382 results about "Delay spread" patented technology

A wireless communications adapts its mode of operation between spatial multiplexing and non-spatial multiplexing in response to transmission-specific variables. An embodiment of a wireless communications system for transmitting information between a base transceiver station and a subscriber unit includes mode determination logic. The mode determination logic is in communication with the base transceiver station and the subscriber unit. The mode determination logic determines, in response to a received signal, if a subscriber datastream should be transmitted between the base transceiver station and the subscriber unit utilizing spatial multiplexing or non-spatial multiplexing. In an embodiment, the mode determination logic has an input for receiving a measure of a transmission characteristic related to the received signal. In an embodiment, the mode determination logic includes logic for comparing the measured transmission characteristic to a transmission characteristic threshold and for selecting one of spatial multiplexing and non-spatial multiplexing in response to the comparison of the measured transmission characteristic to the transmission characteristic threshold. In an embodiment, the transmission characteristic includes at least one of delay spread, post-processing signal-to-noise ratio, cyclical redundancy check (CRC) failure, residual inter-symbol interference, mean square error, coherence time, and path loss. By adapting the mode of operation in response to transmission-specific variables, the use of spatial multiplexing can be discontinued in unfavorable conditions. Additionally, because the wireless communications system can adapt its mode of operation between spatial multiplexing and non-spatial multiplexing, the communications system is compatible with both subscriber units that support spatial multiplexing and subscriber units that do not support spatial multiplexing.

A method and apparatus for adaptive beam-steering are disclosed. In one embodiment, the method comprises performing adaptive beam steering using multiple transmit and receive antennas, including iteratively performing a pair of training sequences, wherein the pair of training sequences includes estimating a transmitter antenna-array weight vector and a receiver antenna-array weight vector.

An apparatus and method for canceling ISI in a broadband wireless communication system are provided. In a transmitter of the broadband wireless communication system, a controller acquires a CP length, a puncturing pattern, and a time sample interval according to a delay spread. A puncturer punctures coded data in the puncturing pattern. An IFFT processor IFFT-processes the punctured coded data and outputs sample data. A CP inserter generates an OFDM symbol by inserting a copy of a last part of the sample data before the sample data. Here, the length of the last part of the sample data is equal to the CP length. A D/A converter converts the OFDM symbol to an analog signal at a sampling rate determined by the time sample interval.

The invention concerns a method and an apparatus implementing the method. In the method is determined in a mobile node whether the mobile node supports mobile node specific cyclic prefixes. The mobile node transmits to a base station node an indication whether the mobile node supports mobile node specific cyclic prefixes. The base station node measures a delay spread of a radio resource transmitted by the mobile node. The mobile node receives an indication of an uplink direction cyclic prefix length from the base station node. The mobile node forms a cyclic prefix of the uplink direction cyclic prefix length selected from a useful symbol, adds the cyclic prefix in front of the useful symbol and transmits a signal comprising the cyclic prefix and the useful symbol to the base station.

A frame structure for support of large delay spread deployment scenarios (e.g., cellular system operation in large cell sizes or low frequency bands) is generally presented. In this regard a method is introduced comprising partitioning a radio frame into a plurality of equal-sized (or non-equal-sized) sub-frames to simplify system implementation. Other embodiments are also disclosed and claimed.

A wireless communications device which may include a wireless receiver for receiving wireless signals comprising unknown data portions over a channel, and a demodulator connected to the wireless receiver. The demodulator may be for estimating a delay spread and a fade rate associated with the channel, determining a desired time-domain interpolation filter based upon the estimated fade rate, and determining a desired frequency-domain interpolation filter based upon the estimated delay spread. The demodulator may further generate channel estimates for the unknown data portions based upon the desired time-domain interpolation filter and the desired frequency-domain interpolation filter, and determine the unknown data portions based upon the channel estimates.

A method and apparatus are provided for automatic data rate control in wireless communication systems, such as wireless LANs. A wireless communication device according to the present invention includes a data rate controller that adapts a transmission rate based on a channel correlation measure. The channel correlation measure may be, for example, eigenvalues or singular values of a channel matrix. The data rate controller may also consider the signal quality, channel delay spread or both in determining a data rate.

The present invention relates to a method and a simulator for simulating an RF channel between a radio transmitter and a radio receiver located at a far distance from one another, in which radio channel multipath propagation occurs, and with which simulation at least part of the phenomena caused by the multipath propagation to the radio signal, such as delay spread, attenuation and Doppler shift are implemented. As taught by the method, an RF signal (fin) is moved to a lower frequency (fIF), and from said lower frequency signal (fIF) thus produced samples are taken and written in a memory at a predetermined write frequency (fw). The stored samples are read from the memory after a period of time of the length of the propagation delay (tDi) of each propagation path (i) to be simulated from the storage in the memory at a read frequency (fPi) predetermined for each propagation path (i) to be simulated, said read frequency differing from the write frequency (fw), when the frequency difference ( DELTA f01) of said write frequency (fw) and the propagation-specific read frequency (fRi) represent the Doppler shift of the frequency occurring in each propagation path (i).

The invention provides a method and device for iterative hybrid time-frequency domain block equalization of signals received via a communication channel subject to multipath interference. The equalization method includes frequency-domain equalization of blocks of received signals in a forward path, and time-domain inter-block echo correction and intra-block cyclic echo addition in the feedback path. The invention can be used for equalizing signals transmitted without cyclic prefix and subjected to multi-path interference with long delay spread.

The invention discloses a self-adapting channel estimating method applied to 3GPP LTE system. The method comprises the following steps: (1) the LS (least square) channel estimating value at a pilot tone is computed according to reference signals in a receiving data field; (2) interpolation in the time domain is performed according to current frame pilot tone channel estimated value data and reserved delay frame pilot tone channel estimated value data, and a pilot matrix encrypted is obtained through computing; (3) channel delay spread is estimated according to LS estimation value at the pilot tone, then radio frequency channel filtering coefficient is selected according to the delay spread, and the frequency domain estimation value is computed; and (4) channel Doppler spread is estimated according to the LS estimation value at the pilot tone, then time domain filtering coefficient is selected according to the Doppler spread, and the time domain channel estimation value is computed. The self-adapting channel estimating method provided by the invention has a self-adapting capability to channel characteristics, reduces the occupancy rate and working consumption of hardware resource, improves the estimating speed and reduces computation delay of an estimator.

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.

A MIMO transmission system and method of an OFDM-based wireless LAN system. The MIMO transmission system includes multiple transmission paths to channel antennas and receives and encodes plural rows of bit streams. The MIMO transmission system does not transmit the plural rows of bit streams through the same paths and channel antennas, but sequentially switches, OFDM-modulates, and sends bits of each bit stream to the plural paths such that the bit streams are not transmitted through the same paths and channel antennas. Through the bit exchange among the channel antennas, the MIMO transmission system can enhance diversity gains by the channel encoding in flat-fading environments having a small RMS delay spread.

A telecommunications system and method is disclosed for deliberately producing synchronous timing jitters in order to dynamically shift the delay spread within the overlap zone in a simulcast system. At a synchronous periodic rate, the timing differential between transmission of the signal from the control point to each of the transmitters can be continuously adjusted to continuously change the relative timing between multiple received signals in the overlap zone. Alternatively, the timing adjustments can be performed only upon reception of a retransmission request. In either case, the timing adjustments are performed so as to not be noticed by the mobile subscriber.

The present invention relates to an apparatus and method of estimating a channel based on a channel delay spread in a mobile communication system. Pilot subcarriers are inserted between data subcarriers at predetermined intervals to estimate a channel at locations of the pilot subcarriers. An approximate channel delay spread value is estimated by using an autocorrelation value of a pilot signal. Then, a channel for data subcarriers between the pilot subcarriers is estimated by using a Wiener finite impulse response (FIR) filter that has a separate coefficient according to the estimated delay spread value. Accordingly, by changing the Wiener FIR filter coefficient according to the delay spread value of the channel, it is possible to estimate the channel so as to be adaptive for a change of the channel over time. Since the filter coefficients, which are calculated in advance, are used, it is possible to reduce the amount of calculation required when calculating the filter coefficients. As a result, an apparatus for estimating a channel can be easily achieved.

The invention provides a channel estimation method for Orthogonal Frequency Division Multiplexing system and a device thereof. The channel estimation method comprises the following steps: A. calculating according to the frequency domain channel estimation of a reference signal to obtain the delay spread of the channel; B. generating a frequency domain interpolation coefficient according to the delay spread; C. carrying out interpolation according to the frequency domain interpolation coefficient and the frequency domain channel estimation of the reference signal to obtain the channel estimation of the whole frequency of the position where the reference signal is located; D. calculating according to the frequency domain channel estimation at different time domain positions to obtain the coherence time of the channel; E. generating a time domain interpolation coefficient according to the coherence time; and F. carrying out interpolation according to the time domain interpolation coefficient and the channel estimation of the whole frequency located with the range of the coherence time to obtain the whole channel estimation of the time domain and the frequency domain. In light of the invention, the channel estimation result can self-adaptively change with the change of the channel.

The invention discloses a training sequence reconstruction-based channel estimation method and a training sequence reconstruction-based channel estimation system. The method comprises the following steps: acquiring a known channel estimation result; according to the known channel estimation result, constructing linear convolution of former frame transmitted data and a channel and the linear convolution of a transmitted training sequence and a channel impulse response; eliminating inter-block interference of data on a training sequence; obtaining a cyclic convolution, of the training sequence and the channel impulse response, serving as a reconstruction item; according to the reconstruction item, reconstructing the training sequence; and performing channel estimation by utilizing the reconstructed training sequence, and updating a channel estimation result. The method and the system of the invention can ensure that a TDS-OFDM system can also obtain relatively accurate channel estimation when maximum delay extension of the channel exceeds the guard space length of the training sequence, simultaneously improves the accuracy of the channel estimation and improves the spectrum utilization ratio and the mobility performance of the system.

Disclosed is a link margin adaptation method using feedback information of a wireless communication system. For transmission and reception of data between two nodes of the wireless communication system, a transmission node requests a receiving node to transmit a link margin. The transmission node receives the link margin, and selects one of a white noise table or a delay spread table according to a delay spread value between the two nodes. Then, the transmission node adapts a link between the two nodes to a transmission mode and decides a transmission rate to transmit data at the decided transmission rate, thereby improving transmission capacity of the wireless communication system, obtaining the optimum link state, extending power utilization time of stations, and reducing interference between stations.

A system for processing radio frequency (RF) signals includes a searcher and a plurality of Cluster Path Processor (CPPs). The searcher detects a maximum signal energy level and position of at least one of a plurality of individual distinct path signals in a signal cluster of a first information signal, wherein at least a portion of the plurality of individual distinct path signals is received within a duration of a corresponding delay spread. The sampling position is used as a starting sampling location by the plurality of CPPs, including a first information signal CPP and a second information signal CPP. Fine sampling positions of the plurality of CPPs are based upon channel energy estimates for the plurality of individual distinct path signals. CPP outputs are employed to produce channel estimates, which are themselves used in subsequent equalization operations. Sampling positions may change over time in order to satisfy alignment criteria.

A base station may generate and transmit a transport stream including a sequence of frames. A frame may include a plurality of partitions, where each partition includes a corresponding set of OFDM symbols. For each partition, the OFDM symbols in that partition may have a corresponding cyclic prefix size and a corresponding FFT size, allowing different partitions to be targeted for different collections of user devices, e.g., user devices having different expected values of maximum delay spread and/or different ranges of mobility. The base station may also dynamically re-configure the sample rate of each frame, allowing further resolution in control of subcarrier spacing. By allowing the cyclic prefixes of different OFDM symbols to have different lengths, it is feasible to construct a frame that conforms to a set payload duration and has arbitrary values of cyclic prefix size per partition and FFT size per partition. The partitions may be multiplexed in time and/or frequency.