WO2009023985A1

WO2009023985A1 - Feedback method of mbs service and wireless communication system

Info

Publication number: WO2009023985A1
Application number: PCT/CN2007/002502
Authority: WO
Inventors: Dongyao Wang; Jimin Liu; Xiaobing Leng; Wei Ni
Original assignee: Alcatel Shanghai Bell Co., Ltd.; Alcatel Lucent
Priority date: 2007-08-20
Filing date: 2007-08-20
Publication date: 2009-02-26

Abstract

A method for performing feedback for multi-broadcast service of wireless communication system based on OFDMA is disclosed. The method includes the following steps: a base station allocates an unique identification to at least one user station within the multi-broadcast group, and sends indication message of the feedback channel to user stations within the multi-broadcast group through sub-frame of downlink; in which, the indication message of the feedback channel indicates the feedback channel of each user station in the uplink; and the user stations feedback corresponding message to the base station on their respective feedback channel. Dueto the feedback channel of each user station is uniquely determined through the position in two-dimensional space of frequency and time. The present invention improves the capability of uplink, and does not need great calculation. Furthermore, the present invention allocates different meanings of feedback information for different codes, which makes the user station not need to feed back specific information, and can realize the information feedback by only feeding back corresponding codes.

Description

Feedback method and wireless communication system for MBS service

The present invention is directed to a feedback technology for MBS services, and specifically relates to a feedback method and a wireless communication system for MBS services in an OFDMA-based network, which can support MBS services from user stations to base stations with high efficiency. Feedback to improve the uplink's capabilities without incurring large computational complexity. Background technique

The development of signal processing and communication technologies has made digital multimedia services (MBS) a reality and has facilitated the commercialization of high definition television (HDTV), digital video broadcasting (DVB) and digital audio broadcasting (DAB). The technology currently used to transport MBS services over wired networks is broadcast/multicast technology, which allows data to be sent from a single source entity to a receiving entity. With the rapid development of audio technology and the growth of wireless users, these MBS services will be realized in the wireless network. Therefore, the industry has considered implementing MBS services in 3G and future wireless communication networks.

With the development of wireless communication technologies, the MAC layer multicast and broadcast services have begun to support multiple wireless communication standards, such as 3GPP and WiMAX. When a subscriber station wants to receive multicast services belonging to the same multicast service group, the subscriber station SS is required to join the multicast service group. Then, all subscriber stations in the multicast service group can receive the multicast service. In this case, when transmitting data packets of a multicast service to a plurality of subscriber stations, the base station only needs to transmit once. Therefore, the base station can effectively use the downlink resources as compared with the unicast technology in which the base station transmits the respective data to each subscriber station. Figure 1 shows a schematic diagram of implementing multicast in a wireless communication network. As shown in Figure 1, the base station BS will transmit data packets of a certain multicast service, and multiple subscriber stations can simultaneously receive data packets of these multicast services.

However, in some cases, a feedback procedure for multicast traffic is required in a wireless network, because without a feedback process, the base station sometimes cannot continue to perform multicast traffic, or the system operates in a low performance state. Therefore, the wireless communication system in the case of multicast must support the ARQ (Automatic Repeat Request) mechanism as in the case of unicast. After the base station BS transmits the multicast data packets to the subscriber stations SS in the multicast service group, the subscriber stations SS should feed back ACK or NACK to let the base station know if they correctly received the transmitted multicast data packets. This can help the base station BS manage the wireless more effectively. Resources and improve the utilization efficiency of spectrum resources of the entire wireless network. However, for feedback messages from the subscriber station SS to the base station BS, the base station 3S should allocate uplink resources for all subscriber stations SS. This kind of operation will cause a lot of waste on the uplink.

OFDM/OFDMA technology is an increasingly widely used high data rate broadband communication technology because of its high spectral efficiency and tolerance for severe delay spread. As is well known, OFDMA has been considered as the basic technology of B3G and 4G wireless communication systems. OFDMA's high data rate capability provides strong support for MBS services in future communications networks. Therefore, it is necessary to provide a more efficient feedback method by combining with OFDM/OFDMA technology to support multicast services.

For the above problem, a feedback method has been proposed in an 802.16-based OFDM communication system. The method proposes that the base station BS allocates two unique CDMA codes (Cumulative ACK (CA) codes and ARQ feedback request (AFR) codes) to each subscriber station SS in the multicast service group, wherein the CA code is used to notify the base station BS The subscriber station SS has successfully received the multicast data packet transmitted after the correct reception of the data packet, and the AFR code is the bandwidth request code used to obtain the bandwidth required to transmit the ARQ feedback message to the base station BS. The transmission of these CDMA codes is carried out in a common area. Since these CDMA codes are orthogonal to each other, and each subscriber station SS is assigned a different CDMA code, there is no collision between them. Since the scheme based on these CDMA codes requires few uplink resources to support the feedback mechanism in the multicast service, the uplink capability can be significantly increased compared to the original scheme based system.

However, the above feedback method has some problems: (1) The amount of calculation is too large, because the base station BS is required to perform correlation operations in each multicast feedback slot, and the base station BS should have all CDMA codes (in IEEE802.16) 256 CDMA codes), which requires a large number of operations; (2) Although the CDMA codes are orthogonal, the number of CDMA codes that the base station BS can correctly detect at the same time in practical applications is still limited. That is, if there are too many subscriber stations SS transmitting CDMA codes in the same multicast feedback slot, there will still be collision problems. This will cause feedback to fail and limit the size of the supported multicast service groups. Therefore, a more efficient feedback method is needed to improve the ability of the uplink feedback link without incurring large computational complexity. Summary of the invention

The present invention has been accomplished in view of the above problems. The object of the present invention is to provide an application to an OFDMA network. The feedback method in the network and the corresponding communication system can support the feedback from the user station to the base station under the MBS service with high efficiency, thereby improving the capability of the uplink and without causing large computational complexity.

In an aspect of the present invention, a method for feeding back a multicast service in an OFDMA-based wireless communication system is provided, the method comprising: the base station assigning a unique identification code to at least one user station in the multicast service group, and Transmitting a feedback channel indication message to a subscriber station of the multicast group through a downlink subframe, the feedback channel message indicating a feedback channel of each user station in the uplink; and feedback from the user station to the base station in respective feedback channels The corresponding message.

According to an embodiment of the invention, each subscriber station in the multicast service group is assigned a unique identification code. According to an embodiment of the present invention, the respective feedback channels of the subscriber stations are determined by the sub-areas occupied by the positions of the subcarriers and the positions of the symbols in the predetermined region of the uplink subframe.

According to an embodiment of the invention, the message fed back to the base station is a predefined codeword.

According to an embodiment of the invention, the codeword is modulated on subcarriers in the region.

According to an embodiment of the invention, the subcarriers are data subcarriers.

According to an embodiment of the invention, the spear carrier comprises a data carrier and a pilot subcarrier.

According to an embodiment of the invention, the predetermined areas are distributed in a single subframe.

According to an embodiment of the invention, the predetermined area is distributed in a plurality of subframes.

According to an embodiment of the invention, the identification code may be assigned only to subscriber stations within the multicast service group that need to provide feedback.

In another aspect of the present invention, an OFDMA-based wireless communication system is provided, comprising a base station and at least one user station constituting a multicast service group, wherein the base station transmits the at least one subscriber station through a downlink subframe And transmitting a feedback channel indication message, the feedback channel indication message indicating a feedback channel of each user station in the uplink; and at least one user station feeding back a corresponding message to the base station in a respective feedback channel.

With the method and communication system of the present invention, since the feedback channel of each subscriber station is uniquely determined by the position in the two-dimensional space of frequency and time, the capability of the uplink is improved, and a large amount of calculation is not required. In addition, the meaning of different feedback information is assigned to different codewords, so that the user station does not need to feed back specific information, but only feedbacks the corresponding code to implement information feedback to the base station. DRAWINGS The above features and advantages of the present invention will become more apparent from the detailed description of the appended claims.

2 is a diagram showing a frame structure of an uplink and a downlink in a wireless communication system according to an embodiment of the present invention;

Figure 3 shows a schematic diagram of assigning sub-areas for each subscriber station as a feedback channel in a downlink subframe;

FIG 4 shows a schematic diagram of a wireless communication system according to an embodiment of the present invention into the data transmission fi ¹ and the feedback process. detailed description

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the figures, the same reference numerals are used to refer to the same or similar components. Detailed descriptions of well-known functions and structures incorporated herein will be omitted for clarity and conciseness, otherwise they will obscure the subject of the invention.

Fig. 2 is a diagram showing the frame structure of an uplink and a downlink in a TOD mode in a wireless communication system according to an embodiment of the present invention. As shown in FIG. 2, a downlink subframe, a TTG (transmission/reception gap), and an uplink sub-frame are periodically distributed along a time axis in a two-dimensional space composed of a frequency (subcarrier) and a time (symbol). Frame, RTG (Receive/Transmit Gap) In the uplink subframe, the preamble part indicates the start of a frame, which is used by the subscriber station to establish synchronization with the base station, and the FCH (Frame Control Header) indicates the frame control header, DL— The MAP is a Medium Access Control (MAC) message that defines the resource allocation on the downlink subframe. The UL-MAP is also a medium access control message that defines the resource allocation on the uplink subframe.

According to an embodiment of the present invention, one area in an uplink subframe is defined in a UL-MAP as a feedback channel of each user station, and an area of these feedback channels in an uplink subframe is referred to as a multicast feedback area, The respective feedback channels of the respective subscriber stations are further defined therein.

FIG. 3 shows a schematic diagram of assigning sub-areas for each subscriber station as a feedback channel in a downlink subframe. As shown in FIG. 3, the multicast feedback area is divided into sub-areas of the same size, for example, 2 subcarrier X3 symbols, which can be sorted in a pre-agreed manner (time priority as illustrated in the figure). Each subscriber station in the multicast service group can match its respective feedback letter according to the assigned unique identification number. Road. As can be seen from Figure 2, each sub-region includes two pilot carriers and four data carriers. In the example shown in FIG. 2, the N sub-areas are divided into two columns, but the base station can also allocate different types of areas, and only need to be composed of N sub-areas.

As described above, each multicast sub-area is considered a feedback channel, so subscriber stations in the multicast service group can use the corresponding feedback channel to transmit feedback messages. For example, as shown in Figure 3, the multicast service group includes N subscriber stations, each assigned its own number 0, 1, 2, ... N-l. Thus, the N sub-areas in the multicast feedback area correspond to the corresponding user stations, respectively. For example, the zeroth sub-area corresponds to the first user station in the multicast service group, the first sub-area corresponds to the second user station in the multicast service group, ... the N-1th sub-area corresponds to The Nth subscriber station in the multicast service group.

Additionally, in accordance with an embodiment of the present invention, the feedback messages are associated with different codewords, and they are modulated onto different data carriers during the feedback process. The table below shows the mapping between codewords and quadrature modulation.

Table 1

If the i-th user station in the multicast service group has successfully received the data packet of the multicast service transmitted in the k-th frame, the feedback message carried by the corresponding feedback channel is 0x00. Otherwise, the feedback message is 0x01. Moreover, if the i-th subscriber station SS in the multicast service group requests to change the modulation and coding mode (MCS) of the multicast service, the feedback message is 0x10 in the case of requesting an increase in the MCS, in the case of requesting reduction of the MCS. The feedback message is 0x11.

Here, let M _h ( 1 <= h <= 4) be the modulation symbol index of the h th modulation symbols, and they are modulated in a QPSK manner orthogonally to each other in the feedback channel, wherein

= exp ' ~) Λ = ex (7 ~)

3 = exp(-/ - ^)

After receiving the feedback message from the subscriber station SS, the base station BS analyzes these feedback messages and most Optimize its scheduling behavior to provide higher quality of service multicast services for subscriber stations in a multicast service group, such as retransmission, system capabilities (increasing or decreasing MCS).

In the case of a predetermined time period, if the base station BS does not receive a feedback message from a certain subscriber station, such as the i-th subscriber-station, the base station BS considers that the i-th subscriber station has left the The service group is broadcast and the multicast service data is no longer sent to it, and the number assigned to the subscriber station and the size of the multicast feedback area in the multicast service group are updated. In this way, the base station can adjust the size of the multicast feedback region in the downlink subframe in real time as the data of the subscriber station in the multicast service group changes, thereby improving the adaptability of the wireless communication system.

An example of a feedback method according to an embodiment of the present invention will now be described with reference to FIG. 4 is a diagram showing a process of data transmission and feedback by a wireless system in accordance with an embodiment of the present invention.

A wireless communication system according to an embodiment of the present invention includes a base station BS and at least one subscriber station SS, wherein at least one subscriber station SS constitutes a multicast service group. As described above, in the case of the MBS service, the base station BS transmits the data packet of the MBS service to each subscriber station SS in the multicast service group. In the case where the subscriber station SS receives the MBS data packet from the base station BS, or if the reception condition deteriorates, the subscriber station needs to feed back information to the base station BS through the respective feedback channels as described above, such as an acknowledgement message (ACK), A negative response message (NACK) increases the MCS (modulation and coding scheme) and reduces the MCS.

For example, in the case of WiMAX (EEE802.16e), as shown in FIG. 3, after the MBS service is initialized, the subscriber station SS transmits a DSA-REQ message to the base station BS to request to establish a multicast link with the base station BS, and add the set. Fixed multicast business group.

After receiving the DSA-REQ message, the base station BS can accept the subscriber station SS to join the multicast service group, that is, send a DSA-RSP message to the subscriber station SS, the message not only includes relevant configuration information for receiving the multicast service. In addition, it carries a unique number assigned to the subscriber station, such as a serial number (N-1). Next, the base station BS transmits a data packet of an MBS service, such as a mobile TV program, to the subscriber station. The subscriber station SS can also receive data packets for these multicast services.

If the subscriber station SS successfully receives the data packet (OK), the codeword (0x00) is fed back to the base station BS by the feedback channel defined in the downlink subframe, which indicates an affirmative response message.

Then, the base station BS continues to transmit the multicast service data packet to the subscriber station SS. If an error (ERROR) occurs during the reception of the subscriber station SS, the subscriber station SS feeds back the codeword (0x01) to the base station BS, which indicates a negative response message, that is to say the subscriber station has not successfully received the multicast service data packet. In this kind of In this case, the base station BS resends the multicast service data packet.

In the process of transmitting data, as the communication environment changes, the subscriber station SS needs the base station to change its system capabilities, such as increasing the MCS or reducing the MCS. In the case where the subscriber station SS requests to increase the MCS, the codeword 0x10 is transmitted to the base station BS through the feedback channel defined in the uplink subframe. In the case where the subscriber station SS desires to reduce the MCS, the code 0x11 is transmitted to the base station BS through the feedback channel defined in the uplink subframe.

As described above, if there are N-1 subscriber stations in a multicast service group receiving multicast services simultaneously, each subscriber station can be assigned a unique identification code, for example, 0, 1, ... N- 2. When a new subscriber station requests to join the multicast service group, it requests the base station to join by the DSA-REQ message. The base station BS then assigns a unique identification code, such as N-1, to the subscriber station using the DSA-RSP message.

Conversely, if there is a subscriber station requesting to leave the multicast service group, the base station can update the identification codes of the remaining subscriber stations in the multicast service group and can redistribute the feedback channels of the respective subscriber stations.

In addition, the above description is that the feedback area of the multicast service is set in a single downlink subframe, but in the case where the interval between two consecutive transmissions of the multicast service is greater than one frame, the allocated multicast feedback The zone will be multiple frames that can span across domains.

Finally, in order to improve the efficiency, the base station BS may not assign a valid identification code to some user stations SS, but only assign a valid identification code to the user station that needs feedback, thereby reducing the size of the multicast feedback area and saving uplink. The bandwidth resource of the link.

The above description is only used to implement the embodiments of the present invention, and those skilled in the art should understand that any modifications or partial substitutions without departing from the scope of the present invention should fall within the scope defined by the claims of the present invention. The scope of the invention should be determined by the scope of the claims.

Claims

Rights request

A method for feeding back a multicast service in an OFDMA-based wireless communication system, comprising the steps of:

The base station sends a feedback channel indication message to at least one user station constituting the multicast service group by using a downlink subframe, the feedback channel message indicating a feedback channel of each user station in the uplink; and the feedback of the user station The corresponding message is fed back to the base station in the channel.

2. The method of claim 1 wherein each subscriber station in the multicast service group is assigned a unique identification code.

3. The method of claim 1, wherein the respective feedback channels of the subscriber stations are determined by the sub-areas occupied by the locations of the subcarriers and the locations of the symbols in the predetermined region of the uplink subframe.

4. The method of claim 1 wherein the message fed back to the base station is a predefined codeword.

5. The method of claim 4, wherein the codeword is modulated on subcarriers in the region.

6. The method of claim 5, wherein the subcarriers are data subcarriers.

7. The method of claim 5 wherein the subcarriers comprise a data carrier and a pilot subcarrier.

8. The method of claim 1, wherein the predetermined area is distributed in a single subframe.

9. The method of claim 1, wherein the predetermined area is distributed in a plurality of subframes.

The method of claim 2 wherein said identification code is assignable only to subscriber stations within the multicast service group that require feedback.

11. An OFDMA-based wireless communication system comprising a base station and at least one subscriber station constituting a multicast service group, wherein

The base station transmits a feedback channel message to the at least one user station through a downlink subframe, the feedback channel message indicating a feedback channel of each user station in the uplink;

At least one user station feeds back a corresponding message to the base station in a respective feedback channel.

The wireless communication system according to claim 11, wherein the feedback channel of each of the subscriber stations is determined by a sub-area occupied by the position of the subcarrier and the position of the symbol in the predetermined region of the uplink subframe.