CN107579762B - Multi-cell cooperative precoding method based on quantification and channel information statistics - Google Patents
Multi-cell cooperative precoding method based on quantification and channel information statistics Download PDFInfo
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- CN107579762B CN107579762B CN201710600377.4A CN201710600377A CN107579762B CN 107579762 B CN107579762 B CN 107579762B CN 201710600377 A CN201710600377 A CN 201710600377A CN 107579762 B CN107579762 B CN 107579762B
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Abstract
The invention discloses a multi-cell cooperative precoding method based on quantification and channel information statistics, which comprises the following steps: the base station acquires statistical CSI of users in a cell, the users estimate respective channel state information according to a received pilot channel, the base station acquires rough instantaneous channel state information, the instantaneous channel state information is shared among the base stations through an information sharing link, and after the base station acquires the statistical CSI and quantized instantaneous CSI of all the users in the cell, a new precoding matrix W is obtained through linear combination, and the base station transmits data to the users by using the precoding matrix W. The invention has the beneficial effects that: compared with a precoding algorithm based on single statistical channel information, due to the fact that instantaneous channel state information adopting low-order quantization is added, the direction of a precoding vector obtained based on the statistical channel information can be calibrated to a certain extent, and therefore better performance can be obtained; the method can effectively improve the total rate performance of the system and improve the throughput of the system.
Description
Technical Field
The invention belongs to the field of mobile communication, and relates to a multi-cell cooperative precoding method based on quantification and channel information statistics.
Background
With the rapid development of wireless communication technology and mobile internet, people are continuously making higher demands on mobile communication speed. However, system resources such as available spectrum and transmit power in wireless communication systems are limited and cannot meet the increasing rate requirements. Research shows that a future mobile communication system must have extremely high spectrum resource utilization rate, and therefore a Multiple-Input Multiple-Output (MIMO) technology is introduced, and the MIMO technology can effectively utilize spatial multiplexing and diversity gain by opening up spatial domain resources, improve wireless channel capacity and spectrum utilization rate in multiples without increasing system bandwidth and antenna transmission power, but cause serious co-channel interference. Since the downlink mimo system terminal is limited by the battery capacity and the chip processing speed, it is necessary to introduce mimo precoding technology to eliminate the co-channel interference in advance and reduce the terminal complexity.
In currently applied 3G, 4G and future 5G wireless communication systems, due to the increase of the requirement for transmission rate and the sharp increase of the number of users, a signal transmission scheme of the communication system is often required to have adaptive characteristics and robustness in order to adapt to a complex and variable wireless channel environment. The precoding algorithm based on the closed-loop MIMO architecture can enable the wireless communication system to adjust the signal transmission strategy according to the channel condition, thereby obviously improving the system capacity and further improving the frequency spectrum utilization rate. The traditional precoding algorithm research is based on the perfect CSI fed back by the user, but in the actual commercial wireless communication system, the precondition assumption is not necessarily true because the rate of the uplink feedback channel is low. In a Time Division Duplex (TDD) system, a base station may obtain downlink CSI for precoding design by using reciprocity of uplink and downlink channels; in a Frequency Division Duplex (FDD) system, the user must feed back downlink CSI to the base station through an uplink channel. Because the rate of the uplink channel is low, the user cannot perfectly feed back the downlink CSI, and therefore how the user performs the quantization feedback on the CSI by using the limited uplink channel resource becomes an urgent problem to be solved.
To further improve the spectrum efficiency of the cellular system, 3GPP LTE will tend to co-frequency deployment, thereby causing cell edge users to suffer from larger co-frequency interference. In order to reduce the influence of the inter-cell co-channel interference, a precoding technology based on cooperation can be performed between adjacent base stations, so that interference avoidance is realized. However, in order to implement cooperation, channel state information and/or data information needs to be shared between base stations, and as the number of cooperating base stations increases and the data rate increases, a huge requirement is made on the bandwidth of a shared link between base stations, which leads to an increase in construction cost. Therefore, the requirement of information sharing on the shared link between the base stations needs to be reduced as much as possible, and the amount of shared information is reduced on the premise of ensuring certain performance requirements.
Disclosure of Invention
In view of the above drawbacks or needs of the prior art, the present invention provides a multi-cell cooperative precoding method based on quantization and statistics of channel information.
Before describing the specific steps of the present invention, some abbreviations and symbols are defined. E {. denotes the desired operation, tr {. denotes the trace of the matrix, and superscript H denotes the conjugate transpose operation.
The method comprises the following specific steps:
step 1: the base station acquires all statistical channel information of the terminal in the cell, including the statistical channel information of the downlink from each cooperative base station to the terminal. Because the statistical channel information is often determined by the position, azimuth angle, etc. of the terminal, it can be obtained by uplink channel estimation; or may be obtained by the terminal feeding back at intervals for greater accuracy.
Step 2: the base station sends downlink pilot frequency sequences to all users, the users estimate respective channel state information according to the received pilot frequency, vector quantization of fewer bits is carried out, and then the vector quantization is fed back to the base station, and the base station obtains rough instantaneous channel state information.
And step 3: the base stations share instantaneous channel state information through an information sharing link, and share statistical channel information as required.
And 4, step 4: after the base station obtains statistical channel information and quantized instantaneous channel state information of all users in a cell and an adjacent cooperative cell, precoding matrixes F and G are respectively designed based on a signal-to-leakage-and-noise ratio (SLNR). In this patent, all terminals are configured with one antenna.
For instantaneous channel state information:
the signal-to-leakage-and-noise ratio SLNR of the kth user is
Wherein I represents an identity matrix, Nt represents the number of antennas configured by the base station,
indicating the instantaneous signal from the k base station to the i base station user obtained by the base station after the feedback of the terminalTrack status information, GkRepresenting the precoding matrix of the kth base station, GkIs designed such that SLNRk is maximum, GkCan choose
The feature vector corresponding to the largest feature value. In order to ensure that the transmission power is unchanged after precoding, the precoding matrix is required to meet the transmission power limitation condition.
For statistical channel state information:
the k-th user has an average signal-to-leakage-and-noise ratio SLNR of
Wherein R iskiIs the statistical channel state information of the user of the ith base station of the kth base station. FkIs designed such that SLNRk is maximum, FkCan choose
The feature vector corresponding to the largest feature value. In order to ensure that the transmission power is unchanged after precoding, the precoding matrix is required to meet the transmission power limitation condition.
And 5: and carrying out linear combination on the F and the G to obtain a new precoding vector. In order to ensure that the transmission power is unchanged after precoding, the precoding matrix is required to meet the transmission power limitation condition.
Step 6: and obtaining a precoding matrix W, and sending data to the user by the base station by using the precoding matrix W.
Wherein, the statistical CSI of the user is regarded as unchanged at the coherence time. And when the statistical CSI of the user is changed remarkably, updating the statistical channel state information.
The invention has the beneficial effects that: compared with the precoding method based on the single quantized channel state information, since only the quantized channel information with a smaller number of bits and the statistical channel information with long-term stability need to be fed back and shared, the method has: (1) the feedback bit number can be reduced, and the feedback overhead is reduced; (2) the requirement of the cooperation among the base stations on the bandwidth of the information sharing link is reduced; (3) because the feedback bits are few, the codebook is small, and the search space of the terminal for vector quantization of the channel vector is reduced. Compared with a precoding algorithm based on single statistical channel information, due to the fact that instantaneous channel state information adopting low-order quantization is added, the direction of a precoding vector obtained based on the statistical channel information can be calibrated to a certain extent, and therefore better performance can be obtained; the method can effectively improve the total rate performance of the system and improve the throughput of the system.
Drawings
Figure 1 is a cellular network formed by a plurality of cells;
FIG. 2 is a schematic diagram of a user angle of arrival;
FIG. 3 is a precoding method based on quantized channel state information and statistical channel state information;
FIG. 4 is a simulated performance curve of an embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention are described in detail below with reference to the accompanying drawings.
Fig. 1 is a schematic diagram of a cellular network composed of multiple cells, and is described in conjunction with fig. 2 and fig. 3.
As shown in fig. 3, the precoding method based on quantization and statistics of channel state information includes the following specific steps:
step 1: the base station acquires all statistical channel information of the terminal in the cell, including the statistical channel information of the downlink from each cooperative base station to the terminal. For convenience of representation, it is assumed that there are K base stations, each base station has Nt transmit antennas, only one resource block is allocated to a single user at the same time in a cell, and the user has only 1 receive antenna. The base station needs to obtain statistical channel information, R, for each userikWherein
And the statistical channel information of the users from the ith base station to the kth base station is shown.
Obtaining statistical channel information As shown in FIG. 2, the arrival angle and the angle spread of the uplink signal are estimated using the uplink channel or the feedback channel to estimate RikAnd continuously estimating the angle of the uplink signal, and updating the statistical channel information when the arrival angle exceeds a threshold value, and sharing the statistical channel information with other cooperative base stations.
Step 2: the base station sends down pilot training to all users, the users estimate their own channel state information according to the received pilot channel, and through vector quantization of less bits, then the feedback link feeds back the channel state information to the base station, and the base station obtains the rough instantaneous channel state information.
Here, we design the generation codebook by a method based on random vector quantization. The codebook at the user end is expressed as
FB is the number of bits fed back. Each user projects own information to each vector in the gamma, and calculates the maximum projection value according to the following principle to select a feedback index value:
wherein the content of the first and second substances,
the direction of the information estimated by user k and fed back to the base station is
User k will
The base station searches corresponding vector code words from a quantization codebook stored by the base station, thereby reconstructing the user k channel direction information
Whereby the base station gets the instantaneous of the userChannel state information
And step 3: the base stations share the instantaneous channel state information through an information sharing link; and sharing the statistical channel information according to the need, namely when the base station finds that the change of the arrival angle of a certain terminal exceeds a threshold value, sharing the statistical channel information.
And 4, step 4: after the base station obtains the statistical CSI and the quantized instantaneous CSI of all users in the cell, precoding matrixes F and G are respectively designed based on the signal-to-leakage-and-noise ratio (SLNR).
Wherein, for instantaneous channel state information:
the signal-to-leakage-and-noise ratio SLNR of the kth base station is
I denotes an identity matrix Nt which denotes the number of antennas configured by the base station,
representing instantaneous channel state information, G, estimated by the terminal and fed back from the kth base station to the ith base station userkRepresenting the precoding matrix of the kth base station, GkIs designed such that SLNRk is maximum, GkCan choose
The feature vector corresponding to the largest feature value. In order to ensure that the transmission power is unchanged after precoding, the precoding matrix is required to meet the transmission power limitation condition.
For statistical channel state information:
the signal-to-leakage-and-noise ratio SLNR of the kth base station is
And 5: the precoding matrix Fk based on statistical channel state information and the precoding matrix Gk of instantaneous channel state information of the base station k aiming at the terminal of the cell are obtained through the step 4, a new precoding matrix Wk is obtained through linear combination, and the new precoding matrix Wk can be obtained through linear combination
For the choice of ρ, we maximize the SINR ρ. We can initialize ρ to 0 so that ρ varies from 0 to 1, and calculate the value Wk by taking ρ of the value corresponding to the maximum SINR.
Step 6: and obtaining a precoding matrix Wk, and sending data to the terminal by the base station by using the precoding matrix Wk.
Wherein, the statistical CSI of the user is regarded as unchanged at the coherence time. And when the statistical CSI of the user is changed remarkably, updating the statistical channel state information.
Fig. 4 shows a simulation curve of the present embodiment. As can be seen from the figure, under both low snr and high snr, the proposed scheme can obtain a certain performance gain compared to the precoding scheme that only uses statistical channel information and low-order quantized channel information. Of course, the gain is more pronounced after a signal-to-noise ratio of 10 dB. The validity of the proposed scheme is verified.
It should be understood that equivalent substitutions and changes to the technical solution and the inventive concept of the present invention should be made by those skilled in the art to the protection scope of the appended claims.
Claims (2)
1. A multi-cell cooperative precoding method based on quantization and statistics of channel information is characterized in that the method comprises the following steps:
step 1: a base station acquires all statistical channel state information of users in a cell, wherein the statistical channel state information comprises the statistical channel state information of downlinks from all cooperative base stations to the users;
step 2: the base station sends downlink pilot frequency sequences to all users, the users estimate respective channel state information according to the received downlink pilot frequency sequences, vector quantization with less bits is carried out, and then the vector quantization is fed back to the base station, and the base station obtains rough quantized instantaneous channel state information;
and step 3: the quantized instantaneous channel state information is shared among all the cooperative base stations through an information sharing link, and the statistical channel state information is shared according to the requirement;
and 4, step 4: after the base station obtains the statistical channel state information and the quantized instantaneous channel state information of all users in the cell and the adjacent cooperative cell, precoding matrixes F corresponding to the statistical channel state information are respectively designed based on the signal-to-leakage-and-noise ratio SLNRkAnd a precoding matrix G corresponding to the quantized instantaneous channel state informationk(ii) a Only one resource block is allocated to a single user at the same time in a cell, and each user is configured with 1 receiving antenna;
wherein, a precoding matrix G corresponding to quantized instantaneous channel state information is designed based on a signal-to-leakage-and-noise ratio (SLNR)kThe method comprises the following steps:
the signal-to-leakage-and-noise ratio SLNR of the user of the kth base station is
Wherein K represents the number of base stations, tr {. cndot.) represents the trace of the matrix, superscript H represents the operation of conjugate transpose, I represents the identity matrix, Nt represents the number of transmitting antennas configured by the base stations,
indicating quantized instantaneous channel state information of the user from the kth base station to the ith base station obtained by the base station after the estimation and feedback by the user,
representing quantized instantaneous channel state information, G, of the user from the kth base station to the kth base station, estimated by the user and fed back to the base stationkA precoding matrix corresponding to the quantized instantaneous channel state information, G, representing the kth base stationkIs designed such that SLNRkMaximum, GkSelecting
The characteristic vector corresponding to the maximum characteristic value; wherein, in order to ensure the transmission power of the base station after precoding not to be changed, a precoding matrix G is optimizedkMaking it meet the transmit power limiting condition;
designing a precoding matrix F corresponding to statistical channel state information based on a signal-to-leakage-and-noise ratio (SLNR)kThe method comprises the following steps:
the average signal-to-leakage-and-noise ratio SLNR of the user of the kth base station is
Wherein K represents the number of base stations, E {. cndot.) represents the desired operation, RkiIs statistical channel state information, R, for users from the kth base station to the ith base stationkkIs the statistical channel state information of the users from the kth base station to the kth base station; fkIs designed such that E { SLNRkMax, FkSelecting
The characteristic vector corresponding to the maximum characteristic value; wherein, in order to ensure the transmission power of the base station after precoding not to be changed, a precoding matrix F is optimizedkMaking it meet the transmit power limiting condition;
and 5: for precoding matrix FkAnd a precoding matrix GkPerforming linear combination to obtain a precoding matrix Wk(ii) a Wherein, to ensure the transmission of the pre-coded base stationOptimizing a precoding matrix W with constant transmit powerkMaking it meet the transmit power limiting condition;
step 6: base station using precoding matrix WkAnd sending the data to the user.
2. The method of claim 1, wherein the step 1 comprises:
under the condition that K base stations exist and each base station has Nt transmitting antennas, the base station obtains statistical channel state information R of each userkiWherein, in the step (A),
representing statistical channel state information for users from the kth base station to the ith base station.
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| CN102142938A (en) * | 2011-03-29 | 2011-08-03 | 东南大学 | Signal-to-leakage-and-noise ratio-based precoding construction method in limited feedback system |
| WO2012063190A1 (en) * | 2010-11-12 | 2012-05-18 | Telefonaktiebolaget L M Ericsson (Publ) | Methods and systems for precoder selection assisted by demodulation reference signals (dm-rs) |
| CN105162507A (en) * | 2015-07-29 | 2015-12-16 | 华中科技大学 | Signal to leakage noise ratio (SLNR)-based two-stage precoding method in large-sale MIMO FDD system |
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| WO2012063190A1 (en) * | 2010-11-12 | 2012-05-18 | Telefonaktiebolaget L M Ericsson (Publ) | Methods and systems for precoder selection assisted by demodulation reference signals (dm-rs) |
| CN102142938A (en) * | 2011-03-29 | 2011-08-03 | 东南大学 | Signal-to-leakage-and-noise ratio-based precoding construction method in limited feedback system |
| CN105162507A (en) * | 2015-07-29 | 2015-12-16 | 华中科技大学 | Signal to leakage noise ratio (SLNR)-based two-stage precoding method in large-sale MIMO FDD system |
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