Claims:STATEMENT OF CLAIMS
We Claim:
1. A time synchronization method for performing a cell search by a User Equipment (UE), the method comprising:
obtaining a downlink radio frame;
computing 62 coefficients corresponding to 62 central subcarriers, from the downlink radio frame, by performing 2048-to-62 conversion by a partial FFT;
extracting a data carried by the 62 central subcarriers; and
performing the cell search in accordance with the data.
2. The method of claim 1, wherein the data is used to detect a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS).
3. The method of claim 1, wherein the 2048-to-62 conversion is performed by:
splitting 2048-to-62 conversion to two 1024-to-62 conversion;
splitting one of 1024-to-62 conversion to two 512-to-62 conversion;
splitting one of 512-to-62 conversion to two 256-to-62 conversion;
splitting one of 256-to-62 conversion to two 128-to-62 conversion; and
splitting one of 128-to-62 conversion to two 64-to-62 conversion.
4. A User Equipment (UE) for performing a cell search, the UE comprising:
a downlink radio frame obtaining unit configured to obtain a downlink radio frame;
a coefficients computing unit configured to compute 62 coefficients corresponding to 62 central subcarriers, from the downlink radio frame, by performing 2048-to-62 conversion by a partial FFT;
a data extracting unit configured to extract a data carried by the 62 central subcarriers; and
a cell search performing unit configured to perform the cell search in accordance with the data.
Dated this 7th Day of February, 2017 Signatures:

Arun Kishore Narasani
Patent Agent
, Description:FIELD OF INVENTION
The embodiments herein relate a communication system, and more specifically to a time synchronization method for performing a cell search in a Long Term Evolution (LTE) system.
BACKGROUND OF INVENTION
The LTE for radio access is based on an Orthogonal Frequency-Division Multiplexing (OFDM) technology. Signals to be transmitted are first mapped to different orthogonal subcarriers in a frequency domain and then an Inverse Fast Fourier Transform (IFFT) is applied in the LTE system. The IFFT operation yields the OFDM symbols which modulate a Radio Frequency (RF) carrier. At a receiver side of the LTE system, an output of the RF carrier is first subjected to a Fast Fourier Transform (FFT) operation before any meaningful data is extracted.
When a User Equipment (UE) is powered on, the UE has to first synchronize itself with eNodeB frame timings. Further, the UE has to identify a cell and gather all the relevant system information before registering on to the eNodeB. In order to facilitate cell identification and frame synchronization, the LTE specifies two synchronization signals: a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS). The two signals are transmitted twice per radio frame. Since the LTE system provides a variable system bandwidth of 1.4 - 20 MHz, the PSS and the SSS are transmitted using 62 subcarriers in central 6 Resource Blocks (RBs). The central 6 RBs correspond to 1.08 MHz bandwidth, hence the UE can identify the cell and can synchronize with the eNodeB irrespective of the transmission bandwidth.
The subcarriers in a LTE frame have a spacing of 15KHz. correspondingly the OFDM symbol interval is selected to be (1/15) msec, so that the subcarriers are orthogonal over a time duration. In order to accommodate the maximum bandwidth of 20 MHz, the IFFT size is selected to be 2048. Thus, each OFDM symbol consists of 2048 samples. In order to extract the 62 coefficients corresponding to 62 central subcarriers, there is a need of a partial 2048-to-62 point FFT.
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

The principal object of the embodiments herein to provide a time synchronization method for performing a cell search by a UE.
Another object of the embodiments herein is to compute 62 coefficients corresponding to 62 central subcarriers by performing 2048-to-62 conversion by a partial FFT.
Another object of the embodiments herein is to extract a data carried by the 62 central subcarriers.
SUMMARY
Embodiments herein disclose a time synchronization method for performing a cell search by a User Equipment (UE). The method includes obtaining a downlink radio frame. Further, the method includes computing 62 coefficients corresponding to 62 central subcarriers from the downlink radio frame. The 62 coefficients corresponding to 62 central subcarriers are computed by performing 2048-to-62 conversion using a partial FFT. Further, the method includes extracting a data carried by the 62 central subcarriers. Furthermore, the method includes performing the cell search in accordance with the data.
In an embodiment, the data is used to detect a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS).
In an embodiment, the 2048-to-62 conversion is performed by splitting 2048-to-62 conversion to two 1024-to-62 conversion, splitting one of 1024-to-62 conversion to two 512-to-62 conversion, splitting one of 512-to-62 conversion to two 256-to-62 conversion, splitting one of 256-to-62 conversion to two 128-to-62 conversion, and splitting one of 128-to-62 conversion to two 64-to-62 conversion.
Embodiments herein disclose a User Equipment (UE) for performing a cell search. The UE includes a downlink radio frame obtaining unit configured to obtain a downlink radio frame. A coefficients computing unit is configured to compute 62 coefficients corresponding to 62 central subcarriers from the downlink radio frame. The 62 coefficients corresponding to 62 central subcarriers are computed by performing 2048-to-62 conversion using a partial FFT. A data extracting unit is configured to extract a data carried by the 62 central subcarriers. A cell search performing unit is configured to perform the cell search in accordance with the data.
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 obtaining a downlink radio frame. The computer executable program code when executed causing the actions including computing 62 coefficients corresponding to 62 central subcarriers by performing 2048-to-62 conversion by a partial FFT. The computer executable program code when executed causing the actions including extracting a data carried by the 62 central subcarriers. The computer executable program code when executed causing the actions including performing the cell search in accordance with the data.
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
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:
FIG. 1 illustrates an overview of a system for performing a cell search by a UE, according to the embodiments as disclosed herein;
FIG. 2 illustrates various units of the UE, according to the embodiments as disclosed herein;
FIG. 3 is flow diagram illustrating a method for performing a cell search by the UE, according to the embodiments as disclosed herein;
FIG. 4 is a circuit diagram depicting splitting 2048-to-62 point partial FFT to two 1024-to-62 point partial FFTs, according to embodiments as disclosed herein;
FIG. 5 is a circuit diagram depicting splitting 1024-to-62 point partial FFT to two 512-to-62 point partial FFTs, according to embodiments as disclosed herein;
FIG. 6 is a circuit diagram depicting splitting 512-to-62 point partial FFT to two 256-to-62 point partial FFTs, according to embodiments as disclosed herein;
FIG. 7 is a circuit diagram depicting splitting 256-to-62 point partial FFT to two 128-to-62 point partial FFTs, according to embodiments as disclosed herein;
FIG. 8 is a circuit diagram depicting splitting 128-to-62 point partial FFT to two 64-to-62 point partial FFTs, according to embodiments as disclosed herein;
FIG. 9 is a circuit diagram depicting splitting 64-to-62 point partial FFT to two 32-to-31 point partial FFTs, according to embodiments as disclosed herein;
FIG. 10 is a circuit diagram depicting splitting 32-to-31 point partial FFT to two regular 16 point FFTs, according to embodiments as disclosed herein;
FIG. 11 is a circuit diagram depicting splitting 2048-to-62 point partial FFT to four 512-to-62 point partial FFTs by two stages, according to embodiments as disclosed herein; and
FIG. 12 illustrates a computing environment implementing a mechanism for performing the cell search by the UE, according to embodiments as disclosed herein.

DETAILED DESCRIPTION OF INVENTION
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.
Embodiments herein provide a time synchronization method for performing a cell search by a User Equipment (UE). The method includes obtaining a downlink radio frame. Further, the method includes computing 62 coefficients corresponding to 62 central subcarriers from the downlink radio frame. The 62 coefficients corresponding to 62 central subcarriers are computed by performing 2048-to-62 conversion using a partial FFT. Further, the method includes extracting a data carried by the 62 central subcarriers. Furthermore, the method includes performing the cell search in accordance with the data.
In order to extract only the data carried by the 62 subcarriers coefficients, the method designs the 2048–to–62 point partial FFT that computes only the necessary 62 subcarriers coefficients. This results in improving the fast cell search process. The proposed partial FFT eliminates computations that are necessary for the remaining coefficients.
The proposed FFT follows a decimation-in-time structure of the regular FFT, but eliminates the branches which are not necessary. This results in improving the fast cell search process. The proposed FFT can be used by the UE to extract the PSS and SSS from the downlink radio frame by reducing the complex complexity process.
Referring now to the drawings, and more particularly to FIGS. 1 through 12, there are shown preferred embodiments.
FIG. 1 illustrates an overview of a system 100 for performing the cell search by the UE 102, according to the embodiments as disclosed herein. The system 100 includes the UE 102 and a cell 104. The UE 102 may also be referred to as a mobile station, a terminal, an access terminal, a subscriber unit, a station, or the like. The UE 102 can be, for example but not limited to, a cellular phone, a Personal Digital Assistant (PDA), a wireless communication device, a handheld device, a laptop computer, or the like.
The UE 102 is configured to obtain the downlink radio frame from eNodeB. Further, the UE 102 is configured to compute 62 coefficients corresponding to 62 central subcarriers from the downlink radio frame. The 62 coefficients corresponding to 62 central subcarriers are computed by performing 2048-to-62 conversion using a partial FFT.
In an embodiment, the 2048-to-62 conversion is performed by splitting 2048-to-62 conversion to two 1024-to-62 conversion. In an example, for an IFFT of size 2048, the central 62 subcarriers correspond to the frequency indices 1, 2, … 31 and 2017, 2018, … 2047. These coefficients can be obtained by combining outputs of two 1024-to-62 point FFTs as shown in FIG. 4. W_N here equals e^+ -2pj/N¦ .
In an embodiment, one of 1024-to-62 conversion is split to two 512-to-62 conversion. In an example, each 1024-to-62 point FFT can be split into two 512-to-62 point FFTs, as shown in the FIG. 5.
In an embodiment, one of 512-to-62 conversion is split to two 256-to-62 conversion. In an example, each 512-to-62 point FFT is split to two 256-to-62 point FFTs as shown in the FIG. 6.
In an embodiment, one of 256-to-62 conversion is split to two 128-to-62 conversion. In an example, each 256-to-62 point FFT is split into two 128-to-62 point FFTs as shown in the FIG. 7.
In an embodiment, one of 128-to-62 conversion is split to two 64-to-62 conversion. In an example, each 128-to-62 point FFT is split into two 64-to-62 point FFTs as shown in the FIG. 8.
Further, the each 64-to-62 point FFT is split into two 32-to-31 point FFTs as shown in the FIG. 9.
Further, each 32-to-31 point FFT is derived by combining the outputs of two regular 16 point FFTs as shown in the FIG. 10. Thus, the 2048-to-62 point partial FFT will have the same structure until the fourth stage of a regular 2048 point FFT. From there onwards until the last stage, the outputs at different stages are suitably combined by the partial FFTs. The number of outputs at each stage gets reduced by half till reaching the last stage.
As shown in the FIG. 11 illustrates that splitting of the 2048-to-62 partial FFT to four 512-to-62 FFTs by two stages. The twiddle factors are suitably changed to correspond to N=2048. The number of outputs at the second stage is 2*62 = 124. If the N = 64, the number of outputs doubles each time, the proposed method decrementing by one stage further backwards by splitting all N-to-62 point FFTs to (N/2)-to-62 point FFTs. Thus the total number of points computed is equal to: 62*(1 + 2 + 4 + 8 + 16 + 32) + 64*31 + 4*2048 = 14082.
In contrast to this, the regular 2048 point FFT will compute 2048*11 = 22528 points. Therefore, the proposed 2048-to-62 point partial FFT over the regular 2048 point FFT is (22528-14082)*100/22528 = 37.5 %. This results in reducing the complex computation process.
Further, the UE 102 is configured to extract the data carried by the 62 central subcarriers. In accordance with the data, the UE 102 is configured to perform the cell search.
In an embodiment, the data is used to detect the PSS and the SSS.
The FIG. 1 shows the limited overview of the system 100 but, it is to be understood that other embodiments are not limited thereto. Further, the system 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.
FIG. 2 illustrates various units of the UE 102, according to the embodiments as disclosed herein. The UE 102 includes a downlink radio frame obtaining unit 202, a coefficients computing unit 204, a data extracting unit 206 and a cell search performing unit 208. The downlink radio frame obtaining unit 202 is configured to obtain the downlink radio frame. The coefficients computing unit 204 is configured to compute 62 coefficients corresponding to 62 central subcarriers from the downlink radio frame. The 62 coefficients corresponding to 62 central subcarriers are computed by performing 2048-to-62 conversion using a partial FFT.
In an embodiment, the 2048-to-62 conversion is performed by splitting 2048-to-62 conversion to two 1024-to-62 conversion, splitting one of 1024-to-62 conversion to two 512-to-62 conversion, splitting one of 512-to-62 conversion to two 256-to-62 conversion, splitting one of 256-to-62 conversion to two 128-to-62 conversion, and splitting one of 128-to-62 conversion to two 64-to-62 conversion.
Further, the data extracting unit 206 is configured to extract the data carried by the 62 central subcarriers. The cell search performing unit 208 is configured to perform the cell search in accordance with the data.
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.
FIG. 3 is flow diagram 300 illustrating a method for performing the cell search by the UE 102, according to the embodiments as disclosed herein. At step 302, the method includes obtaining the downlink radio frame. In an embodiment, the method allows the downlink radio frame obtaining unit 202 to obtain the downlink radio frame. At step 304, the method includes computing 62 coefficients corresponding to 62 central subcarriers by performing 2048-to-62 conversion by the partial FFT. In an embodiment, the method allows the coefficients computing unit 204 to compute 62 coefficients corresponding to 62 central subcarriers by performing 2048-to-62 conversion by the partial FFT.
In an embodiment, the 2048-to-62 conversion is performed by splitting 2048-to-62 conversion to two 1024-to-62 conversion, splitting one of 1024-to-62 conversion to two 512-to-62 conversion, splitting one of 512-to-62 conversion to two 256-to-62 conversion, splitting one of 256-to-62 conversion to two 128-to-62 conversion, and splitting one of 128-to-62 conversion to two 64-to-62 conversion.
At step 306, the method includes extracting the data carried by the 62 central subcarriers. In an embodiment, the method allows the data extracting unit 206 to extract the data carried by the 62 central subcarriers. At step 308, the method includes performing the cell search in accordance with the data. In an embodiment, the method allows the cell search performing unit 208 to perform the cell search in accordance with the data.
In an embodiment, the proposed method can be implemented in multi-cell environment.
In the LTE system 100 for radio access, the PSS and SSS in the downlink signal are transmitted using 62 subcarriers in central 6 RBs. Using only 6 RBs has the advantage that the UE 102 can identify the cell and can synchronize with the eNodeB irrespective of the transmission bandwidth. The cell search and time synchronization are performed before any other tasks (such as frequency synchronization, channel estimation, or the like). Since these operations need to be performed as fast as possible, the UE 102 need to extract only the data carried by the 62 subcarriers.
In order to extract only the data carried by the 62 subcarriers coefficients, the method designs the 2048–to–62 point partial FFT that computes only the necessary 62 subcarriers coefficients. This improving the fast cell search process. The proposed partial FFT eliminates computations that are necessary for the remaining coefficients.
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.
FIG. 12 illustrates a computing environment 1202 implementing a mechanism for performing the cell search by the UE 102, according to the embodiments as disclosed herein. The computing environment 1202 comprises at least one processing unit 1208 that is equipped with a control unit 1204, an Arithmetic Logic Unit (ALU) 1206, a memory 1210, a storage unit 1212, a plurality of networking devices 1216 and a plurality Input / Output (I/O) devices 1214. The processing unit 1208 is responsible for processing the instructions of the technique. The processing unit 1208 receives commands from the control unit 1204 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 1206.
The overall computing environment 1202 can be composed of multiple homogeneous or heterogeneous cores, multiple CPUs of different kinds, special media and other accelerators. The processing unit 1208 is responsible for processing the instructions of the technique. Further, the plurality of processing units 1204 may be located on a single chip or over multiple chips.
The technique comprising of instructions and codes required for the implementation are stored in either the memory unit 1210 or the storage 1212 or both. At the time of execution, the instructions may be fetched from the corresponding memory 1210 or storage 1212, and executed by the processing unit 1208.
In case of any hardware implementations various networking devices 1216 or external I/O devices 1214 may be connected to the computing environment 1202 to support the implementation through the networking unit and the I/O device unit.
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 through 12 include blocks which can be at least one of a hardware device, or a combination of hardware device and software module.
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.