64 results about "Clipping noise" patented technology

The method contains the following steps. First, in a MCM system with N sub-carriers, the baseband signal blocks Xj, j=1, 2, . . . ,B are supplemented with zeros and processed with LN-point IFFT, respectively, to obtain L-time oversampled time-domain signal blocks xj, j=1,2, . . . ,B. Then, xj undergoes Q Time Domain Circular Shifts or Frequency Domain Circular Shifts to obtain Q signal blocks {tilde over (x)}j(i<sub2>j< / sub2>), ij=1,Λ,Q. Subsequently, a B×B unitary transform is performed against ( x1,{tilde over (x)}2(i<sub2>2< / sub2>), . . . ,{tilde over (x)}B(i<sub2>B< / sub2>)). After the unitary transform, for each (i2, . . . ,iB) a combination having B time-domain signal blocks is obtained as follows: ({tilde over (y)}1(i<sub2>2< / sub2>, . . . ,i<sub2>B< / sub2>),{tilde over (y)}2(i<sub2>2< / sub2>, . . . ,i<sub2>B< / sub2>), . . . ,{tilde over (y)}B(i<sub2>2< / sub2>, . . . ,i<sub2>B< / sub2>)=( x1,{tilde over (x)}2(i<sub2>2< / sub2>), . . . ,{tilde over (x)}B(i<sub2>B< / sub2>)) cU where U is the B×B unitary matrix, and c is an arbitrary constant (c≠0). Finally, the total QB-1 combinations are compared against each other to select a best candidate for transmission that could produce the lowest peak value, or the smallest PAPR, or the lowest clipping noise power.

Methods and apparatus are provided for reducing clipping noise from an OFDM signal, the methods and apparatus are operable to carry out actions including: (a) transforming a received orthogonal frequency division multiplexed (OFDM) signal from a transmission channel into the frequency domain, the OFDM signal having been subject to a clipping function prior to transmission in order to reduce the peak-to-average power ratio (PAPR); (b) recovering data symbols from the transformed OFDM signal, which include clipping noise; (c) estimating the clipping noise in the frequency domain based on the data symbols; and (d) subtracting the estimated clipping noise from the transformed OFDM signal.

An apparatus for correcting clipping distortion of a receiver system includes: an equalizer which generates a first equalization signal by equalizing a frequency domain clipping signal via a first equalization coefficient correcting a channel distortion, and generates a second equalization signal by equalizing the frequency domain clipping signal via a second equalization coefficient correcting the clipping distortion and the channel distortion; and a signal reconstruction unit which receives the first equalization signal and the second equalization signal from the equalizer, determines a transmission symbol by performing a hard decision with respect to the second equalization, and reconstructs a signal by using an amplitude of the transmission symbol and a phase of the first equalization signal when a level of the amplitude of the transmission symbol is greater than or equal to a reference value.

The invention discloses an ADO-OFDM (asymmetrical-clipping and DC bias orthogonal frequency division multiplexing) visible light communication system based on an improved algorithm. The system comprises a transmitter end and a receiver end. An ACO-OFDM signal of the transmitter end is transmitted on odd subcarriers, while a DCO-OFDM signal is transmitted on even subcarriers; after IFFT (inverse fast Fourier transform), asymmetrically clipping is carried out on the odd subcarriers, while the signal on the even subcarriers is subjected to DC bias to generate a single-polarity signal; and then, the odd subcarriers and the even subcarriers are merged to form an ADO-OFDM signal. By increasing the power of the ACO-OFDM input signal in data mapping, error rate of the system is reduced, and reliability can be improved. At the receiver end, the ACO-OFDM signal is subjected to estimation and optimization based on the newly-recovered DCO-OFDM signal, and furthermore, influence of the clipping noise on the DCO-OFDM signal is eliminated through the optimized and regenerated ACO-OFDM signal, thereby improving the received signal and improving system reliability.

The invention discloses a method for suppressing a signal peak-to-average ratio based on an active constellation extension ACE algorithm in an OFDM system for mainly solving the problem that the signal peak-to-average ratio in an orthogonal frequency division multiplexing OFDM system in the prior art is too high. The specific steps comprise: (1) modulating a bit stream; (2) transforming a transmission mode; (3) performing upsampling on a parallel signal; (4) clipping a frequency domain signal to obtain clipping noise; (5) defining a scalable range of a constellation point (6) performing activeconstellation extension ACE on the frequency domain signal; (7) correcting the preliminarily extended frequency domain signal; and (8) sending a frequency domain transmission signal. The method disclosed by the invention has the advantages of being suitable for the OFDM system of a high-order orthogonal amplitude modulation and having low implementation complexity, and the power utilization rateof a communication system transmitter is improved.

There is disclosed a technique in which any peaks above a threshold level are reduced, but not clipped, such that the effects of such peaks is reduced. Although the implementation of the technique preferably includes a clipping step, it is performed on the front-end rather than as the last step in the technique, such that the output signal is not a clipped signal. Any noise introduced by the clipping step, so-called clipping noise, is preferably filtered out of the useful frequency band of the signal.

The method contains the following steps. First, in a MCM system with N sub-carriers, the baseband signal blocks Xj, j=1, 2, . . . ,B are supplemented with zeros and processed with LN-point IFFT, respectively, to obtain L-time oversampled time-domain signal blocks xj, j=1,2, . . . ,B. Then, xj undergoes Q Time Domain Circular Shifts or Frequency Domain Circular Shifts to obtain Q signal blocks {tilde over (x)}j(i<sub2>j< / sub2>), ij=1, Λ, Q. Subsequently, a B×B unitary transform is performed against ( x1, {tilde over (x)}2(i<sub2>2< / sub2>), . . . , {tilde over (x)}B(i<sub2>B< / sub2>)). After the unitary transform, for each (i2, . . . , iB) a combination having B time-domain signal blocks is obtained as follows: ({tilde over (y)}1(i<sub2>2< / sub2>, . . . , i<sub2>B< / sub2>), {tilde over (y)}2(i<sub2>2< / sub2>, . . . , i<sub2>B< / sub2>), . . . , {tilde over (y)}B(i<sub2>2< / sub2>, . . . ,i<sub2>B< / sub2>))=( x1, {tilde over (x)}2(i<sub2>2< / sub2>), . . . , {tilde over (x)}B(i<sub2>B< / sub2>)) cU where U is the B×B unitary matrix, and c is an arbitrary constant (c≠0). Finally, the total QB−1 combinations are compared against each other to select a best candidate for transmission that could produce the lowest peak value, or the smallest PAPR, or the lowest clipping noise power.

The invention provides a clipping noise estimation and elimination method based on compressive sensing and a device thereof. The method comprises the steps that coarse estimation is performed on the position of clipping noise according to time domain signal frames so that prior information of the position of clipping noise is obtained; discrete Fourier transform is performed on the time domain signal frames and a frequency domain observation sequence is obtained, a frequency domain estimation sequence and a noise estimation sequence are obtained according to the frequency domain observation sequence, a selection matrix is obtained according to choice criteria and an observation vector and an observation matrix are obtained according to the selection matrix; a target vector is estimated by adopting a compressive sensing algorithm based on prior information auxiliary so that a clipping noise sequence is obtained; and the clipping noise sequence is subtracted from the currently received time domain signal frames so that the signal frames after elimination of clipping noise signals can be obtained. According to the clipping noise estimation and elimination method based on compressive sensing, clipping noise in an OFDM system can be accurately estimated through relatively low complexity under a peak limited channel so that dynamic range of the signals can be effectively expanded, receiving signal quality can be enhanced and system robustness can be enhanced.

The invention discloses a multiple-input-multiple-output asymmetric clipping optical orthogonal frequency division multiplexing modulation (MIMO ACO-OFDM) iteration receiving method in a wireless optical communication system, wherein the method is characterized by detecting a minimum mean square error (MMSE) of a receiving signal by using a linear approximation model of clipping operation at a receiving end and statistical property of clipping noise on the basis of a traditional MIMO ACO-OFDM receiving algorithm, and eliminating the clipping noise in an iterative manner. The improved receiving method provided by the invention can effectively reduce performance loss of the system caused by the clipping noise and greatly reduce the bit error rate in comparison with a traditional MIMO ACO-OFDM receiver. Simultaneously, the method of the invention reduces the complexity of each iterative computation and the number of needed iterations, and therefore the method of the invention is easy for engineering realization.

A method and an apparatus for generating a standard cancellation signal includes: setting weight values according to frequency points of a current cell and its neighboring cells; according to the frequency points of the current cell and neighboring cells and the weight values of the frequency points, performing Fourier transform to obtain a corresponding time-domain signal; and performing highest amplitude normalization on the time-domain signal and performing a cyclic shift to obtain a standard cancellation signal. The embodiments generate a standard cancellation signal according to frequency points of the current cell and its neighboring cells, so that the current cell and its neighboring cells share the peak clipping noise, and therefore helping improve the peak clipping performance of the current cell or reduce the EVM distortion.

Embodiments include a system, method, and computer program product that receives an Orthogonal Frequency Division Multiplexing (OFDM) symbol, and utilizes a weighted gradient-based adaptive peak cancellation convergence algorithm to create a peak cancellation signal to reduce a peak-to-average power ratio (PAPR) as well as induced error rates of the OFDM symbol. Iterations of the weighted gradient-based adaptive peak cancellation convergence algorithm produce a peak cancellation signal that converges to a desired peak cancellation signal that satisfies a targeted PAPR. Some embodiments utilize a priori knowledge of a power spectral density of clipping noise and pre-defined transmission constraints in the frequency domain to create a peak cancellation signal with specific and desired spectral density properties. For example, some peak reduction tones (PRTs) may be scaled to take advantage of available power resources associated with the pre-defined transmission constraints, where the scaling is specific to each PRT.

Techniques are described that can be used to reduce interference in a desired channel by one or more other channels. A radio includes a level detect logic that is responsive to both the frequency offset and amplitude of undesired signals and sets the gain applied to received signals based on the offset frequency and determined amplitude of undesired signals. For example, detection of a signal amplitude in an interfering signal in a channel adjacent to the desired channel may be made. Detection of a signal amplitude in an interfering signal in a channel other than the adjacent channel and desired channel may also be made. Based on detection of one or more interfering channel, a gain of an input signal may be adjusted. Interference arising from at least spectral re-growth of noise and clipping noise may be reduced.

A bit allocation method and apparatus for a multicarrier modulation signal and a system where the method includes: determining a signal to noise ratio margin according to a predefined probability of a maximum clipping noise that can be allowed by the system; and allocating the number of modulating bits and power in each subcarrier for a multicarrier modulation signal according to the signal to noise ratio margin. By presetting a signal to noise ratio margin for a clipping noise, tolerance of the signal for the clipping noise is increased, and bit error rate is efficiently lowered.