CN105871763A - Channel equalization method and system based on QR decomposition - Google Patents

Abstract

The invention discloses a channel equalization method and system based on QR decomposition. The method comprises the following steps that preprocessing based on discrete Fourier transform is carried out on each OFDM signal at the transmitting end in advance; a channel equalization algorithm based on QR decomposition is adopted at the receiving end, and the preprocessed OFDM signals are restored. The OFDM signals at the transmitting end in a visible light communication system are preprocessed, and the channel equalization algorithm based on QR decomposition is adopted at the receiving end for the first time, and the influence caused by frequency selective fading is effectively reduced; meanwhile, the transmitting condition of a channel does not need to be known at the transmitting end, moreover, in the actual application process, additional specific adjustment does not need to be carried out for the different conditions, the complexity and the cost are reduced, and transmitting performance is remarkably improved.

Description

A kind of channel equalization method decomposed based on QR and system

Technical field

The present invention relates to optical communication field, be specifically related to a kind of based on QR decompose channel equalization method and System.

Background technology

In current visible light communication system, due to the problem of wire length, from two or more differences The light that sends of light source bigger time delay, this time delay can be caused to cause letter at receiving terminal at receiving terminal Number frequency selective fading.In order to process this frequency selective fading, can be at OFDM (Orthogonal Frequency Division Multiplexing, OFDM) system Middle employing bit and power preequalization compensate this kind of decline, but this method needs to be known a priori by letter The feature in road, this can increase complexity in actual applications；Also the ofdm signal to transmitting terminal is had to use The coded system of Alamouti code (Alamouti code), to increase the ability of the anti-frequency decay of signal, But this mode is in actual applications, the signal produced due to light source has been encoded into different code sources, Need to increase the quantity of emitter.

In view of this, for visible light communication system, it is badly in need of designing a kind of new channel equalization method, Higher and relatively costly the asking of complexity is there is with the method for the existing process frequency selective fading of solution Topic.

Summary of the invention

The technical problem to be solved is to design a kind of new channel equalization method, existing to solve With the presence of the higher and relatively costly problem of the method complexity of process frequency selective fading.

In order to solve above-mentioned technical problem, the technical solution adopted in the present invention is to provide a kind of based on QR The channel equalization method decomposed, comprises the following steps:

At transmitting terminal, each ofdm signal is beforehand with pretreatment based on discrete Fourier transform；

The Channel Equalization Algorithm decomposed based on QR is used, to the OFDM letter through pretreatment at receiving terminal Number recover.

In technique scheme, at transmitting terminal, each ofdm signal is beforehand with based on discrete fourier The pretreatment of conversion specifically includes following steps:

At transmitting terminal, ofdm signal is divided into multiple subband, and to the ofdm signal on each subband Do discrete Fourier transform, more each ofdm signal is done inverse discrete Fourier transform, generate OFDM time-domain signal.

In technique scheme, specifically include following steps:

Use S_MVRepresent the ofdm signal of actual transmissions, after transmission, the OFDM received Frequency-region signal R_MVRepresent, R_MVCan be with table after first passing around pretreatment based on discrete Fourier transform It is shown as:

R_MV=Diag (H_MV)PS_MV (1)

In formula (1), H_MVRepresent the frequency response of channel；Diag(H_MV) represent H_MVEnter Row diagonal matrix operates；P represents the N × N square obtained after pre-processing based on discrete Fourier transform Battle array, the element representation of the row k of P, l row is

Next the data carried out channel in QR decomposition and sub-carrier equalize, and define matrix M=Diag (H_MV) P, and matrix M is carried out QR decomposition, then formula (1) can be expressed as:

R_MV=MS_MV=QR_MVS_MV (2)

In formula (2), R_MVFor upper triangular matrix, Q is chief of a tribe's matrix；

The right and left at formula (2) is all multiplied by QH, then formula (2) can be expressed as:

${\tilde{R}}_{MV}=Q^H{R}_{MV}=R_{MV}{S}_{MV}---\left(3\right)$

Due to R_MVFor upper triangular matrix, thenI-th element can be expressed as:

${\tilde{R}}_{MV}^i=R_{MV}^{i,i}{S}_{MV}^i+\underset{m=i+1}{\overset{MV}{\Σ}}{R}_{MV}^{i,m}{S}_{MV}^m---\left(4\right)$

In formula (4),Represent R_MVThe i-th row m column element, then i-th subcarrier On dataSubcarrier i+1 can be passed through ... the data on MV are recovered, such as formula (5) Shown in:

$S_{MV}^i=\frac{{\tilde{R}}_{MV}^i-{\mathrm{\&Sigma;}}_{m=i+1}^{MV}{R}_{MV}^{i,m}<S_{MV}^m>}{R_{MV}^{i,i}}---\left(5\right)$

In formula (5),RepresentData after judgement.

In technique scheme, described H_MVEstimate to obtain by channel.

Present invention also offers a kind of channel equalization system decomposed based on QR, including transmitting terminal and reception End,

At transmitting terminal, produce baseband signal to be sent by signal generator, utilize multiple LED to divide Other each baseband signal is modulated, generates light intensity modulated signal, and send to receiving terminal；

At receiving terminal, photodetector receives the light intensity modulated signal that transmitting terminal sends, by numeral Signal processing apparatus carries out channel equalization and judgement to recover baseband signal to light intensity modulated signal.

In technique scheme, described digital signal processing device includes low pass filter, oscillograph And LED.

Present invention firstly provides and the ofdm signal of transmitting terminal in visible light communication system is pre-processed, And the Channel Equalization Algorithm decomposed based on QR is used at receiving terminal, significantly reduce frequency selectivity and decline Fall the impact brought, and meanwhile, requires no knowledge about the transmission conditions of channel at transmitting terminal, and in reality In application process, the present invention need not carry out extra specific adjustment for different conditions, reduces Complexity and cost, and considerably improve transmission performance.

Accompanying drawing explanation

The actual application scenarios figure that Fig. 1 provides for the embodiment of the present invention；

A kind of channel equalization method flow chart decomposed based on QR that Fig. 2 provides for the embodiment of the present invention；

Fig. 3 shows for the structure of a kind of based on QR decomposition the channel equalization system that the embodiment of the present invention provides It is intended to.

Detailed description of the invention

The present invention is by pre-processing the ofdm signal of transmitting terminal, i.e. at transmitting terminal to each OFDM Signal is beforehand with discrete Fourier transform, more each ofdm signal is done inverse discrete Fourier transform, makes The data obtained on each ofdm signal on each subcarrier are interrelated so that work as frequency selective fading The when of generation on certain subcarrier, remaining does not occurs the subcarrier of obvious frequency selective fading can To be used for the information recovering on this subcarrier (subcarrier of occurrence frequency Selective intensity).Meanwhile, Use the Channel Equalization Algorithm decomposed based on QR at receiving terminal, the ofdm signal through pretreatment is entered Row recovers so that the data on the subcarrier of each ofdm signal can be recovered simultaneously.

Below in conjunction with specification drawings and specific embodiments, the present invention is described in detail.

As it is shown in figure 1, be the actual application scenarios figure of the embodiment of the present invention, in a practical situation, electricity The difference of line length can cause the signal received in some overlapping region occurrence frequency selectivity to decline Fall, if difference power is less, more can cause the strongest frequency selective fading.

Embodiments provide a kind of channel equalization method decomposed based on QR, as in figure 2 it is shown, Comprise the following steps:

S1, at transmitting terminal, each ofdm signal is beforehand with pretreatment based on discrete Fourier transform, I.e. DFT (Discrete Fourier Transform, discrete Fourier transform) demodulates.

S2, the Channel Equalization Algorithm decomposed based on QR in receiving terminal employing, to the OFDM through pretreatment Signal recovers.

S1 specifically includes following steps: at transmitting terminal, ofdm signal is divided into V subband, and to often Ofdm signal on individual subband is the DFT of M point, and each ofdm signal is the IDFT of N point the most again (Inverse Discrete Fourier Transform, inverse discrete Fourier transform) (wherein, N > MV), generate OFDM time-domain signal.

The idiographic flow of the channel equalization method that the present invention provides is: use S_MVRepresent actual transmissions Ofdm signal, after transmission, the OFDM frequency-region signal R received_MVRepresent, R_MVFirst Can be expressed as after first passing through DFT demodulation:

R_MV=Diag (H_MV)PS_MV (1)

In formula (1), H_MVRepresent the frequency response of channel, can estimate to obtain by channel； Diag(H_MV) represent H_MVCarry out diagonal matrix operation；P represents through becoming based on discrete fourier The N N matrix obtained after changing pretreatment, the element representation of the row k of P, l row is

Next the data carried out channel in QR decomposition and sub-carrier equalize, and define matrix M=Diag (H_MV) P, and matrix M is carried out QR decomposition, then formula (1) can be expressed as:

R_MV=MS_MV=QR_MVS_MV (2)

In formula (2), R_MVFor upper triangular matrix, Q is chief of a tribe's matrix；

The right and left at formula (2) is all multiplied by QH, then formula (2) can be expressed as:

${\tilde{R}}_{MV}=Q^H{R}_{MV}=R_{MV}{S}_{MV}---\left(3\right)$

Due to R_MVFor upper triangular matrix, thenI-th element can be expressed as:

${\tilde{R}}_{MV}^i=R_{MV}^{i,i}{S}_{MV}^i+\underset{m=i+1}{\overset{MV}{\&Sigma;}}{R}_{MV}^{i,m}{S}_{MV}^m---\left(4\right)$

From formula (4) it can be seen thatNot by subcarrier 1,2 ..., the impact of i, wherein, Represent R_MVThe i-th row m column element, then the data on i-th subcarrierCan pass through Subcarrier i+1 ... the data on MV are recovered, as shown in formula (5):

$S_{MV}^i=\frac{{\tilde{R}}_{MV}^i-{\mathrm{\&Sigma;}}_{m=i+1}^{MV}{R}_{MV}^{i,m}<S_{MV}^m>}{R_{MV}^{i,i}}---\left(5\right)$

In formula (5),RepresentData after judgement, from formula (5) it can be seen that The method using QR to decompose can disposably recover whole ofdm signal, due on all subcarriers Data are associated, so this programme significantly reduces certain or some subcarriers and selects because of frequency Property decline suffered by impact.

The embodiment of the present invention additionally provides a kind of channel equalization system decomposed based on QR, as it is shown on figure 3, Including transmitting terminal 10 and receiving terminal 20,

At transmitting terminal 10, produce baseband signal to be sent by signal generator, utilize multiple LED Respectively each baseband signal is modulated, generates light intensity modulated signal, and send to receiving terminal 20.

At receiving terminal 20, photodetector receives the light intensity modulated signal that transmitting terminal 10 sends, passes through Digital signal processing device carries out channel equalization and judgement to recover base band letter to light intensity modulated signal Number.

Digital signal processing device includes low pass filter, oscillograph and LED.

Identical ofdm signal is sent to each LED (this enforcement only with an emitter by this programme Example is as a example by two LED) on, reduce complexity and cost.

The present invention is not limited to above-mentioned preferred forms, and anyone makes under the enlightenment of the present invention Structure changes, and every have same or like technical scheme with the present invention, each falls within the guarantor of the present invention Within the scope of protecting.

Claims (6)

1. the channel equalization method decomposed based on QR, it is characterised in that comprise the following steps:

At transmitting terminal, each ofdm signal is beforehand with pretreatment based on discrete Fourier transform；

The Channel Equalization Algorithm decomposed based on QR is used, to the OFDM letter through pretreatment at receiving terminal Number recover.

2. the channel equalization method decomposed based on QR as claimed in claim 1, it is characterised in that Transmitting terminal each ofdm signal is beforehand with pretreatment based on discrete Fourier transform specifically include with Lower step:

At transmitting terminal, ofdm signal is divided into multiple subband, and to the ofdm signal on each subband Do discrete Fourier transform, more each ofdm signal is done inverse discrete Fourier transform, generate OFDM time-domain signal.

3. the channel equalization method decomposed based on QR as claimed in claim 1, it is characterised in that Specifically include following steps:

Use S_MVRepresent the ofdm signal of actual transmissions, after transmission, the OFDM received Frequency-region signal R_MVRepresent, R_MVCan be with table after first passing around pretreatment based on discrete Fourier transform It is shown as:

R_MV=Diag (H_MV)PS_MV (1)

In formula (1), H_MVRepresent the frequency response of channel；Diag(H_MV) represent H_MVEnter Row diagonal matrix operates；P represents the N × N square obtained after pre-processing based on discrete Fourier transform Battle array, the element representation of the row k of P, l row is

Next the data carried out channel in QR decomposition and sub-carrier equalize, and define matrix M=Diag (H_MV) P, and matrix M is carried out QR decomposition, then formula (1) can be expressed as:

R_MV=MS_MV=QR_MVS_MV (2)

In formula (2), R_MVFor upper triangular matrix, Q is chief of a tribe's matrix；

The right and left at formula (2) is all multiplied by QH, then formula (2) can be expressed as:

${\tilde{R}}_{MV}=Q^H{R}_{MV}=R_{MV}{S}_{MV}---\left(3\right)$

Due to R_MVFor upper triangular matrix, thenI-th element can be expressed as:

${\tilde{R}}_{MV}^i=R_{MV}^{i,i}{S}_{MV}^i+\underset{m=i+1}{\overset{MV}{\&Sigma;}}{R}_{MV}^{i,m}{S}_{MV}^m---\left(4\right)$

In formula (4),Represent R_MVThe i-th row m column element, then i-th subcarrier On dataSubcarrier i+1 can be passed through ... the data on MV are recovered, such as formula (5) Shown in:

$S_{MV}^i=\frac{{\tilde{R}}_{MV}^i-{\mathrm{\&Sigma;}}_{m=i+1}^{MV}{R}_{MV}^{i,m}<S_{MV}^m>}{R_{MV}^{i,i}}---\left(5\right)$

In formula (5),RepresentData after judgement.

4. the channel equalization method decomposed based on QR as claimed in claim 3, it is characterised in that Described H_MVEstimate to obtain by channel.

5. the channel equalization system decomposed based on QR, it is characterised in that include transmitting terminal and connect Receiving end,

At transmitting terminal, produce baseband signal to be sent by signal generator, utilize multiple LED to divide Other each baseband signal is modulated, generates light intensity modulated signal, and send to receiving terminal；

At receiving terminal, photodetector receives the light intensity modulated signal that transmitting terminal sends, by numeral Signal processing apparatus carries out channel equalization and judgement to recover baseband signal to light intensity modulated signal.

6. the channel equalization system decomposed based on QR as claimed in claim 5, it is characterised in that Described digital signal processing device includes low pass filter, oscillograph and LED.