Claims:

STATEMENT OF CLAIMS

We Claim:

1. A time synchronization method for performing a cell search by a communication device, the method comprising:

performing a coarse symbol timing estimation;
detecting a Primary Synchronization Signal (PSS) in a time domain based on a set of reference sequences, in response to the coarse symbol timing estimation;
detecting a Secondary Synchronization Signal (SSS) after performing a channel estimation, wherein the SSS is performed based on the detection of the PSS;
performing the cell search based on a physical layer cell ID.

2. The method of the claim 1, wherein the coarse symbol timing estimation is performed based on a Cyclic Prefix (CP) structure of a radio frame.

3. The method of the claim 1, wherein the coarse symbol timing is estimated based on a Minimum Mean Square Error (MMSE) metric.
4. The method of the claim 1, wherein performing the coarse symbol timing estimation includes:
shifting a received data based on a first set of predefined samples;
computing a mean squared error (MSE) metric over a sliding window of a second set of predefined samples;
minimizing the MSE over each segment of the first set of predefined samples; and
obtaining a symbol timing estimate by adding the CP length.

5. The method of the claim 1, wherein detecting the PSS includes:
pre-computing an Inverse Fast Fourier Transform (IFFT) of Zadoff-Chu (ZC) sequences after padding zeros;
extracting an Orthogonal Frequency Division Multiple Access (OFDM) symbol length vector starting within predefined samples from the coarse symbol timing estimation;
obtaining a correlation between a block and each of the reference sequence;
obtaining a maximum correlation coefficient over a predefined interval;
comparing the maximum correlation coefficient with a preset threshold; and
estimating a channel frequency response at a set of subcarriers carrying a PSS after applying Fast Fourier Transform (FFT), when the maximum correlation coefficient is greater than the preset threshold.

6. The method of the claim 1, wherein detecting the SSS includes:
extracting a symbol preceding a PSS symbol;
applying a partial FFT to each symbol to extract only the 62 subcarriers carrying the SSS, after extracting two symbols at two CP lengths;
generating a set of scrambling sequences;
generating a reference sequence;
correlating the generated set of scrambling sequences circularly with the reference sequence; and
computing a cell ID from a group ID.

7. A communication device for performing a cell search, the communication device comprising:
a coarse symbol timing estimation unit configured to perform a coarse symbol timing estimation;
a Primary Synchronization Signal (PSS) detecting unit configured to detect a PSS in a time domain based on a set of reference sequences, in response to the coarse symbol timing estimation;
a Secondary Synchronization Signal (SSS) configured to detect a SSS after performing a channel estimation, wherein the SSS is performed based on the detection of the PSS; and

a cell search performing unit configured to perform the cell search based on a physical layer cell ID.

Arun Kishore Narasani

Patent Agent

, Description:FIELD OF INVENTION

[0001] The embodiments herein relate a communication system, and more specifically to a method and a communication device for performing a cell search in a Long Term Evolution (LTE) system.

BACKGROUND OF INVENTION

[0002] The Long Term Evolution (LTE) specified by a 3rd Generation Partnership Project (3GPP) is one of a standard for mobile wireless communications. The 3GPP aims to provide a new radio-access technology geared to higher data rates, low latency, and greater spectral efficiency. Target peak data rates for a downlink signal and an uplink signal in the LTE system are set at 100 Mbps and 50 Mbps respectively within a 20 MHz bandwidth, corresponding to respective peak spectral efficiencies of 5 and 2.5 bps/Hz. A variable system bandwidth of 1.4-20 MHz provides greater flexibility in a spectrum utilization depending on an application requirement. The spectral efficiency targets are designed to be achieved by employing advanced air-interface techniques such as Single-Carrier Frequency Division Multiple Access (SC-FDMA) in the uplink signal, Orthogonal Frequency Division Multiple Access (OFDMA) in the downlink signal, and Multiple-Input Multiple-Output (MIMO) multi-antenna technologies.

[0003] One of the most crucial design issues in the LTE system is an initial cell search and timing and frequency synchronization. When a User Equipment (UE) (e.g., communication device) is powered ON, the UE has to first synchronize itself with an eNodeB frame timings. Further, the UE has to identify the cell and gather all the relevant System Information (SI) before registering on to the LTE system. In the LTE system, a LTE downlink physical layer utilizes an OFDMA. Since the OFDM based systems are very sensitive to symbol timing errors, it is very important to determine the correct symbol starting position before executing other tasks (e.g., frequency synchronization, channel estimation, or the like). Unlike the previous standards, the LTE system is fully Internet Protocol (IP) based. All the relevant cell specific system information are transmitted as Physical Downlink Broadcast Channel (PBCH) within the physical layer. To be able to extract the information, the UE must identify a frame boundary and identify the cell ID.

[0004] In order to aid in the process of the frame synchronization and identification of cell, the LTE specifies two synchronization signals: a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS). The PSS is one of three Zadoff-Chu (ZC) sequences which are transmitted using central 62 subcarriers twice within a radio frame. The SSS is a binary sequence of +1's and -1's, which is transmitted by the same subcarriers twice within the radio frame. The LTE system specifies 504 unique physical layer cell identities. The physical layer cell identities are grouped into 168 unique physical layer cell identity groups, where each group containing three unique identities. The detection of the PSS provides the cell ID within the group, denoted as , and the detection of the SSS provides the group ID, denoted as .

[0005] In the conventional methods, there are many time and frequency synchronization techniques for the OFDM based systems. In one of the conventional methods, the method provides a design considerations for the synchronization signals in the LTE system. In another conventional methods, the method provides a cell search procedure in which both the PSS and SSS are detected in the frequency domain using correlation based approaches.

[0006] 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

[0007] The principal object of the embodiments herein to provide a time synchronization method for performing a cell search by a communication device.

[0008] Another object of the embodiments herein is to perform a coarse symbol timing estimation.

[0009] Another object of the embodiments herein is to detect a PSS in a time domain based on a set of reference sequences.

[0010] Another object of the embodiments herein is to detect a SSS after performing a channel estimation.

SUMMARY

[0011] Embodiments herein disclose a time synchronization method for performing a cell search by a communication device. The method includes performing a coarse symbol timing estimation. Further, the method includes detecting a Primary Synchronization Signal (PSS) in a time domain based on a set of reference sequences. Further, the method includes detecting a Secondary Synchronization Signal (SSS) after performing a channel estimation. The SSS is performed based on the detection of the PSS. Furthermore, the method includes performing the cell search based on a physical layer cell ID.

[0012] In an embodiment, the coarse symbol timing estimation is performed based on a Cyclic Prefix (CP) structure of a radio frame.

[0013] In an embodiment, the coarse symbol timing is estimated based on a Minimum Mean Square Error (MMSE) metric.

[0014] In an embodiment, the method includes shifting a received data based on a first set of predefined samples and computing a mean squared error (MSE) metric over a sliding window of a second set of predefined samples. Further, the method includes minimizing the MSE over each segment of the first set of predefined samples. Further, the method includes obtaining a symbol timing estimate by adding the CP length. Furthermore, the method includes performing the coarse symbol timing estimation.

[0015] In an embodiment, the method includes pre-computing an Inverse Fast Fourier Transform (IFFT) of Zadoff-Chu (ZC) sequences after padding zeros. Further, the method includes extracting an Orthogonal Frequency Division Multiple Access (OFDM) symbol length vector starting within predefined samples from the symbol timing estimation. Further, the method includes obtaining a correlation between a block and each reference sequence. Further, the method includes obtaining a maximum correlation coefficient over a predefined interval. Further, the method includes comparing the maximum correlation coefficient with a preset threshold. Further, the method includes estimating a channel frequency response at a set of subcarriers carrying a PSS after applying Fast Fourier Transform (FFT), when the maximum correlation coefficient is greater than the preset threshold. Furthermore, the method includes detecting the PSS.

[0016] In an embodiment, the method includes extracting a symbol preceding a PSS symbol. Further, the method includes applying a partial FFT to each symbol to extract only the 62 subcarriers carrying the SSS, after extracting two symbols at two CP lengths. Further, the method includes generating a set of scrambling sequences. Further, the method includes generating the reference sequence. Further, the method includes correlating the estimated sequence circularly with the reference sequence. Further, the method includes computing a group ID. Further, the method includes detecting the SSS.

[0017] Embodiments herein disclose a communication device for performing a cell search. The communication device includes a coarse symbol timing estimation unit configured to perform a coarse symbol timing estimation. A Primary Synchronization Signal (PSS) detecting unit is configured to detect a PSS in a time domain based on a set of reference sequences. A Secondary Synchronization Signal (SSS) is configured to detect a SSS after performing a channel estimation. The SSS is performed based on the detection of the PSS. A cell search performing unit is configured to perform the cell search based on a physical layer cell ID.

[0018] 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

[0019] 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:

[0020] FIG. 1 is an overview of a LTE system for performing a cell search by a communication device, according to the embodiments as disclosed herein;

[0021] FIG. 2 is a schematic illustration of a LTE downlink frame structure;

[0022] FIG. 3 is a schematic illustration of a slot structure for a normal CP;

[0023] FIG. 4 is a schematic illustration of a PSS and a SSS with Type 1 (Frequency Division Duplex (FDD)) frame;

[0024] FIG. 5 is a graph illustrating a ZC sequence multiplied with its complex conjugate and padded with zeros;

[0025] FIG. 6 is a graph illustrating a correlation between an Inverse Fast Fourier Transform (IFFT) of zero-padded PSS ZC sequence and input time domain signal;

[0026] FIG. 7 is a flow diagram illustrating a method for performing a cell search by the communication device, according to the embodiments as disclosed herein;

[0027] FIG. 8 is a block diagram illustrating a time synchronization, according to the embodiments as disclosed herein;

[0028] FIG. 9 is a schematic illustration of coarse estimation of symbol boundaries, according to the embodiments as disclosed herein;

[0029] FIG. 10 is a flow diagram illustrating a method for performing the coarse symbol timing estimation, according to the embodiments as disclosed herein;

[0030] FIG. 11 is a flow diagram illustrating a method for detecting the PSS in the time domain, according to the embodiments as disclosed herein;

[0031] FIG. 12 is a flow diagram illustrating a method for detecting the SSS along with a channel estimation, according to the embodiments as disclosed herein;

[0032] FIG. 13 is a graph depicting a Mean Square Error (MSE) metric computed over one slot duration, according to the embodiments as disclosed herein;

[0033] FIG. 14 is a graph depicting a MSE metric around a symbol boundary, according to the embodiments as disclosed herein;

[0034] FIG. 15 is a graph depicting an absolute value of a correlation with time-domain ZC sequences around the PSS, according to the embodiments as disclosed herein;

[0035] FIG. 16 is a graph depicting a frame boundary detection performance at Signal to Noise Ratio (SNR) equal to 10 dB, according to the embodiments as disclosed herein;

[0036] FIG. 17 is a graph depicting a frame boundary detection performance at SNR equal to 20 dB, according to the embodiments as disclosed herein;

[0037] FIG. 18 is a graph depicting a frame boundary detection performance at SNR equal to 30 dB, according to the embodiments as disclosed herein; and

[0038] FIG. 19 illustrates a computing environment implementing a mechanism for performing a cell search, according to embodiments as disclosed herein.

DETAILED DESCRIPTION OF INVENTION

[0039] 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.

[0040] Embodiments herein disclose a time synchronization method for performing a cell search by a communication device. The method includes performing a coarse symbol timing estimation. Further, the method includes detecting a Primary Synchronization Signal (PSS) in a time domain based on a set of reference sequences. Further, the method includes detecting a Secondary Synchronization Signal (SSS) after performing a channel estimation. The SSS is performed based on the detection of the PSS. Furthermore, the method includes performing the cell search based on a physical layer cell ID.

[0041] Unlike the conventional methods and the conventional systems, the detection of the SSS includes estimating and equalizing the channel at the SSS using the detected PSS, determining the CP (normal or extended) from the absolute value of the correlation during the index detection of the first interleaving sequence, and searching the second interleaving sequence index around the first index instead of searching over the entire range. Thus, improving the fast cell search in a robust manner.
[0042] The proposed method detects the PSS in a time–domain so that the FFT operation is avoided. The proposed method simplifies the correlation computation process and decreases a search window size about the coarse symbol timing estimation.

[0043] Unlike the conventional methods, instead of considering all possible cell IDs, the proposed method first searches over a small list of cell IDs used in a recent past, thus decreasing the correlation computation time during the PSS and SSS detection.

[0044] Referring now to the drawings, and more particularly to FIGS. 1 through 19, there are shown preferred embodiments.

[0045] FIG. 1 is an overview of a LTE system 1000 for performing a cell search by a communication device 100, according to the embodiments as disclosed herein. In an embodiment, the LTE system 1000 includes the communication device 100 and a plurality of cells (i.e., cell 1 and cell 2). The communication device 100 can be, for example but not limited to, a smart phone, a Personal Digital Assistant (PDA), a tablet computer or the like. In an embodiment, the communication device 100 includes a communication interface unit 102, a coarse symbol timing estimation unit 104, a PSS detecting unit 106, a SSS detecting unit 108, a physical layer cell identification unit 110, and a cell search performing unit 112. Before the communication device 100 can communicate over the LTE system 1000 using the communication interface unit 102, the communication device 100 typically needs to perform the cell search to acquire frequency and symbol synchronization to the cell (e.g., cell 1 or cell 2) and detect the physical-layer identity of the cell.

[0046] The coarse symbol timing estimation unit 104 is configured to perform the coarse symbol timing estimation. In an embodiment, the coarse symbol timing estimation is performed based on the CP structure of a radio frame. In an embodiment, the coarse symbol timing is estimated based on a MMSE metric.

[0047] Based on the coarse symbol timing estimation, the PSS detecting unit 106 is configured to detect the PSS in the time domain based on a set of reference sequences. After detecting the PSS, the SSS detecting unit 108 is configured to detect the SSS) along with the channel estimation. The channel estimation is performed prior to the detection of the SSS. Further, the physical layer cell identification unit 110 is configured to identify the physical layer cell ID based on the PSS and the SSS. Based on the physical layer cell ID, the cell search performing unit 112 is configured to perform the cell search.

[0048] Although FIG. 1 shows exemplary units of the communication device 100, in other implementations, the communication device 100 may include fewer components, different components, differently arranged components, or additional components than depicted in the FIG. 1. Additionally or alternatively, one or more components of the communication device 100 may perform functions described as being performed by one or more other components of the communication device 100.

[0049] FIG. 2 is a schematic illustration of a LTE downlink frame structure. The LTE standard specifies two types of radio frame structures: Type 1 (i.e., Frequency Division Duplex (FDD)) and Type 2 (i.e., Time Division Duplex (TDD)). Both structures are specified over frame timing of 10 msec. Each radio frame consists of 20 slots numbered from 0 to 19 and one slot duration is 0.5 msec. In an embodiment, the radio frame consists of 10 subframes, where each subframe spanning two slots or 1 msec. Each slot consists of 7 OFDM symbols or 6 OFDM symbols depending on whether the CP is of type normal or extended, respectively.

[0050] In the frequency domain, the signal in each slot is described by a resource grid of the subcarriers. 12 subcarriers make a Resource Block (RB). The subcarriers have a spacing of 15 KHz, and each RB spans 180 KHz in the frequency domain. The RBs consist of resource elements, where each resource element corresponds to one subcarrier in the frequency domain and one OFDM symbol in the time domain. The LTE radio frame structure in time and frequency domains is shown in the FIG. 2.

[0051] Further, corresponding to the subcarrier spacing of 15KHz, the OFDM symbol interval is selected to be msec. This makes all the subcarriers orthogonal over this time duration. Each OFDM symbol consists of 2048 samples. Thus the sampling period is sec. The slot consists of 15360 samples, a subframe consists of 30720 samples, and a frame consists of 307200 samples. The additional number of samples in the slot other than the samples for the OFDM symbols account for the CP as shown in the FIG. 3.

[0052] LTE synchronization signals:

[0053] PSS: The PSS sequence in the LTE downlink is one of three Zadoff-Chu sequences. Each ZC corresponds to one of three physical layer cell IDs in the group. The PSS is sent over the central 6 RBs. Only the central 62 subcarriers are used out of the 72 subcarriers. The remaining 10 subcarriers are kept reserved. The PSS is sent every 5 milliseconds, and twice in the radio frame. In the case of the FDD, the PSS is sent in the last OFDM symbol of every 1st and 11th slot of the frame (refer to the FIG. 4). In the case of the TDD, the PSS is sent in the 3rd symbol of every 3rd and 13th slot of the frame. The generation and mapping of the Zadoff-Chu sequence to the resource elements are specified in sections 6.11.1.1 and 6.11.1.2 of the standard. The PSS sequence is given by

where denotes the root index. The physical cell ID within the group is denoted by . The root index is equal to 25, 29, and 34 corresponding to values 0, 1, and 2 respectively.
[0054] SSS: The SSS is also sent over the central 6 RBs. Like the PSS, only 62 subcarriers are used, the remaining 10 subcarriers are kept reserved. In case of the FDD, the SSS is sent in the symbol immediately preceding the symbol carrying PSS. In case of the TDD, the SSS is sent 3 symbols earlier than the PSS symbol. Unlike the PSS, the SSS is the binary sequence which is a interleaving of two length-31 binary sequences. The sequence is scrambled with another sequence which is generated using . The generation of the SSS and the mapping to resource elements are specified in the section 6.11.2.1 and 6.11.2.2 of the standard.

[0055] Detection of the reference sequences in the time-domain: In the LTE, the PSS is the ZC sequence in the frequency domain and is distributed over the central 62 subcarriers. The corresponding OFDM signal in the time domain is the inverse FFT of not only the ZC sequence coefficients, but also resource element values in other subcarriers outside the central 6 RBs. The time domain OFDM signal is therefore not the ZC sequence. Furthermore, the ZC sequence is used as the PSS has length 62. The IFFT size used in the OFDMA is 2048 so as to accommodate the maximum bandwidth of 20 MHz. Even if the technique reserves all other subcarriers except the central 62 subcarriers, the time domain OFDM symbol is not the ZC sequence. Therefore, in order to detect the ZC sequence in the time domain, the proposed method need to use the equivalent time-domain representations.

[0056] Consider a vector of samples in the time domain. Let us denote it by . In order to check if contains the ZC sequence , the method first applies the FFT on , extracts the coefficients corresponding to central 62 subcarriers, and then correlates them with . The absolute value of the correlation can be written as , where denotes the Discrete Fourier Transform (DFT) matrix of order , and is a rectangular matrix of size 62x2048 for extracting only the coefficients corresponding to central 62 subcarriers. The term can be rewritten as , where denotes the IFFT of after padding zeros. Thus, the ZC sequence can be equivalently represented by the length- reference sequence .

[0057] The ZC sequences have constant amplitude value of 1. Thus when the ZC sequence is multiplied by its complex conjugate element-wise, the proposed method obtains 1 at all 62 subcarriers. If the method pads zeros to , then the resulting product sequence will similar as in the FIG. 5. The IFFT of this sequence is easy to compute. Ignoring the scale factor, the method obtains the IFFT as

[0058] This can be simplified as

[0059] Further, the element-wise multiplication in the frequency domain results in a circular convolution in the time domain. Because of the CP structure and the symmetry of the ZC sequences, the method can show that the circular convolution is the same as the correlation.

[0060] Further, in the case of an identity channel (i.e., a channel without any additive noise and with unity impulse response), the correlation of a reference sequence with the PSS symbol in time-domain will have the same value as the above formula (with a scale factor) if the PSS is the corresponding ZC sequence. At earlier samples, up to the beginning of the CP, the correlation will be given by the above formula exactly. However, at later samples, part of the input vector will overlap with the CP of the next OFDM symbol. Therefore the formula will only represent an approximation within a few sample locations.

[0061] FIG. 6 is a graph illustrating a correlation between the IFFT of zero-padded PSS ZC sequence and input time domain signal. When the channel has multipaths with additive noise, the correlation computation as before will lead to a convolution with the above function with some additive noise. If the channel impulse response length is relatively much smaller compared to the main lobe width, then the peak of the correlation will be around the peak of the function computed above, which happens at the beginning of the OFDM symbol carrying the PSS.
[0062] FIG. 7 is a flow diagram 700 illustrating a method for performing the cell search by the communication device 100, according to the embodiments as disclosed herein. At step 702, the method includes performing the coarse symbol timing estimation. In an embodiment, the method allows the coarse symbol timing estimation unit 104 to perform the coarse symbol timing estimation. At step 704, the method includes detecting the PSS in the time domain based on the set of reference sequences. In an embodiment, the method allows the PSS detecting unit 106 to detect the PSS in the time domain based on the set of reference sequences.

[0063] At step 706, the method includes detecting the SSS along with the channel estimation. The SSS is performed based on the detection of the PSS. The channel estimation is performed prior to the detection of the SSS. In an embodiment, the method allows the SSS detecting unit 108 to detect the SSS along with the channel estimation. At step 708, the method includes performing the cell search based on the physical layer cell ID. In an embodiment, the method allows the cell search performing unit 112 to perform the cell search based on the physical layer cell ID.

[0064] The various actions, acts, blocks, steps, and the like in the flow diagram 700 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.

[0065] FIG. 8 is a block diagram illustrating the time synchronization scheme, according to the embodiments as disclosed herein. The proposed method performs the cell search using the time synchronization scheme. The time synchronization scheme includes two steps, first is a coarse symbol timing estimation using a Cyclic Prefix (CP) structure of a radio frame, and second is a fine timing estimation using the PSS and the SSS. The coarse symbol timing estimation is estimated based on a Minimum Mean Square Error (MMSE) techniques. Further, the method detects the PSS and SSS around the coarse estimates. After detecting the PSS and SSS, the method provides a physical layer cell ID.

[0066] In an embodiment, the proposed method first coarsely estimates the symbol beginning using the CP structure of the LTE downlink frame. Then the symbol containing the primary synchronization signal is detected by correlating the three Zadoff-Chu sequences in the time domain with blocks of samples around the coarse estimation. The detection of the secondary synchronization signal then follows after the channel estimation and equalization. Thus, the proposed method is quite robust in identifying the cell ID.

[0067] In an embodiment, the initial cell search and synchronization procedure is followed by an extraction and decoding of a Physical Broadcast Channel (PBCH). The PBCH channel contains all cell specific system information such as the cell ID, CP, frame type, bandwidth, etc. The detected cell ID can be confirmed during the PBCH decoding process.

[0068] The detection of the SSS includes estimating and equalizing the channel at the SSS using the detected PSS, determining the CP (normal or extended) from the absolute value of the correlation during the index detection of the first interleaving sequence, and searching the second interleaving sequence index around the first index instead of searching over the entire range. Thus, improving the cell search fast.

[0069] Coarse symbol time estimation: The symbol boundaries are estimated using the CP structure of the LTE downlink radio frame. The received data is shifted by 2048 samples (OFDM symbol length) and is multiplied with the original data element-wise after being complex-conjugated. Then, the Mean Squared Error (MSE) metric is calculated over a sliding window of 144 samples (normal CP length for all symbols except the 1st symbol in the case of FDD). The minimum value of the MSE metric over each non-overlapping segment of 2048 samples is assumed to be the starting sample of the CP preceding the symbol. The detailed steps are given in the following and the procedure is illustrated in the FIG. 9.

[0070] FIG. 10 is a flow diagram 702 illustrating a method for performing the coarse symbol timing estimation, according to the embodiments as disclosed herein. The steps (702a to 702e) are performed by the coarse symbol timing estimation unit 104.

[0071] At step 702a, the method includes shifting the received data based on the first set of predefined samples. In an embodiment, the method allows the coarse symbol timing estimation unit 104 to shift the received data to left by 2048 samples based on the below equation. where denotes the received samples from RF and denotes its length.

[0072] At step 702b, the method includes computing the MSE metric over the sliding window of a second set of predefined samples. In an embodiment, the method allows the coarse symbol timing estimation unit 104 to compute the MSE metric over the window of 144 samples based on the below equation.

[0073] At step 702c, the method includes minimizing the MSE over each segment of the first set of predefined samples. In an embodiment, the method allows the coarse symbol timing estimation unit 104 to minimize the MSE over each segment of 2048 samples based on the below equation.

where denotes the starting sample index of the CP for the th symbol.
[0074] At step 702d, the method includes obtaining the symbol timing estimate by adding the CP length. In an embodiment, the method allows the coarse symbol timing estimation unit 104 to obtain the symbol timing estimate by adding the CP length based on the below equation.
,
where denotes the starting sample of the th symbol.
[0075] At step 702e, the method includes performing the coarse symbol timing estimation.
[0076] The various actions, acts, blocks, steps, and the like in the flow diagram 702 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.
[0077] Fine time estimation: The fine timing estimation starts with the detection of the PSS. This provides the cell ID within the group ( ) and 5 milliseconds timing synchronization. This is followed by the channel estimation at the subcarriers carrying the PSS and then the detection of the SSS after the channel equalization. This provides the group ID of the cell ( ) based on the unique cell ID ( ), frame synchronization, and the CP type (normal or extended).

[0078] FIG. 11 is a flow diagram illustrating a method for detecting the PSS in the time domain, according to the embodiments as disclosed herein. The PSS is detected in the time domain. The coarse symbol timing provided by the previous step is used as the initialization in the PSS detection. The steps (704a to 704f) are performed by the PSS detecting unit 106.

[0079] At step 704a, the method includes pre-computing the IFFT of the ZC sequences after padding zeros. In an embodiment, the method allows the PSS detecting unit 106 to pre-compute the IFFT of the ZC sequences after padding zeros. Corresponding to the ZC sequence in the frequency domain, let us denote the reference sequence in the time-domain by .

[0080] At step 704b, the method includes extracting the OFDM symbol length vector. In an embodiment, the method allows the PSS detecting unit 106 to extract the OFDM symbol length vector starting within 10 samples from the coarse estimate based on the below equation.

[0081] At step 704c, the method includes obtaining the correlation between the block and each reference sequence. In an embodiment, the method allows the PSS detecting unit 106 to obtain the correlation between the block and each reference sequence :
,
where ‘h’ denotes complex conjugate transpose.

[0082] At step 704d, the method includes obtaining the maximum correlation coefficient value. In an embodiment, the method allows the PSS detecting unit 106 to obtain the maximum correlation coefficient value over the interval.

[0083] At step 704e, the method includes determining whether the correlation coefficient value is greater than a preset threshold. In an embodiment, the method allows the PSS detecting unit 106 to compare the correlation coefficient value with the preset threshold. If the value is larger than the threshold, then the symbol timing and the cell ID are known. If the correlation coefficient value is not greater than the preset threshold, the method move to step 704b.


where denotes the maximum value of the correlation with an identity channel, and denotes the starting sample index of the PSS symbol.
[0084] If the correlation coefficient value is greater than the preset threshold, at step 704f, the method includes estimating the channel frequency response. In an embodiment, the method allows the PSS detecting unit 106 to estimate the channel frequency response at the 62 subcarriers carrying the PSS after applying FFT based on the below equation:
,
where denotes the FFT of the detected PSS symbol at the kth subcarrier.

[0085] The various actions, acts, blocks, steps, and the like in the flow diagram 704 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.
[0086] SSS detection: Let consider that the FDD frame structure is used in the SSS detection. The SSS is transmitted by the same subcarriers as those of the PSS in the immediately preceding symbol. So, the method considers that these channel parameters remain the same for the SSS subcarriers as well. Unlike the PSS, the SSS is a binary sequence of +1’s and -1’s formed after the interleaving of two sequences which depend on two parameters and . These two parameters are derived from the group ID of the cell ( ). Further, these two sequences are scrambled with two binary sequences which depend on . Therefore the detection algorithm proceeds by first deriving the scrambling sequences, then finding the values of and , and then finally computing the value of by a simple table look-up procedure.

[0087] FIG. 12 is a flow diagram 706 illustrating a method for detecting the SSS along with the channel estimation, according to the embodiments as disclosed herein. The steps (706a to 706g) are performed by the SSS detecting unit 108.

[0088] At step 706a, the method includes extracting the symbol immediately preceding the PSS symbol. At step 706b, the method includes applying the partial FFT to each symbol.
[0089] In an embodiment, the method allows the SSS detecting unit 108 to extract the symbol immediately preceding the PSS symbol. Since the CP length is not yet known, the SSS detecting unit 108 extracts two symbols at two CP lengths. Further, the SSS detecting unit 108 applies the partial FFT to each symbol to extract only the 62 subcarriers carrying the SSS.

[0090] At step 706c, the method includes equalizing each of these two vectors. In an embodiment, the method allows the SSS detecting unit 108 to equalize each of these two vectors by dividing by the channel frequency response estimated earlier using the PSS. Further, the SSS detecting unit 108 removes the imaginary parts of the coefficients and quantizes the real values to +1 or -1 depending on whether they are positive or negative. Let the two vectors be denoted by and .

[0091] At step 706d, the method includes generating two scrambling sequences. In an embodiment, the method allows the SSS detecting unit 108 to generate two scrambling sequences and using . Further, the SSS detecting unit 108 to divide the even coefficients of the equalized vectors and by to get two estimates of .
[0092] At step 706e, the method includes generating the reference sequence. In an embodiment, the method allows the SSS detecting unit 108 to generate the reference sequence and circularly correlates it with the two estimates of . Further, the SSS detecting unit 108 compares the maximum correlations for the two sequences. If yields higher correlation value, the CP is of type ‘normal’, otherwise the CP is of type ‘extended’. The circular shift corresponding to the maximum value gives the estimate of .
[0093] Further, the SSS detecting unit 108 generates the reference sequence , and utilizes the estimated value of to generate the scrambling sequence . If the CP is normal, the SSS detecting unit 108 divides the odd numbered coefficients of by the product sequence to obtain an estimate of the sequence . Otherwise, divide the odd numbered coefficients of for the same purpose.

[0094] At step 706f, the method includes correlating the estimated sequence circularly with the reference sequence. In an embodiment, the method allows the SSS detecting unit 108 to correlate the estimated sequence circularly with the reference sequence . The circular shift yielding the maximum correlation value within from the estimate is an estimate of . If , then the slot containing the SSS has index 0 (subframe number 0), else it has index 10 (subframe number 5). In the latter case, swap the values of and .

[0095] Further, using the and values, at step 706g, the method computing the group ID from standard table 6.11.2.1-1. Further, the SSS detecting unit 108 computes the absolute cell ID as . Based on the slot number, the SSS detecting unit 108 computes the starting sample of the frame.

[0096] The various actions, acts, blocks, steps, and the like in the flow diagram 706 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.

[0097] FIG. 13 is a graph depicting the MSE metric computed over one slot duration, according to the embodiments as disclosed herein. The proposed synchronization scheme is implemented in the LTE downlink physical layer at the receiver side at 20 MHz bandwidth. The transmitted radio frame is Type 1 (FDD) at the normal CP. The total number of resource blocks and subcarriers are 100 and 1200 respectively. The IFFT size is 2048, thus the sampling period is 1/(15x2048) msec (i.e., 32.55 microsec) and there is 2048 samples per OFDM symbol. The proposed method simulates the channel with different additive white Gaussian noise levels (SNR=10 dB, 20 dB, and 30 dB) and with different number of multipaths (1 to 5). The multipath channel is simulated using the channel model. For each number of multipaths, the method simulates 100 channels at each SNR. At each instance, the method selects the transmitting cell ID randomly within 0 and 503. The method considers only one transmitting antenna. Since the PSS and SSS are transmitted from the same antenna ports.

[0098] As shown in the FIG. 13, the system utilizes a channel having 5 multipaths with AWGN corresponding to 30 dB, there are seven dips corresponding to seven symbols. Further, these dips are not as sharp as they appear. When look closely, the graph illustrates that the MSE metric decreases and increases around the minimum location are gradual (FIG. 14). This is expected since the sliding window moves by one sample at a time in this case.

[0099] FIG. 14 is a graph depicting a MSE metric around a symbol boundary, according to the embodiments as disclosed herein.

[00100] FIG. 15 is a graph depicting an absolute value of the correlation with time-domain ZC sequences around the PSS, according to the embodiments as disclosed herein. In this case, the cell ID is 134, thus the actual ZC sequence transmitted as PSS corresponds to . The correct ZC sequence produces the highest peak and is above the threshold.

[00101] The method estimates that the starting sample of the frame and computed the offset from the true starting sample.

[00102] FIG. 16 is a graph depicting the frame boundary detection performance at SNR equal to 10 dB, according to the embodiments as disclosed herein.

[00103] FIG. 17 is a graph depicting the frame boundary detection performance at SNR equal to 20 dB, according to the embodiments as disclosed herein. FIG. 18 is a graph illustrating the frame boundary detection performance at SNR equal to 30 dB, according to the embodiments as disclosed herein.

[00104] The different colors (e.g., gray and black) denotes different channel filter lengths, or equivalently different number of multipaths. For each case, the graph realizes the 100 channels and computes the percentage offsets over these channels. The graph indicates that the offsets are limited to a few samples only. As the number of multipaths increases, the offset may increase slightly. However, the proposed algorithm is able to detect the starting sample correctly at majority of occasions. The small amount of offset can be corrected in the subsequent step. As another observation, the graph indicates that the additive channel noise is decreased and the detection performance generally improves. Further, the detected cell ID is identical to the true cell ID.

[00105] FIG. 19 illustrates a computing environment 1902 implementing a mechanism for performing the cell search, according to the embodiments as disclosed herein. The computing environment 1902 comprises at least one processing unit 1908 that is equipped with a control unit 1904, an Arithmetic Logic Unit (ALU) 1906, a memory 1910, a storage unit 1912, a plurality of networking devices 1916 and a plurality Input / Output (I/O) devices 1914. The processing unit 1908 is responsible for processing the instructions of the technique. The processing unit 1908 receives commands from the control unit 1904 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 1906.

[00106] The overall computing environment 1902 can be composed of multiple homogeneous or heterogeneous cores, multiple CPUs of different kinds, special media and other accelerators. The processing unit 1908 is responsible for processing the instructions of the technique. Further, the plurality of processing units 1904 may be located on a single chip or over multiple chips.
[00107] The technique comprising of instructions and codes required for the implementation are stored in either the memory unit 1910 or the storage 1912 or both. At the time of execution, the instructions may be fetched from the corresponding memory 1910 or storage 1912, and executed by the processing unit 1908.

[00108] In case of any hardware implementations various networking devices 1916 or external I/O devices 1914 may be connected to the computing environment 1902 to support the implementation through the networking unit and the I/O device unit.

[00109] 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 19 include blocks which can be at least one of a hardware device, or a combination of hardware device and software module.

[00110] 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.