CN106470172B - Fast Fourier transform gain adjusting circuit and method - Google Patents
Fast Fourier transform gain adjusting circuit and method Download PDFInfo
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- CN106470172B CN106470172B CN201510498323.2A CN201510498323A CN106470172B CN 106470172 B CN106470172 B CN 106470172B CN 201510498323 A CN201510498323 A CN 201510498323A CN 106470172 B CN106470172 B CN 106470172B
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Abstract
A fast Fourier transform gain adjustment circuit and method. The fast Fourier transform gain adjusting circuit obtains a plurality of pilot signals from the frequency domain signal, and counts the pilot energy parameter of the pilot signals to determine an ideal gain value according to the pilot energy parameter. The fast Fourier transform gain adjustment circuit determines whether to change the current gain value according to whether the ideal gain value is equal to the current gain value. When the current gain value is determined to be changed, the fast Fourier transform gain adjusting circuit adjusts the current gain value up or down according to the adjustment interval and the adjustment mode, and adjusts the frequency domain signal by using the adjusted and reduced current gain value to generate an output signal.
Description
Technical Field
The present invention relates to a Fast Fourier Transform (FFT) gain adjustment circuit and method, and more particularly, to a Fast Fourier Transform (FFT) gain adjustment circuit and method using a pilot signal.
Background
In recent years, communication signal transmitting and receiving devices have been widely deployed to provide communication services such as voice, video, packet data, messaging, broadcasting, and the like. Orthogonal Frequency Division Multiplexing (OFDM) systems have been increasingly emphasized because of their tolerance to multipath delay spread and frequency selective fading, efficient spectrum usage, and good interference rejection. OFDM systems are currently widely used in high-bit digital subscriber line (HDSL), Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), Wireless Local Area Network (WLAN), Wireless Metropolitan Area Network (WMAN), and other fields. One of the core techniques in OFDM systems is Fast Fourier Transform (FFT). The method greatly reduces the difficulty of parallel data modulation and demodulation, thereby greatly improving the use possibility of the OFDM system.
Fig. 1 is a block diagram of a receiving device of a conventional ofdm system. Referring to fig. 1, a receiving device 100 of the OFDM system includes an Analog to Digital converter (ADC) 110, a synchronization circuit 120, a fast fourier transform circuit 130, a fast fourier transform gain circuit 140, and a demodulation circuit 150. The analog-to-digital converter 110 of the reception apparatus 100 converts the OFDM analog signal into a digital signal and outputs the digital signal. The synchronization circuit 120 performs a synchronization action, such as preamble processing (preamble processing) of the digital signal. The fast fourier transform circuit 130 receives the time domain signal after the synchronization processing, and performs fast fourier transform on the time domain signal to obtain a frequency domain signal. The frequency domain signal outputted from the fft circuit 130 shows the phase and amplitude of each carrier (carrier) of the OFDM signal. The fast fourier transform gain circuit 140 uses the gain value to adjust the frequency domain signal to eliminate the effect of the previous stage circuit when the time domain signal is converted into the frequency domain signal. The demodulation circuit 150 demodulates the frequency domain signal adjusted by the fft gain circuit 140, for example, by QAM, to obtain the original signal sent by the transmitting device.
However, since each stage of circuit has different effects on the carrier signals with different frequencies and the signal transmission channel also has different effects on the carrier signals with different frequencies, how to determine the gain value for adjusting the frequency domain signal output by the fft circuit 130 is one of the important issues that those skilled in the art are interested in.
Disclosure of Invention
Accordingly, the present invention provides a fast fourier transform gain adjustment circuit and method, which can determine a gain value for adjusting a frequency domain signal according to energy statistics of a pilot signal, and further avoid the performance of an OFDM receiver from being affected by fast variation of the gain value.
The invention provides a fast Fourier transform gain adjusting circuit, which comprises a signal energy statistic module, a gain decision module, a gain judgment module and a gain change and signal adjusting module. The signal energy statistic module is configured to receive the frequency domain signal, obtain a plurality of pilot signals from the frequency domain signal, and count pilot energy parameters of the pilot signals. The gain determining module is coupled to the signal energy counting module and configured to receive the pilot energy parameter and determine an ideal gain value according to the pilot energy parameter. The gain determining module is coupled to the gain determining module and configured to receive the ideal gain value and determine whether to issue a gain change request according to whether the ideal gain value is equal to the current gain value. The gain change and signal adjustment module is coupled to the gain determination module. When the gain judging module sends a gain change request to the gain changing and signal adjusting module, the gain changing and signal adjusting module is configured to adjust the current gain value up or down according to the adjustment interval and the adjustment mode, and adjust the frequency domain signal by using the adjusted up or down current gain value to generate an output signal.
In an embodiment of the invention, when the gain determining module does not issue the gain change request, the gain change and signal adjustment module is configured to maintain the current gain value and adjust the frequency domain signal by using the current gain value to generate the output signal.
In an embodiment of the invention, when the adjustment mode is the first mode, the gain change and signal adjustment module is configured to determine whether a start of frame signal in the frequency domain signal is received, and adjust the current gain value up or down in response to receiving the start of frame signal.
In an embodiment of the invention, when the adjustment mode is the second mode, the gain change and signal adjustment module is configured to count a number of symbols (symbols) in the frequency domain signal, determine whether the number of symbols is equal to a predetermined value, and adjust the current gain value up or down in response to the number of symbols being equal to the predetermined value.
In an embodiment of the invention, the gain change and signal adjustment module is configured to determine whether the current gain value is equal to the ideal gain value. When the current gain value is not equal to the ideal gain value, the gain change and signal adjustment module is configured to continuously add or continuously subtract the adjustment distance from the current gain value until the current gain value is equal to the ideal gain value.
In an embodiment of the invention, the signal energy counting module is configured to calculate an energy value of each pilot signal, and count the number of pilot signals corresponding to each of the plurality of energy intervals according to the energy value of each pilot signal. The pilot energy parameter includes the number of pilot signals.
In an embodiment of the invention, the gain determining module records a threshold and is configured to determine the ideal gain value according to the comparison of the number of pilot signals with the threshold.
In an embodiment of the invention, the signal energy statistic module is coupled to the fast fourier transform circuit. The fast fourier transform circuit is configured to receive the time domain signal and perform a fast fourier transform on the time domain signal to generate a frequency domain signal.
From another perspective, the present invention provides a fast fourier transform gain adjustment method, comprising the following steps. A plurality of pilot signals are obtained from the frequency domain signal, and pilot energy parameters of the pilot signals are counted. The ideal gain value is determined according to the pilot energy parameter. Determining whether to change the current gain value according to whether the ideal gain value is equal to the current gain value. When the current gain value is determined to be changed, the current gain value is adjusted to be increased or decreased according to the adjustment interval and the adjustment mode, and the frequency domain signal is adjusted by the increased or decreased current gain value to generate an output signal.
Based on the above, by continuously counting the pilot energy parameter of the pilot signal, the present invention can determine an ideal gain value more suitable for the current signal transmission environment according to the pilot energy parameter varying with time, and adjust the frequency domain signal output by the fast fourier transform circuit by using the current gain value closer to the ideal gain value. Thus, the ideal gain value determined by counting the pilot signal energy can greatly improve the signal quality of the receiving device of the OFDM system. Moreover, the present invention can adjust the current gain value based on the statistical signal characteristics counted by the OFDM signal in a period of time, and can further avoid the influence of the too fast variation frequency of the current gain value on the performance of the OFDM receiver.
In order to make the aforementioned and other features and advantages of the invention more comprehensible, embodiments accompanied with figures are described in detail below.
Drawings
Fig. 1 is a block diagram of a receiving device of a conventional OFDM system.
Fig. 2A is a block diagram of a receiving device of an OFDM system according to an embodiment of the invention.
Fig. 2B is a block diagram of a fast fourier gain circuit according to an embodiment of the invention.
Fig. 3 is a flowchart illustrating a fast fourier transform gain adjustment method according to an embodiment of the invention.
Fig. 4A is a flowchart illustrating adjusting the current gain value and adjusting the frequency domain signal in the first mode according to an embodiment of the invention.
Fig. 4B is a flowchart illustrating adjusting the current gain value and adjusting the frequency domain signal in the second mode according to an embodiment of the invention.
Description of the reference numerals
100. 200: receiving apparatus
110. 210: analog-to-digital converter
120. 220, and (2) a step of: synchronous circuit
130: fast Fourier transform circuit
140: fast Fourier transform gain circuit
150. 250: demodulation circuit
230: FFT circuit
240: FFT gain circuit
241: signal energy statistics module
242: gain decision module
243: gain judging module
244: gain changing and signal adjusting module
245: temporary storage device
S1: OFDM signal
D1, D2: time domain signal
f 1: frequency domain signal
f 2: output signal
P1: pilot energy parameter
request _ 1: gain change request
Gi: ideal gain value
Gn: current gain value
st: adjusting the pitch
T1: preset value
S301 to S304, S401 to S406, S411 to S416: step (ii) of
Detailed Description
Fig. 2A is a block diagram of a receiving device of an OFDM system according to an embodiment of the invention. Referring to fig. 2A, a receiving device 200 is a signal receiving and processing device capable of demodulating a modulated signal modulated by OFDM technology. The receiving device 200 may be disposed in a portable electronic device or a digital television, for example, to provide a function of receiving an external signal according to various standards. For example, the receiving device 200 may support the european DVB-T (Digital video broadcasting-television) standard and be installed in a Digital television or a set top box, but the invention is not limited thereto.
The receiving apparatus 200 includes an analog-to-digital converter 210, a synchronization circuit 220, a Fast Fourier Transform (FFT) circuit 230, an FFT gain circuit 240, and a demodulation circuit 250. The adc 210 samples the OFDM signal S1 in analog form to generate a time domain signal D1 in digital form. The synchronization circuit 220 receives the time domain signal D1 and performs synchronization signal processing on the time domain signal D1 to generate a time domain signal D2. For example, the synchronization circuit 220 may detect a preamble or symbol (symbol) boundary in an OFDM frame to ensure that the FFT circuit 230 only performs fast fourier transform on the OFDM symbols with the cyclic prefix removed.
When the time domain signal D2 generated after the cyclic prefix portion is removed is transmitted to the FFT circuit 230, the FFT circuit 230 performs fast fourier transform on the time domain signal D2 to convert the time domain signal D2 back to the frequency domain signal f 1. The FFT circuit 230 may perform, for example, 2048-point, 4096-point, or 8192-point fast fourier transforms, which is not a limitation of the present invention. Thereafter, the FFT gain circuit 240 adjusts the frequency domain signal f1 with the current gain value to generate an output signal f2, and provides the output signal f2 to the demodulation circuit 250 for demodulation. It should be noted that the FFT gain circuit 240 of the present embodiment may adjust the current gain value according to the signal characteristics of the OFDM signal S1. In more detail, the FFT gain circuit 240 of the present embodiment determines a better ideal gain value by counting the energy of the pilot signal (pilot signal), and adjusts the current gain value to the ideal gain value.
The pilot signal described above may be required for a range of different purposes of the receiving apparatus 200, such as channel estimation, synchronization, coarse frequency offset estimation, and fine frequency offset estimation. Since the amplitude and phase of the pilot signal are known a priori, the channel impulse response can be estimated based on the received pilot signal. In addition, if the receiving device 200 has knowledge of the pilot signal pattern, the receiving device 200 will be able to extract the received pilot signal from the appropriate location or subcarrier in the OFDM frame. Therefore, the FFT gain circuit 240 of the present embodiment can extract the pilot signals in the OFDM frame and count the energy of the pilot signals, so as to determine the ideal gain value according to the pilot energy parameters of the pilot signals. Thus, the FFT gain circuit 240 gradually adjusts the current gain value to the ideal gain value at an appropriate time, and adjusts the frequency domain signal f1 output by the FFT circuit by using the adjusted current gain value. The FFT gain circuit 240 determines the timing point for adjusting the current gain value by detecting the start signal of the OFDM frame or counting the OFDM symbols, for example.
An embodiment of how the FFT gain circuit 240 determines the ideal gain value and gradually adjusts the current gain value at appropriate time is described in detail below. Fig. 2B is a block diagram of a fast fourier gain circuit according to an embodiment of the invention. The FFT gain circuit 240 includes a signal energy statistic module 241, a gain determination module 242, a gain determination module 243, a gain change and signal adjustment module 244, and a register 245.
The signal energy statistic module 241 is coupled to the FFT circuit 230 to receive the frequency-domain signal f1, obtain a plurality of pilot signals from the frequency-domain signal f1, and count the pilot energy parameters P1 of the pilot signals. The gain determining module 242 is coupled to the signal energy counting module 241 for receiving the pilot energy parameter P1 and determining the ideal gain Gi according to the pilot energy parameter P1. The gain determining module 243 is coupled to the gain determining module 242, and receives the ideal gain value Gi, and determines whether to issue the gain change request _1 according to whether the ideal gain value Gi is equal to the current gain value Gn. The gain change and signal adjustment module 244 is coupled to the gain determination module 243 and the register 245, and adjusts the frequency domain signal f1 according to the current gain value Gn. The register 245 stores an adjustment interval st for adjusting the current gain value Gn.
In the present embodiment, the current gain value Gn used by the gain change and signal adjustment module 244 is adjusted over time rather than being a fixed value. When the gain determining module 243 sends the gain change request _1 to the gain change and signal adjusting module 244, the gain change and signal adjusting module 244 increases or decreases the current gain value Gn according to the adjustment distance st and the adjustment mode, and adjusts the frequency domain signal f1 by using the increased or decreased current gain value Gn to generate the output signal f 2. In contrast, when the gain determining module 243 does not send the gain change request _1 to the gain change and signal adjusting module 244, the gain change and signal adjusting module 244 maintains the current gain value Gn and adjusts the frequency domain signal f1 by using the current gain value Gn to generate the output signal f 2.
It should be noted that the gain change and signal adjustment module 244 returns the adjusted up or adjusted down current gain value Gn to the gain determination module 243, so that the gain determination module 243 can continuously obtain the latest current gain value Gn. Furthermore, after receiving the pilot energy parameter P1, the gain determining module 242 may receive another pilot energy parameter P1 corresponding to the next statistical time point over time, and determine the ideal gain value Gi again according to the another pilot energy parameter P1. In this way, the gain determining module 242 may determine whether to issue the gain change request _1 according to whether the latest ideal gain value Gi is equal to the latest current gain value Gn, and the gain change and signal adjusting module 244 may adjust the current gain value Gn according to the updated ideal gain value Gi in response to receiving the gain change request _ 1.
Fig. 3 is a flowchart illustrating a fast fourier transform gain adjustment method according to an embodiment of the invention. The embodiment shown in fig. 3 is applicable to the FFT gain circuit 240 shown in fig. 2B, and the following description will be provided with various elements of the FFT gain circuit 240, but the invention is not limited thereto.
Referring to fig. 2B and fig. 3, in step S301, the signal energy statistic module 241 obtains a plurality of pilot signals from the frequency domain signal f1 and counts a pilot energy parameter P1 of the pilot signals. In the present embodiment, the pilot energy parameter P1 includes the number of pilot signals respectively corresponding to a plurality of energy intervals. In detail, the signal energy statistic module 241 can calculate the energy value of each pilot signal. In this embodiment, as shown in formula (1), the signal energy statistic module 241 calculates the sum of the square of the real component I and the square of the imaginary component Q of each pilot signal, and then calculates the root to obtain the energy value of each pilot signal.
However, the present invention is not limited to calculating the energy value of the pilot signal using equation (1). In another embodiment, the signal energy statistic module 241 can obtain the amplitude value of each pilot signal according to equation (2) as the energy value of each pilot signal.
After the signal energy statistic module 241 obtains the energy values of the pilot signals, the signal energy statistic module 241 may count the number of the pilot signals corresponding to a plurality of energy intervals according to the energy value of each pilot signal (i.e. the number of the pilot signals corresponding to the plurality of energy intervals in the pilot energy parameter P1). In other words, the signal energy statistic module 241 classifies the pilot signals into one of the energy intervals according to the energy value of each pilot signal, and the number of the pilot signals represents the number of the pilot signals classified into the energy intervals.
More specifically, the signal energy statistic module 241 may determine the FFT window length and obtain the number of pilot signals in a single FFT window by extracting the pilot signals in the single FFT window. For example: FFT window length L =32768 x 10 symbols, and the current FFT window includes 5600 pilot signals. Then, the signal energy statistic module 241 performs energy calculation on each pilot signal to obtain an energy value of each pilot signal.
Finally, the signal energy counting module 241 counts the number of pilot signals corresponding to each energy interval according to the energy value of each pilot signal. For example, in the example where the previous FFT window includes 5600 pilot signals, the signal energy statistics module 241 may count that the first energy interval includes 100 pilot signals (number of pilot signals N1=100), the second energy interval includes 1000 pilot signals (number of pilot signals N2=1000), the third energy interval includes 1500 pilot signals (number of pilot signals N3=1500), the fourth energy interval includes 2000 pilot signals (number of pilot signals N4=2000), and the fifth energy interval includes 1000 pilot signals (number of pilot signals N5= 1000). The first energy interval N1 corresponds to an interval with an energy value greater than 512. The second energy interval N2 is between energy values 256 and 512. The third energy interval N3 is between energy values 128 and 256. The fourth energy interval N4 is between energy values 64 and 128. The fifth energy interval N5 is between energy value 0 and energy value 64. It should be noted that the number and the distinction of the energy intervals are only exemplary, and are not intended to limit the present invention.
Returning to the process of fig. 3, after obtaining the number of pilot signals corresponding to each energy interval, in step S302, the gain determining module 242 determines the ideal gain value Gi according to the pilot energy parameter P1. Further, the gain determining module 242 records a threshold THR and determines the desired gain Gi by comparing the number of pilot signals in the pilot energy parameter P1 with the threshold. Further, the gain determining module 242 stores a threshold value THR and a plurality of ideal gain values. The desired gain values stored in the gain determining module 242 are, for example, 0.5, 0.8, 1, 1.5, or 2, which is not limited in the present invention. The gain determining module 242 may compare the number of pilot signals in the pilot energy parameter P1 with a threshold value, and select the most appropriate ideal gain value Gi according to the comparison result.
For example, table 1 illustrates examples of desired gain values and applicable conditions according to an embodiment of the present invention.
In the example of Table 1, by comparing the threshold THR and the pilot numbers N1-N4, the gain determination module 242 sequentially determines whether the pilot numbers N1-N4 in the pilot energy parameter P1 satisfy the first to fourth conditions. For example, assuming that the threshold THR is 300, when the gain determination module 242 determines that the number N2 of the pilot signals in the second energy interval is greater than 300 and the number N1 of the pilot signals in the first energy interval is less than 300, the gain determination module 242 determines that the ideal gain Gi is equal to 0.8.
In step S303, the gain determining module 243 determines whether to change the current gain value Gn according to whether the ideal gain value Gi is equal to the current gain value Gn. When the gain determining module 243 finds that the current gain value Gn is not equal to the ideal gain value Gi, the gain determining module 243 sends a gain change request _1 to the gain change and signal adjusting module 244.
In step S304, when the gain determining module 243 determines to change the current gain value, the gain changing and signal adjusting module 244 increases or decreases the current gain value Gn according to the adjustment distance st and the adjustment mode, and adjusts the frequency domain signal f1 by using the increased or decreased current gain value Gn to generate the output signal f 2. In detail, the gain change and signal adjustment module 244 may subtract the adjustment distance st from the current gain value Gn to obtain the current gain value Gn closer to the ideal gain value Gi, or the gain change and signal adjustment module 244 may add the adjustment distance st to the current gain value Gn to obtain the current gain value Gn closer to the ideal gain value Gi. Therefore, by adjusting the setting of the interval st, the invention can avoid the influence of the too large variation amplitude of the current gain-increasing value on the performance of the OFDM system.
After step S304, the FFT gain circuit 240 cyclically performs step S301 ~ S304 to select the most appropriate ideal gain value according to the currently received frequency domain signal and adjust the current gain value accordingly, in detail, as time increases, the FFT gain circuit 240 continuously counts the pilot energy parameters corresponding to different time points, so as to adaptively determine the most appropriate ideal gain value according to the current frequency domain signal, that is, the ideal gain value Gi may be continuously updated as time changes, in addition, the gain change and signal adjustment module 244 periodically or non-periodically adjusts the current gain value Gn. at the time point determined by the adjustment mode, that is, the current gain value Gn may be continuously adjusted to approach the ideal gain value Gi as time changes, and the ideal gain value Gi is selected according to the statistical characteristics of the current frequency domain signal.
It should be noted that the gain change and signal adjustment module 244 may adjust the current gain value Gn at different time points in different adjustment modes. The following examples are individually listed for detailed description.
Fig. 4A is a flowchart illustrating adjusting the current gain value and adjusting the frequency domain signal in the first mode according to an embodiment of the invention. Referring to fig. 4A, in step S401, the gain change and signal adjustment module 244 receives a gain change request. In step S402, when the adjustment mode is the first mode, the gain change and signal adjustment module 244 determines whether a frame start signal in the frequency domain signal is received, so as to adjust the current gain value up or down in response to receiving the frame start signal. That is, when the determination in step S402 is negative, it means that the gain change and signal adjustment module 244 has not detected the frame start signal in the OFDM frame, so that the gain change and signal adjustment module 244 does not change and maintains the current gain value in step S406, and adjusts the frequency domain signal f1 output by the FFT circuit 230 using the current gain value Gn in step S405.
On the other hand, when the determination in step S402 is yes, the gain change and signal adjustment module 244 detects a frame start signal in the OFDM frame. In response to detecting the start of frame signal, in step S403, the gain change and signal adjustment module 244 determines whether the current gain value Gn is equal to the ideal gain value Gi. Based on the determination of step S402, the gain change and signal adjustment module 244 checks whether the current gain value Gn needs to be adjusted at every other frame period. When the current gain value Gn is equal to the ideal gain value Gi (yes in step S403), continuing to step S406, the gain change and signal adjustment module 244 does not change and maintains the current gain value Gn, and adjusts the frequency domain signal f1 output by the FFT circuit 230 using the current gain value Gn adjusted to the ideal gain value Gi in step S405.
In addition, when the current gain value Gn is not equal to the ideal gain value Gi (no in step S403), in step S404, the gain change and signal adjustment module 244 adds or subtracts the adjustment distance st to the current gain value Gn. In step S405, the gain change and signal adjustment module 244 adjusts the frequency domain signal f1 output by the FFT circuit 230 by using the current gain value Gn after being adjusted up or down. For example, assuming that the ideal gain value Gi is 1.6, the current gain value Gn is 1.0, and the adjustment interval st is 0.2, the gain change and signal adjustment module 244 will adjust the current gain value Gn from 1.0 to 1.6 in steps after receiving the frame start signal three times without changing the ideal gain value Gi. However, the above assumptions are merely exemplary and are not intended to limit the present invention.
It should be noted that after step S404, the gain change and signal adjustment module 244 returns the adjusted up or adjusted down current gain value Gn to the gain determination module 243, so that the gain determination module 243 updates the current gain value Gn. Accordingly, after step S405, the process returns to step S401 again. That is, the gain change and signal adjustment module 244 will cyclically execute the overall process shown in fig. 4A to determine whether to adjust the current gain value according to the most suitable ideal gain value and the updated current gain value. For example, assume that the ideal gain value Gi is 1.6, the current gain value Gn is 1.0, and the adjustment pitch st is 0.2. If the ideal gain value Gi is updated to 0.8 during the period when the current gain value Gn is gradually increased from 1.0 to 1.6, the gain change and signal adjustment module 244 will not continuously increase the current gain value Gn any more but gradually decrease the current gain value Gn to 0.8 according to the updated ideal gain value Gi. However, the above assumptions are merely exemplary and are not intended to limit the present invention.
Fig. 4B is a flowchart illustrating adjusting the current gain value and adjusting the frequency domain signal in the second mode according to an embodiment of the invention. Referring to fig. 4B, in step S411, the gain change and signal adjustment module 244 receives a gain change request. In step S412, when the adjusting mode is the second mode, the gain change and signal adjusting module 244 counts the symbol number of the symbols in the frequency domain signal f1, and determines whether the symbol number is equal to the predetermined value T1, so as to adjust the current gain value Gn up or down in response to the symbol number being equal to the predetermined value T1. The gain change and signal adjustment module 244 reads the predetermined value T1 from the register 245. That is, when the determination in step S412 is negative, it means that the gain change and signal adjustment module 244 has not counted enough symbols, so that the gain change and signal adjustment module 244 does not change and maintain the current gain value Gn in step S416, and adjusts the frequency domain signal f1 output by the FFT circuit 230 using the current gain value Gn in step S415.
On the other hand, if the determination in step S412 is yes, the representative gain change and signal adjustment module 244 counts a sufficient number of symbols. In response to counting the sufficient number of symbols, in step S413, the gain change and signal adjustment module 244 determines whether the current gain value Gn is equal to the ideal gain value Gi. When the current gain value Gn is equal to the ideal gain value Gi (yes in step S413), continuing to step S416, the gain change and signal adjustment module 244 does not change and maintains the current gain value Gn, and adjusts the frequency domain signal f1 output by the FFT circuit 230 using the current gain value Gn adjusted to the ideal gain value Gi in step S407.
In addition, when the current gain value Gn is not equal to the ideal gain value Gi (no in step S413), in step S414, the gain change and signal adjustment module 244 adds or subtracts the adjustment distance st to the current gain value Gn. In step S415, the gain change and signal adjustment module 244 adjusts the frequency domain signal f1 output by the FFT circuit 230 by using the current gain value Gn after being adjusted up or down. It can be appreciated that, compared to triggering the adjustment of the current gain value by the start of frame signal, the method of triggering the adjustment of the current gain value by counting the number of symbols is more flexible, and the adjustment frequency can be accelerated without affecting the signal quality in a specific application environment.
Similar to fig. 4A, after step S415, the gain change and signal adjustment module 244 returns the adjusted up or adjusted down current gain value Gn to the gain determination module 243, so that the gain determination module 243 updates the current gain value Gn. Accordingly, after step S415, the process returns to step S411 again. That is, the gain change and signal adjustment module 244 will cyclically execute the overall process shown in fig. 4B to determine whether to adjust the current gain value according to the most suitable ideal gain value and the updated current gain value.
In summary, the present invention can select an ideal gain value more suitable for the current signal transmission environment by counting the energy values of the pilot signals, and gradually adjust the current gain value to the ideal gain value, so as to adjust the frequency domain signal output by the fast fourier transform circuit by using the current gain value closer to the ideal gain value. Therefore, the signal quality in the OFDM system can be improved, and the performance of a receiving device of the OFDM system can be improved. Furthermore, the present invention determines whether to adjust the current gain value by counting the energy value of the pilot signal in one OFDM frame or a plurality of symbols, so as to further avoid the performance of the OFDM receiving device being affected by the too fast variation frequency of the current gain value.
Although the present invention has been described with reference to the above embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention.
Claims (14)
1. A fast fourier transform gain adjustment circuit, comprising:
a signal energy statistic module configured to receive a frequency domain signal, obtain a plurality of pilot signals from the frequency domain signal, calculate an energy value of each of the plurality of pilot signals, and calculate a pilot energy parameter of each of the plurality of pilot signals according to the energy value of each of the plurality of pilot signals, wherein the pilot energy parameter includes a number of pilot signals corresponding to each of energy intervals;
a gain determining module, coupled to the signal energy counting module, configured to receive the pilot energy parameter and compare the number of pilot signals corresponding to each of the energy intervals with a threshold according to the pilot energy parameter to determine an ideal gain value, wherein the threshold represents a predetermined number of signals;
a gain determining module, coupled to the gain determining module, configured to receive the ideal gain value and determine whether to issue a gain change request according to whether the ideal gain value is equal to a current gain value; and
a gain change and signal adjustment module coupled to the gain determination module,
when the gain judging module sends the gain change request to the gain changing and signal adjusting module, the gain changing and signal adjusting module is configured to adjust the current gain value according to an adjustment interval and an adjustment mode, and adjust the frequency domain signal by using the adjusted current gain value to generate an output signal.
2. The fft gain adjustment circuit of claim 1, wherein when the gain determination module does not issue the gain change request to the gain change and signal adjustment module, the gain change and signal adjustment module is configured to maintain the current gain value and adjust the frequency domain signal with the current gain value to generate the output signal.
3. The fft gain adjustment circuit of claim 1, wherein when the adjustment mode is a first mode, the gain change and signal adjustment module is configured to determine whether a start of frame signal in the frequency domain signal is received and to increase or decrease the current gain value in response to receiving the start of frame signal.
4. The fft gain adjustment circuit of claim 1, wherein when the adjustment mode is a second mode, the gain change and signal adjustment module is configured to count the number of symbols of the symbol in the frequency domain signal, determine whether the number of symbols equals a predetermined value, and increase or decrease the current gain value in response to the number of symbols being equal to the predetermined value.
5. The fast Fourier transform gain adjustment circuit of claim 1, wherein the gain change and signal adjustment module is configured to pass the current gain value after being adjusted up or down back to the gain determination module,
the gain determination module is configured to receive another pilot energy parameter after receiving the pilot energy parameter, and update the ideal gain value according to the another pilot energy parameter, so that the gain determination module determines whether to issue the gain change request according to whether the updated ideal gain value is equal to the current gain value returned, and the gain change and signal adjustment module adjusts the current gain value up or down according to the updated ideal gain value in response to receiving the gain change request.
6. The fast fourier transform gain adjustment circuit of claim 1, wherein the gain change and signal adjustment module is configured to determine whether the current gain value is equal to the ideal gain value,
when the current gain value is not equal to the ideal gain value, the gain change and signal adjustment module is configured to add or subtract the adjustment interval from the current gain value.
7. The fast fourier transform gain adjustment circuit of claim 1, wherein the threshold is recorded in the gain determination module.
8. The fast Fourier transform gain adjustment circuit of claim 1, wherein the signal energy statistic module is coupled to a fast Fourier transform circuit,
the fast fourier transform circuit is configured to receive a time domain signal and perform fast fourier transform on the time domain signal to generate the frequency domain signal.
9. A fast fourier transform gain adjustment method, the method comprising:
obtaining a plurality of pilot signals from a frequency domain signal and calculating the energy value of each pilot signal;
calculating a pilot energy parameter of the pilot signals according to the energy value of each of the pilot signals, wherein the pilot energy parameter includes the number of pilot signals corresponding to each energy interval;
comparing the pilot signal quantity corresponding to each of the energy intervals with a threshold value according to the pilot energy parameter to determine an ideal gain value, wherein the threshold value represents a preset signal quantity;
determining whether to change the current gain value according to whether the ideal gain value is equal to a current gain value; and
when the current gain value is determined to be changed, the current gain value is adjusted up or down according to an adjustment interval and an adjustment mode, and the frequency domain signal is adjusted by the adjusted up or down current gain value to generate an output signal.
10. The fast fourier transform gain adjustment method of claim 9, further comprising:
when the current gain value is not changed, the current gain value is maintained, and the frequency domain signal is adjusted by using the current gain value to generate the output signal.
11. The fft gain adjustment method of claim 9, wherein the step of up-scaling or down-scaling the current gain value according to the adjustment interval and the adjustment mode and adjusting the frequency domain signal by the up-scaled or down-scaled current gain value to generate the output signal comprises:
when the adjustment mode is a first mode, it is determined whether a frame start signal in the frequency domain signal is received, and the current gain value is adjusted up or down in response to receiving the frame start signal.
12. The fft gain adjustment method of claim 9, wherein the step of up-scaling or down-scaling the current gain value according to the adjustment interval and the adjustment mode and adjusting the frequency domain signal by the up-scaled or down-scaled current gain value to generate the output signal comprises:
when the adjustment mode is a second mode, the number of symbols of symbol in the frequency domain signal is counted, and whether the number of symbols is equal to a predetermined value is determined, and the current gain value is increased or decreased in response to the number of symbols being equal to the predetermined value.
13. The fft gain adjustment method of claim 9, wherein the step of up-scaling or down-scaling the current gain value according to the adjustment interval and the adjustment mode and adjusting the frequency domain signal by the up-scaled or down-scaled current gain value to generate the output signal comprises:
judging whether the current gain value is equal to the ideal gain value; and
when the current gain value is not equal to the ideal gain value, the adjustment interval is added or subtracted from the current gain value.
14. The fast fourier transform gain adjustment method of claim 9, further comprising:
a time domain signal is received and fast Fourier transformed to generate the frequency domain signal.
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| US5854758A (en) * | 1995-08-28 | 1998-12-29 | Seiko Epson Corporation | Fast fourier transformation computing unit and a fast fourier transformation computation device |
| US7499508B2 (en) * | 2001-04-03 | 2009-03-03 | Agere Systems Inc. | Method and apparatus for adjusting the gain of an if amplifier in a communication system |
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| CN101826848B (en) * | 2010-04-15 | 2013-07-31 | 复旦大学 | Automatic gain control system in orthogonal frequency division multiplexing receiver and method |
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| US7499508B2 (en) * | 2001-04-03 | 2009-03-03 | Agere Systems Inc. | Method and apparatus for adjusting the gain of an if amplifier in a communication system |
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