HK1035463B - A base band digital signal processing method based on smart antenna and interference cancellation - Google Patents

Description

Baseband processing method based on intelligent antenna and interference cancellation

Technical Field

The present invention relates to a processing technique for interference cancellation signals in a wireless communication system base station using a smart antenna, and more particularly, to a baseband processing method based on a smart antenna and interference cancellation.

Background

In modern wireless communication systems, particularly in Code Division Multiple Access (CDMA) wireless communication systems, it is desirable to use so-called Smart Antenna technology (Smart Antenna) in order to increase system capacity, increase system sensitivity, and achieve longer communication distances at lower transmit powers.

In the chinese patent application entitled time division duplex synchronous code division multiple access wireless communication system with smart antenna (application No. 97104039.7, publication No. CN1165458, publication No. 97.11.19), a base station structure of a wireless communication system using modern smart antenna is disclosed, which comprises an antenna array composed of one or more antennas, a corresponding radio frequency feeder cable and a set of coherent radio frequency transceivers. According to different reactions of signals from a user terminal received by each antenna unit in the antenna array, a baseband processor obtains a spatial feature vector and a signal arrival Direction (DOA) of the signals, and then uses a corresponding algorithm to realize the beam forming of the receiving antenna. Any one of the antennas, the corresponding rf feeder cable, and the coherent rf transceiver is referred to as a link. The weight of each link obtained from the uplink receiving beam forming is used for the downlink transmitting beam forming, and all functions of the intelligent antenna can be achieved under the condition of symmetrical electric wave propagation.

The main body of modern wireless communication is mobile communication. Referring to ITU recommendation M1225, since mobile communications are operated in a complex and diverse mobile environment, severe time-varying and multipath propagation effects must be considered. In the above patent application and many published technical documents, the research on the beamforming algorithm of the smart antenna is involved, and the conclusion is that the stronger the function is, the more complicated the algorithm is. However, in mobile communication environment, beam forming must be completed in real time, and the time for completing the algorithm is in the order of microseconds, which is limited by the state of modern microelectronics, and in such a short time, a Digital Signal Processor (DSP) or an application specific chip (ASIC) cannot realize too complex real-time processing. In the face of the above contradiction, in this mobile communication environment, the simple and real-time algorithm of the smart antenna cannot solve the problem of multipath propagation, and thus cannot completely solve the problem of CDMA system capacity.

On the other hand, to solve the interference problem caused by multipath propagation, technologies such as Rake receiver and Joint Detection (Joint Detection) are studied in depth, and are widely used in cdma mobile communication systems. However, for the wireless communication system using smart antenna technology, the Rake receiver or the multi-user detection technology is not easy to be used directly, and the main reasons are: the multi-user detection technology processes CDMA signals of multiple code channels, and directly solves information of all users at one time through matrix inversion after channel estimation and a matched filter, while the intelligent antenna technology separately carries out beam forming on each CDMA code channel, and is difficult to utilize the advantage of diversity brought by user multipath; the Rake receiver technology synthesizes the main multipath components of users, but it will destroy the phase relation of each antenna of the antenna array, and the number of users is the same as the spreading factor due to the limitation of its principle, so it can not work under the condition of full code channel.

There is a two-dimensional smart antenna technology under study, whose algorithm is still immature and quite complex. Another method is to perform multi-user detection after using the smart antenna, but at this time, each code channel must be processed separately because each code channel is already separated, and as a result, the multi-user detection function cannot be fully exerted, but the complexity of baseband signal processing is greatly increased.

In view of the above, in order to provide higher capacity and better performance for CDMA wireless communication systems, it is necessary to find an interference cancellation method that is simple, works in real time, and is convenient for use in a CDMA wireless communication system based on smart antennas.

Disclosure of Invention

The invention aims to design a baseband processing method based on an intelligent antenna and interference cancellation, and a new digital signal processing method is designed to enable a code division multiple access mobile communication system or other wireless communication systems applying the method to solve the interference such as multipath propagation and the like while using the intelligent antenna and obtain good effect.

The purpose of the invention is realized as follows: a baseband processing method based on intelligent antenna and interference cancellation is characterized by comprising the following steps:

A. carrying out channel estimation on the sampled data output signals from each link antenna unit and the radio frequency receiver by using a known user training sequence to obtain the response of all users on all channels;

B. on the basis of channel estimation, utilizing intelligent antenna beam forming to extract useful symbol-level signals from the despread sampling data output signals;

C. carrying out data reconstruction on the obtained useful symbol level signals, and scrambling to obtain chip level reconstruction signals;

D. subtracting a reconstructed signal from the sampled data output signal to realize interference elimination;

E. and C, repeatedly executing the steps B to D until the signal-to-noise ratio of all the users is larger than a given threshold value, or stopping when the cycle times of repeatedly executing the steps B to D reach a set time, and recovering the signal results of all the users.

The step A is completed by a channel estimation module, and the channel response contains a matrix related to the training sequence of each user, and the matrix is calculated and stored in advance.

The step B comprises the following steps: utilizing a power estimation module to carry out power estimation on the responses of all users on all channels, and calculating the power distribution conditions of the main paths and the multi-paths of all users in a search window; sending the calculated power distribution situation to a signal generator for signal generation, comprising: calculating the point of maximum peak power of each user; storing the location of the peak point in a storage location marked as a power point; at this power point, the smart antenna algorithm is used to obtain the despreading results of all signals at this point.

When the point of maximum peak power of each user is calculated, the adjustment parameters are sent to the sending module of the user whose strongest path is not synchronous with the base station on the same point with other users.

The step B also comprises the following steps: and sending the despreading result to a signal-to-noise ratio estimation module at the same time, estimating the signal-to-noise ratios of all users, and continuing to execute the step C, D, E for users with low signal-to-noise ratios, wherein the users with high signal-to-noise ratios directly output user signal results.

The estimating the signal-to-noise ratio of the user comprises: calculating the power of the user; judging that the power exceeds a certain threshold value as effective power; calculating the variance of all effective power signals on the points of the corresponding constellation diagram; and when the variance is greater than the given threshold value, judging that the signal-to-noise ratio of the user is low, and when the variance is less than the given threshold value, judging that the signal-to-noise ratio of the user is high.

And step C, reconstructing the original signal in a signal reconstruction module, and solving the components of all user signals and multipath on each antenna unit.

And the step D is to carry out interference cancellation in the interference cancellation module.

And E, the step is carried out in a judging module, and when the cycle number of interference elimination reaches the preset number of times less than or equal to the length of the search window, the interference elimination is stopped, and a result of a recovery signal is output.

And E, the step is carried out in a judging module, and when the signal-to-noise ratios of all the signals are greater than a given threshold value, the interference elimination is stopped, and a signal recovery result is output.

The essence of the method of the invention is to shape each multipath of each channel within the length of the search window, extract useful signals, and then superpose the useful signals, thereby making the best use of the benefits of space diversity and time diversity, and having good results even if the system has serious multipath interference and white noise interference. The method has limited calculation amount and can be completely realized by a Digital Signal Processor (DSP) or a Field Programmable Gate Array (FPGA) which is commercially available at present.

Drawings

Fig. 1 is a block diagram of a wireless communication base station using smart antennas;

fig. 2 is a schematic diagram of an implementation structure of a smart antenna and an interference cancellation method;

fig. 3 is a flow chart of an implementation of a smart antenna and interference cancellation method.

Detailed Description

The technology of the present invention will be further explained with reference to the following embodiments and the accompanying drawings

Referring to fig. 1, a system according to the present invention is a mobile communication system having a smart antenna and interference cancellation, or a wireless communication system such as a wireless subscriber loop system, and fig. 1 shows a base station structure in the system. The antenna system mainly comprises N identical antenna units 201A, 201B, a. All rf transceivers 203 use the same local oscillator signal source 208 to ensure that the rf transceivers in a base station operate coherently. Each rf transceiver has an analog-to-digital converter (ADC) and a digital-to-analog converter (DAC), so that the baseband input and output of all rf transceivers 203 are digital signals, and they are connected to the baseband processor 204 through a high-speed digital bus 209. The drawing 100 shows a base station apparatus.

The present invention only discusses the interference cancellation method for the received signal in the baseband processing of the structure shown in fig. 1, and the working mode of implementing the smart antenna and the interference cancellation is completed in the baseband processor 204 regardless of the processing of the transmitted signal.

It is assumed that the CDMA wireless communication system is designed with K code channels (channels), and the smart antenna system is composed of N antenna units and N rf transceivers, and has N links. The output data sampled by the A/D converter of the RF receiver in each link is S₁(n)，S₂(n)，...，S_i(n)，...S_NAnd (n) is the nth Chip (Chip), and taking data Si (n) sampled by an analog-to-digital converter of the 203i radio frequency receiver from the ith receiving link as an example, the Si (n) enters the baseband processor 204 as an input signal. The baseband processor 204 includes N rf transceivers 203A, 203B,. and 203i,. and 203N corresponding to N links, channel estimation modules 210A, 210B,. and 210i,. and 210N, and a smart antenna interference cancellation module 211, output data S of N links₁(n)，S₂(n)，...，S_i(n)，...S_N(N) respectively sending the channel response signals h to the corresponding channel estimation modules 210A, 210B, a., 210i., 210N and the smart antenna interference cancellation module 211, wherein each channel estimation module 210A, 210B, a., 210i., 210N outputs a channel response signal h₁，h₂，...h_i，...h_NTo smart antenna interferenceThe canceling module 211 outputs a synchronization adjustment parameter S, and the smart antenna interference canceling module 211 outputs a synchronization adjustment parameter S_S(K) To a downlink transmission module and outputting the result S of the interference cancellation of the smart antenna_ca+1，K(d) To a channel decoding module, where hi ═ h_i，1，h_i，2，...，h_i，k]。

The Si (n) signal enters the channel estimation module 210i, and K channel impulse responses, denoted as h, can be obtained by estimating K channel conditions through a pre-known training sequence (Pilot) or Midamble)_i，kWhere i is denoted as the ith antenna and k denotes the kth channel.

The specific treatment process comprises the following steps: the known training sequence of the kth user is m_kThe value of the training sequence received on the ith antenna is e_iThen there isEquation (1) where n is the nth chip, w is the search window length, n_oiWhite noise received for the ith antenna. Equation (1) may be further rewritten as

e_i＝Gh_i，k+n_oi..

The estimate of the channel can be expressed as

h_i，k＝(G^*TG)^-1G^*Te_i＝M_1i..

Where M is a matrix associated only with the training sequences of the respective users, which can be calculated and stored in advance, the channel estimation speed can be greatly increased since it is not necessary to calculate it in real time.

Respectively calculating the responses of all users on all channels according to the process to obtain h_i，kThe result is input to the smart antenna interference cancellation module 211, which further processes the signal to recover the signals for all users.

Referring to fig. 2, the process of interference cancellation by the antenna interference cancellation module 211 is shown. The channel response h calculated by the channel estimation module 210i_i，kFirst, the power estimation is performed in the power estimation module 220, and the power distribution of the main paths and the multi-paths of K users (the same K channels) in the search window is calculated asFormula (4)

Then, the maximum peak power point of each user is calculated, if the strongest path of some users is not at the same point as the strongest paths of other users, it indicates that the user is not synchronous with the base station, the base station will notify the user in the downlink channel and adjust it to be synchronous with other users, the adjusting parameter is the above-mentioned S_S(K)。

Then, the distribution of the total power of the main path and the multi-path of the kth user in the search window is calculated asFormula (5)

Wherein m is a point in the search window, the obtained signal generator 221 generates a signal, and the signal generator 221 also outputs channel response signals from the channel estimation modules 210A, 210B,. 210i.. 210NAnd output data S of N links₁(n)，S₂(n)，...，S_i(n)，...S_N(n)。

The signal generator 221 first calculates the position of the peak point in power _ abs, stores the calculated result in power _ point, and makes power _ abs (power _ point) equal to 0 so that this point is not calculated again when interference is made next time, and then uses smart antenna algorithm at power _ point to obtain the result of despreading all signals at this point, namelyFormula (6)

Wherein, C_q，kIs the spreading code of the kth user, pn _ code (1) is the scrambling code, S_ca，k(d) Is the result of the last interference cancellation, the initial value S_o，k(d) Outputs the result S as 0_ca+1，K(d) Is symbol-level. Obviously, S is started because the user is not completely synchronized and there is severe multipath interference and white noise in the system_ca+1，K(d) Is a coarse result.

Will S_ca+1，K(d) To the snr estimation module 224 and the signal reconstruction module 222. The snr estimation module 224 is used to estimate the snr of each user, and the signal generated by the signal generator 221 is already descrambled, despread, and demodulated, and there are many methods for estimating the snr of each user, one of them is: for the k-th user, its power is first calculated asFormula (7)

If the power exceeds a certain threshold value, the power is called effective power, all signals with the effective power are subjected to variance on the points of the corresponding constellation diagram, if the variance is larger than the given threshold value, the signal-to-noise ratio of the user is lower, and the S is lower_ca+1，K(d) The value of (a) is not reliable, and interference elimination is needed; conversely, if the variance is less than a given threshold, the signal-to-noise ratio for this user is higher, with S_ca+1，K(d) The value of (a) is trusted and no interference cancellation is required. The purpose of using the snr estimation module is to simplify the calculation of interference cancellation, which is not necessary for the trusted signal.

The signal reconstruction module 222 utilizes S_ca+1，K(d) The original signal is reconstructed, the reconstructed signal is at the chip level

S_ca+1，k(Q(d-1)+q)＝S_ca+1，k(d)C_q，kEquation (8) is given as pn _ code (1)

Then, the components of K user signals on N antennas are calculated asFormula (9)

The results of the N antenna recovery are sent to the interference cancellation module 223 for interference cancellation, in order

S_i(n)＝S_i(n)-S’_ca+1，iEquation (10)

The function of the decision block 225 is to decide when the interference cancellation is stopped, and there are two decision conditions: the signal-to-noise ratio of all signals is larger than a given threshold value; and 2, the cycle number of the interference elimination reaches a set number, the cycle number is less than or equal to the length of the search window, and the cycle number is determined by the processing capacity of chips such as a digital signal processor, an FPGA and the like in the range. As long as any one of the two conditions is met, the processing process of the interference cancellation method of the intelligent antenna is ended, and a recovery signal result S is output_ca+1，k(d)。

Referring to fig. 3, a processing flow of the method for intelligent antenna interference cancellation is illustrated by taking 8 antennas as an example.

The function block 301, calculating the power of the channel estimate by the power estimation module 220; functional blocks 303, 304, find the maximum value in the power by the signal generating module 221, calculate the deviation, and set this value as 0, and despread at its deviation point, beam-forming, obtain the result and send signal-to-noise ratio judging module 225 and signal reconstruction module 222 through judging module 225 at the same time; the function block 302, sending out the synchronization adjustment Ss (k); the function block 308, reconstructs the data, computing the components of the reconstructed data on 8 antennas; the function block 309 subtracts the components of the reconstructed data on 8 antennas from the receive _ data, the obtained result is still stored in the receive _ data, and the function blocks 303 to 309 are repeatedly executed, when the function block 305 determines that the snr is large or small, and when the snr is cycled to the specified times or the snrs of all users meet the requirements through the function block 306 determination module 225, the interference cancellation is finished, and the function block 307 outputs the result of the recovered signal.

The present invention is primarily directed to code division multiple access wireless communication systems, including Time Division Duplex (TDD) and Frequency Division Duplex (FDD) code division multiple access wireless communication systems. Any engineer engaged in the development of a wireless communication system, knowing the basic principle of a smart antenna and having basic knowledge of digital signal processing, can design a high quality smart antenna system using the method of the present invention and use it for various mobile communication or wireless subscriber loop systems to achieve high performance.

Claims (10)

1. A baseband processing method based on intelligent antenna and interference cancellation is characterized by comprising the following steps:

A. carrying out channel estimation on the sampled data output signals from each link antenna unit and the radio frequency receiver by using a known user training sequence to obtain the response of all users on all channels;

B. on the basis of channel estimation, utilizing intelligent antenna beam forming to extract useful symbol-level signals from the despread sampling data output signals;

C. carrying out data reconstruction on the obtained useful symbol level signals, and scrambling to obtain chip level reconstruction signals;

D. subtracting a reconstructed signal from the sampled data output signal to realize interference elimination;

E. and C, repeatedly executing the steps B to D until the signal-to-noise ratio of all the users is larger than a given threshold value, or stopping when the cycle times of repeatedly executing the steps B to D reach a set time, and recovering the signal results of all the users.

2. The baseband processing method based on smart antenna and interference cancellation according to claim 1, wherein: the step A is completed by a channel estimation module, and the channel response contains a matrix related to the training sequence of each user, and the matrix is calculated and stored in advance.

3. The baseband processing method based on smart antenna and interference cancellation according to claim 1, wherein: the step B comprises the following steps: utilizing a power estimation module to carry out power estimation on the responses of all users on all channels, and calculating the power distribution conditions of the main paths and the multi-paths of all users in a search window; sending the calculated power distribution situation to a signal generator for signal generation, comprising: calculating the point of maximum peak power of each user; storing the location of the peak point in a storage location marked as a power point; at this power point, the smart antenna algorithm is used to obtain the despreading results of all signals at this point.

4. The baseband processing method based on smart antenna and interference cancellation according to claim 3, wherein: when the point of maximum peak power of each user is calculated, the adjustment parameters are sent to the sending module of the user whose strongest path is not synchronous with the base station on the same point with other users.

5. The baseband processing method based on smart antenna and interference cancellation according to claim 1, wherein: the step B also comprises the following steps: and sending the despreading result to a signal-to-noise ratio estimation module at the same time, estimating the signal-to-noise ratios of all users, and continuing to execute the step C, D, E for users with low signal-to-noise ratios, wherein the users with high signal-to-noise ratios directly output user signal results.

6. The baseband processing method based on smart antenna and interference cancellation according to claim 5, wherein: the estimating the signal-to-noise ratio of the user comprises: calculating the power of the user; judging that the power exceeds a certain threshold value as effective power; calculating the variance of all effective power signals on the points of the corresponding constellation diagram; and when the variance is greater than the given threshold value, judging that the signal-to-noise ratio of the user is low, and when the variance is less than the given threshold value, judging that the signal-to-noise ratio of the user is high.

7. The baseband processing method based on smart antenna and interference cancellation according to claim 1, wherein: and step C, reconstructing the original signal in a signal reconstruction module, and solving the components of all user signals and multipath on each antenna unit.

8. The baseband processing method based on smart antenna and interference cancellation according to claim 1, wherein: and the step D is to carry out interference cancellation in the interference cancellation module.

9. The baseband processing method based on smart antenna and interference cancellation according to claim 1, wherein: and E, the step is carried out in a judging module, and when the cycle number of interference elimination reaches the preset number of times less than or equal to the length of the search window, the interference elimination is stopped, and a result of a recovery signal is output.

10. The baseband processing method based on smart antenna and interference cancellation according to claim 1, wherein: and E, the step is carried out in a judging module, when the signal-to-noise ratios of all the signals are greater than a given threshold value, the interference elimination is stopped, and a result of recovering the signals is output.