Claims:STATEMENT OF CLAIMS
We Claim:
1. A method for performing a cell search in an Orthogonal Frequency Division Multiplexing (OFDM) system by a Radio Frequency (RF) receiver, the method comprising:
obtaining In-phase and Quadrature phase (IQ) signals in a digital domain at a predefined frequency;
computing a Fast Fourier Transform (FFT) of a predefined size of the IQ signals at a predetermined center frequency;
performing a circular shift of FFT corresponding to at least one predetermined center frequency;
determining whether the Physical Cell Identifier (PCID) is identified;
detecting a Received Signal Strength Indicator (RSSI), Reference Signal Received Power (RSRP), and EUTRA Absolute Radio-Frequency Channel Number (ERFCN) in response to determining that the PCID is identified; and
selecting a Long-Term Evolution (LTE) cell in accordance with the detected RSSI, RSRP, and ERFCN.
2. The method of claim 1, wherein the method further comprises:
repeatedly performing cyclic shifts of FFT by multiple predetermined center frequencies till a threshold is reached;
detecting multiple PCIDs based on the cyclic shift of FFT;
shortlisting detected PCIDs for RF carriers; and
selecting a LTE cell associated with highest RSRQ among plurality of RSRQs of identified cells corresponding to the multiple PCIDs.
3. The method of claim 1, wherein determining whether the PCID is identified based on the cyclic shift of FFT includes performing Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS) correlation.
4. The method of claim 1, wherein the predetermined center frequency corresponds to an E-UTRA band.
5. The method of claim 1, wherein the IQ signals are obtained by digitally demodulating with a set of frequencies to obtain sequences of IQ signals, wherein subcarrier frequencies in each IQ signal corresponds to a set of raster frequencies.
6. A Radio Frequency (RF) receiver for performing a cell search in an Orthogonal Frequency Division Multiplexing (OFDM) system, the RF receiver is configured to:
obtain In-phase and Quadrature phase (IQ) signals in digital domain at a predefined frequency;
compute a Fast Fourier Transform (FFT) of a predefined size of the IQ signals at a predetermined center frequency;
perform circular shift of FFT corresponding to at least one predetermined center frequency;
determine whether the Physical Cell Identifier (PCID) is identified;
detect Received Signal Strength Indicator (RSSI), Reference Signal Received Power (RSRP), and EUTRA Absolute Radio-Frequency Channel Number (ERFCN) in response to determining that the PCID is identified; and
select a Long-Term Evolution (LTE) cell in accordance with the detected RSSI, RSRP, and ERFCN.
7. The RF receiver of claim 6, wherein the RF receiver is configured to:
repeatedly perform cyclic shifts of FFT by multiple predetermined center frequencies till a threshold is reached;
detect multiple PCIDs based on the cyclic shift of FFT;
shortlist detected PCIDs for RF carriers; and
select a LTE cell associated with highest RSRQ among plurality of RSRQs of identified cells corresponding to the multiple PCIDs.
8. The RF receiver of claim 6, wherein determine whether the PCID is identified based on the cyclic shift of FFT includes performing Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS) correlation.

9. The RF receiver of claim 6, wherein the predetermined center frequency corresponds to an E-UTRA band.
10. The RF receiver of claim 6, wherein the IQ signals are obtained by digitally demodulating with a set of frequencies to obtain sequences of IQ signals, wherein the subcarrier frequencies in each IQ signal corresponds to a set of raster frequencies.
Dated this 19th Day of April, 2017 Signatures:
Arun Kishore Narasani
Patent Agent
, Description:FIELD OF INVENTION
[0001] The present disclosure relates to a wireless communication, and more particularly to a method for performing a cell search in an Orthogonal Frequency Division Multiplexing (OFDM) system by a Radio Frequency (RF) receiver.
BACKGROUND OF INVENTION
[0002] In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), higher layers send a LTE frequency band of interest to a RF front-end (RFE) through a L1 Controller for detection of a PCIDs in a power-ON mode. According to the 3GPP LTE specifications TS36.101, there are Frequency Division Duplex (FDD) and Time Division Duplex (TDD) Evolved Universal Terrestrial Radio Access (EUTRA) bands (band numbers 15, 16 are reserved) with different carrier frequencies with ranges (Range of NDL) and bandwidths for Uplink (UL) and Downlink (DL). The Range of NDL is also called as Range of EARFCN (Absolute Radio Frequency Channel Number) which is within 0-65535 range. While the power-on mode for a given EUTRA band, the full bandwidth between FDL_low and FDL_high is to be scanned by a UE. The UE scans from FDL_low to FDL_high in steps of 100 kHz, called the 100 kHz raster scanning. Within each supported EUTRA band, a User Equipment (UE) needs to search only on the 100 kHz carrier frequency grid. When the UE is activated (powered-on), the higher layers send a cell detection request (i.e., EUTRA band number) to a PHY controller which provides control signals to the RF front-end (RFE) through a RF interface (e.g., RFAPI) to begin a network search at FDL_low till the end FDL_high. A receiver of the UE receives the IQ samples at a desired sampling rate Fs and initiates the cell-searcher for cell acquisition. Upon completion of the search if a valid cell is found by the cell searcher block then the cell parameters are stored and uploaded corresponding to the cell. The parameters that are stored corresponding to detected cell are Physical Cell Identifier (PCID), Master Information Block (MIB), System Information Block (SIB) and physical measurements like Reference Signal Received Quality (RSRQ) and Reference Signal Received Power (RSRP). Upon detection (or no detection) of the cell by the cell-searcher, the PHY controller triggers the RFE through a RFAPI for tuning the RF to next frequency (FDL_low 100 kHz). The process repeats for every increment of 100 kHz raster frequency until the band is searched for whole range (Range of NDL). The higher layers prepare the list of detected cells and corresponding cell parameters, selects the cell with highest RSRP (or RSRQ) and directs the RF through PHY controller on which detected cell (usually based the highest detected RSRQ) the UE to camp on, accordingly the PHY controller sends the control to the RFE to tune to the UL and the DL frequencies for camping on.
[0003] In the conventional method where the RFE will to tune to all the frequency ranges (Range of NDL) starting from FDL_low and ending at FDL_high in steps of 100 kHz raster frequency increment. For example, for EUTRA band-1 the FDL_low = 2110MHz and FDL_high = 2170MHz the number of times the RFE to be tuned to all raster frequencies is 600 times (Range of NDL=0:599). This results in a significant amount of interactions between baseband (L1 Controller) and the RFE.
[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 performing a cell search in an OFDM system by a RF receiver.
[0006] Another object of the embodiments herein is to provide a mechanism for obtaining IQ signals in digital domain at a predefined frequency.
[0007] Another object of the embodiments herein is to provide a mechanism for computing a Fast Fourier Transform (FFT) of a predefined size of the IQ signals at a predetermined center frequency.
[0008] Another object of the embodiments herein is to provide a mechanism for performing circular shift of FFT corresponding to at least one predetermined center frequency.
[0009] Another object of the embodiments herein is to provide a mechanism for determining whether the Physical cell identifier (PCID) is identified.
[0010] Another object of the embodiments herein is to provide a mechanism for detect RSSI, RSRP, and ERFCN in response to determining that the PCID is identified
[0011] Another object of the embodiments herein is to provide a mechanism for selecting a LTE cell in accordance with the detected RSSI, RSRP, and ERFCN.
[0012] Another object of the embodiments herein is to provide a mechanism for repeatedly performing cyclic shifts of FFT by multiple predetermined center frequencies till a threshold is reached.
[0013] Another object of the embodiments herein is to provide a mechanism for detecting multiple PCIDs based on the cyclic shift of FFT.
[0014] Another object of the embodiments herein is to provide a mechanism for shortlisting detected PCIDs for RF carriers.
[0015] Another object of the embodiments herein is to provide a mechanism for selecting a LTE cell associated with highest RSRQ among plurality of RSRQs of identified cells corresponding to the multiple PCIDs.
SUMMARY
[0016] Embodiments herein disclose a method for performing a cell search in an OFDM system by a RF receiver. The method includes obtaining IQ signals in a digital domain at a predefined frequency. Further, the method includes computing a Fast Fourier Transform (FFT) of a predefined size of the IQ signals at a predetermined center frequency. Further, the method includes performing a circular shift of the FFT corresponding to the at least one predetermined center frequency. Further, the method includes determining whether a Physical Cell Identifier (PCID) is identified. Further, the method includes detecting a Received Signal Strength Indicator (RSSI), a Reference Signal Received Power (RSRP), and a EUTRA Absolute radio-frequency channel number (ERFCN) in response to determining that the PCID is identified. Furthermore, the method includes selecting a LTE cell in accordance with the detected RSSI, the RSRP, and the ERFCN.
[0017] In an embodiment, the method includes repeatedly performing cyclic shifts of the FFT by multiple predetermined center frequencies till a threshold is reached. Further, the method includes detecting multiple PCIDs based on the cyclic shift of FFT and shortlisting the detected PCIDs for RF carriers. Further, the method includes selecting the LTE cell associated with highest RSRQ among plurality of RSRQs of identified cells corresponding to the multiple PCIDs.
[0018] In an embodiment, the PCID is identified is determined by performing the PSS and SSS correlation.
[0019] In an embodiment, the predetermined center frequency corresponds to an E-UTRA band.
[0020] In an embodiment, the IQ signals are obtained by digitally demodulating with a set of frequencies to obtain sequences of IQ signals.
[0021] In an embodiment, the subcarrier frequencies in each IQ signal corresponds to a set of raster frequencies.
[0022] Embodiments herein disclose a RF receiver for performing cell search in an OFDM system. The RF receiver is configured to obtain IQ signals in a digital domain at a predefined frequency. Further, the RF receiver is configured to compute a Fast Fourier Transform (FFT) of a predefined size of the IQ signals at a predetermined center frequency. Further, the RF receiver is configured to perform a circular shift of the FFT corresponding to at least one predetermined center frequency. Further, the RF receiver is configured to determine whether a Physical Cell Identifier (PCID) is identified. Further, the RF receiver is configured to detect the RSSI, the RSRP, and the ERFCN in response to determining that the PCID is identified. Further, the RF receiver is configured to select a LTE cell in accordance with the detected RSSI, RSRP, and ERFCN.
[0023] 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 obtaining IQ signals in digital domain at a predefined frequency. The computer executable program code when executed causing the actions including computing a FFT of a predefined size of the IQ signals at a predetermined center frequency. The computer executable program code when executed causing the actions including performing circular shift of FFT corresponding to at least one predetermined center frequency. The computer executable program code when executed causing the actions including determining whether the PCID is identified. The computer executable program code when executed causing the actions including detecting the RSSI, the RSRP, and the ERFCN in response to determining that the PCID is identified. The computer executable program code when executed causing the actions including. The computer executable program code when executed causing the actions including selecting a LTE cell in accordance with the detected RSSI, RSRP, and ERFCN.
[0024] 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
[0025] 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:
[0026] FIG. 1 shows a physical layer controller for controlling a Radio Frequency (RF) for tuning to different frequencies based on higher layers request, according to an embodiment as disclosed herein;
[0027] FIG. 2 illustrates a cell selection, cell camp-on and digital baseband tuning procedure, according to an embodiment as disclosed herein;
[0028] FIG. 3 depicts a relationship between centre carrier frequencies, subcarrier indices and raster frequencies, according to an embodiment as disclosed herein;
[0029] FIG. 4 is a graph illustrating raster frequencies aligning with specific frequencies based on a cyclic shift, according to an embodiment as disclosed herein;
[0030] FIG. 5 is a block diagram illustrating various units of a RF receiver for performing a cell search in the OFDM system, according to an embodiment as disclosed herein;
[0031] FIG. 6 is a flow diagram illustrating a method for performing a cell search in the OFDM system, according to an embodiment as disclosed herein; and
[0032] FIG. 7 illustrates a computing environment implementing the method for performing cell search in the OFDM system, according to an embodiment as disclosed herein.

DETAILED DESCRIPTION OF INVENTION
[0033] 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.
[0034] The embodiments herein provide a method for performing a cell search in an OFDM system by a RF receiver. The method includes obtaining IQ signals in a digital domain at a predefined frequency. Further, the method includes computing a FFT of a predefined size of the IQ signals at a predetermined center frequency. Further, the method includes performing a circular shift of the FFT corresponding to the at least one predetermined center frequency. Further, the method includes determining whether a PCID is identified. Further, the method includes detecting a Received Signal Strength Indicator (RSSI), a Reference Signal Received Power (RSRP), and a EUTRA Absolute radio-frequency channel number (ERFCN) in response to determining that the PCID is identified. Furthermore, the method includes selecting a LTE cell in accordance with the detected RSSI, the RSRP, and the ERFCN.
[0035] Unlike conventional systems and methods, the proposed method can be used to digitally tune the In-phase and Quadrature-phase (IQ) signals received from Analog to Digital Converter (ADC) for scanning multiple base stations in baseband at 100 KHz raster frequency as specified in a LTE standard.
[0036] The proposed method can be used to scan the bandwidth of EUTRA Bands of the LTE with the raster frequency 100 KHz (or any other) by the digital tuning (i.e., demodulating) of the IQ signals with 0 KHz, 5 KHz and 10KHz frequency shifts then taking the FFT of 0, 5, 10KHz frequency shifted IQ signals at the multiples of 15KHz subcarrier spacing. The method performs the cell search and downlink process in LTE for the EUTRA band.
[0037] The proposed method can be used to perform a raster scanning search for neighbourhood LTE base stations with granularity of 5 KHz which is a multiplication factor of subcarrier spacing 15 KHz as well as 100 KHz raster frequency. The large FFT (in an example, 6614 point FFT) is performed on OFDM symbols received from ADC such that the 100 KHz raster aligns with indices of 5 KHz subcarriers along the frequency axis. The desired spectrum around the 100 KHz frequency which is an integer multiple of 5 KHz spacing is used for cell search.
[0038] The proposed method allows a communication unit (not shown) to perform a message exchanges between the RF unit which encompasses the ADC, PHY controller (i.e., L1 controller), cell searcher and higher layers in the LTE system.
[0039] The proposed method can be used to perform the raster scanning of the RF by every 100 kHz with a digital baseband tuning procedure. The proposed method can be used to perform the Raster Scanning of RF by large FFT with the subcarrier spacing of 5 KHz.
[0040] Referring now to the drawings and more particularly to FIGS. 1 through 7, where similar reference characters denote corresponding features consistently throughout the figure, there are shown preferred embodiments.
[0041] FIG. 1 shows a physical layer controller for controlling a RF for tuning to different frequencies based on higher layers request, according to an embodiment as disclosed herein. FIG. 2 illustrates a cell selection, cell camp-on and digital baseband tuning procedure, according to an embodiment as disclosed herein.
[0042] Raster Scanning of the RF by every 100kHz with digital baseband tuning procedure:
[0043] In order to reduce the number of baseband and the RFE interactions and efficiently process the DL IQ signals and detect the presence of cells with respective PCID, MIB and SIB information in a given EUTRA LTE band, the physical layer controller allows the cell-search and cell selection procedure using a Digital Baseband Tuning (DBT). The Cell Search (CS) block design based on the concept of DBT will detect the PCID, MIB and SIB of each cell present within the EUTRA band selected with less number of baseband and RFE interactions as the raster scanning is digitally done within cell-search block in the baseband. The cell-search block is also called as an acquisition block as it acquires the cell information through a synchronization procedure.
[0044] Each frequency band is regulated to allow operation in only a certain set of channel bandwidths, as shown in Table 1. Some frequency bands do not allow operation in the narrow bandwidth modes below 5 MHz, while others do not allow operation in the wider bandwidths, generally 15 MHz or above. ‘—’ denotes that the channel bandwidth is not supported in the specific band; ‘NA’ indicates the channel bandwidth is too wide to be supported in the band.
EUTRA Band DL BW (MHz) Channel BW (MHz)
1.4 3 5 10 15 20
1 60 - - 12 6 4 3
2 60 42 20 12 6 4 3
3 75 53 25 15 7 5 3
4 45 32 15 9 4 3 2
5 25 17 8 5 2 - -
6 10 - - 2 1 NA NA
7 70 - - 2 1 4 3
8 35 25 11 7 3 - -
9 35 - - 7 3 2 1
10 60 - - 12 6 4 3
11 20 - - 4 2 1 1
12 17 12 6 3 1 - NA
13 10 - - 2 1 NA NA
14 10 - - 2 1 NA NA
17 12 - - 2 1 NA NA
18 15 - - 3 1 1 NA
19 15 - - 3 1 1 NA
20 30 - - 6 3 2 1
21 15 - - 3 1 1 NA
22 80 - - 16 8 6 4
23 20 14 6 4 2 - -
24 34 - - 6 3 - -
25 65 46 21 13 6 4 3
Table 1
[0045] Raster Scanning of RF by large FFT with the subcarrier spacing of 5KHz:
[0046] The FFT of IQ signal for each FFT window of size NFFT the FFT is taken 3 times the size of the NFFT. The subcarrier spacing results becomes Fsc/3 where if Fsc=15 KHz then the frequency spacing of subcarriers in the above result will become Fsc/3 (In an example: 5 KHz) where 100 KHz raster scanning is multiple of Fsc/3 =5KHz. The raster scanning of 100 KHz shift and cell search can be performed.
[0047] Digital Baseband Tuning (DBT) procedure:
[0048] As shown in the FIG.1, the L1 controller (i.e., Physical Layer Controller) controls the RF for tuning to different frequencies based on the higher layers request. The L1 controller may reside inside the baseband processor or inside the higher layers processor.
[0049] The L1 controller utilizes the following equation for calculating the new RF centre frequency to be sent to the RFE.
FDL = FDL_low + 0.1(NDL – NOffs-DL)
[0050] Further, the DBT procedure drastically reduces number of computations for each EUTRA band search where each band is split into multiple subbands and each subband is searched for the PCIDs. The reduced complexity of computations depends on the Fs sampling frequency. Higher the subband bandwidth (high sampling rate) lesser the computations for DBT search. In an example, consider 30.72MHz sampled aliasing free IQ signal received by the baseband. Then the 2048 FFT of OFDM symbols results into 1200 subcarriers corresponding to 20MHz LTE signal. As shown in the FIG. 2, the UE shifts the FFT spectrum center frequency by 100 KHz and searches for the cell. The shift in center frequency needs to be done only by an integer multiple m, of 100 kHz, i.e., ?f = m x 100, where ?f is in kHz.
[0051] Since the timing alignment with respect to start of OFDM symbol for taking FFT is not known, the method is used to determine the OFDM pattern of the LTE slot which is implemented through a Cyclic Prefix (CP) correlation based procedure. Further, if a valid eNodeB LTE signal is present then a pattern of CP based slot correlation (1 subframe =1ms=2slots) with 7 correlation peaks would be present. Upon detection of the presence of the 7 correlation peaks, the method can detect the start of the LTE OFDM symbol but with unknown OFDM symbol number in the slot and corresponding subframe number. The next procedure is detect the PSS correlation which will determine the start of the 5ms periodicity of LTE Frame.
[0052] Let X(f) denotes the FFT of time domain symbol, x(n), of length NFFT. In the LTE system, the spacing between two subcarriers, X(f) and X(f+1) is 15 kHz. In order to shift the center frequency of the signal, x(n) by ?f, the procedure multiplies the time domain signal by exp(-j2p ?f kn/15NFFT), as shown in the equation below. This is a well-known property of the Fourier transform.
X(f + ?f/15) = ?x(n)exp{(-j2pfn/NFFT) ( ?f/15)}, f = 0,…,NFFT – 1
[0053] As can be seen from the above equation, the shift in center frequency, can be achieved by performing FFT on x(n) and then circularly shifting X(f) when ?f is a multiple of 15, or when m = …-6, -3, 0, 3, 6, … However, since only every 3rd shift is an integer multiple of 15 kHz, Further, the procedure multiplies the time domain signal by the appropriate exponential term and then performs the FFT. Thus, the method performs 250 FFTs per 25MHz band in the worst case scenario when all possible 100 kHz frequencies were searched.
[0054] In the enhancement, the method recognizes that when ?f is a non-integer multiple of 15kHz, the decimal part of ?f /15 takes only one of two values, 0.3333… or 0.6666… Thus, the appropriate shift in the center frequency can be achieved by multiplying the time domain signal with exp(j2pn/3) or exp(j4pn/3) and then circularly shifting the resulting FFT output by the integer part of ?f /15. The enhancement is encapsulated by the following equations.
X(f) = ?x(n)exp(-j2pfn/NFFT), f = 0,…,NFFT – 1
X(f + ?f/15) = circshift(X(f), ?f/15), m = …,-6,-3,0,3,6,….
X(f’) = ?x(n)exp{(-j2pfn/NFFT) (2/3)}, f = 0,…,NFFT – 1
X(f + ?f/15) = circshift(X(f’), floor(?f/15)), m = …,-5,-2,1,4,….
X(f”) = ?x(n)exp{(-j2pfn/NFFT) (1/3)}, f = 0,…,NFFT – 1
X(f + ?f/15) = circshift(X(f”), floor(?f/15)), m = …,-4,-1,2,5,….
[0055] The above sets of equations are represented pictorially in table 2 below. It is obvious from the table 2 that X(f) aligns with the 100 kHz center frequency when m is a multiple of 3. Further hops can be achieved by circular shifts. Similarly, when m = … -5,-2,1,4,… x(n) should be multiplied by exp{(-j2pfn/NFFT) (2/3)} and then appropriately shifted circularly. Again, for m = …-4,-1,2,5,…, x(n) should be multiplied by exp{(-j2pfn/NFFT) (1/3)} and then circular shifted.
Fc0

Fc1

Fc2

CS RF
-600 -9000
-580 -8700
-560 -8400
-540 -8100
-520 -7800
-500 -7500
-480 -7200
-460 -6900
-440 -6600
-420 -6300
-400 -6000
-380 -5700
-360 -5400
-340 -5100
-320 -4800
-300 -4500
-280 -4200
-260 -3900
-240 -3600
-220 -3300
-200 -3000
-180 -2700
-160 -2400
-140 -2100
-120 -1800
-100 -1500
-80 -1200
-60 -900
-40 -600
-20 -300
0 0
20 300
40 600
60 900
80 1200
100 1500
120 1800
140 2100
160 2400
180 2700
200 3000
220 3300
240 3600
260 3900
280 4200
300 4500
320 4800
340 5100
360 5400
380 5700
400 6000
420 6300
440 6600
460 6900
480 7200
500 7500
520 7800
540 8100
560 8400
580 8700
600 9000
CS RF
-593 -8900
-573 -8600
-553 -8300
-533 -8000
-513 -7700
-493 -7400
-473 -7100
-453 -6800
-433 -6500
-413 -6200
-393 -5900
-373 -5600
-353 -5300
-333 -5000
-313 -4700
-293 -4400
-273 -4100
-253 -3800
-233 -3500
-213 -3200
-193 -2900
-173 -2600
-153 -2300
-133 -2000
-113 -1700
-93 -1400
-73 -1100
-53 -800
-33 -500
-13 -200
7 100
27 400
47 700
67 1000
87 1300
107 1600
127 1900
147 2200
167 2500
187 2800
207 3100
227 3400
247 3700
267 4000
287 4300
307 4600
327 4900
347 5200
367 5500
387 5800
407 6100
427 6400
447 6700
467 7000
487 7300
507 7600
527 7900
547 8200
567 8500
587 8800
CS RF
-587 -8800
-567 -8500
-547 -8200
-527 -7900
-507 -7600
-487 -7300
-467 -7000
-447 -6700
-427 -6400
-407 -6100
-387 -5800
-367 -5500
-347 -5200
-327 -4900
-307 -4600
-287 -4300
-267 -4000
-247 -3700
-227 -3400
-207 -3100
-187 -2800
-167 -2500
-147 -2200
-127 -1900
-107 -1600
-87 -1300
-67 -1000
-47 -700
-27 -400
-7 -100
13 200
33 500
53 800
73 1100
93 1400
113 1700
133 2000
153 2300
173 2600
193 2900
213 3200
233 3500
253 3800
273 4100
293 4400
313 4700
333 5000
353 5300
373 5600
393 5900
413 6200
433 6500
453 6800
473 7100
493 7400
513 7700
533 8000
553 8300
573 8600
593 8900

Table 2
EUTRA
Band DL RF tuning (MHz)
FDL_low –FDL_high
MHz BW
MHz NOffs-DL Range of NDL FC0 FC1 FC2 FC3 FC4
1 2110 - 2170 60 0 0 – 599 2110 2127.10 2144.20 2163.10 -
2 1930 - 1990 60 600 600-1199 1930 1947.10 1964.20 1983.10 -
3 1805 - 1880 75 1200 1200 – 1949 1805 1822.10 1839.20 1858.10 1875.2
4 2110 - 2155 45 1950 1950 – 2399 2110 2127.10 2144.20 - -
5 869 - 894 25 2400 2400 – 2649 869 886.100 903.200 - -
6 875 - 885 10 2650 2650 – 2749 875 892.100 - - -
7 2620 - 2690 70 2750 2750 – 3449 2620 2637.10 2654.20 2673.10 2690.2
8 925 - 960 35 3450 3450 – 3799 925 942.100 959.200 - -
9 1844.9 - 1879.9 35 3800 3800 – 4149 1844.90 1862 1879.10 - -
10 2110 - 2170 60 4150 4150 – 4749 2110 2127.10 2144.20 2163.10
11 1475.9 - 1495.9 20 4750 4750 – 4949 1475.90 1493 1510.10 1529
12 729 - 746 17 5010 5010 - 5179 729 746.100 - -
13 746- 756 10 5180 5180 – 5279 746 763.100 - -
14 758 - 768 10 5280 5280 – 5379 758 775.100 - -
17 734 - 746 12 5730 5730 – 5849 734 751.100 - -
18 860 - 875 15 5850 5850 – 5999 860 877.100 - -
19 875 - 890 15 6000 6000 – 6149 875 892.100 - -
20 791 - 821 30 6150 6150 – 6449 791 808.100 825.200 -
21 1495.9 - 1510.9 15 6450 6450 – 6599 1495.90 1513 - -
22 3510 - 3590 80 6600 6600 – 7399 3510 3527.10 3544.20 3563.10 3580.2
23 2180 - 2200 20 7500 7500 – 7699 2180 2197.10 - -
24 1525 - 1559 34 7700 7700 - 8039 1525 1542.10 1559.20 -
25 1930 - 1995 65 8040 8040 - 8689 1930 1947.10 1964.20 1983.10 2000.2
Table 3
[0056] Further, the table 3 indicates that relationship between the downlink signal and the RF tuning range in the EUTRA band.
[0057] Further, the procedure ensures that the UE needs to perform only 3 FFTs for each 20 MHz subband search. As expected, the results are identical to that of multiplying the time domain signal by exp(-j2p ?f kn/15NFFT).
[0058] FIG. 3 depicts a relationship between centre carrier frequencies, subcarrier indices and raster frequencies, according to an embodiment as disclosed herein.
[0059] FIG. 4 is a graph illustrating raster frequencies aligning with specific frequencies based on a cyclic shift, according to an embodiment as disclosed herein.
[0060] FIG. 5 is a block diagram illustrating various units of the RF receiver 500 for performing the cell search in the OFDM system, according to an embodiment as disclosed herein. In an embodiment, the RF receiver 500 includes an IQ signal obtaining unit 502, a computing unit 504, a PCID determining unit 506, a detecting unit 508, a cell selecting unit 510, a communication unit (not shown), and a storage unit (not shown). The communication unit and the storage unit are in communication with the IQ signal obtaining unit 502, the computing unit 504, the PCID determining unit 506, the detecting unit 508, and the cell selecting unit 510.
[0061] Further, the IQ signal obtaining unit 502 is configured to obtain the IQ signals in the digital domain at a predefined frequency (e.g., 100 KHz raster frequency or the like). In an embodiment, the IQ signals are obtained by digitally demodulating with the set of frequencies to obtain sequences of the IQ signals. The subcarrier frequencies in each IQ signal corresponds to the set of raster frequencies.
[0062] After obtaining the IQ signals in the digital domain at the predefined frequency, the computing unit 504 is configured to compute the FFT of a predefined size of the IQ signals at a predetermined center frequency (e.g., 100 KHz, 200 KHZ, 300 KHZ or the like). In an embodiment, the predetermined center frequency corresponds to the E-UTRA band.
[0063] Based on computing the FFT of the predefined size of the IQ signals at the predetermined center frequency, the computing unit 504 is configured to perform the circular shift of the FFT corresponding to the predetermined center frequency. In response to performing the circular shift of the FFT corresponding to the predetermined center frequency, the PCID determining unit 506 is configured to determine whether the PCID is identified. In an embodiment, the PCID is identified by performing PSS, SSS correlation.
[0064] If the PCID is identified, the detecting unit 508 is configured to detect the RSSI, the RSRP, and the ERFCN. Based on the detected RSSI, RSRP, ERFCN, the cell selecting unit 510 is configured to select the LTE cell.
[0065] Further, the computing unit 504 is configured to repeatedly perform the cyclic shifts of FFT by multiple predetermined center frequencies till a threshold is reached. Further, the PCID determining unit 506 is configured to detect the multiple PCIDs based on the cyclic shift of FFT. The cell selecting unit 510 is configured to shortlist the detected PCIDs for the RF carriers. Further, the cell selecting unit 510 is configured to select the LTE cell associated with highest RSRQ among plurality of RSRQs of identified cells corresponding to the multiple PCIDs.
[0066] 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).
[0067] Although the FIG. 5 shows exemplary units of the RF receiver 500 but it is to be understood that other embodiments are not limited thereon. In other embodiments, the RF receiver 500 may include less or more number of units. Further, the labels or names of the units are used only for illustrative purpose and does not limit the scope of the invention. One or more units can be combined together to perform same or substantially similar function to perform the cell search in the OFDM system.
[0068] FIG. 6 is a flow diagram 600 illustrating a method for performing the cell search in the OFDM system, according to an embodiment as disclosed herein. At step 602, the method includes obtaining the IQ signals in the digital domain at the predefined frequency. In an embodiment, the method allows the IQ signal obtaining unit 502 to obtain the IQ signals in the digital domain at the predefined frequency. At step 604, the method includes computing the FFT of the predefined size of the IQ signals at the predetermined center frequency. In an embodiment, the method allows the computing unit 504 to compute the FFT of the predefined size of the IQ signals at the predetermined center frequency.
[0069] At step 606, the method includes performing circular shift of the FFT corresponding to at least one predetermined center frequency. In an embodiment, the method allows the computing unit 504 to perform the circular shift of the FFT corresponding to at least one predetermined center frequency. At step 608, the method includes determining whether the PCID is identified. In an embodiment, the method allows the PCID determining unit 506 to determine whether the PCID is identified.
[0070] At step 610, the method includes detecting the RSSI, the RSRP, and the ERFCN in response to determining that the PCID is identified. In an embodiment, the method allows the detecting unit 508 to detect the RSSI, the RSRP, and the ERFCN in response to determining that the PCID is identified. At step 612, the method includes selecting the LTE cell in accordance with the detected RSSI, RSRP, and ERFCN. In an embodiment, the method allows the cell selecting unit 510 to select the LTE cell in accordance with the detected RSSI, RSRP, and ERFCN.
[0071] The proposed method can be used to perform the raster scanning of the RF by every 100 kHz with a digital baseband tuning procedure. The proposed method can be used to perform the Raster Scanning of RF by large FFT with the subcarrier spacing of 5 KHz.
[0072] The proposed method can be used to digitally tune the In-phase and Quadrature-phase (IQ) signals received from Analog to Digital Converter (ADC) for scanning multiple base stations in baseband at 100 KHz raster frequency as specified in the LTE standard.
[0073] The method can be used to digitally tune the IQ signals received from the ADC to raster frequencies along the EUTRA bands of 3GPP LTE Standards for detecting multiple base stations. The scanning of the RF spectrum with the raster frequency of 100 KHz is accomplished to meet the raster frequency search requirements of 3GPP LTE TS36.101 standard. The proposed method simplifies the tuning the RF for every 100 KHz raster step size for a wide spectrum, as high as 20MHz. The raster tuning is accomplished by computing the FFT of size NFFT, (in an example NFFT = 2048) of IQ signal at the desired centre frequency Fc of the selected EUTRA and circularly shifting the spectral components such that each circular shift corresponds to 100 KHz (or multiples of 100 KHz shift). The IQ signal obtained from the ADC (when the RF is tuned to Fc with bandwidth of 20MHz) is digitally demodulated with 0KHz, 5KHz and 10KHz to obtain 3 sequences of IQ signals where the subcarrier frequencies in each IQ sequence corresponds to a set of raster frequencies. The 3 sequences put together encompasses all the 100 KHz raster frequencies within the 20MHz bandwidth. The subcarrier frequencies around each raster frequency are processed for detecting the presence of LTE eNodeB (LTE base station).
[0074] In the proposed method, for a given EUTRA band, a complete band search will be carried out by tuning the RF to only few centre frequencies. In an example, consider that the EUTRA Band-1 has a bandwidth of 60MHz in downlink, so 4 FFTs of 20MHz bandwidth with NFFT=2048 corresponds to 80MHz which effectively covers 60MHz bandwidth scanning.
[0075] The proposed method can be used to detect the neighborhood LTE base stations with granularity of 5 KHz subcarrier spacing such that the 100 KHz raster frequency is multiplication factor of 5 KHz.
[0076] The proposed method can be used to perform the digitally baseband tuning of neighbouring cells in the OFDM system.
[0077] The various actions, acts, blocks, steps, or the like in the flow diagram 600 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some of the actions, acts, blocks, steps, or the like may be omitted, added, modified, skipped, or the like without departing from the scope of the invention.
[0078] FIG. 7 illustrates a computing environment 702 implementing the method for performing the cell search in the OFDM system, according to an embodiment as disclosed herein. As depicted in the figure, the computing environment 702 comprises at least one processing unit 708 that is equipped with a control unit 704, an Arithmetic Logic Unit (ALU) 706, a memory 710, a storage unit 712, a plurality of networking devices 716 and a plurality Input output (I/O) devices 714. The processing unit 708 is responsible for processing the instructions of the technique. The processing unit 708 receives commands from the control unit 704 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 706.
[0079] The overall computing environment 702 can be composed of multiple homogeneous or heterogeneous cores, multiple CPUs of different kinds, special media and other accelerators. The processing unit 708 is responsible for processing the instructions of the technique. Further, the plurality of processing units 704 may be located on a single chip or over multiple chips.
[0080] The technique comprising of instructions and codes required for the implementation are stored in either the memory unit 710 or the storage 712 or both. At the time of execution, the instructions may be fetched from the corresponding memory 710 or storage 712, and executed by the processing unit 708.
[0081] In case of any hardware implementations various networking devices 716 or external I/O devices 714 may be connected to the computing environment 702 to support the implementation through the networking unit and the I/O device unit.
[0082] 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 7 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.
[0083] 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.