CN106230767A - A kind of based on double Block Error Rates with the adaptive modulation coding method of signal to noise ratio difference - Google Patents

A kind of based on double Block Error Rates with the adaptive modulation coding method of signal to noise ratio difference Download PDF

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CN106230767A
CN106230767A CN201610786915.9A CN201610786915A CN106230767A CN 106230767 A CN106230767 A CN 106230767A CN 201610786915 A CN201610786915 A CN 201610786915A CN 106230767 A CN106230767 A CN 106230767A
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per
mcs
snr
section
thresholding
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CN106230767B (en
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程郁凡
刘小玲
庄倩倩
唐万斌
王小青
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University of Electronic Science and Technology of China
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2697—Multicarrier modulation systems in combination with other modulation techniques
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2626—Arrangements specific to the transmitter only
    • H04L27/2627—Modulators
    • H04L27/2628—Inverse Fourier transform modulators, e.g. inverse fast Fourier transform [IFFT] or inverse discrete Fourier transform [IDFT] modulators
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2649—Demodulators
    • H04L27/265—Fourier transform demodulators, e.g. fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators

Abstract

The invention belongs to communication technical field, relate to a kind of based on double Block Error Rates with the adaptive modulation coding method of signal to noise ratio difference.The present invention uses total PER that system is current, section PER and SNR difference is as the foundation judged, under conditions of system meets transmitting, upper according to the channel condition section of being adaptively adjusted PER, Lower Threshold, the situation of change of more reasonably adaptive channel during communication data transfer, change the MCS of system in real time, the total Block Error Rate of system is made to meet index request, thus it is simple to have realization, strong to channel adaptability, system transfers performance is good, system spectral efficiency can be promoted further while guaranteeing information transmission reliability, be conducive to the feature such as actual application of engineering.

Description

A kind of based on double Block Error Rates with the adaptive modulation coding method of signal to noise ratio difference
Technical field
The invention belongs to communication technical field, relate to a kind of Adaptive Modulation based on double Block Error Rates and signal to noise ratio difference and compile Code method.
Background technology
As the key technology of future communications, OFDM (Orthogonal Frequency Division Multiplexing, OFDM) technology becomes the focus in Communication Studies field, by OFDM technology and Adaptive Modulation It is an important topic of this research field that coding techniques combines.In wireless communications, the characteristic of channel is to become in time Changing, the most how effectively utilizing limited band resource is an important research direction.Adaptive Modulation and Coding is one Planting the technology improving the availability of frequency spectrum, it can change the modulating-coding ginseng of system adaptively according to the change of the characteristic of channel Number, to reach improve system spectral efficiency and maximize the purpose of average throughput.
Traditional Adaptive Modulation and Coding algorithm (M.Moustafa.Threshold decision based on fixed threshold adaptive modulation and coding schemes for OFDM communications[C].Proceedings of the Sixth international conference on Wireless and Optical Communications Networks, 2009,133-136), with channel quality signal to noise ratio (Signal to Noise Ratio, SNR) as sentencing Disconnected foundation, typically required by arranging MCS (Modulation and Coding Scheme, modulation coding mode) switching SNR threshold value, compared with estimating the SNR that obtains, and then provide MCS index value.Fig. 1 be traditional based on fixed threshold from Adapt to the ofdm system structured flowchart of modulating-coding, in this system, transmitter: the information bit channel of user is compiled Code bit, coded-bit bit after channel interleaving is interweaved, the bit after intertexture obtains modulation letter through QAM modulation Number vector, the signal after modulation treatment processes laggard row through OFDM symbol generation, D/A conversion, up-conversion etc. and launches；After transmitting Signal arrives receiver through wireless channel；Receiver: the signal that receiver will receive, through down-converted, A/D conversion Obtaining base band (reception) signal, base band (reception) signal obtains data signal by solving OFDM symbol process, and data signal is through QAM Being reduced to the bit signal after launching after demodulation, channel deinterleaving, channel decoding, this bit signal is again through BLER statistic Process can obtain the Block Error Rate situation of system；The data signal obtained through solving OFDM symbol to process can through signal-to-noise ratio (SNR) estimation To obtain the SNR thresholding needed for signal SNR, the SNR thresholding output switching MCS estimated, SNR thresholding and the SNR warp estimated MCS selection obtains the MCS of system work next time after processing, deliver to chnnel coding, QAM modulation and QAM demodulation, channel respectively and translate Code, the Adaptive Modulation and Coding of completion system processes.
Above-mentioned OFDM Adaptive Modulation and Coding mode based on fixed threshold, according to the change of channel quality, changes adaptively The MCS of change system, under the constraints meeting error rate of system index, if channel conditions is preferable, just selects high-order MCS, if Channel conditions is poor, then selecting low order MCS, its MCS is to be determined by the SNR thresholding of the SNR estimated and setting, i.e. affects MCS Main two factors selected are: one is the setting of SNR thresholding, and two is SNR estimation difference.Have an advantage in that when SNR estimates very Time accurately, system Block Error Rate and system spectral efficiency better performances, but there is obvious shortcoming in the method: one is that needs are carried out SNR estimates thus adds system complexity；Two is the accuracy that the error that SNR estimates affects that MCS selects；Three is SNR thresholding Difficulty is set, because in the wireless channel environment of change, the characteristic of channel changes over time, at different channel conditions Under, SNR thresholding required by the identical Block Error Rate of system also differs, it is difficult to arrange preferable SNR thresholding；Thus this type of method is deposited Selection difficulty in SNR threshold value is big, SNR estimation difference is big on systematic function impact, adaptive modulation coding method is complicated, frequently The defects such as spectrum efficiency is low.
Two-parameter self-adaptive modulation method (the two-parameter self-adaptive modulation method of a kind of orthogonal FDM communication system, Application number: 201410263702.9) using two-parameter as the foundation adjusted, according to total Block Error Rate (the Packet Error received Rate, PER) and section Block Error Rate draw MCS index value.Fig. 2 is the ofdm system structured flowchart of two-parameter Adaptive Modulation, and this is In system, transmitter: the information bit channel coding of user obtains coded-bit, and coded-bit is interweaved through channel interleaving After bit, the bit after intertexture obtains modulated signal vector through QAM modulation, and the signal after modulation treatment is raw through OFDM symbol One-tenth, D/A conversion, up-conversion etc. process laggard row and launch；Signal after transmitting arrives receiver through wireless channel；Receiver: The signal that receiver will receive, obtains base band (reception) signal, base band (reception) signal through down-converted, A/D conversion Obtaining data signal by solving OFDM symbol process, data signal is reduced after QAM demodulation, channel deinterleaving, channel decoding For the bit signal after launching, this bit signal can obtain total PER and the section PER feelings of system again through BLER statistic process Condition；Total PER index provides total PER performance indications of system, processes, through BLER statistic, total PER, section PER and the warp calculated total The PER performance requirement that PER index is given obtains next time after selecting based on biparametric Adaptive Modulation and Coding mode to process The MCS of system work, delivers to chnnel coding, QAM modulation and QAM demodulation, channel decoding, the Adaptive Modulation of completion system respectively Coded treatment.
Above-mentioned based on biparametric OFDM adaptive modulation coding method and OFDM Adaptive Modulation based on fixed threshold Coded method is compared, exist need not to estimate SNR and arrange SNR thresholding, more adapt to different channel circumstance, realize the simplest Etc. advantage, but the method still has the disadvantage that and is more suitable for systematic function change slowly without chnnel coding communication system, Having in the wireless communication system of chnnel coding, under certain MCS, error rate of system declines quickly, if only along with the increase of SNR Depend on total PER and section PER to adjust MCS, ping-pong may be produced at some SNR zero boundary point, cause MCS index value Return concussion, affect the error bit ability of system.
Summary of the invention
To be solved by this invention, it is simply that to provide a kind of based on double Block Error Rates and the Adaptive Modulation and Coding of signal to noise ratio difference Method, the method total PER based on system, section PER and the Adaptive Modulation of SNR difference (Δ SNR) three parameter completion systems Coding, and use the Δ SNR thresholding of adaptive PER thresholding and robust, to overcome tradition fixed threshold method in different nothings SNR thresholding under line channel circumstance arranges the problem of difficulty, and can overcome based on biparametric adaptive modulation coding method MCS ping-pong, thus reach optimize Adaptive Modulation and Coding, be effectively improved the performance of system, guaranteeing communication system number According to promoting the purposes such as system spectral efficiency while transmission reliability further.
The solution of the present invention is under conditions of the basic procedure holding of OFDM transmitter and operation of receiver is constant, In the Adaptive Modulation and Coding processing module based on double Block Error Rates and SNR difference of system, the total Block Error Rate index with system is wanted Asking as retraining, employing total PER of system, section PER and Δ SNR these three parameter are as the foundation of adjustment MCS, at communication process Change the MCS of system the middle change real-time adaptive according to channel, thus realize its goal of the invention.
Now employing of the present invention based on double Block Error Rates and the principle of the adaptive modulation coding method of SNR difference and is depended on According to being described below:
Fig. 3 is present invention ofdm system based on double Block Error Rates and the Adaptive Modulation and Coding of SNR difference functional-block diagram, Block Error Rate (PER) statistical module can get the current total PER of system and section PER, and SNR estimation module can get real-time SNR and estimates Evaluation also calculates difference DELTA SNR between last time estimated value, is transported to Adaptive Modulation and Coding resume module, the tune of its output System, the coded system coding of channel again, QAM modulation, QAM solve and are in harmonious proportion channel decoding process to change current MCS in real time.
The modulation system that the present invention uses includes: BPSK, QPSK, 16QAM, 64QAM, corresponding order of modulation is followed successively by 2, 4、16、64；Chnnel coding uses Turbo coding, including three kinds of code checks: 1/3,1/2 and 2/3, so has 12 kinds of MCS combinations, Sort from low to high according to spectrum efficiency, produce 12 MCS index values；In simulations, according to actually measured error performance, Two performances index value closely only retains one, finally have selected 8 MCS indexes；Each dispatching cycle updates MCS index value, corresponds to certain modulation system and coded system, thus adjusts MCS；Under certain signal to noise ratio, MCS index value Often reducing one-level, the rate of information throughput will reduce, system spectral efficiency also can reduce, but PER can reduce；When MCS index value During increase, the rate of information throughput will improve, system spectral efficiency also can increase, but PER can increase；Therefore the essence of the present invention It is: when total PER and section PER are bigger to reduce PER by reducing MCS index, it is ensured that system transfers performance, but system can be reduced System spectrum efficiency；When total PER and section PER are less, and Δ SNR more than thresholding time then raise MCS index improve system spectrum Efficiency, and ensure system transfers performance, avoid the ping-pong of MCS simultaneously；Remaining situation does not the most adjust MCS index value；Adjust Purpose be make system under meeting total PER indicator conditions, select be best suitable for current radio channel MCS index with reach system frequency The maximization of spectrum efficiency.
In order to describe present disclosure easily, first some parameters are illustrated:
Table 1 parameter declaration
The technical scheme is that a kind of based on double Block Error Rates with the adaptive modulation coding method of signal to noise ratio difference, It is characterized in that, comprise the following steps:
S1, parameter are arranged: according to the reliability requirement of system, the upper and lower threshold value of total PER of initialization system, in section PER, Lower Threshold initial value, section PER thresholding adjusts step value, and Δ SNR thresholding is Δ SNRth, initialize MCS index value；
S2, reception system current PE R: receive system currently total PER and section PER that system BLER statistic module is sent here；
S2, calculating signal to noise ratio difference: current SNR value SNR sent here according to signal-to-noise ratio (SNR) estimation moduleiWith the last time preserved SNR estimated value SNRi-1, calculating current signal difference DELTA SNR: Δ SNR=SNRi-SNRi-1, and update SNRi-1: SNRi-1= SNRi；Subscript i is the natural number more than or equal to 1；
S4, self-adaptative adjustment MCS and section PER thresholding: according to system currently total PER, section PER and Δ SNR, and preset Total upper and lower thresholding of PER, the upper and lower thresholding of section PER, section PER thresholding adjusts step value and Δ SNR thresholding, self-adapted adjustment system MCS, obtains new MCS, the simultaneously upper and lower thresholding of the section of being adaptively adjusted PER, if the MCS index value after current adjustment is Mi；Tool Body method is:
S41, judge the relation of total PER and the upper and lower thresholding of total PER, if total PER is less than total PER Lower Threshold, forward S42 to, If total PER is between the upper and lower thresholding of total PER, forward S43 to, if total PER is more than total PER Upper threshold, forward S44 to；
S42, total PER are less than the process of total PER Lower Threshold: when section PER is less than section PER Lower Threshold, if Mi-1It not the highest Rank, and last MCS is not to lower or last MCS is to lower Δ SNR > Δ SNR simultaneouslyth, then MCS raises one-level；The section of working as When PER is between the upper and lower thresholding of section PER, raise the upper and lower threshold value of section PER, if Mi-1It not under high-order and MCS are not Tune, Δ SNR > Δ SNRthTime, MCS raises one-level；When section PER is more than section PER Upper threshold, raise the upper and lower threshold value of section PER, MCS is constant；Then go to S45；
S43, the total PER process between the upper and lower thresholding of total PER: when section PER is less than section PER Lower Threshold, lower section The upper and lower threshold value of PER, if Mi-1High-order, and MCS be not lower, Δ SNR > Δ SNRthTime, MCS raises one-level；The section of working as When PER is between the upper and lower thresholding of section PER, do not adjust；When section PER is more than section PER Upper threshold, raise the upper and lower door of section PER Limit value, if Mi-1Not being lowest-order, MCS lowers one-level；Then go to S45；
S44, total PER are more than the process of total PER Upper threshold: when section PER is less than section PER Lower Threshold, in downward section PER, Lower threshold, MCS is constant；When section PER is between the upper and lower thresholding of section PER, lower the upper and lower threshold value of section PER, if Mi-1No Being lowest-order, MCS lowers one-level；When section PER is more than section PER Upper threshold, if Mi-1Not being lowest-order, MCS lowers one-level；So After forward S45 to；
S45, change flag Flag of calculating MCS index valuemcsIf: Mi>Mi-1, then Flagmcs=1；If Mi=Mi-1, Then Flagmcs=0；If Mi<Mi-1, then Flagmcs=-1；Update Mi-1: Mi-1=Mi；Wherein, Flagmcs=1: represent on MCS Adjust, Flagmcs=0: represent that MCS keeps constant, Flagmcs=-1: represent that MCS lowers；
S46: output adaptive adjustment result: current MCS index value Mi, MCS change flag Flagmcs, section after adjustment PER Lower Threshold PERsl, section PER Upper threshold PER after adjustmentsu；
S5, update system MCS: QAM modulation that system of being delivered to by new MCS is made a start and Turbo coding module, and deliver to receive The QAM of end solves mediation Turbo decoding module, and transmitting-receiving updates modulation coding mode simultaneously；
Whether S6, the communication of judging terminate: if communication process terminates, forward S7 to, otherwise forward S2 to；
S7, MCS adjust and terminate.
Further, raise in section PER described in step S42, S43, S44, thresholding method particularly includes:
Raise section PER Lower Threshold PERsl: PERsl=min (PERsl(1+FPER),0.2PERtu)；
Raise section PER Upper threshold PERsu: PERsu=min (10PERsl,PERtu)；
Lower in section PER described in step S42, S43, S44, thresholding method particularly includes:
Lower section PER Lower Threshold PERsl: PERsl=max (PERsl(1-FPER),10-6)；
Lower section PER Upper threshold PERsu: PERsu=min (10PERsl,PERtu)。
Beneficial effects of the present invention is, the present invention uses current total PER, section PER and the SNR difference of system as judgement Foundation, under conditions of system meets transmitting, according to the upper and lower thresholding of the channel condition section of being adaptively adjusted PER, The situation of change of more reasonably adaptive channel during communication data transfer, changes the MCS of system in real time, makes the total Block Error Rate of system Meet index request, thus have that realization is simple, strong to channel adaptability, system transfers performance is good, can guarantee that information is transmitted Promote system spectral efficiency while reliability further, be conducive to the feature such as actual application of engineering.
Accompanying drawing explanation
Fig. 1 is tradition Adaptive Modulation and Coding ofdm system schematic diagram based on fixed threshold；
Fig. 2 is based on biparametric Adaptive Modulation and Coding ofdm system schematic diagram；
Fig. 3 is present invention Adaptive Modulation and Coding based on double Block Error Rates and SNR difference ofdm system schematic diagram；
Fig. 4 is that the present invention is based on double Block Error Rates and the flow diagram of the adaptive modulation coding method of SNR difference；
Fig. 5 is self-adaptative adjustment MCS and the detailed annotation of section PER thresholding in Fig. 4；
Fig. 6, Fig. 7 are the specific embodiment of the invention and tradition Adaptive Modulation and Coding based on fixed threshold respectively Ofdm system is simulation run under additive white Gaussian noise channel (Additive White Gaussian Noise, AWGN) The performance comparison schematic diagram of system bit error rate and information source average information rate.
Fig. 8, Fig. 9 are the specific embodiment of the invention and tradition Adaptive Modulation and Coding based on fixed threshold respectively Ofdm system maximum Doppler expand to the extension vehicle channel model of 70Hz (Extended Vehicular A model, The system bit error rate of simulation run under EVA) and the performance comparison schematic diagram of information source average information rate.
Detailed description of the invention
Below in conjunction with the accompanying drawings and embodiment, technical scheme is described in detail:
Present embodiment launching technique (flow process), method of reseptance (flow process) are identical with background technology, use ofdm system, letter Road coding uses Turbo coded system, and modulation system is BPSK, QPSK, 16QAM, 64QAM, between coding and modulation module Adding the spread spectrum of 15 times, modulation coding mode uses based on double Block Error Rates and the Adaptive Modulation and Coding of SNR difference, MCS rope Drawing table as shown in the table, wherein channel information speed is the transfer rate of modulation bit, information source information speed be consider spread spectrum, The transfer rate of the information source information bit after pilot tone and synchronization overhead.
Table 2MCS indexes
Below in conjunction with embodiment and accompanying drawing, describe technical scheme in detail.
S1, parameter are arranged: according to the reliability requirement of system, total PER Upper threshold PER of initialization systemtuBe 0.1, total PER Lower Threshold PERtlIt is 0.0001, section PER Lower Threshold PERslInitial value is 0.01, section PER Upper threshold PERsuInitial value is 0.1, section PER Thresholding adjusts step-length FPERIt is 0.5, Δ SNRthIt is set to 2.5dB (in order to reduce implementation complexity, according to emulation testing gained not With the average of Δ SNR thresholding corresponding for MCS as Δ SNRth), initial MCS is set and indexes MiIt is 1；
S2, reception system current PE R: receive system currently total PER (PER that system BLER statistic module is sent heret) and Section PER (PERs)；
S3, calculating signal to noise ratio difference: the current SNR (SNR sent here according to signal-to-noise ratio (SNR) estimation modulei) and the last time of preservation SNR estimated value (SNRi-1), calculating current signal difference DELTA SNR: Δ SNR=SNRi-SNRi-1, and update SNRi-1: SNRi-1 =SNRi, Δ SNR=0 in season is estimated for the first time；
S4, self-adaptative adjustment MCS and section PER thresholding: including:
S41, judge the relation of total PER and the upper and lower thresholding of total PER, if total PER is less than total PER Lower Threshold (PERt< PERtl), forward S42 to, if total PER (PER between the upper and lower thresholding of total PERtl≤PERt≤PERtu), forward S43 to, if Total PER is more than total PER Upper threshold (PERt>PERtu), forward S44 to；
S42, total PER are less than the process of total PER Lower Threshold: (the PER when section PER is less than section PER Lower Thresholds<PERsl), if Mi-1High-order, and if last MCS be not to lower (i.e. Flagmcs>-1) if or last MCS be to lower (i.e. Flagmcs=-1) Δ SNR > Δ SNR simultaneouslyth, MCS raises one-level (Mi=Mi-1+1)；When section PER is between the upper and lower thresholding of section PER Between time (PERsl≤PERs≤PERsu), raise the upper and lower threshold value of section PER, make PERsl=min (PERsl(1+FPER), 0.2PERtu), PERsu=min (10PERsl,PERtu), if Mi-1It not high-order and Flagmcs>-1、ΔSNR>ΔSNRthTime, MCS raises one-level (Mi=Mi-1+1)；(the PER when section PER is more than section PER Upper thresholds>PERsu), raise the upper and lower thresholding of section PER Value, makes PERsl=min (PERsl(1+FPER),0.2PERtu), PERsu=min (10PERsl,PERtu), the constant (M of MCSi= Mi-1)；Then go to S45；
S43, the total PER process between the upper and lower thresholding of total PER: (PER when section PER is less than section PER Lower Thresholds< PERsl), lower the upper and lower threshold value of section PER, make PERsl=max (PERsl(1-FPER),10-6), PERsu=min (10PERsl, PERtu), if Mi-1It not high-order, and Flagmcs>-1、ΔSNR>ΔSNRthTime, MCS raises one-level (Mi=Mi-1+1)；The section of working as (PER when PER is between the upper and lower thresholding of section PERsl≤PERs≤PERsu), do not adjust (Mi=Mi-1,PERslAnd PERsuNo Become)；(the PER when section PER is more than section PER Upper thresholds>PERsu), raise the upper and lower threshold value of section PER, make PERsl=min (PERsl(1+FPER),0.2PERtu), PERsu=min (10PERsl,PERtu), if Mi-1Not being lowest-order, MCS lowers one-level (Mi =Mi-1-1)；Then go to S45；
S44, total PER are more than the process of total PER Upper threshold: (the PER when section PER is less than section PER Lower Thresholds<PERsl), under Adjust the upper and lower threshold value of section PER, make PERsl=max (PERsl(1-FPER),10-6), PERsu=min (10PERsl,PERtu), MCS Constant (Mi=Mi-1)；(the PER when section PER is between the upper and lower thresholding of section PERsl≤PERs≤PERsu), in downward section PER, Lower threshold, makes PERsl=max (PERsl(1-FPER),10-6), PERsu=min (10PERsl,PERtu), if Mi-1It not minimum Rank, MCS lowers one-level (Mi=Mi-1-1)；(the PER when section PER is more than section PER Upper thresholds>PERsu), if Mi-1It not minimum Rank, MCS lowers one-level (Mi=Mi-1-1)；Then go to S45；
S45, change flag Flag of calculating MCS index valuemcsIf: Mi>Mi-1, then Flagmcs=1；If Mi=Mi-1, Then Flagmcs=0；If Mi<Mi-1, then Flagmcs=-1；Then M is updatedi-1: Mi-1=Mi；
S46: output adaptive adjusts result: export and preserve current MCS index value Mi, MCS change flag Flagmcs, section PER Lower Threshold PERsl, section PER Upper threshold PERsu；
S5, renewal system MCS: by new MCS value MiQAM modulation that the system of delivering to is made a start and Turbo coding module, and give QAM to receiving end solves mediation Turbo decoding module, and transmitting-receiving updates MCS simultaneously；
Whether S6, the communication of judging terminate: if communication process terminates, forward S7 to, otherwise forward S2 to；
S7, MCS adjust and terminate.
Owing to tradition Adaptive Modulation and Coding based on fixed threshold mode can reach optimality when perfect channel estimation Can, emphasis the most of the present invention and this traditional approach carry out performance comparison.
Fig. 6 and Fig. 7 is the specific embodiment of the invention and tradition Adaptive Modulation and Coding based on fixed threshold respectively The system bit error rate of ofdm system simulation run in awgn channel and the Performance comparision of information source average information rate；Wherein adopt 8 kinds of modulation coding modes be shown in Table 2；Sample frequency is that 30.72MHz, FFT count is 2048, and subcarrier spacing is 15kHz, each OFDM symbol takies 1200 subcarriers, and circulating prefix-length is 146, and spreading gain is 15, adaptive scheduling Cycle is 210 OFDM symbol times (about 15ms), the most each dispatching cycle statistical piece PER, update total PER, estimate SNR；If Putting traditional target bit based on fixed threshold adaptive modulation coding method is≤10-3, the inventive method is Unite total PER Upper threshold PERtuBe 0.1, total PER Lower Threshold PERtlIt is 0.0001, section PER Lower Threshold PERslInitial value is 0.01, section PER Upper threshold PERsuInitial value is 0.1, and section PER thresholding adjusts step-length FPERIt is 0.5, Δ SNR threshold delta SNRthFor 2.5dB, initially MCS index is 1, and SNR estimates the non-ideal estimation including free from error perfect estimation and estimation difference less than 2dB, and emulation is counted It is 107；Emulation shows: under the conditions of awgn channel ,-16dB≤SNR≤0dB, when signal to noise ratio does not has estimation difference, the present invention Meeting system performance requirements with the BER of traditional approach, the average information rate of two kinds of algorithms is close；When signal-to-noise ratio (SNR) estimation error not During more than 2dB, the BER fluctuation under traditional approach is very big, and error rate of system is unsatisfactory for system requirements, the system under mode of the present invention BER is more stable, has minor fluctuations in system index claimed range, insensitive to SNR estimation difference, and its error bit ability is bright Showing and be better than traditional approach, information average information rate is slightly below traditional method.
Fig. 8 and Fig. 9 is the specific embodiment of the invention and tradition Adaptive Modulation and Coding based on fixed threshold respectively The system bit error rate of ofdm system simulation run in the EVA channel that maximum Doppler frequency domain is 70Hz and information source average information The Performance comparision of speed；System parameter setting is with the setting in Fig. 6 and Fig. 7；Emulation shows: under EVA 70Hz channel condition, As-12dB≤SNR≤4dB, the BER of the present invention is more stable, insensitive to channel estimation errors, and BER fluctuation is less, information source Average information rate is higher, and the BER under traditional approach has larger fluctuation, information source average information rate to be slightly below mode of the present invention.
Therefore, compared with Adaptive Modulation and Coding mode based on fixed threshold with tradition, the present invention based on double Block Error Rates With the Adaptive Modulation and Coding of signal to noise ratio difference, there is more preferable robustness, to different channels characteristic and signal-to-noise ratio (SNR) estimation error not Sensitivity, the change to channel has more preferable adaptability, under conditions of ensureing system transmitting, has preferable frequency spectrum profit By rate, there is the strongest using value.

Claims (2)

1. one kind based on double Block Error Rates and the adaptive modulation coding method of signal to noise ratio difference, it is characterised in that include following step Rapid:
S1, parameter are arranged: according to the reliability requirement of system, the upper and lower threshold value of total PER of initialization system, the upper and lower door of section PER Limit initial value, section PER thresholding adjusts step value, and Δ SNR thresholding is Δ SNRth, initialize MCS index value；
S2, reception system current PE R: receive system currently total PER and section PER that system BLER statistic module is sent here；
S2, calculating signal to noise ratio difference: current SNR value SNR sent here according to signal-to-noise ratio (SNR) estimation moduleiEstimate with SNR last time preserved Value SNRi-1, calculating current signal difference DELTA SNR: Δ SNR=SNRi-SNRi-1, and update SNRi-1: SNRi-1=SNRi；Subscript I is the natural number more than or equal to 1；
S4, self-adaptative adjustment MCS and section PER thresholding: according to system currently total PER, section PER and Δ SNR, and preset total The upper and lower thresholding of PER, the upper and lower thresholding of section PER, section PER thresholding adjusts step value and Δ SNR thresholding, self-adapted adjustment system MCS, obtains new MCS, the simultaneously upper and lower thresholding of the section of being adaptively adjusted PER, if the MCS index value after current adjustment is Mi；Tool Body method is:
S41, judge the relation of total PER and the upper and lower thresholding of total PER, if total PER is less than total PER Lower Threshold, forward S42 to, if Total PER, between the upper and lower thresholding of total PER, forwards S43 to, if total PER is more than total PER Upper threshold, forwards S44 to；
S42, total PER are less than the process of total PER Lower Threshold: when section PER is less than section PER Lower Threshold, if Mi-1It not high-order, And last MCS is not to lower or last MCS is to lower Δ SNR > Δ SNR simultaneouslyth, then MCS raises one-level；When section PER Time between the upper and lower thresholding of section PER, raise the upper and lower threshold value of section PER, if Mi-1It not that high-order and MCS are not downward, Δ SNR>ΔSNRthTime, MCS raises one-level；When section PER is more than section PER Upper threshold, raising the upper and lower threshold value of section PER, MCS is not Become；Then go to S45；
S43, the total PER process between the upper and lower thresholding of total PER: when section PER is less than section PER Lower Threshold, lower section PER Upper and lower threshold value, if Mi-1High-order, and MCS be not lower, Δ SNR > Δ SNRthTime, MCS raises one-level；When section PER Time between the upper and lower thresholding of section PER, do not adjust；When section PER is more than section PER Upper threshold, raise the upper and lower thresholding of section PER Value, if Mi-1Not being lowest-order, MCS lowers one-level；Then go to S45；
S44, total PER are more than the process of total PER Upper threshold: when section PER is less than section PER Lower Threshold, lower the upper and lower door of section PER Limit value, MCS is constant；When section PER is between the upper and lower thresholding of section PER, lower the upper and lower threshold value of section PER, if Mi-1It not Low order, MCS lowers one-level；When section PER is more than section PER Upper threshold, if Mi-1Not being lowest-order, MCS lowers one-level；Then turn To S45；
S45, change flag Flag of calculating MCS index valuemcsIf: Mi>Mi-1, then Flagmcs=1；If Mi=Mi-1, then Flagmcs=0；If Mi<Mi-1, then Flagmcs=-1；Update Mi-1: Mi-1=Mi；Wherein, Flagmcs=1: represent that MCS raises, Flagmcs=0: represent that MCS keeps constant, Flagmcs=-1: represent that MCS lowers；
S46: output adaptive adjustment result: current MCS index value Mi, MCS change flag Flagmcs, section PER Xiamen after adjustment Limit PERsl, section PER Upper threshold PER after adjustmentsu；
S5, update system MCS: QAM modulation that system of being delivered to by new MCS is made a start and Turbo coding module, and deliver to receiving end QAM solves mediation Turbo decoding module, and transmitting-receiving updates modulation coding mode simultaneously；
Whether S6, the communication of judging terminate: if communication process terminates, forward S7 to, otherwise forward S2 to；
S7, MCS adjust and terminate.
The most according to claim 1 a kind of based on double Block Error Rates with the adaptive modulation coding method of signal to noise ratio difference, its It is characterised by, raises in section PER described in step S42, S43, S44, thresholding method particularly includes:
Raise section PER Lower Threshold PERsl: PERsl=min (PERsl(1+FPER),0.2PERtu)；
Raise section PER Upper threshold PERsu: PERsu=min (10PERsl,PERtu)；
Lower in section PER described in step S42, S43, S44, thresholding method particularly includes:
Lower section PER Lower Threshold PERsl: PERsl=max (PERsl(1-FPER),10-6)；
Lower section PER Upper threshold PERsu: PERsu=min (10PERsl,PERtu)。
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