CN111343692B - Opportunistic NOMA cooperative multicast method - Google Patents
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Abstract
The invention discloses an opportunistic cooperative multicast method, which comprises the steps that a base station according to the worst forwarding link channel gain of each selected multicast user and each unicast user, if the multicast user judges that the worst forwarding link channel gain of all unicast users is the highest, the multicast user is used as the best multicast user to re-encode and modulate unicast user information obtained by decoding signals acquired by the multicast user and forward the unicast user information. The invention considers the link state from multicast user to unicast user in the cooperative multicast method; for one or more unicast users, the performance of the unicast users can be guaranteed under the condition that the link gain from the multicast users to the unicast users is poor.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to an opportunistic NOMA cooperative multicast method.
Background
With the rapid development of mobile communication, the 4G network which is commercially available in a large scale worldwide has not met the user demands of high user density and high mobile scenes. To be "2020 oriented and in the future", 5G has become a research hotspot in the field of global wireless communication. The diversified application scenarios and the multiple growth of performance indicators result in an increasingly scarce radio spectrum resource, which puts severe requirements on the 5G multiple access technology. Among the existing Multiple Access techniques, Non-Orthogonal Multiple Access (NOMA) techniques stand out. The latest research results show that the non-orthogonal multiple access technology transmits a plurality of information streams on channels with overlapped time domains/frequency domains/code domains by different powers, and provides wireless services for a plurality of users on the same wireless resources, so that the system spectrum efficiency and the user access capability can be obviously improved, the user scheduling signaling overhead can be reduced, the access time delay can be shortened, and the terminal energy consumption can be reduced.
Cognitive Radio (CR) is considered to be an effective method to improve spectral efficiency. By reusing the idle authorized frequency band, the utilization rate of the wireless spectrum is improved, and the method becomes an important way for solving the problem of lack of wireless spectrum resources. In a cognitive radio system, a Secondary User (SU) must use a lower transmission power to guarantee the transmission quality of a Primary User (PU), thereby limiting the transmission rate and communication range of the SU. By introducing NOMA into a cognitive radio system (hereinafter CR-NOMA), the chances of SU access to licensed spectrum can be greatly increased. For example, if the traditional multiple access method is adopted, even if the channel condition is poor, the orthogonal spectrum allocated to the PU cannot be accessed by the SU, thereby causing the service delay of the SU to be long and the system throughput to be low. The CR-NOMA ensures that the PU and the SU can be used simultaneously without causing too much reduction of the performance of the PU, thereby effectively improving the frequency spectrum utilization rate.
How to utilize cooperative transmission to further improve the performance of the CR-NOMA system by the multicast service is a problem to be solved. The core idea of cooperative CR-NOMA is that multiple SUs can provide compensation for the opportunity to gain access to the PU spectrum. In other words, the information sent to the PU may be decoded by the SUs with the help of Successive Interference Cancellation (SIC). Therefore, the SUs can be used as a potential relay to assist data transmission of the SU source node, so that not only is the spatial diversity gain of wireless transmission increased and the spectrum utilization rate further improved, but also the anti-fading capability of the SU can be enhanced and the performance of the CR-NOMA system can be improved.
In the current cooperative multicast method, a unicast user is set as a master user, a multicast user is set as a secondary user, and an optimal forwarding node is selected according to channel gains among the multicast users. The cooperative multicast method proves that in the cooperative multicast scheme based on the optimal secondary user forwarding, the grading gain of the secondary users is equal to the number of the multicast users, and the reliability of the cooperative multicast is improved along with the increase of the number of the secondary users. However, although the reliability of the multicast user is fully considered in the method, the performance of the unicast user is not guaranteed, and only two-order diversity gain orders exist.
Disclosure of Invention
The technical problem to be solved by the invention is that although the reliability of the multicast user is fully considered in the current cooperative multicast method, the performance of the unicast user is not ensured.
In order to solve the technical problems, the invention adopts the following technical scheme:
on one hand, the invention provides an opportunistic NOMA cooperative multicast method, a base station simultaneously accesses all multicast users and all unicast users, the base station respectively carries out coding modulation on original signals required by the unicast users and the multicast users and sends the original signals to all multicast users, and the multicast users decode the received signals, which comprises the following steps:
the base station broadcasts the ID sequence of the selected multicast user to each multicast user;
a base station broadcasts a cooperative link channel gain acquisition request signal comprising a selected multicast user ID to each unicast user;
each unicast user responds to the received cooperative link channel gain acquisition request signal and broadcasts the channel gain acquisition request signal to the multicast user selected by the base station;
each selected multicast user receives each unicast user broadcast channel gain acquisition request signal, determines the worst forwarding link channel gain between the selected multicast user and each unicast user, and if the multicast user judges that the worst forwarding link channel gain between the selected multicast user and all unicast users is the highest, the selected multicast user serves as the best multicast user to send a broadcast signaling containing the best multicast user identification and ID to the base station;
and the best multicast user recodes, modulates and forwards the unicast user information obtained by decoding.
In a second aspect, the present invention provides an opportunistic NOMA cooperative multicast method, which is used for simultaneously accessing all multicast users and all unicast users, and is characterized by comprising the following steps: carrying out coding modulation on original signals of unicast users and multicast users and sending the modulated signals to all multicast users; broadcasting the ID sequence of the selected multicast user to each multicast user;
broadcasting a cooperative link channel gain acquisition request signal containing a selected multicast user ID sequence to each unicast user;
and receiving a broadcast signaling sent by a multicast user which is determined to have the highest channel gain of the worst forwarding link with each unicast user in response to a channel gain acquisition request signal sent by each unicast user in the selected multicast users, wherein the broadcast signaling comprises the identification and the ID of the best multicast user.
Further, the selected multicast subscribers are all multicast subscribers.
Further, the multicast users are divided into successful user groups and failed user groups according to the fact that whether the multicast users can successfully decode signals or not, users in all the successful user groups acquire channel gains between the users in the failed user groups, the channel gains are sequenced, and the base station selects the candidate multicast user with the largest channel gain from the successful user groups according to a preset multicast user candidate set base number.
In a third aspect, the present invention provides an opportunistic NOMA cooperative multicast method, which is characterized by comprising the following steps:
the multicast user receives the coded and modulated signal sent by the base station and decodes the coded signal;
the multicast user receives the ID sequence of the selected multicast user broadcasted by the base station;
the selected multicast user receives each unicast user broadcast channel gain acquisition request signal, determines the worst forwarding link channel gain of the selected multicast user and each unicast user, and if the worst forwarding link channel gain of the selected multicast user and each unicast user is judged to be the highest, the selected multicast user is used as the best multicast user to send a broadcast signaling containing the best multicast user identification and ID to the base station;
and the best multicast user recodes, modulates and forwards the unicast user information obtained by decoding.
Further, the receiving, by the multicast subscriber, the ID sequence of the selected multicast subscriber broadcasted by the base station further includes: the method comprises the steps that a multicast user receives a pilot signal broadcasted by a base station, a flag signal of a successful user or a failed user is sent to the base station according to whether a coded signal sent by the base station is decoded successfully or not, the failed user determines channel gain between the failed user and each successful user in response to a multicast-multicast channel gain acquisition signal sent by the base station, an initial value of a timer is set according to the channel gain, the timer is set to finish countdown, the timer counts down to zero, and self ID is broadcasted to the base station.
Further, the receiving, by the multicast subscriber, the ID sequence of the selected multicast subscriber broadcasted by the base station further includes: the method for the multicast user to receive the base station broadcast signal gain acquisition request signal and respond to the request signal to send the result including the self ID comprises the following steps: the multicast user acquires the channel gain of the multicast user and the base station according to the received base station broadcast signal gain acquisition request signal; and setting an initial value of a timer according to the channel gain, setting the timer to count down to zero after the setting is finished, and broadcasting the self ID to the base station.
Further, the method for judging the worst forwarding link channel gain between the unicast user and the unicast user is as follows:
the candidate multicast user receives the channel gain acquisition request signal sent by each unicast user, and determines the worst forwarding link channel gain with each unicast user;
resetting the initial value of the local timer according to the worst forwarding link channel gain, and starting countdown;
the candidate multicast user which counts down to zero firstly broadcasts a signaling to the base station and other candidate multicast users;
the other candidate multicast users cancel in response to the received broadcast signaling.
Further, in response to the receiving base station broadcasting the ID sequence of the selected multicast user, it is determined that the multicast user, who is not the selected multicast user itself, enters an idle state and remains silent.
The invention has the following beneficial technical effects:
the invention considers the link state from the multicast user to the unicast user in the cooperative multicast method, and the unicast user can be ensured under the condition of poor link gain from the multicast user to the unicast user no matter one or a plurality of unicast users;
the invention further comprises presetting a multicast user candidate set base number when constructing the candidate set, eliminating nodes with poor channel conditions, and reducing extra channel loss and overhead between node forwarding;
the method selects the optimal forwarding node, including screening out the multicast user set with better channel conditions from the base station to the multicast users, not only reduces the overhead of the system and the load of the base station, but also ensures that the optimal forwarding node selected after considering the link state between the users and the unicast users can decode the multicast information and the unicast information to a large extent, and can also forward the required information to the unicast users.
Drawings
FIG. 1 is a primary user (unicast user) outage probability for a particular embodiment of the present invention;
FIG. 2 is a secondary user (multicast user) outage probability for a specific embodiment of the present invention;
FIG. 3 illustrates primary user diversity gain in accordance with an embodiment of the present invention
Diversity gain with secondary users
A trade-off relationship;
FIG. 4 is a schematic flow chart of a method according to an embodiment of the present invention;
FIG. 5 is a schematic flow chart of a method according to an embodiment of the present invention;
FIG. 6 is a flowchart illustrating a method according to an embodiment of the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
In a downlink CR-NOMA system, a Base Station (BS) sends unicast information (called unicast User) to a group of Primary Users (PU) and multicast information (called multicast User) to a group of Secondary Users (SU), and N multicast users { d }1,…,dNAnd M unicast users p1,…,pMAnd forming an application scene of the opportunistic NOMA cooperative multicast method provided by the invention.
By using NOMA signaling, PU messages of high priority and SUs messages of low priority are enjoyed for simultaneous transmission from the BS. Assuming that all nodes are equipped with one antenna and operate in half-duplex mode, the channel fading factors of all links in the system are independent of each other and obey random probability distributions of different parameters. The total transmission power of each node is limited by P, and the additive white Gaussian noise is formed by a variance of N0Zero mean complex gaussian variable representation.
In order to improve the spectrum efficiency of the system and the reliability of multicast service, the system accesses unicast users and multicast users in the same wireless resource, and the multicast users forward information to the unicast users, so that the signal receiving quality of the unicast users is improved, and diversity gain is obtained. The best forwarding node is currently selected again based on the channel gain between multicast users. However, although the reliability of the multicast user is fully considered in the selection of the optimal forwarding section, the link state from the multicast user to the unicast user is not considered, and the unicast user is not guaranteed no matter whether one or a plurality of unicast users are provided, under the condition that the link gain from the multicast user to the unicast user is poor. Because the multicast user adopts a decoding-forwarding mechanism, namely the unicast user information is re-coded, modulated and forwarded after decoding is successful, the forwarding signal received by the unicast user is not influenced by the channel quality of a link of the base station-multicast user. Unicast transmission interruption occurs when there is at least one unicast user decoding failure, so unicast transmission reliability is limited by the unicast user with the worst received signal quality.
Suppose a BS and each multicast user dnThe channel fading factor of the inter-link is hb,nBS and unicast user pmThe channel fading factor of the inter-link is hb,mMulticast user dnWith unicast users pmThe channel fading factor of the inter-link is hn,mMulticast user dnWith multicast subscribers dn'Inter-channel fading factor of hn,n'。
In order to ensure the quality of the signal received by the multicast user in the CR-NOMA system, a user candidate set containing only the multicast users with better channel quality is constructed
Firstly, after a base station BS transmits signals to each multicast user, the multicast users are divided into successful users and failed users according to whether the signals can be successfully decoded or not. The candidate set is selected from these successful user groups. All successful users acquire the channel gain between the failed users according to
Calculating worst channel gains, and arranging according to ascending order:
g1＜g2＜…＜gj＜…＜gJ (1)
recording the set of the multicast users with successful decoding as D, and recording the failed users as D
D is J, selecting the multicast user corresponding to the maximum q channel gain values as a candidate multicast user according to the sorting result, and marking as the candidate multicast user
From a candidate set of multicast users
To optimally select one multicast user
Simultaneous access with unicast subscribers, by multicast subscribers
And forwarding the unicast user information. The multicast user adopts a decoding-forwarding mechanism, namely, the unicast user information is re-coded, modulated and forwarded after decoding is successful, and the forwarding signal received by the unicast user is not influenced by the channel quality of a link of the base station-multicast user. Unicast transmission interruption occurs when there is at least one unicast user decoding failure, so unicast transmission reliability is limited by the unicast user with the worst received signal quality. For combining the two reasons, the invention designs the following Max-Min optimal multicast user selection criterion according to the channel gain of the link of the candidate multicast user-unicast user
By selecting the optimal multicast user according to the criterion, the channel gain of the worst forwarding link of the multicast user can be maximized, and the minimum signal-to-noise ratio of the forwarding link is further improved to the maximum extent.
The following are specific embodiments of the present invention:
example 1: a opportunistic NOMA cooperative multicast method, a base station accesses all multicast users and all unicast users simultaneously, the base station carries out coding modulation on original signals required by the unicast users and the multicast users respectively and sends the original signals to all multicast users, and the multicast users decode the received signals, includes the following steps:
the base station broadcasts the ID sequence of the selected multicast user to each multicast user;
a base station broadcasts a cooperative link channel gain acquisition request signal comprising a selected multicast user ID to each unicast user;
each unicast user responds to the received cooperative link channel gain acquisition request signal and broadcasts the channel gain acquisition request signal to the multicast user selected by the base station;
each selected multicast user receives each unicast user broadcast channel gain acquisition request signal, determines the worst forwarding link channel gain between the selected multicast user and each unicast user, and if the multicast user judges that the worst forwarding link channel gain between the selected multicast user and all unicast users is the highest, the selected multicast user serves as the best multicast user to send a broadcast signaling containing the best multicast user identification and ID to the base station;
and the best multicast user recodes, modulates and forwards the unicast user information obtained by decoding.
In a specific embodiment, the base station broadcasts a cooperative link channel gain acquisition request signal including all multicast user IDs to each unicast user. The embodiment considers the link state from the multicast user to the unicast user in the cooperative multicast method, and the unicast user can be ensured under the condition that the link gain from the multicast user to the unicast user is poor for one or a plurality of unicast users.
On the basis of the above embodiment, in order to further eliminate nodes with poor channel conditions and reduce additional channel loss and overhead between node forwarding, the selected multicast user is a candidate multicast user set constructed by the base station according to a preset multicast user candidate set cardinal number, and the method for specifically constructing the candidate multicast user set is as follows:
and the base station selects the candidate multicast user with the maximum channel gain from the successful user groups according to a preset multicast user candidate set base number.
The specific steps of this embodiment are as follows (the specific flowchart is shown in fig. 4):
step 1: the base station broadcasts pilot signals to multicast users; the base station starts a counter with an initial value of 0.
Step 2: after the multicast user receives the pilot signal, the multicast user i belongs to N, and according to whether the user successfully broadcasts a successful or failed mark signal to the base station, the base station adds 1 to a counter of the base station if the successful mark signal is received;
and 3, step 3: the base station broadcasts a multicast-multicast channel gain acquisition signal to each failed user.
And 4, step 4: after the failed multicast user receives the signal, the pilot signal is broadcasted to other multicast users in the set D to obtain the channel gains of the multicast user i and the users in the set D. And repeating the steps 3 to 4 until all the multicast users participate in the process of acquiring the channel gain. Thus all successful users gain the channel with the failed users.
And 5: after the above steps are finished, if the counter of the base station is 0, a value of 0 indicates that the multicast user cannot decode the signal sent to the unicast user and cannot decode the signal of the multicast user, the channel condition is very poor, and the transmission is finished. At this time, the base station broadcasts a signal to cancel relay selection to cancel the next step. Otherwise, the base station broadcasts a relay selection signal to continue the next steps.
Step 6: after receiving the relay-selected signal, successful multicast users in set D calculate the worst channel gain
And 7: successful multicast user starts a timer with an initial value of gj(J ═ 1, …, J), the base station broadcasts its ID with a countdown of 0.
And 8: the base station receives the transmitted ID, sets a counter, and sets an initial value to 0.
And step 9: when the counter is q (q < J), the base station informs all the counting multicast users to stop counting down.
Step 10: the base station constructs an ID sequence for a set of candidate multicast users.
Step 11: base station broadcast multicast user candidate set
ID sequence of (a). Upon receipt of the ID sequenceAfter that, each multicast user autonomously determines whether to become a candidate multicast user.
Step 12: and the base station broadcasts a cooperative link channel gain acquisition request signal to each unicast user to enable the candidate multicast user to acquire the channel gain between the candidate multicast user and the unicast user.
Step 13: the unicast users i e M broadcast pilot signals to the set of candidate multicast users.
Step 14: and the candidate multicast user set acquires the channel gain of the unicast user i belonging to M. Repeating steps 13 and 14 until each multicast subscriber d in the set of candidate multicast subscribersjThe channel gains between itself and all unicast user links are obtained.
Step 15: computing worst forward link channel gains for a set of candidate multicast users
Step 16: the candidate multicast subscriber set starts a timer with an initial value set to
And starts a countdown. Candidate multicast user d who was first counted down to zeronBroadcast signalling "best user" and corresponding
And other candidate multicast users cancel the timer after receiving the signaling and enter an idle state.
Example 2: an opportunistic NOMA cooperative multicast method for simultaneously accessing all multicast users and all unicast users comprises the following steps:
carrying out coding modulation on original signals of unicast users and multicast users and sending the modulated signals to all multicast users;
broadcasting the ID sequence of the selected multicast user to each multicast user;
broadcasting a cooperative link channel gain acquisition request signal containing a selected multicast user ID sequence to each unicast user;
and receiving a broadcast signaling sent by a multicast user which is determined to have the highest channel gain of the worst forwarding link with each unicast user in response to a channel gain acquisition request signal sent by each unicast user in the selected multicast users, wherein the broadcast signaling comprises the identification and the ID of the best multicast user.
On the basis of this embodiment, further, the selected multicast user is all multicast users.
On the basis of embodiment 2, in order to eliminate nodes with poor channel conditions, the selected multicast user is a user in the multicast user candidate set in the specific embodiment. In a specific embodiment (a flowchart of the embodiment is shown in fig. 5), a preferred execution subject of the embodiment is a base station, and a specific method includes the following steps:
step 1: the base station broadcasts a pilot signal to the multicast users; the base station starts a counter, and the initial value is 0;
step 2: after the base station receives the mark signal which is returned by each multicast user and indicates whether the decoding is successful or failed, if the mark signal is successful, a counter of the base station is increased by 1;
and step 3: the base station broadcasts a multicast-multicast channel gain acquisition signal to each failed user.
And 4, step 4: after the failed multicast user receives the signal, the pilot signal is broadcasted to other multicast users in the set D to obtain the channel gains of the multicast user i and the users in the set D, wherein the set D is the set of the multicast users with successful decoding. And repeating the steps 3 to 4 until all the multicast users participate in the process of acquiring the channel gain. Thus all successful users gain the channel with the failed users.
To ensure the quality of the received signal of the multicast user, a user candidate set containing only the multicast users with better channel quality is constructed
The specific method for constructing the multicast user candidate set by the base station comprises the following steps:
if the counter of the base station is 0, the value of 0 indicates that neither the multicast user can decode the signal sent to the unicast user nor the signal of the multicast user can decode the signal of the multicast user, the channel condition is poor, and the transmission is finished. At this time, the base station broadcasts a signal to cancel relay selection to cancel the next step. Otherwise, the base station broadcasts a relay selection signal to continue the next steps.
The base station receives the ID sent by the multicast user which is successfully decoded, and sets a counter, wherein the initial value is 0.
When the counter is q (q < J), the base station informs all the counting multicast users to stop counting down,
the base station constructs an ID sequence for a set of candidate multicast users.
Example 3: an opportunistic NOMA cooperative multicast method for simultaneously accessing all multicast users and all unicast users comprises the following steps: receiving a coded and modulated signal sent by a base station and decoding the coded signal;
the multicast user receives the ID sequence of the selected multicast user broadcasted by the base station;
the selected multicast user receives each unicast user broadcast channel gain acquisition request signal, determines the worst forwarding link channel gain of the selected multicast user and each unicast user, and if the worst forwarding link channel gain of the selected multicast user and each unicast user is judged to be the highest, the selected multicast user is used as the best multicast user to send a broadcast signaling containing the best multicast user identification and ID to the base station;
and the best multicast user recodes, modulates and forwards the unicast user information obtained by decoding.
On the basis of the above embodiment, before the receiving, by the multicast subscriber, the ID sequence of the selected multicast subscriber broadcast by the base station, the method further includes:
the method comprises the steps that a multicast user receives a pilot signal broadcasted by a base station, a flag signal of a successful user or a failed user is sent to the base station according to whether a coded signal sent by the base station is decoded successfully or not, the failed user determines channel gain between the failed user and each successful user in response to a multicast-multicast channel gain acquisition signal sent by the base station, an initial value of a timer is set according to the channel gain, the timer is set to finish countdown, the timer counts down to zero, and self ID is broadcasted to the base station.
On the basis of the above embodiment, the method for each selected candidate multicast user to determine that the worst forwarding link channel gain between itself and each unicast user is the highest is as follows:
the candidate multicast user receives the channel gain acquisition request signal sent by each unicast user, and determines the worst forwarding link channel gain with each unicast user;
resetting the initial value of the local timer according to the worst forwarding link channel gain, and starting countdown;
the candidate multicast user which counts down to zero firstly broadcasts a signaling to the base station and other candidate multicast users;
the other candidate multicast users cancel in response to the received broadcast signaling.
A specific flowchart of this embodiment is shown in fig. 6. The method of the invention selects the optimal forwarding node comprises the step of screening out the multicast user set with better channel conditions from the base station to the multicast users, ensures that the optimal forwarding node selected after considering the link state between the users and the unicast users can decode the multicast information and the unicast information to a large extent, and can forward the required information to the unicast users.
In the above embodiments, the original signals required by the multicast user and the unicast user are coded and transmitted, and the optimal multicast user decodes and forwards the received signals by using the prior art. Preferably, the method is as follows:
base station structure mixed transmission signal SBC(t) and transmitting all users. Firstly, the BS constructs corresponding unit power signals S for unicast users and multicast users respectively0(t) and S1(t) of (d). Then, the BS distributes the available transmission power P according to the preset power distribution ratioBSIn the signal S0(t) and S1And (t) distributing. The base station being the signal S0(t) allocated transmission power of a0PBSIs a signal S1(t) allocated transmission power of a1PBSWhereina0And a1For the power allocation factor, satisfy a0+a11. Finally, the base station superposes the two signals after power distribution to generate the following sending signals
BS broadcasts a transmission signal S to all multicast subscribers and all unicast subscribersBC(t) of (d). Multicast user d after transmission over a radio channelnReceive a signal of
Unicast user pmReceive a signal of
Wherein,
and
respectively representing multicast subscribers dnAnd unicast user pmWhite noise in the white noise spectrum, subject to a complex Gaussian distribution
Multicast subscriber dnAfter receiving the mixed signal, decoding the unicast user signal, wherein the corresponding decoding signal-to-interference-and-noise ratio is
Multicast after removal of unicast user signals by SICUser dnDecoding the desired signal itself, the corresponding decoded signal-to-noise ratio being
Multicast subscribers can decode S simultaneously0(t) and S1(t) is as follows
And
multicast subscriber dnAnd unicast user pmRespectively, are RdAnd Rp。
Optimal multicast user
And recoding, modulating and forwarding the acquired unicast user information.
If multicast user
If the decoding is successful, the obtained unicast user information is re-coded and modulated to obtain a unit power signal S containing the unicast user information0(t) and with a power PdThe signal is forwarded to all unicast users. Unicast user pmAfter receiving the forwarding signal, the signal is combined with the received signal in the direct transmission stage and then decoded, and the combined signal-to-interference-and-noise ratio is
Wherein, G (x)1,x2…) represents a combiner input-output signal-to-noise ratio function, the expression depending on the manner in which the unicast users combine the signals. Taking maximum ratio combining and selective combining as an example, G (x)1,x2…) can be expressed asIn the following form
If multicast user
If decoding fails, the information is not forwarded, and the user p is unicastmDecoding the received signal in the direct transmission phase with a signal to interference plus noise ratio of
2. Multicast reliability analysis of the method of the invention
Suppose a multicast user
And unicast users { p1,…,pMThe target rates of R are respectivelydAnd Rp。
Multicast subscribers
The unicast user signal needs to be decoded from the mixed signal first, and then the desired signal needs to be decoded, and the failure of decoding any one of the two decoding can cause the failure of decoding the multicast user. Thus, multicast subscribers
Can be expressed as
Wherein,
is defined as max [ tau ]p/(a0-a1τd),τd/a1]，
Is defined as
Of the average value of (a). Defining a transmission signal-to-noise ratio as
Available multicast subscribers
Is expressed as
The condition that equation m is satisfied in equation (11) is (a)0-a1τd)>0, which is guaranteed by the inter-signal power allocation and transmission rate setting of the base station. Due to the fact that
Then there is
Substituting the inequality into formula (11) to obtain
Has an upper bound of
According to the ordering statistical theory and the probability statistical theory, the upper bound of the interruption probability given by the formula (13) can be further expressed as Rayleigh fading
Wherein card (·) represents the set · base,
representing channel gain
N' represents θiThe complement in the set 1, …, N. Further derived from equation (14) according to the SNR definition
Has a progressive upper bound of
As can be seen from equation (15), multicast subscribers
A diversity gain of at least
Unicast reliability analysis
When at least one unicast user fails to decode successfully, unicast transmission is interrupted, and the interruption probability can be expressed as
The invention adopts maximum ratio combination, and G (x, y) is max (x, y). The expression from which the outage probability of a unicast user can be derived is
Wherein,
is defined as taup/(a0-a1τd) ζ is defined as μ τp(μ＝Pd/PBS)，λb,mIs the channel gain | hb,m|2Is measured. Mixing Pr (n)*N) is defined as
From the formula (9), G (x, y) ≥ max (x, y), and can be substituted by the formula (16)
Has an upper bound of
When (a)0-a1τd)>At 0, ω1The analytic expression and the high signal-to-noise ratio progressive expression under Rayleigh fading are
ω2The upper bound and progressive upper bound under Rayleigh fading are
Wherein λ isn,mIs the channel gain | hn,m|2Is measured. The combined vertical type (15), formula (19), formula (20) and formula (21) can obtain
The above equation shows that in opportunistic NOMA cooperative multicast, multicast users
A diversity gain of at least
The transmission reliability of the multicast service is effectively guaranteed. In addition, unicast users can obtain through the designed optimal multicast user forwarding mechanism
The order diversity gain effectively improves the transmission reliability of the unicast service.
Simulation results and analysis
The forwarding scheme of the invention, which considers the link between the multicast user and the unicast user, and the traditional scheme, which only considers the link between the multicast user and the multicast user, are simulated and compared under the Rayleigh fading channel.
In order not to lose generality, the base station and the primary users PU are located at coordinates (0,0) and (1,1), respectively, and the secondary users are evenly distributed in a square area of size 1 × 1 in the first quadrant. Average channel gain is set to
di,jFor attribution between nodes i and jNormalized distance, η, represents the path loss coefficient. η is set to 3 corresponding to the urban cellular network environment. In the NOMA system, in order to ensure that the power coefficient distributed to the primary user is larger than that distributed to the secondary user, the power coefficients distributed to the primary user and the secondary user in the first stage and the second stage are respectively set to be 0.8 and 0.2. For Rayleigh fading scenarios, set Rp＝1bps/Hz，Rd＝1.5bps/Hz。
Fig. 1 shows the variation of the primary user outage probability with the signal-to-noise ratio for two schemes when the number of secondary users is 5. It can be seen that the interruption probability of the unicast user is the highest under the conventional scheme. No matter how many candidate set cardinalities are, the probability of interruption is reduced in the scheme adopting the candidate set cardinalities compared with the conventional scheme, because the optimal forwarding node selection in the conventional scheme does not consider the link state from the multicast user to the unicast user, and the system performance is poor as long as the optimal forwarding node fails to forward the required information to the unicast user under the condition that the link gain from the multicast user to the unicast user is poor in one or more unicast users.
The specific embodiment of the invention considers that a multicast user set with better channel condition is firstly screened out from a base station to a multicast user, and then the optimal forwarding node is selected after the link state between the multicast user and a unicast user is considered, so that the optimal forwarding node can decode multicast information and unicast information to the maximum extent, and can forward required information to the unicast user. With radix of 1, the candidate multicast set is a multicast user with the best channel condition, and the performance of the primary user in the scheme is in the lowest state, but the performance is better than that in the conventional scheme as seen from the figure. The interruption probability of the user with the base number of 2 is reduced compared with that with the base number of 1, and the interruption probability of the user with the base number of 3 is further reduced compared with that with the base number of 2, because not only the nodes with poor channel conditions are removed when a candidate set is constructed, the extra channel loss and overhead between node forwarding are reduced, but also more users with better channel conditions are considered, and a better forwarding node can be selected according to the channel gain between the primary user and the secondary user instead of only considering the channel gain between the secondary users, so that the system interruption probability is reduced. In addition, the analysis result also corresponds to the analog value, and the asymptote gives a strict boundary in the high signal-to-noise ratio region.
Fig. 2 shows the variation of the next user interruption probability with the signal-to-noise ratio for the two schemes when the number of secondary users is 5. In the traditional scheme, the interruption probability of a unicast user and the interruption probability of the user when the candidate set cardinality is 1, 2 and 3 are sequentially increased. In the traditional scheme, the situation of the interruption probability of the transmission information among all N multicast users is considered when the interruption probability of the secondary users is calculated, the diversity gain of the scheme is N, namely the upper bound of the interruption probability is 1/rhoN(ii) a The scheme for constructing the candidate set considers the outage probability of q nodes with better channel conditions in N multicast users, and according to multicast reliability analysis (referring to formulas (11) to (15)), the diversity gain of the specific embodiment of the method is q-1, namely the upper bound of the outage probability is 1/rhoq-1. Under the same conditions, q-1<N, as the cardinality increases, so does the outage probability for the secondary user. Comparing fig. 2 and fig. 3, it can be seen that the amplitude of the primary user interruption probability is large, and the increase of the secondary user interruption probability is not obvious. Therefore, the compromise scheme provided by the invention can better improve the performance of the primary user on the premise of reducing the loss of the secondary user.
According to the above two equations
And
it can be seen that when the secondary user candidate set base q increases, on the one hand, the diversity gain of the secondary user
Will be lowered accordingly; on the other hand, if N-q +2>q +1, diversity gain of primary user
The diversity gain of the main user is increased if N-q +2 is less than or equal to q +1
Will be reduced accordingly. After two equations cancel the radix q simultaneously, the diversity gain tradeoff relationship between unicast and multicast users can be expressed as
The corresponding compromise curve is shown in figure 3. Specifically, the number of next users N is 5, the candidate set base number q takes 2,
the candidate set base number q is taken to be 3,
the candidate set base number q is taken to be 4,
it can be seen that as the base number q increases, the diversity gain of the secondary users
Diversity gain for 4 to 2, primary users
Increasing first and then decreasing and reaching a maximum when q is 3. This can also be seen in fig. 1, the diversity gain of the secondary users
Diversity gain of primary user at time 3
With a maximum value of 3. Similarly, when the number N of sub-users is 10, the candidate set base number q is 5, and the sub-users
With master user
Are both 6; candidate set cardinality q is taken to be 6, secondary user
With master user
5 and 6, respectively, main user
A maximum value is reached. In both cases, the diversity order of the secondary user is reduced, but the diversity order of the primary user is greatly improved and has a maximum value. This result still applies for the case of a larger number of secondary users. From the above analysis, as the base number q increases, the diversity gain of the secondary user will decrease, while the diversity gain of the primary user will increase first and then decrease, and when q takes a proper value, it reaches the maximum value, which is much larger than the fixed diversity number 2. Therefore, the base station selects the candidate multicast user set according to the preset multicast user candidate set base number, the defects of the traditional scheme can be overcome, and the diversity gain of the main user can be adjusted to be optimal.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions that execute on the computer or other programmable apparatus are provided
A series of operational steps are performed on a computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
While the present invention has been described with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, which are illustrative and not restrictive, and it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (7)
1. A opportunistic NOMA cooperative multicast method is characterized in that a base station simultaneously accesses all multicast users and all unicast users, the base station respectively carries out coding modulation on original signals required by the unicast users and the multicast users and sends the original signals to all multicast users, and the multicast users decode the received signals, and the method comprises the following steps:
the base station broadcasts the ID sequence of the selected multicast user to each multicast user;
a base station broadcasts a cooperative link channel gain acquisition request signal comprising a selected multicast user ID to each unicast user;
each unicast user responds to the received cooperative link channel gain acquisition request signal and broadcasts the channel gain acquisition request signal to the multicast user selected by the base station;
each selected multicast user receives each unicast user broadcast channel gain acquisition request signal, determines the worst forwarding link channel gain between the selected multicast user and each unicast user, and if the multicast user judges that the worst forwarding link channel gain between the selected multicast user and all unicast users is the highest, the selected multicast user serves as the best multicast user to send a broadcast signaling containing the best multicast user identification and ID to the base station;
the optimal multicast user recodes, modulates and forwards the unicast user information obtained by decoding;
the selected multicast user is a user in the multicast user candidate set, and the method for constructing the multicast user candidate set comprises the following steps:
and the base station selects the candidate multicast user with the maximum channel gain from the successful user groups according to a preset multicast user candidate set base number.
2. An opportunistic NOMA cooperative multicast method for simultaneously accessing all multicast users and all unicast users is characterized by comprising the following steps: carrying out coding modulation on original signals of unicast users and multicast users and sending the modulated signals to all multicast users;
broadcasting the ID sequence of the selected multicast user to each multicast user;
broadcasting a cooperative link channel gain acquisition request signal containing a selected multicast user ID sequence to each unicast user;
receiving a broadcast signaling sent by a multicast user which determines that the channel gain of a worst forwarding link with each unicast user is the highest in response to a channel gain acquisition request signal sent by each unicast user in selected multicast users, wherein the broadcast signaling comprises an optimal multicast user identifier and an ID thereof;
the selected multicast user is a user in the multicast user candidate set, and the method for constructing the multicast user candidate set comprises the following steps:
and the base station selects the candidate multicast user with the maximum channel gain from the successful user groups according to a preset multicast user candidate set base number.
3. An opportunistic NOMA cooperative multicasting method according to claim 2 wherein said selected multicasting subscribers are all multicasting subscribers.
4. An opportunistic NOMA cooperative multicast method for simultaneously accessing all multicast users and all unicast users is characterized by comprising the following steps:
the multicast user receives the coded and modulated signal sent by the base station and decodes the coded signal;
the multicast user receives the ID sequence of the selected multicast user broadcasted by the base station;
the selected multicast user receives each unicast user broadcast channel gain acquisition request signal, determines the worst forwarding link channel gain of the selected multicast user and each unicast user, and if the worst forwarding link channel gain of the selected multicast user and each unicast user is judged to be the highest, the selected multicast user is used as the best multicast user to send a broadcast signaling containing the best multicast user identification and ID to the base station;
the optimal multicast user recodes, modulates and forwards the unicast user information obtained by decoding;
the selected multicast user is a user in the multicast user candidate set, and the method for constructing the multicast user candidate set comprises the following steps:
and the base station selects the candidate multicast user with the maximum channel gain from the successful user groups according to a preset multicast user candidate set base number.
5. The opportunistic NOMA cooperative multicast method according to claim 4, wherein the receiving of the ID sequence of the selected multicast user broadcasted by the base station by the multicast user further comprises: the method comprises the steps that a multicast user receives a pilot signal broadcasted by a base station, a flag signal of a successful user or a failed user is sent to the base station according to whether a coded signal sent by the base station is decoded successfully or not, the failed user determines channel gain between the failed user and each successful user in response to a multicast-multicast channel gain acquisition signal sent by the base station, an initial value of a timer is set according to the channel gain, the timer is set to finish countdown, the timer counts down to zero, and self ID is broadcasted to the base station.
6. The opportunistic NOMA cooperative multicast method according to claim 4, wherein the method for determining that the worst forwarding link channel gain between itself and each unicast user is the highest is as follows:
the candidate multicast user receives the channel gain acquisition request signal sent by each unicast user, and determines the worst forwarding link channel gain with each unicast user;
resetting the initial value of the local timer according to the worst forwarding link channel gain, and starting countdown;
the candidate multicast user which counts down to zero firstly broadcasts a signaling to the base station and other candidate multicast users;
the other candidate multicast users cancel in response to the received broadcast signaling.
7. An opportunistic NOMA cooperative multicasting method according to claim 4 wherein a multicast user that is determined not to be the selected multicast user by itself is entered into an idle state and kept silent in response to the receiving base station broadcasting the ID sequence of the selected multicast user.
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