CN100442904C - Downlink beam shaping method for multicast service system - Google Patents

Abstract

The present invention discloses a descending wave beam shaping method used in a multipoint-to-multipoint casting service system, which comprises steps: the spatial characteristic parameters of multipoint-to-multipoint casting users in a system are estimated; according to the spatial characteristic parameters of the multipoint-to-multipoint casting users and the performance indices of used smart antennas, the multipoint-to-multipoint casting users are grouped; the descending wave beam shaping weight coefficients of each group of users are determined to shape wave beams. If the present invention is utilized, the occupation of code channel resources by the multipoint-to-multipoint casting users can be reduced, and the interference between different users can also be reduced.

Description

Downlink beam forming method for multicast service system

Technical Field

The invention relates to the technical field of mobile communication, in particular to a downlink beam forming method for a multicast service system.

Background

In recent years, smart antenna technology has become one of the most attractive technologies in mobile communications. The intelligent antenna adopts Space Division Multiple Access (SDMA) technology, and distinguishes signals with the same frequency or the same time slot and the same code channel by using the difference of the signals in the transmission direction, thereby maximally utilizing limited channel resources. Compared with a non-directional antenna, the antenna gain of the uplink and the downlink is greatly improved, the transmitting power level is reduced, the signal to noise ratio is improved, and the influence of channel transmission fading is effectively overcome. Meanwhile, because the antenna lobe is directly directed to the user, the interference between the antenna lobe and other users in the cell and between the antenna lobe and users in adjacent cells is reduced, and the multipath effect of a mobile communication channel is also reduced. The CDMA system is a power limited system, and the application of intelligent antenna can raise antenna gain and reduce system interference, so that it can obviously expand system capacity and raise frequency spectrum utilization rate.

The smart antenna essentially utilizes the orthogonality of the space of a plurality of antenna units, namely, the space division multiple access multiplexing function, to improve the capacity and the spectrum utilization rate of the system. The intelligent antenna is completed by the antenna array and the baseband digital signal processing part connected with the antenna array. Two key issues that need to be solved by smart antennas are the direction of the identified signal and the implementation of digital shaping. The radiation pattern in the elevation direction of the smart antenna is the same as that of each antenna element. The directional diagram in azimuth is controlled by the baseband processor, a plurality of beams can be generated simultaneously, and the beams can be shaped randomly within the range of 360 degrees according to the distribution of communication users.

Beamforming is a process of implementing optimal (suboptimal) combination or optimal (suboptimal) allocation of signals according to measurement and estimation parameters. In the traditional wave beam forming algorithm, the phase difference of incoming waves on each antenna unit is calculated according to the incoming wave angle of a desired signal, and the forming coefficient is used for offsetting the phase difference on each unit to enable each unit to have each phase difference

The incoming wave signals on the units are superposed in phase. For a conventional beamforming algorithm, for an incoming wave with a fixed direction, the beamforming system is fixed, and therefore, the shape of the beam pattern is fixed.

In a digital trunking communication system or a mobile communication system with the characteristics of multicast service, a base station sends the same downlink data to a plurality of users, and the coverage Area of message sending can be a sector (cell), a base station (BTS), or a set Area (Area) consisting of a plurality of base stations, or even the whole mobile communication network. In these systems, if the broadcast information is transmitted via an omni-directional coverage beam without beamforming, interference may be caused to other users.

In the traditional beamforming for users, each user needs to be allocated with a code channel, and the code channels correspond to the beams one to one, that is, each code channel can only be transmitted by using a unique beam. For multicast services, the waste of resources is undoubtedly caused. And because the number of users of the multicast user and the spatial distribution thereof are uncertain, and the beam width of the traditional beam forming is not necessarily matched with the angular range of the spatial distribution of the users, if the distribution range of the users is larger than the width of the formed beam, the users fall in the area with lower antenna radiation level, and the receiving quality of the users in the area is influenced.

Disclosure of Invention

The invention aims to provide a downlink beam forming method for a multicast service system, which overcomes the resource waste caused by using the traditional beam forming algorithm in the prior art, saves code channel resources and achieves the forming effect at the same time.

Therefore, the invention provides the following technical scheme:

a downlink beamforming method for a multicast service system, the method comprising the steps of:

A. estimating spatial characteristic parameters of multicast users in the system;

B. grouping users in the group according to the spatial characteristic parameters of the multicast users and the performance indexes of the used intelligent antenna;

C. and determining the downlink beamforming weight coefficient of each group of users to realize beamforming.

The step A comprises the following steps:

a1, the intelligent antenna estimates the space power spectrum of each user according to the uplink signal of the user in the group;

and A2, acquiring the spatial characteristic parameters of the user according to the spatial power spectrum.

The step A1 includes the steps of:

a11, estimating channel impulse response according to the training sequence of multi-user received by the intelligent antenna;

and A12, calculating the space power spectrum of each user according to the channel impulse response estimation result.

Optionally, the spatial power spectrum of each user is calculated by using a Bartlett spectrum estimation method or a Capon spectrum estimation method.

The spatial characteristic parameters of the multicast user comprise: incoming wave angle, half power lobe width center angle.

The step B specifically comprises the following steps:

b1, obtaining the forming beam width of the intelligent antenna;

b2, determining the multicast users contained in each group according to the incoming wave angle of the users, and making the incoming wave angle set of each group of users less than or equal to the forming beam width of the intelligent antenna.

The step C comprises the following steps:

c1, determining the incoming wave direction of each group of users, and setting the incoming wave direction as the central direction of the incoming wave directions of all the users in the group;

and C2, forming the downlink wave beam of each group of users according to the incoming wave direction of each group of users.

Optionally, the step C2 specifically includes:

and selecting a forming weight vector which is closest to the incoming wave direction of each group of users from preset weight vectors to form downlink wave beams of the group of users.

Optionally, the step C2 specifically includes:

setting initial values of the forming weight vectors according to the incoming wave directions of each group of users;

and optimizing the initial value of the shaped weight vector in real time to ensure that the shaped beam is matched with the spatial distribution range of the group of users.

Preferably, the step C further comprises:

setting the maximum number of wave beams;

and when the grouping number of the users in the group is larger than the maximum beam number, selecting the omnidirectional transmission beam.

It can be seen from the above technical solutions that, according to the characteristics of the multicast service, the present invention estimates the spatial characteristic parameters of the multicast users in the mobile communication system with the multicast service, groups the users in the group according to the spatial characteristic parameters of the users in the group and the performance index of the smart antenna, and performs beamforming transmission by using one code channel for each group, thereby effectively saving code channel resources and achieving a better beamforming effect.

Drawings

FIG. 1 is a flow chart of an implementation of the method of the present invention;

fig. 2 is a flow chart of grouping for the mbs users in the method of the present invention.

Detailed Description

The core of the invention lies in that in the mobile communication system with the multicast service, the space characteristic parameters of the multicast users are estimated, the users in the group are grouped according to the space characteristic parameters of the users in the group and the performance index of the intelligent antenna, and each group uses one code channel for forming transmission, thereby avoiding using too many code channel resources.

The skilled person knows that the smart antenna adopts more than two single antenna elements to form an antenna array, signals received by each antenna element are subjected to radio frequency processing and then weighted and summed by using a proper weight value, so that the effect of directional reception can be achieved, and one weight vector corresponds to a certain beam directional diagram. The nature of the weighting is a spatial filtering and the smart antennas can also be considered as a SDMA (spatial division multiple access) technique. In SDMA, signals are received by an antenna array and digital beamforming is performed by digital signal processing, i.e. the phase and amplitude of the signals received by the antenna array are adjusted to enhance the desired signal and attenuate other interfering signals, thereby maximizing the signal-to-noise ratio of the desired signal.

Smart antennas are generally classified into two types. One is a pre-multi-beam intelligent antenna, that is, some beam weights pointing to different directions are preset, and those beam weight weighting results with better received signals are selected for subsequent processing in the communication process. The other is a self-adaptive intelligent antenna, the weight of the antenna is not required to be preset, the weight is continuously updated according to a certain criterion according to the change of the signal space distribution characteristic, the amplitude and the phase of the weight can be freely updated, and when the algorithm is converged, the method can fully utilize the space characteristics of the expected user signal and the interference signal to enable the signal-to-interference-and-noise ratio of the received signal to be maximum.

Since a beam can cover a specific angular range, if the spatial separation of two users of the multicast service is within a beam width range, then the two users can be covered by a shaped beam. Based on the characteristics, the invention groups the users in the group according to the space characteristic parameters of the users in the group and the performance index of the intelligent antenna, and carries out shaped sending on each group of users through a code channel, thereby reducing the occupation of the code channel resources by the multicast users.

In order that those skilled in the art will better understand the technical solution of the present invention, the following detailed description of the present invention is provided in conjunction with the accompanying drawings and embodiments.

Referring to fig. 1, fig. 1 is a flow chart of an implementation of the method of the present invention, including the following steps:

step 101: and estimating the spatial characteristic parameters of the multicast users in the system, such as an incoming wave angle, a half-power lobe width central angle and the like.

Firstly, estimating the spatial power spectrum of each user by the intelligent antenna according to the uplink signal of the user in the group; and then, acquiring the spatial characteristic parameters of the user according to the spatial power spectrum.

The smart antenna can estimate the user spatial power spectrum from the uplink signal of each user in the group.

The channel impulse response on each antenna is estimated using the received training sequence portion of the multi-user. According to actual needs, various channel estimation modes and methods can be adopted.

Assuming a total of K users in the group, the channel estimation matrix for user K is represented as follows:

H^(k)＝[h^(k，1)，h^(k，2)，L，h^(k，Ka)]，k＝1，Λ，K (1)

wherein,

denotes user k and antenna element k_aThe channel impulse response in between.

The spatial correlation matrix can be calculated by:

<math> <mrow> <msubsup> <mi>R</mi> <mi>xx</mi> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msubsup> <mo>=</mo> <msup> <mi>H</mi> <mrow> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> <mi>H</mi> </mrow> </msup> <mo>&CenterDot;</mo> <msup> <mi>H</mi> <mrow> <mo>(</mo> <mi>k</mi> <mo>)</mo> </mrow> </msup> <mo>,</mo> </mrow> </math> k＝1，Λ，K (2)

wherein H^(k)HRepresentation matrix H^(k)A conjugate transpose operation of;

the spatial power spectrum of the user is calculated by the Bartlett spectrum estimation method as follows:

k＝1，Λ，K (3)

wherein,

representing array response vectors, i.e. from

The response of a directional signal on an antenna array is generally expressed as a phase difference between different antennas.

The calculation by Capon spectral estimation method is as follows:

k＝1，Λ，K (4)

wherein,

representing array response vectors, i.e. fromThe response of a directional signal on an antenna array is generally expressed as a phase difference between different antennas.

Of course, the present invention is not limited to the two space power spectrum algorithms, and other calculation methods may be selected to obtain the space power spectrum of the user according to the actual application requirements.

With the spatial power spectrum of the user, the incoming wave angle and the half-wave lobe width central angle of each user can be conveniently obtained.

Calculating the incoming wave angle of each user according to the space power spectrum of the user obtained by the Bartlett spectrum estimation method:

k＝1，Λ，K (5)

wherein,representing the maximum of the discrete spectrum, i.e.

Is measured.

The half-power lobe width central angle of each user can also be calculated by the following formula, and of course, other spatial characteristic parameters representing the user azimuth information can also be adopted:

for example, the angle at which the discrete spectral value is reduced by 3 db from the maximum is:

k＝1，Λ，K (6)

wherein,

discrete spectrum, P, representing user k in frame i_max ^(i，k)Representing the maximum of the discrete spectrum. Or the center direction of the half-power angle is:

k＝1，Λ，K (7)

wherein,

andrepresenting two angles of a 3 db drop in the discrete spectral value from the maximum value, respectively.

Step 102: and grouping the users in the group according to the spatial characteristic parameters of the multicast users and the performance indexes of the used intelligent antenna.

Set the shaped beam width of the smart antenna to

The set of incoming wave angles of the grouped users is omega, in order to optimizeSmall beam coverage, the incoming angles of the users in the group are adjacent, and the angular separation between the 1 st user of the 1 st group and the last user of the last group is guaranteed to be the largest among the angular separation of all adjacent users.

Therefore, the following principles should be satisfied when grouping:

the beam width delta of the group, namely the difference between the maximum value and the minimum value of the incoming wave angles of the users in the group is just less than or equal to

That is, if Ω is increased by one user, Δ will be larger than

Step 103: and determining the downlink beamforming weight coefficient of each group of users to realize beamforming.

If a pre-stored beam is used, the maximum number of beams can be preset, and if the grouped number of users in the group, which is separated according to the grouping principle, is greater than the set maximum number of beams, the omni-directional transmission beam can be selected at this time because the pre-stored beam cannot meet the code channel allocation of the users in the multicast group.

In the forming transmission, the incoming wave direction of the group is defined as the central direction of the incoming wave directions of all users in the group, for example, if the incoming wave directions of the users in the group are {355 °, 3 °, 15 ° }, the incoming wave direction of the group is 10 °. And finding out the forming weight vector in the direction closest to the group incoming wave direction from the preset weight vectors as a downlink forming weight vector to realize the wave beam forming of different user groups.

The initial value of the shaped weight vector can be set according to the incoming wave direction of each group of users; and then, carrying out real-time optimization on the initial value of the shaped weight vector to ensure that the shaped beam is matched with the spatial distribution range of the group of users so as to obtain the shaped beam with higher precision.

Fig. 2 shows the implementation flow of grouping users in a group in the method of the present invention:

step 201: determining the shaped beam width of the antenna according to the performance index of the intelligent antenna

Step 202: creating a new group, and selecting the first user which is not grouped in the group in sequence;

step 203: adding an adjacent user in the group according to the incoming wave angle of the user, and calculating the distribution range of the users in the group;

step 204: judging whether the distribution range of the users in the group is smaller than the width of the shaped wave beam

If the distribution range of the users in the group is smaller than the shaped beam width, go to step 205: the group accepts the newly added user;

then, proceed to step 206: judging whether the user is the last user or not;

if so, go to step 207: ending the grouping process;

otherwise, returning to step 203: sequentially adding a neighboring user within the group;

if the distribution range of the users in the group is larger than the shaped beam width, proceed to step 208: the group refuses to accept the user;

then, returning to step 202: the creation of new groups continues.

Of course, the users of the multicast may also be grouped in other manners according to actual needs, for example, the whole space is divided into a plurality of fixed beams, and it is determined which beam range the user falls in belongs to which group. The incoming wave angle set of each group of users is only required to be smaller than or equal to the shaped beam width of the intelligent antenna used by the system.

The following will further illustrate the implementation of the method of the present invention with reference to specific examples.

Assuming that the smart antenna used is a uniform annular array with M ═ 8 elements, the radius of the annular ring is 0.65 λ, λ is the carrier wavelength, and the shaped beam width of the smart antenna

The preset weight vector is the conjugate of the array response vector, a shaped beam is arranged at an interval of 1 degree, the number of the beams is limited to 3, and the omnidirectional transmission is changed when the number of the beams is more than 3.

Firstly, the incoming wave angles of 8 users are estimated:

in this embodiment, 33 °, 45 °, 61 °, 63 °, 66 °, 91 °, 102 °, 110 °, 116 °;

then, 8 users are grouped:

searching for an initial user according to the criterion that the angle difference between the initial user and the previous user is maximum, the angle difference between the user 1 and the user 8 is 83 degrees, and the initial user is the user 1;

grouping the 8 users according to the flow shown in fig. 2, in this embodiment, the grouping result is that group 1 includes users 1 to 5, and group 2 includes users 6 to 8;

according to the grouping result, determining the central angle of each group of incoming wave directions, and determining a forming weight coefficient:

and if the number of the groups is less than the limit of the number of the wave beams, the wave is shaped and sent.

In this embodiment, the central angle of the group 1 is 49.5 °, which is attributed to the forming angle, that is, the forming angle closest to the group 1 is found according to the forming angle interval and is 50 °; the center angle of group 2 was 109 °.

The beam forming coefficients corresponding to the two central angles obtained by table lookup are:

$w^{\left(1\right)}=\left[\begin{array}{c}-0.7987+0.6017i\\ -0.7474-0.6644i\\ -0.9861+0.1663i\\ 0.9433+0.3320i\\ -0.7987-0.6017i\\ -0.7474+0.6644i\\ -0.9861-0.1663i\\ 0.9433-0.3320i\end{array}\right]$ $w^{\left(2\right)}=\left[\begin{array}{c}0.3018-0.9534i\\ -0.1310+0.9914i\\ -0.8629-0.5054i\\ -0.9399-0.3414i\\ 0.3018+0.9534i\\ -0.1310-0.9914i\\ -0.8629+0.5054i\\ -0.9399+0.3414i\end{array}\right]$

of course, the beam forming coefficients corresponding to the center angles of the groups can be determined by real-time optimization according to the formed beam width of the smart antenna and the center angles of the incoming wave directions of the groups.

While the present invention has been described with respect to the embodiments, those skilled in the art will appreciate that there are numerous variations and permutations of the present invention without departing from the spirit of the invention, and it is intended that the appended claims cover such variations and modifications as fall within the true spirit of the invention.

Claims (10)

1. A downlink beamforming method for a multicast service system, the method comprising the steps of:

A. estimating spatial characteristic parameters of multicast users in the system;

B. grouping users in the group according to the spatial characteristic parameters of the multicast users and the performance indexes of the used intelligent antenna;

C. and determining the downlink beamforming weight coefficient of each group of users to realize beamforming.

2. The downlink beamforming method for mbs system according to claim 1, wherein the step a comprises the steps of:

a1, the intelligent antenna estimates the space power spectrum of each user according to the uplink signal of the user in the group;

and A2, acquiring the spatial characteristic parameters of the user according to the spatial power spectrum.

3. The downlink beamforming method for mbs system according to claim 2, wherein the step a1 comprises the steps of:

a11, estimating channel impulse response according to the training sequence of multi-user received by the intelligent antenna;

and A12, calculating the space power spectrum of each user according to the channel impulse response estimation result.

4. The downlink beamforming method for a multicast service system according to claim 3, wherein the step a12 specifically comprises:

and calculating the spatial power spectrum of each user by using a Bartlett spectrum estimation method or a Capon spectrum estimation method.

5. The downlink beamforming method for mbs system according to any of claims 1 to 4, wherein the spatial characteristic parameter of the mbs user comprises: incoming wave angle, half power lobe width center angle.

6. The downlink beamforming method for a mbs system according to claim 1, wherein the step B specifically comprises:

b1, obtaining the forming beam width of the intelligent antenna;

b2, determining the multicast users contained in each group according to the incoming wave angle of the users, and making the incoming wave angle set of each group of users less than or equal to the forming beam width of the intelligent antenna.

7. The downlink beamforming method for mbs system according to claim 6, wherein the step C comprises the steps of:

c1, determining the incoming wave direction of each group of users, and setting the incoming wave direction as the central direction of the incoming wave directions of all the users in the group;

and C2, forming the downlink wave beam of each group of users according to the incoming wave direction of each group of users.

8. The downlink beamforming method for a mbs system according to claim 7, wherein the step C2 specifically comprises:

and selecting a forming weight vector which is closest to the incoming wave direction of each group of users from preset weight vectors to form downlink wave beams of the group of users.

9. The downlink beamforming method for a multicast service system according to claim 7, wherein the step C2 specifically includes:

setting initial values of the forming weight vectors according to the incoming wave directions of each group of users;

and optimizing the initial value of the shaped weight vector in real time to ensure that the shaped beam is matched with the spatial distribution range of the group of users.

10. The downlink beamforming method for a mbs system according to claim 1, wherein the step C further comprises:

setting the maximum number of wave beams;

and when the grouping number of the users in the group is larger than the maximum beam number, selecting the omnidirectional transmission beam.

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