HK1117955B - Method and system for estimating signal error in a communication system - Google Patents

Description

Method and system for estimating signal error in communication system

Technical Field

The present invention relates to wireless communications, and more particularly, to a method and system for estimating signal error in a communication system.

Background

The increased performance and communication capacity of third generation (3G) wireless systems has led to an increasing number of mobile user equipment being used for voice, data and multimedia communications. For example, Wideband Code Division Multiple Access (WCDMA) is a wireless communication specification that can enhance performance by conveying user traffic using complex modulated Radio Frequency (RF) signals and performing some key protocol functions for mobile user equipment and base station operations.

One such function is initial time-frequency synchronization during which the mobile user equipment and the base station establish a connection. If the mobile user equipment wants to communicate with the base station, it should first search for available cells and request a connection. In the process of searching the cell, the mobile user equipment searches the cell and the corresponding base station, and determines the downlink scrambling code and the common channel frame synchronization of the cell. The mobile user equipment determines the timing of the cell slot of a primary synchronization channel (P-SCH) code (PSC), commonly referred to as a physical Synchronization Channel (SCH), in order to synchronize with the target cell. The mobile user equipment typically uses a single matched filter to find the P-SCH code by determining the filter peaks of the received signal. To complete the synchronization process, in WCDMA, the user equipment may perform frame synchronization and scrambling code group identification operations. The mobile user equipment determines the secondary synchronization channel (S-SCH) code (SSC) of the PCS in the received signal and correlates it with all possible secondary synchronization code sequences. The frame synchronization is determined by the maximum correlation value. After time slot and frame synchronization is achieved, the mobile user equipment may perform any other required operations to complete the network connection.

In order to achieve time synchronization between the mobile user equipment and the base station when establishing a connection during power-up operation, the mobile user equipment needs to lock on to a reference frequency provided by the base station. In most cases, mobile user equipment uses a local voltage controlled oscillator, such as a crystal oscillator, which is used to generate carrier frequencies for the RF and analog portions of the device and a reference digital clock for the digital portion of the device. When a high quality crystal oscillator is used, the uncertainty or frequency deviation of the frequency of the crystal oscillator is very small, and through proper calibration operations, the crystal oscillator can generate an appropriate carrier frequency and/or digital clock signal for time synchronization during power-up operations. However, the cost of high quality crystal oscillators and the cost of calibration operations are very high. In this regard, a low quality crystal oscillator with greater frequency uncertainty can meet cost requirements. However, using a low quality crystal oscillator increases the time required to lock to the reference frequency provided by the base station. In some cases, the increased time can cause many synchronization problems.

The limitations and disadvantages of conventional and existing approaches will become apparent to one of skill in the art, through comparison of some aspects of the present system with those of the present system, after reading the following description and drawings.

Disclosure of Invention

A system and/or method for estimating signal error in a communication system, substantially as shown in at least one of the figures, as set forth more completely in the claims.

According to one aspect of the present invention, there is provided a method for estimating signal error in a communication system, comprising: determining a frequency error of a demodulated received RF signal using a plurality of correlators, wherein at least one of the plurality of correlators is provided with at least one other carrier frequency different from a carrier frequency of the demodulated received RF signal.

In the method of the present invention, the demodulated received RF signal includes a Primary Synchronization Channel (PSC) code of Wideband Code Division Multiple Access (WCDMA).

In the method of the present invention, the method further comprises rotating the carrier frequency of the demodulated received RF signal in I and Q coordinate systems to thereby generate the at least one other carrier frequency.

In the method of the present invention, the method further comprises generating correlation results for each of the plurality of correlators and comparing the correlation results to determine the frequency error of the demodulated received RF signal.

In the method of the present invention, the method further comprises adjusting the VCO frequency according to the frequency error.

In the method of the present invention, the method further comprises adjusting a rotation frequency of the rotator according to the frequency error.

In the method of the present invention, the method further comprises selecting one rotator from a plurality of rotators according to the frequency error.

In the method of the invention, the method further comprises storing correlation results from at least one of the plurality of correlators in a first portion of a memory, and storing correlation results from the remaining ones of the plurality of correlators in at least a portion of the remaining portion of the memory.

In the method of the invention, the method further comprises storing data instead of correlation results in said at least one part of the remainder of said memory when said correlation results from the remainder of said plurality of correlators are no longer needed.

In the method of the present invention, the plurality of correlators includes a PSYNC correlator.

According to one aspect of the present invention, there is provided a machine-readable storage having stored thereon a computer program comprising at least one code segment for estimating a signal error in a communication system, the at least one code segment being executable by a machine, controlling the machine to determine a frequency error of a demodulated received RF signal using a plurality of correlators, wherein at least one other carrier frequency different from a carrier frequency of the demodulated received RF signal is provided to at least one of the plurality of correlators.

In the machine-readable storage of the present invention, the demodulated received RF signal comprises a Primary Synchronization Channel (PSC) code of Wideband Code Division Multiple Access (WCDMA).

In the machine-readable memory of the present invention, the machine-readable memory further comprises a code for rotating a carrier frequency of the demodulated received RF signal in I and Q coordinate systems to thereby generate the at least one other carrier frequency.

In the machine-readable storage of the present invention, the machine-readable storage further comprises a code for generating a correlation result for each of the plurality of correlators and comparing the correlation results to determine the frequency error of the demodulated received RF signal.

In the machine-readable storage according to the present invention, the machine-readable storage further comprises a code for adjusting a VCO frequency according to the frequency error.

In the machine-readable storage according to the present invention, the machine-readable storage further comprises a code for adjusting a rotation frequency of the rotator according to the frequency error.

In the machine-readable storage according to the present invention, the machine-readable storage further comprises a code for selecting one rotator from a plurality of rotators according to the frequency error.

In the machine-readable storage according to the present invention, the machine-readable storage further comprises a code for storing correlation results from at least one of the plurality of correlators in a first portion of the storage, and storing correlation results from the remaining correlators in at least a portion of the remaining portion of the storage.

In the machine-readable memory of the present invention, the machine-readable memory further comprises a code for storing data instead of correlation results in the at least one portion of the rest of the memory when the correlation results from the rest of the plurality of correlators are no longer needed.

In the machine-readable memory of the present invention, the plurality of correlators includes a PSYNC correlator.

According to one aspect of the present invention there is provided a system for estimating signal error in a communication system, the system comprising circuitry for determining a frequency error of a demodulated received RF signal using a plurality of correlators, wherein at least one of the plurality of correlators is provided with at least one other carrier frequency different from the carrier frequency of the demodulated received RF signal.

In the system of the present invention, the demodulated received RF signal includes a Primary Synchronization Channel (PSC) code of Wideband Code Division Multiple Access (WCDMA).

In the system of the present invention, the system further comprises circuitry for rotating the carrier frequency of the demodulated received RF signal in an I and Q coordinate system to thereby generate the at least one other carrier frequency.

In the system of the present invention, the system further includes circuitry for generating correlation results for each of the plurality of correlators and comparing the correlation results to determine the frequency error of the demodulated received RF signal.

In the system of the present invention, the system further comprises a circuit for adjusting the VCO frequency in accordance with the frequency error.

In the system of the present invention, the system further comprises a circuit for adjusting a rotation frequency of the rotator according to the frequency error.

In the system of the present invention, the system further comprises a circuit for selecting one rotator from a plurality of rotators according to the frequency error.

In the system of the invention, the system further comprises circuitry for storing correlation results from at least one of the plurality of correlators in a first portion of a memory and storing correlation results from the remaining ones of the plurality of correlators in at least a portion of the remaining portion of the memory.

In the system of the invention, the system further comprises circuitry for storing data in the at least a portion of the remainder of the memory instead of correlation results when the correlation results from the remainder of the plurality of correlators are no longer needed.

In the system of the present invention, the plurality of correlators includes a PSYNC correlator.

Further features and advantages of the invention, as well as the architecture and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings.

Drawings

FIG. 1 is a schematic diagram of a communication system in which a WCDMA mobile device attempts to establish synchronization with a base station to estimate signal error in accordance with one embodiment of the present invention;

FIG. 2 is a schematic diagram of a system for estimating signal error in a communication system in accordance with one embodiment of the present invention;

FIG. 3 is a schematic diagram of an ACD/CMF module according to one embodiment of the present invention;

FIG. 4 is a schematic view of a spinner according to one embodiment of the present invention;

FIGS. 5a-5d illustrate the use of F according to one embodiment of the present invention_VCOEffect diagram of demodulating RF signal from base station, wherein F_VCOAs derived from the RF signal carrier frequency offset;

FIG. 6 is a diagram of a PSYNC correlator according to one embodiment of the invention;

fig. 7 is a flow chart of a P-SCH data processing procedure in accordance with one embodiment of the present invention.

Detailed Description

The invention will be further explained with reference to the following figures and examples:

certain embodiments of the present invention relate to a method and system for estimating an error signal (errorsignal) in a communication system. Exemplary aspects of the invention include determining a frequency error (frequency error) of a received RF signal using a plurality of correlators, wherein one or more of the correlators are provided with a carrier frequency of the received RF signal and the remaining correlators are provided with one or more other carrier frequencies. The carrier frequency provided to the remaining receive correlators is different from the carrier frequency of the received RF signal. The received RF signal may include a Primary Synchronization Channel (PSC) code for Wideband Code Division Multiple Access (WCDMA). The carrier frequency of the received RF signal may be rotated in the I and Q coordinate systems to generate the other carrier frequencies.

Correlation results may be generated for each of the plurality of correlators and the generated results compared to determine the frequency error of the received RF signal. The determined frequency error may be used to adjust the VCO frequency. Alternatively, the determined frequency error may be used to adjust the rotational frequency of the rotator, or to select a selected rotator from a plurality of rotators (each having a fixed rotational frequency). In accordance with one embodiment of the invention, correlation results from one or more correlators may be stored in a first portion of memory and correlation results from the remaining correlators may be stored in the remaining portion of memory.

Fig. 1 is a diagram of a communication system in which a WCDMA mobile device attempts to establish synchronization with a base station to estimate signal error in accordance with one embodiment of the present invention. As shown in fig. 1, a base station 100 with a carrier frequency Fc and a WCDMA mobile 101 are shown.

In operation, the mobile device 101 may attempt to establish synchronization with the base station 100 during an initial cell search procedure. The mobile device 101 may not know the carrier frequency of the base station 100. Thus, during initial synchronization, the mobile device 101 may select an initial frequency that is within a certain tolerance of the carrier frequency of the base station 100. The mobile device 101 can then use the initial frequency to down-demodulate the base station signal to a baseband frequency. The mobile device 101 can then determine the error between the initial frequency and the carrier frequency of the base station 100. This error can be used to adjust the initial frequency used by the mobile device 101 for subsequent operations.

Fig. 2 is a schematic diagram of a system for estimating signal error in a communication system in accordance with one embodiment of the present invention. As shown in fig. 2, there is shown an RF/analog part comprising an antenna 201, an RF module 204, a Voltage Controlled Oscillator (VCO)203 and a crystal oscillator 202. Also shown in fig. 2 is the baseband processor (BB) portion, which includes an analog-to-digital (a/D) converter/slice (chip) matched filter (ADC/CMF) block 205, rotators 206 and 207, PSYNC correlators 208, 209 and 210, an error estimator block 211, and a processor 212. Fig. 2 may be a portion of a WCDMA mobile device 101.

The antenna 201 may comprise suitable logic and/or circuitry to communicate with at least one base station 100. Communication with the base station 100 includes receiving data over a physical Synchronization Channel (SCH) specified by WCDMA requirements. In this regard, the WCDMA mobile device 101 can receive a Primary Synchronization Code (PSC) over a primary synchronization channel (P-SCH) and a Secondary Synchronization Code (SSC) over a secondary synchronization channel (S-SCH). The network sends a synchronization code to the WCDMA mobile 101 indicating the slot and frame timing. The P-SCH channel may be used to establish initial network synchronization with WCDMA enabled user equipment, such as WCDMA mobile 101.

The RF module 204 may comprise suitable logic, circuitry, and/or code that may enable demodulation of an RF signal received from the antenna 201 to a baseband signal that may be sent to the baseband processor 200 for further processing. The RF module 204 may use F generated by the VCO203_VCOTo demodulate the received RF signal. The VCO203 may comprise suitable logic, circuitry, and/or code that may enable generation of an output signal that may be used by the RF module 204 to demodulate RF signals received from the antenna 201. Frequency F of the signal_VCOWithin certain tolerances so that RF module 204 can operate properly. VCO203 may use crystal 202 to generate a signal having frequency F_VCOOf the signal of (1). The VCO203 needs to be adjusted by the processor 212 so that the RF module 204 can demodulate multiple carrier frequencies.

The ADC/CMF block 205 may comprise suitable logic, circuitry, and/or code that may enable digitizing the baseband signal generated by the demodulated RF signal/RF block 204 and may enable matched filtering of the digitized baseband signal. The ADC/CMF module digitizes the demodulated RF/baseband signal, outputting in-phase (I) and quadrature (Q) versions of the digitized signal (collectively (I/Q)), which are sent to rotator modules 206 and 207. The baseband processor 200 may comprise suitable logic, circuitry, and/or code that may enable further processing of the digitized baseband signal.

The rotator blocks 206 and 207 may comprise suitable logic, circuitry, and/or code that may enable rotation of signals received from the ADC/CMF 205. By rotating the I/Q data received from the ADC/CMF 200 in the I/Q domain, the rotators 206 and 207 can effectively shift the frequency spectrum of the signal received from the ADC/CMF 205. The amount of offset may be preprogrammed into the rotators 206 and 207 by the processor 212. For example, one of the rotators 206 and 207 may be preprogrammed to have its output frequency higher than the initial baseband frequency, and the other rotator may be preprogrammed to have its output frequency lower than the initial baseband frequency. The output of the rotators 206 and 207, still in I/Q format, will then be sent to the PSYNC correlators 208 and 210 for further processing.

The PSYNC correlators 208, 209, and 210 may comprise suitable logic, circuitry, and/or code that may enable processing of a primary synchronization code from a primary synchronization channel in order to synchronize WCDMA mobile devices and base stations in a cellular network. PSYNC correlators 208 and 210 may receive I/Q data from rotators 206 and 207, respectively.

PSYNC correlators 208,209, and 210 may generate search result values that search for a certain frequency grid point at 5120 time positions. PSYNC correlators 208, 209, and 210 may generate signal peaks P for received primary synchronization codes when residing at designated frequencies_MAXAnd noise floor (floor noise) mean value P_N. This process may be repeated for multiple carrier frequencies. The baseband processor 200 may use the signal peak value P_MAXAnd local noise mean value P_NTo detect the primary synchronization code and establish initial synchronization with the cellular network. In, for example, a frequency search operation, the WCDMA mobile 101 may use the PSYNC correlators 208, 209, and 210 to detect the frequency. In addition, PSYNC correlators 208, 209, and 210 may be used to test and determine the offset frequency of the crystal 202 connected to the VCO 203.

The error estimator 211 may comprise suitable logic, circuitry, and/or code that may enable determining F_VCOHow much the deviation from the ideal frequency for demodulating the RF signal received from the antenna 201 is. The error estimator 211 may estimate the error by evaluating the signals P from the correlators 208,209 and 210_MAXAnd P_NTo determine the correlation results for each of the correlators 208,209, and 210. Error estimator 211 may then determine F by interpolating the correlation results_VCOThe frequency error of (2). This estimated frequency error will then be used to adjust the parameters in the VCO203 so that the PSYNC correlator with the unrotated input 209 ends up with the most correlated PSYNC。

In operation, RF signals from the base station 100 are received via the antenna 201 and directed to the RF module 204. F generated based on VCO 204_VCOThe RF module 204 demodulates the received RF signal to a baseband signal. The demodulated signal may be frequency shifted above F by rotators 206 and 207_VCOAnd is less than F_VCO. Using F_VCOThe demodulated initial baseband signal and the rotated baseband signal are sent to respective PSYNC correlators 208,209, and 210. Error estimator 211 determines which of the PSYNC correlators 208, 209, and 210 is the most correlated and sends this information to processor 212. The processor 212 adjusts the VCO203 until the PSYNC correlator 209, which is directly connected to the ADC/CDF module 205, becomes the most correlated correlator, and the process ends. Once the synchronization process is complete, the PSYNC correlators 208 and 210 are no longer needed and these resources are available for other operations.

F_VCOIs directly related to the quality of the crystal 202 and the VCO 203. For example, if a voltage controlled temperature compensated crystal oscillator (VCTXO) is used, the frequency deviation will be relatively small. In contrast, if a non-temperature compensated VCO is used, the frequency deviation will be large. However, VCTXO is generally relatively expensive compared to a non-temperature compensated VCO. By copying the baseband signals above and below the center frequency of the original baseband signal and using multiple PSYNC correlators to detect the primary synchronization code, the problems associated with low quality oscillators can be eliminated and the cost of the system can be reduced.

FIG. 3 is a schematic diagram of an ACD/CMF module according to one embodiment of the invention. As shown in fig. 3, a data path 309 is shown corresponding to a portion of the WCDMA mobile device 101 for processing data received over the primary synchronization channel (P-SCH). In this regard, the data path 309 may correspond to a portion of a WCDMA mobile device 101 such as depicted in fig. 1. The data path 309 may include an antenna 310, an amplifier 302, an analog-to-digital (a/D) converter 303, a slice matched filter (CMF)305, a receiver (Rx) Automatic Gain Controller (AGC)304, a primary synchronization channel (P-SCH) despreader 306, and a matched filter 307.

The antenna 310 may comprise suitable logic and/or circuitry that may be adapted to receive P-SCH data and determine a primary synchronization power density Ec, an interference power density level loc on the antenna, a power density lor on the receive path antenna, and/or a total RF power or total received power spectral density lo, where lo + lor.

The amplifier 302 may comprise suitable logic, circuitry, and/or code that may enable increasing or decreasing the strength of a received signal based on a feedback signal provided by the Rx AGC 304. The A/D converter 303 may comprise suitable logic, circuitry, and/or code that may enable digitizing the output of the amplifier 302 to generate the signal RX_A2D. Signal RX_A2DMay include, for example, 8-bit in-phase (I) and quadrature (Q) signals.

CMF 305 may comprise suitable logic, circuitry, and/or code that may enable matched filtering of the output signal generated by a/D converter 303. The CMF 305 may be used to generate at least one signal that the RxAGC 304 uses to generate a feedback signal 311 to the amplifier 302. CMF 305 may generate signal RX_CMFWhich includes, for example, a 7-bit I/Q signal. The P-SCH despreader 306 may comprise suitable logic, circuitry, and/or code that may be adapted to provide RX_CMFThe signal is despread to generate RX for input to matched filter 307_DSA signal. RX_DSThe signal may comprise, for example, an 8-bit I/Q signal. The matched filter 307 may comprise suitable logic, circuitry, and/or code that may enable RX_DSThe signals are matched filtered and correlated to generate a correlation signal, which may comprise, for example, a 15-bit I/Q signal. The base station will repeat the P-SCH code in each slot. According to the WCDMA standard, one slot interval may include 2560 slices, each of which has a length of 1/3.84e6 seconds. In this regard, 5120 correlation values may be generated, i.e., 2 for each slicing time. Each correlation value generated is assumed to be a boundary of a slot. Thus, 5120 correlation values represent 5120 hypothetical slot boundaries, which can be located anywhere within 2560 chip periods.

FIG. 4 is a schematic view of a spinner according to one embodiment of the invention. As shown in fig. 4, a coefficient generator 400, an index synthesizer (index synthesizer)401, a sin/cos lookup table 402 and a multiplier 403 are shown.

The coefficient generator 400 may comprise suitable logic, circuitry, and/or code that may enable generation of the systems M and N in response to the rotation frequency selection 404. For example, the rotation frequency is selected to be 1(1) corresponding to a rotation frequency of 4 KHz. If this value is selected, the coefficient generator may select the appropriate M and N values so that the rotator may insert a 4KHz rotation into the signal. These values will then be output to the exponent synthesizer.

The index synthesizer 401 may comprise suitable logic, circuitry, and/or code that may be enabled to generate an index for a lookup table that may vary over time with a frequency corresponding to the coefficient M, N, Clk_RefAnd an Inc/Dec signal. For example, the value of the index may cycle through the values 0, 1, 2, 33, 34, 35 at a rate of change F_index＝M·Clk_refand/N, and then repeating. The value of the exponent may be used to select a value from a look-up table. The Inc/Dec signal may be used to change the direction of rotation by changing the exponential output direction from increasing to decreasing.

sin/cos lookup table 402 may comprise suitable logic, circuitry, and/or code that may be enabled to store several values in the lookup table and to compute sin and cos values for one of the several values based on the exponent. For example, the look-up table may store values 0.0, 2.5, 5.0,. 40.0, 42.5, 45.0. For example, if the index value is 3(3), sin/cos lookup table 402 will output cos (5 °) and sin (5 °).

The multiplier 403 may comprise suitable logic, circuitry, and/or code that may enable multiplication of sin and cos signal inputs by I/Q data inputs and output of the result of the multiplication. For example, multiplier 403 may multiply the cos and sin values output by sin/cos lookup table 402 with the I/Q data output by ADC/CMF module 300. The result of the multiplication is provided as an input to a PSYNC correlator connected to rotator 208 or 210.

FIGS. 5a-5d illustrate the use of F according to one embodiment of the present invention_VCOFor RF signals from base stationEffect diagram of line demodulation, wherein F_VCODerived from the RF signal carrier frequency offset. In operation, rotators 206 and 207 of FIG. 2 may receive I/Q data from ADC/CMF205 (shown in FIG. 2) that represents baseband signals demodulated by RF module 204 (shown in FIG. 2). When the RF signal received by the RF module 204 (shown in FIG. 2) is at a frequency F that does not match the carrier frequency of the RF signal_VCOUpon demodulation, the result will be a continuous clockwise rotation (as shown in fig. 5 d) or a continuous counter-clockwise rotation (as shown in fig. 5 b) in the I/Q domain of the baseband signal. Rotators 206 and 207 may compensate for this continuous rotation by applying a constant rotation in the opposite direction to the received I/Q data. Reducing the rotation of the I/Q data will facilitate detection by the PSYNC correlators 208 and 210.

Fig. 6 is a diagram of a PSYNC correlator, in accordance with one embodiment of the present invention. As shown in fig. 6, there is shown an envelope detector 601, an Infinite Impulse Response (IIR) filter 602, a buffer 605, a truncation (truncation) module 603, a reporting function 604, and an IIR noise floor module 606. The data path 600 may correspond to a portion of, for example, a WCDMA mobile device 101 (shown in fig. 1).

The envelope detector 601 may comprise suitable logic, circuitry, and/or code that may enable generation of signals when a measured envelope of in-phase and quadrature signals generated by the matched filter 307 (shown in fig. 3) at a rate of 2 times per slice time is detected. The output of the envelope detector 601 may be, for example, an 8-bit signal, which is sent to the IIR filter 602.

The IIR filter 602 may comprise suitable logic, circuitry, and/or code that may enable digital filtering of a signal received from the envelope detector 601. In this regard, the nth magnitude or envelope of the correlation output input to IIR filter 602 may be filtered using the (n-5120) th magnitude stored in buffer 605. The newly generated filtered output may then be stored in buffer 605, thus ensuring the most up-to-date results for each of 5120 hypotheses. This filtering process can be seen as filtering of 5120 signals. The result output by the IIR filter 602 will be sent in the form of a 12-bit word to, for example, a truncation module 603 and/or a buffer 605.

Buffer 605 may comprise suitable logic, circuitry, and/or code that may enable storage of filtered data and feedback of the stored filtered data to IIR filter 602. Buffer 605 may be implemented using Random Access Memory (RAM).

The truncation module 603 may comprise suitable logic, circuitry, and/or code that may enable truncation of the digital output of the IIR filter 602 into a predetermined number of bits. For example, truncation module 603 may cut 12-bit words into 8-bit words for processing by reporting function 604 and IIR noise floor module 606.

The reporting function 604 may comprise suitable logic, circuitry and/or code that may enable generation of signal peaks P for primary synchronization codes determined for multiple frequencies for operations performed via the data paths 309 and 600_MAX。

IIR noise floor module 606 may comprise suitable logic, circuitry and/or code that may enable generation of noise floor mean P for primary synchronization codes determined for multiple frequencies for operations performed via data paths 309 and 600_N。

In operation, PSYNC correlators 208, 209, and 210 may measure the noise power and peak power for all 5120 hypotheses and combine or filter the current measurement, e.g., hypothesis n, using, for example, a measurement n +5120, where n corresponds to the count (countalue) for each measurement. Peak value of signal P_MAXAnd the noise floor mean value P_NMay be used by error estimation block 211 (shown in fig. 2) in baseband processor 200 to determine which of the PSYNC correlators 208,209, and 210 of fig. 2 is the most correlated correlator, which may then be used to determine F from VCO203 (shown in fig. 2)_VCOFrequency deviation of (2). For example, the processor 212 (shown in FIG. 2) may generate a plurality of control signals to vary the frequency of the crystal oscillator based on the output of the error estimation module 211 to adjust the carrier frequency applied to the RF module 204 (shown in FIG. 2). For generation ofFor each carrier frequency, the ratio of the peak of the signal to the noise floor average may be determined. The corresponding digital control signal may then be used to generate an appropriate carrier frequency that may be used to establish synchronization with the network during power-up operations.

Once the synchronization process is complete, the resources of the PSYNC correlator are no longer needed and, at this point, they can be reallocated. For example, processor 212 may store other data in a portion of buffer 605 corresponding to an unused PSYNC correlator.

Fig. 7 is a flow chart of a P-SCH data processing procedure in accordance with one embodiment of the present invention. The flowchart as in fig. 7 includes a start step 700. In step 701, an RF signal is received and based on an initial VCO frequency F_{VCO_0}The signal is demodulated. The demodulated signal is sent to the ADC/CMF205 (shown in FIG. 2) at step 702, where it is digitized and filtered. At step 703, the output of the ADC/CMF205 (shown in FIG. 2) is split into multiple paths. The first path is connected to a first PSYNC correlator 209 (shown in fig. 2). The second path is connected to a first rotator 206 (shown in fig. 2) which is connected to a second PSYNC correlator 208 (shown in fig. 2). The third path is connected to a second rotator 207 (shown in fig. 2) which is connected to a third PSYNC correlator 209 (shown in fig. 2). In step 703, the error estimator 211 (shown in FIG. 2) determines which of the PSYNC correlators is most correlated.

In step 704, the first PSYNC correlator 209 and the second PSYNC correlator 208 are compared. If the first PSYNC correlator 209 is more correlated than the second PSYNC correlator 208, then in step 705, the first PSYNC correlator 209 and the third PSYNC correlator 210 are compared. If the first PSYNC correlator 209 is more correlated than the third PSYNC correlator 210 in step 705, then no adjustment of the VCO is required because F_VCOJust the appropriate frequency. On the other hand, in step 705, if the first PSYNC correlator 209 is not correlated as well as the third PSYNC correlator 210, F_VCOToo high, the VCO203 needs to be adjusted in step 707 to reduce F_VCOThen heavyGo back to step 701.

Referring again to step 704, if the first PSYNC correlator 209 is not correlated as well as the second PSYNC correlator 208, then the second PSYNC correlator 208 will be compared to the third PSYNC correlator 210 in step 706. If the third PSYNC correlator 210 is more correlated than the second PSYNC correlator 208, F_VCOToo high, the VCO203 needs to be adjusted in step 707 to reduce F_VCOAnd then returns to step 701 again. F if the third PSYNC correlator 210 is less correlated than the second PSYNC correlator 208_VCOToo low, requiring VCO203 to be adjusted in step 707 by increasing F_VCOAnd then returns to step 701 again. The above process is repeated until the first PSYNC correlator 209 becomes the most correlated correlator.

The present invention is characterized by performing channel acquisition for the user equipment 101 (as shown in fig. 1) when there is a large frequency uncertainty in the WCDMA signal, thereby enabling efficient time-frequency search and being used for quantization, i.e., estimation of unknown frequency margin. Therefore, the method can better divide the unknown frequency range into the search grids. This approach may use an RF oscillator 203 (as shown in fig. 2) in WCDMA applications, which has a larger tolerance and therefore lower cost. The method described herein is not limited to WCDMA applications only, but may also be applied in communication systems where the above mentioned problems exist. The approach described herein provides a cost-effective solution to enable the use of a low quality crystal oscillator 202 (shown in fig. 2) in a WCDMA mobile user equipment to support the synchronization operations necessary in establishing and maintaining a connection with the network.

The present invention can be realized in hardware, software, or a combination of hardware and software. The present invention can be realized in a centralized fashion in at least one computer system, or in a distributed fashion where different elements are spread across several interconnected computer systems. Any kind of computer system or other apparatus adapted for carrying out the methods described herein is suited. A typical combination of hardware and software could be a general purpose computer system with a computer program that, when being loaded and executed, controls the computer system such that it carries out the methods described herein. The method is implemented in a computer system using a processor and a memory unit.

The present invention can also be implemented by a computer program product, which comprises all the features enabling the implementation of the methods of the invention and which, when loaded in a computer system, is able to carry out these methods. The computer program in this document refers to: any expression, in any programming language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following: a) conversion to other languages, codes or symbols; b) reproduced in a different format.

While the invention has been described with reference to several embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims (7)

1. A method for estimating signal error in a communication system, characterized by using a plurality of correlators for determining a frequency error of a demodulated received RF signal, wherein at least one of said plurality of correlators is provided with at least one other carrier frequency different from a carrier frequency of said demodulated received RF signal;

the method also includes generating correlation results for each of the plurality of correlators and comparing the correlation results to determine the frequency error of the demodulated received RF signal.

2. The method of claim 1, wherein the demodulated received RF signal comprises a primary synchronization channel code of wideband code division multiple access.

3. The method of claim 1, further comprising rotating a carrier frequency of the demodulated received RF signal in an I and Q coordinate system to thereby generate the at least one other carrier frequency.

4. The method of claim 1, further comprising adjusting a VCO frequency based on the frequency error.

5. A system for estimating signal error in a communication system, the system comprising circuitry for determining a frequency error of a demodulated received RF signal using a plurality of correlators, wherein at least one of the plurality of correlators is provided with at least one other carrier frequency different from a carrier frequency of the demodulated received RF signal; a plurality of correlators output correlation results according to the input carrier frequency;

the system further includes an error estimation module for determining which of the plurality of correlators is most correlated based on the correlation results, and then determining the frequency offset from the most correlated correlator.

6. The system of claim 5, wherein the demodulated received RF signal comprises a primary synchronization channel code of wideband code division multiple access.

7. The system of claim 5, further comprising circuitry for rotating a carrier frequency of the demodulated received RF signal in an I and Q coordinate system to generate the at least one other carrier frequency.