FIELD OF INVENTION
[0001] The present application relates to wireless communication, and more particularly to a method and User Equipment (UE) for achieving synchronization of a PDCCH and a subframe in an Orthogonal Frequency Division Multiplexing (OFDM) system.
BACKGROUND OF INVENTION
[0002] The synchronization of OFDM symbols and subframe timing boundary in a receiver side of a UE is performed using a Cyclic Prefix (CP) in a time-domain and a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS) in a frequency-domain. The CP synchronization provides a boundary of the OFDM symbol and does not reveal an OFDM symbol index and the subframe number. The subframe number identification is achieved by the PSS and SSS which are periodically repeated for every 5 milliseconds, hence the accurate determination of a subframe synchronization duration is approximately 5 milliseconds.
[0003] When the UE wakes up from a Discontinuous Reception (DRX) mode or a sleep state mode, there is a loss of synchronization due to a timing-drift. In the existing methods, the synchronization is achieved by processing the PSS and SSS signals for determining the subframe and OFDM symbols boundary. Following the determination of subframe and OFDM symbols boundary the processing of PDCCH and the corresponding paging channels are performed.
[0004] The above information is presented as background information only to help the reader to understand the present invention. Applicants have made no determination and make no assertion as to whether any of the above might be applicable as Prior Art with regard to the present application.

OBJECT OF INVENTION
[0005] The principal object of the embodiments herein is to provide a method for achieving synchronization of a PDCCH and subframe by a UE in an OFDM system
[0006] Another object of the embodiments herein is to receive in-phase and quadrature-phase (IQ) reference signal resource elements (RS REs) from an Analog-to-Digital Converter (ADC).
[0007] Another object of the embodiments herein is to perform correlation between the received IQ RSREs and pre-stored RS REs to obtain normalized correlation coefficients.
[0008] Another object of the embodiments herein is to compare the normalized correlation coefficients with a predetermined threshold.
[0009] Another object of the embodiments herein is to determine at least one correlation peak along with RS OFDM symbol index associated with the at least one correlation peak based on the comparison result.
[0010] Another object of the embodiments herein is to detect RS OFDM symbol synchronized in time based on the OFDM symbol index and corresponding subframe number of the OFDM symbol.
[0011] Another object of the embodiments herein is to identify phase-shift due to timing-offset of the RS OFDM symbol.
[0012] Another object of the embodiments herein is to adjust the timing-offset corresponding to the received IQ RSREs to achieve time synchronization in accordance with estimated phase-shift in frequency domain.

SUMMARY
[0013] Embodiments herein disclose a method for achieving synchronization of PDCCH and subframe by a User Equipment (UE) in an OFDM system. The method includes receiving in-phase and quadrature-
5 phase (IQ) reference signal resource elements (RS REs) from an Analog-to-digital converter (ADC). Further, the method includes performing correlation between the received IQ RSREs and pre-stored RS REs to obtain normalized correlation coefficients. Further, the method includes comparing the normalized correlation coefficients with a predetermined
0 threshold. Further, the method includes determining at least one correlation peak along with RS OFDM symbol index associated with the at least one correlation peak based on the comparison result. Furthermore, the method includes detecting the RS OFDM symbol synchronized in time based on the OFDM symbol index and corresponding subframe number of the OFDM
5 symbol.
[0014] In an embodiment, the at least one correlation peak from a plurality of correlation peaks is determined when the at least one correlation peak exceed or equal to the predetermined threshold.
[0015] In an embodiment, the method further includes
0 identifying phase-shift due to timing-offset of the RS OFDM
symbol. Further, the method includes adjusting the timing-offset corresponding to the received IQ RSREs to achieve time synchronization in accordance with estimated phase-shift in the frequency domain.
[0016] In an embodiment, the pre-stored RS REs corresponds to
5 one System Frame.
[0017] Embodiments herein disclose a UE for achieving synchronization of PDCCH and subframe in an OFDM system. The UE is configured to receive in-phase and quadrature-phase (IQ) reference signal resource elements (RS REs) from an Analog-to-Digital Converter (ADC).

Further, the UE is configured to perform correlation between the received IQ RSREs and pre-stored RS REs to obtain normalized correlation coefficients. Further, the UE is configured to compare the normalized correlation coefficients with a predetermined threshold. Further, the UE is configured to determine at least one correlation peak along with RS OFDM symbol index associated with the at least one correlation peak based on the comparison result. Furthermore, the UE is configured to detect the RS OFDM symbol synchronized in time based on the OFDM symbol index and corresponding subframe number of the OFDM symbol.
[0018] Accordingly the embodiment herein provides a computer program product including a computer executable program code recorded on a computer readable non-transitory storage medium. The computer executable program code when executed causing the actions including receiving in-phase and quadrature-phase (IQ) reference signal resource elements (RS REs) from an Analog-to-digital converter (ADC). The computer executable program code when executed causing the actions including performing correlation between the received IQ RSREs and pre-stored RS REs to obtain normalized correlation coefficients. The computer executable program code when executed causing the actions including comparing the normalized correlation coefficients with a predetermined threshold. The computer executable program code when executed causing the actions including determining at least one correlation peak along with RS OFDM symbol index associated with the at least one correlation peak based on the comparison result. The computer executable program code when executed causing the actions including detecting RS OFDM symbol synchronized in time based on the OFDM symbol index and corresponding subframe number of the OFDM symbol.
[0019] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the

following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
BRIEF DESCRIPTION OF FIGURES
[0020] This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:
[0021] FIG. 1 illustrates a general overview of achieving synchronization of PDCCH and subframe by a UE in an OFDM system, according to an embodiment as disclosed herein;
[0022] FIG. 2 illustrates various units of the UE for achieving synchronization of PDCCH and subframe in the OFDM system, according to an embodiment as disclosed herein;
[0023] FIG. 3 is a flow diagram illustrating a method for achieving synchronization of PDCCH and subframe in the OFDM system, according to an embodiment as disclosed herein;
[0024] FIG. 4 illustrates a general overview of rapid synchronization of the UE and decoding of a PDCCH, paging channel and other system information after DRX cycle in a LTE system, according to an embodiment as disclosed herein; and
[0025] FIG. 5 illustrates a computing environment implementing a method for achieving synchronization of PDCCH and subframe in the OFDM system, according to an embodiment as disclosed herein.

DETAILED DESCRIPTION OF INVENTION
[0026] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. The term "or" as used herein, refers to a non-exclusive or, unless otherwise indicated. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those skilled in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0027] The embodiments herein provide a method for achieving synchronization of PDCCH and subframe by a User Equipment (UE) in an OFDM system. The method includes receiving in-phase and quadrature-phase (IQ) reference signal resource elements (RS REs) from an Analog-to-digital converter (ADC). Further, the method includes performing correlation between the received IQ RSREs and pre-stored RS REs to obtain normalized correlation coefficients. Further, the method includes comparing the normalized correlation coefficients with a predetermined threshold. Further, the method includes determining at least one correlation peak along with RS OFDM symbol index associated with the at least one correlation peak based on the comparison result. Furthermore, the method includes detecting the RS OFDM symbol synchronized in time based on the OFDM symbol index and corresponding subframe number of the OFDM symbol.

[0028] Unlike the conventional systems and the conventional methods, the proposed method can effectively estimate the timing offset and fast synchronize with RS OFDM symbols corresponding to the subframe. The method can effectively achieve the synchronization of the PDCCH and the subframe by in the OFDM system.
[0029] In the proposed method, when the UE wakes up from a Discontinuous Reception State (DRX), a fast synchronization of the OFDM symbols and detection of a subframe boundary accurately is achieved. The CP does the coarse synchronization of OFDM symbol boundary and the subframe boundary detection and accurate synchronization is achieved rapidly by reference signals (RS) present in the OFDM symbols.
[0030] In the proposed method, the correlation between the set of ideal Reference Signals (RS) of the subframe and the received RS IQ signals post-FFT is performed to determine the index of OFDM symbol in the subframe in an accurate manner.
[0031] The proposed method is applicable for normal mode and extended mode of LTE operation of FDD and TDD UE systems. The proposed is applied to 3GPP LTE and LTE Advanced like Release-8, 9, 10, 11, 12 and above for effectively estimating the timing offset and fast synchronize with RS OFDM symbols corresponding to the subframe. The proposed method is not only limited to the LTE but also applied to any wireless systems based on the synchronization by RS (or pilot signals). The proposed method is provided based on the correlation search for best match between the ideal RS OFDM REs and received RS OFDM REs (subcarriers) in the frequency domain.
[0032] Referring now to the drawings and more particularly to FIGS. 1 through 5, where similar reference characters denote corresponding features consistently throughout the figure, there are shown preferred embodiments.

[0033] FIG. 1 illustrates a general overview of achieving synchronization of PDCCH and subframe by a UE 102 in an OFDM system 100, according to an embodiment as disclosed herein. The OFDM system 100 includes the UE 102 and a base station 104. In an embodiment, the UE 102 can also be called as a mobile unit, a mobile station, a client, terminal or the like. The UE 102 can be for example, but not limited to, a mobile phone, a smart phone, a laptop, or the like. The UE 102 is configured to receive the in-phase and quadrature-phase (IQ) reference signal resource elements (RS REs) by using an Analog-to-Digital Converter (ADC). After receiving the IQ RS REs, the UE 102 is configured to perform correlation between the received IQ RSREs and pre-stored RS REs to obtain normalized correlation coefficients. Based on the normalized correlation coefficients, the UE 102 is configured to compare the normalized correlation coefficients with a predetermined threshold. In response to the comparison result, the UE 102 is configured to determine at least one correlation peak along with RS OFDM symbol index associated with one or more correlation peaks. Based on the OFDM symbol index and corresponding subframe number of the OFDM symbol, the UE 102 is configured to detect RS OFDM symbol synchronized in time domain.
[0034] In an embodiment, the correlation peak from the plurality of correlation peaks is determined when the correlation peak is exceed or equal to the predetermined threshold.
[0035] In an embodiment, the UE 102 is configured to identify phase-shift due to timing-offset of the RS OFDM symbol. Further, the UE 102 is configured to adjust the timing-offset corresponding to the received IQ RSREs to achieve time synchronization in accordance with estimated phase-shift in frequency domain.
[0036] In an embodiment, the pre-stored RS REs corresponds to one system frame.

[0037] The FIG. 1 shows the limited overview of the overview 100 but, it is to be understood that other embodiments are not limited thereto. Further, the overview 100 can include any number of hardware or software components communicating with each other. For example, the component can be, but not limited to, a process running in the controller or processor, an object, an executable process, a thread of execution, a program, or a computer.
[0038] FIG. 2 illustrates various units of the UE 102 for achieving synchronization of PDCCH and subframe in the OFDM system 100, i according to an embodiment as disclosed herein. In an embodiment, the UE includes an IQ reference signal resource element receiving unit 202, a correlation unit 204, a normalized correlation coefficients comparing unit 206, a correlation peak comparing unit 208, a RS OFDM symbol detecting unit 210, a phase-shift identifying unit 212, and a timing-offset adjusting unit 214. Further, a communication unit (not shown) and a storage unit (not shown) are in communication with the IQ reference signal resource element receiving unit 202, the correlation unit 204, the normalized correlation coefficients comparing unit 206, the correlation peak comparing unit 208, the RS OFDM symbol detecting unit 210, the phase-shift identifying unit i 212, and the timing-offset adjusting unit 214.
[0039] The IQ reference signal resource element receiving unit 202 is configured to receive the IQ RS REs from the ADC. After receiving the IQ RS REs from the ADC, the correlation unit 204 is configured to perform the correlation between the received IQ RSREs and the pre-stored RS REs to obtain normalized correlation coefficients. After obtaining normalized correlation coefficients, the normalized correlation coefficients comparing unit 206 is configured to compare the normalized correlation coefficients with the predetermined threshold.

[0040] Based on the comparison result, the correlation peak comparing unit 208 is configured to determine the correlation peak along with the RS OFDM symbol index associated with the correlation peak. Further, the RS OFDM symbol detecting unit 210 is configured to detect the RS OFDM symbol synchronized in time based on the OFDM symbol index and corresponding subframe number of the OFDM symbol.
[0041] Further, the phase-shift identifying unit 212 is configured to identify the phase-shift due to timing-offset of the RS OFDM symbol. After identifying the phase-shift, the timing-offset adjusting unit 214 is configured to adjust the timing-offset corresponding to the received IQ RSREs to achieve time synchronization in accordance with estimated phase-shift in frequency domain.
[0042] Further, the communication unit is configured for communicating internally between internal units and with external devices via one or more networks. The storage unit may include one or more computer-readable storage media. The storage unit may include non-volatile storage elements. Examples of such non-volatile storage elements may include magnetic hard disc, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. In addition, the storage unit may, in some examples, be considered a non-transitory storage medium. The term "non-transitory" may indicate that the storage medium is not embodied in a carrier wave or a propagated signal. However, the term "non-transitory" should not be interpreted that the storage unit is non-movable. In some examples, the storage unit can be configured to store larger amounts of information than a memory. In certain examples, a non-transitory storage medium may store data that can, over time, change (e.g., in Random Access Memory (RAM) or cache).

[0043] Although FIG. 2 shows exemplary units of the UE 102, in other implementations, the UE 102 may include fewer components, different components, differently arranged components, or additional components than depicted in the FIG. 2. Additionally or alternatively, one
5 or more components of the UE 102 may perform functions described as being performed by one or more other components of the UE 102.
[0044] FIG. 3 is a flow diagram 300 illustrating a method for achieving synchronization of PDCCH and subframe in the OFDM system 100, according to an embodiment as disclosed herein. At 302, the method
) includes receiving the IQ RS REs from the ADC. In an embodiment, the method allows the IQ reference signal resource element receiving unit 202 to receive the IQ RS REs from the ADC. At 304, the method includes performing the correlation between the received IQ RSREs and the pre-stored RS REs to obtain normalized correlation coefficients. In an
5 embodiment, the method allows the correlation unit 204 to perform the correlation between the received IQ RSREs and pre-stored RS REs to obtain normalized correlation coefficients.
[0045] At 306, the method includes comparing the normalized correlation coefficients with the predetermined threshold. In an
) embodiment, the method allows the normalized correlation coefficients comparing unit 206 to compare the normalized correlation coefficients with the predetermined threshold. At 308, the method includes determining the correlation peak along with the RS OFDM symbol index associated with the correlation peak. In an embodiment, the method allows correlation peak
5 comparing unit 208 to determine the correlation peak along with RS OFDM symbol index associated with the correlation peak.
[0046] At 310, the method includes detecting the RS OFDM symbol synchronized in the time domain. In an embodiment, the method allows the RS OFDM symbol detecting unit 210 to detect the RS OFDM

symbol synchronized in the time domain. At 312, the method includes identifying the phase-shift due to timing-offset of the RS OFDM symbol. In an embodiment, the method allows the phase-shift identifying unit 212 to identify the phase-shift due to timing-offset of the RS OFDM symbol. At 314, the method includes adjusting the timing-offset corresponding to the received IQ RSREs to achieve time synchronization in accordance with estimated phase-shift in the frequency domain. In an embodiment, the method allows the timing-offset adjusting unit 214 to adjust the timing-offset corresponding to the received IQ RSREs to achieve time synchronization in accordance with estimated phase-shift in the frequency domain
[0047] The various actions, acts, blocks, steps, and the like in the flow diagram 300 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions, acts, blocks, steps, and the like may be omitted, added, modified, skipped, and the like without departing from the scope of the invention.
[0048] FIG. 4 illustrates a general overview of rapid synchronization of the UE 102 and decoding of the PDCCH, paging channel and other system information after DRX cycle in a LTE system, according to an embodiment as disclosed herein. When the UE 102 is in the sleep state or the DRX state, the UE 102 has certain time duration set for a wake up, and the UE 102 receives and decodes a Physical Downlink Control Channel (PDCCH) for extracting a paging channel in a pre-specified subframe number in a pre-specified system frame number. After processing the PDCCH for the paging control channel information, the UE 102 may move for a sleep or continue in connected or idle mode until next DRX control information is received by higher layers.
[0049] The proposed method provides fast synchronization of OFDM symbols and subframe time-boundary. The fast synchronization is

achieved by two steps, first-step is a CP based method followed by the Reference Signals (RS) based synchronization. The accurate timing-synchronization of OFDM symbols and subframe time-boundary is achieved within a duration of less than 3 OFDM symbols. Following synchronization, the decoding of PDCCH control channel for paging information is extracted. The fast synchronization of OFDM symbols after the DRX wake up is achieved by the RS of the corresponding subframe followed by extraction of the accurate timing information arising in the frequency domain correlation of received RS and ideal RS.
[0050] In an example, a System Frame consists of 10 subframes (10ms duration), each subframe of duration of 1 milliseconds. Each subframe has 14 OFDM symbols (indexed as 0,1, 2,...,13) out of which 4 OFDM symbols (0,3,7,11) carry the Reference Signal resource elements (REs which are known pilot subcarriers). The REs corresponding to RS are located along the frequency grid with a pattern as specified by the LTE standards TS36.211 and TS36.212 based on the Cell ID and transmission bandwidth of LTE base station (eNodeB). The 4 RS OFDM symbols corresponding to each subframe 0,1,2,...,9 are unique and have very low correlation. The RS patterns are such that K^M where K is the set of 4 RS OFDM symbols of subframe K and M is the set of 4 RS OFDM symbols of subframe M. Therefore, there are 40 different RS OFDM symbols corresponding to 10 subframes in a given System Frame of 10 milliseconds duration.
[0051] When the UE 102 wakes from the DRX mode, there is a timing misalignment due to timing-drift caused by a ADC clock PPM (parts per million) drift and carrier frequency difference between a transmitting base station (i.e., eNodeB) and a receiving station (i.e., UE 102) local oscillators. In case, the DRX duration is larger the timing misalignment, the timing-misalignment will span from few samples to few OFDM symbols to

few subframes. Therefore, when the UE 102 wakes up, the UE 102 would have considerably drifted from the predetermined reference point of time. In the proposed method, the UE 102 stores all the 40 RS OFDM symbols (ideal and known) corresponding to 1 System Frame of the eNodeB to 5 which UE 102 is in an active connected before the DRX cycle. The REs corresponding to the RS of each OFDM symbol of each subframe in one system frame is pre-computed and stored in a look up table (LUT). The LUT will have 40 columns where each column corresponds to the RS of one OFDM symbol. The 40 columns LUT of 40 OFDM RS REs will be
10 unchanged for any given System Frame during the communication by the eNodeB. When the UE 102 wakes up the timing reference becomes unknown due to random timing-drift caused by the ADC PPM clock drift, LO difference and channel multipath propagation delays. A continuous search of reference points picked along the search grid, for each reference
15 time point the FFT (of size NFFT corresponding to bandwidth of the LTE signal, example FFT size of 2048 for 20MHz LTE signal) is performed after removing the CP. After the FFT, the subcarriers corresponding to the RS are demapped as the received RS RE sequence and correlated with each sequence of 40 sequences (40 columns of RS LUT). The 40 sequences (or
20 columns) of LUT are the ideal REs of RS of all subframes in the system frame. The correlation provides 40 normalized correlation coefficients which are compared with a predefined threshold. The correlation peaks that are greater than or equal to the threshold are compared, if any of the 40 correlation peaks exceed the threshold then it is stored along with OFDM
25 symbol index. Among the selected correlation peaks that exceed or equal the threshold the highest correlation coefficient is detected as the OFDM symbol that is synchronized in time with respect to the RS OFDM symbol index and corresponding subframe. The determination of the OFDM symbol index and the subframe number within the system frame is thus

determined. The timing-synchronization process by using RS OFDM symbol procedure is provided within less than 3 OFDM symbols duration. The detected RS OFDM symbol REs are processed for identifying the phase shift due to timing-drift caused by the ADC PPM, LO difference and channel multipath propagation delays. The timing drift is further corrected for the fine time synchronization.
[0052] The proposed method is based on the estimation of timing
offset from the RS OFDM symbol starting boundary, that means,
processing of post ADC I and Q samples (in-phase and quadrature phase
i samples) after the wake up from DRX. The below information describes
each block operation in the UE 102.
[0053] Block 1: In the UE 102, the higher layers send a wake up message to a Physical Layer (LI) on the expiry of DRX following which LI processor wakes, the block 17 (i.e., ADC) starts sending the IQ samples to a downlink receiver for processing.
[0054] Block 2: Upon receiving the DRX wake-up message, the LI powers on all the downlink modules. The baseband in the LI starts receiving the IQ samples from the ADC.
[0055] Block 3: It picks up the OFDM FFT window with an i approximate time reference. The search for exact match of received RS OFDM symbol and ideal RS OFDM symbol is carried out from this time as the reference time with increment of one sample for every search in the loop until the correlation between the RS REs of received OFDM symbol and RS REs of ideal OFDM symbol is found.
[0056] Block 4: The CP is removed for the CP correlation of the OFDM symbol for the coarse time estimation. The FFT is performed, the guard subcarriers are removed, only data subcarriers are picked up for processing.

[0057] Block 5: The post FFT, the subcarriers (REs) corresponding to the PSS, the SSS and the RS are picked up.
[0058] Block 6: The REs corresponding to the RS signals are interpolated across all the REs of the OFDM symbol. Example, for 20MHz BW LTE signal, there are 200 RS REs out 1200 non-zero subcarriers. The 200 REs are interpolated to 1200 REs.
[0059] Block 7: This block estimates the channel corresponding to the PSS, the SSS and the RS. This block is executed only after detecting the RS OFDM Symbol and the Subframe within the system frame. This block is meant for a fine-time synchronization.
[0060] Block 8: This block stores the ideal PSS, SSS and RS REs OFDM symbols for one system frame for correlation process with received signals.
[0061] Block 9: All 40 sequences or RS OFDM REs corresponding to 1 system frame of 10 millisecond duration are stored in the form of LOOK UP TABLE (LUT). The reference RS REs are picked from post FFT of the received IQ signal and then a correlation is performed between the 40 sequences in LUT and received RS sequence. The correlation processed is continued with a search-grid of 1 sample in the received IQ samples until the correlation peak that exceeds the threshold is detected. The correlation is alternately can be performed for PSS, SSS of Subframe-0 and SSS of Subframe-5.
[0062] Block 10: The correlation peak is compared with the threshold. If does not exceed or not equal the threshold then the search is repeated again by fetching new window of samples from the block 3. The process is repeated until the peak exceeds threshold.
[0063] Block 11: After the correlation peak is detected the OFDM symbol index and the subframe number are determined. This block estimates the fine-time frequency offset by measuring the phase-offset in

the frequency domain by using the HRS, accordingly the fine time offset is derived from the phase-offset.
[0064] Block 12: The time offset estimation corresponds to Sampling Clock Offset (SCO) which is derived in this block from the phase offset obtained from block 11. The fine time offset (i.e., SCO time offset) is used to accurately pick the FFT window for processing in the downlink receiver chain.
[0065] Block 13: After determining the FFT window accurately the CP is removed, the FFT is performed, guard band subcarriers are removed, only data subcarriers (non-zero subcarriers) are preserved. Example, for 20MHz bandwidth, the data subcarriers (or REs) are 1200 out of 2048 subcarriers (or REs).
[0066] Blocks 14-17: These blocks are the components of downlink receiver chain of LTE receiver which correspond to channel estimation, equalization of control and data channels, paging channel decoding and shared-data (D-SCH) channels decoding. After decoded control and data information is passed onto the higher layers.
[0067] Block 18: This block is analog to digital converter (ADC) block which gives out the IQ samples at the desired sampling rate.
[0068] The proposed method is applicable for normal mode and extended mode of LTE operation of FDD and TDD UE systems. The proposed is applied to 3GPP LTE and LTE Advanced like Release-8, 9, 10, 11, 12 and above for effectively estimating the timing offset and fast synchronize with RS OFDM symbols corresponding to the subframe. The proposed method is not only limited to the LTE but also applied to any wireless systems based on the synchronization by RS (or pilot signals). The proposed method is provided based on the correlation search for best match between the ideal RS OFDM REs and received RS OFDM REs (subcarriers) in the frequency domain.

[0069] Although the FIG. 5 shows exemplary blocks of the UE 102 but it is to be understood that other embodiments are not limited thereon. In other embodiments, the UE 102 may include less or more number of blocks. One or more blocks can be combined together to perform same or substantially similar function to achieve synchronization of the PDCCH and the sub frame in the LTE system.
[0070] FIG. 5 illustrates a computing environment 502 implementing the method for achieving synchronization of the PDCCH and the subframe in the OFDM system 100, according to an embodiment as disclosed herein. As depicted in the FIG. 5, the computing environment 502 comprises at least one processing unit 508 that is equipped with a control unit 504, an Arithmetic Logic Unit (ALU) 506, a memory 510, a storage unit 512, a plurality of networking devices 516 and a plurality Input output (I/O) devices 514. The processing unit 508 is responsible for processing the instructions of the technique. The processing unit 508 receives commands from the control unit 504 in order to perform its processing. Further, any logical and arithmetic operations involved in the execution of the instructions are computed with the help of the ALU 506.
[0071] The overall computing environment 502 can be composed of multiple homogeneous or heterogeneous cores, multiple CPUs of different kinds, special media and other accelerators. The processing unit 508 is responsible for processing the instructions of the technique. Further, the plurality of processing units 504 may be located on a single chip or over multiple chips.
[0072] The technique comprising of instructions and codes required for the implementation are stored in either the memory unit 510 or the storage 512 or both. At the time of execution, the instructions may be fetched from the corresponding memory 510 or storage 512, and executed by the processing unit 508.

[0073] In case of any hardware implementations various networking devices 516 or external I/O devices 514 may be connected to the computing environment 502 to support the implementation through the networking unit and the I/O device unit.
[0074] The embodiments disclosed herein can be implemented through at least one software program running on at least one hardware device and performing network management functions to control the elements. The elements shown in the FIGS. 1 to 5 include blocks, elements, actions, acts, steps, or the like which can be at least one of a hardware device, or a combination of hardware device and software module.
[0075] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
Claims:STATEMENT OF CLAIMS
We claim:
1. A method of achieving synchronization of PDCCH and subframe by a User Equipment (UE) in an OFDM system, the method comprising:
receiving in-phase and quadrature-phase (IQ) reference signal resource elements (RS REs) from an Analog-to-digital converter (ADC);
performing correlation between the received IQ RSREs and pre-stored RS REs to obtain normalized correlation coefficients;
comparing the normalized correlation coefficients with a predetermined threshold;
determining at least one correlation peak along with RS OFDM symbol index associated with the at least one correlation peak based on the comparison result; and
detecting RS OFDM symbol synchronized in time based on the OFDM symbol index and corresponding subframe number of the OFDM symbol.
2. The method of claim 1, wherein the at least one correlation peak from a plurality of correlation peaks is determined when the at least one correlation peak exceed or equal to the predetermined threshold.
3. The method of claim 1, wherein the method further comprises:
identifying phase-shift due to timing-offset of the RS OFDM symbol; and
adjusting the timing-offset corresponding to the received IQ RSREs to achieve time synchronization in accordance with estimated phase-shift in frequency domain.
4. The method of claim 1, wherein the pre-stored RS REs corresponds to one System Frame.
5. A User Equipment (UE) for achieving synchronization of PDCCH and subframe in an OFDM system, the UE is configured to:
receive in-phase and quadrature-phase (IQ) reference signal resource elements (RS REs) from an Analog-to-digital converter (ADC);
perform correlation between the received IQ RSREs and pre-stored RS REs to obtain normalized correlation coefficients;
compare the normalized correlation coefficients with a predetermined threshold;
determine at least one correlation peak along with RS OFDM symbol index associated with the at least one correlation peak based on the comparison result; and
detect RS OFDM symbol synchronized in time based on the OFDM symbol index and corresponding subframe number of the OFDM symbol.
6. The UE of claim 5, wherein the at least one correlation peak from a plurality of correlation peaks is determined when the at least one correlation peak exceed or equal to the predetermined threshold.
7. The UE of claim 5, wherein the UE is further configured to:
identify phase-shift due to timing-offset of the RS OFDM symbol; and
adjust the timing-offset corresponding to the received IQ RSREs to achieve time synchronization in accordance with estimated phase-shift in frequency domain.

8. The UE of claim 5, wherein the pre-stored RS REs corresponds to one System Frame.
Dated this 4th Day of April, 2017 Signatures:

Arun Kishore Narasani
Patent Agent
, Description:FIELD OF INVENTION
[0001] The present application relates to wireless communication, and more particularly to a method and User Equipment (UE) for achieving synchronization of a PDCCH and a subframe in an Orthogonal Frequency Division Multiplexing (OFDM) system.
BACKGROUND OF INVENTION
[0002] The synchronization of OFDM symbols and subframe timing boundary in a receiver side of a UE is performed using a Cyclic Prefix (CP) in a time-domain and a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS) in a frequency-domain. The CP synchronization provides a boundary of the OFDM symbol and does not reveal an OFDM symbol index and the subframe number. The subframe number identification is achieved by the PSS and SSS which are periodically repeated for every 5 milliseconds, hence the accurate determination of a subframe synchronization duration is approximately 5 milliseconds.
[0003] When the UE wakes up from a Discontinuous Reception (DRX) mode or a sleep state mode, there is a loss of synchronization due to a timing-drift. In the existing methods, the synchronization is achieved by processing the PSS and SSS signals for determining the subframe and OFDM symbols boundary. Following the determination of subframe and OFDM symbols boundary the processing of PDCCH and the corresponding paging channels are performed.
[0004] The above information is presented as background information only to help the reader to understand the present invention. Applicants have made no determination and make no assertion as to whether any of the above might be applicable as Prior Art with regard to the present application.
OBJECT OF INVENTION
[0005] The principal object of the embodiments herein is to provide a method for achieving synchronization of a PDCCH and subframe by a UE in an OFDM system
[0006] Another object of the embodiments herein is to receive in-phase and quadrature-phase (IQ) reference signal resource elements (RS REs) from an Analog-to-Digital Converter (ADC).
[0007] Another object of the embodiments herein is to perform correlation between the received IQ RSREs and pre-stored RS REs to obtain normalized correlation coefficients.
[0008] Another object of the embodiments herein is to compare the normalized correlation coefficients with a predetermined threshold.
[0009] Another object of the embodiments herein is to determine at least one correlation peak along with RS OFDM symbol index associated with the at least one correlation peak based on the comparison result.
[0010] Another object of the embodiments herein is to detect RS OFDM symbol synchronized in time based on the OFDM symbol index and corresponding subframe number of the OFDM symbol.
[0011] Another object of the embodiments herein is to identify phase-shift due to timing-offset of the RS OFDM symbol.
[0012] Another object of the embodiments herein is to adjust the timing-offset corresponding to the received IQ RSREs to achieve time synchronization in accordance with estimated phase-shift in frequency domain.

SUMMARY
[0013] Embodiments herein disclose a method for achieving synchronization of PDCCH and subframe by a User Equipment (UE) in an OFDM system. The method includes receiving in-phase and quadrature-phase (IQ) reference signal resource elements (RS REs) from an Analog-to-digital converter (ADC). Further, the method includes performing correlation between the received IQ RSREs and pre-stored RS REs to obtain normalized correlation coefficients. Further, the method includes comparing the normalized correlation coefficients with a predetermined threshold. Further, the method includes determining at least one correlation peak along with RS OFDM symbol index associated with the at least one correlation peak based on the comparison result. Furthermore, the method includes detecting the RS OFDM symbol synchronized in time based on the OFDM symbol index and corresponding subframe number of the OFDM symbol.
[0014] In an embodiment, the at least one correlation peak from a plurality of correlation peaks is determined when the at least one correlation peak exceed or equal to the predetermined threshold.
[0015] In an embodiment, the method further includes identifying phase-shift due to timing-offset of the RS OFDM symbol. Further, the method includes adjusting the timing-offset corresponding to the received IQ RSREs to achieve time synchronization in accordance with estimated phase-shift in the frequency domain.
[0016] In an embodiment, the pre-stored RS REs corresponds to one System Frame.
[0017] Embodiments herein disclose a UE for achieving synchronization of PDCCH and subframe in an OFDM system. The UE is configured to receive in-phase and quadrature-phase (IQ) reference signal resource elements (RS REs) from an Analog-to-Digital Converter (ADC). Further, the UE is configured to perform correlation between the received IQ RSREs and pre-stored RS REs to obtain normalized correlation coefficients. Further, the UE is configured to compare the normalized correlation coefficients with a predetermined threshold. Further, the UE is configured to determine at least one correlation peak along with RS OFDM symbol index associated with the at least one correlation peak based on the comparison result. Furthermore, the UE is configured to detect the RS OFDM symbol synchronized in time based on the OFDM symbol index and corresponding subframe number of the OFDM symbol.
[0018] Accordingly the embodiment herein provides a computer program product including a computer executable program code recorded on a computer readable non-transitory storage medium. The computer executable program code when executed causing the actions including receiving in-phase and quadrature-phase (IQ) reference signal resource elements (RS REs) from an Analog-to-digital converter (ADC). The computer executable program code when executed causing the actions including performing correlation between the received IQ RSREs and pre-stored RS REs to obtain normalized correlation coefficients. The computer executable program code when executed causing the actions including comparing the normalized correlation coefficients with a predetermined threshold. The computer executable program code when executed causing the actions including determining at least one correlation peak along with RS OFDM symbol index associated with the at least one correlation peak based on the comparison result. The computer executable program code when executed causing the actions including detecting RS OFDM symbol synchronized in time based on the OFDM symbol index and corresponding subframe number of the OFDM symbol.
[0019] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
BRIEF DESCRIPTION OF FIGURES
[0020] This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:
[0021] FIG. 1 illustrates a general overview of achieving synchronization of PDCCH and subframe by a UE in an OFDM system, according to an embodiment as disclosed herein;
[0022] FIG. 2 illustrates various units of the UE for achieving synchronization of PDCCH and subframe in the OFDM system, according to an embodiment as disclosed herein;
[0023] FIG. 3 is a flow diagram illustrating a method for achieving synchronization of PDCCH and subframe in the OFDM system, according to an embodiment as disclosed herein;
[0024] FIG. 4 illustrates a general overview of rapid synchronization of the UE and decoding of a PDCCH, paging channel and other system information after DRX cycle in a LTE system, according to an embodiment as disclosed herein; and
[0025] FIG. 5 illustrates a computing environment implementing a method for achieving synchronization of PDCCH and subframe in the OFDM system, according to an embodiment as disclosed herein.

DETAILED DESCRIPTION OF INVENTION
[0026] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. The term “or” as used herein, refers to a non-exclusive or, unless otherwise indicated. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those skilled in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0027] The embodiments herein provide a method for achieving synchronization of PDCCH and subframe by a User Equipment (UE) in an OFDM system. The method includes receiving in-phase and quadrature-phase (IQ) reference signal resource elements (RS REs) from an Analog-to-digital converter (ADC). Further, the method includes performing correlation between the received IQ RSREs and pre-stored RS REs to obtain normalized correlation coefficients. Further, the method includes comparing the normalized correlation coefficients with a predetermined threshold. Further, the method includes determining at least one correlation peak along with RS OFDM symbol index associated with the at least one correlation peak based on the comparison result. Furthermore, the method includes detecting the RS OFDM symbol synchronized in time based on the OFDM symbol index and corresponding subframe number of the OFDM symbol.
[0028] Unlike the conventional systems and the conventional methods, the proposed method can effectively estimate the timing offset and fast synchronize with RS OFDM symbols corresponding to the subframe. The method can effectively achieve the synchronization of the PDCCH and the subframe by in the OFDM system.
[0029] In the proposed method, when the UE wakes up from a Discontinuous Reception State (DRX), a fast synchronization of the OFDM symbols and detection of a subframe boundary accurately is achieved. The CP does the coarse synchronization of OFDM symbol boundary and the subframe boundary detection and accurate synchronization is achieved rapidly by reference signals (RS) present in the OFDM symbols.
[0030] In the proposed method, the correlation between the set of ideal Reference Signals (RS) of the subframe and the received RS IQ signals post-FFT is performed to determine the index of OFDM symbol in the subframe in an accurate manner.
[0031] The proposed method is applicable for normal mode and extended mode of LTE operation of FDD and TDD UE systems. The proposed is applied to 3GPP LTE and LTE Advanced like Release-8, 9, 10, 11, 12 and above for effectively estimating the timing offset and fast synchronize with RS OFDM symbols corresponding to the subframe. The proposed method is not only limited to the LTE but also applied to any wireless systems based on the synchronization by RS (or pilot signals). The proposed method is provided based on the correlation search for best match between the ideal RS OFDM REs and received RS OFDM REs (subcarriers) in the frequency domain.
[0032] Referring now to the drawings and more particularly to FIGS. 1 through 5, where similar reference characters denote corresponding features consistently throughout the figure, there are shown preferred embodiments.
[0033] FIG. 1 illustrates a general overview of achieving synchronization of PDCCH and subframe by a UE 102 in an OFDM system 100, according to an embodiment as disclosed herein. The OFDM system 100 includes the UE 102 and a base station 104. In an embodiment, the UE 102 can also be called as a mobile unit, a mobile station, a client, terminal or the like. The UE 102 can be for example, but not limited to, a mobile phone, a smart phone, a laptop, or the like. The UE 102 is configured to receive the in-phase and quadrature-phase (IQ) reference signal resource elements (RS REs) by using an Analog-to-Digital Converter (ADC). After receiving the IQ RS REs, the UE 102 is configured to perform correlation between the received IQ RSREs and pre-stored RS REs to obtain normalized correlation coefficients. Based on the normalized correlation coefficients, the UE 102 is configured to compare the normalized correlation coefficients with a predetermined threshold. In response to the comparison result, the UE 102 is configured to determine at least one correlation peak along with RS OFDM symbol index associated with one or more correlation peaks. Based on the OFDM symbol index and corresponding subframe number of the OFDM symbol, the UE 102 is configured to detect RS OFDM symbol synchronized in time domain.
[0034] In an embodiment, the correlation peak from the plurality of correlation peaks is determined when the correlation peak is exceed or equal to the predetermined threshold.
[0035] In an embodiment, the UE 102 is configured to identify phase-shift due to timing-offset of the RS OFDM symbol. Further, the UE 102 is configured to adjust the timing-offset corresponding to the received IQ RSREs to achieve time synchronization in accordance with estimated phase-shift in frequency domain.
[0036] In an embodiment, the pre-stored RS REs corresponds to one system frame.
[0037] The FIG. 1 shows the limited overview of the overview 100 but, it is to be understood that other embodiments are not limited thereto. Further, the overview 100 can include any number of hardware or software components communicating with each other. For example, the component can be, but not limited to, a process running in the controller or processor, an object, an executable process, a thread of execution, a program, or a computer.
[0038] FIG. 2 illustrates various units of the UE 102 for achieving synchronization of PDCCH and subframe in the OFDM system 100, according to an embodiment as disclosed herein. In an embodiment, the UE includes an IQ reference signal resource element receiving unit 202, a correlation unit 204, a normalized correlation coefficients comparing unit 206, a correlation peak comparing unit 208, a RS OFDM symbol detecting unit 210, a phase-shift identifying unit 212, and a timing-offset adjusting unit 214. Further, a communication unit (not shown) and a storage unit (not shown) are in communication with the IQ reference signal resource element receiving unit 202, the correlation unit 204, the normalized correlation coefficients comparing unit 206, the correlation peak comparing unit 208, the RS OFDM symbol detecting unit 210, the phase-shift identifying unit 212, and the timing-offset adjusting unit 214.
[0039] The IQ reference signal resource element receiving unit 202 is configured to receive the IQ RS REs from the ADC. After receiving the IQ RS REs from the ADC, the correlation unit 204 is configured to perform the correlation between the received IQ RSREs and the pre-stored RS REs to obtain normalized correlation coefficients. After obtaining normalized correlation coefficients, the normalized correlation coefficients comparing unit 206 is configured to compare the normalized correlation coefficients with the predetermined threshold.
[0040] Based on the comparison result, the correlation peak comparing unit 208 is configured to determine the correlation peak along with the RS OFDM symbol index associated with the correlation peak. Further, the RS OFDM symbol detecting unit 210 is configured to detect the RS OFDM symbol synchronized in time based on the OFDM symbol index and corresponding subframe number of the OFDM symbol.
[0041] Further, the phase-shift identifying unit 212 is configured to identify the phase-shift due to timing-offset of the RS OFDM symbol. After identifying the phase-shift, the timing-offset adjusting unit 214 is configured to adjust the timing-offset corresponding to the received IQ RSREs to achieve time synchronization in accordance with estimated phase-shift in frequency domain.
[0042] Further, the communication unit is configured for communicating internally between internal units and with external devices via one or more networks. The storage unit may include one or more computer-readable storage media. The storage unit may include non-volatile storage elements. Examples of such non-volatile storage elements may include magnetic hard disc, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. In addition, the storage unit may, in some examples, be considered a non-transitory storage medium. The term “non-transitory” may indicate that the storage medium is not embodied in a carrier wave or a propagated signal. However, the term “non-transitory” should not be interpreted that the storage unit is non-movable. In some examples, the storage unit can be configured to store larger amounts of information than a memory. In certain examples, a non-transitory storage medium may store data that can, over time, change (e.g., in Random Access Memory (RAM) or cache).
[0043] Although FIG. 2 shows exemplary units of the UE 102, in other implementations, the UE 102 may include fewer components, different components, differently arranged components, or additional components than depicted in the FIG. 2. Additionally or alternatively, one or more components of the UE 102 may perform functions described as being performed by one or more other components of the UE 102.
[0044] FIG. 3 is a flow diagram 300 illustrating a method for achieving synchronization of PDCCH and subframe in the OFDM system 100, according to an embodiment as disclosed herein. At 302, the method includes receiving the IQ RS REs from the ADC. In an embodiment, the method allows the IQ reference signal resource element receiving unit 202 to receive the IQ RS REs from the ADC. At 304, the method includes performing the correlation between the received IQ RSREs and the pre-stored RS REs to obtain normalized correlation coefficients. In an embodiment, the method allows the correlation unit 204 to perform the correlation between the received IQ RSREs and pre-stored RS REs to obtain normalized correlation coefficients.
[0045] At 306, the method includes comparing the normalized correlation coefficients with the predetermined threshold. In an embodiment, the method allows the normalized correlation coefficients comparing unit 206 to compare the normalized correlation coefficients with the predetermined threshold. At 308, the method includes determining the correlation peak along with the RS OFDM symbol index associated with the correlation peak. In an embodiment, the method allows correlation peak comparing unit 208 to determine the correlation peak along with RS OFDM symbol index associated with the correlation peak.
[0046] At 310, the method includes detecting the RS OFDM symbol synchronized in the time domain. In an embodiment, the method allows the RS OFDM symbol detecting unit 210 to detect the RS OFDM symbol synchronized in the time domain. At 312, the method includes identifying the phase-shift due to timing-offset of the RS OFDM symbol. In an embodiment, the method allows the phase-shift identifying unit 212 to identify the phase-shift due to timing-offset of the RS OFDM symbol. At 314, the method includes adjusting the timing-offset corresponding to the received IQ RSREs to achieve time synchronization in accordance with estimated phase-shift in the frequency domain. In an embodiment, the method allows the timing-offset adjusting unit 214 to adjust the timing-offset corresponding to the received IQ RSREs to achieve time synchronization in accordance with estimated phase-shift in the frequency domain
[0047] The various actions, acts, blocks, steps, and the like in the flow diagram 300 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions, acts, blocks, steps, and the like may be omitted, added, modified, skipped, and the like without departing from the scope of the invention.
[0048] FIG. 4 illustrates a general overview of rapid synchronization of the UE 102 and decoding of the PDCCH, paging channel and other system information after DRX cycle in a LTE system, according to an embodiment as disclosed herein. When the UE 102 is in the sleep state or the DRX state, the UE 102 has certain time duration set for a wake up, and the UE 102 receives and decodes a Physical Downlink Control Channel (PDCCH) for extracting a paging channel in a pre-specified subframe number in a pre-specified system frame number. After processing the PDCCH for the paging control channel information, the UE 102 may move for a sleep or continue in connected or idle mode until next DRX control information is received by higher layers.
[0049] The proposed method provides fast synchronization of OFDM symbols and subframe time-boundary. The fast synchronization is achieved by two steps, first-step is a CP based method followed by the Reference Signals (RS) based synchronization. The accurate timing-synchronization of OFDM symbols and subframe time-boundary is achieved within a duration of less than 3 OFDM symbols. Following synchronization, the decoding of PDCCH control channel for paging information is extracted. The fast synchronization of OFDM symbols after the DRX wake up is achieved by the RS of the corresponding subframe followed by extraction of the accurate timing information arising in the frequency domain correlation of received RS and ideal RS.
[0050] In an example, a System Frame consists of 10 subframes (10ms duration), each subframe of duration of 1 milliseconds. Each subframe has 14 OFDM symbols (indexed as 0,1, 2,…,13) out of which 4 OFDM symbols (0,3,7,11) carry the Reference Signal resource elements (REs which are known pilot subcarriers). The REs corresponding to RS are located along the frequency grid with a pattern as specified by the LTE standards TS36.211 and TS36.212 based on the Cell ID and transmission bandwidth of LTE base station (eNodeB). The 4 RS OFDM symbols corresponding to each subframe 0,1,2,…,9 are unique and have very low correlation. The RS patterns are such that K?M where K is the set of 4 RS OFDM symbols of subframe K and M is the set of 4 RS OFDM symbols of subframe M. Therefore, there are 40 different RS OFDM symbols corresponding to 10 subframes in a given System Frame of 10 milliseconds duration.
[0051] When the UE 102 wakes from the DRX mode, there is a timing misalignment due to timing-drift caused by a ADC clock PPM (parts per million) drift and carrier frequency difference between a transmitting base station (i.e., eNodeB) and a receiving station (i.e., UE 102) local oscillators. In case, the DRX duration is larger the timing misalignment, the timing-misalignment will span from few samples to few OFDM symbols to few subframes. Therefore, when the UE 102 wakes up, the UE 102 would have considerably drifted from the predetermined reference point of time. In the proposed method, the UE 102 stores all the 40 RS OFDM symbols (ideal and known) corresponding to 1 System Frame of the eNodeB to which UE 102 is in an active connected before the DRX cycle. The REs corresponding to the RS of each OFDM symbol of each subframe in one system frame is pre-computed and stored in a look up table (LUT). The LUT will have 40 columns where each column corresponds to the RS of one OFDM symbol. The 40 columns LUT of 40 OFDM RS REs will be unchanged for any given System Frame during the communication by the eNodeB. When the UE 102 wakes up the timing reference becomes unknown due to random timing-drift caused by the ADC PPM clock drift, LO difference and channel multipath propagation delays. A continuous search of reference points picked along the search grid, for each reference time point the FFT (of size NFFT corresponding to bandwidth of the LTE signal, example FFT size of 2048 for 20MHz LTE signal) is performed after removing the CP. After the FFT, the subcarriers corresponding to the RS are demapped as the received RS RE sequence and correlated with each sequence of 40 sequences (40 columns of RS LUT). The 40 sequences (or columns) of LUT are the ideal REs of RS of all subframes in the system frame. The correlation provides 40 normalized correlation coefficients which are compared with a predefined threshold. The correlation peaks that are greater than or equal to the threshold are compared, if any of the 40 correlation peaks exceed the threshold then it is stored along with OFDM symbol index. Among the selected correlation peaks that exceed or equal the threshold the highest correlation coefficient is detected as the OFDM symbol that is synchronized in time with respect to the RS OFDM symbol index and corresponding subframe. The determination of the OFDM symbol index and the subframe number within the system frame is thus determined. The timing-synchronization process by using RS OFDM symbol procedure is provided within less than 3 OFDM symbols duration. The detected RS OFDM symbol REs are processed for identifying the phase shift due to timing-drift caused by the ADC PPM, LO difference and channel multipath propagation delays. The timing drift is further corrected for the fine time synchronization.
[0052] The proposed method is based on the estimation of timing offset from the RS OFDM symbol starting boundary, that means, processing of post ADC I and Q samples (in-phase and quadrature phase samples) after the wake up from DRX. The below information describes each block operation in the UE 102.
[0053] Block 1: In the UE 102, the higher layers send a wake up message to a Physical Layer (L1) on the expiry of DRX following which L1 processor wakes, the block 17 (i.e., ADC) starts sending the IQ samples to a downlink receiver for processing.
[0054] Block 2: Upon receiving the DRX wake-up message, the L1 powers on all the downlink modules. The baseband in the L1 starts receiving the IQ samples from the ADC.
[0055] Block 3: It picks up the OFDM FFT window with an approximate time reference. The search for exact match of received RS OFDM symbol and ideal RS OFDM symbol is carried out from this time as the reference time with increment of one sample for every search in the loop until the correlation between the RS REs of received OFDM symbol and RS REs of ideal OFDM symbol is found.
[0056] Block 4: The CP is removed for the CP correlation of the OFDM symbol for the coarse time estimation. The FFT is performed, the guard subcarriers are removed, only data subcarriers are picked up for processing.
[0057] Block 5: The post FFT, the subcarriers (REs) corresponding to the PSS, the SSS and the RS are picked up.
[0058] Block 6: The REs corresponding to the RS signals are interpolated across all the REs of the OFDM symbol. Example, for 20MHz BW LTE signal, there are 200 RS REs out 1200 non-zero subcarriers. The 200 REs are interpolated to 1200 REs.
[0059] Block 7: This block estimates the channel corresponding to the PSS, the SSS and the RS. This block is executed only after detecting the RS OFDM Symbol and the Subframe within the system frame. This block is meant for a fine-time synchronization.
[0060] Block 8: This block stores the ideal PSS, SSS and RS REs OFDM symbols for one system frame for correlation process with received signals.
[0061] Block 9: All 40 sequences or RS OFDM REs corresponding to 1 system frame of 10 millisecond duration are stored in the form of LOOK UP TABLE (LUT). The reference RS REs are picked from post FFT of the received IQ signal and then a correlation is performed between the 40 sequences in LUT and received RS sequence. The correlation processed is continued with a search-grid of 1 sample in the received IQ samples until the correlation peak that exceeds the threshold is detected. The correlation is alternately can be performed for PSS, SSS of Subframe-0 and SSS of Subframe-5.
[0062] Block 10: The correlation peak is compared with the threshold. If does not exceed or not equal the threshold then the search is repeated again by fetching new window of samples from the block 3. The process is repeated until the peak exceeds threshold.
[0063] Block 11: After the correlation peak is detected the OFDM symbol index and the subframe number are determined. This block estimates the fine-time frequency offset by measuring the phase-offset in the frequency domain by using the HRS, accordingly the fine time offset is derived from the phase-offset.
[0064] Block 12: The time offset estimation corresponds to Sampling Clock Offset (SCO) which is derived in this block from the phase offset obtained from block 11. The fine time offset (i.e., SCO time offset) is used to accurately pick the FFT window for processing in the downlink receiver chain.
[0065] Block 13: After determining the FFT window accurately the CP is removed, the FFT is performed, guard band subcarriers are removed, only data subcarriers (non-zero subcarriers) are preserved. Example, for 20MHz bandwidth, the data subcarriers (or REs) are 1200 out of 2048 subcarriers (or REs).
[0066] Blocks 14-17: These blocks are the components of downlink receiver chain of LTE receiver which correspond to channel estimation, equalization of control and data channels, paging channel decoding and shared-data (D-SCH) channels decoding. After decoded control and data information is passed onto the higher layers.
[0067] Block 18: This block is analog to digital converter (ADC) block which gives out the IQ samples at the desired sampling rate.
[0068] The proposed method is applicable for normal mode and extended mode of LTE operation of FDD and TDD UE systems. The proposed is applied to 3GPP LTE and LTE Advanced like Release-8, 9, 10, 11, 12 and above for effectively estimating the timing offset and fast synchronize with RS OFDM symbols corresponding to the subframe. The proposed method is not only limited to the LTE but also applied to any wireless systems based on the synchronization by RS (or pilot signals). The proposed method is provided based on the correlation search for best match between the ideal RS OFDM REs and received RS OFDM REs (subcarriers) in the frequency domain.
[0069] Although the FIG. 5 shows exemplary blocks of the UE 102 but it is to be understood that other embodiments are not limited thereon. In other embodiments, the UE 102 may include less or more number of blocks. One or more blocks can be combined together to perform same or substantially similar function to achieve synchronization of the PDCCH and the subframe in the LTE system.
[0070] FIG. 5 illustrates a computing environment 502 implementing the method for achieving synchronization of the PDCCH and the subframe in the OFDM system 100, according to an embodiment as disclosed herein. As depicted in the FIG. 5, the computing environment 502 comprises at least one processing unit 508 that is equipped with a control unit 504, an Arithmetic Logic Unit (ALU) 506, a memory 510, a storage unit 512, a plurality of networking devices 516 and a plurality Input output (I/O) devices 514. The processing unit 508 is responsible for processing the instructions of the technique. The processing unit 508 receives commands from the control unit 504 in order to perform its processing. Further, any logical and arithmetic operations involved in the execution of the instructions are computed with the help of the ALU 506.
[0071] The overall computing environment 502 can be composed of multiple homogeneous or heterogeneous cores, multiple CPUs of different kinds, special media and other accelerators. The processing unit 508 is responsible for processing the instructions of the technique. Further, the plurality of processing units 504 may be located on a single chip or over multiple chips.
[0072] The technique comprising of instructions and codes required for the implementation are stored in either the memory unit 510 or the storage 512 or both. At the time of execution, the instructions may be fetched from the corresponding memory 510 or storage 512, and executed by the processing unit 508.
[0073] In case of any hardware implementations various networking devices 516 or external I/O devices 514 may be connected to the computing environment 502 to support the implementation through the networking unit and the I/O device unit.
[0074] The embodiments disclosed herein can be implemented through at least one software program running on at least one hardware device and performing network management functions to control the elements. The elements shown in the FIGS. 1 to 5 include blocks, elements, actions, acts, steps, or the like which can be at least one of a hardware device, or a combination of hardware device and software module.
[0075] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.