Abstract:
The present invention is aimed at techniques for detecting the “partial loss” of an upper layer frame. One technique envisions a detection platform adapted to determine whether a packet is a final packet for a particular upper layer frame. A comparator platform then compares packets received free of transmission errors with variables indicative of whether all received packets in the particular upper layer frame have been received correctly when a final packet is detected. A transmission platform then sends a signal indicative of whether the packets received without transmission errors constitute the particular upper layer frame so that lost packets can be retransmitted quickly.

Description:
FIELD OF THE INVENTION 
   This invention relates to the fields of wireless and wire line communication networks and, more specifically, to methods and devices for the detection of the partial loss of an upper layer frame. 
   BACKGROUND OF THE INVENTION 
   A common function of a data communication system is to successfully send data “packets” containing desired information from a transmission point or node to a reception point or node. Before going further, it should be understood that the term “node” may indicate one or more hardware, software or firmware elements which may be combined or used separately to carry out transmission and/or reception of packets, etc. . . . In order for such a system to perform efficiently, bits of information are grouped together to form an “upper layer frame”. Upper layer frames are then further subdivided or concatenated into packets, the basic units used for transmission in a communication network. 
   A communication network&#39;s efficiency is measured by how many packets it can successfully send from a transmission node to a reception node in a given time period. This measurement is known as a network&#39;s “throughput”. Another measure of network efficiency is the amount of time it takes for a packet to get from a transmission node to a reception node. This performance metric is known as “delay”. An ideal communication network will transmit the maximum amount of packets between network nodes in the least amount of time. 
   Several factors prevent both wire line and wireless communication networks from achieving ideal throughput and delay performance. Principally among them are transmission failures caused by interference, weak transmissions or faulty reception. One known technique used to minimize network transmission failures utilizes an Automatic Repeat Request (ARQ) retransmission method of error correction. ARQ retransmission uses a “reverse acknowledgement” channel. This channel can be a stand-alone channel or multiplexed with a “reverse data channel”. A reverse acknowledgement channel allows a reception node to provide a transmission node with the status of transmitted packets. These status messages are aptly called “acknowledgements”. 
   ARQ retransmission is used, for example, in a radio link control protocol developed for third generation, 3G communication networks (3G is short for third generation, 3GPP/UMTS radio link protocol communication networks). These networks support wireless bandwidth requirements for telephone calls, global positioning systems, email, Internet access, videoconferencing and streaming audio and video. Today, 3G networks allow data to be transmitted between a transmission node and reception node over a range of 8 kb/sec to 2 MB/sec. Future enhancements may enable 3G networks to transmit data up to 10 MB/sec. An efficient ARQ retransmission method is essential in order to maintain network protocol integrity for commercial applications, especially when it comes to 3G networks which require high data transfer rates. 
   Before describing the details of the present invention, it may be helpful to first present a simplified explanation of ARQ retransmission and how it applies to 3G networks. 
   Referring to  FIG. 1 , there is depicted a simplified block diagram of a conventional communication network  100  comprising a communications channel  110 , an acknowledgement channel  112 , a reception node  104  and a transmission node  102 . In an existing ARQ retransmission method, the transmission node  102  is adapted to send packets stored in a memory unit  106 , which can also be referred to as a transmission buffer, along the communication channel  110  to a reception memory unit  108 , which can also be referred to as a reception buffer, for examination. Circuitry in the reception node  104  is adapted to examine the incoming packets in the reception memory unit  108  to determine whether they have been transmitted successfully, as further discussed below. If the reception node  104  receives a packet that contains corrupted data, the reception node  104  circuitry is adapted to send a status or acknowledgement message back to the transmission node  102  on the acknowledgement channel  112 . More to the point, the reception node  104  will only be adapted to send an acknowledgement when corrupted data is received. This type of ARQ retransmission method is known in the art as a “negative” acknowledgement (NACK) method. 
   Alternatively, the reception node  104  may be adapted to send an acknowledgement via the acknowledgement channel  112  to the transmission node  102  only when it is determined that a packet sent via communication channel  110  has been received without errors. This type of ARQ retransmission method is known in the art as a “positive” acknowledgement method. In this method, the transmission node  102  is adapted to wait for a predetermined time period to receive an acknowledgement from the reception node  104 . If an acknowledgement is not received within the predetermined time period, the transmission node  102  is adapted to retransmit the unacknowledged packet stored in the memory unit  106  to the reception node  104 . 
   It is known in the art that positive and negative ARQ retransmission methods can be combined into a “general” ARQ retransmission method where acknowledgements are sent from a reception node to a transmission node on an acknowledgement channel for every previously transmitted packet in the memory unit. Based on the received acknowledgements, the transmission node will be adapted to determine whether a given previously transmitted packet stored in the memory unit needs to be retransmitted to the reception node. Generally, the transmission node is adapted to wait until it receives an acknowledgement before it makes any decision on whether to continue to hold previously transmitted packets in the memory unit or to clear the unit for the next incoming stream of packets. 
   As mentioned above, a specific use of a general ARQ retransmission method is in 3G networks. Within a so-called “protocol stack” of a 3G network, a radio link control (RLC) layer contains protocols (e.g., a series of set instructions) used to carry out ARQ retransmission.  FIG. 2  is a simplified block diagram illustrating components of an RLC layer  200  relevant to our discussion. As shown, layer  200  comprises a transmission unit  202  and reception unit  210 . 
   The path of a packet can be traced through the RLC layer  200 . Upper layer(s)  102   u  send upper layer frames to the transmission unit  202  which is adapted to process such frames as follows. Before the upper layer frames can be transmitted, segmenting unit  204  is adapted to segment and/or concatenate them into packets. Thereafter, an RLC header unit  206  is adapted to add an RLC header to each packet. Packets are then placed in the memory unit  106  to wait for transmission. (Note that the memory unit may function as either a transmission or retransmission buffer and that these elements may be implemented either by one or more devices, platforms, programs or the like or separate devices). A multiplexer circuit  208  is adapted to select which packets from memory unit  106  will be transmitted during a next “transmission time interval” (TTI) and to calculate when the selected packets will be submitted to a lower layer  102   l  for actual transmission. If the memory unit  106  is implemented using separate transmission and retransmission elements, the selected packets can come from the transmission buffer element, retransmission buffer element or both. 
   A Medium Access Control (“MAC”) layer (not shown) determines the number of packets which can be transmitted per TTI and sends this information to RLC Layer  200  via pathway  300 . Header unit  206  is then further adapted to set certain fields, which may represent a variety of protocol variables, within each packet selected for transmission. 
   Subsequently, selected packets are transmitted via transmission lower layer section  102   l  to reception lower layer  104   l.    
   The reception section  210  is adapted to receive transmitted packets from the reception lower layer  104   l.  An expansion unit  212  is adapted to expand the received packets into separate packets and to place them in a reception memory unit  108  until packets associated with an entire reconstructed upper layer frame have been received. 
   At this point, the reception section  210  is adapted to generate and send acknowledgements and status information on individual packets stored in the reception memory unit  108  to the transmission section  202  as follows. A transceiving unit  214  is adapted to analyze whether the packets within the reception memory unit  108  have been received without errors. The unit  214  is further adapted to send this information to a transmission unit  216  via reverse link  112 . (A separate element, such as a reception node transmission unit, may also be adapted to send this information.) 
   Unit  216  is adapted to control the multiplexer circuit  208  in order to select packets for transmission during the next TTI. When packets are successfully received and acknowledged, a reception header unit  218  is adapted to remove the RLC header from each packet, reassemble the frame and to send the reassembled frame to upper layer  104   u.    
   It is generally believed that frequent acknowledgements allow retransmissions to be carried out quickly, which benefits delay performance and overall system efficiency. In addition, frequent acknowledgements allow a memory unit (transmission buffer) to be cleared more frequently. This reduces the likelihood that the memory unit will overflow. Furthermore, frequent acknowledgements can prevent instances of protocol stalling, which occurs when a transmission node is unable to transmit packets even though there are packets available for transmission in its memory unit. 
   On the other hand, frequent acknowledgements consume the bandwidth of a reverse link, degrade the throughput and delay performance of the reverse link and interfere with other transmissions. 
   For these and a variety of reasons, current acknowledgement techniques are inefficient. To be efficient, a communication network, including a 3G network, must make efficient use of its limited bandwidth to send the most amount of information in the least amount of time. While, as discussed above, existing acknowledgement techniques generally facilitate faster communications, these techniques must also be utilized efficiently or their benefit to a system&#39;s performance will be lost. Therefore, it is unacceptable to allow an uncontrolled volume of acknowledgement signals to be sent to a transmission node. 
   There is a particular need in the art of wireless and wire line communication network protocols, especially RLC layer acknowledgement protocols utilized in 3G communication networks, for acknowledgment techniques that balance the need to retransmit negatively or unacknowledged packets with the need to maintain overall network efficiency. Further, retransmission must be managed so that error correction can be invoked as fast as possible, but is utilized conservatively to prevent excessive delays and protocol stalling. 
   There is also a need in the art for techniques adaptable to rectify transmission errors occurring in 3G and other communication networks that improve the throughput of the network and reduce delays relative to current retransmission schemes. For data communication, where the integrity of the upper layer frames is essential to reliable service, such techniques should also be able to detect whether the transmission time of an upper layer frame has been prolonged, and appropriately retransmit associated packets to reduce the packet delay for the upper layer frame. 
   Finally, there is a need in the art for data packet retransmission techniques that incorporate the performance enhancing characteristics described above and are general enough to be incorporated into a variety of data communication networks, not just 3G communication networks. 
   SUMMARY 
   Accordingly, the present invention envisions techniques for detecting the partial loss of an upper layer frame. A detection platform determines whether a received packet is a final packet in a particular upper layer frame. A comparator platform is then adapted to compare variables indicative of whether all packets in the particular upper layer frame have been received correctly when a final packet is detected. Finally, a transmission platform is adapted to send a signal indicative of whether a correct version of the particular upper layer frame was received so lost packets can be retransmitted quickly. 
   Other features of the present invention will become apparent upon reading the following detailed description of the invention, taken in conjunction with the accompanying drawings and the appended claims. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a simplified block diagram of a conventional communication network with an acknowledgement channel from a reception node to a transmission node. 
       FIG. 2  is a simplified block diagram illustrating elements of an RLC layer which may be used to carry out techniques envisioned by the present invention. 
       FIG. 3  is a flow diagram illustrative of techniques according to embodiments of the present invention. 
       FIG. 4  is a block diagram of a radio network controller according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Those skilled in the art should note that while certain elements of the following invention are referred to as transmission or reception nodes, the functions of these elements can be carried out by the same program, module or device, such as a transceiver. The nomenclature in the discussion above and below is used merely to present features and functions of the invention in a clearer form, rather than to limit any particular program, module or device that may be utilized to implement these features and functions. 
   One embodiment of the present invention is implemented within a 3G communication network. However, the present invention is robust enough to be applied to any communication network that utilizes retransmission. The protocol stack for a preferred 3G communication protocol consists of a few layers, among them the RLC layer, a lower layer and a MAC layer. The present invention envisions the retransmission of packets from the RLC layer. In one embodiment of the present invention, a TTI comprises a predetermined time interval that begins when an RLC layer sends packets to a lower layer for transmission. 
   Before going any further, it should be understood that the elements shown in  FIG. 2  may be modified to carry out the features and functions envisioned by the present invention as described below. 
     FIG. 3  is a flow diagram illustrative of a technique for detecting the partial loss of an upper layer frame. In one embodiment, this technique utilizes a “detection of missing data packets” RLC protocol that causes an acknowledgement transmission to be sent from a reception node, such as node  104  in  FIG. 2  to a transmission node  102  when the partial loss of an upper layer frame is detected. This technique manages the volume of acknowledgement signals and thus, maximizes network efficiency and speed. In this embodiment, each upper layer frame is associated with a variable, predetermined time period which may be reset whenever an acknowledgement transmission is triggered by missing packets in the upper layer frame. The acknowledgement transmission takes the form of a “status report” packet, but because the inventions envisioned by the inventors are not limited to any particular communications protocol, other methods of sending acknowledgement signals are equally suitable. 
   In operation, a transmission node  102  is adapted to transmit packets and the reception lower layer  104   l  is adapted to receive at least one previously transmitted packet in step  300 . A platform  216   p  is adapted to transmit at least one packet in a particular upper layer frame and to implement various other functions using any combination of hardware, software and/or firmware. The received packets are then routed to the reception memory unit  108  for analysis by the unit  214 . The unit  214  comprises a platform  214   p  which again may comprise hardware, software, firmware or any combination of these elements adapted to implement the various functions described below. The platform  214   p  comprises a transmission platform adapted to send acknowledgement signals. 
   Continuing, when a packet is successfully received, then the platform  214   p  is adapted to update a receiver variable, which can be a receiver state variable, VR(R), indicative of the sequence number (SSN) of the next in sequence packet expected to be received. If a received packet contains corrupted data, it can be discarded from the reception memory unit  108  in step  306  because retransmission will be necessary. 
   It should be noted that in the RLC protocol environment, the platform  216   p  may be adapted to set a polling bit in a “packet header” in order to instruct platform  214   p  to send an acknowledgement signal for previously transmitted packets at any time as in step  308 . If the polling bit is set then, notwithstanding other trigger protocols in step  310 , the platform  214   p  is adapted to send an acknowledgement transmission back to platform  216   p  regarding the status of the previously transmitted packets in step  312 . 
   The platform  214   p  may further comprise a comparator platform that is adapted to determine that a received packet is the final packet for a particular upper layer frame as in step  314 . The platform  214   p  is further adapted to compare the SSN of the received packet with the receiver state variable VR(R) to determine whether they are equal in step  316 . If they are not equal, this indicates that there are one or more packets that have not been successfully received for the particular upper layer frame. 
   If the predetermined time period associated with a particular upper layer frame has expired in step  320 , the platform  214   p  is further adapted to send an acknowledgement signal indicative of whether a correct version of the particular upper layer frame was received. (As stated above, it should be noted that the acknowledgement signal triggered by the “detection of missing data packets” RLC protocol is regulated by a predetermined time period associated with the upper layer frame.) In an alternative embodiment, the platform  214   p  is adapted to send another signal indicative of which additional packets of the correct version of the particular upper layer frame need to be received in step  312 . For example, this signal could contain a complete list of missing sequence numbers representing the packets that need to be retransmitted in order to reconstitute the upper layer frame. The predetermined time period associated with the particular upper layer frame is reset when the platform  214   p  sends an acknowledgement signal in step  322 . On the other hand, if the platform  214   p  determines that the magnitudes of the state variables are equal and the received packet is determined by the platform  214   p  to be the last in-sequence packet of the particular upper layer frame, then the entire particular upper layer frame has been successfully received. 
   In another embodiment, if the platform  214   p  determines that the received packet is not the final packet for the particular upper layer frame, then the platform  214   p  is further adapted to determine whether the received packet belongs to a next particular upper layer frame in step  318 . If the received packet does not belong to a next particular upper layer frame, then there are still packets yet to be received for the (current) particular upper layer frame. If, though, the received packet does belong to a next particular upper layer frame, then the state variables for the current particular upper layer frame are not equal in step  316  and at least the final packet for the current particular upper layer frame has not been successfully received. If the predetermined time period associated with the current particular upper layer frame has expired in step  320 , the platform  214   p  is adapted to send a signal indicative of which additional packets of the correct version of the particular upper layer frame need to be received from platform  216   p  as in the embodiment described above. The platform  214   p  resets the predetermined time period when it sends an acknowledgement signal in step  322 . 
   In yet another alternative embodiment, the received packet may comprise a “super field” series of header control bits that identifies the packet&#39;s particular upper layer frame. The platform  214   p  is further adapted to detect whether a received packet comprises a super field and to analyze the super field to determine whether the packet is in a particular upper layer frame. Likewise, the platform  214   p  is adapted to analyze the super field to determine whether the packet is in a next particular upper layer frame. 
   In summation, unless platform  216   p  requests status information by setting a polling bit in accordance with the RLC protocol, the platform  214   p  is adapted to limit the number of acknowledgement signals sent to a transmission node  102  by detecting all of the missing packets for a particular upper layer frame and waiting for a predetermined time period to expire before sending an acknowledgement transmission to platform  216   p.    
     FIG. 4  is a simplified block diagram of a device  400 , such as a traffic processing unit (TPU) adapted to retransmit packets according to one embodiment of the present invention. TPU  400  may comprise one or more platforms  401 – 404  for carrying out the features and functions of the present invention described above. TPU  400  may be located within a radio network controller. 
   The present invention has been described with regard to particular embodiments, all of which are intended to be illustrative rather than restrictive. Alternate embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. For example, some or all of the platforms and components in the transmission section  202  and reception section  210  may be combined or further divided into additional components. Further, each platform and component may comprise a software/firmware program or programs, hardware or some combination of the two adapted to carry out the features and functions of the inventions described above and below. The scope of the present invention is described by the appended claims and supported by the foregoing description.