CN116249222A - Multi-channel ALOHA random access method based on NOMA clustering - Google Patents
Multi-channel ALOHA random access method based on NOMA clustering Download PDFInfo
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Abstract
The application discloses a multichannel ALOHA random access method based on NOMA clustering, which comprises the following steps: applied to a base station, comprising: receiving a pilot sequence which is randomly selected from a preset pilot sequence set by any active user terminal and is sent by a randomly selected channel; judging whether the pilot frequency sequence is selected by only one user terminal, and determining the pilot frequency collision-free user terminal; performing NOMA clustering on a plurality of pilot collision-free user terminals, distributing exclusive transmission channels for each cluster, and broadcasting a clustering result and the exclusive transmission channels corresponding to each cluster in a cell; demodulating the received data information according to the clustering result and the exclusive transmission channel corresponding to each cluster; the data information is sent by any active user terminal based on the self transmission power and the self transmission channel. The method is more remarkable in the condition of a large number of access clients, the clustering is easier to succeed, and the method is very suitable for random requests of mass equipment access networks in the Internet of things.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to a multi-channel ALOHA random access method based on NOMA clustering and an Internet of things communication system.
Background
With the continuous development of the internet of things, the number of clients requesting to access the network is also increasing explosively. Machine type communication (Machine Type Communications, MTC) is one of the key areas in the internet of things, and how to access more MTC devices faces serious challenges. Compared with the traditional random access mode, the ALOHA protocol has the advantages of low signaling overhead, quick response and the like, and is widely applied to MTC equipment access with large data burst quantity and low node communication quantity.
In the prior art, J.Choi proposes a random access scheme (hereinafter referred to as EP-RA scheme) based on the ALOHA protocol. However, the EP-RA scheme only allows one user terminal to perform data transmission in the channel, and cannot meet the situation of accessing the multi-user terminal in the channel, and once a plurality of user terminals exist in the channel and use the same pilot frequency, the problem of low success rate of accessing the user terminal can occur.
Therefore, the invention provides a multi-channel ALOHA random access method based on NOMA clustering and an internet of things communication system, which solve the problem that when the number of user ends requesting access increases, the success rate of access is low, and the success rate of the user ends can be improved under the condition of reducing complexity as much as possible.
Disclosure of Invention
In view of the foregoing, it is necessary to provide a multi-channel ALOHA random access method based on NOMA clustering and an internet of things communication system, so as to solve the technical problem that the random access scheme of the existing internet of things communication system only allows one user terminal to perform data transmission in a channel, and when the number of user terminals requesting access increases, the access success rate is low.
In order to solve the above problems, the present invention provides a multi-channel ALOHA random access method based on NOMA clustering, which is applied to a base station, and includes:
receiving a pilot sequence, wherein the pilot sequence is randomly selected from a preset pilot sequence set by any active user terminal and is sent through a randomly selected channel;
judging whether the pilot frequency sequence is selected by only one user terminal or not; when the pilot frequency sequence is selected by only one user terminal, determining the user terminal as a pilot frequency collision-free user terminal;
performing NOMA clustering on a plurality of pilot non-collision user terminals, distributing an exclusive transmission channel for each NOMA cluster, and broadcasting a clustering result and the exclusive transmission channel corresponding to each NOMA cluster in a cell;
demodulating the received data information according to the clustering result and the exclusive transmission channel corresponding to each NOMA cluster; the data information is sent by any active user terminal based on self transmission power and self transmission channel; the self-transmission power and the self-transmission channel of the user terminal are determined according to the self-user terminal type obtained by the clustering result and the dedicated transmission channel corresponding to each NOMA cluster.
Further, performing NOMA clustering on a plurality of pilot collision-free user terminals, including:
calculating the Rayleigh fading gains of a plurality of pilot frequency collision-free user terminals, and sequencing the user terminals according to the Rayleigh fading gains to obtain gain sequencing of the user terminals;
taking the pilot frequency non-collision user end with the maximum Rayleigh fading gain as a central user end of a first NOMA cluster, and clustering a preset number of pilot frequency non-collision user ends meeting preset clustering conditions in sequence according to the gain sequencing to obtain the first NOMA cluster;
and taking the user terminal with the biggest Rayleigh fading coefficient in the rest pilot frequency non-collision user terminals in the gain sequencing as the central user terminal of the next NOMA cluster, and continuing to cluster according to the clustering condition until the rest pilot frequency non-collision user terminals in the gain sequencing cannot reach the preset quantity.
Further, the preset clustering condition comprises a transmission power constraint condition and a signal-to-noise ratio constraint condition;
the transmission power constraint conditions are:
wherein beta is k,i The Rayleigh fading coefficient of the ith user end in the kth NOMA cluster is represented; beta k,1 The Rayleigh fading coefficient of the 1 st user end in the kth NOMA cluster is represented; p is p k,i Representing the ith user end in the kth NOMA cluster; p is p k,1 Representing the 1 st user end in the kth NOMA cluster; ρ represents the power backoff size;
the signal-to-noise ratio constraint conditions are as follows:
wherein h is k,i Representing the channel coefficient of the ith user side in the kth NOMA cluster; h is a k,j Representing channel coefficients of a jth user terminal in a kth NOMA cluster; sigma (sigma) 2 Representing the noise power of the channel.
Further, clustering the preset number of pilot frequency collision-free user ends meeting the preset clustering condition sequentially according to the gain sorting comprises the following steps:
clustering a preset number of user ends meeting the transmission power constraint condition into NOMA clusters;
judging whether a user side in the NOMA cluster meets the preset signal-to-noise ratio constraint condition or not;
when the user terminals in the NOMA cluster do not meet the preset signal-to-noise ratio constraint condition, comparing the channel gain difference between every two user terminals in the NOMA cluster, and randomly deleting one of the two user terminals with the smallest channel gain difference;
and continuing to judge whether the rest user terminals in the NOMA cluster meet the preset signal-to-noise ratio constraint condition or not until all the user terminals in the NOMA cluster meet the preset signal-to-noise ratio constraint condition.
Further, the pilot sequence is expressed as:
wherein N is m,i Representing a user terminal aggregate set for selecting an ith pilot frequency in an mth channel; ρ n Representing the uplink transmitting power of the user terminal n; h is a n Representing the channel coefficients between the user side n and the base station,
g n represents a small-scale fading vector and obeys a circularly symmetric complex gaussian distribution with a mean value of 0 and a variance of 1, beta n Representing the slow fading coefficient between the base station and the user terminal n; s is S i Indicating the pilot frequency selected by the ith user side; z is Z m Representing a Gaussian white noise matrix, obeying a mean of 0 and a variance of sigma 2 Is a circularly symmetric complex gaussian distribution.
Further, determining whether the pilot sequence is selected by only one ue includes:
estimating whether any pilot sequence in any channel is selected by only the unique user terminal based on a least square method; when the pilot sequence is selected only by a unique user terminal, the ID information of the unique user terminal is determined.
Further, the clustering result includes: a user end which is successfully clustered and a central user end of each NOMA cluster;
the step of determining the self user terminal type of the user terminal according to the clustering result comprises the following steps: judging whether the user terminal is a user terminal with successful clustering and is a central user terminal of the NOMA cluster;
if the type of the self user terminal is NOMA cluster center user terminal, the self transmission power is the transmission power distributed by the base station; if the type of the self user terminal is a user terminal with successful clustering but not a central user terminal, self transmission power is calculated according to Rayleigh fading channel coefficient sequencing; if the type of the self user terminal is the user terminal which is not clustered successfully, the self transmission power is preset standard transmission power, and one channel is randomly selected from the rest channels to carry out data transmission.
Further, demodulating the received data information according to the clustering result and the dedicated transmission channel corresponding to each NOMA cluster, including:
demodulating the data information transmitted by the user terminal which is successfully clustered by adopting a SIC algorithm; judging whether the channel selected by the user side which is not clustered successfully is selected by a unique user side or not; if only one user side data information exists in the channel, demodulating the user side data information and sending an ACK message; otherwise, the base station transmits a NACK message.
Further, the base station and the user station perform information transmission based on an ALOHA protocol.
The invention also provides a communication system of the Internet of things, which comprises a user terminal and a base station,
the user terminal is used for randomly selecting a pilot sequence from a preset pilot sequence set, randomly selecting a channel and transmitting the pilot sequence to the base station;
the base station is used for judging whether the pilot frequency sequence is selected by only one user terminal; when the pilot frequency sequence is selected by only one user terminal, determining the user terminal as a pilot frequency collision-free user terminal; performing NOMA clustering on a plurality of pilot non-collision user terminals, distributing an exclusive transmission channel for each NOMA cluster, and broadcasting a clustering result and the exclusive transmission channel corresponding to each NOMA cluster in a cell;
the active user end is also used for determining the type of the user end according to the clustering result, determining the self transmission power and the self transmission channel according to the type of the user end and the dedicated transmission channel corresponding to each NOMA cluster, and sending the data information to the base station based on the self transmission power and the self transmission channel;
the base station is further configured to demodulate the received data information according to the clustering result and the dedicated transmission channel corresponding to each NOMA cluster.
Compared with the prior art, the invention has the beneficial effects that: firstly, a base station receives a pilot sequence, judges whether the pilot sequence in a channel is selected by only one user terminal, and determines a pilot collision-free user terminal; secondly, NOMA clustering is carried out on pilot frequency collision-free user terminals, the user type of each user terminal is determined, and a dedicated transmission channel is allocated to each NOMA cluster; and finally, the base station demodulates the received data information according to the clustering result and the exclusive transmission channel corresponding to each NOMA cluster.
In the method, the base station judges whether the user terminal is a pilot collision-free user terminal according to the pilot sequence, NOMA clustering is carried out on the pilot collision-free user terminal, the clustering is more obvious under the condition of more access user terminals, the clustering is more successful, and the method is very suitable for random requests of mass equipment in the Internet of things for accessing the network. The base station demodulates the data of the user terminal according to the clustering result and the exclusive channel corresponding to each NOMA cluster, so that the channel resource utilization rate is greatly increased, and the successful access rate of the user terminal is improved.
Drawings
Fig. 1 is a schematic flow chart of an embodiment of a multi-channel ALOHA random access method based on NOMA clustering provided by the present invention;
fig. 2 is a schematic diagram showing the comparison between the effect of an embodiment of a multi-channel ALOHA random access method based on NOMA clustering and an EP-RA method provided by the present invention;
fig. 3 is a schematic structural diagram of an embodiment of an internet of things communication system provided by the invention.
Detailed Description
Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form a part hereof, and together with the description serve to explain the principles of the invention, and are not intended to limit the scope of the invention.
Prior to the description of the embodiments, related terms of the present application will be explained first.
NOMA technology: NOMA, non-orthogonal multiple access technology, non-orthogonal code division multiple access technology, which changes the exclusive use of a single user terminal into the sharing of multiple user terminals, and can simultaneously transmit multiple data on one channel. The non-orthogonal transmission of the transmitting power of the user terminal is distributed at the transmitting terminal, the interference information is actively introduced, the interference is eliminated at the receiving terminal, and the correct demodulation is realized. The NOMA technology not only can improve the spectrum efficiency, but also can support large-scale connection, and is widely applied to random access.
Power domain NOMA: the core idea is to obtain multiplexing gain by superposing a plurality of user terminals on a power domain under different channel gains. At the transmitting end, signals generated by different user ends are directly overlapped together after channel coding and modulation, and a plurality of user ends share the same time-frequency resource. At the receiving end, a multi-user detection algorithm, such as serial interference cancellation, is used for detection according to the received power difference of different user ends. By this way of increasing the complexity of the receiver, the spectral efficiency is increased.
SIC: successive Interference Cancellation, SIC, serial interference cancellation. In the SIC process, each user terminal regards signals of other user terminals as interference to decode, and if the decoding is successful, the interference caused by the simultaneous occupation of time-frequency resources can be relieved by subtracting the signals from the received signals.
ALOHA protocol: ALOHA protocol is a network protocol developed by university of hawaii in the united states, the data link layer in the OSI model, belonging to one of the random access protocols (Random Access Protocol). The protocol can be divided into a pure ALOHA protocol and a slotted (segmented) ALOHA protocol. Pure ALOHA is to select a moment retransmission completely randomly after detecting a collision; the time slot (segmented) ALOHA segments the frequency channel in time, and the data is transmitted in fixed time slots, so that the randomness of data transmission is reduced to reduce the collision probability, and the purpose of improving the utilization rate of the frequency channel is achieved.
The embodiment of the invention provides a multi-channel ALOHA random access method based on NOMA clustering, which is applied to a base station, wherein a flow diagram of the method is shown in fig. 1, and the method comprises the following steps:
step S101: receiving a pilot sequence, wherein the pilot sequence is randomly selected from a preset pilot sequence set by any active user terminal and is sent through a randomly selected channel;
step S102: judging whether the pilot frequency sequence is selected by only one user terminal or not; when the pilot frequency sequence is selected by only one user terminal, determining the user terminal as a pilot frequency collision-free user terminal;
step S103: performing NOMA clustering on a plurality of pilot non-collision user terminals, distributing an exclusive transmission channel for each NOMA cluster, and broadcasting a clustering result and the exclusive transmission channel corresponding to each NOMA cluster in a cell;
step S104: demodulating the received data information according to the clustering result and the exclusive transmission channel corresponding to each NOMA cluster; the data information is sent by any active user terminal based on self transmission power and self transmission channel; the self-transmission power and the self-transmission channel of the user terminal are determined according to the self-user terminal type obtained by the clustering result and the dedicated transmission channel corresponding to each NOMA cluster.
Compared with the prior art, the multi-channel ALOHA random access method based on NOMA clustering provided by the embodiment firstly, a base station receives a pilot sequence and judges whether the pilot sequence in the channel is selected by only one user terminal or not, and determines that the pilot has no collision; secondly, NOMA clustering is carried out on pilot frequency collision-free user terminals, the user type of each user terminal is determined, and a dedicated transmission channel is allocated to each NOMA cluster; and finally, the base station demodulates the received data information according to the clustering result and the exclusive transmission channel corresponding to each NOMA cluster. In the method of the embodiment, the base station judges whether the user terminal is a pilot collision-free user terminal according to the pilot sequence, and NOMA clustering is carried out on the pilot collision-free user terminal, so that the clustering is more remarkable under the condition of more access user terminals, the clustering is more successful, and the method is very suitable for random requests of mass equipment in the Internet of things for accessing the network. The base station demodulates the data of the user terminal according to the clustering result and the exclusive channel corresponding to each NOMA cluster, so that the channel resource utilization rate is greatly increased, and the successful access rate of the user terminal is improved.
As a preferred embodiment, in step S101, the pilot sequence is expressed as:
wherein N is m,i Representing a user terminal aggregate set for selecting an ith pilot frequency in an mth channel; ρ n Representing the uplink transmitting power of the user terminal n; h is a n Representing the channel coefficients between the user side n and the base station,
g n represents a small-scale fading vector and obeys a circularly symmetric complex gaussian distribution with a mean value of 0 and a variance of 1, beta n Representing the slow fading coefficient between the base station and the user terminal n, said beta n And path loss is associated with shadowing fading; s is S i Indicating the pilot frequency selected by the ith user side; z is Z m Representing a Gaussian white noise matrix, obeying a mean of 0 and a variance of sigma 2 Is a circularly symmetric complex gaussian distribution.
As a specific embodiment, each active user end in the cell is in a preset orthogonalization pilot pool
A pilot sequence is randomly selected and one of the K channels is randomly selected to transmit the pilot sequence to the base station.
As a preferred embodiment, in step S102, determining whether the pilot sequence is selected by only one ue includes:
estimating whether any pilot sequence in any channel is selected by only the unique user terminal based on a least square method; when the pilot sequence is selected only by a unique user terminal, the ID information of the unique user terminal is determined.
As a specific embodiment, the base station may obtain, by using a least square method, channel information corresponding to the ith pilot sequence in the mth channel, and if the ith pilot is selected by only one ue, the channel information is the channel information of the unique ue, in this way, ID information sent by the ue may be correctly detected, and the ue is marked as a non-pilot collision ue, and is clustered by NOMA.
As a preferred embodiment, in step S103, NOMA clustering is performed on a plurality of the pilot collision-free clients, including:
calculating the Rayleigh fading gains of a plurality of pilot frequency collision-free user terminals, and sequencing the user terminals according to the Rayleigh fading gains to obtain gain sequencing of the user terminals;
taking the pilot frequency non-collision user end with the maximum Rayleigh fading gain as a central user end of a first NOMA cluster, and clustering a preset number of pilot frequency non-collision user ends meeting preset clustering conditions in sequence according to the gain sequencing to obtain the first NOMA cluster;
and taking the user terminal with the biggest Rayleigh fading coefficient in the rest pilot frequency non-collision user terminals in the gain sequencing as the central user terminal of the next NOMA cluster, and continuing to cluster according to the clustering condition until the rest pilot frequency non-collision user terminals in the gain sequencing cannot reach the preset quantity.
As a preferred embodiment, the preset clustering condition includes a transmission power constraint condition and a signal-to-noise ratio constraint condition;
the transmission power constraint conditions are:
wherein beta is k,i The Rayleigh fading coefficient of the ith user end in the kth NOMA cluster is represented; beta k,1 The Rayleigh fading coefficient of the 1 st user end in the kth NOMA cluster is represented; p is p k,i Representing the ith user end in the kth NOMA cluster; p is p k,1 Representing the 1 st user end, namely the central user end, in the kth NOMA cluster; ρ represents the power backoff, i.e., the power of the latter ue is reduced by ρ dB from the power of the last ue;
the signal-to-noise ratio constraint conditions are as follows:
wherein h is k,i Representing the channel coefficient of the ith user side in the kth NOMA cluster; h is a k,j Representing channel coefficients of a jth user terminal in a kth NOMA cluster; sigma (sigma) 2 Representing the noise power of the channel.
When the signal-to-noise ratio is greater than the threshold SINR 0 At this time, the base station can demodulate the data of the user terminal through the SIC.
As a preferred embodiment, clustering, according to the gain ranking, a preset number of pilot non-collision clients that meet a preset clustering condition sequentially includes:
clustering a preset number of user ends meeting the transmission power constraint condition into NOMA clusters;
judging whether a user side in the NOMA cluster meets the preset signal-to-noise ratio constraint condition or not;
when the user terminals in the NOMA cluster do not meet the preset signal-to-noise ratio constraint condition, comparing the channel gain difference between every two user terminals in the NOMA cluster, and randomly deleting one of the two user terminals with the smallest channel gain difference;
and continuing to judge whether the rest user terminals in the NOMA cluster meet the preset signal-to-noise ratio constraint condition or not until all the user terminals in the NOMA cluster meet the preset signal-to-noise ratio constraint condition.
As a specific embodiment, the base station firstly uses the ue with the biggest rayleigh fading gain as the central ue of the first NOMA cluster, and counts the preset number (e.g., M) of ues meeting the preset transmission power constraint condition into the first NOMA cluster;
then checking whether a user side in the first NOMA cluster meets a preset signal-to-noise ratio constraint condition or not; if not, comparing the channel gain differences between every two user terminals in all clusters, randomly deleting one of the two user terminals with the smallest channel gain difference, and then continuously checking whether the rest user terminals in the clusters meet the preset signal-to-noise ratio constraint condition; until all the user terminals in the cluster simultaneously meet two constraint conditions of preset transmission power and preset signal-to-noise ratio;
the user end with the biggest Rayleigh fading coefficient in the rest pilot frequency non-collision user ends is used as the center user end of the next NOMA cluster, and clustering is continued according to the two constraint conditions of the transmission power and the preset signal to noise ratio until M user ends cannot be found out;
and finally, broadcasting the user terminal with successful clustering, the central user terminal of each NOMA cluster and the dedicated channel transmission resources allocated to each NOMA cluster to all the user terminals by the base station.
As a preferred embodiment, in step S104, the clustering result includes: a user end which is successfully clustered and a central user end of each NOMA cluster;
the step of determining the self user terminal type of the user terminal according to the clustering result comprises the following steps: judging whether the user terminal is a user terminal with successful clustering and is a central user terminal of the NOMA cluster;
if the type of the self user terminal is NOMA cluster center user terminal, the self transmission power is the transmission power distributed by the base station; if the type of the self user terminal is a user terminal with successful clustering but not a central user terminal, self transmission power is calculated according to Rayleigh fading channel coefficient sequencing; if the type of the self user terminal is the user terminal which is not clustered successfully, the self transmission power is preset standard transmission power, and one channel is randomly selected from the rest channels to carry out data transmission.
As a specific embodiment, after receiving the feedback information, the ue first determines whether the ue is successful in clustering and is the central ue of the NOMA cluster.
If the clustering is successful and the cluster center user terminal is used, the transmission power P distributed by the system is recorded 0 Will P 0 As own transmission power; if clustering is successful but not the central user terminal, sorting according to Rayleigh fading channel coefficients, and P 0 - (k-1) ρ calculates the respective transmission power (k is the number of orders of the rayleigh fading channel coefficients, ρ is a preset user side power backoff factor). And the user terminal with successful clustering transmits data information according to the respective transmission power, and the used channel is a dedicated channel allocated by the base station for the NOMA cluster to which the base station belongs.
If the user terminal is the user terminal which is not clustered successfully, the user terminal randomly selects one channel from the rest channels to carry out data transmission, and the transmission power of the channel is transmitted according to the transmission power which can reach the Qos requirement in the network.
As a preferred embodiment, in step S104, demodulating the received data information according to the clustering result and the dedicated transmission channel corresponding to each NOMA cluster includes:
demodulating the data information transmitted by the user terminal which is successfully clustered by adopting a SIC algorithm; judging whether the channel selected by the user side which is not clustered successfully is selected by a unique user side or not; if only one user side data information exists in the channel, demodulating the user side data information and sending an ACK message; otherwise, the base station transmits a NACK message.
As a specific embodiment, after receiving the data information, the base station demodulates the data information transmitted by the user end with successful NOMA clustering by adopting the SIC algorithm in the channel allocated to each cluster. Because the user terminals in the NOMA cluster are successfully clustered under the condition of meeting the power constraint and the signal-to-noise ratio constraint, wherein the power constraint makes the power of the cluster by all the user terminals different, and the signal-to-noise ratio constraint makes all the user terminals in the cluster meet the QoS requirement of the network, all the user terminals in the cluster can successfully perform SIC demodulation. In any channel which is not exclusive to the NOMA cluster, if only one user side data information exists in the channel, the base station can successfully demodulate the user side data information and send an ACK message; otherwise, the base station may send a NACK message. Wherein, ACK and NACK are broadcast messages, and the ACK message at least comprises user end ID, information of successful demodulation of user end data information and the like; the NACK message includes information that the user side information is not successfully demodulated.
As a preferred embodiment, the base station and the user terminal perform information transmission based on ALOHA protocol. Because the signaling overhead of the ALOHA protocol is low, the base station and the user side utilize the ALOHA protocol to transmit information, so that the response speed is improved, and the cost of random access is reduced.
In order to verify the effect of the method of the present invention, the access method of the present application is compared with the access method of EP-RA, and fig. 2 is a graph showing the change of the number of successful access clients according to the number of active clients in the present invention, and the number of successful access clients in the EP-RA scheme in the background art. According to curve change, the number of successfully accessed user terminals is obviously improved compared with that of the EP-RA scheme, and the number of successfully accessed user terminals is increased along with the increase of the number of active user terminals. The method adopts the ALOHA protocol, has low signaling overhead and quick response, and can reduce the cost of random access; the NOMA clustering is carried out on the non-pilot collision user terminal based on the transmission power constraint and the signal-to-noise ratio constraint, and the SIC algorithm is combined to demodulate the data of the user terminal, so that the channel resource utilization rate is greatly increased, and the successful access rate of the user terminal is improved.
The embodiment of the invention also provides a communication system of the Internet of things, which comprises a user side and a base station,
the user terminal is used for randomly selecting a pilot sequence from a preset pilot sequence set, randomly selecting a channel and transmitting the pilot sequence to the base station;
the base station is used for judging whether the pilot frequency sequence is selected by only one user terminal; when the pilot frequency sequence is selected by only one user terminal, determining the user terminal as a pilot frequency collision-free user terminal; performing NOMA clustering on a plurality of pilot non-collision user terminals, distributing an exclusive transmission channel for each NOMA cluster, and broadcasting a clustering result and the exclusive transmission channel corresponding to each NOMA cluster in a cell;
the active user end is also used for determining the type of the user end according to the clustering result, determining the self transmission power and the self transmission channel according to the type of the user end and the dedicated transmission channel corresponding to each NOMA cluster, and sending the data information to the base station based on the self transmission power and the self transmission channel;
the base station is further configured to demodulate the received data information according to the clustering result and the dedicated transmission channel corresponding to each NOMA cluster.
The invention discloses a multi-channel ALOHA random access method based on NOMA clustering, which comprises the steps that firstly, a base station receives a pilot sequence and judges whether the pilot sequence in a channel is selected by only one user terminal or not, and a pilot collision-free user terminal is determined; secondly, NOMA clustering is carried out on pilot frequency collision-free user terminals, the user type of each user terminal is determined, and a dedicated transmission channel is allocated to each NOMA cluster; and finally, the base station demodulates the received data information according to the clustering result and the exclusive transmission channel corresponding to each NOMA cluster.
In the method, the base station judges whether the user terminal is a pilot collision-free user terminal according to the pilot sequence, NOMA clustering is carried out on the pilot collision-free user terminal, the clustering is more obvious under the condition of more access user terminals, the clustering is more successful, and the method is very suitable for random requests of mass equipment in the Internet of things for accessing the network. The base station demodulates the data of the user terminal according to the clustering result and the exclusive channel corresponding to each NOMA cluster, so that the channel resource utilization rate is greatly increased, and the successful access rate of the user terminal is improved.
The present invention is not limited to the above-mentioned embodiments, and any changes or substitutions that can be easily understood by those skilled in the art within the technical scope of the present invention are intended to be included in the scope of the present invention.
Claims (10)
1. A multi-channel ALOHA random access method based on NOMA clustering, applied to a base station, characterized by comprising:
receiving a pilot sequence, wherein the pilot sequence is randomly selected from a preset pilot sequence set by any active user terminal and is sent through a randomly selected channel;
judging whether the pilot frequency sequence is selected by only one user terminal or not; when the pilot frequency sequence is selected by only one user terminal, determining the user terminal as a pilot frequency collision-free user terminal;
performing NOMA clustering on a plurality of pilot non-collision user terminals, distributing an exclusive transmission channel for each NOMA cluster, and broadcasting a clustering result and the exclusive transmission channel corresponding to each NOMA cluster in a cell;
demodulating the received data information according to the clustering result and the exclusive transmission channel corresponding to each NOMA cluster; the data information is sent by any active user terminal based on self transmission power and self transmission channel; the self-transmission power and the self-transmission channel of the user terminal are determined according to the self-user terminal type obtained by the clustering result and the dedicated transmission channel corresponding to each NOMA cluster.
2. The method for performing NOMA clustering on a plurality of pilot collision-free ues according to claim 1, comprising:
calculating the Rayleigh fading gains of a plurality of pilot frequency collision-free user terminals, and sequencing the user terminals according to the Rayleigh fading gains to obtain gain sequencing of the user terminals;
taking the pilot frequency non-collision user end with the maximum Rayleigh fading gain as a central user end of a first NOMA cluster, and clustering a preset number of pilot frequency non-collision user ends meeting preset clustering conditions in sequence according to the gain sequencing to obtain the first NOMA cluster;
and taking the user terminal with the biggest Rayleigh fading coefficient in the rest pilot frequency non-collision user terminals in the gain sequencing as the central user terminal of the next NOMA cluster, and continuing to cluster according to the clustering condition until the rest pilot frequency non-collision user terminals in the gain sequencing cannot reach the preset quantity.
3. The multi-channel ALOHA random access method based on NOMA clustering according to claim 2, wherein the preset clustering conditions include a transmission power constraint condition and a signal-to-noise ratio constraint condition;
the transmission power constraint conditions are:
wherein beta is k,i The Rayleigh fading coefficient of the ith user end in the kth NOMA cluster is represented; beta k,1 The Rayleigh fading coefficient of the 1 st user end in the kth NOMA cluster is represented; p is p k,i Representing the ith user end in the kth NOMA cluster; p is p k,1 Represents the 1 st use in the kth NOMA clusterA client; ρ represents the power backoff size;
the signal-to-noise ratio constraint conditions are as follows:
wherein h is k,i Representing the channel coefficient of the ith user side in the kth NOMA cluster; h is a k,j Representing channel coefficients of a jth user terminal in a kth NOMA cluster; sigma (sigma) 2 Representing the noise power of the channel.
4. The method for multi-channel ALOHA random access based on NOMA clustering according to claim 3, wherein clustering the preset number of pilot collision-free clients satisfying a preset clustering condition sequentially according to the gain ranking comprises:
clustering a preset number of user ends meeting the transmission power constraint condition into NOMA clusters;
judging whether a user side in the NOMA cluster meets the preset signal-to-noise ratio constraint condition or not;
when the user terminals in the NOMA cluster do not meet the preset signal-to-noise ratio constraint condition, comparing the channel gain difference between every two user terminals in the NOMA cluster, and randomly deleting one of the two user terminals with the smallest channel gain difference;
and continuing to judge whether the rest user terminals in the NOMA cluster meet the preset signal-to-noise ratio constraint condition or not until all the user terminals in the NOMA cluster meet the preset signal-to-noise ratio constraint condition.
5. The method for multi-channel ALOHA random access based on NOMA clustering according to claim 1, wherein the pilot sequence is expressed as:
wherein N is m,i Representing the mth letterSelecting a user terminal set of the ith pilot frequency in the channel; ρ n Representing the uplink transmitting power of the user terminal n; h is a n Representing the channel coefficients between the user side n and the base station,
g n represents a small-scale fading vector and obeys a circularly symmetric complex gaussian distribution with a mean value of 0 and a variance of 1, beta n Representing the slow fading coefficient between the base station and the user terminal n; s is S i Indicating the pilot frequency selected by the ith user side; z is Z m Representing a Gaussian white noise matrix, obeying a mean of 0 and a variance of sigma 2 Is a circularly symmetric complex gaussian distribution.
6. The method for multi-channel ALOHA random access based on NOMA clustering of claim 1, wherein determining whether the pilot sequence is selected by only one ue comprises:
estimating whether any pilot sequence in any channel is selected by only the unique user terminal based on a least square method; when the pilot sequence is selected only by a unique user terminal, the ID information of the unique user terminal is determined.
7. The NOMA clustering-based multi-channel ALOHA random access method of claim 1, wherein the clustering result comprises: a user end which is successfully clustered and a central user end of each NOMA cluster;
the step of determining the self user terminal type of the user terminal according to the clustering result comprises the following steps: judging whether the user terminal is a user terminal with successful clustering and is a central user terminal of the NOMA cluster;
if the type of the self user terminal is NOMA cluster center user terminal, the self transmission power is the transmission power distributed by the base station; if the type of the self user terminal is a user terminal with successful clustering but not a central user terminal, self transmission power is calculated according to Rayleigh fading channel coefficient sequencing; if the type of the self user terminal is the user terminal which is not clustered successfully, the self transmission power is preset standard transmission power, and one channel is randomly selected from the rest channels to carry out data transmission.
8. The NOMA cluster-based multi-channel ALOHA random access method of claim 7 wherein demodulating the received data information according to the clustering result and the dedicated transport channel corresponding to each NOMA cluster comprises:
demodulating the data information transmitted by the user terminal which is successfully clustered by adopting a SIC algorithm; judging whether the channel selected by the user side which is not clustered successfully is selected by a unique user side or not; if only one user side data information exists in the channel, demodulating the user side data information and sending an ACK message; otherwise, the base station transmits a NACK message.
9. The multi-channel ALOHA random access method based on NOMA clustering according to claim 1, wherein the base station and the ue perform information transmission based on ALOHA protocol.
10. The utility model provides an thing networking communication system, includes user terminal and basic station, its characterized in that:
the user terminal is used for randomly selecting a pilot sequence from a preset pilot sequence set, randomly selecting a channel and transmitting the pilot sequence to the base station;
the base station is used for judging whether the pilot frequency sequence is selected by only one user terminal; when the pilot frequency sequence is selected by only one user terminal, determining the user terminal as a pilot frequency collision-free user terminal; performing NOMA clustering on a plurality of pilot non-collision user terminals, distributing an exclusive transmission channel for each NOMA cluster, and broadcasting a clustering result and the exclusive transmission channel corresponding to each NOMA cluster in a cell;
the active user end is also used for determining the type of the user end according to the clustering result, determining the self transmission power and the self transmission channel according to the type of the user end and the dedicated transmission channel corresponding to each NOMA cluster, and sending the data information to the base station based on the self transmission power and the self transmission channel;
the base station is further configured to demodulate the received data information according to the clustering result and the dedicated transmission channel corresponding to each NOMA cluster.
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