DESC:FIELD OF INVENTION
The present invention relates to a wireless communication networks and more particularly relates to a method of performing frequency scan prior to cell search. The present application is based on, and claims priority from an Indian Application Number 201641006186 filed on 23rd February, 2016, the disclosure of which is hereby incorporated by reference herein.
BACKGROUND OF INVENTION
In general, a mobile station (MS) is capable of communicating with different wireless networks. Typically, the MS performs a search when powered ON for detecting at least one network operator from which it can obtain signals. Autonomous search procedures are initiated by the MS in an idle mode or a connected mode to search for better network operators. Cell search time is imperative in saving overall power consumption of the MS.
The MS performs a frequency scan across a frequency band in order to find the network operator from which it can obtain signals. The frequency scan includes attempting acquisition on each operating frequency of the wireless network operator. The MS camps on a cell in a wireless network after performing the frequency scan. Since, there may be many frequencies in a given frequency band, the frequency scan may be time consuming, for example, in the order of minutes for a crowded frequency band on which many network operators deployed. The long duration of frequency scan causes long delay in obtaining signals, which is highly undesirable and also increases camping time.
In existing systems, to reduce the camping time, a two stage frequency scan approach is used. First a coarse frequency scan is performed on one or more bands of interest. When the MS performs the coarse frequency scan on one or more bands, the MS obtains a spectral estimate. The spectral estimate thus obtained can be used to extract information, such as received signal strength indication (RSSI), transmission bandwidth, RAT, of the possible cells present in the bands. With the extracted information, the MS shortlists the bands of interest on which fine frequency scan can be performed. However, in the existing systems, in case of coarse frequency scanning, the MS performs the scan by tuning to each frequency at a time and collecting time domain samples for a minimum time interval. After scanning each frequency for the minimum time interval, the frequencies with RSSI above a specific threshold are shortlisted for performing fine frequency scanning. Although, the existing systems reduce the camping time of the MS, the MS still needs to perform frequency scan for a significant time interval in two different stages of frequency scanning (i.e., coarse frequency scanning and fine frequency scanning) as mentioned above.
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 is to provide a method of performing frequency scan prior to cell search by a mobile station (MS).
Another object of the embodiments herein is to provide a method for faster detection of base station(s) within a bandwidth detected by the MS.
Another object of the embodiments herein is to provide a method for detecting base station(s) by performing scan across intra-band or inter-band.
Another object of the embodiments herein is to provide a method by which the MS can reduce battery power consumption significantly by eliminating frequency scanning on entire bandwidth.
Another object of the embodiments herein is to provide a method for faster detection of base station(s) based on spectral energy detection using frequency domain transformation techniques.
SUMMARY
Accordingly the embodiments herein provide a method of performing frequency scan prior to cell search by a mobile station (MS). The method includes extracting in-phase and quadrature phase (IQ) samples in each orthogonal frequency division multiplexing (OFDM) symbol of a subframe. The method includes estimating a power spectral density (PSD) after transforming the IQ samples to a frequency domain. The method includes calculating an average of PSDs for a plurality of OFDM symbols. The method includes filtering the average of PSDs. Further, the method includes applying a transformation technique to transform the average of PSDs to obtain an analytic signal. Furthermore, the method includes detecting an operating frequency of a base station in response to determining a peak in the analytic signal.
In an embodiment, detecting the operating frequency of the base station includes finding a maximum peak and a minimum peak in the analytic signal and detecting the operating frequency of the base station in accordance to the maximum peak and the minimum peak.
The method includes scanning the detected operating frequency for detecting the base station. The method includes detecting availability of consecutive peaks to the determined peak. The method includes finding a consecutive maximum peak and a corresponding minimum peak in the analytic signal in response to detecting that consecutive peak is available. Further, the method includes detecting the operating frequency range of a neighboring base station based on the consecutive maximum peak and the corresponding minimum peak.
In an embodiment, the transformation technique is a Hilbert transform.
In an embodiment, the maximum and minimum peak is determined using a four-quadrant inverse tangent.
Accordingly the embodiments herein provide a computer program product comprising computer executable program code recorded on a computer readable non-transitory storage medium. The computer executable program code when executed causing the actions including extracting in-phase and quadrature phase (IQ) samples in each OFDM symbol of a subframe. The computer executable program code when executed causing the further actions including estimating a power spectral density (PSD) for each OFDM symbol after transforming the IQ samples to a frequency domain. The computer executable program code when executed causing the further actions including calculating an average of PSDs for a plurality of OFDM symbols. The computer executable program code when executed causing the further actions including filtering the average of PSDs. The computer executable program code when executed causing the further actions including applying a transformation technique to transform the average of PSDs to obtain an analytic signal. The computer executable program code when executed causing the further actions including detecting an operating frequency of a base station in response to determining a peak in the transformed analytic signal.
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 a wireless communication network in which a mobile station (MS) performs frequency scan prior to cell search, according to an embodiment as disclosed herein;
FIG. 2 illustrates a block diagram of receiver side of the MS, according to an embodiment as disclosed herein;
FIG. 3 shows various units in a receiver of the MS, according to an embodiment as disclosed herein;
FIG. 4a is a flow chart illustrating a method of performing frequency scan by the MS for detecting a base station, according to the embodiments as disclosed herein;
FIG. 4b is a flow chart illustrating a method of performing frequency scan by the MS for detecting a neighboring base station, according to the embodiments as disclosed herein;
FIG. 5 is a graph showing a power spectral density (PSD) of an orthogonal frequency division multiplexing (OFDM) symbol, according to the embodiments as disclosed herein;
FIG. 6 is a graph showing an average of PSDs for a plurality of OFDM symbols, according to an embodiment as disclosed herein;
FIG. 7 is a graph showing a four quadrant inverse tangent of an analytic signal, according to the embodiments as disclosed herein;
FIGS. 8a-8c are graphs for detecting base stations in an example simulation setup, according to an embodiment as disclosed herein; and
FIG. 9 illustrates a computing environment implementing the method of performing frequency scan prior to cell search by the MS, according to the 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.
The embodiments herein achieve a method of performing frequency scan prior to cell search by a mobile station (MS). The method includes extracting in-phase and quadrature phase (IQ) samples in each orthogonal frequency division multiplexing (OFDM) symbol of a subframe. The method includes estimating a power spectral density (PSD) after transforming the IQ samples to a frequency domain. The method includes calculating an average of PSDs for a plurality of OFDM symbols. The method includes filtering the average of PSDs. Further, the method includes applying a transformation technique to transform the average of PSDs to obtain an analytic signal. Furthermore, the method includes detecting an operating frequency of a base station in response to determining a peak in the analytic signal.
Unlike the conventional method, the proposed method allows the MS to perform the scanning in an efficient way by detecting the operating frequency of base station(s) by processing the IQ samples. The proposed method provides faster detection of base station(s) within a bandwidth, detected by the MS. With the proposed method, the MS performs scan only on the detected operating frequencies of the base stations rather than scanning the entire bandwidth. The proposed method reduces the camping time of the MS. Further, with the proposed method the MS can reduce battery power consumption significantly by eliminating frequency scanning on the entire bandwidth.
Referring now to the drawings and more particularly to FIGS. 1 through 9 where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments.
FIG. 1 illustrates a wireless communication network 100 in which a mobile station (MS) performs frequency scan prior to cell search, according to an embodiment as disclosed herein. As depicted in the FIG. 1, the wireless communication network 100 includes a mobile station (MS) 102, a base station 104a, a base station 104b and a base station 104c. The base stations 104a, 104b and 104c operate on frequencies f1, f2 and f3 respectively. The base station 104b and 140c are the neighboring base stations to the base station 104a.
In an embodiment, the MS 102 can be a mobile phone, a smart phone, user equipment (UE), a radio station, a tablet, or any other communication device.
The MS 102 performs the frequency scan to detect each of the base stations 104a, 104b and 104c. The MS 102 extracts time domain IQ samples received from the base stations 104a, 104b and 104c. The IQ samples are extracted in each OFDM symbol of the subframe. The time domain IQ samples are converted to frequency domain by applying Discrete Fourier Transform (DFT) or Fast Fourier Transform (FFT). After extracting the IQ samples in each OFDM symbol, the PSD is calculated for each OFDM symbol. Further, average of PSDs is calculated for the plurality of OFDM symbols. The calculated average of PSDs is smoothened by filtering.
In an embodiment, the transformation technique is applied to transform the average of PSDs to obtain the analytic signal. A maximum peak and a minimum peak detected in the analytic signal using a four-quadrant inverse tangent technique. The distance between the maximum peak and the minimum peak is computed for detecting operating frequency(s) of the base station(s). The MS 102 performs scanning on the detected operating frequency(s) for detecting the base station(s) in the wireless communication network 100.
The above described steps involved in performing the frequency scan are detailed in conjunction with figures in the later parts of the description.
FIG. 2 illustrates a block diagram of receiver side of the MS 102, according to an embodiment as disclosed herein. As depicted in the FIG. 2, the receiver side of the MS 102 includes an antenna, a radio frequency (RF) unit 202, an ADC 204, a low pass filter (LPF) 206, an automatic gain control (AGC) 208, and receiver 210. The RF unit 202 receives signals through the antenna. In an embodiment, the RF unit 202 is tuned to the bandwidth of 30.72 MHz to detect the LTE signals received from the base stations 102a, 102b and 102c respectively.
The ADC 204 converts analog IQ samples to digital IQ samples and sends the converted digital IQ samples to the LPF 206.
The LPF 206 removed unwanted frequencies in the bandwidth of 30.72MHz and sends the desired bandwidth to the receiver 210.
The AGC 206 updates the gains once for every four OFDM symbols and the gain value is initialized to a value corresponding to a weakest signal expected in a frequency being scanned by the MS. The AGC 208 decreases the gain value starting from the initial gain, i.e., if the estimated gain is less than the current gain being used, then the newly estimated gain will be used for future scans. This way of updating gain is used to increase the chances of detection of the weakest signal while causing minimum saturation.
The receiver 210 performs one or more actions for performing frequency scan prior to cell search. The receiver 210 includes various units communicating with each other for performing the frequency scan on a detected operating frequency of the base station(s). In an embodiment, the receiver 210 is an OFDM receiver.
The various units in the receiver 210 are described in conjunction with the FIG. 3.
FIG. 3 illustrates various units in a receiver 210 of the MS 102, according to an embodiment as disclosed herein. As depicted in the FIG. 2, the receiver 210 includes an IQ samples extraction unit 302, a PSD estimation unit 304, a filtering unit 306, a transformation unit 308, a peak detection unit 310, a frequency detection unit 312 and a frequency scanning unit 314.
The IQ samples extraction unit 302 extracts the IQ samples in each OFDM symbol of the subframe. The IQ samples are time domain samples. In an example, there exist 2048 IQ samples in each OFDM symbol of the subframe. The total number of OFDM symbols in the subframe is 15. The IQ samples extraction unit 302 extracts the IQ samples from each OFDM symbols among the 15 OFDM symbols present in the subframe. After extracting the IQ samples in each OFDM symbol, the IQ samples extraction unit 302 sends the extracted IQ samples to the PSD calculation unit 304.
The PSD estimation unit 304 calculates PSD for each OFDM symbol. The PSD calculation unit 302 transforms the time domain IQ samples to a frequency domain by applying discrete Fourier transform (DFT) or Fast Fourier Transform (FFT).
Consider x (n) denotes time domain IQ samples, where the time domain samples are indexed by n=0,1,2,… ,NFFT-1. The FFT of x(n) for mth OFDM symbol is represented as
X_k^m = ?_(n=0)^(NFFT-1)¦?x(n) e^(-i2pk n/NFFT) ?,k=0,1,2,… ,NFFT-1 (1)
The index ‘k’ denotes the frequency index while computing the FFT. The PSD of the above frequency domain OFDM symbol can be computed for X_k^m, k=0,1,2,… ,NFFT-1.
In case, when there are 15 OFDM symbols in the subframe, then the PSD estimation unit 304 estimates the PSD for each OFDM symbol present in the subframe. In an embodiment, the FFT is performed on a real valued discrete signal to obtain the analytic signal as represented below.
The FFT of length NFFT is performed (in the equation (1)) on (P_dB ) ¯ and store the output as (P_fdB ) ¯.
where (P_dB ) ¯= {?P_dB?_0,?P_dB?_1,…,?P_dB?_(NFFT-1) }
NFFT point one side discrete time analytic signal transform is performed. .
(P_Z ) ¯={¦(?P_dB?_l, l=0, NFFT/2 @2?P_dB?_l, l ?[1,NFFT/2-1] @0 , l ?[NFFT/2+1,NFFT-1] )¦(2)
An inverse FFT is performed for NFFT point on (P_Z ) ¯
Further, when the PSD for each OFDM symbol is calculated, then the PSD estimation unit 304 calculates the average of PSDs for the plurality of OFDM symbols present in the subframe. The average of PSDs for the plurality of OFDM symbols can be represented as
?P_dB?_l= 10*log_10?{1/N [?_(m=0)^(N-1)¦P_l^m ] },
l=0,1,2,… ,NFFT-1. (3)
The filtering unit 306 filters the average of PSDs to smoothen the obtained average of PSDs. In an example, a moving average filter is applied on the obtained average of PSDs to smoothen the average of PSDs. In an example, the length of the moving average filter is selected as 32.
The transformation unit 308 applies the transformation technique to transform the average of PSDs to obtain the analytic signal. In an embodiment, the H ¯ can be obtained by applying Hilbert transform as represented below.
H ¯=hilbert((P_dB ) ¯ ), (4)
where (P_dB ) ¯= {?P_dB?_0,?P_dB?_1,…,?P_dB?_(NFFT-1) }
In an example, the peak detection unit 310 detects the peak in the analytic signal using the four-quadrant inverse tangent technique.
In an embodiment, the peak detection unit 310 determines a maximum peak and a minimum peak in the transformed analytic signal.
The four-quadrant inverse tangent technique displays a step-up deviation if the base station signal is present. A sudden rise with a peak (the maximum peak) at the start of the bandwidth and a sudden fall (minimum peak) in the PSD at end of the bandwidth indicates the presence of the base station transmission within the bandwidth defined by the start and end boundaries.
Further, the peak detection unit 310 detects the availability of consecutive peaks to determine maximum peak and the minimum peak in the analytic signal. In case, when the consecutive peak is determined in the analytic signal, then the peak detection unit 310 detects a maximum peak and a minimum peak in the analytic signal.
The frequency detection unit 312 detects the operating frequency of the base station in accordance to the maximum peak and the minimum peak. The frequency detection unit 312 computes a distance between the maximum peak and the minimum peak to detect the operating frequency of the base station. The distance between the maximum peak and the minimum peak is computed in terms of frequency to determine the operating frequency of the base station.
If consecutive peaks are determined in the analytic signal, then the frequency detection unit 312 detects the operating frequency of a neighboring base station in accordance to the maximum peak and the minimum peak. The frequency detection unit 312 computes a distance between the maximum peak and the minimum peak to detect the operating frequency of the neighboring base station.
The frequency scanning unit 314 performs scanning on the detected operating frequency for detecting the base station. The frequency scanning unit 314 is centered around the detected operating frequency for detecting the base station. In an example, if the detected operating frequency is 9MHz (which is computed based on the distance between the maximum peak and the minimum peak in the transformed analytic signal), then the frequency scanning unit 314 is centered around 9MHz to detect the base station.
In another example, if the frequency detection unit 312 detects the neighboring base station on an operating frequency of 12MHz, then the frequency scanning unit 314 performs scan on the 12MHz frequency to detect the neighboring base station. The frequency scanning unit 314 is centered around 12MHz to detect the neighboring base station.
FIG. 4a is a flow chart 400a illustrating a method of performing frequency scan by the MS for detecting a base station, according to the embodiments as disclosed herein. At step 402a, the method includes extracting IQ samples in each OFDM symbol of the subframe. The method allows the IQ samples extraction unit 302 to extract the IQ samples in each OFDM symbol of the subframe. In an example, there exist 2048 IQ samples in each OFDM symbol of the subframe. The total number of OFDM symbols in the subframe is 15. The IQ samples extraction unit 302 extracts the IQ samples from each OFDM symbols among the 15 OFDM symbols present in the subframe.
At step 404a, the method includes estimating the PSD for each OFDM symbol after transforming the IQ samples to the frequency domain. The method allows the PSD estimation unit 304 to estimate the PSD for each OFDM symbol after transforming the IQ samples to the frequency domain. The PSD estimation unit 304 transforms the time domain IQ samples to a frequency domain by applying DFT or FFT. In case, when there are 15 OFDM symbols in the subframe, then the PSD estimation unit 304 estimates the PSD for each OFDM symbol present in the subframe
At step 406a, the method includes calculating an average of the PSDs for a plurality of OFDM symbols. The method allows the PSD estimation unit 304 to calculate the average of the PSDs for the plurality of OFDM symbols. When the PSD for each OFDM symbol is calculated, then the PSD estimation unit 304 calculates the average of PSDs for the plurality of OFDM symbols present in the subframe. The average of PSDs for the plurality of OFDM symbols can be calculated using the equation (2).
At step 408a, the method includes filtering the average of PSDs. The method allows the filtering unit 306 to filter the average of PSDs. In an example, a moving average filter is applied on the obtained average of PSDs to smoothen the average of PSDs.
At step 410a, the method includes applying the transformation technique to transform the average of PSDs to obtain the analytic signal. The method allows the transformation unit 308 to apply the transformation technique to transform the average of PSDs to obtain the analytic signal. The transformed analytic signal can be obtained by applying by applying Hilbert transform using the equation (4). Although the Hilbert transform is applied to transform the average of the PSDs to obtain the analytic signal, it should be understood to a person of ordinary skilled in the art that any other frequency domain transformation technique can be applied to transform the average of PSDs to obtain the analytic signal. At step 412a, the method includes finding a maximum peak and a minimum peak in the transformed analytic signal. The method allows the peak detection unit 310 to detect the maximum peak and the minimum peak in the transformed analytic signal. The peak detection unit 310 detects the peak in the transformed analytic signal using the four-quadrant inverse tangent technique. The four-quadrant inverse tangent technique, displays a step-up deviation if the base station signal is present. A sudden rise with a peak (the maximum peak) at the start of the bandwidth and a sudden fall (minimum peak) in the PSD at end of the bandwidth of the base station indicates the presence of the base station transmission within the bandwidth defined by the start and end boundaries. Although the proposed method utilizes the four-quadrant inverse tangent technique to detect the maximum peak and the minimum peak in the analytic signal, it should to be understood to a person of ordinary skilled in the art that any other techniques can be used to detect the maximum peak and the minimum peak in the analytic signal.
At step 414a, the method includes detecting the operating frequency of a base station in accordance to the maximum peak and the minimum peak. The method allows the frequency detection unit 312 to detect operating frequency of a base station in accordance to the maximum peak and the minimum peak. In an example, the frequency detection unit 312 computes a distance between the maximum peak and the minimum peak to detect the operating frequency of the base station. The distance between the maximum peak and the minimum peak is computed in terms of frequency to determine the operating frequency of the base station. The computation of distance between the maximum peak and the minimum peak for determining the operating frequency of the base station is provided for descriptive purpose, it should to be understood to a person of ordinary skilled in the art that any other measure can be used to determine the operating frequency of the base station based on the detected maximum peak and the minimum peak.
At step 416a, the method includes scanning the detected operating frequency for detecting the base station 104a. The method allows the frequency scanning unit 314 to scan the detected operating frequency for detecting the base station 104a. The frequency scanning unit 314 is centered around the detected operating frequency for detecting the base station 104a. In an example, if the detected operating frequency is 7MHz (which is computed based on the distance between the maximum peak and the minimum peak in the transformed analytic signal), then the frequency scanning unit 314 is centered around 7MHz to detect the base station 104a.
The various actions, acts, blocks, steps, or the like in the method 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
FIG. 4b is a flow chart 400b illustrating a method of performing frequency scan by the MS for detecting a neighboring base station, according to the embodiments as disclosed herein. The steps 402b-408b of the flow chart 400b is performed after performing the steps 402a-416a as described in the flow chart 400a in the FIG. 4a. At step 402b, the method includes detecting availability of consecutive peaks to a determined peak. The method allows the peak detection unit 310 to detect the availability of consecutive peaks to the determined peak. The four-quadrant inverse tangent displays a step-up deviation if the neighboring base station signal is present. A sudden rise with a peak (the maximum peak) at the start of the bandwidth edge and a sudden fall (minimum peak) in the PSD at end of the bandwidth indicates the presence of the neighboring base station transmission within the bandwidth defined by the maximum peak and the minimum peak.
At step 404b, the method includes finding a maximum peak and a minimum peak in the analytic signal. The method allows the peak detection unit 310 to detect the maximum peak and the minimum peak in the transformed analytic signal. In case, when the consecutive peak is determined in the analytic signal, then the peak detection unit 310 detects a maximum peak and a minimum peak in the analytic signal.
At step 406b, the method includes detecting the operating frequency of a neighboring base station in accordance to the maximum peak and the minimum peak. The method allows the frequency detection unit 312 to detect the operating frequency of a neighboring base station in accordance to the maximum peak and the minimum peak. If consecutive peaks are determined in the analytic signal, then the frequency detection unit 312 detects the operating frequency of the neighboring base station in accordance to the maximum peak and the minimum peak. The frequency detection unit 312 computes a distance between the maximum peak and the minimum peak to detect the operating frequency of the neighboring base station 104b or 104c.
At step 408b, the method includes scanning the detected operating frequency of the neighboring base station 104b or 104c. The method allows the frequency scanning unit 314 to scan the detected operating frequency of the neighboring base station 104b or 104c. The frequency scanning unit 314 is centered around the detected operating frequency for detecting the neighboring base station. In an example, if the detected operating frequency is 13MHz (which is computed based on the distance between the maximum peak and the minimum peak in the transformed analytic signal), then the frequency scanning unit 314 is centered around 13MHz to detect the neighboring base station 104b or 104c.
The various actions, acts, blocks, steps, or the like in the method 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.
FIG. 5 is a graph showing a PSD of an OFDM symbol, according to the embodiments as disclosed herein. The PSD of a single OFDM symbol which has rapid variations in the spectrum is shown in the FIG. 5.
FIG. 6 is a graph showing an average of PSDs for a plurality of OFDM symbols, according to an embodiment as disclosed herein. The average of the PSDs for the plurality of OFDM symbols (i.e., 15 OFDM symbols) which shows fewer variations is shown in the FIG. 6.
FIG. 7 is a graph showing a four quadrant inverse tangent of an analytic signal, according to the embodiments as disclosed herein. The four-quadrant inverse tangent displays a step-up deviation if the base station signal is present. A sudden rise with a peak at the start of the bandwidth and sudden fall in the PSD at end of the bandwidth of the radio base station indicates the presence of the base station transmission within the bandwidth defined by the start and end boundaries as shown in the FIG. 7. The start of the bandwidth of the base station is indicated by the maximum peak and end of the bandwidth of the base station is indicated by the minimum peak. The distance in terms of frequency units between the maximum peak and the minimum peak is shown by a line with an arrow in the FIG. 7.
FIGS. 8a-8c is graphs for detecting base stations in an example simulation setup, according to an embodiment as disclosed herein. The simulation is performed on extracted IQ samples. The simulation parameters for simulation setup are considered as sampling rate at 30.72MHz; NFFT Length as 2048; Filtering unit 306 length as 32 (i.e., a moving average filter length as 32).
The RF unit 202 is tuned to a bandwidth as wide as 30.72 MHz, where three base stations are detected through their corresponding maximum peak and the minimum peak over the span of 30MHz. The PSD of the IQ samples for a single OFDM symbol which has rapid variations is shown in the FIG.8a. The average of PSDs estimated for the plurality of the OFDM symbols is shown in the FIG. 8b. It should be noted that the graph shown in the FIG. 8b has less variations with respect to the graph shown in the FIG. 8a.
A first base station is detected based on a distance between a maximum peak 1 and a minimum peak 1. A second base station is detected based on a distance between a maximum peak 2 and a minimum peak 2. A third base station is detected based on a distance between a maximum peak 3 and a minimum peak 3 as shown in the FIG. 8c. The base stations are detected along with their transmitting bandwidths.
FIG. 9 illustrates a computing environment implementing the method of performing frequency scan prior to cell search by the MS, according to the embodiments as disclosed herein. As depicted the computing environment 900 comprises at least one processing unit 906 that is equipped with a control unit 902 and an Arithmetic Logic Unit (ALU) 904, a memory 908, a storage unit 910, plurality of networking devices 808 and a plurality Input output (I/O) devices 912. The processing unit 906 is responsible for processing the instructions of the algorithm. The processing unit 906 receives commands from the control unit 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 904.
The overall computing environment 900 can be composed of multiple homogeneous and/or heterogeneous cores, multiple CPUs of different kinds, special media and other accelerators. The processing unit 906 is responsible for processing the instructions of the algorithm. Further, the plurality of processing units 808 may be located on a single chip or over multiple chips.
The algorithm comprising of instructions and codes required for the implementation are stored in either the memory 908 or the storage 910 or both. At the time of execution, the instructions may be fetched from the corresponding memory 908 and/or storage 910, and executed by the processing unit 906.
In case of any hardware implementations various networking devices 914 or external I/O devices 912 may be connected to the computing environment 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 9 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.
,CLAIMS:STATEMENT OF CLAIMS
We claim:
1. A method of performing frequency scan prior to cell search by a mobile station, the method comprising:
extracting in-phase and quadrature phase (IQ) samples in each OFDM symbol of a subframe;
estimating a power spectral density (PSD) for each orthogonal frequency division multiplexing (OFDM) symbol after transforming the IQ samples to a frequency domain;
calculating an average of PSDs for a plurality of OFDM symbols;
filtering the average of PSDs;
applying a transformation technique to transform the average of PSDs to obtain an analytic signal; and
detecting an operating frequency of a base station in response to determining a peak in the analytic signal.
2. The method of claim 1, wherein detecting the operating frequency of the base station includes:
finding a maximum peak and a minimum peak in the analytic signal; and
detecting the operating frequency of the base station in accordance to the maximum peak and the minimum peak.
3. The method of claim 1, wherein the method further comprises scanning the detected operating frequency for detecting the base station.
4. The method of claim 2, wherein the method further comprises:
detecting availability of a consecutive peaks to the determined peak;
finding a maximum peak and a minimum peak in the analytic signal; and
detecting an operating frequency of a neighboring base station in accordance to the maximum peak and the minimum peak.
5. The method of claim 2, wherein the transformation technique is a Hilbert transform.
6. The method of claim 2, wherein the maximum and minimum peak is determined using a four-quadrant inverse tangent.
7. A computer program product comprising computer executable program code recorded on a computer readable non-transitory storage medium, the computer executable program code when executed causing the actions including:
extracting in-phase and quadrature phase (IQ) samples in each orthogonal frequency division multiplexing (OFDM) symbol of a subframe;
estimating a power spectral density (PSD) for each OFDM symbol after transforming the IQ samples to a frequency domain;
calculating an average of PSDs for a plurality of OFDM symbols;
filtering the average of PSDs;
applying a transformation technique to transform the average of PSDs to obtain an analytic signal; and

detecting an operating frequency of a base station in response to determining a peak in the transformed analytic signal.

Dated this 28th Day of November, 2016

Signatures: Arun Kishore Narasani
Patent Agent