CN105721115A - Automatic repeat request method needing no error check code - Google Patents

Abstract

The invention discloses an automatic repeat request method needing no error check codes. The method comprises that a receiving end sets an optimum channel coefficient threshold, wherein through adoption of the threshold, an average receiving bit error rate can be minimized; a receiving end estimates a channel; when a channel coefficient amplitude is less than the threshold, the receiving end sends one bit of negative acknowledge (NAK) to the sending end; otherwise, the receiving end does not feed back and expresses acknowledgement; and the sending end sends a next frame or repeat according to the response. According to the method, the sending end does not need the error check codes and channel information; the channel coefficient threshold of the receiving end can be adjusted flexibly; ACK/NAK feedback only needs one bit; the performance of the method is better than the conventional ARQ; diversity reception and sending power control of ideal channel information are realized; and the diversity gain is increased linearly along with effective signal to noise ratio.

Description

A kind of automatic retransmission request method without error check code

Technical field

The present invention relates to a kind of automatic retransmission request method without error check code, based on effective signal-to-noise ratio, thresholding is optimized, it is adaptable to wireless communication technology field.

Background technology

The two kinds of error control strategies being widely used in data communication are that forward error controls FEC and HARQ ARQ.ARQ retransmits, by error checking and correction and data, the raising realizing reliability of communication system.Error check code conventional for ARQ in Modern communication standards is CRC, such as Ethernet, WLAN, LTE (Long Term Evolution).Additive white Gaussian noise channel AWGN design constant when being originally for ARQ, also can directly apply to wireless fading channel.

The raising of reliability is depended on the re-transmission to detection error frame by ARQ.It is known that re-transmission can reduce the handling capacity of system.And often unheeded, retransmit and also improve the total transmission energy being properly received needed for frame.Conventional reliability index average received bit error rate and Validity Index are handled up quantitative analysis, are all based on tradition signal to noise ratio.Signal to noise ratio is defined as symbol energy and the ratio of AWGN power spectral density, namely

${\mathrm{\γ}}_T=\frac{2{\mathrm{\σ}}^2{E}_{b,T}}{N_0}$

Wherein E_b,TIt is that every bit sends energy, and is not counted in the energy needed for retransmitting.And effectively receive the transmission energy actually E needed for every bit_b=E [L] E_b,T, wherein E [L] is average transmission number of times.Therefore, effective signal-to-noise ratio should be defined as

$\mathrm{\γ}=\frac{2{\mathrm{\σ}}^2{E}_b}{N_0}$

As shown in Figure 1 under awgn channel, the average transmission number of times of traditional ARQ using CRC during due to middle low signal-to-noise ratio is higher, and therefore based on the average received performance of BER of effective signal-to-noise ratio, actual not have the performance based on tradition signal to noise ratio of display in document so good.It practice, the average received bit error rate of ARQ is more a lot of than the System level gray correlation of zero defect verification when middle low signal-to-noise ratio, and the not monotone decreasing with the increase of effective signal-to-noise ratio.

In radio communication, signal, except by AWGN influence of noise, is also subject to the property the taken advantage of complex channel coefficient of time-varying.The channel of corresponding each channel coefficients is equivalent to the awgn channel of different signal to noise ratio.ARQ directly applies to wireless fading channel, and the performance under deep fade is obviously poor.The no matter value size of average signal-to-noise ratio, when instantaneous signal-to-noise ratio is less, the instantaneous poor-performing of ARQ.It is average in the performance of different signal to noise ratio awgn channels that the average behavior of fading channel is equivalent to it.Therefore ARQ is also poor in the average behavior of harmonic(-)mean signal to noise ratio.The ARQ analysis of application CRC and Hamming code be all show above phenomenon, there is certain universality.

Summary of the invention

It is an object of the invention to overcome above-mentioned existing ARQ problem under wireless fading channel harmonic(-)mean signal to noise ratio, a kind of automatic retransmission request method without error check code is proposed, by to channel coefficients monitoring and the repeat requests condition based on channel coefficients, improving the reliability of communication flexibly.

It is an object of the invention to be achieved through the following technical solutions: a kind of automatic retransmission request method without error check code, the method comprises the following steps:

(1) the channel coefficients thresholding h of receiving terminal is set^TH；

(2), after the information of transmitting terminal is modulated, it is transmitted in units of frame.

(3) receiving terminal amplitude according to the Signal estimation channel coefficients received.

(4) receiving terminal is by channel coefficients amplitude and channel coefficients thresholding h set in advance^THRelatively.When channel coefficients amplitude is less than this thresholding, receiving terminal sends the negative response of 1 bit (NAK) to transmitting terminal.When channel coefficients amplitude is more than or equal to thresholding, receiving terminal then sends the affirmative acknowledgement (ACK) of 1 bit or with not feedback representation affirmative, and is demodulated judgement to received signal.

(5) transmitting terminal receives response, sends next frame according to response or retransmits, if particularly as follows: receive ACK response or be not received by response, then sending next frame；If receiving NAK response, then retransmit.

Further, in step 1, channel coefficients thresholding is set by following steps:

(1.1) receiving terminal obtains following parameter by channel estimating: channel coefficients h, variance 2 σ of rayleigh fading channel coefficient², the bilateral power spectral density N of AWGN₀/2。

(1.2) assuming that receiving terminal can realize perfect channel estimation, receiving terminal receives the instantaneous bit error rate of every bit signal and is represented by:

$P\left(e_b\right|\left|h\right|)=\frac{1}{2}erfc\left(\sqrt{\frac{{\mathrm{\αE}}_{b,T}{\left|h\right|}^2}{N_0}}\right)-c\·{\mathrm{erfc}}^2\left(\sqrt{\frac{{\mathrm{\αE}}_{b,T}{\left|h\right|}^2}{N_0}}\right)---\left(1\right)$

Wherein erfc is Gauss error function, e_bRepresent bit error code event, E_b,T(the known general knowledge of this area) is determined by modulation system for the energy per bit sent, constant α and c.Formula (1) can be approximately

$P\left(e_b\right|\left|h\right|)=\frac{1}{2}erfc\left(\sqrt{\frac{{\mathrm{\αE}}_{b,T}{\left|h\right|}^2}{N_0}}\right)---\left(2\right)$

Using Qie Nuofu circle, formula (1) upper bound is

$P\left(e_b\right|\left|h\right|)\≤\frac{1}{2}\exp (-\frac{{\mathrm{\αE}}_{b,T}{\left|h\right|}^2}{N_0})---\left(3\right)$

(1.3) utilizing Bayes theorem, receiving terminal receives the bit error rate of frame and is expressed as

$P\left(e_b\right|\left|h\right|>\left|h^{TH}\right|)=\frac{P(e_b,|h|>|h^{TH}\left|\right)}{P\left(\right|h|>|h^{TH}\left|\right)}=\frac{{\∫}_{{\left|h^{TH}\right|}^2}^{\mathrm{\∞}}P\left(e_b\right|x={\left|h\right|}^2)p_{{\left|h\right|}^2}\left(x\right)dx}{{\∫}_{{\left|h^{TH}\right|}^2}^{\mathrm{\∞}}{p}_{{\left|h\right|}^2}\left(x\right)dx}---\left(4\right)$

Wherein, | h^TH| for the thresholding of receiving terminal；

Instantaneous bit error rate in the multiple Gauss distribution of substitution channel coefficients h and formula (3), receiving bit error rate is

$P\left(e_b\right|\left|h\right|>\left|h^{TH}\right|)<\frac{1}{2}\frac{1}{e^{-\mathrm{\&rho;}}\mathrm{\&alpha;}\mathrm{\&gamma;}+1}\exp (-{\mathrm{\&rho;e}}^{-\mathrm{\&rho;}}\mathrm{\&alpha;}\mathrm{\&gamma;})---\left(5\right)$

Wherein ρ=| h^TH|²/2σ²For normalization channel coefficients thresholding, γ is the effective signal-to-noise ratio considering retransmission energy.Formula (4) can be approximately

$P\left(e_b\right|\left|h\right|>\left|h^{TH}\right|)\&ap;\frac{1}{2\mathrm{\&alpha;}\mathrm{\&gamma;}}\exp (-{\mathrm{\&rho;e}}^{-\mathrm{\&rho;}}\mathrm{\&alpha;}\mathrm{\&gamma;}+\mathrm{\&rho;})---\left(6\right)$

(1.4) trying to achieve, based on formula (6), the optimum threshold value minimizing average received bit error rate is

$\left|h_o^{TH}\right|=\mathrm{\&sigma;}\sqrt{2\&lsqb;1-W\left(\frac{e}{\mathrm{\&alpha;}\mathrm{\&gamma;}}\right)\&rsqb;}---\left(7\right).$

The present invention compared with prior art, has the advantage that

(1) information of transmitting terminal is modulated and sends in units of frame, does not do requirement to whether this information is encoded.Without error checking and correction coding or other error checking methods；When design object and channel conditions change need to be adjusted, it is not necessary to changing frame length and code length, therefore circuit realiration is relatively simple.

(2) receiving terminal amplitude according to the Signal estimation channel coefficients received.Channel estimating is the steps necessary of coherent demodulation, therefore without changing the original channel estimating part of receiving terminal.

(3) channel coefficients amplitude is compared by receiving terminal with the channel coefficients thresholding pre-set, to determine transmission and the signal demodulation of ACK/NAK response.Thresholding can carry out adjusting in real time under line or on line according to the long-term situation of different design objects and channel, and the realization of method is comparatively flexible.

(4), after transmitting terminal receives ACK/NAK response, any retransmission protocol can be used to continue to send next frame/re-transmission, be such as but not limited to traditional stop-and-wait, rollback N frame and selective retransmission.Therefore any existing transmitting terminal retransmission protocol it is applicable to, it is not required that amendment transmitting terminal.

(5) the overall bit-error rate performance of the present invention is along with the increase of effective signal-to-noise ratio and monotone decreasing, it is simple to determine the signal to noise ratio reached needed for error rate performance requirement.Bit error rate performance is better than without retransmission system, uses traditional ARQ of CRC, transmitting terminal to have continuously the transmission power control communication system of desirable channel condition information CSI, and transmitting terminal of the present invention is without channel condition information.The realized diversity gain of the present invention linearly increases with effective signal-to-noise ratio, and trends towards infinity, namely singly enters to have more the fixed reception gain of SIMO system more than tradition.

Accompanying drawing explanation

Fig. 1 be tradition ARQ under awgn channel based on the performance of BER of effective signal-to-noise ratio.

Fig. 2 is the system block diagram of the inventive method.

Fig. 3 is the performance of BER of the inventive method example.

Detailed description of the invention

Below in conjunction with accompanying drawing, the example of the present invention is elaborated.This example is carried out under premised on technical solution of the present invention, gives detailed embodiment and performance evaluation, but protection scope of the present invention is not limited to following example 1.Comprise the following steps:

Step one, receiving terminal sets channel coefficients thresholding, and when actual channel coefficients this thresholding of low mistake, channel is considered unreliable.

Step 2, the information of transmitting terminal, without chnnel coding, is modulated by binary phase shift keying (BPSK), sends in units of frame length k=12.

Step 3, channel is rayleigh fading channel.Receiving terminal can realize perfect channel estimation, obtains channel coefficients h accurately.

Step 4, receiving terminal is by channel coefficients amplitude | h | and the channel coefficients thresholding pre-set | h^TH| compare.When | h | < | h^TH| time, receiving terminal sends the negative response of 1 bit (NAK) to transmitting terminal.As | h | > | h^TH| time, receiving terminal then sends the affirmative acknowledgement (ACK) of 1 bit, and carries out BPSK demodulation to received signal.

Step 5, after transmitting terminal receives ACK/NAK response, uses traditional stop-and-wait, rollback N frame and selective retransmission agreement to retransmit.The performance of BER of these retransmission protocols is identical.

The method setting channel coefficients thresholding in step one is as follows:

Step 1.1, receiving terminal obtains following parameter by channel estimating: channel coefficients h, variance 2 σ of rayleigh fading channel coefficient², the bilateral power spectral density N of AWGN₀/2。

Step 1.2, it is assumed that receiving terminal can realize perfect channel estimation.When channel coefficients is h, receiving terminal receives the instantaneous bit error rate of every bit signal and is represented by

$P\left(e_b\right|\left|h\right|)=\frac{1}{2}erfc\left(\sqrt{\frac{{\mathrm{\&alpha;E}}_{b,T}{\left|h\right|}^2}{N_0}}\right)-c\&CenterDot;{\mathrm{erfc}}^2\left(\sqrt{\frac{{\mathrm{\&alpha;E}}_{b,T}{\left|h\right|}^2}{N_0}}\right)---\left(1\right)$

Wherein erfc is Gauss error function, e_bRepresent bit error code event, E_b,TFor the energy per bit sent, as the known general knowledge of this area, constant α and c are determined by modulation system.Different modulation systems, constant α is different with c value, and (1) formula can be approximately

$P\left(e_b\right|\left|h\right|)=\frac{1}{2}erfc\left(\sqrt{\frac{{\mathrm{\&alpha;E}}_{b,T}{\left|h\right|}^2}{N_0}}\right)---\left(2\right)$

Using Qie Nuofu circle, (1) formula upper bound is

$P\left(e_b\right|\left|h\right|)\&le;\frac{1}{2}\exp (-\frac{{\mathrm{\&alpha;E}}_{b,T}{\left|h\right|}^2}{N_0})---\left(3\right)$

Wherein, the constant that BPSK modulation /demodulation optimum receiver is corresponding is α=1.

Step 1.3, utilizes Bayes theorem, and automatic retransmission request method receiving terminal receives the bit error rate of frame and is expressed as

$P\left(e_b\right|\left|h\right|>\left|h^{TH}\right|)=\frac{P(e_b,|h|>|h^{TH}\left|\right)}{P\left(\right|h|>|h^{TH}\left|\right)}=\frac{{\&Integral;}_{{\left|h^{TH}\right|}^2}^{\mathrm{\&infin;}}P\left(e_b\right|x={\left|h\right|}^2)p_{{\left|h\right|}^2}\left(x\right)dx}{{\&Integral;}_{{\left|h^{TH}\right|}^2}^{\mathrm{\&infin;}}{p}_{{\left|h\right|}^2}\left(x\right)dx}---\left(4\right)$

Wherein, | h^TH| for the thresholding of receiving terminal；

Substituting into multiple Gauss distribution and the instantaneous bit error rate in (3) formula of channel coefficients h, receiving bit error rate is

$P\left(e_b\right|\left|h\right|>\left|h^{TH}\right|)<\frac{1}{2}\frac{1}{e^{-\mathrm{\&rho;}}\mathrm{\&gamma;}+1}\exp (-{\mathrm{\&rho;e}}^{-\mathrm{\&rho;}}\mathrm{\&gamma;})---\left(5\right)$

Wherein ρ=| h^TH|²/2σ²For normalization channel coefficients thresholding, γ is the effective signal-to-noise ratio considering retransmission energy.When middle high s/n ratio, formula (4) can be approximately

$P\left(e_b\right|\left|h\right|>\left|h^{TH}\right|)\&ap;\frac{1}{2\mathrm{\&gamma;}}\exp (-{\mathrm{\&rho;e}}^{-\mathrm{\&rho;}}\mathrm{\&gamma;}+\mathrm{\&rho;})---\left(6\right)$

Step 1.4, tries to achieve, based on (6) formula, the optimum threshold value minimizing average received bit error rate and should be

$\left|h_o^{TH}\right|=\mathrm{\&sigma;}\sqrt{2\&lsqb;1-W\left(\frac{e}{\mathrm{\&gamma;}}\right)\&rsqb;}---\left(7\right)$

Thresholding value is set to optimal value0.5 σ and 2 σ, by the average received performance of BER under rayleigh fading channel is carried out theoretical analysis and numerical method, result is shown in Fig. 3.The performance of the present invention using optimum thresholding is better than threshold value 0.5 σ and 2 σ.

Comparing for justice, the example being below used for comparing uses identical BPSK to modulate with the present invention, perfect channel estimation.

Example 2 for comparing: without retransmission system.

Example 3 for comparing: tradition ARQ transmitting terminal information bit length k=12, adds redundancy function 4 bit through CRC-4 coding.Receiving terminal CRC check makes mistakes and feeds back NAK；Verification is by then feeding back ACK, and carries out BPSK demodulation to received signal.

Example 4 for comparing: singly entering to have more (SIMO) diversity reception can realize diversity by time, frequency and three kinds of space mode.Same frame information is repeated to send L time by time diversity.L different frequency range of same frame information is sent by frequency diversity simultaneously.Space diversity receives same frame information by L root antenna.Three receives L time the signal of same frame information and carries out maximum-ratio combing.Under identical total effective signal-to-noise ratio (after diversity merging), time, frequency and space can realize identical diversity gain L.

Example 5 for comparing: transmitting terminal has continuously the transmission power control system of desirable channel condition information.Accurate channel coefficients h zero defect is fed back to transmitting terminal without time delay by receiving terminal.Transmitting terminal is according to precise channel coefficient, to minimize the target adjustment transmit power of bit error rate.

As it is shown on figure 3, the error performance of present example along with the increase of effective signal-to-noise ratio monotone decreasing, it is simple to determine that reaching average received performance of BER requires required signal to noise ratio.The error performance of the present invention is better than, without retransmission system, using the ARQ of CRC also superior to tradition.The realized diversity gain of the present invention linearly increases with effective signal-to-noise ratio, and trends towards infinity, namely more than the fixed reception diversity gain of example 4 tradition SIMO system.The error performance of the present invention also overall example 5 transmitting terminal that is better than has continuously the transmission power control system of desirable channel condition information；And transmitting terminal of the present invention is without channel condition information, channel status only feeds back to transmitting terminal with the ACK/NAK of a bit, and feedback quantity is little.

Claims (2)

1. the automatic retransmission request method without error check code, it is characterised in that the method comprises the following steps:

(1) the channel coefficients thresholding h of receiving terminal is set^TH；

(2), after the information of transmitting terminal is modulated, it is transmitted in units of frame.

(3) receiving terminal amplitude according to the Signal estimation channel coefficients received.

(4) receiving terminal is by channel coefficients amplitude and channel coefficients thresholding h set in advance^THRelatively.When channel coefficients amplitude is less than this thresholding, receiving terminal sends the negative response of 1 bit (NAK) to transmitting terminal.When channel coefficients amplitude is more than or equal to thresholding, receiving terminal then sends the affirmative acknowledgement (ACK) of 1 bit or with not feedback representation affirmative, and is demodulated judgement to received signal.

(5) transmitting terminal receives response, sends next frame according to response or retransmits, if particularly as follows: receive ACK response or be not received by response, then sending next frame；If receiving NAK response, then retransmit.

2. according to claim 1 without error check code automatic retransmission request method, it is characterized in that, in step 1, channel coefficients thresholding is set by following steps:

(1.1) receiving terminal obtains following parameter by channel estimating: channel coefficients h, variance 2 σ of rayleigh fading channel coefficient², the bilateral power spectral density N of AWGN₀/2。

(1.2) assuming that receiving terminal can realize perfect channel estimation, receiving terminal receives the instantaneous bit error rate of every bit signal and is represented by:

$P\left(e_b\right|\left|h\right|)=\frac{1}{2}erfc\left(\sqrt{\frac{{\mathrm{\&alpha;E}}_{b,T}{\left|h\right|}^2}{N_0}}\right)-c\&CenterDot;{\mathrm{erfc}}^2\left(\sqrt{\frac{{\mathrm{\&alpha;E}}_{b,T}{\left|h\right|}^2}{N_0}}\right)---\left(1\right)$

Wherein erfc is Gauss error function, e_bRepresent bit error code event, E_b,T(the known general knowledge of this area) is determined by modulation system for the energy per bit sent, constant α and c.Formula (1) can be approximately

$P\left(e_b\right|\left|h\right|)=\frac{1}{2}erfc\left(\sqrt{\frac{{\mathrm{\&alpha;E}}_{b,T}{\left|h\right|}^2}{N_0}}\right)---\left(2\right)$

Using Qie Nuofu circle, formula (1) upper bound is

$P\left(e_b\right|\left|h\right|)\&le;\frac{1}{2}\exp (-\frac{{\mathrm{\&alpha;E}}_{b,T}{\left|h\right|}^2}{N_0})---\left(3\right)$

(1.3) utilizing Bayes theorem, receiving terminal receives the bit error rate of frame and is expressed as

$P\left(e_b\left|\right|h|>|h^{TH}|\right)=\frac{P(e_b,|h|>|h^{TH}\left|\right)}{P\left(\right|h|>|h^{TH}\left|\right)}=\frac{{\&Integral;}_{{\left|h^{TH}\right|}^2}^{\mathrm{\&infin;}}P\left(e_b\right|x={\left|h\right|}^2)p_{{\left|h\right|}^2}\left(x\right)dx}{{\&Integral;}_{{\left|h^{TH}\right|}^2}^{\mathrm{\&infin;}}{p}_{{\left|h\right|}^2}\left(x\right)dx}---\left(4\right)$

Wherein, | h^TH| for the thresholding of receiving terminal；

Instantaneous bit error rate in the multiple Gauss distribution of substitution channel coefficients h and formula (3), receiving bit error rate is

$P\left(e_b\right|\left|h\right|>\left|h^{TH}\right|)<\frac{1}{2}\frac{1}{e^{-\mathrm{\&rho;}}\mathrm{\&alpha;}\mathrm{\&gamma;}+1}\exp (-{\mathrm{\&rho;e}}^{-\mathrm{\&rho;}}\mathrm{\&alpha;}\mathrm{\&gamma;})---\left(5\right)$

Wherein ρ=| h^TH|²/2σ²For normalization channel coefficients thresholding, γ is the effective signal-to-noise ratio considering retransmission energy.Formula (4) can be approximately

$P\left(e_b\right|\left|h\right|>\left|h^{TH}\right|)=\frac{1}{2\mathrm{\&alpha;}\mathrm{\&gamma;}}\exp (-{\mathrm{\&rho;e}}^{-\mathrm{\&rho;}}\mathrm{\&alpha;}\mathrm{\&gamma;}+\mathrm{\&rho;})---\left(6\right)$

(1.4) trying to achieve, based on formula (6), the optimum threshold value minimizing average received bit error rate is

$\left|h_o^{TH}\right|=\mathrm{\&sigma;}\sqrt{2\&lsqb;1-W\left(\frac{e}{\mathrm{\&alpha;}\mathrm{\&gamma;}}\right)\&rsqb;}---\left(7\right).$