English:
[0001] The present invention relates to a method and system to enhance the coverage of uplink packet voice application—Voice over IP (VoIP). Specifically, the invention relates to assigning multiple hybrid automatic repeat request (HARQ) processes simultaneously for one VoIP user.
[0002] With new technologies such as advanced multi-antennas, carrier aggregation, orthogonal frequency division multiple access (OFDMA), system capacities of cellular networks have been increased significantly. The voice application was traditionally carried over circuit switch networks, with dedicated physical channels. Once the dedicated channel is allocated to a user, it remains to be reserved for that user until the call is ended. To meet the ever growing demand for data traffic, the wireless networks are migrating from circuit voice switch to packet switch. The emerging 4G cellular networks would be full IP serviced, including for voice. The voice application carried over IP networks is called VoIP. Compared to circuit switch voice, VoIP allows dynamic resource allocation to match the voice activities and multiple voice users can compete for the same resources during the calls. Speed coding study shows that when a user is talking over the phone, there is no voice activity for about half of time during which the user is either pausing or remaining silent to listen. VoIP traffic is only allocated with physical resources when the user is in talk spurt, thus significantly improves the resource utilizations. Advanced technologies such as HARQ can be applied for VoIP so that the transmission can adapt to the fast fading of the channel, thereby saving radio resources. With the above features, VoIP generally can increase the voice capacity of a system compared to circuit switch voice.
[0003] Although VoIP can deliver higher capacity of voice, its coverage is generally poorer than circuit switch voice. The main reason is the discontinuous transmission of VoIP packet. Discontinuous transmission is a fundamental characteristic of data transmission in 3G and 4G cellular networks. By restricting a data packet within a short transmit time interval (TTI) for example in the order of 1 millisecond, dynamic scheduling can be efficiently carried out. The short TTI also enables fast HARQ retransmission, with round trip time (RTT) in the order of 8-10 milliseconds, which is helpful for link adaptation to fast fading. Since 3G and 4G wireless standards are wideband, typical of 5~20 MHz, the short TTI provides finer granularity for resource allocation at least in time domain, so that smaller packet can also be efficiently scheduled. It also fits the bursty nature of data traffics. However, short TTI and bursty transmission are not favourable to users at cell edges where the coverage is often limited by the maximum transmit power of the terminals for uplink traffics.
[0005] Even with 4 TTI bundling, the coverage of VoIP still cannot match that of circuit switch voice. For example, in 3G UMTS, the TTI of circuit switch voice is 20 milliseconds. In LTE, the TTI of VoIP with TTI bundling is 4 milliseconds. Given that voice packets from upper layer would arrive at physical layer every 20 milliseconds during a talk spurt, the over- the-air transmission should be finished within 20 milliseconds, to avoid the accumulation and delay at the transmission queue. The round trip time (RTT) in the case of 4 TO bundling is a little longer than without TTI bundling, in the order of 12 to 16 milliseconds. That means the transmission should be finished with two HARQ transmissions. So effectively, about 8 milliseconds are spent on a VoIP packet transmission, which is significantly shorter than 20 millisecond TTI of UMTS circuit switch voice. In another word, the issue of discontinuous transmission is not completely solved by TTI bundling, which leads to the remaining gap in coverage between circuit switch voice and VoIP.
[0006] In accordance with one aspect, the present invention comprises a method of improve the uplink coverage of VoIP by assigning multiple HARQ processes simultaneously for a VoIP user during a talk spurt. Each VoIP packet is assigned an HARQ process.
[0007] According to the present invention, different physical resources can be allocated for different HARQ processes of a VoIP user.
[0008] According to the present invention, semi-persistent scheduling can be applied to either one of the HARQ processes for a VoIP user.
[0010] In another aspect, the invention comprises a system whose VoIP uplink coverage can be improved by assigning multiple HARQ processes for a VoIP user. The system comprises different physical resources allocated for different HARQ processes of a VoIP user, with possible semi-persistent scheduling and TTI bundling in either one of the HARQ processes.
[0011] Figure 1 shows an example of assigning multiple HARQ processes simultaneously for a VoIP user.
[0012] The invention considers improving the continuity of VoIP transmission by assigning multiple HARQ processes simultaneously for one VoIP user during a talk spurt. In conventional VoIP, one HARQ process is assigned for each VoIP user, in order to simplify the MAC layer and physical layer processing. Since the round trip time (RTT) of HARQ is at least 8 ms, using only one HARQ process results in transmission gap between HARQ (re)transmissions, even when 4 TTI bundling is used.
[0013] The invention is illustrated in an example shown in Figure 1. Two HARQ processes are allocated for this particular VoIP user that is in a talk spurt. Upon two VoIP packets arrive from the upper layer, each VoIP packet would be assigned with an HARQ processes, i.e., VoIP packet 1 is assigned HARQ proc_id = 0, with lighter gray color. VoIP packet 2 is assigned HARQ proc_id = 1, with darker gray color. Packet 2 is transmitted 4 milliseconds after Packet 1 is transmitted. One TTI or one subframe (SF) equals one millisecond. 4-TTI bundling (over 4 consecutive subframes) is applied to each HARQ process. Different HARQ processes can use different physical resources as seen in Figure 1. Semi-persistent scheduling is assumed where the physical resources for each HARQ process remain the same for both initial transmissions (1stHARQ) and retransmissions (2ndHARQ). The round trip time is 8 milliseconds. By assigning two HARQ processes simultaneously, there is only a gap of 4 milliseconds when there is no transmission at all, significantly smaller than assigning only one HARQ process at a time.
[0014] Figure 1 is just one example. In fact, it is found that if 8-TTI bundling is allowed, the gap can be completely eliminated by assigning two HARQ processes simultaneously for a VoIP user.
[0015] It should be understood that the methods and devices of the present invention may be executed employing machines and apparatus including simple and complex computers. Moreover, the architecture and methods described above can be stored, in part or in full, on forms of machine-readable media. For example, the operations of the present invention could be stored on machine-readable media, such as magnetic disks or optical disks, which arc accessible via a disk drive (or computer-readable medium drive). Alternatively, the logic to perform the operations as discussed above, could be implemented in additional computer and/or machine readable media, such as discrete hardware components as large-scale integrated circuits (LSI's), application-specific integrated circuits (ASIC's), firmware such as electrically erasable programmable read-only only memory (EEPROM's); and the like.
[0016] Many modifications and alterations of the new methods and systems described herein may be employed by those skilled in the art without departing from the spirit and scope of the invention which is limited only by the claims.

中文:
[0001]本发明涉及用于增强上行分组话音应用的覆盖,即用于增强IP上的话音传输(VoIP)的覆盖的方法和系统。具体地,本发明涉及为一个VoIP用户同时分配多个混合自动重传请求(HARQ)过程。
[0002]利用比如先进的多天线、载波聚合、正交频分多址接入(OFDMA)的新技术,蜂窝网络的系统容量已经显著提高。话音应用传统上是在电路交换网络上进行的,并使用专用的物理信道。一旦专用信道被分配给用户,该专用信道将一直为该用户保留,直到呼叫结束。为了满足对数据业务日益增长的需求,无线网络从电路话音交换演进到分组交换。正在出现的4G蜂窝网络将是全IP服务的(其中包括对话音的服务)。在IP网络上进行的话音应用被称作VoIP。与电路交换话音相比,VoIP允许动态资源分配以匹配话音活动,并且多个话音用户可以在呼叫期间竞争相同的资源。速度编码研究表明当用户正通过电话交谈时,其中有大约一半的时间是没有话音活动的,在这段时间用户要么停顿,要么保持沉默进行倾听。VoIP业务仅在用户发表谈话时(talkspurt)被分配以物理资源,从而显著提高了资源的使用。比如HARQ的高级技术可以被用于VoIP,使得传输能够适应信道的快速衰落,从而节省无线资源。利用上面的特点,VoIP通常能够提高系统相对于电路交换话音的话音容量。
[0003]虽然VoIP能够传递高话音容量,但是其覆盖通常比电路交换话音的要差。主要原因是VoIP分组是不连续传输的。不连续传输是在3G和4G蜂窝网络中的数据传输的基本特性。通过将数据分组限制在短的传输时间间隔(TTI)之内(例如在1毫秒的量级),可以有效地执行动态调度。短TTI也使快速HARQ重传成为可能,其具有在8至10毫秒量级的往返时间(RTT),这对于快速衰落的链路自适应是有益的。因为3G和4G无线标准带宽较宽,通常是5MHz至20MHz,所以短TTI至少在时域中提供了用于资源分配的更精细的粒度,使得更小的分组也能够被有效调度。这同样适合数据业务的突发特性。然而,短TTI和突发传输对小区边缘用户不利,因为在小区边缘的覆盖通常受到终端用于上行业务的最大发射功率的限制。
[0005]即使使用4个TTI绑定,VoIP的覆盖仍然不能匹配电路交换话音的覆盖。例如,在3GUMTS中,电路交换话音的TTI是20毫秒。在LTE中,利用TTI绑定的VoIP的TTI是4毫秒。给定来自高层的话音分组将在发表谈话期间每20毫秒到达物理层,那么在空口的传输将在20毫秒之内完成,以避免传输队列的累积和延迟。在4个TTI绑定情况下的往返时间(RTT)比不使用TTI绑定时稍长,在12至16毫秒的量级。这意味着传输将利用两个HARQ传输完成。如此有效地,大约8毫秒的时间用于VoIP分组传输,这显著短于UMTS电路交换话音的20毫秒的TTI。换句话说,不连续传输的问题并没有被TTI绑定完全解决,这导致了在电路交换话音和VoIP之间的覆盖中残留的间隙。
[0006]根据一个方面,本发明包括用于通过为发表谈话期间的VoIP用户同时分配多个HARQ过程来提高VoIP的上行覆盖的方法。每个VoIP分组被分配一个HARQ过程。
[0007]根据本发明,不同的物理资源能够被分配给VoIP用户的不同的HARQ过程。
[0008]根据本发明,对VoIP用户的两个HARQ过程的每一个都可以应用半持续调度。
[0010]在另一个方面,本发明包括其VoIP上行覆盖能够通过为VoIP用户分配多个HARQ过程而提高的系统。系统包括为VoIP用户的不同的HARQ过程分配的不同物理资源,在两个HARQ过程的每一个中使用可能的半持续调度和TTI绑定。
[0011]图1示出了为VoIP用户同时分配多个HARQ过程的示例。
[0012]本发明考虑通过为发表谈话期间的VoIP用户同时分配多个HARQ过程来提高VoIP传输的连续性。在传统的VoIP中,为每个VoIP用户分配一个HARQ过程,以简化MAC层和物理层的处理。因为HARQ的往返时间(RTT)是至少8毫秒,所以仅仅使用一个HARQ过程导致了在HARQ传输(重传)之间的传输间隙,即使使用4个TTI绑定时也是这样。
[0013]在图1中以示例方式示出了本发明。两个HARQ过程被分配给了正在发表谈话的这个特定的VoIP用户。当来自高层的两个VoIP分组到达时,每个VoIP分组将被分配一个HARQ过程,即VoIP分组1被分配HARQproc_id=0,并用较浅的灰色表示。VoIP分组2被分配HARQproc_id=1,并用较深的灰色表示。分组2在分组1传输4毫秒之后传输。一个TTI或一个子帧(SF)等于一毫秒。4个TTI绑定(在4个连续子帧上)被应用于每个HARQ过程。如图1中所示,不同的HARQ过程可以使用不同的物理资源。假定采用半持续调度,其中用于每个HARQ过程的物理资源对于初始传输(第一个HARQ)和重传(第二个HARQ)保持相同。往返时间是8毫秒。通过同时分配两个HARQ过程,其中在完全没有传输时仅有4毫秒的间隙,显著小于一次仅分配一个HARQ过程的间隙。
[0014]图1仅仅是一个示例。事实上,已经发现如果允许8个TTI绑定,那么通过同时为VoIP用户分配两个HARQ过程,间隙能够被完全消除。
[0015]应当理解的是,本发明的方法和设备可以运用包括简单计算机和复杂计算机的机器和装置执行。而且,上述结构和方法可以被部分存储或全部存储在各种形式的机器可读介质上。例如,本发明的操作能够被存储在比如通过磁盘驱动器(或计算机可读介质驱动器)可以访问的磁盘或光盘的机器可读介质上。可选择地,用来执行上述操作的逻辑可以在另外的计算机和/或比如分离的硬件组件(如大规模集成电路(LSI)、专用集成电路(ASIC)、比如电可擦除可编程的只读存储器(EEPROM)的固件)等的机器可读介质上实现。特定实施方式的实现还可以采用机器实现(包括网页实现)的计算机软件的形式。
[0016]在此描述的新方法和系统的许多修改和改变可以被本领域的那些技术人员所采用,而没有背离本发明的精神和范围,本发明的精神和范围仅由权利要求所限定。