CN100392995C - A downlink multi-user scheduling method in a multi-transmitting antenna and multi-receiving antenna system - Google Patents

Abstract

The present invention discloses a downlink multi-user scheduling method in a multi-transmitting antenna and multi-receiving antenna system, comprising: the first step, the user terminal selects a subset of base station transmitting antennas according to the estimated channel information; the second step, the user terminal The selected antenna subset indicator and channel state information are fed back; in the third step, the scheduling algorithm determines the allocation relationship between the base station transmit antenna and the user terminal in the next transmission time slot according to the fed back information and other information of the user. The present invention combines MIMO antenna selection technology with multi-user diversity, not only makes full use of the multi-antenna system at the base station, provides space diversity gain or channel capacity gain, but also provides multi-user diversity, thereby improving the data throughput of the system. It can provide services for user terminals with different numbers of antennas at the same time, compatible with multiple modes of MIMO, SISO, SIMO and MISO, and does not require the number of antennas of user terminals, so it has strong versatility.

Description

A downlink multi-user scheduling method in a multi-transmitting antenna and multi-receiving antenna system

technical field

The invention relates to the field of wireless communication, in particular to a downlink multi-user diversity and scheduling method in a multiple-input multiple-output system.

Background technique

The MIMO wireless communication system is a system that simultaneously applies multiple antennas to the transmitting end and the receiving end. It is assumed that the number of antennas at the transmitting end is _NT , and the number of antennas at the receiving end is _NR . It is proven to greatly increase the channel capacity of the system. In theory, the channel capacity of a MIMO system is proportional to the minimum number of transmitting antennas and receiving antennas. In addition, it does not need to expand the spectrum width, so it has high spectrum efficiency.

The MIMO system mainly has two kinds of system applications: one is spatial multiplexing, such as D-BLAST or V-BLAST, which demultiplexes data streams into _NT sub-data streams and sends them out on _NT different transmitting antennas. At the receiving end, the wireless signal received by each receiving antenna is the superposition of _NT data streams. In the space channel environment introduced by MIMO, as long as _NR ≥ _NT , space-time processing technology can be used to separate and detect _NT data streams. This application aims to make full use of the information capacity provided by the spatial channel and increase the transmission rate. But the characteristics of the spatial channel will greatly affect the performance of the system. If the spatial channel correlation is small, the channel capacity is large and the transmission rate is high. If the spatial correlation is large, the channel capacity is small and the transmission rate is low. The correlation of the spatial channel is largely related to the angle of arrival (DOA), angle of emission (DOD), angular spread, and antenna spacing of the antennas at the two ends of the transceiver.

Another application of MIMO systems is space-time coding (STBC and STTC). Space-time coding provides antenna diversity gain and coding gain for the system by designing codewords in a two-dimensional space composed of space and time. But the performance of diversity gain is also greatly affected by the spatial channel correlation.

In order to reduce the complexity and cost of MIMO systems, MIMO antenna selection technology has attracted widespread attention. The antenna selection technology of MIMO is to select a subset with the best performance from _NT ( _NR ) antennas at the transmitting end and (or) receiving end according to a certain principle. These principles can be maximization of capacity, maximization of sub-stream output signal-to-noise ratio (SNR), or minimization of bit error rate (BER), among others. The research results show that whether it is space multiplexing or space-time coding, after combining antenna selection technology, the system performance can be close to the situation when all antennas are used, that is, antenna diversity gain is provided. In the case of correlated MIMO fading channels, there is even a capacity gain.

N_T(N_T+1)个活跃的用户。On the other hand, the research results of information theory point out that multiuser diversity is an effective way to increase the data throughput of multiuser systems. Multi-user diversity utilizes the relatively independent channel statistical characteristics experienced by different users, and dynamically allocates system resources to one or more users according to channel quality, thereby achieving a diversity effect and improving the data throughput of the entire system . Because the data packet business can tolerate the time delay caused by multi-user scheduling more than the traditional voice business, the multi-user diversity technology is very suitable for high-speed data transmission services. Multi-user diversity has been adopted by the HSDPA standard of 3GPP. For the downlink with _NT transmit antennas, it has been proved in theory that at any moment, the transmission strategy for maximizing data throughput should include _NT to

_NT ( _NT +1) active users.

The multi-user system in the MIMO application environment has the following characteristics: the number of antennas at the base station is fixed. The number of antennas at each user terminal is different, and the number of antennas is small due to the size of the terminal. Therefore, each user may work in different antenna modes, namely MIMO, Single Send Multiple Receive (SIMO), or Multiple Send Single Receive (MISO). When designing a multi-user system in a MIMO environment, it is often necessary to consider compatibility with this aspect.

The multi-user diversity and scheduling system in the MIMO application environment currently has the following existing technologies.

Prior art 1:

Lucent Technologies, Inc., "Throughput simulations for MIMO and transmit diversity enhancements to HSDPA," 3GPP TSG RAN WGl, TSGR1#17(00)1388

Use the Round Robin Scheduling System (RRS). In a certain time slot, the RRS algorithm selects a user from multiple active users to transmit data in a definite round-robin manner (that is, regardless of the user's channel conditions), and allocates all _NT transmit antennas to the selected user. The scheduling method provides users with equal and fair opportunities to use MIMO channels. However, this approach does not take advantage of the multi-user diversity inherent in multi-user systems, resulting in a capacity equivalent to that of a single-user system.

Prior art 2:

Lucent Technologies US PATENT 2002/0094834 A1 (Jul, 18, 2002): "Method for simultaneously conveying information to multiple mobiles with multiple antennas". The basic idea of this method is as follows.

Under the control of the scheduling algorithm, each antenna of the antenna array can work in two modes. The first mode is: one or a group of users are pre-assigned to certain antennas. According to the channel state information of the pre-allocated users, the scheduling algorithm decides which pre-allocated user's data information each antenna is used to transmit in a certain period of time.

In the second mode, users are not pre-assigned to any particular antenna. The scheduling algorithm monitors various channel state information fed back by users, and selects the most suitable antenna for a certain user to transmit user data in a certain period of time. Equivalent to SIMO mode.

Prior art 3:

Qualcomm US PATENT 6662024 B2 (Dec. 9, 2003): "Method and apparatus for allocating downlink resources in a multiple-input multiple-output (MIMO) communication system". The basic idea of this patent is as follows.

This method designs three different data transmission modes. In MIMO mode, all downlink data streams are assigned to a single terminal with multiple antennas (ie MIMO terminal). In N-SIMO mode, a single data stream is assigned to a specific terminal, and each terminal uses multiple antennas, which is a SIMO terminal. In the hybrid mode, downlink resources can be allocated to SIMO and MIMO terminals in combination. By simultaneously transmitting data to multiple SIMO terminals, a MIMO terminal, or a combination thereof, the transmission capacity of the system is increased. This patent provides a downlink scheduling method. The scheduler selects an optimal working mode according to various factors, such as the service required by the terminal. At the same time, the scheduler selects a specific group of users to allow them to transmit data at the same time, and allocates available transmit antennas to these selected users to achieve higher optimized system performance. The specific method is: divide the terminals of a mobile communication system into one or more sets to correspond to a combination of data transmission. Each set is a unique combination of one or more terminals and defines it as a hypothesis. In a hypothesis, a certain combination of antenna allocation for one or more terminals is defined as a sub-hypothesis. After evaluating the performance of each sub-hypothesis of each hypothesis, a sub-hypothesis is selected, and the terminal in this sub-hypothesis is scheduled to transmit data on a specific antenna.

The disadvantage of the prior art 1 is that: users are only scheduled in time, without using the variation of each user's space channel; the time scheduling does not take into account the diversity gain of multiple users.

The disadvantage of prior art 2 is that in the first mode, users are fixedly pre-allocated to certain antennas. Although this can simplify the algorithm design, the overall performance will be significantly affected, which is a sub-optimal solution; and in the second mode, the user is only dynamically assigned a transmitting antenna at the base station. This will limit the user's maximum downlink data transmission rate.

The disadvantage of prior art 3 is that the scheduling algorithm estimates the performance of each sub-hypothesis of each hypothesis to schedule users. Although this algorithm can be regarded as an optimal multi-user scheduling algorithm, its computational complexity is undoubtedly quite high of. When the number of users who need to transmit data is large and the number of antennas is large, the amount of computation is beyond the system's load.

Contents of the invention

The technical problem solved by the present invention is to provide a downlink multi-user scheduling method in a multi-transmit antenna multi-receive antenna system, which can make full use of the space resources of the MIMO system, in order to achieve the purpose of optimizing system performance (such as data throughput). The prior art either does not make full use of the spatial channel resources of the MIMO system, or the computational complexity is too large for the system to bear. The present invention fully considers the two factors of the computational complexity and the overall performance of the system, and improves the overall performance of the system as much as possible on the basis of reducing the computational complexity.

The downlink multi-user scheduling method in the multi-transmit antenna multi-receive antenna system proposed by the present invention includes the following processing procedures:

In the first step, the user terminal selects a subset of base station transmit antennas according to the estimated channel information;

In the second step, the user terminal feeds back the selected antenna subset indicator and channel state information;

In the third step, the scheduling algorithm determines the distribution relationship between the base station transmitting antenna and the user terminal in the next transmission time slot according to the feedback information and other information of the user.

The first step specifically includes: all user terminals to transmit data estimate their respective MIMO channel state information by receiving the steering signals sent by all base station transmit antennas on the downlink, and the user terminals select the base station transmit antenna according to the estimated channel information. a subset.

The selection principle of the base station transmit antenna can be maximization of channel capacity or minimization of channel correlation or maximization of output SNR or minimization of BER, and each user terminal can set a different selection principle for itself.

The number of antennas in the antenna subset can be dynamically determined according to actual system applications or changes in actual channel quality. If it is space multiplexing, the number of antennas in the antenna subset can be set to be the same as the number of user terminal antennas or less than the number of user terminal antennas to meet the requirements of low-speed data transmission; if space-time coding is used, the antennas The number of antennas in the subset may be greater than the number of antennas in the user terminal.

The specific expression form of the channel state information in the second step is related to the realization form of the system: if the sending end of the system needs all the channel state information, each user can feed back all the channel information related to the selected antenna subset and the desired service The subset indicator of the base station antenna; if the system sender only needs part of the channel state information, each user can only feed back part of the channel information and the subset indicator of the base station antenna; if the system sender does not need any channel state information, each user can The user can only feed back the channel state indicator and the indicator of the subset of base station antennas to the scheduling algorithm of the sending end.

The third step specifically includes the following processes:

1) The scheduling algorithm calculates the priority authority of each user according to the channel state information of the received user;

In the process of determining user priority, it is necessary to consider not only the data characteristics of each user, the fairness of transmission allocation, but also the principle of optimal system performance and the channel state information of each user.

2) arrange the users into a priority descending queue according to the user's priority value;

3) According to the order of priority, determine the next user for antenna allocation;

4) For a selected user to be allocated, decide whether to allocate the desired antenna to the user according to the base station transmitting antenna selected by the user and the usage of the base station transmitting antenna;

5) When the base station transmit antenna is assigned to multiple users at the same time, assign different orthogonal codes or different subcarrier frequencies in the MIMO-OFDM system to the users sharing the transmit antenna array;

6) Until all antennas or users have been allocated, the scheduling ends.

The present invention is a two-dimensional multi-user diversity and scheduling method implemented not only in time but also in space (base station antenna). This method is a multi-user scheduling algorithm that occurs in each time period to determine the spatial scheduling of multi-users in the next time period. Before the arrival of the next time period, the scheduling algorithm allows all user terminals to use MIMO antenna selection technology to determine and select the transmitting antenna of the base station, and feed back this information and channel state information to the transmitting end, and the scheduling algorithm then Determine the allocation relationship between users and base station antennas in the next period. In a certain period of time, the multi-antenna system at the base station can be allocated to multiple relatively low-speed users or users with a small number of antennas; it can also be allocated to a high-speed user in a certain period of time. When the antenna system of the base station is allocated to multiple users in a certain period of time, other methods need to be used to separate the users. For example, orthogonal codes (such as Walsh codes) are used for multi-user access; or in a MIMO-OFDM system, different subcarrier frequency groups may also be used.

By adopting the method of the invention, compared with the prior art, a relatively simple multi-user scheduling algorithm is adopted to improve the overall performance of the system. This method combines MIMO antenna selection technology with multi-user diversity, which not only makes full use of the multi-antenna system at the base station, provides space diversity gain or channel capacity gain, but also provides multi-user diversity, thereby improving the data throughput of the system. The present invention can also provide services for user terminals with different antenna numbers at the same time, is compatible with multiple modes of MIMO, SISO, SIMO and MISO at the same time, and does not require the number of antennas of user terminals, so it has strong versatility.

Description of drawings

Fig. 1 is a schematic diagram of the composition of the multi-transmitting antenna and multi-receiving antenna system used in the present invention;

Fig. 2 is a basic working flow chart of the multi-user scheduling method of the present invention.

Detailed ways

Below in conjunction with accompanying drawing 1 and accompanying drawing 2 the implementation of technical scheme is described in further detail:

The multi-user scheduling method of the present invention is made up of following steps to the multi-user scheduling of next time period:

1. All user terminals to transmit data estimate their respective MIMO channel state information by receiving common pilot signals sent by all transmit antennas of the base station on the downlink; according to these channel state information, select a channel state information for themselves according to a certain principle The optimal subset of base station transmit antennas.

2. Each user feeds back the antenna subset indicator and related channel state information to the base station.

3. The scheduling algorithm calculates the priority authority of each user according to the feedback channel state information of the user.

4. According to the user's priority value, the users are arranged into a priority queue, the users with high priority are in the front, and the users with low priority are in the back.

5. Take the first user in the priority queue, that is, the user with the highest priority; allocate the base station transmitting antenna according to the user's requirements.

6. Check whether all base station antennas are allocated, if yes, go to step 11; if not, go to the next step.

7. Check whether the current user is the end of the priority queue, that is, whether all users have been checked. If yes, go to step 11; if no, go to next step.

8. Fetch the next user in the queue.

9. Check whether the antenna selected by the user conflicts with the allocated antenna, if there is a conflict, go to step 7; if not, go to the next step.

10. Assign desired base station transmit antennas; go to step 6.

11. When the base station antenna system is allocated to multiple users at the same time, each of these users is allocated a unique orthogonal code or subcarrier frequency group in the OFDM system. End this schedule.

Assuming that the number of transmitting antennas at the base station is N _T =4, there are 6 active users AF in a certain period of time, that is, 6 users with data transmission requirements. At this time, the multi-user scheduling method described in the present invention is used to determine the allocation of base station transmit antennas in the next time period. This method is a multi-user scheduling algorithm that occurs in each period, and the specific length of a period is determined by the system.

In this specific embodiment, the steps of the multi-user scheduling method of the present invention are as follows:

1) All six user terminals to transmit data estimate their respective MIMO channel state information by receiving the common steering signal sent by the base station’s transmitting antenna on the downlink; according to these channel state information, select the best channel state information for themselves according to a certain principle. A subset of optimal base station transmit antennas.

The principle may be maximization of channel capacity, or minimization of channel correlation, or maximization of output SNR, or minimization of BER, and so on. Each user terminal can set different rules for itself.

Meanwhile, the number of antennas in the antenna subset may be determined according to actual system applications. In the case of spatial multiplexing (such as BLAST), it can be set to be the same as the number of user terminal antennas, or smaller than the number of user terminal antennas to meet the requirements of low-speed data transmission. If space-time coding (such as STBC) is used, the number of antenna subsets may be greater than the number of antennas of the user terminal. The number of antennas in the antenna subset may also be dynamically determined according to changes in actual channel quality.

2) Users A-F feed back the information of the subset of transmitting antennas they have selected and the channel state information to the base station.

If the system sender needs all MIMO channel state information, each user can feed back all channel information of the selected antenna subset and the subset indicator of the base station antenna desired to be served;

If only part of the MIMO channel state information is needed at the system transmitter, each user can only feed back part of the channel information and the subset indicator of the base station antenna;

If the transmitting end of the system does not need any MIMO channel state information, each user can only feed back the channel state indicator and the subset indicator of the base station antenna to the scheduling algorithm of the transmitting end.

3) According to the channel state information of each user, the base station calculates the priority of each user.

In the process of determining user priority, it is necessary to consider not only the data characteristics of each user (such as the requirement for delay, etc.), the fairness of transmission allocation, but also the principle of optimal system performance.

It is assumed that information such as the number of terminal antennas of each user terminal, the selected antenna subset fed back, and the priority is shown in Table 1 at this time.

Table 1: Active user information table

User A User B User C User D User E User F number of antennas 2 4 1 2 2 1 priority 1 2 3 4 5 6 The serial number of the selected antenna (1, 3) (1, 2, 3, 4) (4) (2, 3) (2) (2, 4)

Among them, the priority of the user is higher with a smaller value. It can be seen from the table that users A to D are MIMO users, user E is a SIMO user, and user F is a MISO user.

4) Arrange the users in a descending queue according to their priority; that is

User A→User B→User C→User D→User E→User F

5) Allocate antennas to user A with the highest priority according to its needs, that is, allocate antennas 1 and 3 to user A.

6) Check that all base station transmit antennas are not allocated, and user A is not at the end of the queue.

7) Take the next user in the priority queue, that is, user B.

8) Check whether the antenna selected by user B conflicts with the allocated antenna. Because antenna 1 and antenna 3 have been allocated, it is determined that there is a conflict, and no antenna is allocated to user B.

9) Check that user B is not the end of the queue.

10) Take the next user in the priority queue, that is, user C. Since antenna 4 selected by user C is not assigned, antenna 4 is assigned to it.

11) Check that all base station transmit antennas are not allocated, and user C is not at the end of the queue.

12) Get the next user in the priority queue, that is, user D. Since antenna 3 has been allocated, user D is not scheduled to use antenna resources.

13) Check that user D is not the end of the queue.

14) Get the next user in the priority queue, that is, user E. Since antenna 2 selected by user E is not assigned, antenna 2 is assigned to it.

15) The base station antennas have all been allocated. Assign a Walsh orthogonal code to each of users A, C and E.

16) In the next time period, scheduled users A, C and E use the antenna of the base station to receive downlink data simultaneously.

Claims (8)

1. a downlink multi-user scheduling method in a multi-transmission antenna multi-reception antenna system, is characterized in that the method comprises: In the first step, the user terminal selects a subset of base station transmit antennas according to the estimated channel information; In the second step, the user terminal feeds back the selected antenna subset indicator and channel state information; In the third step, the scheduling algorithm calculates the priority value of each user according to the channel state information fed back by the user terminal, and then determines the allocation relationship between the base station transmitting antenna and the user terminal in the next transmission time slot according to the priority value of each user and other information of the user , when the base station transmit antennas are allocated to multiple users at the same time, different orthogonal codes or different subcarrier frequencies in the OFDM system are allocated to the users sharing the transmit antenna array. 2. The method according to claim 1, wherein the first step specifically comprises: all user terminals with data to be transmitted estimate their respective Channel information, the user terminal selects a subset of base station transmit antennas based on the estimated channel information. 3. The method according to claim 1 or 2, wherein the selection principle of the base station transmitting antenna is maximization of channel capacity or minimization of channel correlation or maximization of output SNR or minimization of BER, and each user terminal is Set different selection principles yourself. 4. The method according to claim 1 or 2, wherein the number of antennas in the antenna subset is dynamically determined according to actual system applications or changes in actual channel quality. 5. The method according to claim 4, wherein if it is spatial multiplexing, the number of antennas in the antenna subset is set to be the same as the number of user terminal antennas or less than the number of user terminal antennas to apply to low-speed data Transmission requirements; if space-time coding is used, the number of antennas in the antenna subset is greater than the number of antennas in the user terminal. 6. The method according to claim 1, characterized in that, the specific form of expression of the channel state information in the second step is related to the realization form of the system: If the base station needs all the channel state information, each user feeds back all the channel information related to the selected antenna subset and the subset indicator of the base station antenna that wants to be served: if the system sender only needs part of the channel state information, each user The user only feeds back part of the channel information and the subset indicator of the base station antenna; If the base station does not need any channel state information, each user only feeds back the channel state indicator and the subset indicator of the base station antenna to the scheduling algorithm of the base station. 7. The method according to claim 1, characterized in that the third step specifically comprises the following processes: 1) The scheduling algorithm calculates the priority weight value of each user according to the channel state information fed back by the user terminal; 2) arrange the users into a priority descending queue according to the user's priority value; 3) According to the order of priority, determine the next user for antenna allocation; 4) For a selected user to be allocated, decide whether to allocate the desired antenna to the user according to the base station transmitting antenna selected by the user and the usage of the base station transmitting antenna; 5) Until all antennas or users have been assigned, the scheduling ends. 8. The method according to claim 7, characterized in that, in the process of determining user priority in said step 1), it is necessary to consider the data characteristics of each user, the fairness of transmission allocation and the optimal performance of the system. The optimal principle and fully consider the channel state information of each user.

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