CN104301019A - Co-channel interference suppression method based on receiving blind beamforming for spaceborne AIS - Google Patents

Abstract

The invention discloses a spaceborne AIS co-channel interference suppression method based on receiving blind beamforming. The signal detection module of the spaceborne AIS receiver performs blind beamforming before signal detection, and the blind beamforming uses the constant mode of the user signal itself to achieve beamforming. The present invention uses a constant modulus algorithm to implement blind beamforming on user signals, separates desired signals from interference signals and restores desired signals, has high frequency spectrum utilization, can significantly suppress co-channel interference, and obviously improves the bit error performance of signal detection.

Description

Co-channel interference suppression method based on receiving blind beamforming for spaceborne AIS

technical field

The invention relates to the field of wireless communication, in particular to a spaceborne AIS co-channel interference suppression method based on receiving blind beamforming.

Background technique

Ship Automatic Identification System (AIS) is a multi-category high-tech new navigation aid and safety information system integrating modern communication, information technology and network. It is a broadcast automatic reporting system that works in the VHF frequency band and adopts SOTDMA communication technology. , consisting of on-board equipment and a base station. The equipment on board can automatically broadcast static information such as the ship’s name, destination, and voyage, as well as dynamic information such as ship position, speed, and course, to other ships and base stations in the SOTDMA network, and can also automatically receive relevant information from other ships in the SOTDMA network . The base station can grasp the dynamics of maritime traffic in a timely manner based on the obtained report information of each ship, and improve the efficiency of sea area monitoring. AIS has established an information platform between ship-shore and ship-to-ship, which provides an important means for the realization of maritime traffic information management, and has become an advanced tool to promote navigation safety and improve shipping traffic efficiency.

As the application of spaceborne AIS in the field of global maritime traffic monitoring has attracted increasing attention, it is very meaningful to study spaceborne AIS. Large noise and strong interference will seriously affect the reception of multi-channel satellite signals. At present, the receiver beamforming of most satellite signals depends on the direction of arrival of the signal, and the spectrum utilization rate is not high; single-antenna receivers have serious co-channel interference, and the bit error performance is poor.

Therefore, a new method is needed to solve the co-channel interference problem of spaceborne AIS.

Contents of the invention

The technical problem to be solved by the present invention is to provide a space-borne AIS co-channel interference suppression method based on receiving blind beamforming to significantly suppress co-channel interference and improve the bit error performance of signal detection.

The present invention adopts the following technical solutions for solving the problems of the technologies described above:

The spaceborne AIS is based on the co-channel interference suppression method of receiving blind beamforming. The signal detection module of the spaceborne AIS receiver performs blind beamforming before signal detection. The blind beamforming uses the constant mode characteristic of the user signal itself to realize beamforming.

As a further optimization scheme of the present invention's spaceborne AIS co-channel interference suppression method based on receiving blind beamforming, the specific steps for calculating the output signal matrix after blind beamforming are as follows:

Step 1), the binary AIS signal a _i,k ∈{±1}(i=1,2,...P) sent by each ship is first differentially encoded into b _i,k :

b _i,k =a _i,k b _i,k-1

Among them, P is the number of ships, and k is the serial number of the binary AIS signal;

Step 2), bi _{, k} are modulated by GMSK into the baseband GMSK signal s _i (t), the baseband GMSK signal s _i (t) is uniformly sampled at t=kT to obtain s _i (k)=s _i (kT), Among them, T is the sampling period;

Step 3), the baseband sampling signal passes through the Gaussian white noise channel, and after N times of sampling, the antenna array receiving signal model is obtained:

X=AS+N

Among them, X∈C ^M×N represents the received signal matrix, S∈C ^P×N represents the transmitted signal matrix, N∈C ^M×N represents the noise signal matrix, A∈C ^M×P represents the array direction matrix, and M represents the antenna array The number of receiving antennas;

Step 4), calculate the output signal matrix Y=W ^H X after the blind beamforming, where W is the blind beamforming weight matrix.

As a further optimization scheme of the co-channel interference suppression method based on receiving blind beamforming of the spaceborne AIS in the present invention, the blind beamforming weight matrix W is solved by using an analytical constant modulus algorithm.

As a further optimization scheme of the space-borne AIS-based co-channel interference suppression method based on receiving blind beamforming in the present invention, the M is an integer greater than or equal to 1 and less than or equal to 100.

As a further optimization scheme of the space-borne AIS-based co-channel interference suppression method based on receiving blind beamforming in the present invention, the M is 50.

Compared with the prior art, the present invention adopts the above technical scheme and has the following technical effects:

The spaceborne AIS adopted is based on the co-channel interference suppression method of receiving blind beamforming. The blind beamforming module is added before the signal detection module of the spaceborne AIS receiver. The blind beamforming requires less prior conditions and does not require reference signals ( Such as the angle of arrival of the signal), but using the characteristics of the user signal itself to realize beamforming, the spectrum utilization rate is high, and the co-channel interference can be significantly suppressed, and the bit error performance of signal detection can be significantly improved.

Additional aspects and advantages of the invention will be set forth in part in the description which follows, and will become apparent from the description, or may be learned by practice of the invention.

Description of drawings

Fig. 1 is a system model according to one embodiment of the present invention.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment, further illustrate the present invention, should be understood that these embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention, after having read the present invention, those skilled in the art will understand various aspects of the present invention Modifications in equivalent forms all fall within the scope defined by the appended claims of this application.

The co-channel interference suppression method for spaceborne AIS based on receiving blind beamforming of the present invention includes: adding a blind beamforming module before the signal detection module of the spaceborne AIS receiver, and the blind beamforming module uses the constant mode characteristic of the user signal itself to realize the beam take shape.

As a preferred solution, the baseband signal sent by the ship is a GMSK modulated signal, there are P said ships, and the binary AIS signal a _i,k ∈{±1}(i=1,2,...P) sent by each ship , first differentially encoded as b _i,k , b _i,k ＝a _i,k b _i,k-1 , and then GMSK modulated to become baseband GMSK signal s _i (t); baseband GMSK signal s _i (t) Uniformly sample at time t=kT to obtain s _i (k)=s _i (kT); the baseband sampling signal passes through the Gaussian white noise channel, and after N times of sampling, the antenna array receiving signal model is obtained: X=AS+N, X∈ C ^M×N represents the received signal matrix, S∈C ^P×N represents the transmitted signal matrix, N∈C ^M×N represents the noise signal matrix, A∈C ^M×P represents the array direction matrix; the output signal matrix after blind beamforming Y = W ^H X, W is the blind beamforming weight matrix.

As a preferred solution, an analytical constant modulus algorithm is used to solve the blind beamforming weight matrix W.

As shown in Figure 1, consider an AIS system with a low-orbit satellite and P ships. The receiver of the satellite is equipped with an equidistant linear array composed of M isotropic radiation antenna elements, and the distance between the elements is d. Ships S1, S2, ..., SP send binary AIS signals a _i,k ∈{±1}(i=1,2,...,P) respectively, first differentially encoded as b _i,k , b _i,k =a _{i ,k} b _i,k-1 , and then undergoes GMSK modulation to become a baseband GMSK signal s _i (t). The baseband GMSK signal s _i (t) (i=1, 2, . . . P) is uniformly sampled at time t=kT, and s _i (k)=s _i (kT). The signal passes through the Gaussian white noise channel and after N times of sampling, the received signal model of the antenna array is obtained as: X=AS+N. According to the received signal X of the array, the blind beamforming weight matrix W is found to restore the transmitted signal. After blind beamforming, the output signal matrix is Y=W ^H X. In fact, the output signal Y of the blind beamforming is the estimated value of the transmitted signal S. Finally, the two-bit differential monitoring algorithm is used for the signal matrix Y to detect the binary AIS signals a _i,k (i=1,2,...,P) sent by the ship.

The invention utilizes a constant modulus algorithm to realize blind beamforming on user signals, separates the desired signal from the interference signal and recovers the desired signal. It does not need the angle of arrival of the reference signal, but uses the characteristics of the user signal itself to realize beamforming, which has a high spectrum utilization rate, can significantly suppress co-channel interference, and significantly improve the bit error performance of signal detection.

Claims (5)

1. spaceborne AIS is based on the co-channel interferences suppression method receiving blind beamforming, it is characterized in that: the signal detection module of spaceborne AIS receiver carries out blind beamforming before carrying out input, and described blind beamforming utilizes the constant modulus property of subscriber signal itself to realize beam forming.

2. spaceborne AIS according to claim 1 is based on the co-channel interferences suppression method receiving blind beamforming, it is characterized in that, the concrete steps calculating the output signal matrix after blind beamforming are as follows:

Step 1), the binary system ais signal a that each boats and ships are sent _i,k∈ ± 1} (i=1,2 ... P) first differential coding is b _i,k:

b _i,k＝a _i,kb _i,k-1

Wherein, P is the quantity of boats and ships, and k is the sequence number of binary system ais signal;

Step 2), by b _i,kbe base band GMSK signal s through GMSK modulation _i(t), base band GMSK signal s _it () obtains s at t=kT moment uniform sampling _i(k)=s _i(kT), wherein, T is the sampling period;

Step 3), baseband sampling signal by Gaussian white noise channel, and obtains antenna array receiver signal model after N sampling:

X＝AS+N

Wherein, X ∈ C ^{m × N}represent Received signal strength matrix, S ∈ C ^{p × N}represent and send signal matrix, N ∈ C ^{m × N}represent noise signal matrix, A ∈ C ^{m × P}represent array direction matrix, M represents the reception antenna number of aerial array;

Step 4), calculate the output signal matrix Y=W after blind beamforming ^hx, wherein, W is blind beamforming weight matrix.

3. spaceborne AIS according to claim 2 is based on the co-channel interferences suppression method receiving blind beamforming, it is characterized in that, utilizes parsing constant modulus algorithm to solve described blind beamforming weight matrix W.

4. spaceborne AIS according to claim 2 is based on the co-channel interferences suppression method receiving blind beamforming, and it is characterized in that, described M is more than or equal to the integer that 1 is less than or equal to 100.

5. spaceborne AIS according to claim 2 is based on the co-channel interferences suppression method receiving blind beamforming, and it is characterized in that, described M is 50.