CN106936556B - Time-frequency two-dimensional sparse code multiple access method for narrowband Internet of things - Google Patents

Time-frequency two-dimensional sparse code multiple access method for narrowband Internet of things Download PDF

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CN106936556B
CN106936556B CN201710129644.4A CN201710129644A CN106936556B CN 106936556 B CN106936556 B CN 106936556B CN 201710129644 A CN201710129644 A CN 201710129644A CN 106936556 B CN106936556 B CN 106936556B
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time
frequency resource
signals
access
scheduling
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CN106936556A (en
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杨懋
左晓亚
雷蕾
白志城
闫中江
李波
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Northwestern Polytechnical University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0037—Inter-user or inter-terminal allocation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0037—Inter-user or inter-terminal allocation
    • H04L5/0039—Frequency-contiguous, i.e. with no allocation of frequencies for one user or terminal between the frequencies allocated to another
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/003—Arrangements for allocating sub-channels of the transmission path
    • H04L5/0044—Arrangements for allocating sub-channels of the transmission path allocation of payload
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L5/00—Arrangements affording multiple use of the transmission path
    • H04L5/0091—Signaling for the administration of the divided path
    • H04L5/0094—Indication of how sub-channels of the path are allocated
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/04—Wireless resource allocation
    • H04W72/044—Wireless resource allocation based on the type of the allocated resource
    • H04W72/0446—Resources in time domain, e.g. slots or frames

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Abstract

The invention provides a time-frequency two-dimensional sparse code multiple access method for narrowband Internet of things, which relates to the technical field of communication, the method is characterized in that a narrow band is divided into time slots, N time-frequency resource units form an SCMA time-frequency resource block, a cellular mobile or wireless local area network communication system is used for indicating the SCMA time-frequency resource block to be used for uplink scheduling, uplink scheduling-free, uplink mixed scheduling and downlink, and the SCMA only works in a frequency domain changed into time-frequency two-dimensional work. Under the condition of the same bit error rate, the number of users is increased by 1.5 times, the network throughput is increased by 1.5 times, and the performance of the mobile communication system is greatly improved.

Description

Time-frequency two-dimensional sparse code multiple access method for narrowband Internet of things
Technical Field
The invention relates to the technical field of communication, in particular to a multiple access method.
Background
The Internet of Things (IoT) is an important component of a new generation of communication technology, and refers to the Internet with connected objects, which is a necessary trend for the development of wireless and mobile networks.
The core and foundation of the internet of things is the internet, which is a network that extends and expands on the basis of the internet and requires support of traditional wireless networks due to the mobility characteristics of its devices. However, due to the cost, power saving requirements, and limited traffic volume of a single transmission of a single device of the IoT device, the IoT device has a narrowband feature, while the conventional cellular networks (3G and 4G) and wireless local area networks (IEEE 802.1x) have a high-rate broadband feature, which causes a contradiction between the narrowband of the IoT device and the broadband of the conventional wireless network.
To address this conflict, wireless networks have shown a trend in recent years to support IoT using narrowband, i.e., narrowband internet of things. Cellular networks 3GPP (The 3rd Generation Partnership Project) have completed The work of NB-IoT (Narrow Band Internet of Things, NB-IoT) standards in 2016, and Wireless Local Area Networks (WLANs) have established LRLP (Long Range Low Power) working group and WUR (Wake-Up Receiver) working group, both focusing on narrowband IoT.
At present, due to the fact that the number of IoT devices is increased sharply, the narrowband IoT is required to significantly increase the number of users and the total capacity on the basis of keeping the narrowband characteristics of the narrowband IoT. The Sparse Code Multiple Access (SCMA) (sparse Code multiple access) to be adopted by 5G is a novel non-orthogonal multiple access technology, which significantly improves the number of user connections, network capacity and spectrum utilization rate on the premise of no change in bandwidth, but due to the broadband characteristic of 5G, the SCMA used in 5G requires User Equipment (UE) to have the capability of transmitting and receiving multiple channels/subcarriers, which contradicts the current requirements of cost, energy saving and narrowband IoT devices.
In summary, a multiple access method for obtaining non-orthogonal multiple access advantages based on narrowband IoT is lacking.
Disclosure of Invention
In order to overcome the defects of the prior art, a non-orthogonal multiple access method is applied to a narrow-band IoT (Internet of things), so that the connection number of users, the spectrum efficiency and the network capacity are improved, the invention provides a time-frequency two-dimensional sparse code multiple access method for the narrow-band Internet of things, wherein the previous SCMA (sparse code multiple access) only changes from frequency domain work to time-frequency two-dimensional work, namely an SCMA Resource Block changes from N channels/sub-carriers to N time slots or N time-frequency Resource units (RB), so that a communication system can simultaneously obtain performance advantages in two aspects: on one hand, the original narrow-band characteristic of the IoT equipment is kept, and the requirements of cost and energy conservation are met; on the other hand, the number of user connections, the spectrum utilization rate and the network capacity are improved.
The technical scheme adopted by the invention for solving the technical problem comprises the following steps:
step 1: the system being divided into time slots on a narrow band
The cellular mobile or wireless local area network communication system is divided into time slots (slots) on a narrow band, and then step 2 is carried out, and the specific working modes are divided into the following two types according to different access modes:
mode 1: the system is divided into time slots, all communication nodes are aligned in time, and the nodes access channels on different time slots respectively;
mode 2: the system operates in a competition access mode, at the moment, the node time does not need to be aligned, a random competition mode is adopted for accessing a channel, a base station enters a time slot mode after sending a trigger frame, and the channel is accessed on a time slot which is divided by a downlink signaling after all the nodes are aligned in time;
step 2: forming an SCMA time-frequency resource block by the N time-frequency resource units, and indicating the SCMA time-frequency resource block to be used for uplink scheduling, uplink scheduling-free, uplink mixed scheduling and downlink by using a cellular mobile or wireless local area network communication system;
if the time-frequency resource block is used for uplink scheduling, turning to step 3;
if the time-frequency resource block is used for uplink scheduling-free, turning to step 4;
if the time-frequency resource block is used for uplink mixed scheduling, turning to step 5;
if the time-frequency resource block is used for indicating downlink, turning to step 6;
and step 3: the step of executing uplink scheduling access comprises the following specific steps:
step 3.1: the scheduled user equipment UE maps the coded information flow after channel coding into N paths of signals according to the codebook, and the N paths of signals s1，s2，s3，...，snAnd N time frequency resource units r1，r2，r3，...，rnThe non-zero signals of at least two UEs are mapped to the same time frequency resource unit, and the signals are sent one by one according to the time sequence of the time frequency resource unit;
step 3.2: the base station stores the signals superposed by a plurality of users after each time frequency resource unit receives the signals, and executes multi-user joint detection after the transmission of N time frequency resource units is finished, wherein the multi-user joint detection uses a message passing algorithm or a maximum likelihood algorithm, and the information of the users can be separated and extracted;
and 4, step 4: the uplink scheduling-free access executing steps are as follows:
step 4.1: the UE accesses the rule according to the scheduling-free mode: accessing with a probability P or judging whether to access according to competition backoff access, wherein the probability P is a random number between 0 and 1 which is reported by a base station to a user in downlink signaling, if not, exiting the uplink scheduling-free access step, and if so, executing the step 4.2;
step 4.2: the scheduled UE maps the coded information stream into N paths of signals according to a codebook, the N paths of signals correspond to N time-frequency resource units one by one, non-zero signals of at least two UEs are mapped to the same time-frequency resource unit, and the signals are sent one by one according to the time-frequency resource units;
step 4.3: the base station stores the signals superposed by a plurality of users after each time frequency resource unit receives the signals, and executes multi-user joint detection after the transmission of N time frequency resource units is finished, wherein the multi-user joint detection uses a message passing algorithm or a maximum likelihood algorithm, and can separate and extract user information;
and 5: the method for executing the uplink hybrid scheduling access specifically comprises the following steps:
step 5.1: the UE which is not scheduled accesses the network according to the scheduling-free access rule: accessing with probability P or judging whether to access according to competition backoff access, if not, exiting the uplink mixed scheduling access step, and if so, executing step 5.2;
step 5.2: the scheduled UE and the scheduling-free UE which judges to be accessed map the coded information flow into N paths of signals according to a codebook, the N paths of signals correspond to N time frequency resource units one by one, the non-zero signals of at least two UEs are mapped to the same time frequency resource unit, and the signals are sent one by one according to the N time frequency resource units;
step 5.3: the base station stores the signals superposed by a plurality of users after each time frequency resource unit receives the signals, and executes multi-user joint detection after the transmission of N time frequency resource units is finished, wherein the multi-user joint detection uses a message passing algorithm or a maximum likelihood algorithm, and the information of the users can be separated and extracted;
step 6: the downlink access is executed, and the specific steps are as follows:
step 6.1: the base station respectively maps the coded information streams sent to a plurality of UE into N paths of signals according to a codebook, the N paths of signals correspond to N time frequency resource units one by one, at least two non-zero signals of the UE are mapped to the same time frequency resource unit, then the signals sent to all the UE on the same channel are superposed, and the signals are sent one by one according to the time frequency resource units;
step 6.2: and the UE to receive data stores the signals superposed by the plurality of users after each time-frequency resource unit receives the signals, executes multi-user joint detection after the transmission of the N time-frequency resource units is finished, and separates and extracts the information of the UE.
The method has the advantages that the SCMA technology is expanded from the frequency domain to time-frequency two-dimensional work by adopting time-frequency two-dimensional sparse code non-orthogonal multiple access, so that the narrowband characteristic of the IoT equipment is ensured, the connection number, the spectrum utilization rate and the network capacity of mobile communication users are improved, compared with the prior art, the number of the users is improved by 1.5 times and the network throughput is improved by 1.5 times under the condition of the same bit error rate, and the performance of a mobile communication system is greatly improved.
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FIG. 1 is a schematic diagram of the present invention, wherein FIG. 1(a) is a time domain SCMA schematic diagram, and FIG. 1(b) is a time-frequency two-dimensional SCMA schematic diagram.
Fig. 2 is a flowchart of a first embodiment of the invention.
FIG. 3 is a flow chart of a second embodiment of the present invention.
FIG. 4 is a flow chart of a third embodiment of the present invention.
FIG. 5 is a flow chart of a fourth embodiment of the present invention.
Fig. 6 is a flow chart of a fifth embodiment of the present invention.
Fig. 7 is a graph of network throughput performance of the present invention.
Wherein, sta (station) is a station.
Detailed Description
The invention is further illustrated with reference to the following figures and examples.
Fig. 1 is a schematic diagram of the present invention, in which fig. 1(a) is a time-domain SCMA schematic diagram, which is a SCMA obtained by changing a conventional frequency-domain SCMA into a time-domain SCMA, and is mainly directed to a single-channel system, and fig. 1(b) is a time-frequency two-dimensional SCMA schematic diagram, which is mainly directed to a multi-channel system.
Example one
As shown in fig. 2, the first embodiment describes a pure time domain SCMA method in the case of a 5G cellular network with only one narrowband IoT channel, where the narrowband IoT is divided into multiple slots, and N slots constitute one SCMA resource block, and the UE transmits data using the resource block.
Step 1: each frame of the narrowband IoT is divided into slots, and the N slots are allocated to a group of UEs as one SCMA resource block.
The method comprises the following specific steps:
step 1.1: each frame on the narrowband IoT is divided into 10 slots, and as a typical configuration, the present invention supports other flexible slot division modes, which are determined by specific wireless network protocols, based on the frame structure of the fourth generation mobile communication system (4G) in the example of fig. 2.
Step 1.2: in fig. 2, Slot 0 is used for scheduling resource allocation, slots 1 to 4 and slots 5 to 8 are respectively used as 2 SCMA resource blocks for 2 groups of UEs, and Slot 9 is used for user equipment to feed back uplink data requirements.
Turning to the step 2;
step 2: an SCMA resource block adopts any one of three modes of authorization, authorization-free and semi-authorization, so that UE accesses a channel, the uplink condition is specifically transferred to the step 3, and the downlink condition is transferred to the step 4;
and step 3: the UE accesses a channel and sends uplink data, and the specific steps are as follows:
step 3.1: the accessed UE maps the coded information stream into N paths of signals according to the codebook, the N paths of signals correspond to N time domain resource units one by one, the nonzero signals of at least two UEs are mapped to the same time domain resource unit, and the signals are sent one by one according to the time domain resource units;
step 3.2: the base station stores the signals superposed by the users after each time domain resource unit receives the signals, executes multi-user joint detection after the transmission of the N time domain resource units is finished, and separates and extracts the information of the users.
And 4, step 4: according to the adopted scheduling rule, when the downlink access is carried out, the specific steps are as follows:
step 4.1: an Access Point (AP) respectively maps coded information streams sent to a plurality of UE into N paths of signals according to a codebook, the N paths of signals correspond to N time domain resource units one by one, at least two non-zero signals of the UE are mapped to the same time domain resource unit, then each path of signals are superposed, and the signals are sent one by one according to the time domain resource units;
step 4.2: and the UE to receive data stores the signals superposed by the plurality of users after each time domain resource unit receives the signals, executes multi-user joint detection after the transmission of the N time domain resource units is finished, and separates and extracts the information of the users.
Example two
As shown in fig. 3, the second embodiment describes a time domain SCMA method in a case where there are multiple independent narrowband IoT channels in a 5G cellular network, that is, in a case where the first embodiment is extended to multiple independent narrowband channels, the multiple narrowband IoT channels are respectively divided into multiple slots, and N slots on each narrowband constitute one SCMA resource block, different narrowband channels are independent from each other, and a UE transmits data using the resource block.
Step 1: and dividing each narrow-band IoT frame into time slots, and taking N time slots on each narrow band as an SCMA time-frequency resource block to be distributed to a group of UEs for use.
The method comprises the following specific steps:
step 1.1: each frame on the narrow band is divided into time slots, in the example of fig. 3, 10 time slots are respectively divided into 2 channels based on a 4G frame structure as a typical configuration, and the time slot division mode is determined by a specific wireless network protocol.
Step 1.2: in fig. 3, a Slot 1-4 of a channel 1 is an SCMA resource block and is allocated to an STA 1-6 for use; slot 1-4 of channel 2 is a SCMA resource block, which is allocated for use by STAs 7-12.
Turning to the step 2;
step 2: each narrow band bears the UE working on the channel, and the SCMA resource block adopts any one of authorization, authorization-free and semi-authorization modes, so that the UE accesses the respective narrow band channel.
Specifically, the uplink condition is transferred to the step 3, and the downlink condition is transferred to the step 4;
and step 3: according to the adopted scheduling rule, the UE accesses and sends uplink data, and the specific steps are as follows:
step 3.1: the UE accessed to each narrow band maps the coded information flow into N paths of signals according to a codebook, the N paths of signals correspond to N time domain resource units one by one, the non-zero signals of at least two UEs are mapped to the same time domain resource unit, and the signals are sent one by one according to the time domain resource units;
step 3.2: the base station stores the signals superposed by the users after each time domain resource unit receives the signals, executes multi-user joint detection after the transmission of the N time domain resource units is finished, and separates and extracts the information of the users.
And 4, step 4: according to the adopted scheduling rule, when the downlink access is carried out, the specific steps are as follows:
step 4.1: the AP respectively maps the coded information streams sent to the multiple UEs on each narrow band into N paths of signals according to a codebook, the N paths of signals correspond to N time domain resource units one by one, at least two non-zero signals of the UEs can be mapped to the same time domain resource unit, then each path of signals are superposed, and the signals are sent one by one according to the time domain resource units;
step 4.2: and each time domain resource unit of the UE which is to receive data on the narrow band of the UE receives the signals superposed by a plurality of users and then stores the signals, and after the transmission of the N time domain resource units is finished, multi-user joint detection is executed to separate and extract the information of the UE.
EXAMPLE III
As shown in fig. 4, the third embodiment describes a time-frequency two-dimensional SCMA method in the case of multiple narrowband channels in a 5G cellular network, that is, the channels in the second embodiment are changed to be non-independent, multiple slots and multiple channels form an SCMA resource block, and the UE transmits data using the resource block.
Step 1: the narrow-band channel is divided into time slots, and N time slots on a plurality of narrow bands are used as an SCMA time frequency resource block and are distributed to a group of UE for use.
The method comprises the following specific steps:
step 1.1: each frame on the narrowband is divided into time slots, and in fig. 2, two channels are divided into 10 time slots respectively, as a typical configuration, but the invention supports other flexible time slot division modes, which are determined by a specific wireless network protocol.
Step 1.2: the N slots on the multiple narrowband channels together form one SCMA resource block, which is allocated to the UE for use. As shown in fig. 4, Slot 1-2 of channel 1 and Slot 1-2 of channel 2 together form a resource block, which is allocated to STA 1-6; the Slot 3-4 of the channel 1 and the Slot 3-4 of the channel 2 form a resource block together, and the resource block is allocated to the STA 7-12 for use;
turning to the step 2;
step 2: the SCMA resource block adopts any one of three modes of authorization, authorization-free and semi-authorization, so that the UE is accessed.
Specifically, the uplink condition is transferred to the step 3, and the downlink condition is transferred to the step 4;
and step 3: according to the adopted scheduling rule, the UE accesses and transmits uplink data, and the specific steps are as follows.
Step 3.1: each accessed UE maps the coded information stream into N paths of signals according to a codebook, the N paths of signals correspond to N time frequency resource units one by one (at least two non-zero signals of the UE are mapped to the same time frequency resource unit), and the signals are sent one by one according to the time frequency resource units;
step 3.2: and the base station stores the signals superposed by the plurality of users after each time-frequency resource unit receives the signals, executes multi-user joint detection after the transmission of the N time-frequency resource units is finished, and separates and extracts the information of the users.
And 4, step 4: according to the adopted scheduling rule, when the downlink access is carried out, the specific steps are as follows:
step 4.1: the AP respectively maps the coded information streams sent to the multiple UEs into N paths of signals according to a codebook, the N paths of signals correspond to N time frequency resource units one by one, at least two non-zero signals of the UEs can be mapped to the same time frequency resource unit, then each path of signals are superposed, and the signals are sent one by one according to the time frequency resource units;
step 4.2: and the UE to receive data stores the signals superposed by the plurality of users after each time-frequency resource unit receives the signals, executes multi-user joint detection after the transmission of the N time-frequency resource units is finished, and separates and extracts the information of the UE.
Example four
As shown in fig. 5, in the fourth embodiment, a time-frequency two-dimensional SCMA method of a TDMA structure with multiple narrowband channels is described, where the multiple narrowband channels are divided into time slots, the multiple time slots on the multiple channels form an SCMA resource block, and a pseudo-random sequence is used to hop a narrowband channel value, and the UE transmits data using the resource block.
Step 1: the method comprises the steps of dividing a narrow-band channel into time slots, hopping the narrow-band channel based on a pseudo-random sequence, informing the pseudo-random sequence of UE by AP through downlink signaling, and distributing N time slots of the narrow-band channel as a time-frequency SCMA resource block to the UE accessing the channel at the moment.
Step 1.1: the narrow band is divided into time slots, and in fig. 4, the total 6 channels are divided into 8 time slots respectively, as a typical configuration, but the invention supports other flexible time slot division modes, which are determined by a specific wireless network protocol.
Step 1.2: n time slots on a plurality of narrow-band channels based on pseudo-random sequence hopping form an SCMA resource block together and are distributed to the UE for use.
Turning to the step 2;
step 2: the SCMA resource block adopts any one of three modes of authorization, authorization-free and semi-authorization, so that a user can access the SCMA resource block.
Specifically, the uplink condition is transferred to the step 3, and the downlink condition is transferred to the step 4;
and step 3: according to the adopted scheduling rule, the UE accesses and sends uplink data, and the specific steps are as follows:
step 3.1: each accessed UE maps the coded information stream into N paths of signals according to a codebook, the N paths of signals correspond to N time-frequency resource units one by one, the non-zero signals of at least two UEs are mapped to the same time-frequency resource unit, and the signals are sent one by one according to the time-frequency resource units;
step 3.2: and the AP stores the signals superposed by the plurality of users after each time-frequency resource unit receives the signals, executes multi-user joint detection after the transmission of the N time-frequency resource units is finished, and separates and extracts the information of the users.
And 4, step 4: according to the adopted scheduling rule, when the downlink access is carried out, the specific steps are as follows:
step 4.1: the AP respectively maps the coded information streams sent to the multiple UEs into N paths of signals according to the codebook, the N paths of signals correspond to N time frequency resource units one by one (at least two non-zero signals of the UEs can be mapped to the same time frequency resource unit), then each path of signals are superposed, and the signals are sent one by one according to the time frequency resource units;
step 4.2: and the UE to receive data stores the signals superposed by the plurality of users after each time-frequency resource unit receives the signals, executes multi-user joint detection after the transmission of the N time-frequency resource units is finished, and separates and extracts the information of the UE.
EXAMPLE five
As shown in fig. 6, the fifth embodiment focuses on the case where the narrowband IoT uses the time domain SCMA approach in WLAN. A narrow-band channel is divided into a plurality of time slots in the TXOP, N time slots form an SCMA resource block, and the UE transmits data by using the resource block.
Step 1: the cellular mobile or wireless local area network communication system works in a competition mode, when the IoT transmission is required, a Legacy preamble protection channel is firstly sent to indicate the time of the IoT transmission, and other STAs cannot compete for an access channel in the period;
turning to the step 2;
step 2: sending Trigger Frame to schedule uplink transmission, and allocating SCMA resource block to multiple STAs in transmission opportunity (TXOP);
turning to the step 3;
and step 3: the distributed SCMA resource block adopts any one of authorization, authorization-free and semi-authorization modes, so that a user can access the SCMA resource block.
Specifically, the uplink condition is transferred to the step 4, and the downlink condition is transferred to the step 5;
and 4, step 4: according to the adopted scheduling rule, the UE accesses and sends uplink data, and the specific steps are as follows:
step 4.1: each accessed UE maps the coded information stream into N paths of signals according to a codebook, the N paths of signals correspond to N time-frequency resource units one by one, the non-zero signals of at least two UEs are mapped to the same time-frequency resource unit, and the signals are sent one by one according to the time-frequency resource units;
step 4.2: and the AP stores the signals superposed by the plurality of users after each time-frequency resource unit receives the signals, executes multi-user joint detection after the transmission of the N time-frequency resource units is finished, and separates and extracts the information of the users.
And 5: according to the adopted scheduling rule, when the downlink access is carried out, the specific steps are as follows:
step 5.1: the AP respectively maps the coded information streams sent to the multiple UEs into N paths of signals according to a codebook, the N paths of signals correspond to N time frequency resource units one by one, at least two non-zero signals of the UEs can be mapped to the same time frequency resource unit, then each path of signals are superposed, and the signals are sent one by one according to the time frequency resource units;
step 5.2: and the UE to receive data stores the signals superposed by the plurality of users after each time-frequency resource unit receives the signals, executes multi-user joint detection after the transmission of the N time-frequency resource units is finished, and separates and extracts the information of the UE.
The present invention simulation aims to compare the performance gains of time-domain non-orthogonal multiple access and orthogonal multiple access in network throughput and user connection number.
The simulation is based on the first embodiment, wherein each 10ms is set as an MAC frame, each frame is composed of 10 time slots, the 0 th time slot is used for resource scheduling, 1-4 and 5-8 time slots are respectively one SCMA time frequency resource block, data of each user are distributed in a plurality of time slots for transmission and are mutually non-orthogonal, and the 9 th time slot is used for information feedback.
Time domain non-orthogonal parameter setting based on sparse coding: every 6 user groups share 4 time slots, 2 user groups are shared in one MAC frame, the maximum constellation point number mapped in each data layer is 4, the number of nonzero elements in a codebook is 2, and an 1/2-code-rate LDPC channel coding mode is adopted in a channel coding mode.
The parameter configuration of the communication system adopting QPSK modulation mode is adopted for the control group, the TDMA mode is adopted for the time domain, and the LDPC channel coding mode of 1/2 code rate is adopted for the channel coding mode.
As shown in fig. 7, under the condition of the same number of time slots, the total throughput of the time-domain non-orthogonal system is approximately twice the total throughput of the orthogonal system, so that it is proved that under the condition that the non-orthogonal communication system can provide a bit error rate which is smaller or comparable to the orthogonal communication system under the condition of the same number of time slots, the total throughput is 1.5 times that of the non-orthogonal communication system, and the performance advantage is remarkable.

Claims (1)

1. A time-frequency two-dimensional sparse code multiple access method facing to a narrow-band Internet of things is characterized by comprising the following steps:
step 1: the system being divided into time slots on a narrow band
The cellular mobile or wireless local area network communication system is divided into time slots on a narrow band, and the specific working modes are divided into the following two types:
mode 1: the system is divided into time slots, all communication nodes are aligned in time, and the nodes access channels on different time slots respectively;
mode 2: the system operates in a competition access mode, at the moment, the node time does not need to be aligned, a random competition mode is adopted for accessing a channel, a base station enters a time slot mode after sending a trigger frame, and the channel is accessed on a time slot which is divided by a downlink signaling after all the nodes are aligned in time;
step 2: forming an SCMA time-frequency resource block by the N time-frequency resource units, and indicating the SCMA time-frequency resource block to be used for uplink scheduling, uplink scheduling-free, uplink mixed scheduling and downlink access by using a cellular mobile or wireless local area network communication system;
if the time-frequency resource block is used for uplink scheduling, turning to step 3;
if the time-frequency resource block is used for uplink scheduling-free, turning to step 4;
if the time-frequency resource block is used for uplink mixed scheduling, turning to step 5;
if the time frequency resource block is used for indicating downlink access, turning to step 6;
and step 3: the step of executing uplink scheduling access comprises the following specific steps:
step 3.1: the scheduled user equipment UE maps the coded information flow after channel coding into N paths of signals according to the codebook, and the N paths of signals s1，s2，s3，...，snAnd N time frequency resource units r1，r2，r3，...，rnThe non-zero signals of at least two UEs are mapped to the same time frequency resource unit, and the signals are sent one by one according to the time sequence of the time frequency resource unit;
step 3.2: the base station stores the signals superposed by a plurality of users after each time frequency resource unit receives the signals, and executes multi-user joint detection after the transmission of N time frequency resource units is finished, wherein the multi-user joint detection uses a message passing algorithm or a maximum likelihood algorithm, and the information of the users can be separated and extracted;
and 4, step 4: the uplink scheduling-free access executing steps are as follows:
step 4.1: the UE accesses the rule according to the scheduling-free mode: accessing with a probability P or judging whether to access according to competition backoff access, wherein the probability P is a random number between 0 and 1 which is reported by a base station to a user in downlink signaling, if not, exiting the uplink scheduling-free access step, and if so, executing the step 4.2;
step 4.2: the scheduled UE maps the coded information stream into N paths of signals according to a codebook, the N paths of signals correspond to N time-frequency resource units one by one, non-zero signals of at least two UEs are mapped to the same time-frequency resource unit, and the signals are sent one by one according to the time-frequency resource units;
step 4.3: the base station stores the signals superposed by a plurality of users after each time frequency resource unit receives the signals, and executes multi-user joint detection after the transmission of N time frequency resource units is finished, wherein the multi-user joint detection uses a message passing algorithm or a maximum likelihood algorithm, and can separate and extract user information;
and 5: the method for executing the uplink hybrid scheduling access specifically comprises the following steps:
step 5.1: the UE which is not scheduled accesses the network according to the scheduling-free access rule: accessing with probability P or judging whether to access according to competition backoff access, if not, exiting the uplink mixed scheduling access step, and if so, executing step 5.2;
step 5.2: the scheduled UE and the scheduling-free UE which judges to be accessed map the coded information flow into N paths of signals according to a codebook, the N paths of signals correspond to N time frequency resource units one by one, the non-zero signals of at least two UEs are mapped to the same time frequency resource unit, and the signals are sent one by one according to the N time frequency resource units;
step 5.3: the base station stores the signals superposed by a plurality of users after each time frequency resource unit receives the signals, and executes multi-user joint detection after the transmission of N time frequency resource units is finished, wherein the multi-user joint detection uses a message passing algorithm or a maximum likelihood algorithm, and the information of the users can be separated and extracted;
step 6: the downlink access is executed, and the specific steps are as follows:
step 6.1: the base station respectively maps the coded information streams sent to a plurality of UE into N paths of signals according to a codebook, the N paths of signals correspond to N time frequency resource units one by one, at least two non-zero signals of the UE are mapped to the same time frequency resource unit, then the signals sent to all the UE on the same channel are superposed, and the signals are sent one by one according to the time frequency resource units;
step 6.2: and the UE to receive data stores the signals superposed by the plurality of users after each time-frequency resource unit receives the signals, executes multi-user joint detection after the transmission of the N time-frequency resource units is finished, and separates and extracts the information of the UE.
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