC being performed in particular situations in systems with time, space, frequency or polarisation diversity
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
    • H04W72/542—Allocation or scheduling criteria for wireless resources based on quality criteria using measured or perceived quality
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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Abstract

The invention discloses a NOMA downlink communication method in a directional antenna scene, and belongs to the technical field of wireless communication. Aiming at the problem that the traditional NOMA scheme cannot be directly applied to a directional antenna scene, the invention provides a two-user or multi-user downlink communication method aiming at the directional antenna scene, the far-end user antennas of the central site of the invention all transmit far-end user signals, the transmitting power of the near-end user antennas is distributed among two users, and in the near-end user antennas, the power distribution factors corresponding to the near-end users and the far-end users are mu and 1-mu respectively; in addition, the far-end user antenna is not directly aimed at the far-end user, but is biased to the near-end user by a certain angle, so that the equivalent SNR requirement of the near-end user on the far-end user in SIC is ensured. The NOMA technical scheme is applied to the downlink in the directional antenna scene, and when the included angle of the communication link of the two users is smaller, compared with the existing FDMA and other orthogonal multiple access or SDMA access technologies, the communication capacity can be improved.

Description

NOMA downlink communication method under directional antenna scene
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a NOMA downlink communication method in a directional antenna scene.
Background
In the field of wireless communication technology, multiple access is one of important key technologies, and provides reliable guarantee for point-to-multipoint communication scenarios. The conventional multiple access technology is mainly orthogonal multiple access, that is, each user of point-to-multipoint communication adopts mutually orthogonal time/frequency/code resource, there is no interference between each other, and the implementation of the receiver is relatively simple. Common orthogonal multiple access techniques include frequency division multiple access (Frequency Division Multiple Access, FDMA), time division multiple access (Time Division Multiple Access, TDMA), code division multiple access (Code Division Multiple Access, CDMA), orthogonal frequency division multiple access (Orthogonal Frequency Division Multiple Access, OFDMA).
With the increasing demands of people for wireless communication applications, especially with the rapid development of the mobile internet and the driving of internet of things and internet of things, the limited communication orthogonal resources cannot meet the application demands, and the existing orthogonal multiple access communication mechanism faces a great challenge. In this context, many emerging multiple access communication technologies are being sought, with non-orthogonal multiple access (Non Orthogonal Multiple Access, NOMA) gaining wide attention in the industry. Unlike conventional orthogonal multiple access, NOMA can serve multiple users simultaneously within the same time/frequency/codeword resource block, and interference between multiple users can be effectively suppressed by performing serial interference cancellation (Successive Interference Cancellation, SIC) in the receiver. Under the condition that the number of orthogonal resources is certain, NOMA can serve more users, and large-scale access application is ensured; in the case that the number of users is fixed, the granularity of communication resource division can be reduced by adopting NOMA, and a single user can obtain more time/frequency/code word resources. In summary, NOMA can increase the capacity of a point-to-multipoint communication system and can reduce the latency required for resource allocation.
In view of the fact that the theoretical capacity of each orthogonal multiple access technique is the same, in the present invention, FDMA is used to represent the conventional orthogonal multiple access technique and frequency is used as an orthogonal resource for convenience of description. The NOMA technology simultaneously serves multiple users in the same time/frequency/codeword resource block, and is distinguished by being allocated with different powers, and fig. 1 is a schematic diagram showing comparison of FDMA and NOMA in K user scenarios. In FDMA case, each user gets only a small part of the total system, while in NOMA case, each user gets all frequency resources. The SIC process of NOMA data receiving is carried out according to the power from large to small, when receiving the user signal with larger power, the user signal with smaller power is regarded as noise, then the signal is reconstructed according to the result of receiving the data by the user with larger power and subtracted from the received signal, and then the receiving of the user signal with smaller power is completed. In theory, NOMA can realize frequency resource sharing among any multiple users, but in practical implementation, to avoid excessive complexity, NOMA technology is usually applied between two users, that is, the number of users is twice the number of frequency resources of the system.
The invention mainly focuses on NOMA downlink in case of two users, fig. 2 presents a schematic view of a prior art system implementation, where s 1 S 2 The original transmitted signals of the near-end user and the far-end user respectively. On the premise of normalizing the sending power of the central site, the power distribution factors corresponding to the near-end user and the far-end user are mu and 1-mu (0 < mu < 1), and the signals are sent after being overlapped. Because of the greater attenuation experienced by the far end user, it is often necessary to distribute more power than the near end user, i.e., 0 < mu < 1/2. The near-end user receiver adopts SIC to complete data receiving, firstly, the near-end user signal is regarded as a part of noise, the far-end user signal is demodulated and decoded, the form of the far-end user in the received signal is reconstructed according to the obtained far-end user data, then the reconstructed signal of the far-end user is subtracted from the received signal to complete interference elimination, and then the demodulation and decoding of the near-end user signal are executed to obtain the required near-end user data result. In the far-end user receiver, the near-end user signal is directly used as a part of noise to complete demodulation and decoding, and received data is obtained.
The capacity gain of NOMA over FDMA is mainly determined by the power allocation factor μ, and theoretically, in order to obtain the maximum capacity sum, power should be allocated to all near-end users closer to the central site, but this would result in the far-end users not being able to access. Thus, both users typically need to meet a certain capacity threshold, and in general, the lower capacity limit can be set to the respective capacities in the case of FDMA.
The power allocation problem in fig. 2 can be described as
Figure BDA0002361416850000021
Figure BDA0002361416850000022
Figure BDA0002361416850000023
Here, the bandwidth at the time of capacity calculation is assumed to be 1Hz, γ represents the signal-to-noise ratio (Signal to Noise Ratio, SNR) at the time of total allocation of power and frequency resources to the near-end users, and γ/λ (λ > 1) is the SNR at the time of total allocation of power and frequency resources to the far-end users. From the free space attenuation model, λ can be considered as the square of the ratio of the distance of the far-end user to the near-end user from the central site. Equation (1. A) and equation (1. B) represent that the capacity of the near-end user and the far-end user, respectively, is not smaller in the NOMA case than in the FDMA case (assuming average allocation of both user frequency and power resources in the FDMA case). It can be deduced that the power allocation factor satisfying the maximization of formula (1) is exactly equal to formula (1. B), i.e
Figure BDA0002361416850000031
In this case, the power of the far-end user only needs to make its capacity equal to the capacity constraint lower limit, and the power is allocated to the near-end user as much as possible to obtain the maximum capacity gain (it can be deduced that NOMA must be not less than FDMA case under the power allocation factor shown in equation (2)).
Under the existing NOMA technical system, if the remote user receiver can correctly receive the data of the remote user, the near user receiver can also correctly receive the data of the remote user, so that the SIC is completed. This isBecause the equivalent SNR when performing far-end user signal demodulation at the near-end user is
Figure BDA0002361416850000032
Which must be larger than the equivalent SNR at the far end user, i.e +.>
Figure BDA0002361416850000033
The constraint term of equation (1) therefore does not include a capacity constraint for receiving far-end user data at the near-end user.
The existing NOMA technical scheme is designed based on an omni-directional antenna scene, namely the strength of a received signal is fixed as long as the distance between a user and a central site is the same. However, in order to ensure the effectiveness of signal transmission in practical situations, a directional antenna is generally required to be adopted, so as to obtain a certain antenna gain. This is particularly common in fixed wireless communication scenarios, such as wireless mobile backhaul, wireless video surveillance, and the like. At the central site, an antenna is configured for each user, and signals corresponding to the users are transmitted. Fig. 3 is a schematic diagram of directional transmission when the included angle θ between two user communication links is large, the central station has two antennas, which are respectively aligned to the near-end user and the far-end user, and transmits signals of the two users, and due to spatial isolation, interference existing between the two users is small even in the same frequency resource, so as to form a space division multiple access (Space Division Multiple Access, SDMA) mode. In the near-end user receiver, the signal of the far-end user is regarded as noise, and interference is not required to be eliminated through SIC; while at the far-end user receiver, the near-end user's signal is also treated as noise. In short, under the condition that the included angle of the communication links between the users is larger, SDMA increases a new multiplexing dimension compared with the traditional FDMA, so that the resource multiplexing efficiency can be improved exponentially without considering the application of NOMA technology.
When the communication link included angle θ is smaller, the antenna space isolation is smaller, the interference between two users is stronger, and each user receiver cannot directly treat the signal of the other user as noise. Existing FDMA and other orthogonal multiple access techniques can be directly applied, but FDMA has a smaller system capacity, and it is necessary to explore how to increase the system capacity based on NOMA techniques.
However, existing NOMA technology cannot be directly applied to directional antenna scenarios. In one aspect, the power allocation under existing NOMA technology is not applicable to directional antenna scenarios because existing power allocation schemes assume that the central site transmits a unique superimposed signal. However, in the case of directional antennas, where each user is equipped with an antenna at a central site, signals of the corresponding user are transmitted separately, and the prior art solution does not consider the problem of power allocation in this case. On the other hand, the SNR requirement of the far-end user when the near-end user performs the SIC does not need to be considered in the existing NOMA technology, because the far-end user signal power received by the near-end user is necessarily greater than the corresponding signal power received by the far-end user, as long as the far-end user receiver can normally demodulate the signal of the far-end user, the near-end user can also demodulate the signal of the far-end user. In the directional antenna scenario, due to directional isolation between antennas, the power of the far-end user signal received by the near-end user may be smaller than the corresponding signal power received by the far-end user, so that not only the SNR requirement of the signal itself but also the equivalent SNR requirement of the far-end user in the SIC process need to be considered in the near-end user receiver.
Disclosure of Invention
The invention mainly aims at the two-user or multi-user downlink of a directional antenna scene, and provides an applicable NOMA technical scheme under the condition of smaller included angle of a communication link, so that the capacity is improved relative to the orthogonal multiple access such as FDMA.
The invention discloses a NOMA downlink communication method under a directional antenna scene, which aims at a dual-user downlink of the directional antenna scene, and specifically comprises the following steps:
recording the included angle of the communication link as theta; the remote user antennas of the central site all transmit remote user signals, the transmitting power of the near-end user antennas is distributed among two users, and in the near-end user antennas, the power distribution factors corresponding to the near-end users and the remote users are mu and 1-mu;
the near-end user antenna is directly aligned with the near-end user itself, and the far-end user antenna is aligned with the near-end user itselfThe near-end user is inclined at a certain angle
Figure BDA0002361416850000041
Wherein->
Figure BDA0002361416850000042
As a preferred embodiment of the present invention, the angle
Figure BDA0002361416850000043
The determination method of (2) is as follows:
1) Order the
Figure BDA0002361416850000044
When the method is used, the power distribution factor mu of the antenna of the near-end user is calculated on the condition that the near-end user and the far-end user can accurately receive the far-end user data 1 Mu and mu 2 I.e.
Figure BDA0002361416850000051
The function g (·) represents the gain at a certain direction angle relative to the alignment position, which becomes smaller with increasing offset angle; gamma represents SNR at which only the near-end user is operating; λ is the square of the ratio of the distance of the far-end user to the near-end user from the central site, and γ/λ is the SNR of only the far-end user when working;
when mu is present 1 ＜μ 2 Turning to step 2), otherwise turning to step 3);
2) Gradually biasing the direction of the antenna of the remote user of the central site towards the near user for different offset angles
Figure BDA00023614168500000511
The power distribution factor mu is calculated respectively according to the following steps 1 Mu and mu 2 ，
Figure BDA0002361416850000052
Until it is searched for
Figure BDA0002361416850000053
So that mu 1 ＝μ 2 Satisfy condition->
Figure BDA0002361416850000054
Offset angle for the end-user antenna;
3) Setting the pointing offset angle of the far-end user antenna
Figure BDA0002361416850000055
Further, the method for determining the power distribution factor μ is as follows:
in step 2), when it is found that
Figure BDA0002361416850000056
So that mu 1 ＝μ 2 When the same power distribution factor is recorded as a near-end user antenna power distribution factor mu which is finally adopted;
in step 3), when the remote user antenna pointing offset angle is set
Figure BDA0002361416850000057
When the near-end user antenna power distribution factor is +.>
Figure BDA0002361416850000058
The power distribution factor mu calculated at that time 2 。
As a preferred embodiment of the present invention, searching in step 2) is performed
Figure BDA0002361416850000059
Methods such as dichotomy and Newton method can be used.
As a preferable scheme of the invention, the signals sent by the antennas of the near-end user and the far-end user are respectively expressed as
Figure BDA00023614168500000510
S 2 Wherein s is 1 For near-end user signals s 2 Is a far-end user signal.
The invention further discloses a NOMA downlink communication method in the directional antenna scene, which aims at the multi-user downlink of the directional antenna scene; wherein the number of multi-user finger users is more than 2;
the method comprises the following steps: the multi-users are grouped, each group does not exceed two users, then the communication method aiming at the downlink of the two users is adopted in each group with two users, and an orthogonal multiple access method or an SDMA method is adopted among the users in each group.
The NOMA technical scheme is applied to the downlink in the directional antenna scene, and when the included angle of the communication link of the two users is smaller, the communication capacity can be improved compared with the existing FDMA and other orthogonal multiple access or SDMA access technologies.
Drawings
FIG. 1 is a diagram showing the comparison of FDMA and NOMA resource multiplexing;
FIG. 2 is a schematic diagram of an implementation of a prior NOMA solution;
fig. 3 is a schematic diagram of directional transmission when the included angle of the communication link is large;
FIG. 4 is a schematic diagram of directional transmission with a small included angle of the communication link;
FIG. 5 is a schematic illustration of a NOMA solution according to the present invention;
FIG. 6 is a flow chart of an implementation of the technical scheme of the invention;
FIG. 7 is a parabolic antenna pattern for an Andrew corporation 15GHz bin diameter of 0.3 m;
FIG. 8 is a graph of capacity versus remote users 400m from a central site;
fig. 9 is a graph of capacity versus distance of a remote user 2000m from a central site.
Detailed Description
The invention is further illustrated and described below in connection with specific embodiments. The technical features of the embodiments of the invention can be combined correspondingly on the premise of no mutual conflict.
As shown in fig. 5, the main technical strategies of the present invention include: firstly, in the aspect of power distribution, because the link attenuation of a far-end user is large, the far-end user antenna of a central site transmits far-end user signals completely, the transmitting power of a near-end user antenna is distributed among two users, and in the near-end user antenna, the power distribution factors corresponding to the near-end user and the far-end user are mu and 1-mu respectively; second, because of the directional isolation of the antenna from the far-end user signal to the near-end user, the far-end user antenna is no longer directly aimed at the far-end user itself, but is angled toward the near-end user
Figure BDA0002361416850000061
Thereby guaranteeing the equivalent SNR requirement of the near-end user to the far-end user in SIC.
Under the technical scheme of the invention, the parameters to be solved comprise the power distribution factor mu of the near-end user antenna of the central site and the angle offset of the far-end user antenna
Figure BDA0002361416850000062
Maximizing the sum of the capacity of the near-end user and the far-end user, the problem can be modeled as
Figure BDA0002361416850000063
Figure BDA0002361416850000071
Figure BDA0002361416850000072
Here, the function g (·) represents the gain at a certain direction angle with respect to the alignment position, which becomes smaller with an increase in the offset angle; gamma represents SNR when only near end user is active (near end user occupies all frequency resources, center site near end user antenna is aimed at near end user and all power is distributed equallyTo the near-end user); λ is the square of the ratio of the distance of the far-end user to the near-end user from the central site, and γ/λ is the SNR at which only the far-end user is working (the far-end user occupies all frequency resources, the central site far-end user antenna is aimed at the far-end user and all power is allocated to the far-end user). In formula (3), log 2 (1+mu gamma) is the capacity of the near-end user under the unit bandwidth under the NOMA technical scheme;
Figure BDA0002361416850000073
representing the capacity of the far-end user of the present invention at a unit bandwidth. Equation (3. A) indicates that the capacity of the near-end user cannot be lower than the corresponding FDMA case where the SNR becomes 2 y because the bandwidth is halved and the antenna transmission power is unchanged; equation (3.b) represents the remote user's capacity C 2 Nor below the corresponding FDMA case and calculated capacity +.>
Figure BDA0002361416850000074
Not less than the capacity C of the far-end user 2 That is, the SIC stage of the near-end user can be ensured to correctly receive the signal of the far-end user.
The remote user's capacity is essentially min { C 1 ,C 2 }, wherein C 1 Along with it
Figure BDA0002361416850000075
Is increased by an increase of C 2 Along with->
Figure BDA0002361416850000076
Is decreased by an increase in (c). When C occurs 1 ＜C 2 In this case, the antenna angle offset of the remote user can be increased>
Figure BDA0002361416850000077
So that the difference between the two is reduced, thereby improving the capacity of the far-end user when +.>
Figure BDA0002361416850000078
When increasing to theta, canProof to get C 1 Strictly greater than C 2 Thus must be able to find one
Figure BDA0002361416850000079
So that C 1 ＝C 2 . Also, if C 1 ＞C 2 Can be reduced by->
Figure BDA00023614168500000710
So that the difference between the two is reduced, but when +.>
Figure BDA00023614168500000711
The equal sign may still not be available. In short, C 1 ＞C 2 Only at +.>
Figure BDA00023614168500000712
It is only possible to appear when 0, but in +.>
Figure BDA00023614168500000713
At times there must be C 1 ＝C 2 。
It can be deduced that the antenna angle offset at a given remote user
Figure BDA00023614168500000714
When the total capacity of the two users shown in formula (3) increases with the increase of the power division factor mu, according to +.>
Figure BDA00023614168500000715
And +.>
Figure BDA00023614168500000716
Can get->
Figure BDA0002361416850000081
To maximize the total capacity, the power division factor should be maximized, and μ can be obtained in combination with the analysis of formula (2. B) and above 1 ≥μ 2 Mu, and mu 1 ＞μ 2 Only at
Figure BDA0002361416850000082
And 0.
To sum up, as shown in fig. 6, the near-end user antenna power allocation factor μ and the far-end user antenna angular offset are solved
Figure BDA0002361416850000083
The process of (1) is as follows:
s01, on the premise that the capacity of the far-end user is equal to FDMA, the antenna of the far-end user points to an offset angle
Figure BDA0002361416850000084
When the near-end user and the far-end user can accurately receive the far-end user data respectively as shown in (4), calculating the near-end user antenna power distribution factor mu 1 Mu and mu 2 ，
When mu is present 1 ＜μ 2 Turning to S02, otherwise turning to S03;
s02, gradually biasing the direction of the antenna of the remote user of the central site towards the near user, for different offset angles
Figure BDA0002361416850000085
Calculating power distribution factors mu respectively as shown in (4) 1 Mu and mu 2 Until +.>
Figure BDA0002361416850000086
So that mu 1 ＝μ 2 And the same power distribution factor is recorded as the power distribution factor of the near-end user antenna finally adopted by the scheme, which satisfies the condition +.>
Figure BDA0002361416850000087
Offset angle for end-user antenna (note: mu as can be found from equation (4) 1 Along with->
Figure BDA0002361416850000088
Monotonically increasing, μ 2 Along with->
Figure BDA0002361416850000089
Monotonically decreasing. Thus, search +.>
Figure BDA00023614168500000810
Can be obtained by adopting simple methods such as dichotomy and Newton method;
s03, setting the pointing offset angle of the far-end user antenna
Figure BDA00023614168500000811
And the near-end user antenna power allocation factor is +.>
Figure BDA00023614168500000812
The power distribution factor mu calculated at that time 2 。
In theory, after the power division factor μ is obtained, the satisfaction condition of the formula (3. A) needs to be verified, and if the satisfaction condition is not satisfied, it is stated that the higher capacity than FDMA cannot be obtained by adopting the NOMA technical scheme of the present invention in the corresponding scenario. However, if the capacity of the technical scheme of the invention cannot exceed FDMA, the included angle of the communication link between two users is already large, and then higher capacity than FDMA can be obtained by adopting SDMA. Therefore, in practical application, the capacity of the technical scheme of the invention is only required to be compared with SDMA, if the capacity is larger than the SDMA capacity, the technical scheme of the invention is adopted, otherwise, SDMA is adopted.
It should be noted that in a practical scenario, when the number of users is greater than two, the users may be grouped by using a related user grouping algorithm, where each group does not exceed two users, then the communication method for the downlink of two users described in the present invention is used in each group with two users, and the existing orthogonal multiple access technology or SDMA technology is used between each group of users.
The simulation results are given below in combination with the actual scenario.
The antenna pattern refers to a parabolic antenna with a diameter of 0.3m at a frequency point of 15GHz by Andrew company, as shown in fig. 7. The distance between the near-end user and the central site is set to be 200m, and the SNR of the near-end user is gamma=30dB only when the near-end user works, and the included angle range of the communication link between the far-end user and the near-end user is set to be 0-5 degrees.
Fig. 8 shows a capacity comparison for a remote user at a distance of 400m from the central site, corresponding λ= (400/200) 2 =4. It can be seen that the present invention has a capacity gain of about 10% relative to FDMA, and that the present invention is also larger relative to SDMA capacity when the communication link angle is less than 3.5 degrees. The capacity of the SDMA scheme is significantly affected by the angle of the communication link, and when the angle is smaller, the capacity is even lower than FDMA.
Fig. 9 shows a capacity comparison for a remote user at a distance of 2000m from a central site, corresponding λ= (2000/200) 2 =100. In this case, the present invention provides a capacity gain of about 40% with respect to FDMA. Therefore, the larger the difference of the communication distance between two users, the more remarkable the capacity gain of the NOMA technical scheme in the directional antenna scene, which has similar characteristics with the NOMA technology in the existing omni-directional antenna scene. When the included angle of the communication link is smaller than 4 degrees, the technical scheme of the invention has larger capacity relative to SDMA. In addition, it can be seen that when the link included angle is greater than 4 degrees, the capacity of the technical scheme of the invention has a tendency of slowly decreasing, because the adverse effect of the antenna directivity isolation on the SIC of the near-end user is gradually enhanced. In a word, the invention has stronger application value when the included angle of the two-user communication link is smaller under the directional antenna scene, and particularly, the capacity gain is more outstanding when the difference of the communication distances of the two users is larger.
The foregoing examples illustrate only a few embodiments of the invention and are described in detail herein without thereby limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims (6)

1.A NOMA downlink communication method in a directional antenna scenario, characterized in that: aiming at a dual-user downlink of a directional antenna scene, recording the included angle of a communication link as theta;
the remote user antennas of the central site all transmit remote user signals, the transmitting power of the near-end user antennas is distributed among two users, and in the near-end user antennas, the power distribution factors corresponding to the near-end users and the far-end users are mu and 1-mu respectively;
the near-end user antenna is directly aligned with the near-end user itself, and the far-end user antenna is inclined to the near-end user by a certain angle
Figure FDA0002361416840000011
Wherein the method comprises the steps of
Figure FDA0002361416840000012
2. The NOMA downlink communication method in a directional antenna scenario according to claim 1, wherein: said angle
Figure FDA0002361416840000013
The determination method of (2) is as follows:
1) Order the
Figure FDA0002361416840000014
When the method is used, the power distribution factor mu of the antenna of the near-end user is calculated on the condition that the near-end user and the far-end user can accurately receive the far-end user data 1 Mu and mu 2 I.e.
Figure FDA0002361416840000015
The function g (·) represents the gain at a certain direction angle relative to the alignment position, which becomes smaller with increasing offset angle; gamma represents SNR at which only the near-end user is operating; λ is the square of the ratio of the distance of the far-end user to the near-end user from the central site, and γ/λ is the SNR of only the far-end user when working;
when mu is present 1 ＜μ 2 Turning to step 2), otherwise turning to step 3);
2) Gradually biasing the direction of the antenna of the remote user of the central site towards the near user for different offset angles
Figure FDA00023614168400000110
The power distribution factor mu is calculated respectively according to the following steps 1 Mu and mu 2 ，
Figure FDA0002361416840000016
Until it is searched for
Figure FDA0002361416840000017
So that mu 1 ＝μ 2 Satisfy condition->
Figure FDA0002361416840000018
Offset angle for the end-user antenna;
3) Setting the pointing offset angle of the far-end user antenna
Figure FDA0002361416840000019
3. The NOMA downlink communication method in a directional antenna scenario according to claim 2, wherein: the method for determining the near-end user power distribution factor mu is as follows:
in step 2), when it is found that
Figure FDA0002361416840000021
So that mu 1 ＝μ 2 When the same power distribution factor is recorded as a near-end user antenna power distribution factor mu which is finally adopted;
in step 3), when the remote user antenna pointing offset angle is set
Figure FDA0002361416840000022
When the near-end user antenna power distribution factor is +.>
Figure FDA0002361416840000023
The power distribution factor mu calculated at that time 2 。
4. The NOMA downlink communication method in a directional antenna scenario according to claim 2, wherein: searching in step 2)
Figure FDA0002361416840000024
When the method is used, the dichotomy method or the Newton method can be adopted.
5. The NOMA downlink communication method in a directional antenna scenario according to claim 1, wherein: the signals sent by the antennas of the near-end users and the far-end users are respectively expressed as
Figure FDA0002361416840000025
S 2 Wherein s is 1 For near-end user signals s 2 Is a far-end user signal.
6. A NOMA downlink communication method in a directional antenna scenario, characterized in that: the method is directed to a multi-user downlink for a directional antenna scenario; wherein the number of multi-user finger users is more than 2;
grouping multiple users, not more than two users per group, and then employing the method of any of claims 1-5 within each group of two users, employing either an orthogonal multiple access method or an SDMA method between each group of users.
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