CN106788782A - Underwater sound communication network OFDM Link Physical Layers and MAC layer cross-layer communication method - Google Patents
Underwater sound communication network OFDM Link Physical Layers and MAC layer cross-layer communication method Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B13/00—Transmission systems characterised by the medium used for transmission, not provided for in groups H04B3/00 - H04B11/00
- H04B13/02—Transmission systems in which the medium consists of the earth or a large mass of water thereon, e.g. earth telegraphy
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
- H04L1/0002—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate
- H04L1/0003—Systems modifying transmission characteristics according to link quality, e.g. power backoff by adapting the transmission rate by switching between different modulation schemes
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
- H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
- H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
- H04L1/1806—Go-back-N protocols
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Abstract
The present invention is to provide a kind of underwater sound communication network OFDM Link Physical Layers and MAC layer cross-layer communication method.The present invention, by physical layer and the method for MAC layer cross-layer data interaction, is optimized for the purpose of reasonable distribution channel resource, raising network throughput to network performance.Physical layer adjusts order of modulation, code rate and frequency diversity exponent number according to underwater acoustic channel environment self-adaption, realize the data transfer of different rates, to adapt to the underwater acoustic channel of quick time-varying, MAC layer uses improved CSMA/CA agreements, improve the data packet retransmission probability of success, reduce data transmission delay, by the cross layer design between physical layer and MAC layer, solve the problems, such as that the packet loss that the factors such as the quick time-varying of underwater acoustic channel and propagation delay time long cause is high low with efficiency of transmission, so as to improve the spectrum efficiency of underwater sound communication network handling capacity and system.
Description
Technical field
The present invention relates to a kind of underwater sound wireless sensor network, specifically a kind of underwater sound communication network OFDM chains
Road physical layer and MAC layer cross-layer communication method.
Background technology
The surface of the earth 70% is covered by ocean, and the vast oceans contain huge resource.In Global land resource day
It is becoming tight the today constantly deteriorated with environment, sight is turned to ocean, exploitation marine resources, Development of Marine warp by countries in the world one after another
Important planning direction of the Ji as each maritime state.Underwater sound communication network is the effective means for obtaining ocean environment parameter,
The aspects such as the detection of marine environmental monitoring, marine resources development, natural calamity early warning, harbour and offshore have highly important work
With.For some underwater acoustic networks, the requirement such as handling capacity, efficiency of transmission, propagation delay to network is higher, therefore research is efficient
Underwater sound wireless sensor network there is important Research Significance.
However, underwater acoustic channel is compared with terrestrial radio radio channel, with limited bandwidth and the analogous biography of data frame length
Sowing time prolongs and the features such as quick time-varying, causes that underwater sound wireless sensor network packet loss is high, propagation delay time is long, energy ezpenditure
Greatly, the low problem of network throughput.In order to solve the problem, in addition to being separately optimized each layer protocol of network, cross-layer protocol design
For optimization underwater acoustic network performance provides a kind of effective method.
Cross-layer protocol design of the main research based on physical layer and MAC layer of the invention, open report related to the present invention
Including：(the P.Xie and J.-H.Cui.R-MAC of bibliography 1:An Energy-Efficient MAC Protocol for
Underwater Sensor Networks[C].International Conf.on Wireless Algorithm,
Systems,and Applications(WASA 2007).Chicago,Illinois,USA,2007,pp:187-198.) carry
A kind of controllable RMAC agreements (RMAC-PC) of transimission power are gone out, RMAC have been improved by the cross layer design of MAC layer and physical layer
The energy efficiency of agreement.(J.M.Jornet, M.Stojanovic, and M.Zorzi.On the Joint Frequency of document 2
and Power Allocation in a Cross-Layer Protocol for Underwater Acoustic
Networks[C].IEEE J.Oceanic.Engineering.2010,Vol.35,No.4,pp:936-947.) for three-dimensional
Multihop network, it is proposed that a kind of cross-layer protocol design method of combined optimization physical layer, MAC layer and Internet improves channel frequently
Band utilization rate, adjusts transmission signal power, centre frequency and bandwidth, so as to reduce the energy of every bit according to network node density
Consumption.In the above documents, the quick time-varying of underwater acoustic channel is not accounted for the influence between physical layer and MAC layer and two layers
Between be closely connected.
The content of the invention
When the high packet loss caused present invention aim at a kind of underwater acoustic channel that can reduce complexity of offer and transmission long
Prolong problem, the underwater sound communication network OFDM Link Physical Layers for improving network throughput and system spectral efficiency lead to MAC layer cross-layer
Letter method.
The object of the present invention is achieved like this：
Step 1：Network node detects whether channel is busy by the way of virtual carrier sensing in wireless network communication, by interception data frame generation
For RTS/CTS handshake procedure collision frees, if nodal test is to data frame, judge whether this node is destination node, if
The non-destination node of this node, the then network for passing the data frame busy channel set of time node point in data frame frame head
It is NAV with vector, holding is mourned in silence and avoids conflict, after channel idle, node random back；
Step 2：If destination node unsuccessful demodulation data frame, node reverts back ack signal, while physical layer estimates channel
Information effective signal-to-noise ratio is ESNR, and ESNR is fed back into sending node by ack signal；
Step 3：If destination node demodulating data frame fail, and detect demodulation unsuccessfully caused by conflict, this
When destination node broadcast NACK control frames, definition NACK now is type I, is designated as NACK1；
Step 4：If destination node demodulating data frame fails, and detecting demodulation is badly drawn by channel circumstance
Rise, now destination node replys NACK control frames, and definition NACK now is Type II, is designated as NACK2, is included in NACK2
Channel time T shared by retransmitting data framebusyIt is PSNR with channel information pilot SNR；
Step 5：If destination node detection data frame fails, node does not make any reaction, for sending node,
ACK waits time-out；
Step 6：If sending node receives ack signal, represent that a upper data frame is successfully transmitted, then node carry out with
Machine is kept out of the way, and is ready for sending next data frame, and next frame data modulation parameter is determined by the ESNR for feeding back；
Step 7：If sending node receives NACK1 signals or ACK waits time-out, now node is moved back at random
Keep away, after back off time terminates, node sends the data frame with the repetition of former frame identical modulation parameter, when number of retransmissions is more than
During set maximum retransmission, the data frame is abandoned；
Step 8：If sending node receives NACK2 signals, the node carries out reduction of speed rate pair according to the PSNR of feedback
Data frame is retransmitted at once, after other child nodes listen to NACK2, the T in NACK2busyNAV vectors are set, keep mourning in silence
Avoid conflict.
The present invention can also include：
1st, the network node is detected whether channel is busy by the way of virtual carrier sensing in wireless network communication and specifically included：Design first
A kind of physical layer protocol data unit is PPDU frame structures, and PPDU includes lead code, frame head and the part of payload three, wherein frame
Head includes the channel time shared by current data frame Successful transmissions, is expressed as
Tbusy=Tdata+TACK+2Tdelay+Tprocess
Wherein, TdataRepresent data frame length, TACKRepresent ACK frame lengths, TdelayRepresent between source node and destination node
Propagation delay, TprocessThe time shared by signal transacting is represented, when other nodal tests to the data frame and unsuccessful demodulation
After frame head obtains the temporal information, node sets NAV vectors and keeps silent, it is to avoid collision, wherein propagation delay is at the beginning of network
Acquisition is measured by way of transmitting short message mutually between node during beginningization, and to time delay after each Successful transmissions data frame
Value is updated.
If the 2, the destination node unsuccessful demodulation data frame, node reverts back ack signal is specifically included：Work as destination node
After unsuccessful demodulation data frame, estimate that channel calculation effective signal-to-noise ratio ESNR, ESNR computational methods are as follows：
Wherein, s [k] is the data that k-th carrier wave of frequency domain sends, and z [k] is the data of k-th subcarrier reception of frequency domain,It is k-th channel frequency response of carrier estimation, SDThe set of the location index of data carrier is represented, due to data
Unsuccessful demodulation, so now s [k] is known, ESNR describes received signal strength using the data after equilibrium instead of pilot tone, makes an uproar
The inter-carrier interference that ambient noise, channel estimation errors and Doppler effect correction residual error cause is contained in sound, ESNR is used
In assessment channel status, after data are demodulated successfully, ESNR is fed back into source node by ack signal, be next data frame
The selection of modulation parameter provides foundation.
If the 3rd, destination node demodulating data frame failure, and detect demodulation and unsuccessfully caused by conflict, this
When destination node broadcast NACK1 control frames, specifically include：Destination node demodulates failure cause according to data frame, feeds back different
Control information, when demodulation fails what is caused by conflict, now retransmits in order to avoid next each node and causes conflict, purpose again
One NACK1 control frame of node broadcasts informs all nodes, shows that previous frame data there occurs conflict.
If the 4th, the destination node demodulating data frame failure, and detecting demodulation is badly drawn by channel circumstance
Rise, now destination node broadcast NACK2 control frames are specifically included：Destination node demodulates failure cause, feedback according to data frame
Different control information, when demodulation failure is badly caused by channel circumstance, node broadcasts NACK2 signals are included in the signal
Channel time T shared by retransmitting data framebusy, after other nodes receive NACK2 signals, learn in following Tbusy
In time, channel will be occupied, so that keep mourning in silence, and former sending node reduces speed and resends previous frame data immediately,
Pilot SNR PSNR is contained in NACK2 simultaneously, the information is used to help the suitable tune of sending node retransmission data frame selection
Parameter processed, PSNR computational methods are as follows：
Wherein, z [k] is the data of k-th subcarrier of frequency domain for receiving, SpAnd SNRespectively pilot frequency carrier wave and unloaded ripple
The set of location index.
5th, next frame data modulation parameter is determined to specifically include by the ESNR for feeding back：Physical layer uses OFDM modulation methods
Formula, by Joint regulation order of modulation, code rate and frequency diversity exponent number, realizes the data transfer of different rates, by three
The combination of individual parameter selects several groups of modulation parameters as data frame modulation parameter, the bit error rate or the Packet Error Ratio door according to setting
Limit, it is interval to obtain the corresponding ESNR of every group of parameter, modulation of the source node according to selected by the ESNR of feedback determines next frame data
Parameter.
6th, the PSNR according to feedback carries out reduction of speed rate and retransmits data frame at once to specifically include：When data demodulate mistake
When, using PSNR as channel performance assessment level, PSNR has reacted current channel conditions, and source node is known according to the PSNR of feedback
Data, so as to select to adapt to the modulation parameter of current channel condition, are carried out reduction of speed rate re-transmission by road current channel conditions.
The present invention by the information exchange of physical layer and MAC layer with it is shared, self-adaptative adjustment data transfer and medium are accessed
Scheme, so as to reach the purpose of optimization network performance.
Affairs underwater sound communication network cross-layer protocol design method of the present invention, can reduce the height that the underwater acoustic channel of complexity causes
Packet loss and transmission delay problem long, so as to effectively improve the spectrum efficiency of network throughput and system.
The device have the advantages that：
The cross-layer protocol mainly realizes data interaction between physical layer and MAC layer and shared, according to underwater acoustic channel situation,
Self-adaptative adjustment message transmission rate and automatic repeat request mechanism, when underwater acoustic channel is all right, using two-forty
OFDM modulation systems and improved CSMA/CA agreements, realize the data transfer of two-forty；When underwater acoustic channel situation is deteriorated at that time,
The data transfer probability of success is improved using the method for reducing speed；When underwater acoustic channel badly cannot extremely communicate, using what is kept out of the way
Method is waited and retransmitted；When data-bag lost, can intelligence differentiation data-bag lost reason, and carried out according to the reason for different
Retransmit or keep out of the way treatment accordingly.By physical layer and the cross layer design of MAC layer, under different channel situations, can be most
The utilization channel resource of limits, cannot be made full use of under high s/n ratio when solving traditional use fixed-rate transmission channel,
The problem of handling capacity dramatic decrease under low signal-to-noise ratio.
Brief description of the drawings
Fig. 1 is the Packet Error Ratio performance of different transmission mode
Fig. 2 is by the use of ACK as feedback link schematic diagram；
Fig. 3 is PPDU data frame structures；
Fig. 4 is improved CSMA/CA agreements basic flow sheet；
Fig. 5 a are cross layer design transmitting node flow chart；Fig. 5 b are cross layer design receiving node flow chart.
Specific embodiment
Citing below describes OFDM Link Physical Layers and MAC layer cross-layer design method and its advantage in detail.
Physical layer and MAC layer cross layer design, it is desirable to which physical layer can send parameter according to channel situation, Adaptive Modulation
, so as to realize the data transfer of different rates, in this process, it is related to selection, feedback link and the channel of modulation parameter
Assessment level etc., is illustrated to OFDM Adaptive Modulation and Coding and correlation technique first.
(1) OFDM Adaptive Modulation and Coding technology
A. modulation parameter selection
The core concept of Adaptive Modulation and Coding is：Ensureing the not sane performance of sacrificial system or the constant premise of Packet Error Ratio
Under, being changed according to wireless channel environment, the adjustment emission parameter of self adaptation changes traffic rate, to greatest extent using channel,
Realize the throughput-maximized of network.A kind of selection of self-adaptative adjustment emission parameter is exactly the modulation for selecting different parameters to combine
Scheme, the different group parameters of selection have different traffic rates, so as to adapt to the change of varying environment, this programme are given below
Modulation parameter selection scheme.
Modulation system mainly considers that BPSK, QPSK and 8PSK are modulated, i.e., order of modulation is respectively 2,3,4, and coding is using volume
Product coding, code rate is respectively 1/2,1/3,1/4, and frequency diversity exponent number is respectively 1,2,3, and frequency diversity number is 1 i.e. expression
Without diversity.The modulation parameter group that several combinations constitute candidate is selected in the selection of modulation parameter from this three groups of parameters, section
Point can reasonably select the modulation parameter of packet that will be transmitted according to the channel information of feedback.For three parameters, there is many
Kind of combination, but the combination for having two or the above has identical or close message transmission rate, therefore, it is main in text
By two kinds of criterion Selecting All Parameters：One is, when the combination of different parameters has identical message transmission rate, to select error code/bag
Rate performance is best；Two is that, when the combination of different parameters has close error code/bag rate performance, selection message transmission rate is most
Big.
The transmission mode and design parameter of the OFDM Adaptive Modulation and Coding scheme selections of table 1
According to parameters Choice Criteria, candidate parameter of 6 groups of parameters as OFDM Adaptive Modulation and Coding is have chosen altogether, respectively
Pattern 1~6 is defined as, as shown in table 1, signal frequency range is 4kHz~8kHz, message transmission rate to the specific parameter chosen
Scope is 0.685kbps~5.950kbps.The Packet Error Ratio curve of different transmission mode is as indicated with 1.
B. feedback link
The Main Function of feedback link is that the channel information that destination node is obtained is passed into source node, and source node is according to anti-
The channel information self-adaptative adjustment transmitting terminal modulation parameter of feedback, so that adaptive channel environment.To be solved two ask feedback link
Topic is：One be how feedback information, two be feed back what information.In the present invention, the performance evaluation that destination node will mainly be estimated
Parameter effective signal-to-noise ratio (ESRN) feeds back to source node.
The mac-layer protocol of present invention design does not include RTS/CTS control frames, and simultaneously using two kinds of controls of ACK and NACK
Frame, so the channel information that destination node is estimated feeds back to source node by ack/nack signal, as shown in Fig. 2 destination node
Channel information is obtained according to data frame, this information is then fed back into source node by ACK/NACK, source node is according to feedback
Channel parameter determines the modulation parameter of next data frame.
C. channel estimating criterion
Adaptive Modulation and Coding technology mainly includes both sides content, is on the one hand the acquisition of channel information, by letter
Road estimates etc. that technology accurately obtains current channel information, accurate with certain channel indicating mode or Performance Evaluation criterion and have
The situation of the reaction channel of effect；On the one hand it is the adaptively selected of modulation parameter, according to the channel environmental information for obtaining, self adaptation
Adjustment emission parameter with the change of adaptive channel.The selection scheme of modulation parameter is shown above, then how is node
Corresponding modulation parameter, the i.e. On The Choice of channel estimating criterion are selected according to channel information.Performance Evaluation criterion is being determined
Afterwards, it is assumed that in the case where ensureing to be not higher than certain Packet Error Ratio, according to the error performance of different modulating parameter, it may be determined that correspondence
Performance Evaluation criterion under Packet Error Ratio thresholding, such as received signal to noise ratio may thereby determine that the corresponding channel of different modulating parameter
Assessment is interval, and the channel parameter according to feedback can determine the modulation parameter that next packet is selected.
Conventional Performance Evaluation criterion has input signal-to-noise ratio (Input SNR, ISNR), pilot SNR (Pilot at present
SNR, PSNR) and effective signal-to-noise ratio (Effective SNR, ESNR) etc., ISNR is the signal power and noise that receiver is received
The ratio of power, can be expressed as
Wherein, noise when y [n] and v [n] represent the signals and associated noises of time domain reception with no signal respectively.ISNR be from
The rough relation for describing signal and noise, and accurate description underwater acoustic channel that cannot be comprehensive is to the shadow of OFDM symbol
Ring, including the ICI that Doppler causes etc., and when signal to noise ratio is smaller, the application condition that the method is estimated is big.
Pilot datas and unloaded wave number according to estimates channel interference to OFDM symbol of the PSNR using frequency domain, pilot data are retouched
The intensity of signal is stated, empty carrier data describes the size of noise and interference, and pilot SNR can be expressed as
Wherein, z [k] is the data of k-th subcarrier of frequency domain for receiving, SpAnd SNRespectively pilot frequency carrier wave and unloaded ripple
The set of location index, PSNR is while noise jamming is considered, it is also contemplated that due to the inter-carrier interference that Doppler causes.No
When there is Doppler or removing Doppler completely, the secondary lobe interference of other carrier waves is zero point at unloaded ripple, therefore unloaded ripple
Noise item is only included, when there is residual Doppler, the interference of other carrier waves is not zero at unloaded ripple.So, PSNR can be with
Reflect the influence of noise and residual Doppler simultaneously, but PSNR is calculated before equilibrium, does not account for the shadow on many ways
Ring, therefore still cannot comprehensively describe channel information.
ESNR is using the data estimation signal to noise ratio after unsuccessful demodulation.If launch and k-th subcarrier data difference of reception
It is s [k] and z [k],It is the channel frequency response of k-th subcarrier of estimation, then has
Wherein, v [k] not only contained and disturbed between ambient noise and residual carrier, while further comprises channel estimation errors
The interference for bringing, ESNR can be expressed as
Wherein, SDThe set of the location index of data carrier is represented, due to data unsuccessful demodulation, so now s [k]
It is known.Different from PSNR, ESNR describes received signal strength using the data after equilibrium instead of pilot tone, is included in noise item
The inter-carrier interference that ambient noise, channel estimation residual error and Doppler effect correction residual error cause, thus more fully
Describe channel environmental information, different channel circumstances are assessed, with good uniformity.But the premise of the algorithm is to need
Want unsuccessful demodulation data, obtain the data message for sending, when data demodulation failure is sent, ESNR will be smaller than actual value.
(2) improved CSMA/CA agreements
CSMA/CA agreements carry out channel booking by exchanging RTS and CTS control frames, so as to effectively avoid data frame
Conflict, improves network throughput.For terrestrial radio network, propagation delay is very small, much smaller than the length of data frame,
Can ignore.But for underwater sound wireless network, propagation delay is very long, can be comparable with data frame length, although pass through
Handshake procedure can effectively reduce collision, but the exchange RTS and CTS process busy channel times are very long, reduce channel usage
Rate.Therefore the present invention proposes a kind of improved CSMA/CA agreements, and the agreement does not use the RTS/CTS handshake to carry out channel
Reservation, but the method virtually intercepted is used, the data frame for intercepting other nodes judges whether channel is busy, and increased two
NACK control frames are planted, for notifying that source node data frame demodulates failure cause, the PHY/MAC cross-layers that the design is mainly below set
Meter is serviced.
, by exchanging RTS/CTS control frame reserve channels, other child nodes are by controlling the frame signal can be with for CSMA/CA agreements
Know current data frame transmission take channel time, but propose improved CSMA/CA agreements, do not use handshake pre-
About channel, but judge whether channel is busy by interception data frame, while the method for also using virtual carrier sensing in wireless network communication is intercepted
Channel.Before specific agreement is introduced, physical layer protocol data unit (PPDU, the PLCP Protocol of proposition is first introduced
Data Unit) frame structure, namely the physical layer signal of actual transmissions data frame structure.
PPDU data frames are main by lead code (Preamble), frame head (Header) and payload (Payload) three
It is grouped into, as shown in figure 3, lead code is mainly used in waking up receiving device, makes it synchronous with signal is received, from LFM letters in text
Number as lead code.It is exactly frame head (PLCP Header) after lead code terminates, physical layer modulation parameter is included in frame head, such as passes
Defeated data length, modulation coding mode etc., receiver will select when decoding process and decision terminate according to these parameters
Data receiver.Sending node address, receiving node address are further comprises in the frame head and the channel of data frame occupancy is transmitted
Time span, i.e. two-way time.The frame head similar to a short RTS claim frame, when node listens to the data frame and obtains
After information in frame head, judge whether the data frame belongs to this node, if this node is destination node, continue behind demodulation
Payload, otherwise, then stop demodulation payload below, and two-way time in frame head sets the node
NAV values, while holding is mourned in silence.Last part is payload or frame main body, and the part is modulated using OFDM, specific length
It is variable according to transmission data length, and modulation parameter is according to channel circumstance self-adaptative adjustment.
Propose improved CSMA/CA agreements basic flow sheet as shown in figure 4, when node have data to send when, first
Judge whether channel is idle, and whether it is mainly zero by decision node NAV in itself that whether channel is idle, if zero table
Show channel idle, otherwise represent busy.If channel idle, and the competition window of node is zero, then send data frame, if other are sub
Node listens to the data frame, then the two-way time in frame head sets the NAV vectors of node, and holding is mourned in silence.If herein
Period node has data is activation, then postpone to send, and when NAV is zero, the node is kept out of the way, and when the channel is idle, keeps out of the way meter
Number device is gradually reduced, and when channel is busy, then freezes the counter, until when Counter Value is zero, starting to send data frame.Such as
Fruit packet is correctly demodulated, then destination node is replied ACK confirmation packets and correctly transmitted.When two or the above node simultaneously
Send data frame and transmission time interval is less than the time interval to that can listen to, then collided in receiving terminal, cause number
Demodulated according to frame and failed, now receiving node can detect data frame conflict, while broadcast a NACK frame signal (being defined as
NACK1), notify that sending node data frame transfer failure, and bust this cause due to colliding.When in channel only one
Individual data frame transfer, but when badly causing data frame transfer to fail due to channel circumstance, the same reply one of receiving node
NACK frame signals (are defined as NACK2), notify sending node data frame transfer unsuccessfully because channel circumstance badly causes.
(3) physical layer/MAC layer cross layer design
Consider centralized network topological structure, network is made up of a host node and several child nodes.Physical layer (PHY)
Main to use OFDM Adaptive Modulation and Coding technologies, mac-layer protocol uses improved CSMA/CA agreements, PHY/MAC cross layer designs
Main thought is：The channel information of estimation is passed to MAC layer by PHY, and detects failure cause when data frame transfer fails,
MAC layer selects suitable transport parameters for physical layer according to channel information, and corresponding according to the design of data frame transfer failure cause
Keep out of the way/ARQ mechanism, increase data frame and retransmit the probability of success, and reduce propagation delay time, so as to improve network throughput.
Cross layer design transmitting node and receiving node flow chart are as shown in figure 5, first, introducing receiving node and receiving data frame
Process.Receiving node persistently detects lead code, judges whether to receive data frame, the main method detection related using copy
Lead code, after detecting lead code, receiving node demodulates frame head and obtains the length of payload demodulation parameter and data frame, and
Proceed demodulation, meanwhile, receiving node keeps detection lead code.After sending node transmitting data frame, for receiving node
State can be divided into following four situation：
1. detect data frame and correctly demodulate, ACK acknowledgement frames are replied, while estimating channel information ESNR, this is believed
Breath feeds back to sending node by ack signal；
2. data frame is detected, but demodulating data frame fails, and detect that demodulation failure cause is caused by conflict,
NACK control frames are now broadcasted, definition NACK now is type I, is designated as NACK1.
3. data frame is detected, but demodulating data frame fails, and data frame demodulation failure cause is by channel circumstance
Severe to cause, such as signal to noise ratio is low, many ways and doppler interference are serious etc., now reply NACK signal, and definition is now
NACK is Type II, is designated as NACK2, modulation parameter when including that PSNR is used to indicate to retransmit simultaneously in NACK2 signals.
4. data frame is not detected by, and detection failure cause includes that burst noise or interference cause preamble detection to fail, count
Cause detection unsuccessfully etc. according to frame conflict, now receiving node does not do any response, for sending node, then ACK waits time-out.
For sending node, after data frame is sent, the ack/nack signal replied, similarly, sending node are waited
State can be divided into following three kinds of situations：
1. ack signal is received, represents that a upper data frame is successfully transmitted, then node carries out random back, and prepares hair
Next data frame is sent, next frame data modulation parameter is determined by the ESNR for feeding back.
2. receive NACK1 signals or ACK and wait time-out, now node carries out random back, then with previous frame
Identical modulation parameter repeats to send the frame data, when number of retransmissions is more than 3, abandons the data frame.
3. NACK2 signals are received, admission control is represented because channel circumstance badly causes, if now node is moved back
Keep away and with former speed retransmitting data frame, it is low to retransmit the probability of success, and keeping out of the way can cause the propagation delay time to increase, and reduce the profit of channel
With rate.Therefore, cause if admission control is channel, node reduces speed at once again according to the channel information of feedback
The frame data are transmitted, the re-transmission probability of success can be improved, and reduce propagation delay time, other nodes are protected after listening to NACK2 signals
Hold and mourn in silence.
Claims (7)
1. a kind of underwater sound communication network OFDM Link Physical Layers and MAC layer cross-layer communication method, it is characterized in that：
Step 1：Network node detects whether channel is busy by the way of virtual carrier sensing in wireless network communication, is replaced by interception data frame
RTS/CTS handshake procedure collision frees, if nodal test is to data frame, judge whether this node is destination node, if this
The non-destination node of node, the then network allocation for passing the data frame busy channel set of time node in data frame frame head
Vector is NAV, and holding is mourned in silence and avoids conflict, after channel idle, node random back；
Step 2：If destination node unsuccessful demodulation data frame, node reverts back ack signal, while physical layer estimating channel information
Effective signal-to-noise ratio is ESNR, and ESNR is fed back into sending node by ack signal；
Step 3：If destination node demodulating data frame fails, and detects demodulation and is unsuccessfully caused by conflict, now mesh
Node broadcasts NACK control frames, definition NACK now is type I, is designated as NACK1；
Step 4：If destination node demodulating data frame fails, and detecting demodulation is badly caused by channel circumstance
, now destination node broadcast NACK control frames, definition NACK now is Type II, is designated as NACK2, comprising weight in NACK2
Pass channel time T shared by data framebusyIt is PSNR with channel information pilot SNR；
Step 5：If destination node detection data frame fails, node does not make any reaction, for sending node, ACK
Wait time-out；
Step 6：If sending node receives ack signal, represent that a upper data frame is successfully transmitted, then node is moved back at random
Keep away, and be ready for sending next data frame, next frame data modulation parameter is determined by the ESNR for feeding back；
Step 7：If sending node receives NACK1 signals or ACK waits time-out, now node carries out random back, moves back
After the time of keeping away terminates, node sends the data frame with the repetition of former frame identical modulation parameter, when number of retransmissions is more than set
During the maximum retransmission put, the data frame is abandoned；
Step 8：If sending node receives NACK2 signals, the node carries out reduction of speed rate to data according to the PSNR of feedback
Frame is retransmitted at once, after other child nodes listen to NACK2, the T in NACK2busyNAV vectors are set, and holding is mourned in silence and avoided
Conflict.
2. underwater sound communication network OFDM Link Physical Layers according to claim 1 and MAC layer cross-layer communication method, its feature
It is：The network node is detected whether channel is busy by the way of virtual carrier sensing in wireless network communication and specifically included：A kind of thing is designed first
Reason layer protocol data cell is PPDU frame structures, and PPDU includes lead code, frame head and the part of payload three, and wherein frame head includes
Channel time shared by current data frame Successful transmissions, is expressed as
Tbusy=Tdata+TACK+2Tdelay+Tprocess
Wherein, TdataRepresent data frame length, TACKRepresent ACK frame lengths, TdelayRepresent the biography between source node and destination node
Sowing time prolongs, TprocessThe time shared by signal transacting is represented, when other nodal tests to the data frame and unsuccessful demodulation frame head
After obtaining the temporal information, node sets NAV vectors and keeps silent, it is to avoid collision, wherein propagation delay is in netinit
When measuring acquisition by way of transmission short message mutually between node, and time delay value is entered after each Successful transmissions data frame
Row updates.
3. underwater sound communication network OFDM Link Physical Layers according to claim 1 and MAC layer cross-layer communication method, its feature
It is：If destination node unsuccessful demodulation data frame, node reverts back ack signal is specifically included：When destination node unsuccessful demodulation number
After frame, estimate that channel calculation effective signal-to-noise ratio ESNR, ESNR computational methods are as follows：
Wherein, s [k] is the data that k-th carrier wave of frequency domain sends, and z [k] is the data of k-th subcarrier reception of frequency domain,For
K-th channel frequency response of carrier estimation, SDThe set of the location index of data carrier is represented, because data are successfully solved
Adjust, so now s [k] is known, ESNR describes received signal strength using the data after equilibrium instead of pilot tone, in noise item
The inter-carrier interference that ambient noise, channel estimation errors and Doppler effect correction residual error cause is contained, ESNR is used to assess
Channel status, after data are demodulated successfully, source node is fed back to by ESNR by ack signal, is next data frame modulation ginseng
Several selections provides foundation.
4. underwater sound communication network OFDM Link Physical Layers according to claim 1 and MAC layer cross-layer communication method, its feature
It is：If destination node demodulating data frame fail, and detect demodulation unsuccessfully caused by conflict, now destination node is wide
NACK1 control frames are broadcast, is specifically included：Destination node demodulates failure cause according to data frame, feeds back different control information, works as solution
Adjust what failure was caused by conflict, now retransmitted in order to avoid next each node and cause conflict again, destination node broadcasts one
NACK1 control frames inform all nodes, show that previous frame data there occurs conflict.
5. underwater sound communication network OFDM Link Physical Layers according to claim 1 and MAC layer cross-layer communication method, its feature
It is：If destination node demodulating data frame fails, and detects demodulation and is unsuccessfully badly caused by channel circumstance, now mesh
Node broadcasts NACK2 control frames, specifically include：Destination node demodulates failure cause according to data frame, feeds back different controls
Information, when demodulation failure is badly caused by channel circumstance, node broadcasts NACK2 signals contain re-transmission data in the signal
Channel time T shared by framebusy, after other nodes receive NACK2 signals, learn in following TbusyIn time, channel
Will be occupied, so that keep mourning in silence, and former sending node reduces speed and resends previous frame data immediately, while in NACK2
Pilot SNR PSNR is contained, the information is used to help sending node retransmission data frame and selects suitable modulation parameter, PSNR
Computational methods are as follows：
Wherein, z [k] is the data of k-th subcarrier of frequency domain for receiving, SpAnd SNThe respectively position of pilot frequency carrier wave and unloaded ripple
The set of index.
6. underwater sound communication network OFDM Link Physical Layers according to claim 1 and MAC layer cross-layer communication method, its feature
It is that ESNR of the next frame data modulation parameter by feeding back determines to specifically include：Physical layer uses OFDM modulation systems, passes through
Joint regulation order of modulation, code rate and frequency diversity exponent number, realize the data transfer of different rates, by three parameters
Combination selects several groups of modulation parameters as data frame modulation parameter, according to the bit error rate or Packet Error Ratio thresholding of setting, obtains
The corresponding ESNR of every group of parameter is interval, modulation parameter of the source node according to selected by the ESNR of feedback determines next frame data.
7. underwater sound communication network OFDM Link Physical Layers according to claim 1 and MAC layer cross-layer communication method, its feature
It is that the PSNR according to feedback carries out reduction of speed rate and retransmit data frame at once to specifically include：When data demodulate mistake, use
Used as channel performance assessment level, PSNR has reacted current channel conditions to PSNR, and source node is known currently according to the PSNR of feedback
Data, so as to select to adapt to the modulation parameter of current channel condition, are carried out reduction of speed rate re-transmission by channel conditions.
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