CN108540271A - A kind of Alamouti transmission methods, wireless communication system suitable for FBMC/OQAM - Google Patents

Abstract

The invention belongs to the technical field of wireless communication, and discloses an Alamouti transmission method suitable for FBMC/OQAM and a wireless communication system. The Alamouti transmission method suitable for FBMC/OQAM utilizes block transmission of data to approximately offset the FBMC/OQAM system The built-in imaginary part interference; through block transmission of data in the frequency domain, the symmetry of the block structure is used to offset the imaginary part interference that comes with the FBMC system. Compared with the prior art, the present invention can work normally in low-delay scenarios and time-selective channels, and also has good performance in frequency-selective channels. Since the present invention adopts the block transmission in the frequency domain, no time delay is required during demodulation, and the system performance is better than the traditional time domain block transmission scheme under the time selective channel.

Description

A kind of Alamouti transmission method applicable to FBMC/OQAM, wireless communication system

technical field

The invention belongs to the technical field of wireless communication, and in particular relates to an Alamouti transmission method suitable for FBMC/OQAM and a wireless communication system.

Background technique

At present, the existing technologies commonly used in the industry are as follows: With the large-scale commercial use of 4G, the research and development of the fifth-generation mobile communication technology (5G) for 2020 and the future has become a hot spot in the industry. Compared with 4G, which was dominated by mobile broadband services in the past, 5G will not only provide a transmission rate of 10Gbit/s, support Embb (Enhanced Mobile Broadband) scenarios, but also support IoT services with strict technical requirements, including industrial control The URLLC (Ultra High Reliability and Low Latency) business represented by the company and the mMTC (Massive Machine Type Communication) business represented by environmental monitoring. These services put forward new requirements for multi-carrier technology. The current mainstream multi-carrier technology is OFDM technology. Its core idea is to divide the channel into multiple mutually orthogonal sub-channels, and convert the high-speed data stream into parallel low-speed sub-data streams, so that the signal bandwidth on each sub-channel is reduced. will be smaller than the associated bandwidth of the channel. At the same time, in the OFDM system, each symbol needs to add a cyclic prefix (CP) before sending to ensure that the subcarriers can still be orthogonal under multipath channels, which increases the anti-multipath capability of the system. The most critical point is that the OFDM system can use IFFT/FFT to realize fast modulation and demodulation. It is precisely based on the above advantages that OFDM is widely used in today's wireless communication systems, such as LTE, WiMax, Wlan, DVB-T, DAB, etc. But OFDM, which has many advantages, also has its disadvantages. The introduction of cyclic prefix reduces the transmission efficiency of the system, especially in the case of a good channel, too long CP will lead to waste of time-frequency resources. And in some bad channels, when the CP length is less than the channel maximum multipath delay, the system still has inter-symbol interference (ISI). Due to the relative movement of the transmitter and receiver in the real channel will cause Doppler frequency shift, the local crystal oscillator of the transmitter and the receiver does not match and other factors, the carrier frequency offset of the system exists, and the OFDM system requires strict synchronization of each subcarrier , which is a big test for the carrier frequency estimation and calibration of the system. Another disadvantage of the OFDM system is that the side lobes are large, which reduces the accuracy of the system's perception of the spectrum, and the large side lobes occupy more energy. In order to make up for the above shortcomings of OFDM, some experts have proposed the use of multi-carrier technology based on filter banks. Since the FBMC system uses a prototype filter with good time-frequency localization characteristics, which ensures the independence between sub-channels, it does not need to use a cyclic prefix to provide a guard interval, and its sidelobe attenuation is larger than that of OFDM. The subcarriers are strictly synchronized. Due to the above advantages, FBMC technology has become one of the candidate waveforms for 5G, satellite communication. MIMO technology realizes multiple transmissions and multiple receptions through multiple antennas. It can double the system channel capacity without increasing spectrum resources and antenna transmission power. It has been regarded as the core technology of wireless communication. However, because the FBMC system is only orthogonal in the real number domain instead of the complex number domain, the imaginary part interference exists inside the FBMC system, which makes some MIMO technologies that have been applied to OFDM unable to be directly applied to the FBMC system. As the simplest MIMO technology, how to combine Alamouti technology with FBMC has become the focus of current research. Among them, the CDMA technology is used to overcome the self-interference of the FBMC system, but its application is limited due to the need for a large number of codewords; the idea of iterative interference elimination is used, but the complexity of the scheme is relatively high. For block transmission in the time domain, this scheme can achieve good results on flat channels. However, this scheme cannot be directly applied to time-selective channels or low-latency scenarios.

To sum up, the existing problems in the existing technology are: CDMA technology needs a large number of codewords to overcome the self-interference of the FBMC system, which limits its application; the idea of iterative interference elimination is relatively high in complexity. For block transmission in the time domain, this scheme can achieve good results on flat channels, but it cannot be directly applied to time-selective channels or low-latency scenarios.

The difficulty and significance of solving the above technical problems: Due to the high complexity of the first two schemes, the time-domain block transmission scheme cannot work normally under time-selective channels, which affects their practical applications. Therefore, it is meaningful to propose a low-complexity technical solution that can work normally under time-selective channels.

Contents of the invention

Aiming at the problems existing in the prior art, the present invention provides an Alamouti transmission method and a wireless communication system suitable for FBMC/OQAM.

The present invention is achieved in this way, an Alamouti transmission method suitable for FBMC/OQAM, said Alamouti transmission method suitable for FBMC/OQAM. The entire frequency domain is divided into multiple block structures by using two antennas at the sending end, and each block is divided into two sub-blocks. In order to prevent interference between sub-blocks need to insert 0. A block structure in antenna 1 and a corresponding block structure in antenna 2 together form an Alamouti block. In order to cancel the inherent interference inside the FBMC system, the phase rotation factors of the left and right sub-blocks need to be conjugated.

Further, the Alamouti transmission method applicable to FBMC/OQAM comprises the following steps:

Step 1, the sending end performs QPSK constellation mapping and serial-to-parallel conversion on the data stream first, performs OQAM preprocessing, and converts the complex signal into two real signals;

Step 2: Divide the N _c subcarriers into N _c /N _F block structures, each block has a size of _NF , and each block structure is further divided into left and right sub-blocks with a size of _NF /2-1, Insert 0 between subblocks;

Step 3, the data transmitted by antenna 1 is expressed as a _k,n , the data transmitted by antenna 2 is expressed as b _k,n , and FBMC modulation is performed on the data on the two antennas respectively;

Step 4, the received signal is obtained as:

r(m)=h _a s _a (m)+h _b s _b (m)+n(m);

Where h _a , h _b are two channels, n(m) is the additive background noise with power spectral density N ₀ /2;

Step 5, perform FBMC demodulation to obtain the received signal at the time-frequency point (k, n):

Step 6, using the classic Alamouti demodulation scheme for demodulation to obtain:

Step seven, the block transmission in the frequency domain by the FBMC filter can offset the characteristics of self-interference, for Divide both sides by get:

Step 8: Perform OQAM demodulation on x _k,n and y _k,n to convert real numbers into complex numbers; then perform parallel-to-serial conversion and QPSK constellation demapping to restore the original signal.

Further, the step 3 carries out FBMC modulation to obtain

Where g(m) is the prototype filter designed by the PHYDYAS project team, θ _k,n = j ^(k+n) , when 1≤k≤N _F /2-1, the left half sub-block θ _k,n satisfies the following condition:

At this time, the right half sub-block's Need to meet the conjugate condition with the left half sub-block θ _k,n :

Further, the step five performs the following operations on the received signal of the time-frequency point (k, n):

Indicates to take the real part of the complex number z.

Another object of the present invention is to provide a wireless communication system applying the Alamouti transmission method suitable for FBMC/OQAM.

To sum up, the advantages and positive effects of the present invention are: compared with the prior art, the present invention can work normally in low-delay scenarios and time-selective channels, and also has good performance in frequency-selective channels. Since the present invention adopts the block transmission in the frequency domain, no time delay is required during demodulation, and the system performance is better than the traditional time domain block transmission scheme under the time selective channel.

When the Doppler is large, the performance of the traditional block transmission in time domain decreases obviously, but the performance of this method remains almost unchanged. It shows that when the multipath delay increases, the performance of this solution only drops a little, and normal communication is still possible.

Description of drawings

FIG. 1 is a schematic diagram of a frequency domain block transmission structure provided by an embodiment of the present invention;

Fig. 2 is a schematic diagram of a classic Alamouti transmission structure provided by an embodiment of the present invention;

Fig. 3 is the Alamouti-FBMC system block diagram that the embodiment of the present invention provides;

FIG. 4 is a simulation diagram under a multipath channel provided by an embodiment of the present invention;

FIG. 5 is a schematic diagram of performance comparison between block transmission in the frequency domain and block transmission in the time domain under the Doppler channel provided by an embodiment of the present invention;

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the examples. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The invention transmits the data in blocks in the frequency domain and uses the symmetry of the block structure to offset the imaginary part interference inherent in the FBMC system. Compared with the traditional time-domain block transmission Alamouti scheme, the present invention can reduce the time delay of the FBMC system, and the performance is far superior to the time-domain block transmission scheme under the time-selective channel.

The Alamouti transmission method applicable to FBMC/OQAM provided by the embodiment of the present invention includes the following steps:

(1) The sending end performs QPSK constellation mapping and serial-to-parallel conversion on the data stream first, and then performs OQAM preprocessing to convert the complex signal into two real signals.

(2) Divide N _c subcarriers into Each block structure is divided into two sub-blocks with a size of _NF /2-1, and 0 is _inserted between the sub-blocks. Figure 1 is a schematic diagram of an Alamouti frequency domain block.

Among them, k is the number of subcarriers, and n represents the number of symbols.

(3) The data transmitted by antenna 1 is denoted as a _k,n , and the data transmitted by antenna 2 is denoted as b _k,n . Perform FBMC modulation on the data on the two antennas respectively, and you can get:

Where g(m) is the prototype filter designed by the PHYDYAS project team, θ _k,n = j ^(k+n) , when 1≤k≤N _F /2-1, the left half sub-block θ _k,n satisfies the following condition:

At this time, the right half sub-block's Need to meet the conjugate condition with the left half sub-block θ _k,n :

(4) As shown in Figure 2, the received signal is:

r(m)=h _a s _a (m)+h _b s _b (m)+n(m);

Among them, h _{a and} h _b are two channels, which are assumed to be known. n(t) is the additive background noise with power spectral density N ₀ /2.

(5) FBMC demodulation is carried out to obtain the received signal at the time-frequency point (k, n);

(6) Demodulate with the classic Alamouti demodulation scheme to obtain:

Indicates to take the real part of the complex number z.

(7) Using the FBMC filter in the frequency domain block transmission can offset the characteristics of self-interference, for Divide both sides by get:

(7) Perform OQAM demodulation on x _k,n , y _k,n to change real numbers into complex numbers. Then parallel-to-serial conversion and QPSK constellation demapping are performed, and the original signal is finally restored.

In the embodiment of the present invention, QPSK constellation mapping is adopted, the subcarrier spacing is 15 Hz, and the number of subcarriers is 1024. The prototype filter is the prototype filter designed for the PHYDYAS project. The overlap factor K=4, and the number of paths of the multipath channel is 5. The path delay is uniformly distributed from 0 to τ _max , where τ _max ranges from 10 ^-8 to 10 ^-6 s, and the power delay distribution obeys exponential decay. The time-selective channel adopts the Jakes model, and the Doppler ranges from 0 to 150 Hz.

It can be seen from Fig. 4 that the performance of the present invention is basically the same as that of the traditional method when the maximum multipath delay is small, and the present invention can work normally by reducing the frequency domain block size when the maximum multipath delay increases.

It can be seen from FIG. 5 that the performance of the present invention is basically unchanged under the time-selective channel, while the performance of the traditional block transmission in the time domain drops significantly.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (5)

1. a kind of Alamouti transmission methods suitable for FBMC/OQAM, which is characterized in that described suitable for FBMC/OQAM's Alamouti transmission methods are interfered using the blocky transmission of data come the included imaginary part of approximate counteracting FBMC/OQAM systems；Pass through By data in the enterprising row block shape transmission of frequency domain, left and right sub-block phase rotation coefficient takes conjugation, using the symmetry of block structure, supports The included imaginary part interference of the FBMC systems that disappear.

2. being suitable for the Alamouti transmission methods of FBMC/OQAM as described in claim 1, which is characterized in that described to be applicable in Include the following steps in the Alamouti transmission methods of FBMC/OQAM：

Step 1, transmitting terminal first carry out QPSK constellation mappings and serial to parallel conversion to data stream, carry out OQAM pretreatments, and plural number is believed Number be converted to two real signals；

Step 2, N_cA subcarrier is divided into N_c/N_FA block structure, each block size are N_F, be divided into inside each block structure for The size of left and right two is N_FThe sub-block of/2-1 is inserted into 0 between sub-block；

Step 3, the data that antenna 1 transmits are expressed as a_k,n, antenna 2 transmit data be expressed as b_k,n, respectively on two antennas Data carry out FBMC modulation；

Step 4, obtaining reception signal is：

R (m)=h_as_a(m)+h_bs_b(m)+n(m)；

Wherein h_a, h_bFor two channels, n (m) is that power spectral density is N₀/ 2 additivity ambient noise；

Step 5 carries out FBMC demodulation, obtains the reception signal in time frequency point (k, n)：

Step 6 is demodulated to obtain using classical Alamouti demodulation schemes：

Step 7 can be offset the characteristic of self-interference by FBMC filters in the transmission of frequency domain bulk, rightBoth sides divided by (| h_a |²+|h_b|²) obtain：

Step 8, to x_k,n, y_k,nOQAM demodulation is carried out, real number is become into plural number；It carries out again and goes here and there conversion and QPSK constellation solutions are reflected It penetrates, recovers original signal.

3. being suitable for the Alamouti transmission methods of FBMC/OQAM as claimed in claim 2, which is characterized in that the step Three progress FBMC modulate to obtain

Wherein g (m) is the ptototype filter of PHYDYAS project team design, θ_k,n=j^(k+n), as 1≤k≤N_FWhen/2-1, left half son Block θ_k,nMeet following condition：

At this point, right half sub-blockIt need to meet and half sub-block θ of a left side_k,nConjugate condition：

4. being suitable for the Alamouti transmission methods of FBMC/OQAM as claimed in claim 2, which is characterized in that the step The reception signal of five pairs of time frequency points (k, n) proceeds as follows：

Expression takes the real part of plural z.

5. a kind of using the wireless of the Alamouti transmission methods for being suitable for FBMC/OQAM described in Claims 1 to 4 any one Communication system.