Patent Publication Number: US-9432148-B2

Title: Uplink coverage via autonomous retransmission

Description:
PRIORITY 
     This application is a continuation, under 35 U.S.C. §120, of U.S. application Ser. No. 13/788,377 filed Mar. 7, 2013, which is a continuation, under 35 U.S.C. §120, of U.S. application Ser. No. 12/988,419 filed Oct. 18, 2010, now U.S. Patent No. 8,413,003, which is a national stage filing under 35 U.S.C. §371 of International Patent Application Serial No. PCT/SE08/51394 filed Dec. 2, 2008, and entitled “UPLINK COVERAGE VIA AUTONOMOUS RE-TRANSMISSION” which claims priority to U.S. Provisional Patent Application No. 61/050,370 filed May 5, 2008, all of which are hereby incorporated by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments described herein relate generally to wireless communication systems, and more particularly, to improved uplink coverage in wireless communication systems via autonomous retransmission. 
     BACKGROUND 
     Enhanced uplink (EUL) is proposed in the Third Generation Partnership Project (3GPP) Release 6 to improve uplink performance of Wideband Code Division Multiple Access (WCDMA) systems. Two transmission time intervals (TTIs) are proposed for enhanced uplink, a ten (10) milliseconds TTI and a two (2) milliseconds TTI. The ten milliseconds TTI provides similar cell coverage as previous Universal Mobile Telecommunications System (UMTS) releases, but its cell throughput is too small. The two milliseconds TTI provides better cell throughput than the ten milliseconds TTI, but its cell coverage is insufficient. 
     One technique that improves enhanced uplink coverage is hybrid automatic repeat request (HARQ) retransmission. According to current 3GPP specifications, enhanced uplink HARQ retransmission can occur only after expiration of a round trip time (RTT). Since the RTT for the two milliseconds TTI is sixteen (16) milliseconds and three (3) retransmissions may be required to guarantee reliable reception of a packet, a retransmission delay of forty-eight (48) milliseconds could be introduced by enhanced uplink HARQ. Such a delay may not be acceptable for some delay sensitive services (e.g., voice over Internet protocol (VoIP) services, etc.). 
     Autonomous retransmission has been proposed as an effective way to reduce such HARQ retransmission delay. A core concept of autonomous retransmission is that user equipment (UE) sends a number of retransmissions consecutively, without waiting for receipt of a negative acknowledgment (NACK) before starting the next retransmission. However, if three retransmissions are required, autonomous retransmission may only reduce the retransmission delay to six (6) milliseconds. Some autonomous retransmission techniques describe how a receiver knows that a bundle of transmissions are designated for a single packet, how the receiver decodes the packets transmitted with autonomous retransmission correctly, how to apply autonomous retransmission in high-speed downlink packet access (HSDPA), how to use autonomous retransmission for extended coverage, how to apply autonomous retransmission to notify a non-serving Node B, etc. 
     Although autonomous retransmission is an effective way to improve uplink coverage, it still suffers from several drawbacks. For example, if autonomous retransmission is applied with an excessively large number of transmission attempts or at an inappropriate time, autonomous retransmission will generate unnecessary interference in a system. On the other hand, autonomous retransmission with less (or an inadequate number of) transmission attempts can not take full advantage of the benefits of the technique. 
     SUMMARY 
     It is an object of the invention to overcome at least some of the above disadvantages and to trigger autonomous retransmission at an appropriate time and with an appropriate number of HARQ retransmissions. 
     Embodiments described herein may apply autonomous retransmission techniques to improve enhanced uplink coverage for systems (e.g., WCDMA systems providing two milliseconds TTIs). In one embodiment, for example, user equipment (UE) may receive condition information, may receive communicated information from a base station (BS), and may generate an appropriate number of retransmissions and an appropriate timing for the retransmissions based on the received information. The appropriate number of retransmissions and the appropriate timing for the retransmissions may ensure that enhanced uplink coverage is improved. 
     In an exemplary embodiment, the condition information may include power usage in the user equipment, whether the user equipment is using a minimum usable enhanced dedicated channel (E-DCH) transport format combination (ETFC), a measured downlink channel quality, whether a number of consecutive NACKs are received by the user equipment, etc. The user equipment may trigger autonomous retransmission when power in the user equipment is limited, when the user equipment is using a minimum usable ETFC, and when one of the measured downlink channel quality is less than a predefined threshold or the number of consecutive NACKs received by the user equipment is greater than a predefined number. The user equipment may determine the appropriate number of retransmissions based on a measured power clipping associated with the user equipment. 
     In another exemplary embodiment, the user equipment may estimate a data signal-to-interference ratio (SIR) (also known as a carrier-to-interference ratio (CIR)) associated with a channel, and may determine whether a difference between the estimated data SIR and a SIR for a transport format is greater than a certain decibel level. The user equipment may trigger autonomous retransmission when power in the user equipment is limited, when the user equipment is using a minimum usable ETFC, and when the difference is greater than the certain decibel level. 
     In still another exemplary embodiment, the condition information may include an estimate of the SIR in the base station, positive acknowledgments (ACKs) received by the user equipment, NACKs received by the user equipment, etc. The user equipment may determine the appropriate number of retransmissions, may increase the number of retransmissions when a certain number of consecutive NACKs are received, and may decrease the number of retransmissions when a certain number of consecutive ACKs are received. 
     In a further exemplary embodiment, the base station may determine a required SIR for a transport format, may measure a current SIR associated with the base station, and may calculate the number of retransmissions based on the required SIR and the current SIR. The base station may provide the calculated number of retransmissions to the user equipment (e.g., as the communicated information), and the user equipment may generate the calculated number of retransmissions when power in the user equipment is limited and when the user equipment is using a minimum usable ETFC. 
     Such an arrangement may ensure that autonomous retransmission is triggered at an appropriate time and with an appropriate number of HARQ retransmissions. This may reduce unnecessary interference generated by autonomous retransmission (e.g., such as occurs when the number of autonomous retransmissions are excessively large or not necessary), may reduce packet transmission delay, and may improve cell coverage for delay sensitive services. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a diagram of an exemplary network in which systems and/or methods described herein may be implemented; 
         FIG. 2  illustrates a diagram of exemplary components of a base station depicted  FIG. 1 ; 
         FIG. 3  depicts a diagram of exemplary components of user equipment illustrated in  FIG. 1 ; 
         FIG. 4  depicts a diagram of exemplary interactions among the user equipment and the base station illustrated in  FIG. 1 ; 
         FIG. 5  illustrates another diagram of exemplary interactions among the user equipment and the base station depicted in  FIG. 1 ; 
         FIGS. 6 and 7  depict diagrams of exemplary functional components of the user equipment illustrated in  FIG. 3 ; 
         FIG. 8  illustrates a diagram of an exemplary functional component of the base station depicted in  FIG. 2 ; 
         FIG. 9  depicts a diagram of exemplary interactions among the user equipment and two base stations illustrated in  FIG. 1 ; and 
         FIGS. 10-16  depict flow charts of exemplary processes according to embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. Also, the following detailed description does not limit the invention. 
     Embodiments described herein may apply autonomous retransmission techniques to improve enhanced uplink coverage for systems (e.g., WCDMA systems providing two milliseconds TTIs). The autonomous retransmission techniques described herein may be used to generate an appropriate number of retransmissions and an appropriate timing for the retransmissions, and may ensure that enhanced uplink coverage is improved. 
       FIG. 1  depicts a diagram of an exemplary network  100  in which systems and/or methods described herein may be implemented. As shown, network  100  may include a group of user equipment (UE)  110 - 1  through  110 -L (referred to collectively, and in some instances individually, as “user equipment  110 ”), a radio access network (RAN)  120 , and a core network (CN)  130 . Four pieces of user equipment  110 , a single radio access network  120 , and a single core network  130  have been illustrated in  FIG. 1  for simplicity. In practice, there may be more UEs  110 , random access networks  120 , and/or core networks  130 . Also, in some instances, a component in network  100  (e.g., one or more of user equipment  110 , radio access network  120 , and core network  130 ) may perform one or more functions described as being performed by another component or group of components in network  100 . 
     User equipment  110  may include one or more devices capable of sending/receiving voice and/or data to/from radio access network  120 . In one embodiment, user equipment  110  may include, for example, a wireless telephone, a personal digital assistant (PDA), a laptop computer, etc. In another embodiment, user equipment  110  may receive condition information (e.g., as described in further detail below), may receive communicated information (e.g., as described in further detail below) from base station  122 , and may generate an appropriate number of retransmissions and an appropriate timing for the retransmissions based on the received information. The appropriate number of retransmissions and the appropriate timing for the retransmissions may ensure that enhanced uplink coverage is improved. 
     Radio access network  120  may include one or more devices for transmitting voice and/or data to user equipment  110  and core network  130 . As illustrated, radio access network  120  may include a group of base stations (BSs)  122 - 1  through  122 -M (referred to collectively as “base stations  122 ” and in some instances, individually as “base station  122 ”) and a group of radio network controllers (RNCs)  124 - 1  through  124 -N (referred to collectively as “radio network controllers  124 ” and in some instances, individually as “radio network controller  124 ”). Four base stations  122  and two radio network controllers  124  are shown in  FIG. 1  for simplicity. In practice, there may be more or fewer base stations  122  and/or radio network controllers  124 . Also, in some instances, a component in radio access network  120  (e.g., one or more of base stations  122  and radio network controllers  124 ) may perform one or more functions described as being performed by another component or group of components in radio access network  120 . 
     Base stations  122  (also referred to as “Node Bs”) may include one or more devices that receive voice and/or data from radio network controllers  124  and transmit that voice and/or data to user equipment  110  via an air interface. Base stations  122  may also include one or more devices that receive voice and/or data from user equipment  110  over an air interface and transmit that voice and/or data to radio network controllers  124  or other user equipment  110 . 
     In one embodiment, base station  122  may detect (or estimate) a data SIR associated with a channel, and may determine whether a difference between the detected (or estimated) data SIR and a SIR for a transport format is greater than a certain decibel level. Base station  122  may provide the determination of the difference to user equipment  110  (e.g., as the communicated information), and user equipment  110  may trigger autonomous retransmission when power in the user equipment is limited, when the user equipment is using a minimum usable ETFC, and when the difference is greater than the certain decibel level. 
     In another embodiment, base station  122  may determine a required SIR for a transport format, may measure a current SIR associated with base station  122 , and may calculate a number of retransmissions based on the required SIR and the current SIR. Base station  122  may provide the calculated number of retransmissions to user equipment  110  (e.g., as the communicated information), and user equipment  110  may generate the calculated number of retransmissions. 
     Radio network controllers  124  may include one or more devices that control and manage base stations  122 . Radio network controllers  124  may also include devices that perform data processing to manage utilization of radio network services. Radio network controllers  124  may transmit/receive voice and data to/from base stations  122 , other radio network controllers  124 , and/or core network  130 . 
     A radio network controller  124  may act as a controlling radio network controller (CRNC), a drift radio network controller (DRNC), or a serving radio network controller (SRNC). A CRNC may be responsible for controlling the resources of a base station  122 . On the other hand, an SRNC may serve particular user equipment  110  and may manage connections towards that user equipment  110 . Likewise, a DRNC may fulfill a similar role to the SRNC (e.g., may route traffic between a SRNC and particular user equipment  110 ). 
     As illustrated in  FIG. 1 , a radio network controller  124  may connect to a base station  122  via an Iub interface and to another radio network controller  124  via an Iur interface. 
     Core network  130  may include one or more devices that transfer/receive voice and/or data to a circuit-switched and/or packet-switched network. In one embodiment, core network  130  may include, for example, a Mobile Switching Center (MSC), a Gateway MSC (GMSC), a Media Gateway (MGW), a Serving General Packet Radio Service (GPRS) Support Node (SGSN), a Gateway GPRS Support Node (GGSN), and/or other devices. 
       FIG. 2  illustrates a diagram of exemplary components of base station  122 . As shown in  FIG. 2 , base station  122  may include antennas  210 , transceivers (TX/RX)  220 , a processing system  230 , and an Iub interface (I/F)  240 . 
     Antennas  210  may include one or more directional and/or omni-directional antennas. Transceivers  220  may be associated with antennas  210  and may include transceiver circuitry for transmitting and/or receiving symbol sequences in a network, such as network  110 , via antennas  210 . 
     Processing system  230  may control the operation of base station  122 . Processing system  230  may also process information received via transceivers  220  and Iub interface  240 . Processing system  230  may further measure quality and strength of connection, may determine the frame error rate (FER), and may transmit this information to radio network controller  124 . As illustrated, processing system  230  may include a processing unit  232  and a memory  234 . 
     Processing unit  232  may include a processor, a microprocessor, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or the like. Processing unit  232  may process information received via transceivers  220  and Iub interface  240 . The processing may include, for example, data conversion, forward error correction (FEC), rate adaptation, Wideband Code Division Multiple Access (WCDMA) spreading/dispreading, quadrature phase shift keying (QPSK) modulation, etc. In addition, processing unit  232  may generate control messages and/or data messages, and may cause those control messages and/or data messages to be transmitted via transceivers  220  and/or Iub interface  240 . Processing unit  232  may also process control messages and/or data messages received from transceivers  220  and/or Iub interface  240 . 
     Memory  234  may include a random access memory (RAM), a read-only memory (ROM), and/or another type of memory to store data and instructions that may be used by processing unit  232 . 
     Iub interface  240  may include one or more line cards that allow base station  122  to transmit data to and receive data from a radio network controller  124 . 
     As described herein, base station  122  may perform certain operations in response to processing unit  232  executing software instructions of an application contained in a computer-readable medium, such as memory  234 . A computer-readable medium may be defined as a physical or logical memory device. The software instructions may be read into memory  234  from another computer-readable medium or from another device via antennas  210  and transceivers  220 . The software instructions contained in memory may cause processing unit  232  to perform processes described herein. Alternatively, hardwired circuitry may be used in place of or in combination with software instructions to implement processes described herein. Thus, embodiments described herein are not limited to any specific combination of hardware circuitry and software. 
     Although  FIG. 2  shows exemplary components of base station  122 , in other embodiments, base station  122  may contain fewer, different, or additional components than depicted in  FIG. 2 . In still other embodiments, one or more components of base station  122  may perform one or more other tasks described as being performed by one or more other components of base station  122 . 
       FIG. 3  depicts a diagram of exemplary components of user equipment  110 . As shown in  FIG. 3 , user equipment  110  may include a processing unit  300 , a memory  310 , a user interface  320 , a communication interface  330 , and/or an antenna assembly  340 . 
     Processing unit  300  may include a processor, a microprocessor, an ASIC, a FPGA, or the like. Processing unit  300  may control operation of user equipment  110  and its components. In one embodiment, processing unit  300  may control operation of components of user equipment  110  in a manner described herein. 
     Memory  310  may include a RAM, a ROM, and/or another type of memory to store data and instructions that may be used by processing unit  300 . 
     User interface  320  may include mechanisms for inputting information to user equipment  110  and/or for outputting information from user equipment  110 . 
     Communication interface  330  may include, for example, a transmitter that may convert baseband signals from processing unit  300  to radio frequency (RF) signals and/or a receiver that may convert RF signals to baseband signals. Alternatively, communication interface  330  may include a transceiver to perform functions of both a transmitter and a receiver. Communication interface  330  may connect to antenna assembly  340  for transmission and/or reception of the RF signals. 
     Antenna assembly  340  may include one or more antennas to transmit and/or receive signals through a radio interface. Antenna assembly  340  may, for example, receive RF signals from communication interface  330  and transmit them through the radio interface, and receive RF signals through the radio interface and provide them to communication interface  330 . In one embodiment, for example, communication interface  330  may communicate with a network (e.g., network  100 ) and/or devices connected to a network. 
     As described herein, user equipment  110  may perform certain operations in response to processing unit  300  executing software instructions of an application contained in a computer-readable medium, such as memory  310 . The software instructions may be read into memory  310  from another computer-readable medium or from another device via communication interface  330 . The software instructions contained in memory  310  may cause processing unit  300  to perform processes described herein. Alternatively, hardwired circuitry may be used in place of or in combination with software instructions to implement processes described herein. Thus, embodiments described herein are not limited to any specific combination of hardware circuitry and software. 
     Although  FIG. 3  shows exemplary components of user equipment  110 , in other embodiments, user equipment  110  may contain fewer, different, or additional components than depicted in  FIG. 3 . In still other embodiments, one or more components of user equipment  110  may perform one or more other tasks described as being performed by one or more other components of user equipment  110 . 
       FIG. 4  depicts a diagram of exemplary interactions among user equipment  110  and base station  122 . User equipment  110  and base station  122  may include the features described above in connection with, for example,  FIGS. 1-3 . 
     As shown in  FIG. 4 , user equipment  110  and base station  122  may receive (and/or determine) condition information  410 . Condition information  410  may include power usage in user equipment  110 , whether user equipment  110  is using a minimum usable ETFC, a measured downlink channel quality, whether a number of consecutive NACKs are received by user equipment  110 , measured power clipping in user equipment  110 , an estimate of the SIR in base station  122 , positive acknowledgments (ACKs) received by user equipment  110 , NACKs received by user equipment  110 , etc. 
     As further shown in  FIG. 4 , user equipment  110  and base station  122  may exchange communicated information  420  among each other. Communicated information  420  may include a determination (e.g., by base station  122 ) of a difference between a detected (or estimated) data SIR and a SIR for a transport format, a calculated number of retransmissions based on a required SIR for a transport format and a current SIR associated with base station  122 , etc. 
     User equipment  110  may utilize condition information  410  and/or communicated information  420  to determine timing for retransmissions  430  (e.g., an appropriate time to trigger autonomous retransmission) and a number of retransmissions  440  (e.g., HARQ retransmission attempts for autonomous retransmission). 
     In one exemplary embodiment, user equipment  110  may trigger autonomous retransmission (e.g., timing for retransmissions  430 ) when power in user equipment  110  is limited, when user equipment  110  is using a minimum usable ETFC, and when either the measured downlink channel quality is less than a predefined threshold or the number of consecutive NACKs received by user equipment  110  is greater than a predefined number. In another exemplary embodiment, user equipment  110  may trigger autonomous retransmission (e.g., timing for retransmissions  430 ) when power in user equipment  110  is limited, when user equipment  110  is using a minimum usable ETFC, and when a difference between a detected (or estimated) data SIR and a SIR for a transport format is determined to be greater than a certain decibel level (e.g., three decibels). 
     In one exemplary embodiment, user equipment  110  may determine a number of retransmissions  440 , may increase number of retransmissions  440  when a certain number of consecutive NACKs are received, and may decrease number of retransmissions  440  when a certain number of consecutive ACKs are received. In another exemplary embodiment, base station  122  may determine a required SIR for a transport format, may measure a current SIR associated with base station  122 , and may calculate number of retransmissions  440  based on the required SIR and the current SIR. Base station  122  may provide the calculated number of retransmissions  440  to user equipment  110  (e.g., as communicated information  420 ), and user equipment  110  may generate number of retransmissions  440 . 
     Although  FIG. 4  shows exemplary interactions between user equipment  110  and base station  122 , in other embodiments, user equipment  110  and base station  122  may perform fewer, different, or additional interactions than depicted in  FIG. 4 . 
       FIG. 5  illustrates another diagram of exemplary interactions among user equipment  110  and base station  122 . User equipment  110  and base station  122  may include the features described above in connection with, for example,  FIGS. 1-3 . 
     As shown in  FIG. 5 , user equipment  110  may determine whether it is power limited  510 , and may determine whether it is using a minimum usable ETFC  520 . User equipment  110  may measure a downlink channel quality  530  and may receive one or more NACKs  540 . Downlink channel quality  530  may include a quality (e.g., a common pilot channel (CPICH) committed information rate (CIR) or a channel quality indicator (CIQ)) associated with a downlink channel. User equipment  110  may determine whether a number of consecutive NACKs  540  is greater than a predefined number, and whether downlink channel quality  530  is lower than a predefined threshold. In one exemplary embodiment, if user equipment  110  is power limited  510 , user equipment  110  is using a minimum usable ETFC  520 , and either the number of consecutive NACKs  540  is greater than the predefined number or downlink channel quality  530  is lower than the predefined threshold, user equipment  110  may trigger autonomous retransmission (e.g., timing for retransmissions  430 ). 
     As further shown in  FIG. 5 , base station  122  may receive (or estimate) a data SIR  550 , and may provide data SIR  550  to user equipment  110  (e.g., via communicated information  420 ). User equipment  110  may determine whether a difference between data SIR  550  and a required SIR for transport format associated with the base station  122  is greater than a certain decibel level (e.g., three decibels). In one exemplary embodiment, if user equipment  110  is power limited  510 , user equipment  110  is using a minimum usable ETFC  520 , and the difference between data SIR  550  and a required SIR for a transport format associated with base station  122  is greater than a certain decibel level, user equipment  110  may trigger autonomous retransmission (e.g., timing for retransmissions  430 ). 
     Although  FIG. 5  shows exemplary interactions between user equipment  110  and base station  122 , in other embodiments, user equipment  110  and base station  122  may perform fewer, different, or additional interactions than depicted in  FIG. 5 . 
       FIG. 6  depicts a diagram of exemplary functional components of user equipment  110 . As shown, user equipment  110  may include a retransmission calculator  600 , a retransmission adjuster  605 , and a retransmission timing calculator  610 . In one embodiment, the functions described in connection with  FIG. 6  may be performed by processing unit  300  ( FIG. 3 ). 
     Retransmission calculator  600  may include any hardware, software, or combination of hardware and software that may calculate number of retransmissions  440 . In one embodiment, retransmission calculator  600  may receive a required power offset (P OFFREQ )  615  for a transport format, may receive an actually used power offset (P OFFUSED )  620  for the transport format, and may calculate number of retransmissions  440  based on P OFFREQ    615  and P OFFUSED    620 . In one exemplary embodiment, retransmission calculator  600  may calculate number of retransmissions  440  based on the following:
 
floor(db2lin(P OFFREQ −P OFFUSED )),
 
where “db2lin” may convert decibels to a linear scale (e.g., 0 decibels=1.0) and “floor” may determine a greatest integer less than or equal to an input value. Retransmission calculator  600  may provide number of retransmissions  440  to retransmission adjuster  605 .
 
     Retransmission adjuster  605  may include any hardware, software, or combination of hardware and software that may receive number of retransmissions  440  from retransmission calculator  600 , may receive NACKs  625  and/or ACKs  630  (e.g., received by user equipment  110 ), and may adjust number of retransmissions  440  based on NACKs  625  or ACKs  630 . In one exemplary embodiment, retransmission adjuster  605  may increase number of retransmissions  440  (e.g., by a value of one) when a certain number of consecutive NACKs  625  are received (e.g., by user equipment  110 ). In another exemplary embodiment, retransmission adjuster  605  may decrease number of retransmissions  440  (e.g., by a value of one) when a certain number of consecutive ACKs  630  are received (e.g., by user equipment  110 ). 
     Retransmission timing calculator  610  may include any hardware, software, or combination of hardware and software that may receive a SIR (SIR REQ )  640  required for the transport format, may receive an estimate of a SIR (SIR EST )  645  associated with base station  122 , and may calculate retransmission times  650  (e.g., timing for autonomous retransmission) based on SIR REQ    640  and SIR EST    645 . In one exemplary embodiment, retransmission timing calculator  610  may calculate retransmission times  650  based on the following:
 
floor(db2lin(SIR REQ −SIR EST )),
 
where “db2lin” may convert decibels to a linear scale (e.g., 0 decibels=1.0) and “floor” may determine a greatest integer less than or equal to an input value.
 
     Although  FIG. 6  shows exemplary functional components of user equipment  110 , in other embodiments, user equipment  110  may contain fewer, different, or additional functional components than depicted in  FIG. 6 . In still other embodiments, one or more functional components of user equipment  110  may perform one or more other tasks described as being performed by one or more other functional components of user equipment  110 . 
       FIG. 7  depicts a diagram of exemplary functional components of user equipment  110  that may be used to calculate SIR EST    645 . As shown in  FIG. 7 , user equipment  110  may include an interference calculator  700  and a SIR estimator  710 . In one embodiment, the functions described in connection with  FIG. 7  may be performed by processing unit  300  ( FIG. 3 ). 
     Interference calculator  700  may include any hardware, software, or combination of hardware and software that may receive a transmission power (P TX )  720  of a common pilot channel (CPICH), may receive a received signal code power (RSCP)  730  of the CPICH, and may receive SIR REQ    640 . Interference calculator  700  may measure a path gain (pathgain) to base station  122  based on P TX    720  and RSCP  730 . In one exemplary embodiment, when user equipment  110  chooses ETFC in a minimum ETFC set, interference calculator  700  may estimate an interference (I)  740  at base station  122 , when ACKs arc received, according to the following: 
             I   =         pathgain   ·     P   TX         SIR   REQ       .           
Interference calculator  700  may provide interference  740  to SIR estimator  710 .
 
     SIR estimator  710  may include any hardware, software, or combination of hardware and software that may receive interference  740  from interference calculator  700 , may receive transmission power (P TX )  720 , and may receive a new measured path gain (pathgain new )  750 . In one exemplary embodiment, SIR estimator  710  may assume that a total interference is constant in a short period of time, and may calculate SIR EST    645  in base station  122  according to the following: 
     
       
         
           
             
               SIR 
               EST 
             
             = 
             
               
                 
                   
                     pathgain 
                     new 
                   
                   · 
                   
                     P 
                     TX 
                   
                 
                 I 
               
               . 
             
           
         
       
     
     Although  FIG. 7  shows exemplary functional components of user equipment  110 , in other embodiments, user equipment  110  may contain fewer, different, or additional functional components than depicted in  FIG. 7 . In still other embodiments, one or more functional components of user equipment  110  may perform one or more other tasks described as being performed by one or more other functional components of user equipment  110 . 
       FIG. 8  illustrates a diagram of an exemplary functional component of base station  122 . As shown, base station  122  may include a retransmission calculator  800 . In one embodiment, the functions described in connection with  FIG. 8  may be performed by processing unit  232  ( FIG. 2 ). 
     Retransmission calculator  800  may include any hardware, software, or combination of hardware and software that may receive SIR REQ    640  required for the transport format, may receive a SIR (SIR MEAS )  810  measured in base station  122 , and may calculate number of retransmissions  440  based on SIR REQ    640  and SIR MEAS    810 . In one exemplary embodiment, retransmission calculator  800  may calculate number of retransmissions  440  based on the following:
 
floor(db2lin(SIR REQ −SIR MEAS )),
 
where “db2lin” may convert decibels to a linear scale (e.g., 0 decibels=1.0) and “floor” may determine a greatest integer less than or equal to an input value. Retransmission calculator  800  may provide number of retransmissions  440  to user equipment  110  (e.g., via communicated information  420 ). User equipment  110  may generate the number of retransmissions  440  when power in user equipment  110  is limited and when user equipment  110  is using a minimum usable ETFC.
 
     Although  FIG. 8  shows an exemplary functional component of base station  122 , in other embodiments, base station  122  may contain different or additional functional components than depicted in  FIG. 8 . 
       FIG. 9  depicts a diagram of exemplary interactions among user equipment  110 , base station  122 - 1  (e.g., a serving base station of user equipment  110 ), and base station  122 - 2  (e.g., a non-serving base station of user equipment  110 ). User equipment  110 , base station  122 - 1 , and base station  122 - 2  may include the features described above in connection with, for example,  FIGS. 1-3 . 
     It may be necessary for user equipment  110  to notify a base station (e.g., base station  122 - 1 ) about a number of autonomous retransmissions so that base station  122 - 1  may decode packets correctly. As shown in  FIG. 9 , if user equipment  110  is using a low bit rate service (e.g., VoIP) and since it may be impossible for a low bit rate service to use very large ETFC, user equipment  110  may provide, to base station  122 - 1 , a notification  910  of the number of retransmissions via a very large E-DCH transport format combination indicator (E-TFCI)  920 . Notification  910  may inform base station  122 - 1  that user equipment  110  is using a small E-DCH transport format indicator (ETFI) and several autonomous retransmissions. Base station  122 - 1  may know that user equipment  110  is transmitting with a low bit rate service  930  via a RNC (e.g., RNC  124 - 1 ). 
     As further shown in  FIG. 9 , in order to provide communicated information  420  from base station  122 - 1  to user equipment  110 , base station  122 - 1  may suggest to user equipment  110  as to when to enable autonomous retransmission (and may suggest a corresponding number of retransmission attempts), as indicated by reference number  940 . In one embodiment, base station  122 - 1  may convey enable autonomous retransmission  940  to user equipment  110  via an E-DCH absolute grant channel (E-AGCH), as indicated by reference number  950 . A very large absolute grant (AG) may be used to represent the times of retransmission attempts without confusing user equipment  110  because user equipment  110  may be power-limited and may use a minimum set ETFC. User equipment  110  may not expect to receive very large absolute grants. 
     As also shown in  FIG. 9 , since AG may be sent from serving base station  122 - 1  to user equipment  110  and non-serving base station  122 - 2  may not be aware of this, base station  122 - 1  may provide a notification  960  of a number of retransmissions (for autonomous retransmission) to non-serving base station  122 - 2 . In one embodiment, base station  122 - 1  may convey notification  960  to user equipment  110  via an E-AGCH. 
     Although  FIG. 9  shows exemplary interactions between user equipment  110 , base station  122 - 1 , and base station  122 - 2 , in other embodiments, user equipment  110 , base station  122 - 1 , and base station  122 - 2  may perform fewer, different, or additional interactions than depicted in  FIG. 9 . 
       FIG. 10  illustrates a flow chart of an exemplary process  1000  for determining when to trigger autonomous retransmission according to embodiments described herein. In one embodiment, process  1000  may be performed by user equipment  110 . In other embodiments, some or all of process  1000  may be performed by user equipment  110  in combination with another device or group of devices (e.g., communicating with user equipment  110 ). 
     As illustrated in  FIG. 10 , process  1000  may include determining whether power is limited in user equipment (block  1010 ), determining whether the user equipment is using a minimum usable ETFC (block  1020 ), receiving consecutive negative acknowledgments (NACKs) (block  1030 ), determining whether a number of consecutive NACKs is greater than a predefined number (block  1040 ), measuring downlink channel quality (block  1050 ), and determining whether the measured downlink channel quality is less than a predefined threshold (block  1060 ). For example, in embodiments described above in connection with  FIG. 4 , user equipment  110  may receive (and/or determine) condition information  410 . Condition information  410  may include power usage in user equipment  110 , whether user equipment  110  is using a minimum usable ETFC, a measured downlink channel quality, and whether a number of consecutive NACKs are received by user equipment  110 . 
     Returning to  FIG. 10 , autonomous retransmission may be triggered when the user equipment is power limited, when the user equipment is using the minimum usable ETFC, and when one of the number of consecutive NACKs is greater than the predefined number or the measured downlink channel quality is less than the predefined threshold (block  1070 ). For example, in embodiments described above in connection with  FIG. 4 , user equipment  110  may utilize condition information  410  to determine timing for retransmissions  430  (e.g., an appropriate time to trigger autonomous retransmission). In one example, user equipment  110  may trigger autonomous retransmission (e.g., timing for retransmissions  430 ) when power in user equipment  110  is limited, when user equipment  110  is using a minimum usable ETFC, and when either the measured downlink channel quality is less than a predefined threshold or the number of consecutive NACKs received by user equipment  110  is greater than a predefined number. 
       FIG. 11  illustrates a flow chart of another exemplary process  1100  for determining when to trigger autonomous retransmission according to embodiments described herein. In one embodiment, process  1100  may be performed by user equipment  110 . In other embodiments, some or all of process  1100  may be performed by user equipment  110  in combination with another device (e.g., base station  122 ) or group of devices (e.g., communicating with user equipment  110 ). 
     As illustrated in  FIG. 11 , process  1100  may include determining whether power is limited in user equipment (block  1110 ), and determining of whether the user equipment is using a minimum usable ETFC (block  1120 ). For example, in embodiments described above in connection with  FIG. 4 , user equipment  110  may receive (and/or determine) condition information  410 . Condition information  410  may include power usage in user equipment  110 , and whether user equipment  110  is using a minimum usable ETFC. 
     As further shown in  FIG. 11 , it may be determined whether a difference between a detected (or estimated) data SIR at a base station and a SIR for a transport format is greater than a certain decibel level may be received from the base station (block  1130 ), and autonomous retransmission may be triggered when the user equipment is power limited, when the user equipment is using the minimum usable ETFC, and when the difference is greater than the certain decibel level (block  1040 ). For example, in embodiments described above in connection with  FIG. 5 , user equipment  110  may determine whether a difference between data SIR  550  and a required SIR for a transport format associated with base station  122  is greater than a certain decibel level (e.g., three decibels). In one example, if user equipment  110  is power limited  510 , user equipment  110  is using a minimum usable ETFC  520 , and the difference between data SIR  550  and a required SIR for a transport format associated with base station  122  is greater than a certain decibel level, user equipment  110  may trigger autonomous retransmission (e.g., timing  30  for retransmissions  430 ). 
       FIG. 12  illustrates a flow chart of an exemplary process  1200  for determining a number of retransmissions for autonomous retransmission according to embodiments described herein. In one embodiment, process  1200  may be performed by user equipment  110 . In other embodiments, some or all of process  1100  may be performed by user equipment  110  in combination with another device (e.g., base station  122 ) or group of devices (e.g., communicating with user equipment  110 ). 
     As illustrated in  FIG. 12 , process  1200  may include determining a number of retransmissions (block  1210 ). For example, in embodiments described above in connection with  FIG. 6 , user equipment  110  may include retransmission calculator  600 . Retransmission calculator  600  may calculate number of retransmissions  440 . In one example, retransmission calculator  600  may receive required power offset (P OFFREQ )  615  for a transport format, and may receive actually used power offset (P OFFUSED )  620  for the transport format. Retransmission calculator  600  may calculate number of retransmissions  440  based on P OFFREQ    615  and P OFFUSED    620 . 
     As further shown in  FIG. 12 , positive acknowledgements (ACKs) and/or negative acknowledgements (NACKs) may be received (block  1220 ), the number of retransmissions may be increased when a certain number of consecutive NACKs are received (block  1230 ), and/or the number of retransmissions may be decreased when a certain number of consecutive ACKs are received (block  1240 ). For example, in embodiments described above in connection with  FIG. 6 , user equipment  110  may include retransmission adjuster  605 . Retransmission adjuster  605  may receive number of retransmissions  440  from retransmission calculator  600 , may receive NACKs  625  and/or ACKs  630  (e.g., received by user equipment  110 ), and may adjust number of retransmissions  440  based on NACKs  625  or ACKs  630 . In one example, retransmission adjuster  605  may increase number of retransmissions  440  (e.g., by a value of one) when a certain number of consecutive NACKs  625  are received (e.g., by user equipment  110 ). In another example, retransmission adjuster  605  may decrease number of retransmissions  440  (e.g., by a value of one) when a certain number of consecutive ACKs  630  are received (e.g., by user equipment  110 ). 
     Returning to  FIG. 12 , a received SIR in a base station may be estimated (block  1250 ), and the estimated SIR may be compared with a required SIR in the base station to calculate retransmission times for autonomous retransmission (block  1260 ). For example, in embodiments described above in connection with  FIG. 6 , user equipment  110  may include retransmission timing calculator  610 . Retransmission timing calculator  610  may receive SIR (SIR  REQ )  640  required for the transport format, may receive estimate of a SIR (SIR  EST )  645  associated with base station  122 , and may calculate retransmission times  650  (e.g., timing for autonomous retransmission) based on SIR REQ    640  and SIR EST    645 . In one example, when a number of autonomous retransmissions is adjusted adaptively based on a number of consecutive NACKs (e.g., consecutive NACKs  625 ) and/or consecutive ACKs (e.g., consecutive ACKs  630 ) received, estimation of the received SIR may not be needed, and process blocks  1250  and  1260  may be omitted. 
     Process block  1210  may include the process blocks depicted in  FIG. 13 . As shown in  FIG. 13 , process block  1210  may include receiving (or obtaining) a required power offset (P OFFREQ ) for a transport format (block  1300 ), receiving (or obtaining) an actually used power offset (P OFFUSED ) for the transport format (block  1310 ), and calculating the number of retransmissions according to floor(db2lin(P OFFREQ −Po OFFUSED )) (block  1320 ). For example, in embodiments described above in connection with  FIG. 6 , retransmission calculator  600  may receive required power offset (P OFFREQ )  615  for a transport format, may receive actually used power offset (P OFFUSED )  620  for the transport format, and may calculate number of retransmissions  440  based on the following:
 
floor(db2lin( P   OFFREQ   −P   OFFUSED )),
 
where “db2lin” may convert decibels to a linear scale (e.g., 0 decibels=1.0) and “floor” may determine a greatest integer less than or equal to an input value.
 
     Process block  1250  may include the process blocks depicted in  FIG. 14 . As shown in  FIG. 14 , process block  1250  may include measuring a path gain (pathgain) to the base station via a transmission power (P TX ) of CPICH and a received RSCP of CPICH (block  1400 ), and estimating interference (I) at the base station, when an ACK is received, according to 
             I   =         pathgain   ·     P   TX         SIR   REQ       ⁢           ⁢       (     block   ⁢           ⁢   1410     )     .             
For example, in embodiments described above in connection with  FIG. 7 , user equipment  110  may include interference calculator  700 . Interference calculator  700  may receive transmission power (P TX )  720  of a common pilot channel (CPICH), may receive received signal code power (RSCP)  730  of the CPICH, and may receive SIR REQ    640 . Interference calculator  700  may measure path gain (pathgain) to base station  122  based on P TX    720  and RSCP  730 . In one example, when user equipment  110  chooses ETFC in a minimum ETFC set, interference calculator  700  may estimate interference (I)  740  at base station  122 , when ACKs are received, according to the following:
 
     
       
         
           
             I 
             = 
             
               
                 
                   pathgain 
                   · 
                   
                     P 
                     TX 
                   
                 
                 
                   SIR 
                   REQ 
                 
               
               . 
             
           
         
       
     
     As further shown in  FIG. 14 , process block  1250  may include measuring a new path gain (pathgain new ) to the base station (block  1420 ), determining the estimated SIR (SIR EST ) in the base station according to 
                 SIR   EST     =           pathgain   new     ·     P   TX       I     ⁢           ⁢     (     block   ⁢           ⁢   1430     )         ,         
and calculating the retransmission times according to floor(db2lin(SIR REQ −SIR EST )) (block  1440 ). For example, in embodiments described above in connection with  FIGS. 6 and 7 , user equipment  110  may include SIR estimator  710  and retransmission timing calculator  610 . SIR estimator  710  may receive interference  740  from interference calculator  700 , may receive transmission power (P TX )  720 , and may receive new measured path gain (pathgain new )  750 . In one example, SIR estimator  710  may assume that a total interference is constant in a short period of time, and may calculate SIR EST    645  in base station  122  according to the following:
 
               SIR   EST     =           pathgain   new     ·     P   TX       I     .           
Retransmission timing calculator  610  may receive SIR (SIR REQ )  640  required for the transport format, may receive estimate of a SIR (SIR EST )  645  associated with base station  122 , and may calculate retransmission times  650  (e.g., timing for autonomous retransmission) based on the following:
 
floor(db2lin(SIR REQ −SIR EST )),
 
where “db2lin” may convert decibels to a linear scale (e.g., 0 decibels=1.0) and “floor” may determine a greatest integer less than or equal to an input value.
 
       FIG. 15  illustrates a flow chart of an exemplary process  1500  for determining a number of retransmissions for autonomous retransmission according to embodiments described herein. In one embodiment, process  1500  may be performed by base station  122 . In other embodiments, some or all of process  1500  may be performed by base station  122  in combination with another device (e.g., user equipment  110 ) or group of devices (e.g., communicating with base station  122 ). 
     As illustrated in  FIG. 15 , process  1500  may include determining a required SIR (SIR REQ ) for a transport format (block  1510 ), measuring a current SIR (SIR MEAS ) (block  1520 ), and calculating a number of retransmissions for autonomous retransmission according to floor(db2lin(SIR REQ −SIR MEAS )) (block  1530 ). For example, in embodiments described above in connection with  FIG. 8 , base station  122  may include retransmission calculator  800 . Retransmission calculator  800  may receive SIR REQ    640  required for the transport format, may receive SIR (SIR MEAS )  810  measured in base station  122 , and may calculate number of retransmissions  440  based on SIR REQ    640  and SIR MEAS    810 . In one example, retransmission calculator  800  may calculate number of retransmissions  440  based on the following:
 
floor(db2lin(SIR REQ −SIR MEAS )),
 
where “db2lin” may convert decibels to a linear scale (e.g., 0 decibels=1.0) and “floor” may determine a greatest integer less than or equal to an input value. Retransmission calculator  800  may provide number of retransmissions  440  to user equipment  110  (e.g., via communicated information  420 ). User equipment  110  may generate the number of retransmissions  440  when power in user equipment  110  is limited and when user equipment  110  is using a minimum usable ETFC.
 
       FIG. 16  illustrates a flow chart of an exemplary process  1600  for enabling communications between user equipment  110  and base stations  122  according to embodiments described herein. In one embodiment, process  1600  may be performed by user equipment  110  and base station  122 . In other embodiments, some or all of process  1600  may be performed by user equipment  110  and base station  122  in combination with another device or group of devices (e.g., communicating with user equipment  110  and base station  122 ). 
     As illustrated in  FIG. 16 , process  1600  may begin with receipt, by base station  122 , of information indicating that user equipment is transmitting with a low bit rate service ( 1610 ), using, by user equipment  110 , a large E-TFCI to generate a first notification indicating that user equipment  110  is using small ETFI with several autonomous retransmissions (block  1620 ), providing, by user equipment  110 , the first notification to base station  122  (block  1630 ), and receiving, by base station  122 , the first notification (block  1640 ). For example, in embodiments described above in connection with  FIG. 9 , if user equipment  110  is using a low bit rate service (e.g., VoIP) and since it may be impossible for a low bit rate service to use very large ETFC, user equipment  110  may provide, to base station  122 - 1 , notification  910  of the number of retransmissions via very large E-DCH transport format combination indicator (E-TFCI)  920 . Notification  910  may inform base station  122 - 1  that user equipment  110  is using a small E-DCH transport format indicator (ETFI) and several autonomous retransmissions. Base station  122 - 1  may know that user equipment  110  is transmitting with low bit rate service  930  via a RNC (e.g., RNC  124 - 1 ). 
     Returning to  FIG. 16 , base station  122  may generate a second notification indicating a suggestion when to enable autonomous retransmission and a suggested corresponding number of transmission attempts (block  1650 ), base station  122  may provide the second notification to user equipment  110  (block  1660 ), user equipment  110  may receive the second notification (block  1670 ), and base station  122  may provide, to a non-serving base station, a third notification indicating a number of retransmissions (block  1680 ). For example, in embodiments described above in connection with  FIG. 9 , in order to provide communicated information  420  from base station  122 - 1  to user equipment  110 , base station  122 - 1  may suggest to user equipment  110  as to when to enable autonomous retransmission (and may suggest a corresponding number retransmission attempts), as indicated by reference number  940 . Base station  122 - 1  may convey enable autonomous retransmission  940  to user equipment  110  via an E-DCH absolute grant channel (E-AGCH), as indicated by reference number  950 . A very large absolute grant (AG) may be used to represent the times of retransmission attempts without confusing user equipment  110  because user equipment  110  may be power-limited and may use a minimum set ETFC. Since AG may be sent from serving base station  122 - 1  to user equipment  110  and non-serving base station  122 - 2  may not be aware of this, base station  122 - 1  may provide notification  960  of a number of retransmissions (for autonomous retransmission) to non-serving base station  122 - 2 . 
     Embodiments described herein may apply autonomous retransmission techniques to improve enhanced uplink coverage for systems (e.g., WCDMA systems providing two milliseconds TTIs). In one embodiment, for example, user equipment (UE) may receive condition information, may receive communicated information from a base station (BS), and may generate an appropriate number of retransmissions and an appropriate timing for the retransmissions based on the received information. The appropriate number of retransmissions and the appropriate timing for the retransmissions may ensure that enhanced uplink coverage is improved. 
     Such an arrangement may ensure that autonomous retransmission is triggered at an appropriate time and with an appropriate number of HARQ retransmissions. This may reduce unnecessary interference generated by autonomous retransmission (e.g., such as occurs when the number of autonomous retransmissions are excessively large or not necessary), may reduce packet transmission delay, and may improve cell coverage for delay sensitive services. 
     Embodiments described herein provide illustration and description, but are not intended to be exhaustive or to limit the implementations to the precise form disclosed. Modifications and variations arc possible in light of the above teachings, or may be acquired from practice of the implementations. For example, while series of blocks have been described with regard to  FIGS. 10-16 , the order of the blocks may be modified in other embodiments. Further, non-dependent blocks may be performed in parallel. 
     The exemplary embodiments, as described above, may be implemented in many different forms of software, firmware, and hardware in the implementations illustrated in the figures. The actual software code or specialized control hardware used to implement the exemplary embodiments described herein is not limiting of the invention. Thus, the operation and behavior of the exemplary embodiments were described without reference to the specific software code—it being understood that one would be able to design software and control hardware to implement the exemplary embodiments based on the description herein. 
     Further, certain portions of the invention may be implemented as “logic” that performs one or more functions. This logic may include hardware, such as an application specific integrated circuit, a field programmable gate array, a processor, or a microprocessor, or a combination of hardware and software. 
     Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the invention. In fact, many of these features may be combined in ways not specifically recited in the claims and/or disclosed in the specification. 
     It should be emphasized that the terms “comprises/comprising” when used in the this specification are taken to specify the presence of stated features, integers, steps, or components, but do not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof. 
     No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items. Where only one item is intended, the term “one” or similar language is used. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.