230 results about "Intercarrier interference" patented technology

A femtocell increases efficiency and coverage of a macrocellular network operating in a co-channel manner within the macrocell spectrum by selecting subcarriers for its mobile station using both the subcarrier allocation map received from the macrocell and a spectrum sensing operation. Interference is avoided by selecting only subcarriers not allocated by the macrocell and subcarriers allocated to users not nearby to the femtocell. Interference is eliminated from the received signals using co-channel interference avoidance techniques. Selection of subcarriers for femtocell use may take into consideration inter-carrier interference detected.

According to one embodiment, a method of encoding a plurality of orthogonal frequency division multiplexing (OFDM) signals is disclosed. The method includes: modulating the plurality of OFDM signals according to a modulation scheme, wherein the modulated OFDM signals are mapped to a first axis and a second axis perpendicular to the first axis, and correspond to a first constellation having a plurality of points symmetric with respect to the first axis and the second axis; and differentially encoding the plurality of OFDM signals according to a second constellation plurality of points defined by shifting a position of one of the first constellation plurality of points toward an origin located at an intersection of the first axis and the second axis.

A method and system for wireless communication channel estimation. A frequency offset hypothesis is determined. An interchannel interference (“ICI”) matrix based on the frequency offset hypothesis is generated. Pilot channel estimates based on the ICI matrix are obtained. A correlation error of the pilot channel estimates to the frequency offset hypothesis is calculated. The correlation error is compared with a predetermined correlation error value. The frequency offset hypothesis is updated and the aforementioned steps are iteratively repeated if the correlation error is greater than the predetermined correlation error value. The pilot channel estimates are used to estimate the wireless communication channel.

A synchronization of a pilot assisted channel estimation orthogonal frequency division multiplexing can be achieved by receiving a signal containing pilot symbols, providing an initial time and frequency synchronization to the signal, phase rotating the signal across time, transforming the signal with a fast Fourier transformation, phase rotating the signal across frequency, extracting the pilot symbols and generating a channel estimator. The phase rotating across time and the phase rotating across frequency are controlled by a phase rotation controller in accordance with the channel estimator. The initial time and frequency synchronization synchronizes the signal such that intercarrier interference effects and intersymbol interference effects are negligible. The signal may include plural carrier frequencies each having an arrival timing offset and a frequency offset. The signal may also include delay spread or Doppler spread. The phase rotation controller measures a phase different between the channel estimator at times k and k+Δk, where k is time and Δk is a symbol period and measures a phase difference between the channel estimator at frequencies n and n+Δn, where n is tone frequency and Δn is a frequency spacing between adjacent tones.

The invention discloses a method for generating a pilot frequency sequence. The method comprises the following steps of: selecting OCCs (Orthogonal Cover Code) from an OCC set according to different rules in each code division and frequency division and/or time division hybrid multiplexing demodulation reference signal (DMRS) port by using different code division multiplexing groups and/or generating scrambling sequences of the DMRS according to different rules by using different code division multiplexing groups; and multiplying the selected OCCs with the scrambling sequences to generate a final pilot frequency sequence of each DMRS port. The invention further discloses a device for generating a pilot frequency sequence. By adopting the method and the device, corresponding layers among different code division multiplexing port groups can be lowered, the influence of inter-carrier interference caused by the problems of Doppler frequency shift and timing error on channel estimation is reduced, and the channel estimation accuracy is increased.

Methods and apparatus are described for improving receiver performance in a multicarrier communication network in which an encoded symbol (250) is transmitted over a transmission channel (20) in the communications system. A model of the transmission channel (20) is estimated (718, 760), said model characterising an effect of intercarrier interference on at least one carrier in the multicarrier system. The received symbol (250) is decoded (720, 762) using the estimated model to remove a predicted effect of intercarrier interference. A pre-processor (40) is also described for operation in conjunction with a communications receiver (30) in the network. The pre-processor (40) includes a channel estimator (42) operable to estimate at least one feature of the communication channel based on a received signal. The pre-processor (40) modifies the received signal dependent on the at least one estimated feature and provides the modified signal to the communications receiver (30).

The invention discloses a novel OFDM signal channel estimation combination ICI self elimination method. The sending end pilot frequency design adopts a cluster type pilot frequency OFDM structure with the ICI estimation function. The receiving end is processed according to the following steps: a, converting proceeding FFT of an OFDM sign to a frequency domain, taking out the pilot frequency, and carrying out ICI elimination signal channel estimation; b, carrying out counter modulation after using the signal channel estimation in the first step for coarse balancing; c, using the signal channelestimation in the first step for time domain linear continuous sign signal channel estimation; d, calculating ICI signal channel matrixes through cyclic convolution by using a time domain pulse response structure in the third step, and obtaining ICI interference matrixes; and e, carrying out ICI elimination through combining counter modulation signals in the second step and ICI interference matrixes in the fourth step, and making the judgment after the secondary balancing. The invention solves the problem of influence on OFDM by interference between carrier waves under the condition of lineartime change signal channels, and improves the frequency spectrum utilization rate and the system performance.

A receiver for ICI cancellation in a MIMO system is provided, in which a detection orderer determines a subcarrier detection order according to SINRs of subcarriers in an I-CMOS, a detector receives a vector on the subcarriers and a priori information from a decoder according to the subcarrier detection order and iteratively estimates the received vector using the a priori information, and the decoder decodes an ICI-cancelled signal according to the estimate.

An incremental iterative time-varying channel evaluation and inter carrier interference (ICI) elimination method of fast orthogonal frequency division multiplexing (OFDM) system is applied in the field of wireless communication channel evolution, and is used for channel evaluation based on pilot frequency in the circumstance that a severe ICI influence of a time-varying channel occurs. The incremental iterative time-varying channel evaluation and ICI elimination method of fast OFDM system is characterized in that the sum of an ICI and a channel noise (SIN) is taken as a denosing object of a Kalman wave filter, and the ICI influence when the Kalman wave filter evaluates is eliminated. In addition, an incremental mode is used by data used for iteration, the number of the sub-carrier waves used for measurement increases slowly along two sides of each pilot frequency point in an iterative process, and thus the influence caused by the ICI is suppressed. The performance of the incremental iterative time-varying channel evaluation and ICI elimination method of fast OFDM system is improved significantly compared with an existing algorithm in the circumstance that signal noise ratio (SNR) is small.

The invention provides an inter-carrier interference processing device, a method thereof and a receiver utilizing the device and the method. A reconstruction and cancellation device of the interference between carriers is applied to the receiver of a wireless communication system. The receiver comprises: a pilot frequency extraction unit, a data extraction unit, a signal channel estimation unit and an equalizer unit. The inter-carrier interference processing device comprises: a computing unit of the inter-carrier interference channel parameter for calculating the channel parameter of the channel which causes the inter-carrier interference according to the channel estimation result; a symbol judgment unit for carrying out the symbol judgment on the output and obtaining the symbol of the signal; a reconstruction unit of the inter-carrier interference for reconstructing the inter-carrier interference of the input signal according to the output of the computing unit of the inter-carrier interference channel parameter and the output of the symbol judgment unit; a cancellation processing unit for carrying out the cancellation of the reconstructed inter-carrier interference, and returning the processing result to the pilot frequency extraction unit and the data extraction unit.

An receiver apparatus according to an OFDM system includes a inter-symbol interference suppressing unit configured to modify to a predetermined content a portion of a dominant wave included in a received signal and to modify to a predetermined content a portion of at least one delayed wave included in the received signal, a tentative demodulation unit configured to demodulate a signal inclusive of the modified dominant wave and the modified delayed wave or inclusive of the unmodified dominant wave and the modified delayed wave according to the OFDM system so as to output a tentatively demodulated target symbol, and an inter-carrier interference suppressing unit, wherein the inter-carrier interference suppressing unit includes a first unit configured to further modify the modified portion of the modified delayed wave in response to the tentatively demodulated target symbol, a second unit configured to further modify the modified portion of the modified dominant wave and the modified portion of the modified delayed wave in response to the tentatively demodulated target symbol, and a selecting unit configured to select one of the first unit and the second unit in response to a delay profile.

The invention provides an optical communication method which comprises the steps of: modulating obtained bit stream data to obtain a modulating signal; carrying out differential coding on the modulating signal to obtain a differential coding signal; converting the differential coding signal into an electrical signal; mapping the electrical signal on an optical carrier to form an optical signal; and then transmitting the optical signal. By using the method, on the premise that a frequency spectrum utilization rate is not reduced, the system capability of resisting disturbance among carriers is enhanced; thus, the tolerance of the existing optical communication sysem for resisting laser linewidth, quick change PMD (Physical Media Dependent), nonlinear fiber, disturbance among channels and other damage is enhanced; and system performance is greatly enhanced.

The invention discloses an underwater sound communication device and a method based on time reversal and orthogonal frequency division multiplexing (OFDM) combined treatment. The underwater sound communication device comprises a signal transmitter, a power amplifier, a transmitting transducer, a receiving hydrophone array, a signal receiver and a signal processor, wherein the signal processor comprises a broadband Doppler estimation and compensation module, a time reversal processing module, an OFDM demodulation module, a channel estimation and compensation module and a frequency deviation estimation and compensation module. In the underwater sound communication device, the space time focusing characteristics of the time reversal are utilized to eliminate the multipath influence of the channel; a pulse channel response length can be shortened by the time reversal so as to reduce the length of an OFDM symbol guard interval and improve the communication efficiency; and because the guard interval is reduced, the length of the OFDM symbol can be shortened so as to enlarge a subcarrier frequency interval. With the method disclosed by the invention, interference among subcarriers can be reduced, and the available rate of the OFDM underwater sound communication is further improved.

An apparatus capable of inter-carrier interference (ICI) cancellation in a communication system, the apparatus comprising a detecting module configured to detect an ISI-free region free from inter-symbol interference (ISI) in a guard interval (GI) of a symbol in time domain, a windowing module configured to provide a windowing function in time domain, identifying a weight value in the windowing function based on the ISI-free region, and multiplying a channel response related to the symbol by the windowing function in time domain to obtain a windowing result, wherein the windowing result comprises a first portion corresponding to the ISI-free region and a second region corresponding to an end portion of the symbol, the end portion and the ISI-free region having the same length, and a combination module configured to combine the first portion and the second portion of the windowing result in time domain.

The present invention provides an optical communication method, comprising: performing modulation on the obtained bit stream data to generate modulated signals; performing differential encoding on the modulated signals to generate differentially encoded signals; converting the differentially encoded signals into electrical signals; and mapping the electrical signals onto optical carriers to generate optical signals for transmission. With the present invention, it is possible to enhance the system's capability of resisting inter-carrier interference without decreasing spectrum efficiency, hence improving the tolerance of existing optical communication systems towards laser linewidth, fast-changing PMD, optical fiber nonlinearity, inter-channel interference and other damages, greatly enhancing system performances.

The invention discloses an OFDM (Orthogonal Frequency Division Multiplexing) underwater acoustic communication method with high spectral efficiency under a time-varying double-spread channel condition, and belongs to the technical field of underwater acoustic communication. The method comprises the following steps: carrying out band-pass filtering on a received signal r (k), carrying out front-endprocessing such as ADC (Analog to Digital Converter) conversion into a digital signal, carrying out down-conversion and low-pass filtering, estimating average Doppler by utilizing a fuzzy function method, carrying out resampling and frequency correction, multiplexing the signal, carrying out time domain equalization and frequency domain equalization, carrying out diversity combination, and then adopting the OMP-DCD algorithm to perform residual Doppler compensation. an iterative signal processing technology is adopted, an LDPC decoder and an equalizer are cascaded through soft-in soft-out mapping/demapping and an interleaver/deinterleaver, close information interaction is achieved in the two modules, soft information transmitted in a reciprocating mode is fully utilized, and interferenceof a time-varying double-spread channel is effectively resisted. According to the method, the complexity and the performance can be well compromised, and serious inter-symbol interference, inter-carrier interference and pilot frequency-pilot frequency interference in the transmission process are efficiently solved. And the method is low in complexity and can be realized on the DSP in real time.

A method, and device implementing the method, for adaptively allocating pilot signals in a wireless communication system. The method includes receiving channel data, including channel length (L) data, inter-carrier interference power (P_ICI) data, coherence time (CT) data, and a number of subcarriers (N). The method further includes selecting, when L is greater than a first channel length threshold (L_TH1), a first number of pilot signals between a minimum value of L and a maximum number of pilot signals N_P,MAX, wherein the first number of pilot signals N_P are equally spaced in time according to the CT data, and equally spaced in frequency. Further, the method includes selecting, when L is less than L_TH1 and P_ICI is less than a power threshold (P_TH), a second number of pilot signals such that the second number of pilot signals is between the minimum value of L and N_P,MAX, wherein the second number of pilot signals are equally spaced in time according to the CT data, and equally spaced in frequency. Finally, the method includes selecting, when L is less than L_TH1 and P_ICI is greater than P_TH, a third number of pilot signals such that the third number of pilot signals is equal to n times L (nL), wherein n is an integer, the third number of pilot signals being equally spaced in time according to the CT data, and allocated according to a cluster(n) clustered pilot scheme with a cluster size equal to n, the n-sized clusters being clustered in frequency.

FBMC (Filter Bank Multicarrier) is a special carrier communication mode. Being different from OFDM (Orthogonal frequency division multiplexing), subcarriers of the FBMC are not orthogonal to one another, so that intersymbol interference and inter-carrier interference naturally exist. A traditional OFDM channel estimation method is built on the basis of no intersymbol interference and inter-carrier interference, thereof, to carry out accurate channel estimation, the interference of surrounding symbols to a pilot symbol must be eliminated, and surrounding interference factors are definite under a certain filter bank structure and a prototype filter design. An auxiliary pilot method is such a method that an auxiliary pilot is placed nearby the position of an actual pilot, the value of the auxiliary pilot is determined by virtue of the values of the surrounding symbols and the corresponding interference factors, and the interference of the surrounding symbols to the pilot position is eliminated by virtue of the auxiliary pilot, so as to carry out accurate channel estimation.

The invention provides a design method of an optimal pilot frequency pattern suitable for rapid time-varying sparse estimation. The method is specifically characterized in that more and more testing experiments indicate that wireless channels have sparsity, and the design of the pilot frequency pattern at present is mainly based on a dense multipath conventional channel estimation method, a large number of pilot frequency signals are needed for obtaining accurate channel state information, and the utilization of frequency spectrum resources is low; in addition, the existing sparse channel estimating methods are mostly suitable for slow time-varying or time-invariant channels, the utilization of the channel sparsity is only limited to a time delay domain instead of a Doppler domain, and the influences of intercarrier interference generated by Doppler frequency shift on the channels can be neglected, so that the precision and reliability of the sparse channel estimation method used in the rapid time-varying channel are greatly lowered. Based on the above conditions, the invention provides the design method of the optimal pilot frequency pattern suitable for rapid time-varying sparse estimation, and the provided method is better in robustness and higher in channel estimation precision.

In an environment where the transmission medium leading to the receiver is time-variant within a block of received signals, and where transmission medium has an finite impulse response extending over a number of symbols intervals, a receiver that includes a filter that, based on an estimate of the transmission channel, is controlled to have filter coefficients that minimize inter-carrier interference due to the intra-block time variations in the transmission medium. The estimate channel coefficients are determined from pilot signals and an interpolation process. When the receiver is an OFDM receiver, the pilot signals are advantageously selected to be in clusters that are equally spaced from each other in the time or the frequency domains. This approach applies to multiple antenna, as well as to single antenna arrangements, and to arrangements that do, or do not use space-time coding.