CN102957510B - AMC (Adaptive Modulation and Coding) method based on SC-FDE (Single Carrier-Frequency Domain Equalization) system - Google Patents

Abstract

An SC-FDE system-based AMC method relates to an AMC modulation and encoding method, belonging to the radio field. In order to solve the problem of increased channel overhead and low spectrum efficiency caused by channel estimation and changing strategies at any time during information transmission under the condition of multipath time-varying channel in SC-FDE system, combined AMC technology and SC-FDE system theory Its own characteristics propose a new type of adaptive modulation and coding method, which introduces the strategy duration to constrain the use time of the strategy and the switching frequency of the strategy, so that it can search for the optimal strategy that matches the current channel state in the strategy switching table. Only after the average duration of the currently selected optimal strategy is exceeded, the method selects and switches the next optimal transmission strategy, which reasonably reduces the processing frequency of channel estimation and strategy switching, effectively improves the spectrum efficiency, and improves the system throughput. maximize. The invention is applicable to the technical field of radio communication.

Description

A Method of AMC Based on SC-FDE System

technical field

The invention relates to the radio field, in particular to a novel adaptive modulation and coding method.

Background technique

The scarcity of available spectrum for wireless communications and the rapid growth of diverse service demands generated by wireless portable devices urgently require transmission technologies that support high-speed information transmission and high spectral efficiency. However, the traditional non-adaptive transmission system is designed according to the worst state of the channel, and requires a fixed link margin to maintain acceptable transmission performance, so the channel capacity of the system cannot be fully utilized. The basic idea of adaptive modulation and coding (AMC) technology is to disperse and balance communication in real time through adaptive adjustment of parameters such as symbol transmission rate, modulation scheme, modulation constellation size, coding scheme, and coding efficiency. load. It transmits at a higher rate when the channel condition is good, and gently reduces its data throughput when the channel quality becomes poor. In this way, high channel spectral efficiency can be provided according to the time-varying nature of the channel without sacrificing power and bit error rate.

Single carrier frequency domain equalization (single carrier frequency domain equalization, SC-FDE) technology is obtained by combining traditional single carrier transmission technology with orthogonal frequency division multiplexing (orthogonal frequency division multiplexing, OFDM) technology. SC-FDE system and OFDM system are two typical block transmission systems. The operations performed by the SC-FDE system and the OFDM system are exactly the same, the difference is only in the order of processing, so they have the same system operation complexity. Since they are equalized in the frequency domain, they have the same anti-multipath capability. The difference between the two is that OFDM is judged in the frequency domain and is a multi-carrier system; while SC-FDE is judged in the time domain and is a single-carrier system. Because SC-FDE can overcome OFDM system's high peak-to-average power ratio, high requirements on amplifier linear range, and sensitivity to phase noise and carrier frequency offset.

Contents of the invention

The purpose of the present invention is to solve the problem of increased channel overhead and low spectral efficiency due to channel state changes in the SC-FDE system under the condition of multipath time-varying channels. , this system proposes an AMC method based on SC-FDE system.

The specific implementation steps of a kind of AMC method based on SC-FDE system described in the present invention are:

Step 1, classify the current channel according to the channel classification method adopted by the channel classification module of the SC-FDE adaptive baseband system, and obtain the current channel state information by the channel type;

Step 2, obtain the signal-to-noise ratio SNR information of the current receiver according to the signal-to-noise ratio SNR estimation module of the SC-FDE adaptive baseband system;

Step 3, according to the current channel state information obtained in step 1 and the signal-to-noise ratio SNR information of the current receiver obtained in step 2, select the optimal transmission strategy matching the current channel state in the transmission strategy switching table;

Step 4, delivering the selected optimal transmission strategy to the receiver and the transmitter simultaneously through the feedback channel, and the transmitter and the receiver implement the selected optimal transmission strategy;

Step 5. Calculate the average duration of the currently selected optimal transmission strategy Get the average duration of the optimal transmission strategy

Step 6. The usage time of the current optimal transmission strategy exceeds the average duration of the optimal transmission strategy Return to step 1, and re-select the optimal transmission strategy.

The present invention proposes an adaptive AMC method, which introduces the policy duration to constrain the use time of the policy and the switching frequency of the policy, so that it can not only search for the optimal transmission policy matching the current channel state in the policy switching table, but also The average duration of the selected optimal transmission strategy can be calculated. Only after the average duration of the current optimal transmission strategy is exceeded, the method will select the next optimal transmission strategy, and at the same time reasonably reduce the channel estimation and strategy switching processing frequency, effectively improving spectrum efficiency and maximizing system throughput.

Description of drawings

Fig. 1 is a block diagram of an existing SC-FDE non-adaptive system.

FIG. 2 is a block diagram of the SC-FDE adaptive baseband simulation system of the present invention.

Fig. 3 is a flowchart of a novel AMC method based on the SC-FDE system.

Fig. 4 is the SNR-BER performance curve of each strategy under the Rayleigh channel described in Embodiment 6, in the figure:

Curve 1 represents the SNR-BER performance curve when using the CC-BPSK strategy,

Curve 2 represents the SNR-BER performance curve when using the TPC3226-BPSK strategy,

Curve 3 represents the SNR-BER performance curve when using the TPC6457-BPSK strategy,

Curve 4 represents the SNR-BER performance curve when using the CC-QPSK strategy,

Curve 5 represents the SNR-BER performance curve when using the TPC3226-QPSK strategy,

Curve 6 represents the SNR-BER performance curve when using the LDPC-QPSK strategy,

Curve 7 represents the SNR-BER performance curve when using the TPC6457-QPSK strategy,

Curve 8 represents the SNR-BER performance curve when using the CC-16QAM strategy,

Curve 9 represents the SNR-BER performance curve when using the TPC3226-16QAM strategy,

Curve 10 represents the SNR-BER performance curve when using the TPC6457-16QAM strategy,

Curve 11 represents the SNR-BER performance curve when using the LDPC-16QAM strategy.

Fig. 5 is the SNR-BER performance curve of the selected optimal transmission strategy described in Embodiment 6, in the figure:

Curve 1 represents the SNR-BER performance curve when using the CC-BPSK strategy,

Curve 2 represents the SNR-BER performance curve when using the TPC3226-BPSK strategy,

Curve 3 represents the SNR-BER performance curve when using the TPC6457-BPSK strategy,

Curve 4 represents the SNR-BER performance curve when using the CC-QPSK strategy,

Curve 5 represents the SNR-BER performance curve when using the TPC3226-QPSK strategy,

Curve 6 represents the SNR-BER performance curve when using the LDPC-QPSK strategy.

Fig. 6 is the throughput performance curve of the selected optimal transmission strategy described in Embodiment 6, in the figure:

Curve 1 represents the throughput performance curve when using the CC-BPSK strategy,

Curve 2 represents the throughput performance curve when using the TPC3226-BPSK strategy,

Curve 3 represents the throughput performance curve when using the TPC6457-BPSK strategy,

Curve 4 represents the throughput performance curve when using the CC-QPSK strategy,

Curve 5 represents the throughput performance curve when using the TPC3226-QPSK strategy,

Curve 6 represents the throughput performance curve when using the LDPC-QPSK strategy.

Detailed ways:

Embodiment 1. The specific operation steps of the AMC method based on the SC-FDE system described in this embodiment are as follows:

Step 1, classify the current channel according to the channel classification method adopted by the SC-FDE adaptive baseband system channel classification module, and obtain the current channel state information by the channel type;

Step 2, obtain the signal-to-noise ratio SNR information of the current receiver according to the SC-FDE adaptive baseband system signal-to-noise ratio SNR estimation module;

Step 3, according to the current channel state information obtained in step 1 and the signal-to-noise ratio SNR information of the current receiver obtained in step 2, select the optimal transmission strategy matching the current channel state in the transmission strategy switching table;

Step 4, delivering the selected optimal transmission strategy to the receiver and the transmitter simultaneously through the feedback channel, and the transmitter and the receiver implement the selected optimal transmission strategy;

Step 5. Calculate the average duration of the currently selected optimal transmission strategy Get the average duration of the optimal transmission strategy

Step 6. If the usage time of the current optimal transmission strategy exceeds the average duration of the optimal transmission strategy Return to step 1, and re-select the optimal transmission strategy.

Embodiment 2. This embodiment is a further limitation of the AMC method based on the SC-FDE system described in Embodiment 1. The optimal transmission strategy switching table is obtained by the following method:

Under the off-line state of described SC-FDE self-adaptive baseband system, carry out system emulation to given channel state, obtain the performance curve diagram of bit error rate and signal-to-noise ratio relation, according to the restriction of target bit error rate _Pe , Divide the SNR fading area [γ _i , γ _i+1 ), and determine the switching threshold SNR γ _i of the transmission strategy;

Search for all optimal transmission strategies in the SNR fading region that meet the requirements of the target bit error rate P _e , and combine the optimal transmission strategies that meet the requirements of the target bit error rate P _e into an optimal transmission strategy set, and determine the optimal transmission strategy switching table according to the optimal transmission strategy set.

Specific Embodiment 3. This embodiment is a further limitation of the AMC method based on the SC-FDE system described in Embodiment 2. The signal-to-noise ratio fading region [γ _i , γ _i+1 ) is obtained through the following Determined by the method: make a straight line parallel to the horizontal axis in the performance curve diagram of the relationship between the bit error rate and the signal-to-noise ratio with the value of the target bit error rate _Pe , and the BER-SNR curve of each strategy The intersection points are obtained respectively, and the abscissa corresponding to the obtained intersection points is the switching threshold γ _i of the transmission strategy, and the SNR range between each two thresholds is the signal-to-noise ratio fading region [γ _i , γ _i+1 ).

Embodiment 4. This embodiment is a further limitation of the AMC method based on the SC-FDE system described in Embodiment 2. The optimal transmission strategy is the next transmission time of the SC-FDE adaptive baseband system The modulation mode and coding mode used in the interval, the modulation mode and coding mode are determined according to the modem and codec of the actual system.

Embodiment 5. This embodiment is a further limitation of the AMC method based on the SC-FDE system described in Embodiment 1. In the step 5, the average duration of the currently selected optimal transmission strategy is calculated. specific process;

Solve for the average duration of the optimal transport strategy Using a finite-state Markov model gives the average duration of the solution to the optimal transport strategy The approximate value of , the model approximates the fading of the SNR as a discrete-time Markov process, and the process includes transferring from a state to its adjacent state and keeping the original state unchanged, and the transition probability formula is:

${\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

p _i,j =1-p _i,i+1 -p _i,i-1 (3)

Where i represents the i-th state, and the current state i can only be transferred to the adjacent state i+1 or state i-1, or keep the original state unchanged; formula (1) p _{i, i+1} is The transition probability from state i to state i+1, formula (2) p _{i, i-1} is the probability of state i transitioning to state i-1, formula (3) p _{i, i} is the probability that state i remains the original state , N _i is the level crossing rate in state i SNR γ _i , T _s is the symbol period, π _i is the probability of being in the ith fading area [γ _i , γ _i+1 ): π _i =p (γ _i ≤γ<γ _i+1 ), under the Rayleigh fading channel, the level crossing rate N _i is given by formula (4):

${\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; D.</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\sqrt{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

where _fD is the Doppler frequency, the average duration of the optimal transmission strategy It can be given by formula (5):

$\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

Where T _s is the symbol period, π _i is the probability of being in the i-th fading area [γ _i , γ _i+1 ): π _i =p(γ _i ≤γ<γ _i+1 ), N _i is the The level crossing rate under the signal-to-noise ratio γ _i , p _{i, i+1} is the transition probability from state i to state i+1, p _{i, i-1} is the probability of state i to state i-1; by Signal-to-noise ratio SNR estimation and channel estimation can obtain the average value of receiver-side signal-to-noise ratio respectively and the estimated value of the Doppler frequency f _D , the optimal transmission strategy switching threshold γ _i and the average value of the receiver-side signal-to-noise ratio Substituting the estimated value of Doppler frequency f _D into formula (4), the level crossing rate N _i can be obtained, and finally the average strategy duration of the current strategy can be obtained according to formula (5) [γ _i , γ _i+1 ) probability π _i is:

${\mathrm{<span\; class="notranslate">\; \&pi;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{\overset{{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}}{<span\; class="notranslate">\; \&Integral;</span>}}\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}}}\mathrm{<span\; class="notranslate">\; d\&gamma;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Described AMC method based on SD-FDE, its spectral efficiency is as shown in formula (7):

$\frac{\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; log</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; <</span>{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

where R and B are the data rate and received signal bandwidth respectively, M _i and C _i are the number of modulation constellations and the code rate of the optimal transmission strategy corresponding to the ith fading area [γ _i , γ _i+1 ), and N is The number of optimal transmission strategies.

According to step 1, the switching threshold γ _i (1≤i≤N) of the optimal transmission strategy can be obtained, and it can be substituted into formula (6) to obtain p(γ _i ≤γ<γ _i+1 ); according to step 2, the optimal The optimal transmission strategy determines the number of modulation constellations M _i and coding efficiency C _i , and substitutes the obtained p(γ _i ≤ γ<γ _i+1 ) and the number of modulation constellations M _i and coding efficiency C _i into formula (7) Then the spectral efficiency of the adaptive system using the AMC method can be obtained.

Specific embodiment six, in combination with figure and table, apply the comparative analysis of the AMC method based on the SC-FDE system and the non-adaptive system in the SUI-5 three-path mountainous channel model, and the specific implementation process is as follows:

Firstly, build the block diagram of the SC-FDE adaptive baseband simulation system, as shown in Figure 2, and the specific operation steps can be realized by those skilled in the art according to Figure 2. Figure 2 is a baseband simulation system based on the existing SC-FDE non-adaptive system in Figure 1, adding the AMC method module, channel classification and SNR estimation module; therefore, the SC-FDE adaptive baseband simulation system has adaptive The ability to adjust transmission parameters (modulation, coding) to adapt to time-varying channels. The channel model is selected as the SUI-5 three-path mountain channel model, the delays of each path are 0us, 4us, 10us, the corresponding path gains are 0, -5dB, -10dB, and the maximum Doppler frequency shift f _D is 2.5 Hz. The symbol rate is 6.336Msps, and the target bit error rate is 10 ^-5 .

Estimate channel information; channel estimation adopts least square (LS) algorithm; equalization adopts minimum mean square error (minimum mean square error, MMSE) frequency domain equalization algorithm; SNR estimation adopts MMSE algorithm, and the signal-to-noise ratio is greater than 5dB When the estimation error is less than 1dB; the structure of the frame is that 1 block of data contains 1 frame of pilot frame and 10 frames of data frame; the first frame of each block is a pilot frame, the first 256 bits are used for channel estimation, and the last 256 bits are used for Signal-to-noise ratio estimation. The cyclic prefix (Cyclic Prefix, CP) is 64 bits, and the data frame length is 512 bits.

The modulation methods used are BPSK, QPSK and 16QAM; the encoding methods are (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); thus, a total of 12 strategies are obtained by combining the above parameters, which are denoted as S1-S12. Considering the block code transmission and the limitation of transmission time 1ms in the hypothetical burst communication, the strategy of combining LDPC and BPSK is not adopted. All optional strategies are shown in Table 1.

Table 1 Adaptive Strategy Combination Table

Then, under the channel state of above-mentioned setting, carry out system simulation and obtain BER-SNR performance curve and throughput curve, the BER-SNR performance curve that described simulation obtains is shown in Figure 4, and the BER performance of a kind of strategy is better, and its The better the throughput performance. According to Figure 4, the SNR is divided into 7 fading regions: less than 8, [8,12], (12,15], (15,19], (19,26], (26,31], greater than 31dB; corresponding The strategy switching thresholds are 8dB, 12dB, 15dB, 19dB, 26dB and 31dB respectively. According to Fig. 4, search for the optimal transmission strategy with the largest throughput that satisfies the target bit error rate P _e = 10 ^-5 in each fading area, as shown in Table 2 Shown; The BER-SNR performance curve and the corresponding throughput curve of the strategy screened according to Table 2 are shown in Figures 5 and 6 respectively.

Table 2 Adaptive policy switching table

It can be seen from Table 2 that when the SNR is less than 8dB, the system will not transmit data in order to ensure the target bit error rate P _e =10 ⁻⁵ . At this time, the system only transmits control frames and pilot frames. Only when the estimated value of SNR is greater than 8dB, data transmission starts.

The average received signal-to-noise ratio In the case of , the average duration of each strategy is calculated by the formula (4) and formula (5) described in the fifth embodiment as shown in Table 3.

Table 3 The average duration of each strategy under different signal-to-noise ratios

It can be seen from Table 3 that with the average received SNR The duration of more reliable strategies becomes shorter, while the duration of more effective strategies becomes longer. The average duration of strategy 5 at 10dB and strategy 6 at both SNRs in Table 3 is ignored because it is less than 10 ^-4 ms; the reason for such a small average strategy duration is due to the average received SNR The fading areas that deviate from strategy 5 and strategy 6 are far away, so the probability that the signal-to-noise ratio falls in these regions _is small; The formula (5) calculates L'Hopital's rule should be used to solve the problem; judge whether the time of the currently selected optimal transmission strategy exceeds the average duration of the selected optimal transmission strategy If the currently selected optimal transmission strategy time is within the average strategy duration of the selected optimal transmission strategy If the current selected optimal transmission strategy is within, the currently selected optimal transmission strategy is maintained; if the currently selected optimal transmission strategy time exceeds the average duration of the selected optimal transmission strategy Only then will the selection and switching of new policies be performed.

Table 4 gives the In the case of SC-FDE adaptive baseband system spectrum efficiency. As a comparison, the spectral efficiency of the non-adaptive system is also given in Table 4. The spectral efficiency of the adaptive system is calculated by formula (7). Since the non-adaptive system is designed according to the worst state of the channel, the system can only adopt the most reliable transmission scheme of strategy 1.

It can be seen from Table 4 that under each SNR, the spectral efficiency of the adaptive system using the proposed method is higher than that of the non-adaptive system. along with The spectral efficiency of both systems increases, but the spectral efficiency of the adaptive system increases faster. exist When the value is higher, the advantage of the adaptive system is more obvious; if When , the spectral efficiency of the adaptive system is 215% higher than that of the non-adaptive system, which makes full use of the channel capacity.

Table 4 Comparison of spectral efficiencies of the two systems under different SNRs

In summary, the AMC method can ensure the efficient and reliable transmission of the SC-FDE adaptive system under the Rayleigh multipath channel, that is, it can make the communication system better adapt to the complex and changeable electromagnetic environment of the wireless channel.

Claims (5)

1. based on an AMC method for SC-FDE system, it is characterized in that, the concrete operation step that the method comprises:

Step one, the channel classification method adopted according to the channel classification module of SC-FDE self adaptation baseband system are classified to present 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 baseband system;

The signal to noise ratio snr information of present receiving machine that step 3, the current channel condition information obtained according to step one and step 2 obtain, switches in form at transmission policy and chooses the optimal transmission strategy mated with current channel condition;

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

Step 5, calculate average duration of current selected optimal transmission strategy obtain the average duration of described optimal transmission strategy

Exceed the average duration of described optimal transmission strategy the service time of step 6, current optimal policy return and perform step one, re-start the selection of optimal transmission strategy.

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

Under described SC-FDE self adaptation base band system off-line state, system emulation is carried out to given channel status, obtains 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 region [γ _i, γ _i+1), and determine the handoff threshold signal to noise ratio γ of transmission policy _i;

The decline of search signal to noise ratio allly meets target error rate P in region _ethe optimal transmission strategy in the corresponding signal to noise ratio decline region required, meets target error rate P by described _ethe optimal policy composition optimal policy collection required, and switch form according to this optimal transmission set of strategies determination optimal transmission strategy.

3. a kind of AMC method based on SC-FDE system according to claim 2, is characterized in that, described signal to noise ratio decline region [γ _i, γ _i+1) determined 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 the straight line that is parallel to transverse axis, obtain intersection point respectively with often kind of tactful BER-SNR curve, the abscissa that the intersection point obtained is corresponding is the handoff threshold signal to noise ratio γ of transmission policy _i, the SNR scope between every two thresholdings is signal to noise ratio decline region [γ _i, γ _i+1).

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

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

Solve the average duration of optimal transmission strategy the Markov model of a finite state is adopted to provide the average duration of described solution optimal transmission strategy approximation, the decline of signal to noise ratio is approximately the Markov process of a discrete time by this model, and this process comprises by a state transitions to the state of adjoining with it with maintain the original state constant, and its transition probability formula is:

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

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

p _i,i＝1-p _i,i+1-p _i,i-1(3)

Wherein i represents i-th state, and current status i can only transfer to the state i+1 or state i-1 that adjoin 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,ifor state i maintains the original state probability of state, N _ifor at state i optimal transmission strategy handoff threshold signal to noise ratio γ _iunder level crossing rate, T _sfor symbol period, π _ifor being in i-th decline region [γ _i, γ _i+1) probability: π _i=p (γ _i≤ γ < γ _i+1), under rayleigh fading channel, level crossing rate N _iprovided by formula (4):

$N_i=\sqrt{\frac{2\mathrm{\&pi;}{\mathrm{\&gamma;}}_i}{\stackrel{\&OverBar;}{\mathrm{\&gamma;}}}}{f}_D{e}^{-{\mathrm{\&gamma;}}_i/\stackrel{\&OverBar;}{\mathrm{\&gamma;}}}---\left(4\right)$

Wherein f _dfor Doppler frequency, the average duration of described optimal transmission strategy provided by formula (5):

$\stackrel{\&OverBar;}{{\mathrm{\&tau;}}_i}=\frac{T_s}{p_{i,i+1}+p_{i,i-1}}=\frac{{\mathrm{\&pi;}}_i}{N_{i+1}+N_i}---\left(5\right)$

Wherein T _sfor symbol period, π _ifor being in i-th decline region [γ _i, γ _i+1) probability: π _i=p (γ _i≤ γ < γ _i+1), N _ifor at state i optimal transmission strategy handoff threshold 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}for state i transfers to the probability of state i-1; The mean value of receiver end signal to noise ratio is obtained respectively by signal to noise ratio snr estimation and channel estimating with Doppler frequency f _destimated value, optimal transmission strategy handoff threshold signal to noise ratio γ _iwith the mean value of receiver end signal to noise ratio doppler frequency f _destimated value be updated to formula (4), namely try to achieve level crossing rate N _i, the Average Strategy duration of current strategies is finally tried to achieve again according to formula (5)