141 results about "Coherence time" patented technology

Systems, devices and methods for updating link adaptations in multi-carrier modulated signals between an access point (AP) and a wireless local area network (WLAN) station (STA) include (are configured for) periodically transmitting a channel sounding signal from the AP. The STA receives each unsolicited channel sounding signal and evaluates the current channel conditions between the AP and STA. The AP adjusts a rate of transmission of the channel sounding signals in accordance with the channel coherence time so that the channel estimates performed by the STA will be valid within the time varying characteristics of the channel. Depending on the length of the coherence time for network environment, the channel sounding signals may be AP beacons, low overhead signal fragments with no payload, or a combination of both.

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.

Using precoded space multiplexing of limited fed back, the method defines a group of set of precoded matrix (i.e. precoded codebook) known by transmitter and receiver. Using algorithm of channel estimation to obtain current state information of channel, the receiver selects an optimal precoded matrix from precoded codebooks according to minimized principles of trace of mean square error matrix as well as through a feedback channel, feeds index of the precoded matrix back to the transmitter within coherence time of channel. Based on the said index of the precoded matrix, the transmitter obtains the precoded matrix, and then carries out precoded operations on vectors of transmit signal based on the precoded matrix. Precoded codebook can be designed based on maximized principle of minimum distance between two norms of projections of subspaces. Using limited bit number fed back, the invention raises communication performance.

A system comprising a solid state lattice containing an electronic spin coupled to a nuclear spin; an optical excitation configuration which is arranged to generate first optical radiation to excite the electronic spin to emit output optical radiation without decoupling the electronic and nuclear spins; wherein the optical excitation configuration is further arranged to generate second optical radiation of higher power than the first optical radiation to decouple the electronic spin from the nuclear spin thereby increasing coherence time of the nuclear spin; a first pulse source configured to generate radio frequency (RF) excitation pulse sequences to manipulate the nuclear spin and to dynamically decouple the nuclear spin from one or more spin impurities in the solid state lattice so as to further increase the coherence time of the nuclear spin; a second pulse source configured to generate microwave excitation pulse sequences to manipulate the electronic spin causing a change in intensity of the output optical radiation correlated with the electronic spin and with the nuclear spin via the coupling between the electronic spin and the nuclear spin; and a detector configured to detect the output optical radiation correlated with the electronic spin and the nuclear spin so as to detect a nuclear spin state of the nuclear spin.

Methods, apparatus and computer program products are provided for establishing a time-frequency reference signal pattern configuration in a carrier extension or a carrier segment, such as for cell-specific reference signals (CRS) and/or demodulation reference signals (DM RS). One method includes receiving information regarding a time-frequency reference signal pattern configuration in a carrier extension or carrier segment. The time-frequency reference signal pattern configuration defines a subframe to include a reference signal based upon a time density parameter and defines a resource element to be utilized within the subframe based upon a frequency density parameter. This method also includes receiving reference signals pursuant to the time-frequency reference signal pattern configuration such that reference signals have a coherence time T_coh with at least one subframe including a reference signal in the CE or CS per T_coh and a coherence bandwidth B_coh with at least one resource element containing a reference signal per B_coh.

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.

A secure optical communication scheme uses differential delay D in an unbalanced Mach-Zehender interferometer to provide two copies of the optical source signal at a remote phase modulator separated in time by D. As D is much bigger than the coherence time source, the two copies of the signal are effectively uncorrelated. Both signals are phase-modulated by the remote sender's data and returned to the unbalanced interferometer. The phase modulator will be converted into amplitude modulation by the action of the interferometer.

The invention belongs to the technical field of wireless communication, and specifically relates to a channel estimation method for a multi-user massive MIMO (MU-Massive MIMO) system in the frequency division duplex (FDD) mode. In the multi-user massive MIMO system, according to the method, the combined sparsity of the channel is employed, a sparse signal reconstruction algorithm based on the Bayesian method is introduced to perform channel estimation, the expense of channel estimation is greatly reduced, the channel estimation time is far less than the channel coherence time, the expense of channel estimation is reduced to 20% of the expense by employing a conventional channel estimation method, the channel estimation time is far less than the channel coherence time, and the realization of the massive MIMO channel estimation is possible in reality.

The invention relates to a non-orthogonal multiple access method based on large-scale MIMO. The method comprises the following steps of step 1, determining an optimal demodulation sequence; step 2, determining received power of a user; step 3, determining optimal emission power of the user; step 4, determining a data frame structure, wherein different users accessing the same base station follow the same uplink frame structure for synchronous transmission, and the time slot length used by the user does not exceed the coherence time of a wireless channel; step 5, adopting a pilot selection way,wherein a way of obtaining a pilot frequency by the user is that each user randomly selects the pilot frequency used by the user from a given pilot frequency set independently; and step 6, making a plurality of user terminals send signals to the base station at the optimal transmitting power based on the step 4 and the step 5, and after the base station receives the signals, only estimating a multi-user composite channel at an antenna end by means of the channel hardening capability of the large-scale MIMO, and utilizing a serial interference elimination technology to finally complete the recovery of all user signals.

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.

The present invention relates to a method for minimizing means square estimation error (MSEE) and bit error rate during channel estimation and equalization between a transmitter and a receiver of an orthogonal frequency division multiplexing (OFDM) systems. The method comprises transmitting from said transmitter to said receiver a training sequence for channel estimation being superimposed onto data at specific pilot to data power ratio (PDPR), receiving the OFDM signals along with the training sequence as an input, cross-correlating said received signal to a specific lag determined by the rms delay spread of the channel, with a specific known training sequence stored in a register, and which is also the sequence that is added to the data at the transmitter in the time domain having a prescribed pilot to data power ratio. The cross-correlated data being processed over a length of samples which can be extended to exploit the coherence time of the channel and processed along with the stored values of the inverse of autocorrelation values of superimposed training (ST) sequence so as to obtain a reliable least squares based channel estimate in a way the PDPR is limited or otherwise. The invention also relates to a system comprising means for computing a time domain least squares (LS) based channel estimate at the receiver.

A channel detection system includes an interferometer coupled to a spectrum analyzer to differentiate additive spontaneous emission (ASE) noise from optical channels in a dense wave-division multiplex (DWDM) signal. It is assumed that channels, if present, are centered at frequencies corresponding to a standardized channel grid. The relative delay of the interferometer is chosen to be greater than the coherence time of the ASE noise but less than the coherence time of the channels with the interferometer's free spectral range set to an integer divisor of the channel-to-channel frequency spacing of the grid such that active channels experience a high degree of interference. The phase delay of the interferometer is then adjusted to maximize the interference at each grid-aligned frequency. The spectrum-analyzed outputs are compared (e.g., subtracted from one another and then thresholded) to determine the channels present in the DWDM signal.

A wireless OFDMA telecommunications system comprising a transmitter adapted to transmit, by means of an OFDM modulator, a plurality of data packets destined for receivers of a plurality of users, via the same plurality of transmission channels, the transmission channel of a user being associated with a group of sub-carriers of the OFDM multiplex and a set of OFDM symbol times of a transmission interval, each receiver being adapted to signal to the transmitter the loss of a packet transmitted over the transmission channel of the corresponding user, said transmitter further comprising a packet scheduler adapted to control retransmission of each packet lost by means of said modulator. Each receiver comprises detection means of an outage situation of the transmission channel of the corresponding user and signals this to said transmitter by means of an outage information (OUTAGE/NOUTAGE). In the event of outage, said scheduler prohibits any retransmission of a packet lost over said channel during a predetermined time (T_out) greater than or equal to the coherence time of said channel.

An apparatus and method for determining a pilot pattern in a Broadband Wireless Access (BWA) communication system are provided. In the pilot pattern determining method, an Orthogonal Frequency Division Multiplexing (OFDM) demodulator generates frequency-domain data by fast-Fourier-transform (FFT)-processing a received signal. A pilot pattern decider calculates a coherence bandwidth and a coherence time using subcarrier values received from the OFDM demodulator, and selects one of a plurality of pilot patterns according to the ratio of the coherence bandwidth to the coherence time.

A two-dimensional (2D) magneto-optical trap (MOT) for alkali neutral atoms establishes a zero magnetic field along the longitudinal symmetry axis. Two of three pairs of trapping laser beams do not follow the symmetry axes of the quadruple magnetic field and are aligned with a large non-zero degree angles to the longitudinal axis. In a dark-line 2D MOT configuration, there are two orthogonal repumping beams. In each repumping beam, an opaque line is imaged to the longitudinal axis, and the overlap of these two line images creates a dark line volume in the longitudinal axis where there is no repumping light. The zero magnetic field along the longitudinal axis allows the cold atoms maintain a long ground-state coherence time without switching off the MOT magnetic field, which makes it possible to operate the MOT at a high repetition rate and a high duty cycle.