CN116318280A - Scattered waveform transmission method based on transform domain - Google Patents

Abstract

The invention provides a scattered waveform transmission method based on a transform domain. The invention utilizes the characteristic that channels in different space time are not in deep fading at the same time to carry out weighted combination on two time domain components of a transmitted symbol sequence, thereby combining the transmitted symbols in different space time, and compensating the signal subjected to deep fading by using the signal without deep fading, thereby improving the stability of the system. The signal transformation and inverse transformation operations of the present invention can perfectly restore the original waveform without noise. Compared with the waveform of the existing large-scale MIMO single-carrier system, the waveform design mode of the invention has better diversity performance under the condition of unchanged data rate.

Description

Scattered waveform transmission method based on transform domain

Technical Field

The invention relates to a waveform design method of a wireless communication system, in particular to a scattering waveform transmission method based on two-component combined generalized weighted fractional Fourier transform (Double-component combined generalized weighted fractional Fouriertransform, DCGWFrFT) under a large-scale Multiple-in Multiple-out (MIMO) scattering communication system.

Background

Tropospheric scatter communication technology is a wireless communication technology that uses the scattering effect of the inhomogeneity of the tropospheric medium on radio waves, and the technical basis is the theory of scattering propagation of the tropospheric medium. The troposphere scattering transmission system designed by using the troposphere scattering propagation theory can realize beyond-the-horizon transmission, and has moderate transmission capacity, transmission performance and reliability, and extremely strong anti-nuclear explosion and anti-ionosphere disturbance capabilities. The flow scattering communication technology has irreplaceable functions in a plurality of different communication transmission technologies due to the unique transmission characteristics.

Scatter communication has been developed for more than 60 years from birth, and the capacity problem of scatter communication has become the focus of attention of all countries in the world, for example, the company of comtech in the united states has currently realized communication at 210Mbps, while the scatter transmission rate in China has also reached 50Mbps in model equipment, and has explored 155Mbps in technical research. With the gradual application of the fifth generation mobile communication technology, the high-throughput satellite technology and the millimeter wave high-capacity microwave communication technology in communication, the transmission rate of the next generation communication system is improved as a whole. Scattered communications also require further increases in transmission rates so as not to become a bottleneck for transmission of full network communications.

Massive MIMO technology is one of the important technologies for improving the system capacity of current mobile communication. The theoretical channel capacity of a massive MIMO communication system increases with the number of transceiver antennas without additional transmit power or frequency bands, as compared to a conventional single antenna. Thus, it is envisioned that if massive MIMO technology is introduced into scattering communications, it is also possible to provide a significant communication rate for scattering communications systems, thereby enabling large capacity scattering communications.

Although massive MIMO technology can provide a multiplexing gain and a diversity gain to a system, there is a trade-off between the two gains in the case of a limited number of antennas, and the system cannot provide a spatial diversity gain when a communication data rate is maximized, resulting in difficulty in ensuring communication stability of the system. In order to achieve better diversity performance without loss of communication throughput, consideration is given to providing additional diversity capability by way of waveform design.

Disclosure of Invention

Aiming at the defect that the communication error rate is poor when the number of data streams is more due to the balance of multiplexing gain and diversity gain of the waveform of the existing large-scale MIMO system, the invention provides a scattered waveform transmission method based on a transform domain. The method utilizes the characteristic that channels in different space time are not in deep fading at the same time to carry out weighted combination on two time domain components of a transmitted symbol sequence, so as to combine the transmitted symbols in different space time, and compensate the signal subjected to deep fading by using the signal without deep fading, thereby improving the stability of the system.

The invention adopts the technical scheme that:

a scattered waveform transmission method based on a transform domain comprises a transmitting end operation process and a receiving end operation process;

the operation process of the transmitting end comprises the following steps:

step 1: transmitting terminalModulating bit streams transmitted in M time slots into a transmission symbol sequence

Wherein N is _t For the number of antennas at the transmitting end, M is the number of time slots, < >>

Is a complex set;

step 2: performing two-component combined generalized weighted fractional Fourier transform on the transmitted symbol sequence x to obtain a transformed transmitted symbol sequence z, wherein the transformation formula is as follows:

z＝F ⁺ x

wherein the matrix F is transformed ⁺ The definition is as follows:

wherein, I represents an identity matrix, D represents a normalized discrete Fourier transform matrix, and the transform coefficient is:

wherein j is an imaginary unit, and the parameter θ ₀ And theta ₁ Are all within the interval [0,2 pi ]]Internally randomly generated and satisfy theta ₀ ≠θ ₁ +kpi, k is any integer;

step 3: dividing the transformed transmission symbol sequence z into M segments in sequence, and recording as

And transmitting the ith segment symbol sequence z in the ith slot _i ；

The operation process of the receiving end comprises the following steps:

step 4: through a channel

Then receive signals are obtained:

y _i ＝H _i z _i +w _i

wherein the method comprises the steps of

Representing additive white gaussian noise +.>

Is the noise power, N _r The number of the antennas at the receiving end;

detection of all received signals y using a minimum mean square error detector ₁ ,y ₂ ,...,y _M And (3) obtaining:

wherein the superscript H represents a conjugate transpose;

step 5: combining the detected symbol sequences at M times into a whole, i.e. to let

The superscript T denotes a transpose;

for received symbol sequence

Performing inverse two-component combined generalized weighted fractional Fourier transform to obtain an inverse transformed received symbol sequence +.>

The transformation formula is:

wherein the matrix F is transformed ^- Is defined as

The transform coefficients are:

step 6: for a pair of

Demodulation is performed to obtain an estimated bit stream.

The invention has the following advantages:

1. the invention uses the characteristic that channels in different space time are not in deep fading at the same time to carry out DCGWFrFT on the sending symbol sequence, thereby carrying out weighted combination on the sending symbols in different space time, and compensating fading signals by using signals without deep fading, thereby improving the stability of the system.

2. The invention simultaneously digs the time and space dual characteristics of the system, and has better diversity performance compared with the traditional large-scale MIMO system single carrier system.

3. The invention can realize the improvement of diversity performance without losing data rate, but only with the cost of calculation complexity and time delay. Compared with the existing lifting space-time coding method, the method can ensure the same communication rate and obtain better communication stability.

Drawings

FIG. 1 is a block diagram of a massive MIMO based scattering communication system in accordance with an embodiment of the present invention;

FIG. 2 is a communication flow block diagram based on DCGWFrFT;

FIG. 3 is a schematic diagram of a space-time compensation mechanism for the DCGWFrFT transform and the inverse transform of the signal;

fig. 4 is a graph of performance versus various wave designs (16 for both transmit and receive antennas);

fig. 5 is a graph of performance versus waveform design (number of dual-transmit antennas is 8).

Detailed Description

The present invention will be described in detail with reference to the accompanying drawings.

A scattering waveform transmission method based on a transform domain is disclosed, a large-scale MIMO scattering communication system structure considered by the method is shown in figure 1, and a communication flow based on DCGWFrFT is shown in figure 2. The method comprises the following steps:

the operation process of the transmitting end comprises the following steps:

step 1: the transmitting end modulates the bit streams transmitted by M time slots into a symbol sequence

Wherein N is _t And M is the number of time slots for the number of antennas of the transmitting end.

Step 2: and performing DCGWFrFT on the transmission symbol sequence x to obtain a transformed transmission symbol sequence z. The transformation formula is as follows

z＝F ⁺ x

Wherein the matrix F is transformed ⁺ Is defined as

Where I represents an identity matrix, D represents a normalized discrete Fourier transform matrix, and the transform coefficients are

Wherein the parameter theta ₀ And theta ₁ Are all within the interval [0,2 pi ]]Internally randomly generated and satisfy theta ₀ ≠θ ₁ +kpi, k is any integer.

Step 3: dividing the transformed transmission symbol sequence z into M segments in sequence, and recording as

And transmitting the ith segment symbol sequence z in the ith slot _i 。

Through a channel

And then obtain the received signal

y _i ＝H _i z _i +w _i

Wherein the method comprises the steps of

Representing additive white gaussian noise, N _r For the number of receiving end antennas, < > for>

Is the noise power.

The operation process of the receiving end comprises the following steps:

step 4: detection of all received signals { y using Minimum Mean Square Error (MMSE) detector ₁ ,y ₂ ,...,y _M And get

Step 5: combining the detected symbol sequences at M times into a whole, i.e. to let

For received symbol sequence

The Inverse DCGWFrFT (Inverse DCGWFrFT, IDCGWFrFT) is performed to obtain the Inverse transformed received symbol sequence +.>

The transformation formula is as follows

Wherein the matrix F is transformed ^- Is defined as

Where the transform coefficients are

Step 6: for a pair of

Demodulation is performed to obtain an estimated bit stream.

Description of principle:

step 2 combines the different space-time transmit signals using dcgwfft, while step 5 restores the transformed signal to the original signal using idcgwfrf. The principle and the derivation process of step 2 and step 5 are explained below.

Due to

Is a permutation matrix, so that the fractional Fourier transform F of the two-component combination ⁺ Can be regarded as to transmit symbolsThe sequence x performs weighted combination of different space-time symbols before and after, wherein the weight coefficient is

And->

This process can be represented by fig. 3. It is assumed that the transmitted symbol sequence experiences deep fades in the channel at different times of space. Because the symbols at the same time cannot all experience deep fading at different antenna high probabilities, the symbols at the same antenna cannot all experience deep fading at different time high probabilities, the method has the mechanism that the deep fading signals are compensated by the signals which do not experience deep fading, thereby overcoming the influence of channel fading on the detection performance.

The following demonstrates that the signal transformation and inverse transformation system of the present method can perfectly restore the original signal in a noise-free scenario.

And (3) proving: when no noise exists, the receiving signal of the receiving end is

y _i ＝H _i z _i

In the absence of noise

After passing through an MMSE detector, the obtained product is obtained

Combining to obtain

Finally, the product is obtained after fractional Fourier transform of the combination of the inverse component and the two components

Because of

Due to

And is also provided with

So that

The syndrome is known.

In a word, the invention utilizes the characteristic that channels in different space time are not in deep fading at the same time to carry out weighted combination on two time domain components of a sending symbol sequence, thus combining sending symbols in different space time, and compensating the signal subjected to deep fading by using the signal without deep fading, thereby improving the stability of the system. Theoretical analysis proves that the signal transformation and inverse transformation operation can perfectly restore the original waveform under the condition of no noise. The simulation results are shown in fig. 4 and 5, and the abscissa represents the transmission signal-to-noise ratio (expressed in dB), and the ordinate represents the error rate, wherein the numbers of the transmitting and receiving double-ended antennas in fig. 4 are 16, and the numbers of the transmitting and receiving double-ended antennas in fig. 5 are 8. In the simulation, a 16QAM modulation mode is adopted to modulate data, and different data streams are transmitted on each antenna, and 10 time frames are transmitted in total. Each time frame contains 5000 slots, one symbol being transmitted per slot. The channel state information of different time frames is independently generated, and the scattering channels are randomly generated according to a large-scale MIMO Rayleigh channel model. The parameter at the time of waveform conversion is set to θ ₀ ＝0，θ ₁ =pi/2. Simulation results show that compared with the existing large-scale MIMO single-carrier system, the waveform design mode of the inventionIn the case of constant data rate, when the bit error rate is 10 ^-3 The signal to noise ratio gain of about 2dB can be improved, i.e. better diversity performance is achieved.

Claims (1)

1. The scattered waveform transmission method based on the transform domain is characterized by comprising a transmitting end operation process and a receiving end operation process;

the operation process of the transmitting end comprises the following steps:

step 1: the transmitting end modulates the bit stream transmitted by M time slots into a transmission symbol sequence

Wherein N is _t For the number of antennas at the transmitting end, M is the number of time slots, < >>

Is a complex set;

step 2: performing two-component combined generalized weighted fractional Fourier transform on the transmitted symbol sequence x to obtain a transformed transmitted symbol sequence z, wherein the transformation formula is as follows:

z＝F ⁺ x

wherein the matrix F is transformed ⁺ The definition is as follows:

wherein, I represents an identity matrix, D represents a normalized discrete Fourier transform matrix, and the transform coefficient is:

wherein j is an imaginary number listBit, parameter θ ₀ And theta ₁ Are all within the interval [0,2 pi ]]Internally randomly generated and satisfy theta ₀ ≠θ ₁ +kpi, k is any integer;

step 3: dividing the transformed transmission symbol sequence z into M segments in sequence, and recording as

And transmitting the ith segment symbol sequence z in the ith slot _i ；

The operation process of the receiving end comprises the following steps:

step 4: through a channel

Then receive signals are obtained:

y _i ＝H _i z _i +w _i

wherein the method comprises the steps of

Representing additive white gaussian noise +.>

Is the noise power, N _r The number of the antennas at the receiving end;

detection of all received signals y using a minimum mean square error detector ₁ ,y ₂ ,...,y _M And (3) obtaining:

wherein the superscript H represents a conjugate transpose;

step 5: combining the detected symbol sequences at M times into a whole, i.e. to let

The superscript T denotes a transpose;

for received symbol sequence

Performing inverse two-component combined generalized weighted fractional Fourier transform to obtain an inverse transformed received symbol sequence +.>

The transformation formula is:

wherein the matrix F is transformed ^- Is defined as

The transform coefficients are:

step 6: for a pair of

Demodulation is performed to obtain an estimated bit stream.

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