CN104618300A - DCO-OFDM DC bias and rapid power optimizing method under double restrictions - Google Patents

Abstract

The invention discloses a DCO-OFDM (Direct-Current-Biased Orthogonal Frequency Division Multiplexing) DC bias and rapid power optimizing method under double restrictions aiming at visible light communication. DCO-OFDM DC bias and subcarrier power optimizing is a complex non-convex and non-linear optimizing problem. The DCO-OFDM DC bias and rapid power optimizing method can quickly seek the optimum DC bias Bdc and subcarrier power pk distribution scheme on the conditions of optical power limitation or electric power limitation or both optical power limitation and electric power limitation. The DC bias Bdc and subcarrier power pk obtained through the DCO-OFDM DC bias and rapid power optimizing method can maximize the data rate of the system or minimize the bit error rate in the fixed modulation scheme. The DCO-OFDM DC bias and rapid power optimizing method has the advantages of fast rate of convergence, small calculation amount, easiness in achievement, high result accuracy, etc.

Description

DCO-OFDM direct current biasing under dual restriction and power fast Optimization

Technical field

The present invention relates to visible light communication field, in particular to the fast Optimization of a kind of DCO-OFDM communication system direct current biasing and sub-carrier power.

Background technology

Next-Generation Wireless Communication Systems (5G) will introduce some supplementary access technologies.And the basis of 5G is very likely become based on the visible light communication technology of light-emitting diode (Light Emitting Diode, be called for short LED).General employing intensity modulated direct-detection in LED-based visible light communication system, i.e. transmitting terminal light strong representation signal amplitude, receiving terminal detects light intensity and eats.Transmitting terminal changes the signal of telecommunication into light signal by LED, and light signal is by after dissemination channel, and light signal is converted to the signal of telecommunication by photodiode by receiving terminal, for demodulator circuit process.Because transmission signal vehicle is light intensity, thus require that sending signal must be nonnegative real number.

Current OFDM multi-carrier technology (Orthogonal Frequency DivisionMultiplexing is called for short OFDM), as a kind of effective solution of broadband system, is widely used in visible light communication system.Multi-transceiver technology and visible light communication technology are combined, the advantage of visible light communication and multi-transceiver technology that made it have both is a kind of technology with higher Research Significance and practical value.Be necessary for nonnegative real number owing to sending signal, the multi-transceiver technology in conventional radio frequency needs improvement just can be applied to visible light communication field.Direct current biasing OFDM multi-carrier technology (Direct-Current-BiasedOptical OFDM is called for short DCO-OFDM), as the one in many evolutionary approach, has the high advantage of spectrum efficiency compared to other schemes.DCO-OFDM has superposed DC component on transmission signal, by after superposition still minus part prune, thus make bipolar signal become unipolar signal, to meet the condition of signal nonnegativity in visible light communication.

In DCO-OFDM system, direct current biasing can regulate, but not signal transmission.Excessive direct current biasing can waste energy; And too small meeting causes signal Severe distortion.Thus there is a most suitable direct current biasing.The present invention proposes rapid solving direct current biasing B under a kind of flat weak channel _dcand sub-carrier power the method of largeization system data rates.System after optimization improves systematic function greatly.

Summary of the invention

The invention provides DCO-OFDM system dc in visible light communication and be biased the fast Optimization with sub-carrier power, the direct current biasing B maximizing system velocity can be provided fast _dcand sub-carrier power for achieving the above object, the present invention is achieved through the following technical solutions, and it is characterized in that:

1., for the fast Optimization of DCO-OFDM direct current biasing and sub-carrier power under luminous power restriction, it is characterized in that comprising the following steps:

1) the method is applicable to the DCO-OFDM that in smooth weak channel, luminous power is limited.Wherein system maximum luminous power is P _{o, max}, to be H and noise power be channel coefficients note Optical Signal To Noise Ratio is ${\mathrm{\γ}}_o={\left|H\right|}^2{P}_{o,\max }^2/{\mathrm{\σ}}_n^2,f_o\left(x\right)=(1-{\mathrm{\γ}}_o^{-1})[g\left(x\right)-\mathrm{xQ}\left(x\right)]+x.$ Wherein, $g\left(x\right)=\frac{1}{\sqrt{2\mathrm{\π}}}\exp (-\frac{x^2}{2}),Q\left(x\right)={\∫}_x^{+\∞}\frac{1}{\sqrt{2\mathrm{\π}}}\exp (-\frac{w^2}{2})\mathrm{dw}.$ Given computational accuracy ε is (as 10 ^-5), initialization iterations n=0, x ⁽⁰⁾=0.

2) x is calculated ⁽ⁿ⁺¹⁾=x ⁽ⁿ⁾-f _o(x ⁽ⁿ⁾)/f _o' (x ⁽ⁿ⁾), n=n+1.

3) if | x ⁽ⁿ⁺¹⁾-x ⁽ⁿ⁾| < ∈, then x _o=x ⁽ⁿ⁺¹⁾perform step 4, otherwise perform step 2.

4) optimum direct current biasing is exported with optimum sub-carrier power $p_k=P_{o,\max }^2/p_o^2\left(x_o\right),(k=1,...,K-1),$ Wherein p _o(x)=g (x)-xQ (x).

2., for the fast Optimization of DCO-OFDM direct current biasing and sub-carrier power under electrical power restriction, it is characterized in that comprising the following steps:

1) the method is applicable to the DCO-OFDM that in smooth weak channel, electrical power is limited, and wherein system maximum electric power is P _{e, max}, to be H and noise power be channel coefficients remember that electric signal to noise ratio is ${\mathrm{\&gamma;}}_e={\left|H\right|}^2{P}_{e,\max }/{\mathrm{\&sigma;}}_n^2,f_e\left(x\right)=g\left(x\right)+x[1-Q\left(x\right)]+{\mathrm{\&gamma;}}_e^{-1}x.$ Given computational accuracy ε is (as 10 ^-5), initialization iterations n=0, x ⁽⁰⁾=0.

2) x is calculated ⁽ⁿ⁺¹⁾=x ⁽ⁿ⁾-f _e(x ⁽ⁿ⁾)/f _e' (x ⁽ⁿ⁾), n=n+1.

3) if | x ⁽ⁿ⁺¹⁾-x ⁽ⁿ⁾| < ∈, then x _e=x ⁽ⁿ⁺¹⁾perform step 4, otherwise perform step 2.

4) optimum direct current biasing is exported with optimum sub-carrier power p _k=P _{e, max}/ p _e(x _e), (k=1 ...., K-1), wherein p _e(x)=-xg (x)+(1+x ²) Q (x).

3., for DCO-OFDM direct current biasing and the fast Optimization of sub-carrier power when there is luminous power and electrical power restriction simultaneously, it is characterized in that comprising the following steps:

1) the method is applicable to the DCO-OFDM that in smooth weak channel, luminous power and electrical power are simultaneously limited, and wherein system maximum luminous power is P _{o, max}, system maximum electric power is P _{e, max}, to be H and noise power be channel coefficients note Optical Signal To Noise Ratio is electricity signal to noise ratio is ${\mathrm{\&gamma;}}_e={\left|H\right|}^2{P}_{e,\max }/{\mathrm{\&sigma;}}_n^2.$

2) the limited fast method of the luminous power described in feature 1 obtains x _o.

3) the limited fast method of the electrical power described in feature 2 obtains x _e.

4) if $P_{e,\max }>P_{o,\max }^2,$ Pass through Numerical Methods Solve wherein be a monotonic increase and there is the function at unique zero point.

5) $x_{\mathrm{eo}}=\left\{\begin{array}{cc}{x}_e& \mathrm{if}{\left(\frac{P_{o,\max }}{p_o\left(x_e\right)}\right)}^2\&GreaterEqual;\frac{P_{e,\max }}{p_e\left(x_e\right)}\\ x_o& \mathrm{if}{\left(\frac{P_{o,\max }}{p_o\left(x_o\right)}\right)}^2\&le;\frac{P_{e,\max }}{p_e\left(x_o\right)}\\ x_{\mathrm{int}}& \mathrm{otherwise}\end{array}\right..$

6) optimum sub-carrier power is exported $p_k=\min \{{\left(\frac{P_{o,\max }}{p_o\left(x_{\mathrm{eo}}\right)}\right)}^2,\frac{P_{e,\max }}{p_e\left(x_{\mathrm{eo}}\right)}\},(k=1,...,K-1)$ With optimum direct current biasing $B_{\mathrm{dc}}={-x}_{\mathrm{eo}}\sqrt{p_k}.$

From the above technical solution of the present invention shows that, the present invention can be directly used in DCO-OFDM system.Compare and prior art, its beneficial effect is:

1) this optimization method is used for calculating direct current biasing size B fast _dcwith each sub-carrier power size optimal value, and consider the situation that may occur in multiple reality, comprising: only there is luminous power restriction only there is electrical power restriction and both exist simultaneously.Thus the present invention has very strong practical value.

2) and this optimization method does not need to change the external condition such as system hardware, by means of only simple calculating, just can elevator system performance greatly.The direct current biasing size B adopting this optimization method to obtain _dcwith sub-carrier power size p _k(k=1 ..., K-1) data rate of system can be maximized, or be issued to minimum bit error rate in fixing modulation scheme.

3) optimization method of the present invention carries out Accurate Model based on to system and non-linear process wherein, obtains problem expression formula.Its problem itself is the non-convex optimization problem of a complicated nonlinearity.By changing former problem, obtaining the equivalent form of value of problem, just obtaining the accurate optimal solution of this problem.

4) this optimization method fast convergence rate, amount of calculation is little, is easy to realize, and result precision is high.

Accompanying drawing explanation

Fig. 1 is the reflector block diagram of DCO-OFDM system.

Fig. 2 is the receiver block diagram of DCO-OFDM system.

Fig. 3 is for being 10 in bit error rate ^-5the optimization system of time power limited and the data rate of non-optimization system contrast schematic diagram.Can see that the data rate of system after optimizing is higher than the system do not optimized.

Fig. 4 is for being 10 in bit error rate ^-5time electrical power limited optimization system contrast schematic diagram with the data rate of non-optimization system.Can see that the data rate of system after optimizing is higher than the system do not optimized.

Fig. 5 is for being 10 in bit error rate ^-5time luminous power and the simultaneously limited optimization system of electrical power and non-optimization system RATES schematic diagram.Can see that the data rate of system after optimizing is higher than the system do not optimized.

Fig. 6, for be limited as example with luminous power, considers the bit error rate contrast schematic diagram before and after the lower DCO-OFDM system optimization of 16QAM modulation.Can see that the bit error rate of system after optimizing is lower than the system do not optimized.

Fig. 7 is the schematic diagram of problem feasible zone and optimum point in specific embodiments.In figure, black thin is the contour of speed.

Embodiment

In order to more understand technology contents of the present invention, accompanying drawing is coordinated to be described as follows especially exemplified by instantiation.

Shown in figure 1, according to preferred embodiment of the present invention, the DCO-OFDM transmitter course of work is as follows: DCO-OFDM system has 2K subcarrier, each subcarrier-modulated and carry out power division and obtain symbol S _k, on each subcarrier, power is p _k=E [| S _k| ²].Because optical communication requires that output signal is for real number, thus signal demand meets and S ₀=S _k=0.Due to the symmetry brought, only considers subcarrier k=1 ..., the power of K-1.Time-domain signal s is obtained through fast discrete Fourier inverse transformation (IFFT) _n.Then at time-domain signal s _nupper superposition size is B _dcdC component obtain s _{dc, n}=s _n+ B _dc, and by after Signal averaging DC component still minus part prune to meet nonnegativity requirement, i.e. s _{clip, n}=s _{clip, n}u (s _{clip, n}), wherein u () is unit step function.Finally, digital signal s _{clip, n}signal s is obtained by digital simulation converter (D/A) and LED _dc(t).And s _dct the luminous power of () and electrical power are all limited.Think that the luminous power size of delivery channel is P _o=E [s _dc(t)], electrical power size is and owing to being subject to hardware in reality, the restriction such as energy efficiency and eye-safe, luminous power and electrical power are all limited, i.e. P _o=E [s _dc(t)]≤P _{o, max}with

Shown in figure 2, according to preferred embodiment of the present invention, DCO-OFDM operation of receiver process is as follows: the light signal received obtains the signal of telecommunication by photodiode (Photodiode is called for short PD) and low noise amplifier (LNA).After noise equivalent to LNA all in channel, be denoted as n (t), think that n (t) is variance and is gaussian random process.Digital signal is obtained by frequency overlapped-resistable filter and analog to digital converter (A/D).Then, the signal on each subcarrier is obtained by fast discrete Fourier conversion (FFT).In conjunction with each sub-carrier power size of transmitting terminal, direct current biasing size and channel coefficients, obtain receiving bit by the symbol demodulation of each subcarrier by single carrier balancing technique.

Below in conjunction with above-mentioned preferred embodiment and given design parameter, the invention will be further described.For the most complicated luminous power and the simultaneous situation of electrical power.Given design parameter is as follows, 2K=128; H=1; P _{e, max}=30; P _{o, max}=5; maximize system velocity, solve optimum direct current biasing B _dcwith sub-carrier power p _k(k=1 ...., K-1).

Specific embodiment of the invention step is as follows:

1) known system maximum luminous power is P _{o, max}, system maximum electric power is P _{e, max}, to be H and noise power be channel coefficients calculating Optical Signal To Noise Ratio is electricity signal to noise ratio is

2) fast method that luminous power according to claim 1 is limited obtains x _o=-1.2399.The power of its correspondence and DC component size are the Magen Davids in Fig. 7.

3) fast method that electrical power according to claim 2 is limited obtains x _e=-1.3171.The power of its correspondence and DC component size are the five-pointed stars in Fig. 7.

4) due to solve x _int=arg _xf _eox ()=0, obtains x _int=-2.2037.The power of its correspondence and DC component size are the circles in Fig. 7.

5) $x_{\mathrm{eo}}=\left\{\begin{array}{cc}{x}_e& \mathrm{if}{\left(\frac{P_{o,\max }}{p_o\left(x_e\right)}\right)}^2\&GreaterEqual;\frac{P_{e,\max }}{p_e\left(x_e\right)}\\ x_o& \mathrm{if}{\left(\frac{P_{o,\max }}{p_o\left(x_o\right)}\right)}^2\&le;\frac{P_{e,\max }}{p_e\left(x_o\right)}\\ x_{\mathrm{int}}& \mathrm{otherwise}\end{array}\right..$ Due to ${\left(\frac{P_{o,\max }}{p_o\left(x_e\right)}\right)}^2\&GreaterEqual;\frac{P_{e,\max }}{p_e\left(x_e\right)},x_{\mathrm{eo}}=x_e=-1.3171.$

Thus the five-pointed star in Fig. 7 is optimum point, namely only electrical power limited under optimum point.

6) optimum sub-carrier power is exported with optimum direct current biasing $B_{\mathrm{dc}}=-x_{\mathrm{eo}}\sqrt{p_k}=4.3914.$

Can see from the contour Fig. 7, optimum point (five-pointed star) reaches the maximum rate of system really.Thus the present invention obtains the biased and power of the optimum of system.

Can see in Fig. 5 when luminous power and electrical power restriction exist simultaneously, adopt the scheme of optimum direct current biasing and power greatly to promote compared to the scheme performance of fixing direct current biasing.Fig. 5 is the achievable rate contour map of system.As we can see from the figure, the scheme of best direct current biasing and power is adopted can be issued to higher data rate in lower signal to noise ratio.

It is 10 that Fig. 3 and Fig. 4 reflects in bit error rate respectively ^-5under only there is luminous power and only there is the systematic function of the lower best direct current biasing of electrical power restriction relative to fixing direct current biasing.After optimizing as we can see from the figure, the data rate of system is all higher than the system do not optimized.

Fig. 6 is for luminous power restrictive condition, and fixed modulation is the bit error rate contrast schematic diagram before and after 16QAM, DCO-OFDM system optimization.Can see that the bit error rate of system after optimizing is lower than the system do not optimized.Can see thus, this optimization method is equally applicable to the situation that fixed modulation minimizes bit error rate.Only electrical power restriction and two limit simultaneous results similar, here list no longer one by one.

Although the present invention with preferred embodiment disclose as above, so itself and be not used to limit the present invention.Persond having ordinary knowledge in the technical field of the present invention, without departing from the spirit and scope of the present invention, when being used for a variety of modifications and variations.Therefore, protection scope of the present invention is when being as the criterion depending on those as defined in claim.

Claims (5)

1. the fast Optimization of the lower DCO-OFDM direct current biasing of luminous power restriction and sub-carrier power, is characterized in that comprising the following steps:

1) the method is applicable to the DCO-OFDM that in smooth weak channel, luminous power is limited; Wherein system maximum luminous power is P _{o, max}, to be H and noise power be channel coefficients note Optical Signal To Noise Ratio is ${\mathrm{\&gamma;}}_o={\left|H\right|}^2{P}_{o,\max }^2/{\mathrm{\&sigma;}}_n^2,$ $f_o\left(x\right)=(1-{\mathrm{\&gamma;}}_o^{-1})[g\left(x\right)-\mathrm{xQ}\left(x\right)]+x,$ Wherein, $Q\left(x\right)={\&Integral;}_x^{+\&infin;}\frac{1}{\sqrt{2\mathrm{\&pi;}}}\exp (-\frac{w^2}{2})\mathrm{dw},$ Given computational accuracy ε, initialization iterations n=0, x ⁽⁰⁾=0;

2) x is calculated ⁽ⁿ⁺¹⁾=x ⁽ⁿ⁾-f _o(x ⁽ⁿ⁾)/f _o' (x ⁽ⁿ⁾), n=n+1;

3) if | x ⁽ⁿ⁺¹⁾-x ⁽ⁿ⁾| < ∈, then x _o=x ⁽ⁿ⁺¹⁾perform step 4, otherwise perform step 2;

4) optimum direct current biasing B is exported _dc=-x _op _o,m/ _ap _xo(x _o) and optimum sub-carrier power $p_k=P_{o,\max }^2/p_o^2\left(x_o\right),(k=1,....,K-1),$ Wherein p _o(x)=g (x)-xQ (x).

2. the fast Optimization of the lower DCO-OFDM direct current biasing of luminous power restriction according to claim 1 and sub-carrier power, it is characterized in that, in described step 1, computational accuracy ε is 10 ^-20~ 10 ^-2.

3. the fast Optimization of the lower DCO-OFDM direct current biasing of electrical power restriction and sub-carrier power, is characterized in that comprising the following steps:

1) the method is applicable to the DCO-OFDM that in smooth weak channel, electrical power is limited, and wherein system maximum electric power is P _{e, max}, to be H and noise power be channel coefficients remember that electric signal to noise ratio is ${\mathrm{\&gamma;}}_e={\left|H\right|}^2{P}_{e,\max }/{\mathrm{\&sigma;}}_n^2,$ $f_e\left(x\right)=g\left(x\right)+x[1-Q\left(x\right)]+{\mathrm{\&gamma;}}_e^{-1}x,$ Given computational accuracy ε is (as 10 ^-5), initialization iterations n=0, x ⁽⁰⁾=0;

2) x is calculated ⁽ⁿ⁺¹⁾=x ⁽ⁿ⁾-f _e(x ⁽ⁿ⁾)/f _e' (x ⁽ⁿ⁾), n=n+1;

3) if | x ⁽ⁿ⁺¹⁾-x ⁽ⁿ⁾| < ∈, then x _e=x ⁽ⁿ⁺¹⁾perform step 4, otherwise perform step 2;

4) optimum direct current biasing is exported with optimum sub-carrier power it is 1 years old) middle p _e(x)=-xg (x)+(1+x ²) Q (x).

4. the fast Optimization of the lower DCO-OFDM direct current biasing of luminous power restriction according to claim 3 and sub-carrier power, it is characterized in that, in described step 1, computational accuracy ε is 10 ^-20~ 10 ^-2.

5. DCO-OFDM direct current biasing and the fast Optimization of sub-carrier power when there is luminous power and electrical power restriction, is characterized in that comprising the following steps simultaneously:

1) the method is applicable to the DCO-OFDM that in smooth weak channel, luminous power and electrical power are simultaneously limited, and wherein system maximum luminous power is P _{o, max}, system maximum electric power is P _{e, max}, to be H and noise power be channel coefficients note Optical Signal To Noise Ratio is electricity signal to noise ratio is ${\mathrm{\&gamma;}}_e={\left|H\right|}^2{P}_{\text{e,max}}/{\mathrm{\&sigma;}}_n^2;$

2) fast method that luminous power according to claim 1 is limited obtains x _o;

3) fast method that electrical power according to claim 3 is limited obtains x _e;

4) if pass through Numerical Methods Solve wherein be) monotonic increase and there is the function at unique zero point;

5) $x_{\mathrm{eo}}=\left\{\begin{array}{cc}{x}_e& \mathrm{if}{\left(\frac{P_{o,\max }}{p_o\left(x_e\right)}\right)}^2\&GreaterEqual;\frac{P_{e,\max }}{p_x\left(x_e\right)}\\ x_o& \mathrm{if}\left(\frac{P_{o,\max }}{p_o\left(x_o\right)}\right)2^{}\&GreaterEqual;\frac{P_{e,\max }}{p_e\left(x_o\right)}\\ x_{\mathrm{int}}& \mathrm{otherwise}\end{array}\right.;$

6) optimum sub-carrier power is exported with optimum direct current biasing $B_{\mathrm{dc}}=-x_{\mathrm{eo}}\sqrt{p_k}.$