CN103138817B - A kind of for selecting the method and apparatus of ul transmissions antenna - Google Patents

Abstract

The object of this invention is to provide a kind of for selecting the method and apparatus of ul transmissions antenna; Base station equipment receive respectively from subscriber equipment send via two antennas inquire after reference signal; Inquire after reference signal according to described, determine ul transmissions antenna; According to the determination to described ul transmissions antenna, generate sky line options designator; Described sky line options designator is sent to described subscriber equipment.Compared with prior art, the present invention is according to the SRS quality of each subscriber equipment antenna and propagation delay time, for subscriber equipment selects a suitable antenna with transmitting SRS, balance the channel estimation quality of the down channel of two antennas of subscriber equipment end, improve the performance of downlink beamforming, especially double-current channel rays figuration.

Description

Method and equipment for selecting uplink transmission antenna

Technical Field

The present invention relates to the field of communications technologies, and in particular, to a technique for selecting an uplink transmission antenna in a beamforming system.

Background

In multi-antenna communication systems, such as LTETDD, beamforming (beamforming) is an important technique. The technology can improve the throughput of the system and increase the coverage of the system. The eNB generates beamforming weights based on Sounding Reference Signals (SRS) sent by the user equipment, and applies the weights to downlink transmission with the user equipment.

In modern wireless communication systems, e.g. in LTE, the user equipment typically has two antennas. In a rich scattering environment, the correlation of the two antennas is not large. Therefore, in the uplink, in order to obtain all Channel State Information (CSI), antenna switching is required to improve the performance of the system. Especially in case of dual stream channel beamforming, full CSI will significantly increase the performance of the system.

Since the beamforming weights should be adjusted according to the CSI, the performance of beamforming is highly related to the accuracy of channel estimation. If the weight value is consistent with the instantaneous channel state in the transmission process, the system gain will be larger, otherwise, the system performance is worse. Generally, in a TDD system, downlink channel estimates are obtained from uplink sounding reference signals transmitted by user equipment.

There are two main factors that affect the accuracy of channel estimation:

1. mean Square Error (MSE) between the estimated channel and the true channel of the SRS. In general, a lower signal-to-noise ratio (SINR) of SRS will result in a larger MSE.

2. The time when the user equipment transmits the SRS and the Transmission Delay (TD) when the base station establishes a downlink with the user equipment. Since the channel is time-varying, the beamforming weights will be outdated if the time interval between SRS transmission and DL transmission is too long.

Due to the low correlation of fading between the two antennas of the user equipment, the channel estimation quality of the two antennas of the user equipment will be different. Therefore, the effect of this on beamforming needs to be considered. If the channel quality is unbalanced, e.g., the channel quality of one antenna is much worse than the other, it is equivalent to the true channel rank being close to 1 due to mismatch of channel estimates. This will reduce the system throughput of dual stream channel beamforming.

In the prior art, LTE employs open-loop and closed-loop antenna switching schemes to perform uplink transmission for user equipment. In case of selecting the open-loop antenna, the user equipment can freely switch the transmission antenna without a signal from the eNB. In case of selecting a closed-loop antenna, the eNB determines which antenna is used for transmission at the user equipment by transmitting an antenna indicator (antenna indicator) to the user equipment. In the LTE protocol, it is determined to use an open-loop antenna for transmitting the SRS, and a closed-loop antenna is used when transmitting on a Physical Uplink Shared Channel (PUSCH). The reason for adopting the above scheme is that only the performance of uplink transmission is considered here. SRS transmission is only used as a reference for selecting uplink antennas. However, in the case of downlink beamforming, especially in the case of dual-stream channel beamforming, if the antenna at the user equipment end is severely faded, the estimated channel corresponding to the antenna will be unreliable, and the performance of downlink transmission will be reduced.

Disclosure of Invention

The invention aims to provide a method and equipment for selecting an uplink transmission antenna.

According to an aspect of the present invention, there is provided a method for selecting an uplink transmission antenna at a base station device in a beamforming system, wherein the method comprises:

a, receiving polling reference signals transmitted by two antennas from user equipment respectively;

b, determining an uplink transmission antenna according to the polling reference signal;

c generating an antenna selection indicator according to the determination of the uplink transmission antenna;

d transmitting the antenna selection indicator to the user equipment.

According to another aspect of the present invention, there is also provided a method for assisting selection of uplink transmission antennas at a user equipment side in a beamforming system, wherein the method comprises:

a, respectively sending an inquiry reference signal to base station equipment through two different antennas;

b receiving an antenna selection indicator transmitted from the base station apparatus;

c, according to the uplink transmission antenna designated by the antenna selection indicator, retransmitting the polling reference signal to the base station equipment.

According to still another aspect of the present invention, there is also provided a base station apparatus for selecting an uplink transmission antenna in a beamforming system, wherein the apparatus includes:

the device comprises an interrogation receiving device, a receiving device and a processing device, wherein the interrogation receiving device is used for respectively receiving interrogation reference signals which are sent by two antennas from user equipment;

antenna determining means for determining an uplink transmission antenna based on the interrogation reference signal;

indication generating means for generating an antenna selection indicator in dependence on the determination of the uplink transmission antenna;

indication sending means for sending the antenna selection indicator to the user equipment.

According to still another aspect of the present invention, there is also provided a user equipment for assisting selection of an uplink transmission antenna in a beamforming system, wherein the apparatus comprises:

a first polling transmitting device, configured to transmit, via two different antennas, polling reference signals to a base station device, respectively;

indication receiving means for receiving an antenna selection indicator transmitted from the base station apparatus;

second polling transmitting means for retransmitting the polling reference signal to the base station device according to the uplink transmission antenna specified by the antenna selection indicator.

Compared with the prior art, the invention selects a proper antenna for the user equipment to transmit the SRS according to the SRS quality and the transmission delay of each user equipment antenna, balances the channel estimation quality of the downlink channels of the two antennas at the user equipment end, and improves the performance of downlink beam forming, especially dual-stream channel beam forming.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments made with reference to the following drawings:

fig. 1 shows a schematic diagram of an apparatus for selecting uplink transmit antennas according to an aspect of the invention;

fig. 2 shows a schematic diagram for selecting uplink transmission antennas according to a preferred embodiment of the present invention;

fig. 3 shows a flow diagram of a method for selecting uplink transmit antennas according to another aspect of the invention.

The same or similar reference numbers in the drawings identify the same or similar elements.

Detailed Description

The present invention is described in further detail below with reference to the attached drawing figures.

Fig. 1 shows a schematic diagram of an apparatus for selecting uplink transmit antennas according to an aspect of the invention; the base station device 1 comprises an interrogation receiving device 11, an antenna determining device 12, an indication generating device 13 and an indication sending device 14; the user equipment 2 comprises first probe transmitting means 21, indication receiving means 22 and second probe transmitting means 23.

The respective devices of the base station apparatus 1 and the user equipment 2 cooperate with each other to select an uplink transmission antenna. Specifically, the first interrogation transmitting device 21 in the user equipment 2 transmits interrogation reference signals to the base station equipment via two different antennas respectively; an interrogation receiving device 11 in the base station apparatus 1 receives interrogation reference signals transmitted via two antennas from user equipment, respectively; the antenna determining device 12 determines an uplink transmission antenna according to the polling reference signal; the indication generating means 13 generates an antenna selection indicator according to the determination of the uplink transmission antenna; instructing the transmitting means 14 to transmit the antenna selection indicator to the user equipment; the indication receiving means 22 in the user equipment 2 receives the antenna selection indicator transmitted from the base station apparatus; the second probe transmission device 23 retransmits the probe reference signal to the base station device according to the uplink transmission antenna specified by the antenna selection indicator.

Here, the user equipment 2 may select to use antenna 0 or antenna 1 for SRS transmission at a time. The base station apparatus 1 selects an appropriate antenna for the user equipment 2 based on this, and transmits an antenna selection indicator to the user equipment 2 within the downlink control channel. Upon receiving the antenna selection indicator, the user equipment 2 transmits the SRS using the antenna specified in the antenna selection indicator in the next SRS opportunity.

Preferably, the antenna determining means 12 in the base station apparatus 1 determines the uplink transmission antenna according to the polling reference signal and by combining a Mean Square Error (MSE) between an estimated channel and a true channel of the polling reference signal. In particular, assume thatIs the channel of the s-th transmission antenna on the k-th sub-bandwidth at time t;is the estimated channel response for the s-th transmit antenna over the k-th sub-bandwidth at time t;

the estimation error is then: $Q_k^s\left(t\right)=H_k^s\left(t\right)-{\hat{H}}_k^s\left(t\right)$

from this it can be derived:wherein s ═ 1KS.

In general,depending on the channel estimation algorithm and the current signal-to-noise ratio (SINR) of the received SRS signal.

If the minimum mean square error algorithm is adopted, the correlation error is as follows:

$d_{s,k}^2=\frac{E\left\{{\left(H_k^s\left(t\right)\right)}^2\right\}}{E\left\{{\left(H_k^s\left(t\right)\right)}^2\right\}{\mathrm{SINR}}_k^s+1}$

$=\frac{s_{H,k}^2}{s_{H,k}^2{\mathrm{SINR}}_k^s+1}$

wherein,is the signal-to-noise ratio of the uplink SRS for the s-th transmit antenna over the sub-bandwidth k.Can be obtained from the measurement report and,is equal toWhere s-1 KS. mean square error may be defined as:

which is the ratio of the error power to the channel power. The antenna determination means 12 determines the uplink transmission antenna based on the interrogation reference signal received by the interrogation reception means 11, in combination with the mean square error known from the above.

Preferably, the antenna determining apparatus 12 in the base station device 1 determines the uplink transmission antenna according to the interrogation reference signal, and by combining the time when the user equipment sends the interrogation reference signal and the Transmission Delay (TD) of the downlink established with the user equipment. In particular, assume thatTime of transmission of the last SRS for antenna s of the target user equipment over sub-bandwidth k;is the time of downlink transmission established between user equipments on sub-bandwidth k; the transmission delay is then:in the case of the LTE system, it is,can be measured according to the number of the sub-frames. The antenna determining device 12 determines the uplink transmission antenna according to the polling reference signal received by the polling receiving device 11 and by combining the transmission delay obtained in the above manner.

More preferably, the antenna determining apparatus 12 in the base station device 1 determines the uplink transmission antenna according to the interrogation reference signal, and by combining the mean square error between the estimated channel and the real channel of the interrogation reference signal, the time when the user equipment sends the interrogation reference signal, and the transmission delay of the downlink established with the user equipment. Specifically, at t + t_kThe channel response at a time can be calculated by:

$H_k^s(t+t_k^s)=r_k^s{H}_k^s\left(t\right)+h^s(t+t_k^s)$

wherein,is a gaussian noise random variable. For a channel that is subject to rayleigh fading,can be calculated as(f_DIs the doppler shift). It can be further deduced that:

$H_k^s(t_k+{\mathrm{\τ}}_k^s)={\mathrm{\ρ}}_k^s{H}_k^s\left(t_k\right)+{\mathrm{\η}}^s(t_k+{\mathrm{\τ}}_k^s)$

$={\mathrm{\ρ}}_k^s{\hat{H}}_k^s\left(t_k\right)+{\mathrm{\ρ}}_k^s{Q}_k^s\left(t_k\right)+{\mathrm{\η}}^s(t_k+{\mathrm{\τ}}_k^s)$

in general, only changes need to be made for any of the different conditions, e.g., other channel estimation types, UE rates, channel variations in the time domain, etcAndthe value of (c).

It can be seen that as the transmission delay and the mean square error increase, the channel estimation error also increases. Thus, based on r_kAndthe parameters are calculated using the following formula:

$M\left(s\right)=f\left(\right\{r_k^s\},\{g_k^s\left\}\right)$

note that the useful part here isThe power of the part isThus, one example of defining this parameter is:

$M\left(s\right)=\underset{k=1}{\mathrm{\Σ}}{\left({\mathrm{\ρ}}_k^s\right)}^2(1-{\mathrm{\γ}}_k^s)$

thus, the antenna determining means 12 selects the antenna with the minimum m(s) as the uplink transmission antenna.

The basic idea of selecting uplink transmit antennas is to guarantee the channel estimation quality for each user equipment antenna. Here, the channel estimation quality is determined by the mean square error and the transmission delay. The base station apparatus 1 may continuously select one antenna for the user equipment to improve the accuracy of channel estimation corresponding to the antenna, but this will lengthen the transmission delay of the estimated channel corresponding to the other antenna. Thus, assuming that the rate of the user equipment is low, the chance of uplink transmission of the user equipment antenna with severe fading can be increased while maintaining the quality of the channel estimation of the other antennas. The eNB may combine several received SRSs to improve the channel estimation quality.

Fig. 2 shows a simulation result comparing throughput with and without antenna selection in a lte tdd system. Assuming that the bandwidth is 10MHz, the number of antennas in the eNB is 8, and the number of antennas in the user equipment is 2. The eNB uses the maximized mean square error to estimate the channel response. In the downlink, dual-stream channel beamforming is adopted, and the rate of the user equipment is 30 km/h. In the uplink, the average signal-to-noise ratio of the received SRS is 10dB more relative to the downlink. The transmission delay is from 4ms to 10 ms. As can be seen, a gain of 1dB can be obtained in the intermediate range of SINR.

Fig. 3 shows a flow diagram of a method for selecting uplink transmit antennas according to another aspect of the invention.

The respective steps of the base station apparatus 1 and the user equipment 2 cooperate with each other to select an uplink transmission antenna. Specifically, in step S1, the user equipment 2 sends the polling reference signals to the base station device via two different antennas respectively; the base station device 1 receives the polling reference signals transmitted by two antennas from the user equipment respectively; in step S2, the base station apparatus 1 determines an uplink transmission antenna according to the polling reference signal; in step S3, base station apparatus 1 generates an antenna selection indicator according to the determination of the uplink transmission antenna; in step S4, base station apparatus 1 transmits the antenna selection indicator to the user equipment; the user equipment 2 receives the antenna selection indicator transmitted from the base station equipment; in step S5, the user equipment 2 retransmits the sounding reference signal to the base station apparatus according to the uplink transmission antenna specified by the antenna selection indicator.

Here, the user equipment 2 may select to use antenna 0 or antenna 1 for SRS transmission at a time. The base station apparatus 1 selects an appropriate antenna for the user equipment 2 based on this, and transmits an antenna selection indicator to the user equipment 2 within the downlink control channel. Upon receiving the antenna selection indicator, the user equipment 2 transmits the SRS using the antenna specified in the antenna selection indicator in the next SRS opportunity.

Preferably, in step S2, the base station apparatus 1 determines the uplink transmission antenna according to the polling reference signal and by combining a Mean Square Error (MSE) between an estimated channel and a true channel of the polling reference signal. In particular, assume thatIs the channel of the s-th transmission antenna on the k-th sub-bandwidth at time t;is the estimated channel response for the s-th transmit antenna over the k-th sub-bandwidth at time t;

the estimation error is then: $Q_k^s\left(t\right)=H_k^s\left(t\right)-{\hat{H}}_k^s\left(t\right)$

from this it can be derived:wherein s ═ 1KS.

In general,depending on the channel estimation algorithm and the current signal-to-noise ratio (SINR) of the received SRS signal.

If the minimum mean square error algorithm is adopted, the correlation error is as follows:

$d_{s,k}^2=\frac{E\left\{{\left(H_k^s\left(t\right)\right)}^2\right\}}{E\left\{{\left(H_k^s\left(t\right)\right)}^2\right\}{\mathrm{SINR}}_k^s+1}$

$=\frac{s_{H,k}^2}{s_{H,k}^2{\mathrm{SINR}}_k^s+1}$

wherein,is the signal-to-noise ratio of the uplink SRS for the s-th transmit antenna over the sub-bandwidth k.Can be obtained from the measurement report and,is equal toWhere s-1 KS. mean square error may be defined as:

which is the ratio of the error power to the channel power. In step S2, the base station apparatus 1 determines an uplink transmission antenna from the sounding reference signal received in step S1 in combination with the mean square error known in the above manner.

Preferably, in step S2, the base station device 1 sends the polling reference signal according to the polling reference signal and in combination with the user equipmentTime and Transmission Delay (TD) for establishing a downlink with the user equipment, and determining the uplink transmission antenna. In particular, assume thatTime of transmission of the last SRS for antenna s of the target user equipment over sub-bandwidth k;is the time of downlink transmission established between user equipments on sub-bandwidth k; the transmission delay is then:in the case of the LTE system, it is,can be measured according to the number of the sub-frames. In step S2, the base station apparatus 1 determines an uplink transmission antenna from the sounding reference signal received in step S1, in combination with the transmission delay known in the above manner.

More preferably, in step S2, the base station device 1 determines the uplink transmission antenna according to the interrogation reference signal, and by combining the mean square error between the estimated channel and the true channel of the interrogation reference signal, the time when the user equipment sends the interrogation reference signal, and the transmission delay of the downlink established with the user equipment. Specifically, at t + t_kThe channel response at a time can be calculated by:

$H_k^s(t+t_k^s)=r_k^s{H}_k^s\left(t\right)+h^s(t+t_k^s)$

wherein,is a gaussian noise random variable. For a channel that is subject to rayleigh fading,can be calculated as(f_DIs the doppler shift). It can be further deduced that:

$H_k^s(t_k+{\mathrm{\τ}}_k^s)={\mathrm{\ρ}}_k^s{H}_k^s\left(t_k\right)+{\mathrm{\η}}^s(t_k+{\mathrm{\τ}}_k^s)$

$={\mathrm{\ρ}}_k^s{\hat{H}}_k^s\left(t_k\right)+{\mathrm{\ρ}}_k^s{Q}_k^s\left(t_k\right)+{\mathrm{\η}}^s(t_k+{\mathrm{\τ}}_k^s)$

in general, only changes need to be made for any of the different conditions, e.g., other channel estimation types, UE rates, channel variations in the time domain, etcAndthe value of (c).

It can be seen that as the transmission delay and the mean square error increase, the channel estimation error also increases. Thus, based on r_kAndthe parameters are calculated using the following formula:

$M\left(s\right)=f\left(\right\{r_k^s\},\{g_k^s\left\}\right)$

note that the useful part here isThe power of the part isThus, one example of defining this parameter is:

$M\left(s\right)=\underset{k=1}{\mathrm{\Σ}}{\left({\mathrm{\ρ}}_k^s\right)}^2(1-{\mathrm{\γ}}_k^s)$

thus, in step S2, the base station apparatus 1 selects an antenna having the minimum m (S) as an uplink transmission antenna.

The basic idea of selecting uplink transmit antennas is to guarantee the channel estimation quality for each user equipment antenna. Here, the channel estimation quality is determined by the mean square error and the transmission delay. The base station apparatus 1 may continuously select one antenna for the user equipment to improve the accuracy of channel estimation corresponding to the antenna, but this will lengthen the transmission delay of the estimated channel corresponding to the other antenna. Thus, assuming that the rate of the user equipment is low, the chance of uplink transmission of the user equipment antenna with severe fading can be increased while maintaining the quality of the channel estimation of the other antennas. The eNB may combine several received SRSs to improve the channel estimation quality.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned. Furthermore, it is obvious that the word "comprising" does not exclude other elements or steps, and the singular does not exclude the plural. A plurality of units or means recited in the apparatus claims may also be implemented by one unit or means in software or hardware. The terms first, second, etc. are used to denote names, but not any particular order.

Claims (4)

1. A method for selecting uplink transmission antennas at a base station device side in a beamforming system, wherein the method comprises:

a, receiving polling reference signals transmitted by two antennas from user equipment respectively;

b, determining an uplink transmission antenna according to the polling reference signal, and by combining the mean square error between an estimated channel and a real channel of the polling reference signal, the time for the user equipment to send the polling reference signal and the transmission time delay for establishing a downlink with the user equipment;

c generating an antenna selection indicator according to the determination of the uplink transmission antenna;

d sending the antenna selection indicator to the user equipment;

e, receiving the polling reference signal retransmitted by the user equipment through the uplink transmission antenna.

2. A method for user equipment-side assisted selection of uplink transmission antennas in a beamforming system, wherein the method comprises:

a, respectively sending an inquiry reference signal to base station equipment through two different antennas;

b receiving an antenna selection indicator transmitted from the base station apparatus;

c, according to the uplink transmission antenna designated by the antenna selection indicator, retransmitting the polling reference signal to the base station equipment.

3. A base station apparatus for selecting an uplink transmission antenna in a beamforming system, wherein the apparatus comprises:

the device comprises an interrogation receiving device, a receiving device and a processing device, wherein the interrogation receiving device is used for respectively receiving interrogation reference signals which are sent by two antennas from user equipment;

an antenna determining device, configured to determine an uplink transmission antenna according to the interrogation reference signal, and by combining a mean square error between an estimated channel and a true channel of the interrogation reference signal, and a time when the user equipment sends the interrogation reference signal and a transmission delay of a downlink established with the user equipment;

indication generating means for generating an antenna selection indicator in dependence on the determination of the uplink transmission antenna;

indication sending means for sending the antenna selection indicator to the user equipment;

means for receiving an interrogation reference signal retransmitted by the user equipment through the uplink transmit antenna.

4. A user equipment for assisting selection of uplink transmission antennas in a beamforming system, wherein the apparatus comprises:

a first polling transmitting device, configured to transmit, via two different antennas, polling reference signals to a base station device, respectively;

indication receiving means for receiving an antenna selection indicator transmitted from the base station apparatus;

second polling transmitting means for retransmitting the polling reference signal to the base station device according to the uplink transmission antenna specified by the antenna selection indicator.