CN110972119A - D2D cooperative communication system based on wireless energy collection - Google Patents

D2D cooperative communication system based on wireless energy collection Download PDF

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CN110972119A
CN110972119A CN201911195634.6A CN201911195634A CN110972119A CN 110972119 A CN110972119 A CN 110972119A CN 201911195634 A CN201911195634 A CN 201911195634A CN 110972119 A CN110972119 A CN 110972119A
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information
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communication
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energy
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CN110972119B (en
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王蔚
方成
朱进
段宏睿
徐鹏
杨天若
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Huazhong University of Science and Technology
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/70—Services for machine-to-machine communication [M2M] or machine type communication [MTC]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B5/00—Near-field transmission systems, e.g. inductive or capacitive transmission systems
    • H04B5/70—Near-field transmission systems, e.g. inductive or capacitive transmission systems specially adapted for specific purposes
    • H04B5/79—Near-field transmission systems, e.g. inductive or capacitive transmission systems specially adapted for specific purposes for data transfer in combination with power transfer
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/022—Site diversity; Macro-diversity
    • H04B7/026—Co-operative diversity, e.g. using fixed or mobile stations as relays
    • 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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
    • H04W72/541—Allocation or scheduling criteria for wireless resources based on quality criteria using the level of interference
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
    • H04W72/542—Allocation or scheduling criteria for wireless resources based on quality criteria using measured or perceived quality
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/02—Terminal devices
    • H04W88/04—Terminal devices adapted for relaying to or from another terminal or user
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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Abstract

The invention discloses a D2D cooperative communication system based on wireless energy collection, and belongs to the technical field of wireless communication. According to the invention, the wireless energy collection technology and the relay technology are added into the D2D link, and the D2D node is transformed into a multifunctional node with relay and energy collection capabilities, so that the problem of shortage of frequency spectrum resources in the traditional communication network is solved, the relay function is introduced, the throughput of the system is effectively improved, meanwhile, the communication cost is reduced under the condition that the structure of the existing communication network is not changed, the life cycle of the node is effectively improved by introducing the wireless energy collection technology, and green communication is realized. In the information transmission stage, for an RU, two links related to the RU are provided, wherein the two links are from AP to RU and from DU to RU, and a time slice can be allocated as a parameter transmitted by each link by utilizing a time division multiplexing protocol so that all sections of communication are not overlapped on a time axis, and the problem of mutual interference inside the whole system is avoided.

Description

D2D cooperative communication system based on wireless energy collection
Technical Field
The invention belongs to the technical field of D2D in wireless communication, and particularly relates to a D2D cooperative communication system based on wireless energy collection.
Background
In recent years, with the explosive growth of the number of mobile terminals and the emergence of emerging communication services, significant pressure has been placed on the traditional cellular communication network architecture. The Device-to-Device (D2D) technology can offload the communication traffic between the near-distance devices from the cellular link to the D2D link, and the relay cooperative communication network can overcome the defect that the communication distance of the D2D technology is too short, and by combining the technology with the D2D technology, the communication quality and the system capacity of the system can be improved without changing the existing mobile communication infrastructure, and a foundation is laid for future 'everything interconnection'.
Mobile devices play an increasing role today, but the limited battery capacity has become a "stumbling stone" on the way technology advances. At present, most of the solutions are considered from the viewpoint of energy consumption by improving the structure of the chip, adopting a novel material with lower power consumption, optimizing the operating system of the device, and the like. The wireless energy collection technology can solve the problem of energy consumption of equipment from the perspective of energy supply, and the technology can effectively solve the problem that relay nodes in a relay cooperation network are unwilling to relay due to limited energy, and prolong the working time of the equipment.
Disclosure of Invention
Aiming at the defects and the improvement requirements of the prior art, the invention provides a D2D cooperative communication system based on wireless energy collection, which aims to introduce a wireless energy collection technology to improve the working time of a relay node, realize green communication, and calculate the optimal time slot allocation under the constraints of energy and link state so as to achieve the aim of maximizing the system throughput.
To achieve the above object, according to an aspect of the present invention, there is provided a wireless energy harvesting based D2D cooperative communication system, the system including:
the base station AP is used as a unique energy emission source and is also an information source;
D2D user DU is a mobile device with limited energy, which works only from the collected energy of the wireless electromagnetic waves, and has the following functions: firstly, charging a battery of a base station AP by receiving a signal of the base station AP in a wireless energy collection mode, secondly, storing a data packet sent by the base station AP in an information processing mode, thirdly, forwarding the stored data packet to a target node RU in the information processing mode, and fourthly, sending the data packet of the base station AP to the target node RU in the information processing mode;
a cellular network registered user RU, which is a target node;
AP to DU have both energy transmission link and honeycomb transmission link, AP to RU are honeycomb transmission link, DU to RU are information transmission link;
each link multiplexes AP to RU cellular frequency band communications.
Specifically, the DU in the decode-and-forward mode decodes the AP signal and then forwards the re-encoded signal to the RU.
Specifically, the DU includes a time-switching based rf energy harvesting module that can communicate only after sufficient energy is harvested.
Specifically, in a time slot T, the energy received by the rf energy collection module is:
WT＝∫0 TET·tdt
ET＝η·PAP·hAP，DU
wherein E isTRepresents the power received by the energy harvesting module during a time slot T, η represents the energy conversion efficiency of converting electromagnetic waves into direct current, PAPRepresents the transmission power, h, of the APAP，DURepresenting the channel gain of the link from AP to DU.
Specifically, the single-user system includes: one AP, one DU and one RU, the time slot of one communication process of the single-user system is T, and the T is divided into four parts tau from the time line0、τ1、τ2、τ3And (3) communication is carried out:
(1)τ0in the time slot, the AP sends information, the RU receives the information from the AP, and the DU senses the information sent by the AP to charge;
(2)τ1in the time slot, AP sends information, RU receives the information from AP, and DU receives the information from AP;
(3)τ2in time slot, DU forwards the information received from AP to RU;
(4)τ3slot, DU sends its own information to RU.
Specifically, τ is solved according to the following model0、τ1、τ2、τ3：
Figure BDA0002291044260000031
Figure BDA0002291044260000032
Figure BDA0002291044260000033
subject to
τ0+τ1+τ2+τ3＝T
PAP·rAP，DU -α·τ0＞PDU·(τ2+τ3)
RDU，RU·τ2＞RAP，RU·(1-LAP，DU)·τ1
Wherein r isAP，RURepresents the distance between the AP and RU links, rAP，DURepresents the distance between the AP-to-DU link, rDU，RURepresents the distance between DU and RU links, Rwith-relayRepresenting system throughput, R, with D2D devices participatingwithout-relavRepresenting system throughput, P, without D2D device participationAPRepresenting the transmit power of the AP, α representing the attenuation index of the channel, PDURepresenting the transmission power of the DU, RDDU，RURepresenting the maximum transmission rate, R, of the link from DU to RUAP，RURepresenting the maximum transmission rate, L, of the link from AP to RUAP，DURepresenting the link loss ratio from AP to DU.
In particular, the amount of the solvent to be used,
Figure BDA0002291044260000034
Rwithout-relay＝RAP，RU·(1-LAP，RU)。
specifically, the multi-user system is composed of an AP, a DU, and N RUs, all RUs use the same frequency band to complete AP downlink communication, and the total communication time of the entire system is nxt, where the DU only performs the energy collection function in the 1 st,., (N-1) T slots, and only completes relay communication in the nth slot:
(1) in the 1 st T time slot, the AP sends information, the RU receives the information from the AP, and the DU senses the information sent by the AP to charge;
(2) in the 2 nd to (N-1) th T time slot, the AP sends information, the RU receives the information from the AP, and the DU senses the information sent by the AP to charge;
(3) in the Nth T time slot, first tau0Time slot, AP send information, RUiReceives information from the AP with the DU, after tau1Time slot, DU forwards received information from AP to RUi。
Specifically, the optimal user RU is solved by the following modeli、τ0、τ1：
Figure BDA0002291044260000041
Figure BDA0002291044260000042
subject to
τ0+τ1＝T
PAP·rAP，DU-α·(N-1)T＞PDU·τ1
Figure BDA0002291044260000043
Wherein R isi，without-relavSelecting the ith RU for relay communication on behalf of the DUi，with-relaySystem throughput, P, after selecting the ith RU for relay communication on behalf of the DUAPRepresenting the transmission power, P, of the APDURepresents the DU transmit power, rAP，DURepresenting the distance between the AP to DU link,
Figure BDA0002291044260000046
representing the maximum transmission rate, R, of the link from DU to the ith RUAP，RUiRepresenting the maximum transmission rate, L, of the AP to the ith RU linkAP，RURepresenting the link loss ratio from AP to DU.
In particular, the amount of the solvent to be used,
Figure BDA0002291044260000044
Figure BDA0002291044260000045
wherein the content of the first and second substances,
Figure BDA0002291044260000051
representing the link packet loss rate from the AP to the ith RU,
Figure BDA0002291044260000052
represents the link loss ratio from DU to the ith RU, and c represents the size of one data packet.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained:
(1) according to the invention, the wireless energy collection technology and the relay technology are added into the D2D link, and the D2D node is transformed into a multifunctional node with relay capability and energy collection capability, so that the problem of shortage of spectrum resources in the traditional communication network can be solved, the relay function can be introduced, the throughput of the system is effectively improved, meanwhile, the communication cost is reduced under the condition that the structure of the existing communication network is not changed, and the life cycle of the node is effectively improved by introducing the wireless energy collection technology, so that green communication is realized.
(2) The invention adopts the idea of time division multiplexing and provides a new communication protocol. In the information transmission stage, for an RU, two links related to the RU are provided, wherein one is from an AP to the RU, and the other is from the DU to the RU, and the time can be used as a parameter transmitted by each link by utilizing a time division multiplexing protocol so that the communication sections are not overlapped on a time axis, and the problem of mutual interference in the whole system is avoided.
(3) The invention combines the model and the time allocation protocol for use, selects the corresponding optimal time allocation according to the position of each device in the model and the condition of a channel, maximizes the system throughput to the optimal time allocation criterion of the target design, integrates the energy collection stage and the information transmission stage from AP to RU, and avoids designing a single energy transmission time slot to shorten the communication time of the wireless system. The proposed protocol is a complete time slot arrangement under the constraint of good channel condition and abundant energy, and when some constraint conditions are not met, the relay communication and the D2D communication stage may not be performed, i.e. the system only has cellular communication.
Drawings
Fig. 1 is a schematic structural diagram of a wireless energy harvesting-based D2D cooperative communication system according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a communication process of a single-user system link according to an embodiment of the present invention;
fig. 3 is a diagram illustrating a communication timeslot allocation result of a single-user system according to an embodiment of the present invention;
FIG. 4 is a block diagram of a multi-user system according to an embodiment of the present invention;
fig. 5 is a schematic diagram of a communication process of a multi-user system link according to an embodiment of the present invention;
fig. 6 is a diagram illustrating a communication time slot allocation result of a multi-user system according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1, the present invention provides a wireless energy harvesting based D2D cooperative communication system, the system comprising:
and the base station AP (Access Point) is used as a unique energy emission source and is also an information source.
D2D User DU (D2D User), is a mobile device with limited energy, which works only from the collected wireless electromagnetic wave energy, and has the following functions: the method comprises the steps of firstly, charging a battery of a base station AP by receiving a signal of the base station AP in a wireless energy collection mode, secondly, storing a data packet sent by the base station AP in an information processing mode, thirdly, forwarding the stored data packet to a target node RU in the information processing mode, and fourthly, sending the data packet to the target node RU in the information processing mode.
The DU is only capable of half-duplex (i.e., cannot receive and transmit information simultaneously) communication, i.e., the device has two modes of operation, one being a wireless energy harvesting mode and the other being an information processing mode. The device is an energy-limited device, namely, the device can only obtain required electric energy from electromagnetic waves to maintain the normal operation of the device. The DU is a single antenna mobile device, for example: small-size wearable equipment such as smart watch, cell-phone, bracelet.
The cellular network registers user ru (register user), which is the target node.
An RU is a device that can only transmit information, i.e., has no energy harvesting capability.
All with solid lines with arrows as channels between the links, while different line segments represent different channels. For example, the dotted line with arrows represents an energy transmission link, the solid line with black represents an information transmission link from AP to RU, the dotted line with dots represents an information transmission link from AP to DU, and the dotted line with arrows represents a D2D link from DU to RU, and the whole system is designed as a downlink.
Each link multiplexes AP to RU cellular frequency band communication, so that the utilization rate of frequency spectrum can be improved.
Specifically, the DU serves as a relay node, and after the AP communicates with the RU once, the DU senses and relays missing information to the RU. The DU in the decode-and-forward mode decodes the AP signal after receiving the AP signal, and then forwards the re-encoded signal to the RU.
Specifically, the DU includes a time-switching based rf energy harvesting module that can communicate only after sufficient energy is harvested. In a time slot T, the energy received by the rf energy harvesting module is:
WT＝∫0 TET·tdt
ET＝η·PAP·hAP，DU
wherein E isTRepresents the power received by the energy harvesting module during a time slot T, η represents the energy conversion efficiency of converting electromagnetic waves into direct current, PAPRepresents the transmission power, h, of the APAP，DURepresenting the channel gain of the link from AP to DU.
Specifically, the single-user system includes: the time slot for completing one communication process of the single-user system is T, namely the energy collection process and the information receiving process are completed in the time slot. As shown in FIG. 2, DU is a single antenna half duplexThe device, RU being a cellular communication device and AP being a macro base station, divides T into four parts τ from the time line0、τ1、τ2、τ3Communication is performed with different rectangles representing different transmission phases:
(1)τ0and in the time slot, the AP sends information, the RU receives the information from the AP, and the DU senses the information sent by the AP to charge.
At tau0And in the sub-time slot, due to insufficient energy, only the DU senses the information sent by the AP to charge the energy, and the DU is maintained in an energy collection state.
When the distance between the AP and the DU is too far or the channel state is not good, the DU cannot receive enough energy, and the DU will not perform information transmission and reception but perform a sleep state until the energy collection can meet the requirement.
(2)τ1And in the time slot, the AP sends information, the RU receives the information from the AP, and the DU receives the information from the AP.
At tau1And in the time slot, the AP still maintains the information transmission state, the data packets in the transmission queue are sent to the RU, and the RU receives the information from the AP. In this sub-slot, due to the broadcast nature of the electromagnetic wave, and the DU has filled the required energy in the last slot, the DU switches from the energy harvesting state to the information transmission state, and the DU receives the information from the AP and stores it in the corresponding receive queue.
The RU needs to store the received information for subsequent content verification and failed retransmission. The DU needs to store the received information in order to perform the forwarding process of the next time slot in the case of sufficient energy.
(3)τ2Slot, DU forwards information received from AP to RU.
At tau2In time slot, AP stops sending information, and converts to sleep state,under the premise of sufficient energy, the DU is switched from the information receiving state to the information sending state, the DU decodes the data packets received from the AP from the receiving queue and then re-encodes and forwards the data packets to the RU, and the RU maintains the information receiving state and stores the data packets received from the DU into the receiving queue.
The RU integrates data packets transmitted in two time slots, namely data packets transmitted to the RU by the AP and data packets transmitted to the RU by the DU, de-duplicates the same data packets, and reduces the link packet loss rate of the system and improves the throughput of the system by transmitting the DU to the data packets of the RU.
(4)τ3Slot, DU sends its own information to RU.
At tau3In the time slot, the AP maintains the dormant state, the DU maintains the information sending state, and on the premise of sufficient energy, the DU sends the data packet in the sending queue for sending the self information to the RU through the D2D link.
The RU stores the received data packet in a receive queue.
Specifically, τ is solved according to the following model0、τ1、τ2、τ3：
Figure BDA0002291044260000091
Figure BDA0002291044260000092
Figure BDA0002291044260000093
subject to
τ0+τ1+τ2+τ3＝T
PAP·rAP，DU -α·τ0＞PDU·(τ2+τ3)
RDU，RU·τ2＞RAP，RU·(1-LAP，DU)·τ1
Wherein r isAP，RURepresents the distance between the AP and RU links, rAP，DURepresents the distance between the AP-to-DU link, rDU，RURepresents the distance between DU and RU links, Rwith-relayRepresenting system throughput, R, with D2D devices participatingwithout-relavRepresenting system throughput, P, without D2D device participationAPRepresenting the transmit power of the AP, α representing the attenuation index of the channel, PDURepresenting the transmission power of the DU, RDDU，RURepresenting the maximum transmission rate, R, of the link from DU to RUAP，RURepresenting the maximum transmission rate, L, of the link from AP to RUAP，DURepresenting the link loss ratio from AP to DU.
The specific constraints required for the operation of the entire single-user system are as follows:
the first is the time constraint that the sum of the time of information transmission and energy reception in the system needs to be equal to the total time slot T.
The second is the energy constraint, assuming that the DU does not consume energy to receive information, and the energy required to transmit information is less than the received energy of the radio waves. I.e. DU at0The energy received by the time slot can satisfy tau2Slot complete relay work and tau3The transmission of the slot own information.
The third is the transmission constraint, i.e. the DU is at τ2Time slot will tau1Tau can only be carried out after the data packet received in the time slot is transmitted3D2D of the time slot is active.
In particular, the amount of the solvent to be used,
Figure BDA0002291044260000101
Rwithou-rela＝RAP，RU·(1-LAP，RU)。
in order to increase the system throughput as much as possible, the slot allocation is obtained by the weight linear decreasing particle swarm algorithm according to the constraint as shown in fig. 3.
The parameters of the system of this example are shown in table 1.
TABLE 1 System parameters
GAP，1 Coordinates of AP (0，0)
GDU，1 Coordinates of DU (450m，0)
GRU，1 Coordinates of RU (500m，0)
PAP AP Transmission Power 5kw
PDU Transmission power of DU 100μw
hAP，RU/hAP，DU/hDU，RU Link attenuation factor Exponential distribution obeying a mean value of 1
α Channel attenuationIndex of refraction 3
δ SINR threshold 3
n0 White gaussian noise -90dBm
T Slot cycle 1s
c Packet size 1kb
Within T ═ 1s, τ0333.8ms represents the time required for the process of transmitting information from the AP to the RU and the process of energy harvesting by the DU, τ1482.6ms represents the time for the AP to send information to DU and RU, τ2183.6ms represents the time required for the DU to forward the information received from the AP to the RU, τ3In this scenario, the data packet of the relay link cannot be completely transmitted within the specified time due to the limitation of the transmission rate, and therefore, the relay node DU cannot enter the D2D transmission state within the time slot T.
Specifically, the multi-user system is composed of an AP, a DU, and N RUs, all RUs use the same frequency band to complete AP downlink communication, and the total communication time of the entire system is nxt, where the DU only performs the energy collection function in the 1 st,., (N-1) T slots, and only completes relay communication in the nth slot:
(1) in the 1 st T time slot, the AP sends information, the RU receives the information from the AP, and the DU senses the information sent by the AP to charge;
(2) in the 2 nd to (N-1) th T time slot, the AP sends information, the RU receives the information from the AP, and the DU senses the information sent by the AP to charge;
(3) in the Nth T time slot, first tau0Time slot, AP send information, RUiReceives information from the AP with the DU, after tau1Time slot, DU forwards received information from AP to RUi。
Specifically, the optimal user RU is solved by the following modeli、τ0、τ1：
Figure BDA0002291044260000111
Figure BDA0002291044260000112
subject to
τ0+τ1＝T
PAP·rAP，DU -α·(N-1)T＞PDU·τ1
Figure BDA0002291044260000113
Wherein R isi，without-relavSelecting the ith RU for relay communication on behalf of the DUi，wih-relaySystem throughput, P, after selecting the ith RU for relay communication on behalf of the DUAPRepresenting the transmission power, P, of the APDURepresents the DU transmit power, rAP，DURepresenting the distance between the AP to DU link,
Figure BDA0002291044260000114
representing the maximum transmission rate of the link of the DU to the ith RU,
Figure BDA0002291044260000115
maximum transmission rate, L, of link representing AU to ith RUAP，DURepresenting the link loss ratio from AP to DU.
The first objective function represents the throughput increase rate before and after the ith RU is selected for relay communication. The second objective function represents the energy remaining after the DU has completed the entire communication process.
The first represents the time constraint, i.e., two subslots τ, in selecting the time slot T for the optimal RU user to communicate0、τ1The sum equals the time slot T. The second represents the energy constraint, that is, the energy received by the DU in the T slot of the non-optimal user can satisfy the slot in the T slot of the most optimal user to complete the relay operation. The third represents the transmission constraint, i.e. the DU is at τ in the optimal user communication time slot T1Within a sub-slot can be0And finishing the transmission of all the information received by the sub-time slot.
The communication process in the optimal relay communication time slot can be similar to that of a single-user system, except that the DU is already charged in the previous time slot, so the DU does not need to be charged in the time slot and starts communication directly. In a multi-user scenario, the DU needs to select an optimal RU node to implement relay communication. The invention provides an optimal user selection strategy in a multi-user scene, namely a node DU selects one RU for relay communication, so that the system throughput is maximized, and the residual energy of the DU is maximized after the communication is finished.
In particular, the amount of the solvent to be used,
Figure BDA0002291044260000121
Figure BDA0002291044260000122
wherein the content of the first and second substances,
Figure BDA0002291044260000123
representing the link packet loss rate from the AP to the ith RU,
Figure BDA0002291044260000124
represents the link loss ratio from DU to the ith RU, and c represents the size of one data packet.
For the optimization problem of single user and multi-user, the invention adopts the particle swarm algorithm with the weight linearly decreasing.
As shown in fig. 4, taking a three-RU system as an example, three RUs 1, RU2, and RU3 each use a solid line with arrows as inter-link channels, and different line segments represent different channels. For example, the solid black line represents the energy transmission link, the dashed line represents the AP-to-RU information transmission link, and the dotted dashed line represents the AP-to-DU information transmission link, and the dotted dashed line represents the DU-to-RU D2D link. The three RUs will communicate using different time slots, assuming that the DU relays only within one RU's communication time slot and D2D acts, the remaining two RUs will only act as energy receivers during communication, and therefore the DU needs to select an optimal RU for relaying communication.
As shown in fig. 5, assuming that the optimal RU is still RU3, the communication protocol of the system is as follows:
(1) in the first T slot, the AP sends information, RU1 receives information from the AP, and the DU senses the information sent by the AP to charge.
(2) In the second T slot, the AP sends information, RU2 receives information from the AP, and the DU senses the information sent by the AP to charge.
(3) In the third T slot, first0Time slot, AP sends information, RU3 and DU receive information from AP, and tau after1The time slot, DU, forwards the information received from the AP to RU 3.
The parameters of the system of this embodiment are shown in table 2, and the parameters of the partial channels are also shown in table 1.
TABLE 2
GAP Coordinates of AP (0，0)
GDU Coordinates of DU (400m，0)
GRU1 RU1Coordinates of (2) (330m，0)
GRU2 RU2Coordinates of (2) (420m，50m)
GRU3 RU3Coordinates of (2) (440m，20m)
As shown in fig. 6, the system time slot allocation is as follows: tau is calculated by time distribution weight linear decreasing particle swarm optimization0And τ1Time slot allocation in T1 s, tau0Ms, during which time the information transmitted from the AP is received, τ1During this time period, the DU forwards information 401.9 ms.
Compared with other communication systems, the system solves the problem of shortage of spectrum resources in the existing wireless communication network through the D2D technology, and the D2D technology utilizes equipment with similar physical positions to multiplex communication frequency bands in a cellular network within an interference allowable range, and effectively improves the system capacity and the spectrum efficiency of the communication system without changing the infrastructure of the existing communication network. Compared with other communication systems, the system effectively overcomes the defect of short communication distance of the D2D technology by using a cooperative communication technology, enables the devices in an idle state to have sufficient energy and to perform relay transmission, effectively improves the device utilization efficiency and the energy utilization efficiency in the system, reduces the link packet loss rate of the system, and improves the throughput of the system. Compared with other communication systems, the system introduces a wireless energy collection technology, supplements consumed electric energy by collecting electromagnetic waves in the air, improves the running time of equipment in the system, realizes green communication, and simultaneously under some specific scenes, for example: in devices such as cardiac pacemakers which are inconvenient to replace batteries, "a state of continuous operation" is realized.
The invention provides a new communication protocol based on time switching for the communication system, avoids the possible interference problem in the communication process by using a time-sharing protocol, and simultaneously adopts a wireless energy receiver architecture in a time-sharing mode, the receiver architecture has the advantages that the energy and information can be received by only one antenna, the volume of equipment is effectively reduced, and particularly under the scene that the volume of the equipment to be received is limited, for example: smart watches, etc., which have more application prospects.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. A wireless energy harvesting-based D2D cooperative communication system, the system comprising:
the base station AP is used as a unique energy emission source and is also an information source;
D2D user DU is a mobile device with limited energy, which works only from the collected energy of the wireless electromagnetic waves, and has the following functions: firstly, charging a battery of a base station AP by receiving a signal of the base station AP in a wireless energy collection mode, secondly, storing a data packet sent by the base station AP in an information processing mode, thirdly, forwarding the stored data packet to a target node RU in the information processing mode, and fourthly, sending the data packet of the base station AP to the target node RU in the information processing mode;
a cellular network registered user RU, which is a target node;
AP to DU have both energy transmission link and honeycomb transmission link, AP to RU are honeycomb transmission link, DU to RU are information transmission link;
each link multiplexes AP to RU cellular frequency band communications.
2. The system of claim 1, wherein the DU in the decode-and-forward mode is decoded after receiving the AP signal and then re-encoded signals are forwarded to the RU.
3. The system of claim 1, wherein the DU comprises a time-switch based radio frequency energy harvesting module that is configured to collect sufficient energy before communication.
4. The system of claim 3, wherein during a timeslot T, the energy received by the rf energy harvesting module is:
WT＝∫0 TET·tdt
ET＝η·PAP·hAP，DU
wherein E isTRepresents the power received by the energy harvesting module during a time slot T, η represents the energy conversion efficiency of converting electromagnetic waves into direct current, PAPRepresents the transmission power, h, of the APAP，DURepresenting the channel gain of the link from AP to DU.
5. The system of claim 1, wherein the single-user system comprises: one AP, one DU and one RU, the time slot of one communication process of the single-user system is T, and the T is divided into four parts tau from the time line0、τ1、τ2、τ3And (3) communication is carried out:
(1)τ0in the time slot, the AP sends information, the RU receives the information from the AP, and the DU senses the information sent by the AP to charge;
(2)τ1time slots, AP transmit information, RUs receive information from AP,the DU receives information from the AP;
(3)τ2in time slot, DU forwards the information received from AP to RU;
(4)τ3slot, DU sends its own information to RU.
6. The system of claim 5, wherein τ is solved according to the following model0、τ1、τ2、τ3：
Figure FDA0002291044250000021
Figure FDA0002291044250000022
subject to
τ0+τ1+τ2+τ3＝T
PAP·rAP，DU -α·τ0＞PDU·(τ2+τ3)
RDU，RU·τ2＞RAP，RU·(1-LAP，DU)·τ1
Wherein r isAP，RURepresents the distance between the AP and RU links, rAP，DURepresents the distance between the AP-to-DU link, rDU，RURepresents the distance between DU and RU links, Rwit h-relayRepresenting system throughput, R, with D2D devices participatingwit hout-relavRepresenting system throughput, P, without D2D device participationAPRepresenting the transmit power of the AP, α representing the attenuation index of the channel, PDURepresenting the transmission power of the DU, RDU，RURepresenting the maximum transmission rate, R, of the link from DU to RUAP，RURepresenting the maximum transmission rate, L, of the link from AP to RUAP，DURepresenting the link loss ratio from AP to DU.
7. The system of claim 6,
Figure FDA0002291044250000031
Rwit hout-rel＝RAP，RU·(1-LAP，RU)。
8. the system of claim 1, wherein the multi-user system comprises an AP, a DU, and N RUs, all RUs use the same frequency band to complete the AP downlink communication, and the total communication time of the whole system is nxt, wherein, the DU performs only the energy collection function in the 1 st,., (N-1) T slots, and completes only the relay communication in the nth slot:
(1) in the 1 st T time slot, the AP sends information, the RU receives the information from the AP, and the DU senses the information sent by the AP to charge;
(2) in the 2 nd to (N-1) th T time slot, the AP sends information, the RU receives the information from the AP, and the DU senses the information sent by the AP to charge;
(3) in the Nth T time slot, first tau0Time slot, AP send information, RUiReceives information from the AP with the DU, after tau1Time slot, DU forwards received information from AP to RUi。
9. The system of claim 8, wherein the optimal user RU is solved by the following modeli、τ0、τ1：
Figure FDA0002291044250000032
maxi，2＝PAP·rAP，DU -α·(N-1)T-PDU·τ1
subject to
τ0+τ1＝T
PAP·rAP，DU -α·(N-1)T＞PDU·τ1
Figure FDA0002291044250000033
Wherein R isi，wit hou-relaySelecting the ith RU for relay communication on behalf of the DUi，wi h-relaySystem throughput, P, after selecting the ith RU for relay communication on behalf of the DUAPRepresenting the transmission power, P, of the APDURepresents the DU transmit power, rAP，DURepresenting the distance between the AP to DU link,
Figure FDA0002291044250000034
representing the maximum transmission rate of the link of the DU to the ith RU,
Figure FDA0002291044250000035
representing the maximum transmission rate, L, of the AP to the ith RU linkAP，DURepresenting the link loss ratio from AP to DU.
10. The system of claim 9,
Figure FDA0002291044250000041
Figure FDA0002291044250000042
wherein the content of the first and second substances,
Figure FDA0002291044250000043
representing the link packet loss rate from the AP to the ith RU,
Figure FDA0002291044250000044
represents the link loss ratio from DU to the ith RU, and c represents the size of one data packet.
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