WO2011085512A1

WO2011085512A1 - Method and device for transmitting data packets by using cooperative multiplex based on beamforming

Info

Publication number: WO2011085512A1
Application number: PCT/CN2010/000053
Authority: WO
Inventors: 陈继明; 王伟; 王栋耀; 蒋琦; 沈钢
Original assignee: 上海贝尔股份有限公司; 阿尔卡特朗讯
Priority date: 2010-01-13
Filing date: 2010-01-13
Publication date: 2011-07-21
Also published as: CN102577475A

Abstract

A method for transmitting data packets by using cooperative multiplex based on beamforming in a multi-hop relay system is provided according to the present invention, which includes the following steps: a base station performs a weight processing to the data packets to be transmitted, by using the beamforming vectors corresponding to the channel status information of the relay links for connecting to each relay node, thus obtains the firstly weighted data packets, and the base station transmits the firstly weighted data packets to a plurality of relay nodes through the said relay links (401); a plurality of relay nodes transfer the firstly weighted data packets to a plurality of user terminals by using the same time-frequency resources (403); and, the base station performs the weight processing to the said data packets to be transmitted, by using the beamforming vectors corresponding to the channel status information of the direct links for connecting to each user terminal, thus obtains the secondly weighted data packets, and the base station transmits the secondly weighted data packets to a plurality of user terminals through the said direct links by using the said same time-frequency resources (405).

Description

Method and apparatus for transmitting data packets using beamforming based cooperative multiplexing

Technical field

The present invention relates to the field of mobile communications, and more particularly to a method and a transmitting device for transmitting data packets by using beamforming-based cooperative multiplexing in a multi-hop relay system, wherein the cooperative multiplexing technique utilizes beamforming technology Co-channel interference is reduced, and the best compromise between diversity and multiplexing is achieved without sacrificing link robustness, increasing the data rate. Background technique

Relay technology is a key technology for increasing capacity and expanding coverage areas for the high spectrum efficiency requirements proposed by Advanced LTE (Long Term Evolution). System performance can be further improved by introducing cooperative relay technologies, such as cooperative scheduling and joint processing, in eNBs (base stations) and/or relay nodes (RNs).

The current work mainly emphasizes the cooperative diversity gain of the relay system, in which the relay node helps the transmission source to utilize the spatial diversity of the slow fading channel in a distributed manner, thereby improving the link quality, but ignoring the possibility that it may bring Multiplexing gain. However, in a half-duplex relay network (which is widely used in advanced LTE), since the relay node requires an extra transmission slot, it is difficult to obtain multiplexing gain, especially when the transmission source is configured with only one antenna.

In a multi-hop relay network, a widely used prior art solution is distributed spatial frequency block coding (SFBC) and distributed spatial multiplexing (SM) for cooperative relay because feedback channel state information is not required ( CSI) can effectively improve performance without additional signaling overhead. FIG. 1 shows an illustration of a cooperative relay in which an eNB and an RN can cooperatively provide services for a user terminal (UE). When the eNB and the RN transmit in the SFBC format, that is, in the adjacent subcarriers, the eNB transmits [s ₂ s,] and the RN transmits [s, ' - ₅ ], the array gain and the cooperative receive diversity can be realized. Gain, which improves the transmission quality of the link. When the eNB transmits s, and the RN transmits s ₂ at the same time, the cooperative multiplexing gain is extracted. However, the prior art solutions cannot obtain both the diversity gain and the multiplexing gain.

Another existing solution is to use a frequency reuse technique, that is, in a non-cooperative relay system, in order to increase the throughput of the relay system, when there are multiple RNs served by the eNB, and each RN is a different user Service, multiple RNs can use the same frequency to transmit different signals to different users, as shown in Figure 2. Figure 2 shows a scenario of two RNs and two users. Due to the use of frequency reuse, frequency efficiency can be significantly improved. However, when the distance between multiple RNs is short or the transmit power of the RN is large, due to the frequency Interference between multiple RNs caused by reuse is unavoidable, and as a result, performance deteriorates. It is of course possible to use a certain proportion of frequency reuse to mitigate interference and to obtain a compromise between frequency efficiency and performance, but the throughput gain is limited.

Therefore, there is a need for a beamforming-based cooperative multiplexing scheme that can improve the throughput of a relay system having multiple antennas and achieve a compromise between the rate gain of multiplexing and the diversity gain associated with the distributed architecture. Summary of the invention

The present invention has been made in order to overcome the deficiencies of the prior art. Accordingly, it is an object of the present invention to provide a method and a transmitting device for transmitting data packets by using beamforming-based cooperative multiplexing in a multi-hop relay system, wherein the best diversity and multiplexing are obtained by cooperative multiplexing. Compromise and increase the data rate without sacrificing link robustness, and reduce beam multi-user interference with beamforming techniques. ' ' ,

In order to achieve the above object, according to the present invention, a method for transmitting data packets by using beamforming-based cooperative multiplexing in a multi-hop relay system is proposed, including: a base station utilizing a relay link to each relay node The beamforming vector corresponding to the channel state information weights the data packet to be transmitted to obtain the first weighted data packet, and transmits the first weighted data to the plurality of relay nodes through the relay link. a plurality of relay nodes forwarding the first weighted data packet to a plurality of user terminals using the same time-frequency resource; and the base station utilizing beamforming vectors corresponding to channel state information of the direct link to each user terminal And weighting the data packet to be sent to obtain a second weighted data packet, and transmitting, by using the same time-frequency resource, the second weighted data packet to the plurality of user terminals by using the direct link.

Preferably, the base station and the corresponding relay node perform cooperative scheduling and joint transmission, thereby implementing collaborative space diversity of the user terminal.

Preferably, the transmission of data packets from the base station and the relay node to the user terminal is encoded using the modified spatial frequency block coding SFBC mode.

Preferably, the user terminal combines the received data packets using the SFBC detection method.

Preferably, the multi-hop relay system employs a multiple input multiple output MIM0 system.

In addition, according to the present invention, there is also provided a transmitting end device for transmitting a data packet by using beamforming-based cooperative multiplexing in a multi-hop relay system, comprising: a first weighting processing device, configured to utilize Generating a data packet to be transmitted to a beamforming vector corresponding to channel state information of a relay link of each relay node to obtain a first weighted data packet; and second weighting processing means for utilizing and Weighting a data packet to be transmitted by a beamforming vector corresponding to channel state information of a direct link of each user terminal to obtain a second weighted data packet; and transmitting means for passing the relay chain Transmitting, by the plurality of relay nodes, the first weighted data packet, so that the plurality of relay nodes forward the first weighted data packet to the plurality of user terminals by using the same time-frequency resource; and utilizing the same The time-frequency resource transmits the second weighted data packet to the plurality of user terminals through the direct link. DRAWINGS

The above-described objects, advantages and features of the present invention will become more apparent from the aspects of the description accompanying the accompanying drawings

2 is a schematic diagram showing frequency reuse of the prior art;

3 is a schematic diagram showing a system utilizing beamforming-based cooperative multiplexing according to the present invention; FIG. 4 is a diagram showing transmission using beamforming-based cooperative multiplexing in a multi-hop relay system according to the present invention. Flow chart of a method of data grouping;

Figure 5 is a block diagram showing the structure of a transmitting device that utilizes beamforming-based cooperative multiplexing to transmit data packets in a multi-hop relay system according to the present invention;

Figure 6 is a schematic diagram showing the simulation of the comparison between the system of the present invention and the prior art. detailed description

The present invention proposes a beamforming-based cooperative multiplexing scheme that utilizes intra-cell interference cancellation to obtain an optimal compromise between link robust gain and rate gain.

1) The eNB simultaneously transmits the first weighted data packet to the plurality of RNs involved in the cooperative processing through the relay link in the first stage, wherein the base station utilizes channel state information corresponding to the relay link to each RN The beamforming vector weights the data packets to be transmitted to obtain the first weighted data packet.

2) The RN correctly demodulates the first weighted data packet, and then completes the following process of the second phase: a) Each RN will have encoded data points of the same data content except for symbol and conjugate changes. The group is transmitted to the user, and the transmission between the multiple RNs and the user pair uses the same time-frequency resource; b) At the same time, the eNB utilizes the beamforming vector pair corresponding to the channel state information of the direct link to each UE Data packets in the same phase are weighted by the same data packet to obtain a second weighted data packet, and the second weighted data packet is transmitted to the plurality of UEs through the direct link by using the same time-frequency resource. ;

c) Thus, the transport data packets from the eNB and the RN to the UE form an improved SFBC codeword.

3) These UEs then receive the data packets and combine the received data packets using the SFBC detection scheme.

The cooperative multiplexing scheme according to the present invention is capable of optimizing spatial diversity gain and spatial multiplexing gain, and improving system performance. Preferred embodiments of the present invention will now be described with reference to the accompanying drawings.

The beamforming-based collaborative multiplexing scheme is in principle a distributed multiple-input multiple-output (MIM0) system in a multi-hop environment, as shown in Figure 3. Figure 3 shows a schematic diagram of two RNs and two user terminals (UEs) in an eNB, wherein the same time-frequency resources within a subframe are allocated to the RN, or the RN and the eNB. These nodes work together as distributed antennas to form a virtual MIM0.

Consider a three-node relay system composed of an eNB, an RN, and a UE each having 2 antennas, 1 antenna, and 2 antennas. In the first phase, the eNB transmits two data packets simultaneously to two RNs, where the two data packets are first weighted by the beamforming vector and the two RNs receive the data packets simultaneously. Similar to the multi-user MIM0 scenario, if the beamforming vector is carefully designed, the interference between the two data streams can be mitigated or even completely eliminated. Therefore, the received signal in the first phase can be expressed as:

Where W represents the first hop, , ! = 1, 2 represents the received signal of RN 1 and 2, h , i, j = , 2 is the channel gain of the antenna j' to the ith RN at the eNB, W Is a beamforming matrix, and ^ and ",, = 1, 2 are the transmitted signals from the eNB to RNs 1 and 2 and AWGN.

RNs 1 and 2 receive the weighted data packets and perform decoding and demodulation, respectively. Due to eNB and RN 1 The high quality channel between and 2 can be considered to be completely correct for decoding and demodulation. Thereafter, RNs 1 and 2 are re-encoded and re-modulated and then transmitted to the UE.

Here, in order to obtain the diversity gain, the improved SFBC is used for the transmission signal format, gp, and the data packet is encoded based on the frequency direction after comprehensively considering the transmission data format from the eNB to the UE. Therefore, the signals received by the i-th UE from two adjacent subcarriers of the cooperative link are:

) = ( 1)+

+ 1) ₍₂₎

y : = (k) _X] (k)- h§(k)x ₂ '(k + 1)+ n?(k)

y^(k + l) = 3⁄4 ₂₁ (k)x ₂ (k + 1)+ h^(k) _X ;(k) + n^(k + 1)

Wherein the second hop, , = l, 2 represents the signal received by the two antennas of the i-th UE on the two sub-carriers k and k+1, , " _{J =} 1, 2 is from the j-th RN The channel gain to the nth antenna of the i-th UE, h , ,, «, = l, 2 is the combined channel from the jth channel of the eNB to the nth antenna of the ith UE, , = 1, 2 is a transmission signal from the 1st to the 1st, and ",., = 1, 2 represents the AWGN on two adjacent subcarriers at the two antennas of the i-th UE. Similarly, in order to support multiple users, the transmit signal from the eNB is still weighted by the beamforming vector, expressed as:

Therefore, the combined channel is: (4) Equation (2) can be expressed as a matrix:

(5)

Where Ηί ² )

X = V

X2

"*" means conjugate transpose. Therefore, the signal-to-interference plus noise ratio is:

Where, A, and N represent signal power, interference power, and AWGN power spectral density, respectively.

4 is a flow chart showing a method of transmitting data packets using beamforming-based cooperative multiplexing in a multi-hop relay system in accordance with the present invention.

As shown in FIG. 4, according to the method of the present invention, in step 401, the base station performs weighting processing on data packets to be transmitted by using beamforming vectors corresponding to channel state information of relay links to respective relay nodes. The first weighted data packet, and transmitting the first weighted data packet to the plurality of relay nodes through the relay link. Then, in step 403, the plurality of relay nodes forward the first weighted data packet to the plurality of user terminals by using the same time-frequency resource. Finally, in step 405, the base station performs weighting processing on the data packet to be transmitted by using a beamforming vector corresponding to channel state information of a direct link to each user terminal to obtain a second weighted data packet, and utilizes The same time-frequency resource transmits the second weighted data packet to the plurality of user terminals through the direct link. 5 is a block diagram showing the structure of a transmitting device that transmits data packets using beamforming-based cooperative multiplexing in a multi-hop relay system according to the present invention.

As shown in FIG. 5, a transmitting device (e.g., a base station) according to the present invention includes: a first weighting processing device 501, a second weighting processing device 503, and a transmitting device 505. The first weighting processing means 501 performs weighting processing on the data packets to be transmitted using the beamforming vectors corresponding to the channel state information of the relay links of the respective relay nodes to obtain the first weighted data packets. The second weighting processing means 503 performs weighting processing on the data packet to be transmitted using the beamforming vector corresponding to the channel state information of the direct link to each user terminal to obtain the second weighted data packet. The transmitting device 505 transmits the first weighted data packet to the plurality of relay nodes through the relay link, so that the first weighted data packet is forwarded to the plurality of relay nodes by using the same time-frequency resource. a user terminal; and transmitting the second weighted data packet to the plurality of user terminals over the direct link by using the same time-frequency resource. Using the above analysis, the inventors simulated the performance of the beamforming-based cooperative multiplexing scheme, and for comparison, based on the LTE downlink system, simulated a cellular system without relay nodes and multi-hop using frequency reuse. Following the system, in which the cooperative operation between the eNB and the RN is selected. The simulation parameter settings are shown in Table 1.

Table 1

Parameter value

Cellular layout with a surrounding hexagonal layout, 7 eNodeBs, each eNodeB serves 3 cells

System bandwidth 10 MHz, downlink

ISD 500 m (3GPP Scenario 1)

eNB transmit power 46 dBm

RN transmit power 30 dBm

2 RN per sector of RN per sector

Quantity

Number of UEs per sector 25 UEs per sector

Inside

Scheduling proportional fairness

Downlink HARQ has CC's asynchronous HARQ, maximum triple retransmission, and hop-by-hop HARQ in the relay system

Channel SCM City Macro Height Extension Angle for 3GPP Scenario 1

The eNB antenna is configured with two Tx antennas having an antenna pattern as defined in 3GPP TS 36.81 4 VI .5.1 The RN antenna is configured with one Tx antenna and one Rx antenna, each having an antenna pattern defined in 3GPP TS 36.81 4 VI .5.1

UE antenna configuration 2 Rx antennas (O dBi antenna gain, omnidirectional)

Downstream receiver ω type M C

Control channel overhead z ο], acknowledgment LTE: overhead of 3 symbols of the downlink control channel (DL CCH ) plus the overhead of the demodulation reference signal

CO L=Prob(R)PL _LOS (R) ₊ [1-Prob(R)]PL _NLOS (R), for 2GHz, ? Expressed in km.

Penetration loss 20dB

PL _L0S (R) = 103.4+24.2los10(R)

PL匪(R)= 131. 42.8lo _S 10(R)

Scenario 1: Prob(R)=min(0.018/R, 1)*(1-exp(-R/0.063))+exp(-R/0.063) Scenario 3: Prob(R)=exp(-(R- 0.01) / 1.0)

L=Prob(R)PL _LQS (R) ₊ [1-Prob(R)]PL _{N )S} (R)-B, for 2GHz, /? Expressed in km, where

PL _L0S (R) = 100.7 + 23.5 / og 10 (R)

PL (R) = 125.2 ₊ 36.3log10(R)

Path loss eNodeB

Consumption model to RN based on ITU model ProbiW:

Scenario 1: Prob(R)=min(0.018/R, 1)*(1-exp(-R/0.072))+exp(-R/0.072) Case 3: Prob(R)=exp(-(R- 0.01) / 1. 15)

Where Bonus for donor macro is set to 5dB

L=Prob(R) PL _LQS (R)+[1-Prob(R)]PL _NLOS (R), for 2GHz, R is expressed in km, where

PL _L0S (R) = 103.8+20. /og 10(R)

PL _NLOS (R) = 145.4 ₊ 37.5I0310(R)

Scenario 1: Prob(R)=0.5-min(0.5,5exp(-0. 156/R))+min(0.5,5exp(-R/0.03)) Scenario 3: Prob(R)=0.5-min(0.5 3exp(-0.3/R))+min(0.5, 3exp(-R/0.095)) Table 2 shows the system simulation results using the cooperative multiplexing of the present invention.

Table 2

The bee without the RN is full frequency and the relay system for the cooperative multiplexing relay system is proposed.

System

Average spectral efficiency of the cell 1. 8457 2. 398 2. 6432 (43. 2%)

(bps/Hz/cel l) (29.9%) Cell edge spectral efficiency 0. 018

0. 017 0. 0222 (30. 58%)

(bps/Hz) (5. 88%)

Figure 6 is a schematic diagram showing the simulation of the comparison between the system of the present invention and the prior art. As can be seen from Figures 6 and 2, the present invention achieves a significant increase in user throughput. This is because on the one hand, cooperative multiplexing achieves the best compromise between diversity and multiplexing and increases the data rate without sacrificing link robustness; on the other hand, beamforming technology will reduce multi-users. Interference, and cooperative techniques also avoid co-channel interference.

In addition, it is apparent that the technical solution according to the present invention can be extended to multi-RN cooperative services to multiple UEs in a multi-antenna scenario.

While the invention has been described in terms of the preferred embodiments of the present invention, it will be understood that various modifications, changes and changes may be made to the inventions without departing from the spirit and scope of the invention. Therefore, the present invention should not be limited by the foregoing embodiments, but by the appended claims and their equivalents.

Claims

Rights request

A method for transmitting data packets by using beamforming-based cooperative multiplexing in a multi-hop relay system, comprising:

The base station performs weighting processing on the data packet to be transmitted by using a beamforming vector corresponding to channel state information of the relay link of each relay node to obtain a first weighted data packet, and passes through the relay link Transmitting the first weighted data packet to the plurality of relay nodes;

Multiple relay nodes forwarding the first weighted data packet to a plurality of user terminals using the same time-frequency resource;

The base station weights the data packet to be transmitted by using a beamforming vector corresponding to channel state information of a direct link to each user terminal to obtain a second weighted data packet, and utilizes the same time frequency The resource transmits the second weighted data packet to the plurality of user terminals over the direct link.

2. The method according to claim 1, wherein the base station and the corresponding relay node perform cooperative scheduling and joint transmission, thereby implementing collaborative space diversity of the user terminal.

3. The method according to claim 1, wherein the transmission of data packets from the base station and the relay node to the user terminal is performed using a modified spatial frequency block coding SFBC mode.

4. The method of claim 3, wherein the user terminal combines the received data packets using an SFBC detection method.

5. The method of claim 1, wherein the multi-hop relay system employs multiple input multiple outputs

MIM0 system.

6. A transmitting device for transmitting data packets by using beamforming-based cooperative multiplexing in a multi-hop relay system, comprising:

a first weighting processing apparatus, configured to perform weighting processing on a data packet to be transmitted by using a beamforming vector corresponding to channel state information of a relay link of each relay node to obtain a first weighted data packet;

a second weighting processing apparatus, configured to perform weighting processing on the data packet to be transmitted by using a beamforming vector corresponding to channel state information of a direct link to each user terminal to obtain a second weighted data packet;

a transmitting device, configured to transmit, by using the relay link, the first weighted data to multiple relay nodes Grouping, so that the first weighted data packet is forwarded to the plurality of user terminals by the plurality of relay nodes using the same time-frequency resource; and the plurality of user terminals are transmitted through the direct link by using the same time-frequency resource Transmitting the second weighted data packet.

7. The transmitting device according to claim 6, wherein the multi-hop relay system employs a multiple input multiple output MIM0 system.