CN102957510A - AMC (Adaptive Modulation and Coding) method based on SC-FDE (Single Carrier-Frequency Domain Equalization) system - Google Patents

Abstract

The invention provides an AMC (Adaptive Modulation and Coding) method based on an SC-FDE (Single Carrier-Frequency Domain Equalization) system, relates to an AMC modulation and encoding method, and belongs to the field of wireless radio. In order to solve the problems that the a channel cost is increased and the spectrum efficiency is low under the condition that the SC-FDE system is at a time-varying multi-path channel, caused by that a channel needs to be subjected to estimation and policy exchange at any time when current information is transmitted, the invention provides the adaptive modulation and coding method by combining an AMC technology and self characteristics of an SC-FDE system theory; policy lasting time is introduced to restrict the utilization time of the policy and the switching frequency of the policy, so that the optimal policy which is matched with the current channel state is searched in a policy switching table; only if the average lasting time of the selected optimal policy is exceeded, the method can carry out the next time of the selection and the switching of the optimal transmission policy, so that the channel estimation and policy switching processing efficiencies are reasonably reduced, the spectrum efficiency is effectively improved and the system throughput is maximized. The AMC method based on the SC-FDE system is applicable to the field of a wireless radio communication technology.

Description

A kind of AMC method based on the SC-FDE system

Technical field

The present invention relates to the radio field, be specifically related to a kind of NEW ADAPTIVE modulation coding method.

Background technology

The rapid growth of the diversified service demand that the usable spectrum of radio communication is rare, wireless portable equipment expedites the emergence of is all needed badly and is supported the transmission technology of high speed information transmission and spectral efficient to solve.And traditional non-self-adapting transmission system is according to the design of the worst state of channel, need a fixing link margin keeping acceptable transmission performance, so the channel capacity of system can't be utilized fully.And Adaptive Modulation and Coding (adaptive modulation and coding, AMC) basic thought of technology is exactly by the self adaptation adjustment to symbol transmission rate, modulation scheme, modulation constellation size, encoding scheme, these parameters of code efficiency, in real time the load of dispersion and balanced communication.When channel condition is better, with higher speed rates, and when the channel quality variation, gently reduce its data throughout.Can under the prerequisite of not sacrificing power and bit error rate, according to the time variation of channel, provide higher channel spectrum efficient like this.

Single carrier frequency domain equalization (single carrier frequency domain equalization, SC-FDE) technology is to be obtained in conjunction with OFDM (orthogonal frequency division multiplexing, OFDM) technology by traditional single carrier transmission technology.SC-FDE system and ofdm system are two kinds of typical block transmission systems.The computing that SC-FDE system and ofdm system are done is identical, and difference only is that the order of processing is different, so they have identical system's computational complexity.Owing to be to carry out equilibrium treatment at frequency domain all, so have identical ability of anti-multipath.Both differences are OFDM in frequency domain decision, are a multicarrier system; And SC-FDE adjudicates in time domain, is a single-carrier system.The ofdm system papr is large because SC-FDE can overcome, linearity of amplifier area requirement height, responsive not enough to phase noise and carrier wave frequency deviation.

Summary of the invention

The objective of the invention is in order to solve the SC-FDE system under multipath time varying channel condition, because the variation of channel status, will be at any time during communication to channel carrying out property estimation with change strategy and cause channel overhead to increase, the problem that spectrum efficiency is low, native system proposes a kind of AMC method based on the SC-FDE system.

The specific implementation step of a kind of AMC method based on the SC-FDE system of the present invention is:

Step 1, the channel classification method that adopts according to the channel classification module of SC-FDE self adaptation base band system are classified to current channel, obtain current channel condition information by channel type;

Step 2, obtain the signal to noise ratio snr information of present receiving machine according to the signal to noise ratio snr estimation module of SC-FDE self adaptation base band system;

The signal to noise ratio snr information of the present receiving machine that step 3, the current channel condition information that obtains according to step 1 and step 2 obtain is switched the optimal transmission strategy of choosing in the form with the current channel condition coupling at transmission policy;

Step 4, by feedback channel selected optimal transmission strategy is passed to Receiver And Transmitter simultaneously, described transmitter and receiver is implemented selected optimal transmission strategy;

Step 5, the average duration of calculating current selected optimal transmission strategy

Obtain the average duration of described optimal transmission strategy

Surpass the average duration of described optimal transmission strategy the service time of step 6, current optimal transmission strategy

, return execution in step one, re-start the selection of optimal transmission strategy.

The present invention proposes a kind of self adaptation AMC method, the use duration of tactful duration constraints policy and the switching frequency of strategy have been introduced, make it not only can in tactful switching table, search the optimal transmission strategy that mates with current channel condition, can also calculate the average duration of selected optimal transmission strategy, after only having the average duration of current optimal transmission strategy of surpassing, the method is just carried out the next time selection of optimal transmission strategy, reasonably reduce simultaneously channel estimating and tactful hand-off process frequency, the Effective Raise spectrum efficiency makes the throughput of system maximization.

Description of drawings

Fig. 1 is the block diagram of existing SC-FDE non-self-adapting system.

Fig. 2 is the block diagram of SC-FDE self adaptation base band analogue system of the present invention.

Fig. 3 is a kind of flow chart of the new A MC method based on the SC-FDE system.

Fig. 4 is each tactful SNR-BER performance curve under the embodiment six described Rayleigh channels, among the figure:

Curve 1 is illustrated in the SNR-BER performance curve when using the CC-BPSK strategy,

Curve 2 is illustrated in the SNR-BER performance curve when using the TPC3226-BPSK strategy,

Curve 3 is illustrated in the SNR-BER performance curve when using the TPC6457-BPSK strategy,

Curve 4 is illustrated in the SNR-BER performance curve when using the CC-QPSK strategy,

Curve 5 is illustrated in the SNR-BER performance curve when using the TPC3226-QPSK strategy,

Curve 6 is illustrated in the SNR-BER performance curve when using the LDPC-QPSK strategy,

Curve 7 is illustrated in the SNR-BER performance curve when using the TPC6457-QPSK strategy,

Curve 8 is illustrated in the SNR-BER performance curve when using the CC-16QAM strategy,

Curve 9 is illustrated in the SNR-BER performance curve when using the TPC3226-16QAM strategy,

Curve 10 is illustrated in the SNR-BER performance curve when using the TPC6457-16QAM strategy,

Curve 11 is illustrated in the SNR-BER performance curve when using the LDPC-16QAM strategy.

Fig. 5 is the SNR-BER performance curve of embodiment six described selected optimal transmission strategies, among the figure:

Curve 1 is illustrated in the SNR-BER performance curve when using the CC-BPSK strategy,

Curve 2 is illustrated in the SNR-BER performance curve when using the TPC3226-BPSK strategy,

Curve 3 is illustrated in the SNR-BER performance curve when using the TPC6457-BPSK strategy,

Curve 4 is illustrated in the SNR-BER performance curve when using the CC-QPSK strategy,

Curve 5 is illustrated in the SNR-BER performance curve when using the TPC3226-QPSK strategy,

Curve 6 is illustrated in the SNR-BER performance curve when using the LDPC-QPSK strategy.

Fig. 6 is the throughput performance curve of embodiment six described selected optimal transmission strategies, among the figure:

Curve 1 is illustrated in the throughput performance curve when using the CC-BPSK strategy,

Curve 2 is illustrated in the throughput performance curve when using the TPC3226-BPSK strategy,

Curve 3 is illustrated in the throughput performance curve when using the TPC6457-BPSK strategy,

Curve 4 is illustrated in the throughput performance curve when using the CC-QPSK strategy,

Curve 5 is illustrated in the throughput performance curve when using the TPC3226-QPSK strategy,

Curve 6 is illustrated in the throughput performance curve when using the LDPC-QPSK strategy.

Embodiment:

The concrete operation step of the described AMC method based on the SC-FDE system of embodiment one, present embodiment is as follows:

Step 1, the channel classification method that adopts according to SC-FDE self adaptation base band system channel sort module are classified to current channel, obtain current channel condition information by channel type;

Step 2, obtain the signal to noise ratio snr information of present receiving machine according to SC-FDE self adaptation base band system signal noise ratio SNR estimation module;

The signal to noise ratio snr information of the present receiving machine that step 3, the current channel condition information that obtains according to step 1 and step 2 obtain is switched the optimal transmission strategy of choosing in the form with the current channel condition coupling at transmission policy;

Step 4, by feedback channel selected optimal transmission strategy is passed to Receiver And Transmitter simultaneously, described transmitter and receiver is implemented selected optimal transmission strategy;

Step 5, the average duration of calculating current selected optimal transmission strategy

Obtain the average duration of described optimal transmission strategy

If if surpass the average duration of described optimal transmission strategy the service time of the current optimal transmission strategy of step 6

Return execution in step one, re-start the selection of optimal transmission strategy.

Embodiment two, present embodiment are that described optimal transmission strategy switches form and obtains by following method to the further restriction of the described AMC method based on the SC-FDE system of embodiment one:

Under described SC-FDE self adaptation base band system off-line state, given channel status is carried out system emulation, obtain the performance chart of bit error rate and Between Signal To Noise Ratio, according to target error rate P _eRestriction, divide signal to noise ratio decline zone [γ _i, γ _I+1), and the handoff threshold signal to noise ratio γ of definite transmission policy _i

All satisfy target error rate P in the search signal to noise ratio decline zone _eThe optimal transmission strategy in the corresponding signal to noise ratio decline zone that requires satisfies target error rate P with described _eThe optimal transmission strategy that requires forms the optimal transmission set of strategies, and determines that according to this optimal transmission set of strategies the optimal transmission strategy switches form.

Embodiment three, present embodiment are the further restrictions to the described AMC method based on the SC-FDE system of embodiment two, described signal to noise ratio decline zone [γ _i, γ _I+1) determine by following method: with described target error rate P _eValue in the performance chart of described bit error rate and Between Signal To Noise Ratio, do a straight line that is parallel to transverse axis, obtain respectively intersection point with the BER-SNR curve of every kind of strategy, the abscissa that resulting intersection point is corresponding is the handoff threshold γ of transmission policy _i, the SNR scope between per two thresholdings is signal to noise ratio decline zone [γ _i, γ _I+1).

Embodiment four, present embodiment are the further restrictions to the described AMC method based on the SC-FDE system of embodiment two, described optimal transmission strategy is interior modulation system and the coded system that adopts of described SC-FDE self adaptation base band next Transmission Time Interval of system, and described modulation system and coded system are to determine according to the modulator-demodulator of real system and coder.

Embodiment five, present embodiment are the further restrictions to the described AMC method based on the SC-FDE system of embodiment one, the average duration of calculating current selected optimal transmission strategy in the described step 5

Detailed process;

Find the solution the average duration of optimal transmission strategy

The Markov model of a finite state of employing provides the average duration of described solution optimal transmission strategy Approximation, this model is approximately the Markov process of a discrete time with the decline of signal to noise ratio, and this process comprises that by a state transitions to the state that adjoins with it with maintain the original state constantly, its transition probability formula is:

$p_{i,i+1}=\frac{N_{i+1}{T}_s}{{\mathrm{\π}}_i}---\left(1\right)$

$p_{i,i-1}=\frac{N_i{T}_s}{{\mathrm{\π}}_i}---\left(2\right)$

p _i，i=1-p _i，i+1-p _i，i-1 (3)

Wherein i represents i state, and current status i can only transfer to state i+1 or the state i-1 that adjoins with it simultaneously, or it is constant to maintain the original state; Formula (1) p _{I, i+1}For state i transfers to the transition probability of state i+1, formula (2) p _{I, i-1}For state i transfers to the probability of state i-1, formula (3) p _{I, i}Be the state i probability of state that maintains the original state, N _iFor at state i signal to noise ratio γ _iUnder level crossing rate, T _sBe symbol period, π _iFor being in i decline zone [γ _i, γ _I+1) probability: π _i=p (γ _i≤ γ＜γ _I+1), under the rayleigh fading channel, level crossing rate N _iProvided by formula (4):

$N_i=\sqrt{\frac{2\mathrm{\π}{\mathrm{\γ}}_i}{\stackrel{\‾}{\mathrm{\γ}}}{f}_D{e}^{-{\mathrm{\γ}}_i/\stackrel{\‾}{\mathrm{\γ}}}}---\left(4\right)$

F wherein _DBe Doppler frequency, the average duration of described optimal transmission strategy

Can be provided by formula (5):

${\stackrel{\‾}{\mathrm{\τ}}}_i=\frac{T_s}{p_{i,i+1}+p_{i,i-1}}=\frac{{\mathrm{\π}}_i}{N_{i+1}+N_i}---\left(5\right)$

T wherein _sBe symbol period, π _iFor being in i decline zone [γ _i, γ _I+1) probability: π _i=p (γ _i≤ γ＜γ _I+1), N _iFor at state i signal to noise ratio γ _iUnder level crossing rate, p _{I, i+1}For state i transfers to the transition probability of state i+1, p _{I, i-1}Transfer to the probability of state i-1 for state i; Can be obtained respectively the mean value of receiver end signal to noise ratio by signal to noise ratio snr estimation and channel estimating

With Doppler frequency f _DEstimated value, described optimal transmission strategy handoff threshold γ _iMean value with the receiver end signal to noise ratio

Doppler frequency f _DEstimated value be updated to formula (4), can try to achieve level crossing rate N _i, try to achieve again at last Average Strategy duration of current strategies according to formula (5)

[γ _i, γ _I+1) probability π _iFor:

${\mathrm{\π}}_i=p({\mathrm{\γ}}_i\≤\mathrm{\γ}\≤{\mathrm{\γ}}_{i+1})=\underset{{\mathrm{\γ}}_i}{\overset{{\mathrm{\γ}}_{i+1}}{\∫}}\frac{1}{\stackrel{\‾}{\mathrm{\γ}}}{e}^{-\frac{\mathrm{\γ}}{\mathrm{\γ}}}\mathrm{d\γ}---\left(6\right)$

Described AMC method based on SD-FDE, its spectrum efficiency be as the formula (7):

$\frac{R}{B}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{\log }_2\left(M_i\right)C_{i}p({\mathrm{\γ}}_i\≤\mathrm{\γ}\≤{\mathrm{\γ}}_{i+1})---\left(7\right)$

Wherein R, B are respectively data rate and receive signal bandwidth, M _i, C _iBe respectively i decline zone [γ _i, γ _I+1) modulation constellation number and the code check of corresponding optimal transmission strategy, N is the number of optimal transmission strategy.

Can get the handoff threshold γ of optimal transmission strategy according to step 1 _i(1≤i≤N), its substitution formula (6) can be got p (γ _i≤ γ＜γ _I+1); The optimal transmission strategy that obtains according to step 2 determines that modulation constellation counts M _iWith code efficiency C _i, with the p (γ that has tried to achieve _i≤ γ＜γ _I+1) and described modulation constellation count M _i, code efficiency C _iSubstitution formula (7) can obtain adopting the spectrum efficiency of the Adaptable System of AMC method.

Embodiment six, combination figure, table are to using the comparative analysis based on AMC method and the non-self-adapting system of SC-FDE system in the channel model of mountain area, SUI-5 three footpath, the specific implementation process is as follows:

At first build the block diagram of SC-FDE self adaptation base band analogue system, as shown in Figure 2, concrete operation step is that those skilled in the art can realize according to Fig. 2.Fig. 2 is on the basis of the existing SC-FDE non-self-adapting system of Fig. 1, has added the base band analogue system of AMC method module and channel classification and SNR estimation module; Therefore this SC-FDE self adaptation base band analogue system has possessed self adaptation adjustment transformation parameter (modulation system, coded system) to adapt to the ability of time varying channel.Channel model is elected mountain area, SUI-5 three footpath channel model as, and each footpath time delay is respectively 0us, 4us, 10us, its corresponding path gain is respectively 0 ,-5dB ,-10dB, maximum doppler frequency f _DBe 2.5Hz.Character rate is 6.336Msps, and target error rate is 10 ^-5

Channel information is estimated; Channel estimating adopts least square (least square, LS) algorithm; Balanced least mean-square error (minimum mean square error, MMSE) the frequency domain equalization algorithm that adopts; SNR estimate to adopt the MMSE algorithm, signal to noise ratio during greater than 5dB its evaluated error less than 1dB; The structure of frame is that 1 blocks of data contains 1 frame pilot frame and 10 frame data frames; Every the first frame is pilot frame, and its front 256 are used for channel estimating, and rear 256 are used for signal-to-noise ratio (SNR) estimation.Cyclic Prefix (Cyclic Prefix, CP) is 64, and data frame length is 512.

The modulation system that adopts is BPSK, QPSK and 16QAM; Coded system is (Convolutional code, CC) (2,1,7), Turbo product code (turbo product code, TPC) (32,26), TPC(64,57) and low density parity check code (low density parity check code, LDPC) (6132,8176); Like this, the above-mentioned parameter combination is obtained 12 kinds of strategies altogether, be designated as S1 ~ S12.Consider the restriction of block code transmission and transmission time 1ms in the burst communication of hypothesis, the strategy that LDPC and BPSK make up does not adopt.All optional strategies are as shown in table 1.

Table 1 adaptive strategy combination table

Then under the channel status of above-mentioned setting, carry out system emulation and obtain BER-SNR performance curve and throughput curve respectively shown in Fig. 3,4; A kind of BER performance of strategy is better, and the performance of its throughput is just better.According to Fig. 3 SNR is divided into 7 decline zones: less than 8, [8,12], (12,15], (15,19], (19,26], (26,31], greater than 31dB; Corresponding tactful handoff threshold is respectively 8dB, 12dB, 15dB, 19dB, 26dB and 31dB; Search for according to Fig. 4 and to satisfy target error rate P in the zone that respectively declines _e=10 ^-5The optimal transmission strategy of throughput maximum, as shown in table 2; According to the BER-SNR performance curve of the strategy after table 2 screening and corresponding throughput curve respectively shown in Fig. 5,6.

Table 2 adaptive strategy switching table

By as seen from Table 2: as SNR during less than 8dB, be to guarantee target error rate P _e=10 ^-5Requirement, system will can the transmission of data.This moment system's transmission control frame and pilot frame.The estimated value of only having SNR just begins to carry out transfer of data during greater than 8dB.

In the average received signal to noise ratio

Situation under, calculate each tactful average duration by embodiment five described formulas (4) and formula (5)

As shown in table 3.

Each tactful average duration under the different signal to noise ratios of table 3

By as seen from Table 3, along with the average received signal to noise ratio

Raising, the duration of more reliable strategy shortens, the duration of opposite more efficiently strategy is elongated.In the table 3 under the 10dB average duration of the strategy 6 under strategy 5 and the two kind of signal to noise ratio because less than 10 ^-4Ms and being left in the basket; Causing so, the little Average Strategy duration is because the average received signal to noise ratio

The decline zone of departing from strategy 5 and strategy 6 is far away, so signal to noise ratio drops on these regional probability π _iLess; It should be noted that: because the signal to noise ratio upper bound of strategy 6 is infinite, so calculate by embodiment five described formulas (5)

The time to adopt L′Hospital rule to find the solution; Judge that whether the current selected optimal transmission strategy time surpass selected optimal transmission strategy average duration

If the current selected optimal transmission strategy time is in the selected optimal transmission strategy Average Strategy duration

In, then keep present selected optimal transmission strategy; If the current selected optimal transmission strategy time surpasses selected optimal transmission strategy average duration

Just can carry out choosing and hand-off process of New Policy.

Table 4 has provided

Situation under, adopt the spectrum efficiency of SC-FDE self adaptation base band system.As a comparison, also provided the spectrum efficiency of non-self-adapting system in the table 4.The spectrum efficiency of Adaptable System is calculated by formula (7).Because the non-self-adapting system is according to the design of the worst state of channel, so this system can only adopt strategy 1 the most reliable this transmission plan.

By as seen from Table 4, under every kind of signal to noise ratio, all the spectrum efficiency than non-self-adapting system is high to adopt the Adaptable System of institute's extracting method.Along with

Raising, the spectrum efficiency of two kinds of systems all improves, but the spectrum efficiency of Adaptable System improves sooner.

In the higher situation, the advantage of Adaptable System is more obvious; As

The time, the spectrum efficiency of Adaptable System has improved 215% than the spectrum efficiency of non-self-adapting system, has utilized more fully channel capacity.

The spectrum efficiency of two systems contrast under the different signal to noise ratios of table 4

To sum up analyze, described AMC method can guarantee that the transmission of SC-FDE Adaptable System high efficient and reliable ground namely can make communication system adapt to better the electromagnetic environment complicated and changeable of wireless channel under the Rayleigh multipath channel.

Claims (5)

1. AMC method based on the SC-FDE system is characterized in that concrete operation step:

Step 1, the channel classification method that adopts according to the channel classification module of SC-FDE self adaptation base band system are classified to current channel, obtain current channel condition information by channel type;

Step 2, obtain the signal to noise ratio snr information of present receiving machine according to the signal to noise ratio snr estimation module of SC-FDE self adaptation base band system;

The signal to noise ratio snr information of the present receiving machine that step 3, the current channel condition information that obtains according to step 1 and step 2 obtain is switched the optimal transmission strategy of choosing in the form with the current channel condition coupling at transmission policy;

Step 4, by feedback channel selected optimal transmission strategy is passed to Receiver And Transmitter simultaneously, described transmitter and receiver is implemented selected optimal transmission strategy;

Step 5, the average duration of calculating current selected optimal transmission strategy

Obtain the average duration of described optimal transmission strategy

Surpass the average duration of described optimal transmission strategy the service time of step 6, current optimal policy

Return execution in step one, re-start the selection of optimal transmission strategy.

2. a kind of AMC method based on SC-FDE according to claim 1 is characterized in that, described optimal transmission strategy switches form and obtains by following method:

Under described SC-FDE self adaptation base band system off-line state, given channel status is carried out system emulation, obtain the performance chart of bit error rate and Between Signal To Noise Ratio, according to target error rate P _eRestriction, divide signal to noise ratio decline zone [γ _i, γ _I+1), and the handoff threshold signal to noise ratio γ of definite transmission policy _i

All satisfy target error rate P in the search signal to noise ratio decline zone _eThe optimal transmission strategy in the corresponding signal to noise ratio decline zone that requires satisfies target error rate P with described _eThe optimal policy that requires forms the optimal policy collection, and determines that according to this optimal transmission set of strategies the optimal transmission strategy switches form.

3. a kind of AMC method based on SC-FDE according to claim 2 is characterized in that, described signal to noise ratio decline zone [γ _i, γ _I+1) determine by following method: with described target error rate P _eValue in the performance chart of described bit error rate and Between Signal To Noise Ratio, do a straight line that is parallel to transverse axis, obtain respectively intersection point with the BER-SNR curve of every kind of strategy, the abscissa that resulting intersection point is corresponding is the handoff threshold γ of transmission policy _i, the SNR scope between per two thresholdings is signal to noise ratio decline zone [γ _i, γ _I+1).

4. a kind of AMC method based on SC-FDE according to claim 2, it is characterized in that, described optimal transmission strategy is interior modulation system and the coded system that adopts of described SC-FDE self adaptation base band next Transmission Time Interval of system, and described modulation system and coded system are to determine according to the modulator-demodulator of real system and coder.

5. a kind of AMC method based on SC-FDE according to claim 1 is characterized in that, calculates the average duration of current selected optimal transmission strategy in the step 5

Detailed process;

Find the solution the average duration of optimal transmission strategy

The Markov model of a finite state of employing provides the average duration of described solution optimal transmission strategy Approximation, this model is approximately the Markov process of a discrete time with the decline of signal to noise ratio, and this process comprises that by a state transitions to the state that adjoins with it with maintain the original state constantly, its transition probability formula is:

$p_{i,i+1}=\frac{N_{i+1}{T}_s}{{\mathrm{\π}}_i}---\left(1\right)$

$p_{i,i-1}=\frac{N_i{T}_s}{{\mathrm{\π}}_i}---\left(2\right)$

p _i，i=1-p _i，i+1-p _i，i-1 (3)

Wherein i represents i state, and current status i can only transfer to state i+1 or the state i-1 that adjoins with it simultaneously, or it is constant to maintain the original state; Formula (1) p _{I, i+1}For state i transfers to the transition probability of state i+1, formula (2) p _{I, i-1}For state i transfers to the probability of state i-1, formula (3) p _{I, i}Be the state i probability of state that maintains the original state, N _iFor at state i signal to noise ratio γ _iUnder level crossing rate, T _sBe symbol period, π _iFor being in i decline zone [γ _i, γ _I+1) probability: π _i=p (γ _i≤ γ＜γ _I+1), under the rayleigh fading channel, level crossing rate N _iProvided by formula (4):

$N_i=\sqrt{\frac{{2\mathrm{\π\γ}}_i}{\stackrel{\‾}{\mathrm{\γ}}}}{f}_D{e}^{-{\mathrm{\γ}}_i/\stackrel{\‾}{\mathrm{\γ}}}---\left(4\right)$

F wherein _DBe Doppler frequency, the average duration of described optimal transmission strategy

Can be provided by formula (5):

$\stackrel{\‾}{{\mathrm{\τ}}_i}=\frac{T_s}{p_{i,i+1}+p_{i,i-1}}=\frac{{\mathrm{\π}}_i}{N_{i+1}+N_i}---\left(5\right)$

T wherein _sBe symbol period, π _iFor being in i decline zone [γ _i, γ _I+1) probability: π _i=p (γ _i≤ γ＜γ _I+1), N _iFor at state i signal to noise ratio γ _iUnder level crossing rate, p _{I, i+1}For state i transfers to the transition probability of state i+1, p _{I, i-1}Transfer to the probability of state i-1 for state i; Can be obtained respectively the average mean of receiver end signal to noise ratio by signal to noise ratio snr estimation and channel estimating

With Doppler frequency f _DEstimated value, described optimal transmission strategy handoff threshold γ _iMean value with the receiver end signal to noise ratio

Doppler frequency f _DEstimated value be updated to formula (4), can try to achieve level crossing rate N _i, try to achieve again at last Average Strategy duration of current strategies according to formula (5)

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