CN102820923A - Transmitting light path selecting method for combined diversity reception in MIMO (Multiple-input and Multiple-Output)free space optical communication - Google Patents

Abstract

The invention discloses a transmitting light path selecting method for combined diversity reception in MIMO (Multiple-input and Multiple-Output)free space optical communication, and belongs to the technical field of MIMO free space optical communication. The transmitting light path selecting method comprises the following steps of: carrying out comparison on the light intensity gain after the gains from each laser to Nr detectors and the like are combined to obtain a serial number of the laser with maximum light intensity gain value, and then feedbacking the serial number of the laser to a light path selector at a transmitting end by a low-speed feedback channel so as to enable the transmitting end to select and activate the optimal laser for transmitting light signals. The method disclosed by the invention has the advantages that the system performances of the MIMO free space optical communication modulated on basis of OOK (On-Off Keying) are obviously improved, and compared with maximal-ratio combining reception, the complexity for realizing the method of united equal-gain combining reception, adopted by the invention, on hardware can be reduced.

Description

The emission optical path system of selection of associating diversity reception in the MIMO FSO

Technical field

The present invention relates to the emission optical path system of selection of associating diversity reception in a kind of MIMO FSO, belong to MIMO free space optical communication technology field.

Background technology

As everyone knows, FSO because low cost, good confidentiality, easy for installation, need not the frequency permission etc. advantage, in the radio communication of two-forty closely, get more and more people's extensive concerning.Especially be used to solve the communication of " last kilometer ".Yet; FSO can receive the influence of rain, mist, atmospheric turbulance; There is scintillation effect in the light intensity that receives signal, causes that the signal strength signal intensity random fluctuation changes, particularly under the strong turbulence situation; Light signal can receive serious interference, causes the bigger error rate or short time interrupted communication link.Can effectively resist the signal fadeout that atmospheric turbulance causes in thought (such as transmit diversity techniques orthogonal space time-code, duplication code are arranged, reception diversity technology has high specific merging etc.) the introducing FSO with space diversity, improve the reliability of communication.

The emitting antenna selecting technology is at multiple-input and multiple-output (MIMO; Multiple input-multiple-output) broad research in the system; It has reduced the complexity of radio frequency link on the basis that has kept the effective spatial degrees of freedom of many antennas, and reduces the error rate of system through the channel condition information that transmitting terminal obtains.Because the free space optical channel can be regarded the quasistatic flat fading channel as; It is feasible that transmitting terminal obtains channel condition information through feedback channel; Therefore; In Shi Yiyue, 2009 Bi Chazikasidiluowa Kui (Beatriz Castillo-Vazquez) has now proposed transmitting terminal at " electronics wall bulletin " (Electronics Letters) and utilizes channel condition information to select the light beam transmission path emission diversity method of (being called for short " optical path "), and research is illustrated in that its performance is superior to traditional orthogonal space time-code and duplication code transmit diversity techniques under the strong turbulence condition.

Yet; The Bi Chazikasidiluowa method of Kui now mainly is in Nt laser of transmitting terminal; Utilize channel condition information to select best optical path to launch light signal, receiving terminal only is furnished with a detector, does not make full use of the reception diversity technology in the space diversity.

Summary of the invention

To the defective of prior art, the present invention provides the emission optical path system of selection of associating diversity reception in a kind of MIMO FSO.This method is the emission optical path system of selection that the associating equal gain diversity receives in a kind of strong turbulence MIMO FSO.

Method of the present invention is following:

To a Nt * Nr MIMO free-space optical communication system; Wherein Nt is a number of lasers, and Nr is the photodetector number, supposes not have under the situation of aiming at the error mistake; Adopt the on-off keying OOK modulation system of detection of intensity modulated/directly; Here OOK signal format of considering such as Bi Chazikasidiluowa are now described in the Kui Wenzhang: have Gaussian pulse shape and low duty ratio, its average transmit power is P, the Euclidean distance in the OOK planisphere between two equiprobability signaling points

T wherein _bBe bit period, when adopting kT _bDuring the Gaussian pulse in cycle

1≤i≤Nt, 1≤j≤Nr, i laser is to the light intensity gain I of j detector _IjProbability density obey complex exponential and distribute, promptly

$f_{I_{\mathrm{ij}}}\left(I_{\mathrm{ij}}\right)=e^{-I_{\mathrm{ij}}},I_{\mathrm{ij}}>0---\left(1\right)$

For MIMO FSO environment, I _IjBe a slow fading process and satisfy independent same distribution between each component;

At Nt * Nr MIMO free-space optical communication system, the mathematic(al) representation of the emission optical path system of selection that the associating equal gain diversity that the present invention proposes receives is following:

$I_{\max }=\underset{1\≤i\≤N_t}{\max }\{B_i=\underset{j=1}{\overset{N_r}{\mathrm{\Σ}}}{I}_{\mathrm{ij}}\}$ $K=\underset{1\≤i\≤N_t}{\arg \max }\{B_i=\underset{j=1}{\overset{N_r}{\mathrm{\Σ}}}{I}_{\mathrm{ij}}\}---\left(2\right)$

Wherein, B _iRepresent i laser to gain through the light intensity after the equal gain combining, therefore unite the emission optical path system of selection of equal gain diversity reception and just pass through relatively B to Nr detector ₁～B _NtMaximum I is obtained in light intensity gain after this Nt equal gain combining _Max, then through feedback channel with this maximum the sequence number K of corresponding laser pass to transmitting terminal, thereby make transmitting terminal selected and activate this optimum laser and launch light signal.

The Bi Chazikasidiluowa mathematic(al) representation of the method for Kui now does

$I_m=\underset{1\≤i\≤N_t,j=0}{\max }{I}_{\mathrm{ij}}---\left(3\right)$

(2) formula is compared with (3) formula, can be known I _Max>I _m, the condition bit error rate P under above-mentioned two kinds of methods _b(I _Max), P _b(I _m) do

$P_b(e\backslash I_{\max })=Q\left(\sqrt{2\mathrm{\&gamma;}{I_{\max }}^2}\right)<P_b(e\backslash I_m)=Q\left(\sqrt{2\mathrm{\&gamma;}{{\mathrm{\&xi;I}}_m}^2}\right)---\left(4\right)$

Wherein, Q refers to the Q function, average signal-to-noise ratio γ=P ²T _b/ N ₀, N ₀Be the one-sided power spectrum density of white Gaussian noise.

And then the bit error rate under above-mentioned two kinds of methods does

$P_{b,I_{\max }}={\&Integral;}_0^{\&infin;}{P}_b(e\backslash I_{\max })f\left(I_{\max }\right){\mathrm{dI}}_{\max }<P_{b,I_m}={\&Integral;}_0^{\&infin;}{P}_b(e\backslash I_m)f\left(I_m\right)d{I}_m---\left(5\right)$

Wherein, bit error rate is the integration of the probability density function product of condition bit error rate and light intensity gain, f (I _Max), f (I _m) be respectively I _Max, I _mProbability density function.

(5) formula shows, the method bit error rate of Kui is low now than Bi Chazikasidiluowa in the emission optical path system of selection that the associating equal gain diversity that the present invention proposes receives, and just explaining has significant improvement on the systematic function.

The method that the present invention proposes compare Bi Chazikasidiluowa now the method for Kui significant improvement is arranged on systematic function, and adopt associating equal gain combining method of reseptance to merge method of reseptance and on hardware is realized, can reduce its complexity than high specific.

Description of drawings

Fig. 1 is the free-space optical communication system block diagram based on method of the present invention.

Wherein, 1, the OOK modulator, 2, the optical path selector, 3, the 1st lasers, 4, the 2nd lasers, 5, the 1st detectors, 6, the 2nd detectors, 7, a Nr detector, 8, the equal gain combining receiver, 9, decision device,

1. be feedback channel.

Fig. 2 for method of the present invention and Bi Chazikasidiluowa now the method for Kui Gaussian pulse OOK modulates, number of lasers is the comparison diagram of 2 o'clock bit error rates adopting.

Fig. 3 is a software flow pattern of the present invention.

Embodiment

Embodiment:

With the transmitting terminal number of lasers is 2, and the receiving terminal number of detectors is that the MIMO free-space optical communication system of Nr=2 or 3 is that example is introduced the present invention.System block diagram is as shown in Figure 1: input data sequence carries out the modulation of

Gaussian pulse through the OOK modulator; From two lasers, select an optimum optical path through the optical path selector then, and pass through the laser emission at this optimum optical path place.

The acquisition of optimum optical path is following:

Receiving terminal known channel state information has just been known light intensity gain I _Ij, suppose that the receiving terminal photoelectric conversion efficiency is that 1, an i laser gains through the light intensity after the equal gain combining to Nr (Nr=2 or 3) detector If B ₁＜B ₂, according to (2) formula, can know that the optical path of the 2nd laser is optimum, therefore the sequence number of this laser is fed back to the optical path selector of transmitting terminal through the feedback channel of a low speed, the 2nd laser is chosen and activates and launch thus, otherwise, B ₁>B ₂, selected the 1st laser emission.

As the index of weighing systematic function, emission optical path system of selection that the associating equal gain diversity that the present invention is proposed receives and the Bi Chazikasidiluowa method of Kui now compare with bit error rate in the present invention.Comparative result is as shown in Figure 2, and the software emulation flow chart is as shown in Figure 3.

Among Fig. 2, method of the present invention is 2 or 3 o'clock in the receiving terminal number of detectors, obviously finds out, the method bit error rate of Kui is low now than Bi Chazikasidiluowa for method of the present invention.

Claims (1)

1. the emission optical path system of selection of associating diversity reception in the MIMO FSO is characterized in that,

To a Nt * Nr MIMO free-space optical communication system; Wherein Nt is a number of lasers, and Nr is the photodetector number, supposes not have under the situation of aiming at the error mistake; Adopt the on-off keying OOK modulation system of detection of intensity modulated/directly; Here OOK signal format of considering such as Bi Chazikasidiluowa are now described in the Kui Wenzhang: have Gaussian pulse shape and low duty ratio, its average transmit power is P, the Euclidean distance in the OOK planisphere between two equiprobability signaling points

T wherein _bBe bit period, when adopting kT _bDuring the Gaussian pulse in cycle

1≤i≤Nt, 1≤j≤Nr, i laser obeyed complex exponential to the probability density of the light intensity gain Iij of j detector and distributed, promptly

$f_{I_{\mathrm{ij}}}\left(I_{\mathrm{ij}}\right)=e^{-I_{\mathrm{ij}}},I_{\mathrm{ij}}>0---\left(1\right)$

For MIMO FSO environment, I _IjBe a slow fading process and satisfy independent same distribution between each component;

At Nt * Nr MIMO free-space optical communication system, the mathematic(al) representation of the emission optical path system of selection that the associating equal gain diversity that the present invention proposes receives is following:

$I_{\max }=\underset{1\&le;i\&le;N_t}{\max }\{B_i=\underset{j=1}{\overset{N_r}{\mathrm{\&Sigma;}}}{I}_{\mathrm{ij}}\}$ $K=\underset{1\&le;i\&le;N_t}{\arg \max }\{B_i=\underset{j=1}{\overset{N_r}{\mathrm{\&Sigma;}}}{I}_{\mathrm{ij}}\}---\left(2\right)$

Wherein, B _iRepresent i laser to gain through the light intensity after the equal gain combining, therefore unite the emission optical path system of selection of equal gain diversity reception and just pass through relatively B to Nr detector ₁～B _NtMaximum I is obtained in light intensity gain after this Nt equal gain combining _Max, then through feedback channel with this maximum the sequence number K of corresponding laser pass to transmitting terminal, thereby make transmitting terminal selected and activate this optimum laser and launch light signal;

The Bi Chazikasidiluowa mathematic(al) representation of the method for Kui now does

$I_m=\underset{1\&le;i\&le;N_t,j=0}{\max }{I}_{\mathrm{ij}}---\left(3\right)$

(2) formula is compared with (3) formula, can be known I _Max＞I _m, the condition bit error rate P under above-mentioned two kinds of methods _b(I _Max), P _b(I _m) do

$P_b(e\backslash I_{\max })=Q\left(\sqrt{2\mathrm{\&gamma;}{I_{\max }}^2}\right)<P_b(e\backslash I_m)=Q\left(\sqrt{2\mathrm{\&gamma;}{{\mathrm{\&xi;I}}_m}^2}\right)---\left(4\right)$

Wherein, Q refers to the Q function, average signal-to-noise ratio γ=P ²T _b/ N ₀, N ₀Be the one-sided power spectrum density of white Gaussian noise;

And then the bit error rate under above-mentioned two kinds of methods

does

$P_{b,I_{\max }}={\&Integral;}_0^{\&infin;}{P}_b(e\backslash I_{\max })f\left(I_{\max }\right){\mathrm{dI}}_{\max }<P_{b,I_m}={\&Integral;}_0^{\&infin;}{P}_b(e\backslash I_m)f\left(I_m\right)d{I}_m---\left(5\right)$

Wherein, bit error rate is the integration of the probability density function product of condition bit error rate and light intensity gain, f (I _Max), f (I _m) be respectively I _Max, I _mProbability density function; (5) formula shows, the method bit error rate of Kui is low now than Bi Chazikasidiluowa in the emission optical path system of selection that the associating equal gain diversity that the present invention proposes receives, and just explaining has significant improvement on the systematic function.

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