Patent Publication Number: US-2011051840-A1

Title: Methods, Apparatuses, System, and Related Computer Program Product for Information Transmission

Description:
FIELD OF THE INVENTION 
     The present invention relates to information transmission e.g. in an UL (Uplink) transmission. More specifically, the present invention relates to methods, apparatuses, a system and a related computer program product for information transmission e.g. in the UL part of the UTRAN (UMTS (UMTS Terrestrial Radio Access Network) Terrestrial Radio Access Network) LTE (long term evolution) often referred as 3.9G. Examples of the present invention may relate to message 3 transmission and configuration in RA (random access) procedure, but also to other types of data transmission using e.g. HARQ (hybrid automatic repeat request) (i.e. not limited to RA message 3). 
     BACKGROUND 
     In 3GPP LTE (3 rd  Generation Partnership Project Long Term Evolution), there have been discussions related to information transmission. 
     That is, the balancing of coverage between different LTE physical channels has recently drawn attention in 3GPP, and TTI (transmission time interval) bundling has been proposed as a solution for improving the coverage balance. In TTI bundling, the same data is essentially transmitted in multiple consecutive TTIs before any (HARQ) feedback such as ACK/NACK (acknowledgement/non-acknowledgement) is obtained from the decoding. 
     E.g. in the LTE RA procedure, message 3 refers to the first scheduled UL transmission on a PUSCH (physical uplink shared channel) during the random access. HARQ processing may be applied for message 3. 
     There have been approaches for overcoming the above limitations. However, the delay for the state transition from dormant to active state is limited to e.g. less than 50 ms in LTE and, thus, the number of message 3 retransmission opportunities is limited e.g. to 3, as discussed in 3GPP. The message 3 size may be around 80 bits. On the beginning of the random access procedure, a UE (user equipment) may send a random access burst containing cyclic prefix and preamble sequence on random access channel (RACH). To improve the RACH coverage, the burst can have the 800 ms preamble sequence repeated twice (see RACH preamble format 2 and 3). 
     One such approach is directed to use normal TTI bundling also for the RA message 3. However, due to lack of knowledge on channel and path loss in particular, TTI bundling would need to be applied for all RA message 3 transmissions in the cell where the bundling for RA message 3 is configured. This would lead to unnecessary RA message 3 overhead. 
     In consideration of the above, it is an object of the present invention to overcome one or more of the above drawbacks. In particular, the present invention provides methods, apparatuses, a system and a related computer program product for information transmission. 
     According to the present invention, in a first aspect, this object is for example achieved by a method comprising: 
     generating information to be transmitted; 
     first transmitting, in a first transmission opportunity of n consecutive transmission opportunities, n being an integer greater than 1, the generated information once; and 
     second transmitting, in one transmission opportunity different from the first transmission opportunity, the generated information a number of times different from once. 
     According to further refinements of the invention as defined under the above first aspect, 
     in the second transmitting, the information is respectively transmitted once in a second to an (n−1) st  transmission opportunity of the n consecutive transmission opportunities, and is transmitted more than once in an n-th transmission opportunity of the n consecutive transmission opportunities; 
     the second transmitting is performed by using transmission time interval bundling; 
     the second transmitting is performed by hybrid automatic repeat request retransmission opportunities. 
     According to the present invention, in a second aspect, this object is for example achieved by a method comprising: 
     first receiving, in a first transmission opportunity of n consecutive transmission opportunities, n being an integer greater than 1, information once; and 
     second receiving, in one transmission opportunity different from the first transmission opportunity, the information a number of times different from once. 
     According to further refinements of the invention as defined under the above second aspect, 
     the method further comprises creating, prior to the first receiving, indication information indicating an option for reception of the information the number of times different from once, and signaling the created indication information; 
     the indication information is one of a part of system information and a system information parameter; 
     the system information parameter is a random access channel format; 
     in the signaling after the first receiving, the indication information is comprised in a retransmission scheduling grant; 
     in the second receiving, the information is respectively received once in a second to an (n−1) st  transmission opportunity of the n consecutive transmission opportunities, and is received more than once in an n-th transmission opportunity of the n consecutive transmission opportunities; 
     the second receiving is performed by using transmission time interval bundling; 
     the second receiving is performed by hybrid automatic repeat request retransmission opportunities. 
     According to further refinements of the invention as defined under the above first and second aspects, 
     the information is a random access message 3. 
     According to the present invention, in a third aspect, this object is for example achieved by an apparatus comprising: 
     means for transmitting, in a first transmission opportunity of n consecutive transmission opportunities, n being an integer greater than 1, information to be transmitted once, and for transmitting, in one transmission opportunity different from the first transmission opportunity, the information a number of times different from once. 
     According to further refinements of the invention as defined under the above third aspect, 
     the apparatus further comprises means for generating the information to be transmitted; 
     the means for transmitting is configured to respectively transmit the information once in a second to an (n−1) st  transmission opportunity of the n consecutive transmission opportunities, and to transmit the information more than once in an n-th transmission of the n consecutive transmission opportunities; 
     the means for transmitting is configured to transmit using transmission time interval bundling; 
     the means for transmitting is configured to transmit by hybrid automatic repeat request retransmission opportunities; 
     the apparatus is constituted by one of a user equipment and a terminal. 
     According to the present invention, in a fourth aspect, this object is for example achieved by an apparatus comprising: 
     means for receiving, in a first transmission opportunity of n consecutive transmission opportunities, n being an integer greater than 1, information once, and for receiving, in one transmission opportunity different from the first transmission opportunity, the information a number of times different from once. 
     According to further refinements of the invention as defined under the above fourth aspect, 
     the apparatus further comprises means for creating, prior to the first transmission opportunity, indication information indicating an option for reception of the information the number of times different from once, and means for signaling the created indication information; 
     the indication information is one of a part of system information and a system information parameter; 
     the system information parameter is a random access channel format; 
     the means for signaling is configured to signal, after to the first transmission opportunity, the indication information comprised in a retransmission scheduling grant; 
     the means for receiving is configured to respectively receive the information once in a second to an (n−1) st  transmission opportunity of the n consecutive transmission opportunities, and to receive the information more than once in an n-th transmission opportunity of the n consecutive transmission opportunities; 
     the means for receiving is configured to receive using transmission time interval bundling; 
     the means for receiving is configured to receive by hybrid automatic repeat request retransmission opportunities; 
     the apparatus is constituted by an evolved node B. 
     According to further refinements of the invention as defined under the above third and fourth aspects, 
     the information is a random access message 3; 
     at least one, or more of means for generating, means for transmitting, means for receiving, means for creating, means for signaling and the apparatus is implemented as a chipset or module. 
     According to the present invention, in a fifth aspect, this object is for example achieved by a system comprising: 
     an apparatus according to the third aspect; and 
     an apparatus according to the fourth aspect. 
     According to the present invention, in a sixth aspect, this object is for example achieved by a computer program product comprising code means for performing methods steps of a method according to any one of the first and second aspects, when run on a computer. 
     In this connection, it has to be pointed out that the present invention enables one or more of the following: 
     Providing coverage improvement 
     Causing significantly smaller overhead in bundling 
     Linking the use of bundling e.g. to the RACH format 
     no additional downlink signaling needed 
     Bundling can be done so that maximum delay is not increased. 
     Closing the coverage gap between RACH (preamble) and RA message 3 in particular in the case of repeated RACH preamble sequence, since when comparing the coverage of PUCCH, RACH, and RA message 3 to link simulations, it can be noted that RA message 3 may have the smallest coverage. 
     Satisfying the 50 ms delay requirement for the state transition from dormant to active state of the UE, since the number of re-transmission opportunities cannot be increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the present invention is described herein below with reference to the accompanying drawings, in which: 
         FIG. 1A  shows bundling arrangement examples (Bundle A, B, and C) as well as with the case of without bundling (Basic) and normal bundling (2×Bundle), and  FIG. 1B  shows a comparison of maximum number of TTIs, SNR (signal to noise ratio) requirement and coverage area; 
         FIG. 2  shows the average number of TTIs used e.g. for RA message 3 transmission; 
         FIG. 3  shows a delay cdf (cumulative distribution function) e.g. from the beginning of RA message 3 to beginning of ACK transmission; 
         FIG. 4  shows methods for information transmission according an example of to the present invention; and 
         FIG. 5  shows respective apparatuses (e.g. UE and eNB) for information transmission according to examples of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENT INVENTION 
     Embodiments of the present invention are described herein below by way of example with reference to the accompanying drawings. 
     It is to be noted that for this description, the terms “RA message 3, TTI bundling and HARQ retransmission opportunities” are examples for “information, transmitting information more than once in one transmission and second transmitting”, respectively, without restricting the latter-named terms to the special technical or implementation details imposed to the first-named terms. It is also noted that first transmission and retransmissions may represent different incremental redundancy versions of the same encoded packet. Furthermore, retransmissions may or may not be self-decodable. It is further noted that there are multiple encoding and combining options that may be used in TTI bundling. The bundled transmissions may represent different incremental redundancy versions of the same encoded packet. Furthermore, transmissions may or may not be self-decodable. The bundled transmissions may be transmitted also at different frequencies. 
       FIG. 1A  shows bundling arrangement examples (Bundle A, B, and C) as well as with the case of without bundling (Basic) and normal bundling (2×Bundle), and  FIG. 1B  shows a comparison of maximum number of TTIs, SNR requirement and coverage area. 
     As shown in  FIGS. 1A and 1B , there are provided several bundling arrangements (bundles A to C) as examples according to the present invention. In  FIG. 1A , an example of the first transmitting (to be described later) is denoted with “transmission”, while an example for the second transmitting (to be describe later) is denoted with “1 st  retransmission” to “3 rd  retransmission”. It is to be noted that the terms “transmission” and “retransmission” may also relate to (re)transmission opportunities. As reference examples, there are given a case of no bundling (denoted with “basic”) and basic bundling (denoted with “2×Bundle”). In the basic reference case, the information is transmitted once in the transmission and each retransmission, while in the basic bundling case (“2×Bundle”), the information is transmitted twice in the transmission and each retransmission. 
     According to the bundle cases A to C as examples of the present invention, the information is transmitted once in the transmission (also referred to as “1 st  transmission” hereinafter). In example bundle case A, the information is then transmitted twice in each retransmission (also referred to as “transmissions different from the 1 st  transmission” hereinafter). In example bundle case B, the information is transmitted twice in the 1 st  retransmission, 5 times in the 2 nd  retransmission and is not transmitted in the 3 rd  retransmission. In example case C, the information is transmitted once in the 1 st  retransmission, 6 times in the 2 nd  retransmission and is not transmitted in the 3 rd  retransmission. 
     Corresponding coverage estimates for the reference cases and the example cases of the present invention are shown for 1% BLER (block error rate) in  FIG. 1B . The RACH coverage with preamble repetition is e.g. 94%. According to the basic reference case, sufficient coverage (only 87%) may not be achieved e.g. for RA message 3 with 3 re-transmissions without bundling. Also example bundle cases B and C may provide a favorable coverage of 95%, which is the same as the coverage which may be achieved by the bundle reference case (however, the bundle reference case does so on the expense of a significantly increased average number of TTIs used for transmission, see below). 
       FIG. 2  shows the average number of TTIs used for RA message 3 transmission. 
     In  FIG. 2 , the average number of TTIs used for RA message 3 transmission is shown for the considered SINR (signal to interference plus noise ratio) distribution, showing that the proposed bundling has only a modest impact on the average overhead. That is, example bundle cases A to C may exhibit an average number of TTIs around 1.5, while the basic reference case shows an average TTI number of around 1.2, and the bundle reference case shows an average TTI number of around 2.2. 
     One issue with bundling is the impact on the delay. In practice, bundling may cause even double HARQ RTT (round trip time). 
       FIG. 3  shows a delay cdf (cumulative distribution function) from e.g. the beginning of RA message 3 transmission to beginning of ACK transmission. 
     In  FIG. 3 , the cdf for the delay e.g. from the beginning of RA message 3 transmission to the beginning of positive ACK transmission is shown for the considered SINR cdf of the reference cases (basic, 2×Bundle) and the example cased (Bundles A to C). 
     The delay is calculated with assumptions not favorable for bundling: 
     normal HARQ RTT: 8 ms, 
     HARQ RTT for bundled transmission: 16 ms, and 
     eNB processing time: 3 ms. 
     From  FIG. 3 , it can be seen that the proposed bundling does not increase the maximum delay (see basic reference case around 53 ms), but may even decrease the maximum delay in the example case of bundle C to around 25 ms. Example case bundles A and B may still provide sufficiently low maximum delays of around 45 ms and 32 ms, respectively. 
       FIG. 4  shows methods according to examples of the present invention. Signaling between elements is indicated in horizontal direction, while time aspects between signaling may be reflected in the vertical arrangement of the signaling sequence as well as in the sequence numbers. It is to be noted that the time aspects indicated in  FIG. 4  do not necessarily restrict any one of the method steps shown to the step sequence outlined. This applies in particular to method steps that are functionally disjunctive with each other, for example step S 1 - 1  of generating information to be transmitted may also be performed e.g. prior to step S 2 - 2  of signaling indication information. Within  FIG. 4 , for ease of description, means or portions which may provide main functionalities are depicted with solid functional blocks or arrows and a normal font, while means or portions which may provide optional functions are depicted with dashed functional blocks or arrows and an italic font. 
     As shown in  FIG. 4 , a communication system  200  may comprise a UE  201  and a network  203 . The network  203  in turn may comprise a base station such as the eNB  202 . The eNB  202  may also be disposed as an integral entity with e.g. a gateway entity not shown, or may be connected to the gateway entity not shown. 
     As optional preparatory measures, in step S 2 - 1 , e.g. the eNB  202  may perform creating, prior to a first receiving, indication information indicating an option for reception of the information the number of times different from once. Furthermore, in step S 2 - 2 , e.g. the eNB  202  may perform signaling, to the UE  201 , the created indication information. The indication information may be a part of system information or a system information parameter, such as a random access channel format. Alternatively, the indication information may be comprised, after the first receiving, in a retransmission scheduling grant. Finally, in step S 1 - 1 , e.g. the UE  201  may perform generating the information to be transmitted (e.g. an random access message 3). 
     In step S 1 - 2   a , e.g. the UE  201  may perform first transmitting, in a first transmission opportunity of n consecutive transmission opportunities, n being an integer greater than 1, the generated information once (see e.g. box on arrow for step S 1 - 2   a ). In step S 2 - 3   a , e.g. the eNB  202  may perform receiving, in the first transmission opportunity, the generated information once. 
     In step S 1 - 2   b , e.g. the UE  201  may perform second transmitting, in one transmission opportunity different from the first transmission opportunity, the generated information a number of times different from once (see e.g. box on arrow for step S 1 - 2   b ). Thus, in step S 2 - 3   b , e.g. the eNB  202  may perform receiving, in the one transmission opportunity different from the first transmission opportunity, the generated information the number of times different from once. 
     According to further refinements of the methods relating e.g. to the eNB  202  or UE  201  according to examples of the present invention, the information to be transmitted may be a RA message 3. In addition, the information may respectively be transmitted/received once in a second to an (n−1) st  transmission opportunity of the n consecutive transmission opportunities, and may be transmitted/received more than once in an n-th transmission opportunity of the n consecutive transmission opportunities. Furthermore, the second transmitting may be performed by using transmission time interval bundling or by hybrid automatic repeat request retransmission opportunities. 
       FIG. 5  shows embodiments of respective apparatuses (e.g. UE  201  and BS/RNC  202 ) for information transmission according to examples of the present invention. Within  FIG. 5 , for ease of description, means or portions which may provide main functionalities are depicted with solid functional blocks or arrows and a normal font, while means or portions which may provide optional functions are depicted with dashed functional blocks or arrows and an italic font. 
     The UE  201  may comprise a CPU or core functionality CF (referred to as “CPU” hereinafter)  2011 , a memory  2012 , a transmitter (or means for transmitting) Tx  2013 , an optional receiver (or means for receiving) Rx  2014  and an optional generator (or means for generating)  2015 . The eNB  202  may comprise a CPU  2021 , a memory  2022 , an optional transmitter (or means for transmitting) Tx  2023 , a receiver (or means for receiving) Rx  2024  and an optional creator (or means for creating)  2025 . As indicated by the dashed extensions of the functional blocks of the CPUs  2011  and  2021 , the means for generating  2015  of the UE  201  and/or the means for creating  2025  of the eNB  202  may be functionalities running on the CPUs  2011  and/or  2021  or may alternatively be separate functional entities or means. 
     The CPUs  20   x   1  (wherein x=1 and 2) may respectively be configured to process various data inputs and to control the functions of the memories  20   x   2 , the (optional) transmitters  202   x   3  and the (optional) receivers  20   x   4  (and the means for generating  2015  of the UE  201  as well as the means for creating  2025  of the eNB  202 ). The memories  20   x   2  may respectively serve e.g. for storing code means for carrying out e.g. the respective method according to examples of the invention, when run on the CPUs  20   x   1 . It is to be noted that the (optional) transmitters  20   x   3  and the (optional) receivers  20   x   4  may alternatively be provided as respective integral transceivers (not shown). It is further to be noted that the transmitters/receivers may be implemented i) as physical transmitters/receivers for transceiving e.g. via the air interface (e.g. in case of UE  201  towards the eNB  202 ), or ii) as routing entities e.g. for transmitting/receiving data packets e.g. in a PS (packet switched) network (e.g. between the eNB  202  and a gateway not shown when the eNB  202  and the gateway are disposed as separate network entities), or iii) as functionalities for writing/reading information into/from a given memory area (e.g. in case of shared/common CPUs or memories e.g. of eNB  202  and the gateway not shown when the eNB  202  and the gateway not shown are disposed as an integral network entity), or iv) as any suitable combination of i) to iii). 
     Optionally, e.g. the eNB  202  may comprise the creator (or means for creating)  2025  for creating, prior to a first transmission opportunity, indication information indicating an option for reception of the information the number of times different from once. Furthermore, e.g. the optional transmitter  2023  in conjunction with the CPU  2021  of the eNB  202  may constitute the means for signaling, to the optional receiver  2012  of the UE  201 , the created indication information. The indication information may be a part of system information or a system information parameter, such as a random access channel format. Alternatively, the indication information may be comprised, after the first receiving, in a retransmission scheduling grant. Finally, e.g. the UE  201  may comprise the optional generator (or means for generating)  2015  for generating the information to be transmitted (e.g. an random access message 3). 
     For example, the transmitter  2013  of the UE  201  may perform transmitting, in a first transmission opportunity of n consecutive transmission opportunities, n being an integer greater than 1, the generated information once. And, e.g. the receiver  2024  of the eNB  202  may perform receiving, in the first transmission opportunity, the generated information once. 
     Furthermore, e.g. the transmitter  2013  of the UE  201  may perform transmitting, in one transmission opportunity different from the first transmission opportunity, the generated information a number of times different from once (see e.g. above in conjunction with  FIG. 1 ). Thus, e.g. the receiver  2024  of the eNB  202  may perform receiving, in the one transmission opportunity different from the first transmission opportunity, the generated information the number of times different from once. 
     According to further refinements e.g. of the eNB  202  or UE  201  according to examples of the present invention, the information to be transmitted by the transmitter  2013  of the UE  201  may be a RA message 3. In addition, the transmitter  2013  of the UE  201 /the receiver  2024  of the eNB  202  may respectively be configured to transmit/receive the information once in a second to an (n−1) st  transmission opportunity of the n consecutive transmission opportunities, and to transmit/receive the information more than once in an n-th transmission opportunity of the n consecutive transmission opportunities. Furthermore, the transmitter  2013  of the UE  201  may be configured to transmit using transmission time interval bundling or hybrid automatic repeat request retransmission opportunities. 
     Furthermore, at least one of, or more of the means for generating  2015  of the UE  201 , the means for transmitting  2013  of the UE  201 , the means for receiving  2024  of the eNB  202 , the means for creating  2025  of the eNB  202 , the means for signaling  2021 ;  2023  and the UE  201  and/or the eNB  202 , or the respective functionalities carried out, may be implemented as a chipset or module. 
     Finally, the present invention also relates to a system which may comprise the UE  201  and the eNB  202 . 
     Without being restricted to the details following in this section, the embodiment of the present invention may be summarized as follows: 
     There is provided an efficient TTI bundling method for situations when base station does not have sufficient information on the path loss to reliably estimate the need for bundling before the beginning of data transmission in question. The method may be applied to LTE RA message 3 transmission in particular.
 
TTI bundling may be done only for HARQ re-transmissions. That is, no bundling may used for the first transmission.
 
TTI bundling may be different also for different re-transmissions. A particular example is the case when bundling is done only for the last re-transmission.
 
The use of bundling may be signaled to the terminal as part of system information, or it may be linked to another system information parameter, such as RACH format.
 
The use of bundling for re-transmission may be indicated also on the re-transmission scheduling grant. In such case, the need for bundling is estimated based on the information obtained in the detection and decoding of the first transmission. Alternatively, bundling can be autonomously coupled with the pre-determined re-transmissions of non-adaptive HARQ (having no scheduling grants for retransmissions).
 
     Further Embodiments 
     For the purpose of the present invention as described herein above, it should be noted that 
     an access technology may be any technology by means of which a user equipment can access an access network (or base station, respectively). Any present or future technology, such as WiMAX (Worldwide Interoperability for Microwave Access) or WLAN (Wireless Local Access Network), BlueTooth, Infrared, and the like may be used; although the above technologies are mostly wireless access technologies, e.g. in different radio spectra, access technology in the sense of the present invention may also imply wirebound technologies, e.g. IP based access technologies like cable networks or fixed line. 
     a network may be any device, unit or means by which a station entity or other user equipment may connect to and/or utilize services offered by the access network; such services include, among others, data and/or (audio-) visual communication, data download etc.; 
     generally, the present invention may be applicable in those network/user equipment environments relying on a data packet based transmission scheme according to which data are transmitted in data packets and which are, for example, based on the Internet Protocol IP. The present invention is, however, not limited thereto, and any other present or future IP or mobile IP (MIP) version, or, more generally, a protocol following similar principles as (M)IPv4/6, is also applicable; 
     a user equipment may be any device, unit or means by which a system user may experience services from an access network; 
     method steps likely to be implemented as software code portions and being run using a processor at the network element, are software code independent and can be specified using any known or future developed programming language as long as the functionality defined by the method steps is preserved; 
     generally, any method step is suitable to be implemented as software or by hardware without changing the idea of the present invention in terms of the functionality implemented; 
     method steps and/or devices, units or means likely to be implemented as hardware components at the UE and/or the eNB, or any module(s) thereof, are hardware independent and can be implemented using any known or future developed hardware technology or any hybrids of these, such as MOS (Metal Oxide Semiconductor), CMOS (Complementary MOS), BiMOS (Bipolar MOS), BiCMOS (Bipolar CMOS), ECL (Emitter Coupled Logic), TTL (Transistor-Transistor Logic), etc., using for example ASIC (Application Specific IC (Integrated Circuit)) components, FPGA (Field-programmable Gate Arrays) components, CPLD (Complex Programmable Logic Device) components or DSP (Digital Signal Processor) components; in addition, any method steps and/or devices, units or means likely to be implemented as software components may alternatively be based on any security architecture capable e.g. of authentication, authorization, keying and/or traffic protection; 
     devices, units or means (e.g. UE and/or eNB and their respective means) can be implemented as individual devices, units or means, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device, unit or means is preserved. 
     For ease of clearness, the following table provides a survey of the abbreviations used in the above description. It is to be noted that an “s” following an abbreviation represents the plural of that abbreviation, e.g. “UEs” represents “user equipments”. 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 3GPP 
                 3 rd  generation partnership project 
               
               
                   
                 DL 
                 Downlink 
               
               
                   
                 UL 
                 Uplink 
               
               
                   
                 eNB 
                 Evolved node B 
               
               
                   
                 UTRAN 
                 UMTS Terrestrial Radio Access Network 
               
               
                   
                 UMTS 
                 UMTS Terrestrial Radio Access Network 
               
               
                   
                 HARQ 
                 Hybrid Automatic Repeat Request 
               
               
                   
                 LTE 
                 Long Term Evolution 
               
               
                   
                 PUCCH 
                 Physical Uplink Control Channel 
               
               
                   
                 PUSCH 
                 Physical Uplink Shared Channel 
               
               
                   
                 RA 
                 Random Access 
               
               
                   
                 RACH 
                 Random Access Channel 
               
               
                   
                 TTI 
                 Transmission Time Interval 
               
               
                   
                 UE 
                 User Equipment 
               
               
                   
                 ACK/NACK 
                 Acknowledgement/non-acknowledgement 
               
               
                   
                 Cdf 
                 Cumulative distribution function