Abstract:
Apparatus, and an associated method, that reduces the occurrence of generation of redundant requests for retransmission of packet-formatted data, formatted at a physical layer and at a higher-logical layer, such as at an RLP layer. An estimate of an appropriate delay period is formed. The estimate is responsive to communication conditions in the communication system. When a data packet appears to have been inadequately delivered to the RLP logical layer, a DELAY_DETECTION_WINDOW timer is caused to time out the delay period estimated by the estimator. The request for retransmission, generated at the RLP layer, is permitted, upon expiration of the timer if the data packet has not yet been successfully delivered to the RLP layer and the transmitter has not given up the data packet delivery.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of U.S. patent application Ser. No. 10/285,899 filed Oct. 31, 2002 which is hereby incorporated herein in its entirety by reference. 
     
    
     BRIEF SUMMARY OF THE INVENTION  
       [0002]     The present invention relates generally to a manner by which to coordinate retransmission requests in a packet-based communication system. The communication system utilizes more than one packet-formatting layer, each of which uses a packet retransmission scheme, such as a packet radio communication system that utilizes an RLP (radio link protocol) layer positioned upon a lower-layer that utilizes H-ARQ (hybrid automatic request) packet retransmissions. More particularly, the present invention relates to apparatus, and an associated method, by which selectively to delay RLP, or other, retransmission requests at that layer to provide more time at the lower-layer for the lower-layer retransmission scheme to be carried out. Prior to sending the higher logical-layer retransmission request, a delay time is required to elapse. If, upon timing-out of the delay time, data is not adequately received, the RLP, or other higher logical-layer, retransmission request is sent. And, the delay time is a selectable value, selected responsive to indicia associated with communications in the communication system.  
         [0003]     Improved communication efficiency is provided as redundant retransmission requests, originated at different logical-layers defined in the communication system, to request retransmission of the same data are less likely to be generated.  
       BACKGROUND OF THE INVENTION  
       [0004]     A communication system is used to communicate data between two, or more, separate positions, or entities. In a minimal implementation, a communication system is formed of a first communication station forming a sending station and a second communication station, forming a receiving station. The communication stations are interconnected by way of a communication channel. Data to be communicated by the first communication station is converted, if necessary, into a form to permit its communication upon the communication channel to the second communication station. And, the second communication station operates to detect the data communicated thereto and to recover the informational content thereof.  
         [0005]     A wide variety of different types of communication systems have been developed and are regularly utilized to effectuate communication of the data between the communication stations. And, new types of communication systems, as well as improvements to existing communication systems, have been made possible as a result of advancements in communication technologies.  
         [0006]     A radio communication system is exemplary of a type of communication system that has benefited from advancements in communication technologies. In a radio communication system, the communication channel formed between the communication stations operable therein is defined upon a radio link. As a radio link is utilized upon which to define the communication channel, the need otherwise to utilize a wireline connection extending between the communication stations to define communication channels is obviated. Reduced infrastructure costs are therefore generally associated with radio communication systems. And, a radio communication system can be implemented to form a mobile communication system.  
         [0007]     A cellular communication system is exemplary of a radio communication system that has been made possible due to advancements in communication technologies. A cellular communication system provides for radio communications with mobile stations to permit the telephonic communication to be effectuated therefrom. A cellular communication system is installed throughout a geographical area through the use of spaced-apart base transceiver stations, each of which define a portion of the geographical area, referred to as a cell. When a mobile station is within the cell defined by a base transceiver station, communications are generally effectuable with the base transceiver station that defines the cell.  
         [0008]     Communications are handed-off between successive base transceiver stations when the mobile station travels out of one cell and into other cells, defined by others of the base transceiver stations. Through appropriate positioning of the base transceiver stations and permitting communication hand-offs to successive ones of the base transceiver stations, only relatively low-powered signals need to be generated during telephonic communications between the mobile station and the base transceiver station. As a result, the same channels can be used at different locations of the same cellular communication system. Relatively efficient usage of the frequency spectrum allocated to a cellular communication system is thereby possible.  
         [0009]     Cellular communication systems are constructed, generally, to operate according to an operational specification set forth by a standard body, such as the EIA/TIA. Successive generations of cellular communication systems, incorporating technological advancements, as available, have been defined by operational specifications. First generation and second-generation systems have achieved significant levels of usage, and installation of third-generation and successor-generation systems have been proposed.  
         [0010]     Third-generation systems provide for multi-rate data communication services that utilize packet-formatted data. A so-called CDMA 2000 standard is an exemplary third generation communication system, intended to provide such multi-data rate communication services utilizing communication of packet-formatted data.  
         [0011]     Structure, and functionality, defined in the proposed CDMA 2000 system is defined in terms of logical layers. Other communication systems are analogously defined in such terms. In a CDMA 2000 system, multiple formatting layers are set forth. And, in particular, an RLP (radio link protocol) layer is positioned above a physical layer. The RLP layer utilizes an RLP retransmission scheme while the physical layer utilizes an HARQ (hybrid-automatic request) retransmission scheme. The retransmission schemes define retransmission protocols by which a receiving station selectively requests retransmission of a packet of data upon failure of successful delivery of the data packet to the receiving station. Because retransmission schemes are provided for separate layers, retransmission requests might be sent by both the RLP layer as well as at the physical layer. Such redundancy of retransmission requests are counterproductive to a goal of efficient radio spectrum usage.  
         [0012]     A manner is needed by which to reduce the possibility that the multiple layers of a receiving station might redundantly request retransmission of a data packet.  
         [0013]     It is in light of this background information related to communications in a packet radio communication system that the significant improvements of the present invention have evolved.  
       SUMMARY OF THE INVENTION  
       [0014]     The present invention, accordingly, advantageously provides apparatus, and an associated method, by which to coordinate retransmission requests in a packet-based communication system. The packet-based communication system utilizes more than one packet-formatting layer, each layer utilizing a packet retransmission scheme, such as a packet radio communication system that utilizes an RLP (radio link protocol) layer positioned upon a lower-level layer that utilizes HARQ.  
         [0015]     Through operation of an embodiment of the present invention, a manner is provided by which selectively to delay RLP, or other higher, logical layer, retransmission requests, at that layer to provide more time at the lower layer for the lower-layer retransmission scheme to be carried out.  
         [0016]     The higher logical-layer retransmission request is delayed by a delay time. If, upon expiration of the delay time, data is not adequately received, the RLP, or other higher logical-layer, retransmission request is sent.  
         [0017]     As the possibility that redundant retransmission requests, generated at separate logical layers, is reduced, improved communication efficiency in the communication system is possible. That is to say, multiple retransmission requests, originated at different logical-layers defined in the communication system, that request retransmission of the same data is reduced.  
         [0018]     In one aspect of the present invention, an estimate is made of a suggested time delay of the delay time by which to delay the retransmission request by the higher logical-layer. The estimate is formed responsive to indicia associated with communication conditions in the communication system. The indicia is formed, for instance, of traffic load information indicative of ongoing traffic, i.e., communications, in the communication system, HARQ information associated with active communications, QoS (quality of service) requirements of active, or anticipated, communications in the communication system, communication quality indicative of communication quality of communication activity in the communication system, as well as other types of radio quality information.  
         [0019]     The estimation is formed, in one implementation, at the network part of the radio communication system and communicated to the mobile station whereat the mobile station stores the estimation value. And, in another implementation, the estimation is made at the network part of the communication system, communicated to the mobile station whereat the mobile station selectively modifies, or substitutes, an altered estimation value therefore.  
         [0020]     In another aspect of the present invention, the estimation defines a delay period bounded by an upper value, a lower value, and a suggested value. When data appears at an RLP layer, or other higher-logical-layer, to have been unsuccessfully delivered thereto, a delay period of a delay time within the range of values defined by the delay period is required to expire prior to generation of the retransmission request.  
         [0021]     In another aspect of the present invention, a receiving station, such as a mobile station, that receives packet-formatted data during a communication session, includes a timer called DELAY_DETECTION_WINDOW (DDW) which is capable of timing-out a selected delay time. When the RLP, or other higher logical-layer, of the receiving station fails adequately to receive a data packet, the DDW timer is started. If the packet is not adequately received at the receiving station by the time that the timer times-out, the retransmission request is generated by the RLP, or other higher logical-layer. The delay is instituted to provide an additional time period to permit a lower logical-layer, such as a physical layer, HARQ retransmissions scheme, to effectuate the retransmission of the data packet.  
         [0022]     In one implementation, a retransmission scheme is provided for a cellular communication system constructed, generally, to be operable pursuant to a CDMA 2000 operational specification. The operational specification provides for high-speed, multi data rate communications. The data communications are, for instance, pursuant to a 1xEV-DV packet data service scheme. The communication system is defined in terms of logical layers that include, amongst others, a physical layer and an RLP (radio link protocol) layer positioned thereabove. The base transceiver station includes estimator functionality thereof. The estimator forms an estimate of a suggested RLP layer retransmission delay period. The delay period defines a time period by which a retransmission request is suggested to be delayed at the RLP layer upon determination that a data packet has not successfully been delivered thereto. Once the estimate is formed, an RLP Block of Bits (BLOB) containing an RLP-delay indication is sent by the base station to the mobile station, or other receiving station. And, once delivered to the receiving station, the values contained in the RLP-delay message are extracted and used to set the time-out value of a timer formed thereat. Upon an indication that an RLP layer packet is not successfully delivered to the RLP layer of the mobile station, or other receiving station, a request for retransmission of the packet is delayed until the DDW timer times-out. If, upon expiration of the period timed by the timer, the RLP data packet is not successfully delivered to the RLP layer of the mobile station, a retransmission request is generated. Note that the retransmission request can be generated prior to the expiration of the DDW timer if the mobile station determines that the base transceiver station has given up the delivery of the missing RLP data packet.  
         [0023]     Because the generation of the retransmission request is delayed for a time period corresponding to the suggested, or otherwise responsive to, the estimated time delay, the possibility that redundant retransmission requests, generated at separate logical layers of the receiving station, is reduced.  
         [0024]     In these and other aspects, therefore, apparatus, and an associated method, is provided for a radio communication system. The radio communication system is operable to communicate packet-formatted data between a first communication station and a second communication station. The packet-formatted data is formatted at a first logical layer, utilizing a first-layer acknowledgment mechanism by which the second communication station selectably acknowledges whether the packet formatted data is adequately received thereat at the first logical layer. And, the packet-formatted data is formatted at a second logical layer, utilizing a second-layer acknowledgement mechanism by which the second communication station selectably acknowledges whether the packet-formatted data is adequately received thereat at the second logical layer. Efficient usage of the radio capacity in the radio communication system is facilitated. An estimator is coupled to receive indicia associated with communication characteristics of the first logical layer. The estimator estimates a selected second-layer delay period by which to delay generation, at the second communication station, of a second-layer resend request requesting resending of the packet-formatted data.  
         [0025]     A more complete appreciation of the present invention and the scope thereof can be obtained from the accompanying drawings that are briefly summarized below, the following detailed description of the presently-preferred embodiments of the invention, and the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]      FIG. 1  illustrates a functional block diagram of a communication system in which an embodiment of the present invention is operable.  
         [0027]      FIG. 2  illustrates a functional representation of two logical layers of portions of the communication system shown in  FIG. 1 .  
         [0028]      FIG. 3  illustrates a message sequence diagram listing the signaling generated during operation of an embodiment of the present invention forming a portion of the communication system shown in  FIGS. 1 and 2 .  
         [0029]      FIG. 4  illustrates a representation of an exemplary RLP delay message generated during operation of an embodiment of the present invention.  
         [0030]      FIG. 5  illustrates a method flow diagram listing the method of operation of an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0031]     Referring first to  FIG. 1 , a communication system, shown generally at  10 , provides for the communication of data between spaced-apart communication stations, here a base transceiver station  12  and a mobile station  14 . Communication channels are defined upon radio links  16  extending between the base transceiver station and the mobile station. Data that is communicated by a base transceiver station to the mobile station is communicated upon forward-link channels defined upon the radio links. And, data communicated by the mobile station is communicated upon reverse-link channels defined upon the radio links.  
         [0032]     In the exemplary implementation shown in the figure, the communication system  10  forms a cellular communication system operable, generally, pursuant to a proposed, CDMA 2000 operational specification that provides for high-data rate communication services, such as 1xEV-DO communication services. In other implementations, other types of data services, such as 1XTREME and L3NQS data services proposed for the CDMA 2000 operational specification are instead provided. And, in other implementations, the communication system  10  is representative of cellular communication systems that provide data services pursuant to other operational specifications as well as other types of packet-based communication systems. Accordingly, while the following detailed description shall describe operation of an embodiment of the present invention with respect to its implementation in a CDMA 2000 system that provides 1xEV-DV data communication services, the present invention is analogously implementable in cellular, and other, communication systems operable pursuant to other communication schemes.  
         [0033]     The base transceiver station  12  forms a portion of a radio access network, here also shown to include a radio network controller (RNC)  20 , and a gateway (GWY)  22 .  
         [0034]     The gateway provides for a connection of the radio access network to a core network (CN)  24 , such as a PSTN (public-switched, telephonic network) or PDN (packet data network), e.g., a next-generation telephone system or the internet backbone.  
         [0035]     Communications devices, such as computer servers  25 , are connected to the PDN. Data sourced at a computer server, connected to the core network, is supplied to the mobile station  14  by the formation of a communication path between the data source and the mobile station that extends through the core network, the radio access network, and a radio link  16  extending to the mobile station. Data sourced at a computer server, or other data source, provide a communication service, such as a data broadcast, to the mobile station.  
         [0036]     The data is formatted pursuant to packet formatting schemes, here at multiple, logical layers defined in the system. Here, the logical layers include, amongst others, a physical layer and an RLP (radio link protocol) layer positioned, functionally, thereabove. Packet formatting is performed at both the physical layer and at the RLP layer. And, both of the layers utilize a retransmission scheme in which packets of data are retransmitted if the data packets are not successfully delivered to the intended communication station. Here, for instance, data packets sent by the base transceiver station  12  to the mobile station  14  are positively acknowledged by the mobile station to be received adequately thereat. Otherwise, the data packet is resent by the base transceiver station. Because of the multiple layers of formatting and corresponding multiple layers of retransmissions that might be requested, redundant retransmission requests might well be generated. Through operation of an embodiment of the present invention, the generation of the redundant retransmission requests is less likely to occur.  
         [0037]     Accordingly, in the exemplary implementation, the base transceiver station includes apparatus  26  of an embodiment of the present invention. The apparatus  26  includes functional entities that are shown in block form in the figure. The entities forming the apparatus  26  are implementable in any desired manner such as, for example, by algorithms executable at processing circuitry. The entities of the apparatus  26  are formed at the RLP layer of the base transceiver station. The RLP layer is formed of entities positioned above a physical layer. Portions of the base transceiver station positioned above the segment  28  form parts of higher logical-layers of the base transceiver station. And, elements of the base transceiver station shown below (as shown) of the base transceiver station form the physical layer thereof. Here, the physical layer is shown to include the transceiver circuitry  32  of the base transceiver station.  
         [0038]     Analogously, the mobile station includes further apparatus  26  of an embodiment of the present invention. Again, the entities forming the apparatus  26  positioned at the mobile station are functionally represented and can be implemented in any desired manner, such as by algorithms executable by processing circuitry. The elements of the apparatus are formed at higher logical-layers of the mobile station, here also represented to be positioned above (as-shown), the line segment  28 , designated at  29 . The physical layer of the mobile station is formed of entities positioned beneath (as-shown) of the segment  28 , designated at  31 . Here, the physical layer includes transceiver circuitry  34  of the mobile station.  
         [0039]     The apparatus  26  formed at the base transceiver station is here shown to include an estimator  38  and a delay period message generator  42  coupled thereto. The estimator is coupled to receive communication indicia, herein indicated functionally by way of lines  48  representative of communication characteristics in the communication system. The indicia is formed, for instance, of one or more of indicia types, such as, for example, traffic loading in the communication system, HARQ information of active users in the communication system, QoS requirements associated with the users, and radio quality information associated with the users in the communication system. Additionally, communication indicia input to the estimator further selectably include historical data associated with delay times in the communication system, such as historical values of estimates performed during operation of the estimator.  
         [0040]     Responsive to values of the communication indicia provided thereto, the estimator operates to form values of delay periods that a subsequent request for retransmission of a data packet at the RLP layer should be delayed. The delay period, in one implementation, forms a single, suggested RLP delay. And, in another implementation, the delay period is formed of a range of possible values, bounded by minimum and maximum delay times and including a suggested RLP delay time within the delay period so-defined. The delay period message generator operates to generate a message for communication to the mobile station to report on the estimate made by the estimator. The message formed by the message generator is provided to the transmit part of the transceiver circuitry  32 , thereafter to be broadcast by way of a forward link channel to the mobile station. In the exemplary implementation, the delay period message generated by the message generator forms an RLP Block of Bits (BLOB) that includes an RLP-delay (min, max, suggested) field.  
         [0041]     When the message is received at the mobile station, the message is provided, here by way of the line  48 , to the apparatus  26 . And, more particularly, the values of the RLP delay message are provided to a delay period message detector  52 . The detector operates to detect, and extract values of, the delay period message therefrom and to provide the values to a DELAY_DETECTION_WINDOW (DDW) timer  54  to which the detector is coupled. Upon subsequent detection at the RLP layer of inadequate delivery thereto of a data packet, the timer is caused to time a time period corresponding to the delay period detected by the detector prior to generation of a RLP-layer request for retransmission of the data packet. Upon expiration of the time period timed by the DDW timer, if the data packet is not adequately delivered to the mobile station, the RLP-layer request for retransmission is generated. It should be noted that the mobile station may use several techniques to determine if the base station has given up or missed the delivery of the missing data packet. For example, the mobile station may detect that, after retransmitting an old packet several times unsuccessfully, the base station kicks off sending a new packet with a new sequence number. Hence, the MS can assume the old packet is given up and missed. If the mobile determines that the base station has given up or missed the delivery of the missing RLP data packet, the mobile station may generate the request for the retransmission prior to the expiration of DDW timer.  
         [0042]     The physical layer utilizes an HARQ retransmission scheme. During the delay timed by the timer  54 , the HARQ retransmission procedures are selectably performed, to cause retransmission of the data packet at the physical layer. The HARQ elements  54 , formed at the transceiver circuitry are representative of such HARQ retransmission functions.  
         [0043]      FIG. 2  illustrates a logical-layer representation of parts of the communication system  10  shown in  FIG. 1 . Here, the RLP layer  29  forming the link layer is positioned above the physical layer  31 . The RLP layer functions, amongst other things, to perform decoding, retransmission, and sequencing operations. And, the physical layer performs decoding, ACK/NAK, and other operations.  
         [0044]     Upper layers of the communication system are represented at the block  62  here including, for instance, PPP/IP/TCP(UDP) application layers, all conventionally utilized in packet communication systems. And, positioned beneath the physical layer  31  is the CDMA 2000 1xEV-DV air interface  64 .  
         [0045]     Segments  66  and  68  are representative of passage of good packets from the physical layer to the link layer and retransmission requests for missing packets provided by the link layer to the physical layer.  
         [0046]      FIG. 3  illustrates a message sequence diagram, shown generally at  72 , representative of signaling generated during operation of the apparatus  26  that forms a portion of the communication system  10 , shown in  FIG. 1 . Here, the base transceiver station  12  and the mobile station  14  are separated into logical-layer parts. That is to say, the base transceiver station is here designated by 12-RLP and 12-PHY designate the RLP and physical layers, respectively. And, analogously, the mobile station  12  is represented by the physical layer 14-PHY and the RLP layer 14-RLP, respectively.  
         [0047]     First, and as indicated by the block  74 , packet data service initialization procedures pursuant to, here, formation of a 1xEV-DV communication session are performed. Then, and as indicated by the block  76 , an estimator positioned at the base transceiver station estimates values of an RLP-delay responsive, for instance, to H-ARQ values, or other communication indicia. And, as indicated by the segment  78 , the delay period message, here forming an RLP BLOB containing an RLP-delay (min, max, suggested) values is sent to the mobile station. The contents of the message are provided to the RLP layer 14-RLP of the mobile station. And, subsequently, as indicated by the segments  82 , 1xEV-DV packet data, utilizing an HARQ retransmission scheme, is broadcast from the base transceiver station to the mobile station, here delivered to the RLP-layer 14-RLP thereof.  
         [0048]     To show operation of an embodiment of the present invention, a determination is made at the block  86 , that an RLP frame has not been successfully delivered to the RLP layer of the mobile station. Rather than immediately generating a retransmission request from the RLP layer, the DDW timer  54  (shown in  FIG. 1 ) is instead started. The timer times for the delay time period indicated in the RLP BLOB earlier transmitted to the mobile station and, here, extends for a time period corresponding to the length of the arrow  88 .  
         [0049]     During the period that the RLP-layer timer is timing the delay period, physical layer HARQ retransmissions can be effectuated. And, here, indicated by the segment  92 , a retransmission of an undelivered frame is effectuated. Upon expiration of the timer, if the data packet is not adequately delivered to the RLP layer, the RLP retransmission request is generated. Here, the retransmission request is indicated by the segment  96  that is communicated from the RLP layer 14-RLP of the mobile station to the RLP layer 12-RLP of the base transceiver station. Subsequently, the data packet is retransmitted, indicated by the segment  98 .  
         [0050]      FIG. 4  illustrates a method, shown generally at  104 , of the method of operation of an embodiment of the present invention. The method facilitates efficient usage of radio capacity in a radio communication system that utilizes retransmission schemes at two, or more, logical layers by which the elements of the communication system are defined.  
         [0051]     First, and as indicated by the block  106 , indicia associated with communication characteristics in the communication system are detected. Then, and as indicated by the block  108 , a selected second-layer delay period by which to delay generation, at a second communication station, of a second-layer resend request requesting resending of the packet-formatted data is estimated. The estimate is formed responsive to the indicia detected during the operation of detecting set forth at the block  106 .  
         [0052]     Thereafter, and as indicated by the block  112 , a delay period message is generated. The delay period message contains a value of the selected second-layer delay period. And, as indicated by the block  114 , the delay period message is delivered to the second communication station. And, thereafter, indicated by the block  116 , a time period is timed. Time period is indicated by the value contained in the delay period message when the packet formatted data fails to be adequately delivered to the second logical layer of the second communication station.  
         [0053]     Because of the use of delay period to delay the generation of the second logical layer retransmission request, the possibility that redundant requests, generated at both the physical layer and at the higher logical-layer is reduced.  
         [0054]     The previous descriptions are of preferred examples for implementing the invention, and the scope of the invention should not necessarily be limited by this description. The scope of the present invention is defined by the following claims: