FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
/. Title of the invention:
CHANNEL ESTIMATION IN A WIRELESS NETWORK
2. Applicant(s)
NAME 1 NATIONALITY I ADDRESS
TATA CONSULTANCY Nirmal Building, 9th Floor, Nariman Point,
Indian
SERVICES LIMITED Mumbai, Maharashtra-400021, India
3. Preamble to the description
COMPLETE SPECIFICATION
The following specification particularly describes the invention and the manner in which it
is to be performed.

TECHNICAL FIELD
[0001] The present subject matter relates, in general, to wireless network technology and, in particular, to channel estimation in the wireless network technology.
BACKGROUND
[0002] Wireless network technology includes a variety of radio access network (RAN) technologies, such as, Code Division Multiple Access (CDMA), Universal Mobile Telecommunications System (UMTS), and Global System for Mobile communications (GSM). Long Term Evolution (LTE) is the latest standard in the radio access network technology and provides a user with an improved network access. The LTE includes. amongst other channels, a physical channel, which serves as a transmission channel for carrying user data and control data including control information pertaining to the transmission channel and the user data. The LTE facilitates fast and reliable transmission of data between a user equipment, such as cellular devices, computers, and set top boxes, and a base station, such as an enhanced node B(eNodeB). Data transmissions over a radio access network, however, may get corrupted due to various reasons such as noise in the transmission channel, interference from other transmissions, such as radio; and environmental factors. Additionally, data transmission over these transmission channels may get corrupted owing to distortion due to multipath, which can be caused owing to reflections by objects like building, vehicles, etc. The corruption of the data can cause errors in a signal received by the base station, for example, the distortion due to multi-path can cause errors such as inter-symbol interference (ISI).
[0003] To minimize such errors from the receive signal and reliably receive the data, channel response of the transmission channel through which a transmitted signal travels before reaching the base station is estimated. The estimation of the channel response facilitates determination of channel quality around the user equipment and accordingly the transmitted signal is corrected by a channel equalizer implemented at the base station. For estimating channel response, a variety of channel estimation schemes, which can be blind. semi-blind, or non-blind, are implemented. However, Conventional channel estimation techniques are either not reliable or result in loss of bandwidth,

SUMMARY
[0004] This summary is provided to introduce concepts related to estimation of channel response, which are further described below in the detailed description. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.
|0005] Method(s) and a system(s) for identification of HARQ information carried on a slot of a sub-frame of a transmission channel are described herein. In one implementation, a first reference signal carried on the slot of the transmission channel is regenerated based on regeneration parameters. Based on the regenerated first reference signal, a probabilistic second reference signal corresponding to a second reference signal carried on the slot is determined. Subsequent to estimation of the second reference signal, the HARQ information Js identified based on the probabilistic second reference signaJ.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.
[0007] Fig. 1 illustrates a wireless network environment, in accordance with an embodiment of the present subject matter.
J0008] Fig. 2 illustrates components of a system for identification of control information, transmitted by a user equipment to determine channel response, in accordance with an implementation of the present subject matter.
[0009] Fig 3 illustrates a method for identification of control information to determine channel response, in accordance with an implementation of the present subject matter.
|00010] Fig. 4 illustrates a CQI performance plot based on identification of the HARQ information, according to an embodiment of the present subject matter.

DETAILED DESCRIPTION
[00011] Generally, in a cellular communication system one or more user equipments (UE) are connected to and served by a base station at a given time. The user equipments can include both mobife terminals, such as mobile telephones, personal digital assistants, and computing devices; and fixed terminals, such as televisions, set-to boxes, and the like. The base station can be, for example, an enhanced node 13, The UEs communicate with the base station and other UEs over a wireless network, such as a radio access network. Long Term Evolution (LTE) technology is the latest radio access technology being standardized by the third Generation Partnership Project (3GPP). The LTE technology has high throughput, low latency, plug and play, an improved end-user experience, and a simple architecture resulting in low operating costs. Accordingly, the LTE technology is being implemented in various applications, such as high-definition video applications, high quality audio application, voice over internet protocol (VoIP) applications, and Audio-Video applications under high speed conditions that requires radio link coverage and reliability to be maintained.
[00012] The LTE technology uses various channels to transmit data between a UE and the base station. These channels are used to segregate different types of data, so that the data may be transmitted across the radio access network in an orderly fashion. These channels are divided into three categories, namely, logical channels, transport channels, and physical channels. The logical channel defines what kind of information is to be transferred, while the transport channel defines how the information is to be transferred. The physical channels are transmission channels that carry user data and control information regarding the transmission channels and the user data.
[00013] A physical control channel can be physical downlink control channel (PDCCH) and physical uplink control channel (PUCCH). The PDCCH is used to convey UE specific downlink control information from the base station to the UEs. Similarly, the PUCCH is used to carry uplink control information from the UEs to the base station. Typically, when a receiver of the UE receives the data and the control information, the receiver may derive the control information carried by the transmission channel and use the control information to

decode the position of user data, i.e., where exactly does the .data, corresponding to a user, is present on a data channel, such as, Physical Downlink Shared Channel (PDSCH).
[00014] Generally, transmission channel available for data transmission is segmented into a plurality of equal duration time and frequency intervals. The LTE technology has a concept of radio frames, sub-frames, and slots in a transmission channel. Each LTE radio frame is 10 msec (millisecond) in duration and is divided into ten sub frames, each sub frame being 1.0 msec long. Each sub-frame is further divided into two slots, each slot being 0.5 msec in duration. Still further, each slot may include six or seven symbols. Thus, in the LTE technology data is transmitted over a transmission channel in the form of frames, sub-frames, slots, and symbols.
[00015] The PUCCH carries the control information, such as channel quality indicator (CQJ) information, scheduling requests, and acknowledgement responses. CQI, for example. is a measurement of the communication quality of the transmission channel that carries the user data, i.e., the PDSCH. The CQI can be a value representing a' measure of channel quality for a given channel. Typically, a high value CQI is indicative of a channel with good quality and vice versa.
|00016] When two UE's transmit information simultaneously then there might be overlapping of the information. In order to avoid such overlap of the information, the PUCCH carries SR for scheduling Physical Uplink Shared Channel (PUSCH) and accordingly the UE is allocated one or more resource blocks for the PUCCH. An acknowledgement response can be positive, called ACK, indicating that the UE has received and decoded the data transmitted by the base station. Further, owing to various factors, such as noise in the physical channel, interference from other transmissions, and distortion due to multipath, the acknowledgement response can be negative, called NACK, indicating a retransmission request. Further, the acknowledgement responses can be carried by hybrid automatic repeat request (HARQ) bits.
[00017] The PUCCH has 6 formats, namely, 1, la, lb, 2, 2a, and 2b. In the PUCCH formats 2a and 2b, the HARQ bits are carried on reference signals, which can be demodulated reference signals (DMRS), carried over the PUCCH. The reference signals,

which are actually transmitted by the UE, are to be regenerated at the base station for estimation of PUCCH, i.e., transmission channel response estimation process. The transmission channel response is indicative of the channel quality around the user equipment and accordingly a transmitted signal is corrected. In order to minimize errors in the received signal, the channel response estimation in turn is used to equalize data pertaining to control information for efficient decoding of the CQI bits. For estimating the channel response, a variety of channel estimation schemes, which can be blind, semi-blind, or non-blind, are implemented at the base station.
|00018] Although, the non-blind channel estimation techniques are reliable but such techniques result in loss of bandwidth. On the other hand, the blind channel estimation techniques are efficient in terms of bandwidth but such techniques are often not reliable. Further, the conventional semi-blind techniques though are efficient in terms of bandwidth usage when compared with non blind techniques; however, in such semi-blind techniques the control information present is inadequate to estimate the channel response. For example, in the PUCCH formats 2a and 2b, regeneration of a reference signal carried by the PUCCH in the absence of the information pertaining to the HARQ bits, may provide inaccurate estimate of the transmission channel response.
[00019] According to an embodiment of the present subject matter, methods and systems for identification of control information, such as HARQ bits, for estimation of the transmission channel response are described herein. In one implementation, the control information pertaining to a transmission channel, such as the PUCCH is identified. The PUCCH supports the PUCCH format 2a or 2b. In the PUCCH format 2a and 2b, two reference signals are carried on each slot. A first reference signal carried over a slot of a sub-frame of (he transmission channel is regenerated at the base station using one or more regeneration parameters. The regeneration parameters include spreading factor, reference signal sequence, modulated HARQ bit, etc. In one implementation, based on the regenerated first reference signal, a first channel response corresponding to the slot may be determined.
[00020] This channel response may be used to determine a probabilistic second reference signal. The probabilistic second reference signal represents a probable estimation of the

second reference signal. Further, the probabilistic second reference signal is used to identify HARQ information carried on a slot of the transmission channel. In an example, the HARQ information carried in HARQ field includes modulated HARQ bit (dlO). The identified HARQ information js used to regenerate the second reference signal, which is actually transmitted by the Ug. The base station can use the first and the second reference signal for coherent user data estimation or non-blind user data estimation. The second reference signal can be used for estimation of a second channel response. The first and second channel response may in turn be used for transmission channel estimation. In other words, the transmission channel is determined based on the first and the second reference signal regenerated at the base station. The regeneration of the second reference signal using the HARQ information carried by the transmission channel, i.e., using the actual HARQ information, results in the efficient estimation of the transmission channel response.
[00021] Further, Once the HARQ information is identified for a slot, say, 0lh slot in a sub-frame, we can use the same HARQ information to determine transmission channel response corresponding to another slot, say, Is1 slot of the sub-frame, thereby saving on processing time. Thus, the present subject matter not only provides efficient estimation of transmission channel response for a slot by using HARQ information, which facilitates adequate decoding of CQ1 information, but also provides for efficiency in terms of processing time.
[00022] While aspects of described systems and methods for the estimation of the transmission channel response can be implemented in any number of different computing systems; tf'mraTrrftaTfs, andrbr configurations, the embodiments ace described in (be context of the following exemplary system(s).
EXEMPLARY SYSTEMS [00023] Fig. I illustrates a wireless network environment 100, in accordance with an embodiment of the present subject matter. The network environment implements a radio access network. In one implementation, the radio access network implements a LTE technology for technologies such as Universal Mobile Telecommunications System (UMTS), Evolved-UMTS Terrestrial Radio Access (E-UTRA), Worldwide Interoperability for Microwave Access (\ViMax), wireless local area network (WLAN), and Global System for Mobile communications (GSM). The wireless network environment 100 includes one or

more user equipments 105-1, 105-2... 105-n communicating with a base station 110. The base station 110 is, for example, an enhanced Node B in UMTS or E-UTRA, a base station in WiMax, a base transceiver station in GSM, and access point in WLAN. The one or more user equipments (UE), 105-1, 105-2... 105-n, collectively referred to as the UE(s) 105 can be mobile phones, persona! digital assistants, computers, laptops, handheld computers, portable computers, set top boxes, television, etc.
[00024] Generally, user data, i.e., data to be transmitted by a UE 105 is first encoded and then modulated to generate symbols. These symbols are subsequently mapped onto a transmission channel. Usually, a transmission channel available for data transmission is segmented into a plurality of slots, of equal duration time and frequency, called as resource elements. A single resource element or multiple resource blocks may be allocated for transmitting the user data. When the user data is transmitted, control information may accompany it. In one implementation, the user equipments can transmit uplink information including the control information on a physical channel, such as PUCCH, and user data on a physical channel, such as PUSCH, to the base station 110. The PUCCH carries control information, such as CQ1 information, scheduling requests, and HARQ bits. The HARQ bits contain information pertaining to an acknowledgment response, which can be either a positive response (ACK) or a negative response (NACK). In one implementation, the information is transmitted on the PUCCH supported by the PUCCH formats 2a and 2b. The PUCCH format 2a includes one HARQ acknowledgement, i.e., ACK/NACK bits and the format 2b includes two bits of HARQ acknowledgement.
[00025] The PUCCH format 2a involves transmission of twenty bits of CQ1 and 1 bit of HARQ. Similarly, the PUCCH format 2b has twenty bits of CQI and 2 bits of HARQ. In both the PUCCH formats, the CQI bits can be modulated using quadrature phase shift keying (QPSK.) modulation, which results in ten modulated symbols from d(0) to d(9). In the PUCCH format 2a, a HARQ bit can be modulated using binary phase shift keying (BPSK.) modulation and in the PUCCH format 2b, the HARQ bits can be modulated using the QPSK modulation. The modulation of the HARQ bits results in the one modulated symbol, i.e., d( 10). Further, in the PUCCH formats 2a and 2b, each slot includes two reference signals, say a first reference signal (DMRS1) and a second reference signal (DMRS2). The two

references signals are demodulated reference signals. The second reference signal in each of the slots carries the modulated HARQ bits(dlO).
|00026| In one implementation, when a receiver at the base station 110 receives the user data and the control information carried by the PUCCH, the base station 110 may estimate the transmission channel response by efficiently identifying HARQ information embedded in the second reference signal. In order to efficiently determine a transmission channel response of the transmission channel and to perform efficient decoding of the CQl bits, both the reference signals are to be regenerated at the base station 110. For the purpose, the base station 110 is, for example, associated with a system 120 for estimation of the channel response, The system 120 includes, among other things, regeneration module 125 and an identification module 130. The regeneration module 125 is configured to regenerate a first reference signal based on estimation parameters, such as, spreading factor and reference si'gnaf sequence. Subsequent to regeneration of the first reference signal, the regeneration module 125 determines a channel response associated with the first reference signal hereinafter referred to as first channel response.
[00027] In one implementation, based on the first channel response, the identification module 130 determines a probabilistic second reference signal. The identification module 130, based on the probabilistic second reference signal, identifies HARQ information from the PUCCH. The HARQ information includes information pertaining to the modulated HARQ bit, i.e., dlO. The HARQ information, in the PUCCH format 2a, is the symbol (dlO) generated after modulation of the one bit HARQ carried by the second reference signal. Similarly, the HARQ information, in the PUCCH format 2b, is the symbol (dlO) generated subsequent to modulation of two bit HARQ. Once the HARQ information is identified, the regeneration module 125 regenerates the second reference signal. Using the second reference signal the regeneration module 125 computes a second channel response, i.e., the channel response corresponding to the second reference signal, further, using the first channel response and the second channel response, the transmission channel response for a corresponding slot is determined, which in turn may be used for decoding of the CQI information by the system 120.

[00028] Fig. 2 illustrates components of the system 120 for identifying HARQ information for estimation of channel response, according to an embodiment of the present subject matter. The system 120 can be implemented in computing systems that include, but are not limited to, desktop computers, hand-held devices, multiprocessor systems, personal digital assistants (PDAs), laptops, network computers, cloud servers, minicomputers, mainframe computers, and the like. In one implementation, the system includes interface(s) 205, one or more processor(s) 210, and a memory 215 coupled to the processor(s) 2 10.
[00029) The interfaces 205 may include a variety of software and hardware interfaces, for example, interfaces for peripheral device(s), such as a keyboard, a mouse, an external memory, and a printer. Further, the interfaces 205 may enable the system to communicate with other computing systems, such as web servers and externa! databases. The interfaces 205 can facilitate multiple communications within a wide variety of networks and protocol types, including wired networks, for example local area network (LAN), cable, etc., and wireless networks such as WLAN, cellular, or satellite. For the purpose, the interfaces 205 may include one or more ports for connecting a number of computing systems to each other or to another server computer.
[00030] The processor 210 can be a single processing unit or a number of units, all of which could include multiple computing units. The processor 210 may be implemented as one or more microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, state machines, logic circuitries, and/or any devices that manipulate signals based on operational instructions. Among other capabilities, the processor 210 is configured to fetch and execute computer-readable instructions and data stored in the memory 215.
|00031] The memory 215 may include any computer-readable medium known in the art including, for example, volatile memory such as static random access memory (SRAM) and dynamic random access memory (DRAM), and/or non-volatile memory, such as read only memory (ROM), erasable programmable ROM, flash memories, hard disks, optical disks, and magnetic tapes.

[00032] The memory 215 includes module(s) 220 and data 225. The modules 220, amongst other things, include routines, programs, objects, components, data structures, etc., which perform particular tasks or implement particular abstract data types. The data 225 serves, amongst other things, as a repository for storing data processed, received and generated by one or more of the modules 220. The modules 220 further include, for example, the regeneration module 125, the identification module 130, and other module(s) 230. The other modules 230 may include programs that supplement applications on the system 120, for example, programs in the operating system. The data includes, for example, analysis data 235, reference data 240, and other data 245. The other data 245 includes data generated as a result of the execution of one or more modules in the other modules 230.
[00033] As previously mentioned, the UEs 105 transmit the user data and the control information including the HARQ bits is transmitted over the transmission channel, such as, the PUSCH and PUCCH respectively. In the PUCCH format 2a and 2b, the HARQ bits are embedded in the two reference signals carried by each of the slots in the PUCCH. In an example, the reference signals can be regenerated using the following equation:


z(m) isd(IO)form=l.
. In PUCCH format 2a and 2b, m=l for the second reference signal and accordingly from the above equation it can be seen that the HAR.Q information is required for estimation of the second reference signal. In one implementation, the regeneration module 125 is configured to regenerate the first reference signal and the second reference signal at the base station 110. The first reference signal may be regenerated based on one or more regeneration parameters, such as, spreading factor, reference signal sequence, and modulated HARQ bit.
[00034] For the purpose of explanation, consider that Rx_rst is first received reference signal and Rx_rs2 is second received reference signal, which are received at the base station 110. Further, Rf _rst is actual first reference signal (also referred to as the first reference signal) and Rf _rs2 is actual second reference signal (also referred to as the second reference signal), which are to be regenerated at the base station 110. The first and second reference are actual reference signals that the UE 105 transmitted, while the first received and second received reference signals are reference signal which are actually received at the base station 110. It will be understood that owing channel affects, such as, multipath and reflections, the received first and the received second reference signal can be different from the First and second reference signal respectively. Rx _rs{, and Rx_rs2 may be stored in the reference data 240; while Rf _rs] and Rf _rs2 may be stored in the analysis data 235. Further, to estimate transmission channel response, the first and the second reference signal are to be regenerated at the base station 110.
[00035] For the purpose, the regeneration module 125 regenerates the first reference signal. In the PUCCH formats 2a and 2b, m is 0 and n is greater than or equal to zero and less than or equal to 11, and Z(0) = 1 for the first reference signal. Substituting the values for 2,(m). m and n in equation J. lbe first reference signa) can be represented as:
Rf_rs,= w(m) *Zfm)*r(a,uJn) (2)
The regeneration parameters required for regeneration of the first reference signal are stored in the reference data 240 and are available to the regeneration module 125. The regeneration

module 125 based on the equation (2), regenerates the first reference signal at the base station 110. The regenerated first reference signal can be stored in the analysis data 235.
[00036] In one implementation, the regeneration module 125 is also configured to determine a first channel response for the slot based at least on the first reference signal. The first channel response may be determined using, for example, least square estimation. In one example, the least square estimation is used and the first channel response may be obtained using the following equation:
H_rsi= Rx_rs,/Rf_rs, (3)
where H_rsi is the channel response corresponding to the first reference signal. Since,
Rx-rs\, the first received reference signal, is stored in the reference data 240, and Rf _rS\, the first reference signal regenerated at the base station 110, is stored in the analysis data 235, the first channel response can be determined using equation (2). Further, as explained before, the regeneration module 125 can determine the first channel response based on the first received reference signal and the first reference signal. The first channel response may be stored in the analysis data 235.
[00037] Upon estimation of the first channel response, the identification module 130 determines a probabilistic second reference signal. The probabilistic second reference signal may be determined based at least on the first channel response. The probabilistic second reference signal can be determined using the least square estimation technique and can be represented with the following equation:
Probabilistic_Rf_rs2 =Rx_rs2/ Hrs, (4)
where Rf _rsi is second reference signal, which is to be regenerated at the base station, and Rx_rs2\s second received reference signal, which can be stored at the reference data 240. Thus, the identification module 130 may determine the probabilistic second reference signal based on the first channel response and the second received reference signal.
|00038] Subsequent to determination of the probabilistic second reference signal, the identification module 130 identifies the HARQ information embedded in the second

reference signal. The HARQ information includes information pertaining to the modulated HARQ bit, i.e. d(10). Since, the base station 110 may not have the information regarding the modulated HARQ bit embedded in the second reference signal; therefore, the identification module 130 identifies HARQ information, based at least on the probabilistic second reference signal. In one implementation, the identification module 130 identifies the HARQ information using following equation:
,.Q _ Probabilistic_Rf _rs2/
/w(m)*ruav(n) ^
Equation (5) can be deduced using equation (1). It will be understood that upon substituting for m =1; and Z(l)= dlO in equation (1), equation (5) can be achieved. Since, probabilistic second reference signal is already computed using equation (4), and information pertaining to w('")and r^xjn) is already stored m the reference data 240. Thus, HARQ information can be identified using equation (5). Further, the HARQ information thus identified may be stored in the analysis data 235.
[00039] Once the HARQ information is identified, the regeneration module 125 regenerates the second reference signal. Since all the regeneration parameters required for the regeneration of the second reference signal are now available, the regeneration module 125 may regenerate the second reference signal using the equation (1). Accordingly, the second reference signal can be represented as:

where, in PUCCH format 2a and 2b for the second reference signal, m = 1, 2(1) = d(\0), and information pertaining to w(m)ar\A r(a>u,v(n) is already stored in the reference data 240. Thus, the second reference signal can efficiently be regenerated using equation (6).
[00040] In one implementation, the regeneration module 125 may use the second reference signal to compute second channel response corresponding to the slot. The regeneration module 125 may determine the second channel response in way similar to the estimation of the first channel response, for example, the second channel response may be computed using the least square estimation. The second channel response may be stored in

the analysis data 235. As previously mentioned, each slot in the PUCCH may contain six or seven symbols. Further, the regeneration module 125 may compute the transmission channel response based at least, in part, on the first and the second channel response. The transmission channel responses at the locations or symbols with the reference signals, i.e., the first and the second reference signal are already determined by the regeneration module 125. Further, channel responses at single carrier-frequency division multiple access (SC-FDMA) symbols 2, 3, and 4 can be determined by interpolation and at SC-FDMA symbols 0, 6 by extrapolation of the two channel responses at reference signal locations. Thus, upon combining the channel responses at the all the symbols in the slot, the transmission channel response corresponding to the slot of the PUCCH can be computed.
[00041] Thus, the identification of the HARQ information provides for better estimation of the transmission channel response for a corresponding slot, which in turn provides for better decoding of the CQI bits. In one impfementatfon, the CQI bits may be decoded by the regeneration module 125.
[00042] In one implementation, once the HARQ information is identified for a slot, say. 0n slot in a sub-frame, the regeneration module 125 can use the same F1ARQ information to determine transmission channel response corresponding to another slot, say Is' slot of the same sub-frame. In said implementation, the regeneration module 125 may regenerate a first reference carried on the lsl slot and accordingly determine a first channel response using equation (3). Further, the regeneration module 125 may use the HARQ information, which was identified for the 0lh slot, to regenerate the second reference signal using equation (6). Thus, in this case, the regeneration module 125 need not again identify the HARQ information embedded in the second reference signal, which is required for regeneration of the second reference signal at the base station 110, thereby saving on processing time. Further, as explained previously, the second channel response may be computed based on the regenerated second reference signal. Based on the first and the second channel response for the Is' slot corresponding transmission channel can be determined.
[00043] Fig. 3 illustrates a method 300 for identification of HARQ information to determine channel response of a transmission channel.

[00044] The exemplary methods may be described in the general context of computer executable instructions. Generally, computer executable instructions can include routines, programs, objects, components, data structures, procedures, modules, functions, etc., that perform particular functions or implement particular abstract data types. The methods may also be practiced in a distributed computing environment where functions are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, computer executable instructions may be located in both local and remote computer storage media, including memory storage devices.
[00045] The order in which the methods are described is not intended to be construed as a limitation, and any number of the described method blocks can be combined in any order to implement the method, or an alternative method. Additionally, individual blocks may be deleted from the methods without departing from the spirit and scope of the subject matter described herein. Furthermore, the methods can be implemented in any suitable hardware, software, firmware, or combination thereof.
[00046] In one implementation, the transmission channel is PUCCH, which has format 2a and 2b. Further, transmission of information over the PUCCH is in the form of frames, sub-frames, and slots. Each slot in the PUCCH includes two reference signals, namely, a first reference signal and a second reference signal. Further, the method 300 can be followed for one slot, say, the 0l slot, in a sub-frame and the identified HARQ information, for example, d 10 value, can be used to determine transmission channel response corresponding to the ls1 slot of the sub-frame.
[00047] At block 305, control information and user data transmitted by a UE is received, The control information and the user information are transmitted over a transmission channel, such as a PUCCH. For example, the base station 110 receives the control information, carried over the PUCCH, transmitted by the UE 105. The control information includes, for example, scheduling requests, CQI, and HARQ.
[00048] At block 310, upon receiving the control information, a first reference signal, which is carried by a slot of the transmission channel, is regenerated. The first reference signal can be regenerated -based on one or more regeneration parameters. In an

implementation, the regeneration module 125 regenerates the first reference signal using values of one or more regeneration parameters stored in the reference data 240. Further, the regenerated first reference signal is stored in the analysis data 235,
[00049] At block 315, a first channel response is determined based at least on the regenerated first reference signal. The first channel response is determined using estimation methods, such as. least square estimation. In one implementation, the regeneration module 125 determines the first channel response based on the regenerated first reference signal and a first received reference signal. Additionally, the first channel response is stored in the analysis data 235.
[00050] At block 320. probabilistic second reference signal is determined based at least on
the first channel response. The probabilistic second reference signal represents a probable
estimation of the second reference signal. In an example, the jdentification module 130
ascertains the probabilistic second reference signal.
[00051] At block 325, HARQ information carried on the slot is identified based on the
probabilistic second reference signal. The HARQ information includes a modulated HARQ
bit, which is required for regeneration of the second reference signal. In one implementation,
the identification module 130 is configured to identify the HARQ information based on the
probabilistic second reference signal and one or more regeneration parameters stored in the
reference data 240. Further, the HARQ information thus identified is stored in the analysis
data 235,
[00052J At block 330, the second reference signal is regenerated based on the HARQ
information identified at block 325. For instance, the regeneration module 125 regenerates
the second reference signal using least square estimation.
[00053] At block 335, a second channel response is determined based at least on the
regenerated second reference signal, which in turn is based on the HARQ information
identified at block 325. The second channel response can be determined in a way similar to
the first channel response.
[00054] At block 340, a transmission channel response based on the first and the second
channel response is computed. The transmission response is computed using the first and the

second channel response. For example, the regeneration module 125 computes the transmission channel response for the slot based on the first and the second channel response. [00055] Since, according the embodiments of the present subject matter, the second reference signal is regenerated based on the identified HARQ information, it results in better estimation of the transmission channel response. Further, the transmission channel response can be used to equalize control data, which in turn can be used to decode CQI bits efficiently.

Table 1
PUCCH Formats Performance

EVA 5Hz ETU 70Hz
2a 99.9% 99.9%
2b 99.9% 99.9%
[00056] The performance of the described methods and systems with reference to a probability of correctly identifying of the HARQ information is represented in table 1. The performance is determined with reference to multiples of 100 attempts over the transmission channel. It can be seen from table 1 that for probability of correctly identifying the HARQ information is almost 100%. The performance of the described methods and systems was measured for the transmission channel supported by the PUCCH formats 2a and 2b. User data is transmitted over a transmission channel with extended vehicular A (EVA) mode! with Doppler frequency 5 hertz (Hz) and extended typical urban (ETU) model with Doppler frequency 70 Hz.
[00057] Additionally, Fig. 4 illustrates a CQI performance plot 400 for PUCCH format 2b. The X axis of the CQl performance plot represents signal to noise ratio (SNR) given in dB (Decibles), while the Y axis is bit error rate (BER) obtained for that specific SNR. Further. curve 405 illustrates CQI performance plot with respect to EVA 5Hz and curve 410 is with respect to ETU 70Hz. The CQI performance plot 400 represents the decoding of CQI information, which has been assisted by the efficient estimation of the PUCCH channel using HARQ information as identified by the present subject matter. The CQI information is attempted to decode under the channel conditions EVA 5Hz and ETU 70Hz. Further,

Rayleigh Multipath fading channel, which is modeled based on EVA 5Hz and ETU 70Hz is also used as per 3GPP LTE standards. It can be seen that the identification of the HARQ information, as described in the present subject matter, provides for efficient decoding of the CQI information.
[00058] Although embodiments for identification of HARQ information to determine transmission channel response have been described in language specific to structural features and/or methods, it is to be understood that the invention is not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed as exemplary embodiments for the identification of the HARQ information.

1/We claim:
1. A method for determining a transmission channel response, the method comprising:
regenerating a first reference signal carried on a slot of a sub-frame of a transmission channel based on one or more regeneration parameters;
determining, based at least in part on the regenerated first reference signal, a probabilistic second reference signal corresponding to a second reference signal carried on the slot; and
identifying a hybrid automatic repeat request (HARQ) information carried on the slot, wherein the identifying is based at least on the probabilistic second reference signal.
2. The method as claimed in claim 1, wherein the transmission channel supports one of a physical uplink control channel (PUCCH) format 2a and a PUCCH format 2b.
3. The method as claimed in claim 1, wherein the HARQ information includes a modulated HARQ bit (d( 10)).
4. The method as claimed in claim 1. wherein determining the probabilistic second reference signal further comprises:
computing a first channel response corresponding to the slot based at least on the regenerated first reference signal and a first received reference signal; and
determining the probabilistic second reference signal based at least on the first channel response.
5. The method as claimed in claim 1, wherein the method further comprises:
regenerating the second reference signal based at least on the HARQ information; and
computing a second channel response corresponding to the slot based on the regenerated second reference signal.
6. The method as claimed in claim 1, wherein the method further comprises determining the
transmission channel response corresponding to the slot based at least on a first channel
response and a second channel response.

7. The method as claimed in claim 1, wherein the method further comprises determining the transmission channel response corresponding to another slot in the sub-frame based at least in part on the HARQ information.
8. A system (120) comprising:
a processor (210); and
a memory (215) coupled to the processor (210), the memory (21 5) comprising,
a regeneration module (125) configured to compute a first channel response corresponding to a slot of a sub-frame of a transmission channel, based at least on a regenerated first reference signal; and
an identification module (130) configured to:
determine, based on the first channel response, a probabilistic second reference signal corresponding to a second reference signal carried on the slot; and
identify hybrid automatic repeat request (HARQ) information carried on the slot based at least on the probabilistic second reference signal.
9. The system (120) as claimed in claim 8. wherein the identification module (130) is configured to implement a least square estimation technique to determine the probabilistic second reference signal.
10. The system (120) as claimed in claim 8, wherein the regeneration module (125) is further configured to regenerate a first reference signal to obtain the regenerated reference signal based at least on one or more regeneration parameters.
11. The system (120) as claimed in claim 8, wherein the regeneration module (125) is further configured to:
regenerate the second reference signal based at least on the HARQ information; and
compute a second channel response based on the regenerated second reference signal.
12. The system (120) as claimed in claim 8, wherein the regeneration module (125) is further
configured to determine a transmission channel response corresponding to the slot, based
at least, in part, on the first channel response and a second channel response.

13. The system (120) as claimed in claim 8, wherein the regeneration module (125) is further configured to determine a transmission channel response corresponding to another slot in the sub-frame based on the HARQ information,
14. The system (120) as claimed in claim 8, where the transmission channel is supported on one of a PUCCH format 2a and a PUCCH format 2b.