WO2009121260A1 - 可靠组播的实现方法、系统以及终端和基站 - Google Patents

可靠组播的实现方法、系统以及终端和基站 Download PDF

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Publication number
WO2009121260A1
WO2009121260A1 PCT/CN2009/070740 CN2009070740W WO2009121260A1 WO 2009121260 A1 WO2009121260 A1 WO 2009121260A1 CN 2009070740 W CN2009070740 W CN 2009070740W WO 2009121260 A1 WO2009121260 A1 WO 2009121260A1
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Prior art keywords
base station
terminal
feedback signal
multicast
receiving
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PCT/CN2009/070740
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English (en)
French (fr)
Inventor
郑若滨
王曦
张民
陈雪
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华为技术有限公司
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Publication of WO2009121260A1 publication Critical patent/WO2009121260A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
    • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
    • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
    • H04L1/1867—Arrangements specially adapted for the transmitter end
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L2001/0092—Error control systems characterised by the topology of the transmission link
    • H04L2001/0093—Point-to-multipoint
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/06—Selective distribution of broadcast services, e.g. multimedia broadcast multicast service [MBMS]; Services to user groups; One-way selective calling services

Definitions

  • the present invention relates to the field of communications technologies, and in particular, to a method and system for implementing reliable multicast, and a terminal and a base station. Background technique
  • WIMAX World Interoperability for Microwave Access
  • WIMAX is a broadband wireless access metropolitan area network technology based on the IEEE 802.16 standard. It is often called Wireless MAN (Wireless MAN). Its basic goal is to provide a kind of metropolitan area network.
  • a multi-vendor multi-vendor environment that enables efficient interoperability of broadband wireless access.
  • WIMAX Compared with other current technologies, WIMAX has the characteristics of long transmission distance, high access speed, and wide-format multimedia communication services. It has developed rapidly.
  • MBS Mode Bearer Service
  • IEEE 802.16e The service is specially defined. Considering the mobility, security and service integrity, as well as the one-way and connection characteristics of the service, the MBS service supported by IEEE 802.16e is compared with the ordinary unicast service. There are several characteristics, such as saving air interface resources, macro diversity support MBS mode of multiple base stations (BS, Base Station) and so on.
  • the embodiments of the present invention provide a method and system for implementing reliable multicast, and a terminal and a base station for implementing reliable multicast, which can ensure the integrity and reliability of multicast data.
  • an embodiment of the present invention provides a method for implementing reliable multicast, including:
  • the code division multiple access CDMA codeword used by the uplink ranging channel is sent to the base station as a feedback signal that does not correctly receive the multicast frame;
  • the embodiment of the present invention further provides a method for implementing reliable multicast, which includes: receiving a feedback signal from a terminal that does not correctly receive a multicast frame, where the feedback signal uses a CDMA code used by an uplink ranging channel. Word transmission;
  • the terminal After the terminal allocates the uplink resource for performing the automatic repeat request, the terminal sends a broadcast message to the terminal; after receiving the automatic repeat request from the terminal that the base station retransmits the multicast frame that is not correctly received, the multicast frame is retransmitted to the terminal.
  • the embodiment of the present invention further provides a terminal for implementing reliable multicast, comprising: a feedback signal sending module, configured to: when not receiving a multicast frame from a base station, use a CDMA codeword used by an uplink ranging channel And receiving, by the base station, a broadcast message returned by the base station after successfully receiving the feedback signal, where the feedback signal is sent to the base station;
  • a feedback signal sending module configured to: when not receiving a multicast frame from a base station, use a CDMA codeword used by an uplink ranging channel And receiving, by the base station, a broadcast message returned by the base station after successfully receiving the feedback signal, where the feedback signal is sent to the base station;
  • the retransmission request sending module after receiving the broadcast message from the base station, the broadcast message receiving module sends an automatic retransmission request to the base station, requesting the base station to retransmit the multicast frame that is not correctly received;
  • the multicast frame receiving module is configured to receive a multicast frame that is retransmitted by the base station.
  • the embodiment of the invention further provides a base station for implementing reliable multicast, including:
  • a feedback signal receiving module configured to receive a feedback signal from the terminal that does not correctly receive the multicast frame, where the feedback signal is transmitted by using a CDMA codeword used by the uplink ranging channel;
  • a multicast frame retransmission module after the feedback signal receiving module receives the feedback signal, used After the terminal allocates the uplink resource for performing the automatic retransmission request, the terminal sends a broadcast message to the terminal, and after receiving the automatic retransmission request from the terminal, retransmits the multicast frame to the terminal.
  • the embodiment of the invention further provides a reliable multicast system, including:
  • a base station configured to receive a feedback signal from the terminal that does not correctly receive the multicast frame, where the feedback signal is transmitted by using a CDMA codeword used by the uplink ranging channel; and after the terminal allocates an uplink resource for performing an automatic retransmission request,
  • the broadcast message is sent to the terminal, and after receiving the automatic repeat request from the terminal, the multicast frame is retransmitted to the terminal.
  • the CDMA codeword used by the uplink ranging channel is sent to the base station as a feedback signal that does not correctly receive the multicast frame; and after receiving the acknowledgement signal from the base station, The base station sends an automatic retransmission request, and requests the base station to retransmit the multicast frame that is not correctly received. Therefore, the number of correctly received multicast frames can be increased, and the bandwidth occupied by the uplink resources can be reduced.
  • 1 is a schematic diagram of a generator of a CDMA code of a ranging channel
  • 1 is a schematic diagram of a transmission opportunity of a ranging channel
  • FIG. 3 is a schematic flowchart of a method for implementing reliable multicast according to an embodiment of the present invention
  • Figure 4 (a) and Figure 4 (b) are computer simulation results of multicast retransmission delay
  • Figure 5 (a), Figure 5 (b), and Figure 5 (c) are schematic diagrams of the number of uplink resources saved by the reliable multicast implementation method provided by the present invention compared to the unicast retransmission mechanism under different channel conditions;
  • Figure 6 is a schematic diagram showing the maximum number of SSs that can guarantee the success of all packet loss retransmissions under the conditions of different channel conditions and retransmission delays by computer simulation;
  • FIG. 7 is a schematic structural diagram of a reliable multicast system according to an embodiment of the present invention.
  • FIG. 8 is a schematic diagram of a composition of a terminal for implementing reliable multicast according to an embodiment of the present disclosure
  • FIG. 9 is a schematic diagram of the composition of a terminal for implementing reliable multicast according to an embodiment of the present invention. detailed description
  • the embodiment of the invention provides a method and a system for implementing reliable multicast, and a terminal and a base station for implementing reliable multicast, which ensure the integrity and reliability of the multicast data.
  • the embodiment of the present invention does not send an ACK signal to a correctly received multicast frame based on the NAK mechanism.
  • a NAK signal is transmitted as feedback information for a frame that is not received or not received correctly.
  • the embodiment of the present invention uses the ranging channel of the 802.16 OFDMA mode as the multicast feedback domain, that is, the NAK signal is transmitted in the uplink ranging channel as an example, and the implementation method of the reliable multicast provided by the embodiment of the present invention is described.
  • the uplink ranging channel is a channel for the terminal to perform initial ranging, periodic ranging or bandwidth request in the uplink frame of the OFDMA mode.
  • each terminal is from a specific set of orthogonal CDMA code words: i!
  • the machine selects one as the transmission codeword and uses Binary Phase-Shift Keying (BPSK) modulation to place the uplink ranging channel (lbit per subcarrier).
  • BPSK Binary Phase-Shift Keying
  • each CDMA codeword has a length of 144 bits, and 256 different CDMA codewords are generated by a 15-stage pseudo-random sequence generator.
  • the CDMA generator is shown in Figure 1.
  • Each base station uses a subset of these 256 codewords.
  • the subset is represented by S (0 ⁇ 255), and the codewords in the subset are from S to (S+N+).
  • M+L) mod 256 where the first N codewords are used for initial distance correction, the middle M codewords are used for periodic distance correction, and the last L codewords are used for bandwidth requests. Therefore, the base station can determine the purpose of the message by the received distance correction codeword.
  • a codeword a handover-ranging codeword, is also added.
  • a transmission opportunity in an uplink ranging channel that is, a CDMA codeword is successfully transmitted as a transmission opportunity, which may also be referred to as a transmission slot.
  • a transmission opportunity which may also be referred to as a transmission slot.
  • transmission opportunity there are generally several Transmission opportunity.
  • the method for implementing reliable multicast is: dividing a part of codewords into 256 CDMA codewords that can be used in the uplink ranging channel as a NAK signal code set that the multicast frame fails to receive correctly,
  • the NAK signal is transmitted by the terminal in any time slot in the ranging domain allocated by the base station, that is, in the transmission opportunity of an optional uplink ranging channel.
  • FIG. 3 is a schematic flowchart of a method for implementing reliable multicast according to an embodiment of the present invention, including the following steps:
  • step 100 if the multicast frame from the base station is not received, the terminal sends the CDMA codeword used by the uplink ranging channel to the base station as a feedback signal that does not correctly receive the multicast frame.
  • the terminal selects one CDMA codeword as a feedback signal from the CDMA code set set in advance, and the feedback signal is used by the terminal in any time slot in the ranging domain allocated by the base station, that is, in an uplink ranging channel.
  • the transmission opportunity is transmitted; the feedback signal is specifically a NAK signal.
  • step 101 after receiving the feedback signal, the base station allocates an automatic retransmission request to the terminal. Uplink resources, and send broadcast messages to the terminal;
  • the base station since the base station cannot distinguish which terminal transmits the CDMA multicast frame NAK signal, once the CDMA multicast frame NAK signal is successfully received, the base station sends a broadcast message to all the terminals participating in the multicast,
  • the broadcast message is multicast information, and is used to notify the user station of the received CDMA code and the uplink ranging channel time slot for receiving the CDMA code, and allocate the uplink ARQ space to the terminal in the multicast information;
  • the terminal After receiving the broadcast message sent by the base station, the terminal sends an automatic retransmission request to the base station in the specified ARQ space, requesting the base station to retransmit the multicast frame that is not correctly received. Specifically, the terminal receives the broadcast from the base station. a message, where the broadcast message includes an uplink resource allocated by the base station for the terminal, a CDMA codeword received by the base station, and a time slot for receiving the CDMA codeword;
  • the terminal determines, according to the CDMA codeword received by the base station in the broadcast message and the time slot in which the base station receives the CDMA codeword, whether the CDMA codeword is a CDMA codeword used by a feedback signal sent by the base station, and if yes, passes The base station sends an automatic retransmission request to the base station for its allocated uplink resource.
  • step 103 after receiving the automatic retransmission request from the terminal that the base station retransmits the multicast frame that is not correctly received, the base station retransmits the multicast frame to the terminal;
  • step 104 the terminal receives the multicast frame retransmitted by the base station.
  • the terminal sends the NAK signal of the multicast frame in the uplink ranging channel, since the number of codewords of the NAK code set is limited, if two or more terminals select the same CDMA codeword, and When the uplink transmission channel transmits in the same transmission opportunity, the CDMA code will collide, causing the transmission to fail.
  • the truncated binary exponential algorithm is used to back up a number of time slots, and still select one of the CDMA code sets of the original multicast frame NAK signal for transmission. If the collision still occurs, the truncated binary index is continued. Algorithm process.
  • the embodiment of the present invention adopts a truncated binary exponential algorithm as an example to perform rollback.
  • other fallback algorithms may also be selected.
  • a number r is randomly selected from [0, 1], and the time of r*2t is retracted (2t is the end-to-end round-trip propagation time, for example, the time required to transmit 512 bits in IEEE802.3) .
  • the back step is doubled, and a number r is randomly selected from [0, 1, 2, 3], and the time of r*2t is reversed.
  • a number r is randomly selected from [0, 1 , 2 2 10 -1 ], and the time of r*2t is retreated.
  • the back step is no longer doubled, and a number r is randomly selected from [0, 1 , 2, ..., 2 1() -1], and the time of r*2t is retreated.
  • a number r is randomly selected from [0, 1 , 2, 2 10 -1], and the time of r*2t is retreated.
  • the data frame is discarded and reported to the upper layer protocol.
  • the maximum number of transmissions is 16 times.
  • the step size is doubled each time. This is called the "binary index”.
  • the step size is no longer doubled. This is called "truncation".
  • the timer can be set in the terminal. If the CDMA signal cannot be sent after a certain period of time, the retransmission of the multicast frame is abandoned.
  • the method for implementing the reliable multicast provided by the embodiment of the present invention can improve the number of correctly received multicast frames, and can reduce the bandwidth occupied by the uplink resources in a manner of unicast retransmission.
  • the embodiment of the present invention also performs a simulation test on the implementation method of reliable multicast. Under the existing WIMAX system condition, the retransmission delay can be considered to be effective within 30 ms.
  • the multicast retransmission delay time of the simulation in the embodiment of the present invention is 20ms and 25ms. It should be noted that the multicast retransmission delay time refers to the delay time when the multicast frame that is not correctly received is correctly received by the reliable multicast technology provided by the embodiment of the present invention. .
  • the successful access rate of the multicast retransmission refers to the number of ss that can correctly receive the multicast frame after receiving a multicast frame fails to receive the multicast correctly.
  • the percentage of the ss number of frames refers to the number of ss that can correctly receive the multicast frame after receiving a multicast frame fails to receive the multicast correctly.
  • Backoff start refers to the initial backoff step of the truncated binary exponential backoff algorithm.
  • FIG. 4 it is a computer simulation result of multicast retransmission delay time
  • Figure 4 (a) shows the simulation of the multicast retransmission delay time in 20ms using computer simulation.
  • the number of clients (SS) that transmit CDMA codes is a percentage of the number of SSs (users, ie terminals) that need to be retransmitted.
  • each frame is 5 ms long, and each frame has 6 uplink ranging channel transmission opportunities, and the number of CDMA codes is 16.
  • the number of simulation operations is 100, and the average value is taken.
  • the base station after receiving the NAK signal, the base station immediately sends an acknowledgment signal, and the terminal immediately transmits the ARQ signal after receiving the acknowledgment signal, and the unsuccessfully received multicast signal immediately arranges retransmission.
  • the three processes have no other delay.
  • Figure 4 (b) shows the percentage of ss that successfully transmit CDMA codes within 25ms of the multicast retransmission delay time as a percentage of all ss that need to be retransmitted.
  • the number of users to be retransmitted when Backoff start is 1, the maximum successful access rate of multicast retransmission can be obtained.
  • the number of users is generally not particularly large. For example, it can be seen from the figure that when the number of users requiring retransmission is 20, the successful access rate is close to 100%; when the number of retransmission users is 40, the successful access rate is still above 80%. Under the general microcell and picocell and channel conditions, the present invention can better meet the requirements of user retransmission.
  • Figure 5 (a), Figure 5 (b) and Figure 5 (c) show the number of uplink resources saved by the reliable multicast implementation method provided by the present invention over the unicast retransmission mechanism under different channel conditions.
  • the Gilbert model is used here to simulate the burst loss characteristics of a typical wireless channel.
  • the Gilbert model itself is well known to those skilled in the art and will not be described again here.
  • ⁇ refers to the total average packet loss rate in the model, from 0.05 to 0.25, in steps of 0.05, simulating the classical model.
  • User bit error rate respectively 5xl0- 3, lxlO- 3 and 1x10- 4.
  • ⁇ indicates the proportion of the number of users with the uplink bit error rate, the ratio is different, and the results are different, which are represented by Fig. 5(a) 5(b), 5(c) respectively.
  • 48 bits that is, 6 bytes as an uplink unit, and the vertical axis indicates the number of uplink units.
  • the present invention since the present invention adopts the NAK mechanism, the number of uplink resources required by the present invention is less than that of the single channel model.
  • Figure 6 shows the maximum number of SSs that can guarantee the success of all packet loss retransmissions using computer simulations to simulate different channel conditions and retransmission delays.
  • Both 20ms and 25ms refer to the multicast retransmission delay time, and the definition of 1: 1: 1, 1: 2: 3, 3: 2: 1 and Figure 5 (a), Figure 5 (b) and Figure 5 (c) Same, expressed in bit error rate 5xl0_ 3 , lxlO" 3 The ratio of the number of users to lxlO" 4 .
  • the highest point in the figure shows 0.05, the retransmission delay time is 25ms, and the user bit error rate ratio is 3: 2: 1, as long as the number of multicast users is within 130, all users fail.
  • the correctly received multicast data can be retransmitted successfully.
  • the lowest point shows ⁇ is 0.25, the retransmission delay time is 20ms, and the user bit error rate ratio is 1: 2: 3, as long as the number of multicast users is within 53, all users fail to receive the multicast data correctly. Can be retransmitted successfully.
  • the present invention is capable of meeting the needs of implementation.
  • the embodiment of the present invention is applicable to the case of a microcell or a picocell.
  • FIG. 7 is a schematic structural diagram of a terminal for implementing reliable multicast according to an embodiment of the present invention.
  • the reliable multicast system provided by the embodiment of the present invention includes:
  • the base station 2 is configured to: after receiving the feedback signal from the terminal 1 that the multicast frame is not correctly received, allocate, to the terminal 1, an uplink resource for performing an automatic retransmission request, and send a broadcast message to the terminal; the broadcast message includes the base station receiving a CDMA codeword and a time slot for receiving the CDMA codeword, and the uplink resource; and after receiving the automatic repeat request from the terminal 1, retransmitting the multicast frame to the terminal 1.
  • FIG. 8 is a schematic structural diagram of a terminal for implementing reliable multicast according to an embodiment of the present invention.
  • the terminal includes:
  • the feedback signal sending module 10 is configured to: when the multicast frame from the base station is not received, send the CDMA codeword used by the uplink ranging channel to the base station as a feedback signal that does not correctly receive the multicast frame; An optional one CDMA codeword in the CDMA code set is set in advance as a feedback signal, and optionally a transmission opportunity in the uplink ranging channel is used for transmission; the feedback signal is specifically a NAK signal.
  • the broadcast message receiving module 11 is configured to receive, after the base station successfully receives the feedback signal, The broadcast message returned by the terminal; it should be noted that the broadcast message is multicast information, and is used to notify the terminal of the CDMA code received by the base station and the uplink ranging channel time slot receiving the CDMA code, and in this group Allocating uplink ARQ space to the terminal in the broadcast information;
  • the retransmission request sending module 12 after receiving the broadcast message from the base station, the broadcast message receiving module sends an automatic retransmission request to the base station in the designated ARQ space, requesting the base station to retransmit the multicast frame that is not correctly received;
  • the retransmission request sending module 12 determines, according to the CDMA codeword received by the base station in the broadcast message and the time slot in which the base station receives the CDMA codeword, whether the CDMA codeword is used by the feedback signal sent by itself to the base station.
  • the CDMA codeword if yes, sends an automatic retransmission request to the base station through the uplink resource allocated by the base station.
  • the multicast frame receiving module 13 is configured to receive a multicast frame that is retransmitted by the base station.
  • the terminal sends the NAK signal of the multicast frame in the uplink ranging channel, since the number of codewords of the NAK code set is limited, if two or more terminals select the same CDMA codeword, and When the uplink transmission channel transmits in the same transmission opportunity, the CDMA code will collide, causing the transmission to fail.
  • the acknowledgment signal receiving module 11 of the terminal does not receive the broadcast message returned by the base station within a fixed time, and then notifies the feedback signal sending module 10 to re-transmit the CDMA codeword. Sending the feedback signal.
  • the truncated binary exponential algorithm is used to back up a number of time slots, and still select one of the CDMA code sets of the original multicast frame NAK signal for transmission. If the collision still occurs, the truncated binary index is continued. Algorithm process.
  • the terminal further includes:
  • the back-off time slot calculation module 14 is configured to calculate a back-off time slot by using a back-off algorithm, and the feedback signal sending module 10 re-transmits the NAK signal by using a CDMA codeword in the back-off time slot.
  • FIG. 9 is a schematic diagram of a base station for implementing reliable multicast according to an embodiment of the present invention.
  • the base station for implementing reliable multicast includes:
  • the feedback signal receiving module 20 is configured to receive a feedback signal from the terminal that does not correctly receive the multicast frame, and the feedback signal uses the CDMA codeword used by the uplink ranging channel to transmit the NAK signal and the multicast frame retransmission module 21 After the feedback signal receiving module 20 receives the feedback signal, allocate an uplink resource for performing an automatic retransmission request to the terminal, and send a broadcast message to the terminal, After receiving the automatic retransmission request from the terminal, the multicast frame is retransmitted to the terminal.
  • the multicast retransmission module 21 includes:
  • the resource allocation unit 210 is configured to allocate, to the terminal, an uplink resource that performs an automatic retransmission request, that is, allocate an uplink ARQ space;
  • the broadcast message sending unit 211 is configured to send the CDMA code over broadcast message received by the feedback signal receiving module 20 to the terminal; it should be noted that the base station cannot distinguish which terminal sends the CDMA multicast frame NAK signal, so once Successfully receiving a CDMA multicast frame NAK signal, the base station will send a broadcast message to all participating terminals, the broadcast message is multicast information, used to notify the user station of the received CDMA codeword and receive the CDMA An uplink ranging channel slot of the codeword, and the uplink ARQ space is allocated to the terminal in the multicast information;
  • the retransmission request receiving unit 212 is configured to receive an automatic retransmission request from the terminal that the requesting base station retransmits the multicast frame that is not correctly received;
  • the multicast frame transmitting unit 213 retransmits the multicast frame to the terminal after the retransmission request receiving unit 212 receives the automatic retransmission request from the terminal.
  • the embodiment of the present invention provides a reliable multicast method for a WIMAX system, and a terminal and a base station for implementing the method.
  • the embodiment of the present invention can improve the number of correctly received multicast frames, and can reduce the unicast retransmission mode.

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Description

可靠组播的实现方法、 系统以及终端和基站 技术领域
本发明涉及通信技术领域， 尤其涉及一种可靠组播的实现方法及系统， 以 及终端和基站。 背景技术
随着移动通信与因特网的快速发展， 通信市场正在呈现出话音业务移动化， 数据业务宽带化的发展趋势。微波接入全球互通（ WIMAX, World Interoperability for Microwave Access )作为能够提供高速移动数据业务的一种新的接入网技术， 正在引起越来越多的重视。 WIMAX是一项基于 IEEE 802.16标准的宽带无线接 入城域网技术， 常被称为无线主城域网 （Wireless MAN, Wireless Metropolitan Area Network ), 其基本目标是提供一种在城域网一点对多点的多厂商环境下， 可有效地互操作的宽带无线接入手段。
和目前的其它技术相比， WIMAX具有传输距离远、接入速度高、 能提供广 泛的多媒体通信服务等技术特点， 一时发展非常迅速。
WIMAX系统的空中接口 IEEE 802.16e规范， 为支持光频分多址接入
( OFDM A , Optical Fxt'qiiency Division Multiple Access ) 下的模式承载业务
( MBS , Mode Bearer Service ) 业务进行了特别定义， 考虑到移动性、 安全性 和业务的完整性， 以及业务的单向和连接特点， IEEE 802.16e所支持的MBS业务 与普通单播业务相比有若干特点， 比如节约空口资源、 宏分集支持多基站（BS， Base Station ) 的 MBS模式等等。
发明人在实现本发明的过程中， 发现由于无线信道的传输质量易受大气条 件、 用户装置的衰落特性等影响， 所以在组播的内容发送中可能会产生误码。 因此， 一个或多个用户终端可能接收不到某些组播帧， 或者即使接收到也可能 包含某些误码。 这就需要一种自动重传请求 （ARQ, Automatic Repeat x'eQue.si ) 机制， 比如基于确认 ( ACK, Acknowledgement ) 或者基于未能确认（NAK, Not Acknowledgement ) 的反馈机制等， 在接收端作为已传组播帧的反馈信息， 告诉发送端是否收到了其发送的组播帧。 而在现有的 WIMAX标准里面， 没有 规定组播业务的 ARQ机制， 这样显然不能满足在有组播帧没有正确接收到的情 况下的服务质量 （ QoS , Qual iy of Service )要求。 发明内容
本发明实施例提供一种可靠组播的实现方法和系统， 以及实现可靠组播的 终端和基站， 可保证组播数据的完整性和可靠性。
为了解决上述技术问题， 本发明实施例提供了一种可靠组播的实现方法， 包括：
若没有接收到来自基站的组播帧， 则将上行测距信道使用的码分多址接入 CDMA码字作为没有正确接收到组播帧的反馈信号发送给基站；
接收来自基站的在收到所述反馈信号而发送的广播消息后， 向基站发送自 动重传请求， 请求基站重新传送未能正确接收的组播帧；
接收基站重传的组播帧。
本发明实施例还提供了一种可靠组播的实现方法， 其特征在于， 包括： 接收来自终端的没有正确接收到组播帧的反馈信号， 所述反馈信号利用上 行测距信道使用的 CDMA码字进行传输；
为终端分配进行自动重传请求的上行资源后， 向终端发送广播消息； 接收来自终端的请求基站重新传送未能正确接收的组播帧的自动重传请求 后， 向终端重新传送组播帧。
相应地， 本发明实施例还提供了一种实现可靠组播的终端， 包括： 反馈信号发送模块， 用于在没有接收到来自基站的组播帧， 则将上行测距 信道使用的 CDMA码字作为没有正确接收到组播帧的反馈信号发送给基站； 广播消息接收模块， 用于接收来自基站在成功接收所述反馈信号后返回的 广播消息；
重传请求发送模块， 在广播消息接收模块接收到来自基站的广播消息后， 向基站发送自动重传请求， 请求基站重新传送未能正确接收的组播帧；
组播帧接收模块， 用于接收基站重传的组播帧。
本发明实施例还提供了一种实现可靠组播的基站， 包括：
反馈信号接收模块， 用于接收来自终端的没有正确接收到组播帧的反馈信 号， 所述反馈信号利用上行测距信道使用的 CDMA码字进行传输；
组播帧重传模块， 在所述反馈信号接收模块接收到所述反馈信号后， 用于 为终端分配进行自动重传请求的上行资源后， 向终端发送广播消息， 在接收到 来自终端的所述自动重传请求后， 向终端重新传送组播帧。
本发明实施例还提供了一种可靠组播系统， 包括：
基站， 用于接收来自终端的没有正确接收到组播帧的反馈信号， 所述反馈 信号利用上行测距信道使用的 CDMA码字进行传输； 并为终端分配进行自动重 传请求的上行资源后， 向终端发送广播消息， 在接收到来自终端的所述自动重 传请求后， 向终端重新传送组播帧。
实施本发明实施例 , 具有如下有益效果：
在没有接收到来自基站的组播帧的情况下， 将上行测距信道使用的 CDMA 码字作为没有正确接收到组播帧的反馈信号发送给基站； 并在接收来自基站的 确认信号后， 向基站发送自动重传请求， 请求基站重新传送未能正确接收的组 播帧； 因此， 可以提高正确接收组播帧的数量， 减少上行资源所占用的带宽。 附图说明
图 1是测距信道的 CDMA码的发生器原理图；
图 1是测距信道传输机会示意图；
图 3是本发明实施例提供的可靠组播的实现方法的流程示意图；
图 4 ( a )和图 4 ( b )是组播重传延迟计算机仿真结果图；
图 5 ( a )、 图 5 ( b ) 和图 5 ( c )是在不同信道条件下， 实施本发明提供的 可靠组播实现方法相对单播重传机制节约的上行资源数量的示意图；
图 6是采用计算机仿真方法模拟不同信道状况和重传延迟条件下能够保证 所有丢包重传成功的最大 SS数量的示意图；
图 7是本发明实施例提供的可靠组播系统的结构示意图；
图 8是本发明实施例提供的实现可靠组播的终端的组成示意图；
图 9是本发明实施例提供的实现可靠组播的终端的组成示意图。 具体实施方式
本发明实施例提供了一种可靠组播的实现方法和系统， 以及实现可靠组播 的终端和基站， 保证了组播数据的完整性和可靠性。
本发明实施例基于 NAK机制， 对正确接收的組播帧不发送 ACK信号， 而 对没有接收到或者没有正确接收的帧发送 NAK信号作为反馈信息。本发明实施 例以利用 802.16 OFDMA模式的测距信道， 作为组播反馈域， 即在上行测距信 道中传送 NAK信号为例 , 说明本发明实施例提供的可靠组播的实现方法。
上行测距信道是 OFDMA模式的上行帧中用于终端进行初始测距、 周期测 距或者带宽请求的信道。 为了传输一个测距消息， 每个终端从一组特定的正交 CDMA码字中:i！机地选取一个作为传输码字，用二进制相移监控（ BPSK, Binary Phase-Shift Keying )调制置于上行测距信道（每个子载波 lbit )。
在上行测距信道中， 每个 CDMA码字的长度是 144bits , 由 15级伪随机序 列发生器产生 256 个不同的 CDMA码字。
CDMA的发生器如图 1所示， 每个基站使用这 256个码字的子集， 子集用 S ( 0 ~ 255 )表示， 子集中的码字从第 S个至第 （S+N+M+L ) mod 256个， 其中 前 N个码字用于初始距离修正， 中间 M个码字用于周期距离修正， 后 L个码字 用于带宽请求。 因此基站可以通过接收到的距离修正码字确定消息的用途。
在 802.16e中， 还增加了一种码字， 即切换测距 （handover-ranging )码字， 用 0表示。
如图 2所示， 在上行测距信道中还有传输机会的概念， 即成功传输一个 CDMA码字作为一个传输机会， 也可以称为传输时隙， 在上行测距信道中， 一 般会有若干传输机会。
本发明实施例提供的可靠组播的实现方法即： 为在上行测距信道能使用的 256个 CDMA码字中分出一部分码字作为组播帧没能正确接收的 NAK信号码 集， 所述 NAK信号由终端在基站分配的测距域中的任一时隙内， 即任选一个上 行测距信道的传输机会中进行竟争传输。
具体地， 参见图 3 , 为本发明实施例提供的可靠组播的实现方法的流程示意 图， 包括如下步骤：
在步骤 100, 若没有接收到来自基站的组播帧， 终端则将上行测距信道使用 的 CDMA码字作为没有正确接收到组播帧的反馈信号发送给基站；
具体地终端从提前设定的 CDMA码集中任选一个 CDMA码字作为反馈信 号， 所述反馈信号由终端在基站分配的测距域中的任一时隙内， 即任选一个上 行测距信道中的传输机会进行传输； 所述反馈信号具体为 NAK信号。
在步骤 101， 在接收到所述反馈信号后， 基站为终端分配进行自动重传请求 的上行资源， 并向终端发送广播消息；
具体地， 由于基站不能分辨哪个终端发送了 CDMA的组播帧 NAK信号，所 以， 一旦成功的接收到一个 CDMA的组播帧 NAK信号， 基站将向所有参加组 播的终端发送一个广播消息， 该广播消息为组播信息， 用于通知用户站收到的 CDMA码和接收该 CDMA码的上行测距信道时隙，并且在此组播信息中为终端 分配上行的 ARQ空间；
在步骤 102, 终端接收到基站发来的广播消息后， 在指定的 ARQ空间内向 基站发送自动重传请求， 请求基站重新传送未能正确接收的组播帧； 具体地， 终端接收来自基站的广播消息， 所述广播消息中包含基站为所述终端分配的上 行资源、 所述基站接收到的 CDMA码字以及接收该 CDMA码字的时隙；
终端根据所述广播消息中基站接收到的 CDMA码字和基站接收该 CDMA 码字的时隙， 判断该 CDMA码字是否为自身发送给基站的反馈信号所使用的 CDMA码字， 若是， 则通过所述基站为其分配的上行资源向基站发送自动重传 请求。
在步骤 103，基站接收来自终端的请求基站重新传送未能正确接收的组播帧 的自动重传请求后， 向终端重新传送组播帧；
在步骤 104， 终端接收基站重传的组播帧。
需要说明的是， 终端在上行测距信道内发送组播帧的 NAK信号时， 由于此 NAK码集的码字数量有限， 若两个或者更多的终端选择了同一个 CDMA码字， 并且在上行测距信道的同一个传输机会中进行传输， 则 CDMA码会产生碰撞， 使得传输失败。
此时采用截断的二进制指数算法， 向后回退若干时隙， 并且仍从原有的组播 帧 NAK信号的 CDMA码集中任意选择一个进行传输， 若仍然产生碰撞， 则继 续此截断的二进制指数算法过程。
在此， 本发明实施例采用截断的二进制指数算法为例进行回退， 在实施例中 也可以选择其他的回退算法。
第一次重发时， 从【0， 1】 中随机选择一个数 r， 后退 r*2t的时间（2t为端到 端往返传播时间 , 例如在 IEEE802.3中规定为发送 512bit所需时间）。
第二次重发时， 后退步长加倍， 从【0， 1 , 2, 3】 中随机选择一个数 r， 后 退 r*2t的时间。 第 10次重发时， 从【0, 1 , 2 210-1 ] 中随机选择一个数 r, 后退 r*2t的 时间。
第 11次重发时， 后退步长不再加倍， 从【0, 1 , 2, ...,21()-1】 中随机选择一 个数 r, 后退 r*2t的时间。
第 15次重发时， 从【0, 1 , 2, 210-1】 中随机选择一个数 r, 后退 r*2t 的时间。
如果还不成功， 则丢弃该数据帧， 并向上一层协议报告。 最大发送次数为 16次。 在前 10次重发中， 步长每次都加倍， 这就是所谓"二进制指数"。 在第 10次重发后， 后退步长不再加倍， 这就是所谓 "截断"。
由于无线传输有一定时延的要求， 在本发明实施例中可以在终端设置定时 器， 若超过一定时间仍然不能发送 CDMA信号， 则放弃对该组播帧的重传。
本发明实施例提供的可靠组播的实现方法， 可以提高正确接收组播帧的数 量， 并且相对单播重传的方式， 可以减少上行资源所占用的带宽。
本发明实施例还对可靠组播的实现方法做了仿真试验， 在现有的 WIMAX 系统条件下， 重传延迟在 30ms以内可以认为是有效的。 本发明实施例的仿真取 的组播重传延迟时间为 20ms和 25ms。 需要说明的是， 组播重传延迟时间指某 个未能正确接收到的组播帧经过本发明实施例提供的可靠组播技术进行正确接 收时， 相对该帧正常接收的情况下的延迟时间。
组播重传的成功接入率指在发生了某组播帧未能正确接收的情况下，通过本 方案能最后正确接收到该组播帧的 ss数量占所有未能正确接收到该组播帧的 ss 数量的百分比。
Backoff start指截断二进制指数回退算法的初始回退步长。
参见图 4, 是组播重传延迟时间计算机仿真结果图；
图 4 ( a )显示的是利用计算机仿真方法模拟组播重传延迟时间在 20ms内成 功传输 CDMA码的用户端 （SS) 的数量占所有需要重传的 SS (用户端， 即终 端）数量的百分比。 此处设每帧长 5ms, 每一帧有 6个上行测距信道传输机会， CDMA码数取为 16。 仿真运算次数为 100 次， 取其均值。 另外设基站在收到 NAK信号后， 立即发送确认信号， 终端收到确认信号后立即发送 ARQ信号， 未成功接收的组播信号立即安排重传， 这三个过程没有别的延时。
图 4 ( b )显示的是组播重传延迟时间在 25ms内成功传输 CDMA码的 ss的 数量占所有需要重传的 ss数量的百分比。
其他条件与图 4 (a)—致。
从图 4(a)和图 4(b)可以看出， 在图中需重传的用户数量下， Backoff start 为 1 时， 能够取得最大的组播重传的成功接入率。 这是因为在本发明所适用的 微蜂窝和微微蜂窝的情况下， 用户数量一般不是特别多。 比如从图中可以看出， 当需要重传的用户数量为 20时，成功接入率接近 100%;重传用户数量为 40时， 成功接入率仍然在 80%以上。 在一般的微蜂窝和微微蜂窝以及信道条件下， 本 发明均能较好地满足用户重传的要求。
图 5 (a)、 图 5 (b) 和图 5 (c) 显示的是在不同信道条件下， 实施本发明 提供的可靠组播实现方法相对单播重传机制节约的上行资源数量。
此处利用 Gilbert (吉尔伯特）模型， 模拟典型的无线信道的突发丢包特性。 Gilbert模型本身为本领域的技术人员所熟知的， 在此处不再赘述。 其中 ρι指模 型中的总平均丢包率， 为 0.05到 0.25, 以 0.05为步长， 模拟经典模型。 用户的 误比特率分别为 5xl0-3、 lxlO-3和 1x10- 4。 Ν^Ν^Ν 表示上行误比特率的用户 数量的比例， 比例不同， 结果也不同， 分别用图 5(a) 5(b), 5(c)来表示。 48 bits, 即是 6 bytes 作为一个上行单元， 纵轴表示上行单元的数量。
从图 5 (a)、 图 5 (b)和图 5 (c) 中可以看出， 由于本发明采用 NAK机制， 在经典的信道模型条件下， 本发明所需要的上行资源数量均少于单播重传条件 下的所用上行资源数量， 且信道条件越好， 误比特率越低的用户所占的比例越 大， 节约的上行资源数量越多。
图 6显示的是采用计算机仿真方法模拟不同信道状况和重传延迟条件下能 够保证所有丟包重传成功的最大 SS数量。
20ms与 25ms均指组播重传延迟时间， 以及 1: 1: 1、 1: 2: 3、 3: 2: 1 的定义与图 5 (a)、 图 5 (b)和图 5 (c)相同， 表示在误比特率 5xl0_3、 lxlO"3 和 lxlO"4的用户数量之比。
如图 6所示， 图中最高点显示 ^为 0.05, 重传延迟时间为 25ms, 用户误比 特率比例为 3: 2: 1 时， 只要组播用户的数量在 130之内， 所有用户未能正确 接收到的组播数据均能重传成功。 最低点显示 ^为 0.25， 重传延迟时间为 20ms, 用户误比特率比例为 1: 2: 3时， 只要组播用户的数量在 53之内， 所有用户未 能正确接收到的组播数据均能重传成功。 在微蜂窝与微微蜂窝的条件下， 本发 明能够满足实施使用情况的需要。
如果在用户特别多的情况下， 比如大区制的情况， 若仍然采用本发明实施 例中采用的传输机会， 以及用于组播重传的 CDMA 码字数量等参数， 将因为 CDMA码字在传输机会中的碰撞而不能很好的完成组播重传的要求， 此时可以 考虑修改参数， 比如增加每帧中的传输机会或者采用更多的用于组播重传的 CDMA码字的办法使得成功的组播重传得以实现。不过考虑到 CDMA码字数量 有限， 且在上行中传输机会占用的资源数量不能过大的因素， 本发明实施例适 用于微蜂窝或者微微蜂窝的情况。
参见图 7, 为本发明实施例提供的实现可靠组播的终端的组成示意图； 本发明实施例提供的可靠组播系统， 包括：
基站 2, 用于接收来自终端 1的没有正确接收到组播帧的反馈信号后， 为终 端 1 分配进行自动重传请求的上行资源， 并向终端发送广播消息； 所述广播消 息中包含基站接收到的 CDMA码字和接收该 CDMA码字的时隙， 以及所述上 行资源； 并且在接收到来自终端 1的所述自动重传请求后， 向终端 1重新传送 组播帧。
以下将详细阐述所述终端 1以及基站 2的功能和作用。
参见图 8, 为本发明实施例提供的实现可靠組播的终端的组成示意图； 该终端包括：
反馈信号发送模块 10, 用于在没有接收到来自基站的组播帧时， 则将上行 测距信道使用的 CDMA码字作为没有正确接收到组播帧的反馈信号发送给基 站； 具体地终端从提前设定 CDMA码集中任选一个 CDMA码字作为的反馈信 号，并任选一个上行测距信道中的传输机会进行传输；所述反馈信号具体为 NAK 信号。
广播消息接收模块 11 , 用于接收来自基站在成功接收所述反馈信号后， 向 所述终端返回的广播消息； 需要说明地的是， 该广播消息为组播信息， 用于向 终端通知基站收到的 CDMA码和接收该 CDMA码的上行测距信道时隙， 并且 在此组播信息中为终端分配上行的 ARQ空间；
重传请求发送模块 12,在广播消息接收模块接收到来自基站的广播消息后， 在指定的 ARQ空间向基站发送自动重传请求，请求基站重新传送未能正确接收 的组播帧；
具体地， 重传请求发送模块 12根据所述广播消息中基站接收到的 CDMA 码字和基站接收该 CDMA码字的时隙， 判断该 CDMA码字是否为自身发送给 基站的反馈信号所使用的 CDMA码字， 若是， 则通过所述基站为其分配的上行 资源向基站发送自动重传请求。
组播帧接收模块 13 , 用于接收基站重传的组播帧。
需要说明的是， 终端在上行测距信道内发送组播帧的 NAK信号时， 由于此 NAK码集的码字数量有限， 若两个或者更多的终端选择了同一个 CDMA码字， 并且在上行测距信道的同一个传输机会中进行传输， 则 CDMA码会产生碰撞， 使得传输失败。 当向基站发送没有正确接收到组播帧的 NAK信号后， 终端的确 认信号接收模块 11在定时间内没有收到基站返回的所述广播消息， 则通知反馈 信号发送模块 10通过 CDMA码字重新发送所述反馈信号。
此时采用截断的二进制指数算法， 向后回退若干时隙， 并且仍从原有的组播 帧 NAK信号的 CDMA码集中任意选择一个进行传输， 若仍然产生碰撞， 则继 续此截断的二进制指数算法过程。
因此所述终端还包括：
回退时隙计算模块 14, 用于采用回退算法计算出回退时隙， 则反馈信号发 送模块 10在回退的时隙内通过 CDMA码字重新发送所述 NAK信号。
参见图 9, 为本发明实施例提供的实现可靠組播的基站的组成示意图； 该实现可靠组播的基站， 包括：
反馈信号接收模块 20, 用于接收来自终端的没有正确接收到组播帧的反馈 信号， 所述反馈信号利用上行测距信道使用的 CDMA码字进行传输的 NAK信 号 · 组播帧重传模块 21 ,用于在所述反馈信号接收模块 20接收到所述反馈信号 后， 为终端分配进行自动重传请求的上行资源， 并向终端发送广播消息， 在接 收到来自终端的所述自动重传请求后， 向终端重新传送组播帧。
所述组播重传模块 21包括：
资源分配单元 210, 用于为终端分配进行自动重传请求的上行资源， 即分配 上行的 ARQ空间；
广播消息发送单元 211 , 用于所述反馈信号接收模块 20接收到的 CDMA码 过广播消息发往终端； 需要说明的是， 基站不能分辨哪个终端发送了 CDMA的 组播帧 NAK信号， 所以， 一旦成功的接收到一个 CDMA的组播帧 NAK信号， 基站将向所有参加组播的终端发送一个广播消息， 该广播消息为组播信息， 用 于通知用户站收到的 CDMA码字和接收该 CDMA码字的上行测距信道时隙， 并且在此组播信息中为终端分配上行的 ARQ空间；
重传请求接收单元 212,用于接收来自终端的请求基站重新传送未能正确接 收的组播帧的自动重传请求；
组播帧发送单元 213,在所述重传请求接收单元 212接收到来自终端的自动 重传请求后， 向终端重新传送组播帧。
本发明实施例提供了一种 WIMAX 系统的可靠组播方法及实现该方法的终 端和基站， 采用本发明实施例可以提高正确接收组播帧的数量， 并且相对单播 重传的方式， 可以减少上行资源所占用的带宽。
通过以上的实施方式的描述， 本领域的技术人员可以清楚地了解到本发明 可借助软件加必需的硬件平台的方式来实现， 当然也可以全部通过硬件来实施。 基于这样的理解， 本发明的技术方案对背景技术做出贡献的全部或者部分可以 以软件产品的形式体现出来， 该计算机软件产品可以存储在存储介质中， 如 ROM/RAM、 磁碟、 光盘等， 包括若干指令用以使得一台计算机设备 (可以是个 人计算机， 服务器， 或者网络设备等）执行本发明各个实施例或者实施例的某 些部分所述的方法。
以上所揭露的仅为本发明一种较佳实施例而已， 当然不能以此来限定本发 明之权利范围， 因此依本发明权利要求所作的等同变化， 仍属本发明所涵盖的 范围。

Claims

权 利 要 求
1、 一种可靠组播的实现方法， 其特征在于， 包括：
若没有接收到来自基站的组播帧， 则将上行测距信道使用的码分多址接入 CDMA码字作为没有正确接收到组播帧的反馈信号发送给基站；
接收来自基站的在收到所述反馈信号而发送的广播消息后， 向基站发送自 动重传请求， 请求基站重新传送未能正确接收的组播帧；
接收基站重传的组播帧。
2、 如权利要求 1所述的可靠组播的实现方法， 其特征在于， 所述反馈信号 由终端在基站分配的测距域中的任一时隙内发送至基站。
3、 如权利要求 1或 2所述的可靠组播的实现方法， 其特征在于， 所述方法 还包括：
当向基站发送没有正确接收到组播帧的反馈信号后， 终端在定时间内没有 收到基站返回的所述广播消息 , 则通过 CDMA码字重新发送所述反馈信号。
4、如权利要求 3所述的可靠组播的实现方法，其特征在于，所述通过 CDMA 码字重新发送所述反馈信号包括：
采用回退算法计算出回退时隙， 在回退的时隙内通过 CDMA码字重新发送 所述反馈信号。
5、 如权利要求 3所述的可靠组播的实现方法， 其特征在于， 所述没有正确 接收到组播帧的反馈信号是基于自动重传请求机制的未能确认 NAK信号。
6、 如权利要求 3所述的可靠组播的实现方法， 其特征在于， 所述作为反馈 信号的 CDMA码字选自上行测距信道使用的 CDMA码字集。
7、 如权利要求 1所述的可靠组播的实现方法， 其特征在于， 所述接收来自 基站的在收到所述反馈信号而发送的广播消息后， 向基站发送自动重传请求， 包括：
终端接收来自基站的在收到所述反馈信号而发送的广播消息， 所述广播消 息中包含基站为所述终端分配的上行资源、 所述基站接收到的 CDMA码字以及 接收该 CDMA码字的时隙；
终端根据所述广播消息中基站接收到的 CDMA码字和基站接收该 CDMA 码字的时隙， 判断该 CDMA码字是否为自身发送给基站的反馈信号所使用的 CDMA码字， 若是， 则通过所述基站为其分配的上行资源向基站发送自动重传 请求。
8、 一种可靠组播的实现方法， 其特征在于， 包括：
接收来自终端的没有正确接收到组播帧的反馈信号 , 所述反馈信号利用上 行测距信道使用的 CDMA码字进行传输；
为终端分配进行自动重传请求的上行资源后， 向终端发送广播消息； 接收来自终端的基站重新传送未能正确接收的组播帧的自动重传请求后， 向终端重新传送组播帧。
9、 如权利要求 8所述的可靠组播的实现方法， 其特征在于， 所述向终端发 送广播消息包括：
基站将其接收到的 CDMA码字以及接收该 CDMA码字的时隙连同所述分 配的上行资源通过广播消息发往终端。
10、 一种实现可靠组播的终端， 其特征在于， 包括：
反馈信号发送模块， 用于在没有接收到来自基站的组播帧， 则将上行测距 信道使用的 CDMA码字作为没有正确接收到组播帧的反馈信号发送给基站； 广播消息接收模块， 用于接收来自基站在接收所述反馈信号后返回的广播 消息；
重传请求发送模块， 在广播消息接收模块接收到来自基站的广播消息后， 向基站发送自动重传请求， 请求基站重新传送未能正确接收的组播帧；
组播帧接收模块， 用于接收基站重传的组播帧。
11、 如权利要求 10所述的实现可靠组播的终端， 其特征在于， 当向基站发 送没有正确接收到组播帧的反馈信号后， 终端的广播消息接收模块在定时间内 没有收到基站返回的所述广播消息， 则通知所述反馈信号发送模块通过 CDMA 码字重新发送所述反馈信号。
12、 如权利要求 10所述的实现可靠组播的终端， 其特征在于， 所述终端还 包括：
回退时隙计算模块， 用于采用回退算法计算出回退时隙； 则所述反馈信号 发送模块在所述回退时隙内通过 CDMA码字重新发送所述反馈信号。
13、 一种实现可靠组播的基站， 其特征在于， 包括：
反馈信号接收模块， 用于接收来自终端的没有正确接收到组播帧的反馈信 号， 所述反馈信号利用上行测距信道使用的 CDMA码字进行传输；
组播帧重传模块， 在所述反馈信号接收模块接收到所述反馈信号后， 用于 为终端分配进行自动重传请求的上行资源后， 向终端发送广播消息， 在接收到 来自终端的自动重传请求后， 向终端重新传送组播帧。
14、 如权利要求 13所述的实现可靠组播的基站， 其特征在于， 包括： 所述 组播帧重传模块包括：
资源分配单元， 用于为终端分配进行自动重传请求的上行资源；
广播消息发送单元， 用于将所述反馈信号接收模块接收到的 CDMA码字以 及接收该 CDMA码字的时隙， 连同所述资源分配单元分配的上行资源通过广播 消息发往终端；
重传请求接收单元， 用于接收来自终端的请求基站重新传送未能正确接收 的组播帧的自动重传请求；
组播帧发送单元， 在所述重传请求接收单元接收到来自终端的自动重传请 求后， 向终端重新传送组播帧。
15、 一种可靠组播系统， 其特征在于， 包括：
基站， 用于接收来自终端的没有正确接收到组播帧的反馈信号， 所述反馈 信号利用上行测距信道使用的 CDMA码字进行传输；
为终端分配进行自动重传请求的上行资源后， 向终端发送广播消息； 在接 收到来自终端的所述自动重传请求后， 向终端重新传送组播帧。
PCT/CN2009/070740 2008-03-31 2009-03-11 可靠组播的实现方法、系统以及终端和基站 WO2009121260A1 (zh)

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