439 results about "Symbol period" patented technology

A control method of synchronizing communications between or among a plurality of devices in a communication system includes detecting beacons from the plurality of devices in the communication system, and establishing a reservation for at least a portion of the plurality of devices in the communication system. Each reservation is a frame interval in which to transmit symbols from one device to one or more of the other devices in the communications system. Each frame interval and intra-frame interval is set according to the established reservation. Each frame interval and intra-frame interval is a plural, integral number of symbol periods in duration.

A few high power tones used for synchronization and / or other purposes are transmitted in a FDM system during a period of time, e.g., a symbol transmission time period. During normal data transmission symbol periods signals are transmitted using at least 10 tones, e.g., per symbol time. Less than 5 high power signals are transmitted in a symbol time with at least 80% the maximum total transmitter power transmitted being allocated to the high power signals where the maximum total transmitter power is determined from a period of time which may includes one or more data and / or high power tone transmission periods. When the high power tones are transmitted at most 20% of transmitter power is available for transmitting other tones with the power normally being distributed among multiple tones. Normally some tones which would be transmitted in a symbol time go unused during transmission of the high power signals.

One embodiment relates to a receiver circuit for multi-level amplitude signaling which includes at least three amplitude levels for each symbol period. The receiver circuit includes a peak detector, a reference voltage generator, and a comparator circuit. The peak detector is arranged to detect a peak voltage of the multi-level amplitude signal, and the reference voltage generator uses the peak voltage to generate multiple reference voltages. The comparator circuit uses the multiple reference voltages to detect an amplitude level of the multi-level amplitude signal. Other embodiments and features are also disclosed.

Transceiver circuitry for use in a multiple-input, multiple-output (MIMO), orthogonal frequency-division multiplexing (OFDM), communications environment, is disclosed. Error correction coding according to a fixed-block size code, such as low density parity check (LDPC) coding, is implemented. The codeword length, and codeword arrangement, are selected by determining a minimum number of OFDM symbol periods required for a payload size, and the number of available information bits in those symbol periods. A rule-based approach, for example in a table, is used to select the codeword length, and the number of codewords required. Shortening is then applied to the code, followed by determining whether puncturing or repeating of bits is necessary to efficiently use the available OFDM symbols.

A method and apparatus for providing hopped delay diversity for multiple antenna transmissions. In the method and apparatus, an input symbol stream is offset in time by M symbol periods to generate or offset symbol stream. The offset input stream may be offset so as to lead or lag the original input symbol stream. The original input symbol stream is then transmitted on a first set of N antennas and the offset input symbol stream is transmitted on a second set of N antennas, with transmit diversity techniques applied to the transmissions from the first and second set of N antennas.

Space-time code, and methods for constructing space-time codes are provided. The space-time coder performs a respective linear transformation on each of P sets of K modulated symbols of a modulated symbol stream to produce P sets of T linearly transformed symbols, applies a respective phase rotation to each set of T linearly transformed symbols to produce a respective set of T phase rotated symbols, and performs a threading operation on the sets of T phase rotated symbols to produce P threaded sequences that define M output sequences; the threading operation being such that each threaded sequence is an allocation of output sequences over time of a respective one of the P sets of T phase rotated symbols in which all of the output sequences are used by each threaded sequence; during each of T symbol periods, a respective one of the P threaded sequences includes a symbol from one of the P sets of phase rotated symbols; and at least one symbol from each set of phase rotated symbols appears in each output sequence; where M>=2, 2<=P<=M, and T>=M and M>=K.

A method and apparatus for joint time and frequency synchronization for orthogonal frequency division multiplexing (OFDM) systems. A multitone pilot signal is sent in a designated OFDM symbol period. The receiver synchronizes to the pilot signal in a two-stage procedure. The first stage estimates the frequency offset coarsely with a frequency-domain correlation method and estimates the time offset with smoothed time-domain correlation. In a multipath channel, the smoothed time offset estimate is used to locate a cyclic prefix interval which captures the maximum total signal energy. The second stage improves the frequency estimate with a computationally efficient numerical optimization method.

A control method of searching for a neighboring cell of a mobile station communicating with a base station is provided in a direct sequence CDMA mobile communication system which transmits information by carrying out double modulation using a first spreading code group and a second spreading code. The first spreading code group includes spreading codes that have a same repetition period as an information symbol period and are used in common by the base stations, and the second spreading code has a repetition period longer than the information symbol period. The base stations are assigned different second spreading codes. The control method stores at least one second spreading code and its phase into a first table, which second spreading code corresponds to a perch channel whose second spreading code and phase are known; stores a second spreading code used by a neighboring base station into a second table; searches for a perch channel whose second spreading code and phase are unknown; and searches for a perch channel whose second spreading code and phase are known. The neighboring cell search method can save the power consumption and time required for the mobile station to carry out the cell search with preventing an increase in the total cost of the system.

An apparatus and method for OFDM demodulation establish symbol synchronization to minimize between-symbol interference even under an environment where multipath occurs.An incoming signal is an OFDM signal including a transmission symbol structured by a valid symbol period and a guard interval, and a predetermined synchronization symbol is included in the OFDM signal for every transmission frame. A correlator calculates how a signal generated by a synchronization symbol generator and the OFDM signal are correlated. A correlation calculator then calculates a correlation therefrom. An integrator integrates the calculated correlation by the guard interval. A timing determination device determines symbol timing from the integrated correlation. An FFT window generator outputs operation timing for Fourier transform from the determined symbol timing. Based on the signal outputted from the FFT window generator, the apparatus for OFDM demodulation extracts a signal in the valid symbol period from the transmission symbol for demodulation.

Techniques for deriving eigenvectors based on steered reference and used for spatial processing. A steered reference is a pilot transmission on one eigenmode of a MIMO channel per symbol period using a steering vector for that eigenmode. The steered reference is used to estimate both a matrix Σ of singular values and a matrix U of left eigenvectors of a channel response matrix H. A matrix Ũ with orthogonalized columns may be derived based on the estimates of Σ and U, e.g., using QR factorization, minimum square error computation, or polar decomposition. The estimates of Σ and U (or the estimate of Σ and the matrix Ũ) may be used for matched filtering of data transmission received via a first link. The estimate of U or the matrix Ũ may also be used for spatial processing of data transmission on a second link (for reciprocal first and second links).

A pilot designing method in an uplink OFDMA system is provided. In the uplink OFDMA system, communications are carried out in a frame divided into time-frequency lattices, and each time-frequency lattice includes a plurality of data symbol periods and a plurality of pilot symbol periods intermittently arranged with respect to the data symbol periods. The frame is divided into a plurality of blocks. The blocks are allocated to the terminals. A predetermined allocated pilot time-frequency lattice is shared between adjacent terminals.

In a wireless transmitter having a plurality of spatial streams differentiable at a receiver, wherein data is encoded and transmitted over a communication channel with pilot tones to provide the receiver with information about the effects of the communication channel and / or transmitter impairments and / or receiver impairments on the spatial streams transmitted, the benefits can be provided by identifying a plurality of symbol periods within which symbols representing some of the encoded data are to be transmitted, identifying pilot tone values for the plurality of symbol periods, wherein the identified pilot tone values are such that the receiver, when receiving at least some of the pilot tones having the identified pilot tone values, is provided with signals enabling the receiver to characterize the communication channel and / or transmitter impairments and / or receiver impairments to obtain transmit stream diversity gain, and transmitting the symbols and the pilot tones over the plurality of spatial streams for the plurality of symbol periods. In some embodiments, the pilot tones are orthogonal over space and time or over space and time and frequency, while in others they are semi-orthogonal. Pilot tone values might be of a constant amplitude and phase shifted, or might also have amplitude variations wherein at least two pilot tones are nonzero for spatial streams for a given symbol period.

Methods, systems, and devices for wireless communication are described. In some examples, a wireless system may use a staggered uplink / downlink (UL / DL) format in which the symbol periods of the downlink are offset from the symbol periods of the uplink. Thus, if a user equipment (UE) receives a transmission in a first symbol period, it may decode the transmission and transmit a response in a staggered symbol period (e.g., in a UL control channel symbol period beginning one half of a symbol period after the first symbol period). A base station may then receive the response and, if it is a negative acknowledgement (NACK), retransmit during the third symbol period following the first symbol period. In another example, thin control channels may be used to reduce the round trip time between receiving a transmission and a retransmission.

When signals for two mobile stations PS-A and PS-B are multiplexed using path division, a clock generating unit 52 generates a clock signal so as to delay the timing for transmitting symbols to the mobile station PS-B by 0.5 symbol periods relative to the transmission of symbols to the mobile station PS-A. If the transmission timing is adjusted in this way, a mobile station that picks up symbols which are spatially multiplexed with the signal for the present mobile station but are intended for another mobile station will not be synchronized with the symbols for the other mobile station. The mobile station will not be able to properly demodulate the symbols for the other mobile station, and so can be prevented from outputtin

An OFDM transmitter transmits an OFDM signal by a frame having a plurality of transmission symbol periods constituted of an effective symbol period for transmitting an information bit and a guard interval. The OFDM transmitter includes a guard interval length decider configured to decide a guard interval length in accordance with a feedback signal from an OFDM receiver; and a guard interval length changer configured to change a guard interval length in each transmission symbol period, in accordance with a decided guard interval length without changing a frame length.

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 signal estimation loop includes a postcursor estimator which generates all possible postcursor estimation signals in a first past symbol period which is one symbol earlier based on a past estimated signal in a second past symbol period which is at least two symbols earlier. One of the possible postcursor estimation signals is selected based on the estimated signal to output a postcursor estimation signal to a subtracter in the symbol period. The subtracter subtracts the postcursor estimation signal from an input signal to produce a difference signal which is used to generate the estimated signal.

This invention discloses a method for TD-SCDMA compatible with OFDM technology, which carries out serial parallel conversion to the due-out high speed serial code sheet sequence and generates multiple parallel sub-sequences to be modulated to multiple sub-carriers for parallel transmission to reduce the transmit rate of each channel so as to increase the symbol period and weaken the influence of multi-channel interference, at the same time, it uses the circular prefix as the protection interval, the interference among symbols are reduced greatly and the orthogonality among channels are ensured.

A spread spectrum communications system is provided for reducing the number of required matched filters to simplify the configuration associated with the reception. In a spread spectrum transmitter, a plurality of spread channel signals are synthesized by shifting their respective phases by a time sufficiently shorter than one symbol period. In a spread spectrum receiver, a plurality of spread code sequences are set one by one at a tap of a single matched filter in one symbol period in a time division manner to recover transmitted data.

The invention provides an all-digital receiving method for a satellite-borne AIS.The method comprises the steps that a signal processed through radio frequency digitization and a local carrier are subjected to orthogonal frequency conversion and then filtered to acquire mixed baseband signals, and the mixed baseband signals are separated; burst detection is performed on separated one-way signals; after a frame header is detected, frequency offset estimation is performed, and frequency offset compensation is performed on the baseband signals on the basis of a frequency offset estimation result; a frame header sequence is selected as an input signal for symbol timing synchronization to acquire a symbol timing error estimation value, and optimal sampling point data is interpolated according to the symbol timing error estimation value; information demodulation is performed on the optimal sampling point data by adopting an incoherent Viterbi demodulation algorithm, a bit information sequence is verified on the basis of a cyclic redundancy check code, and an optimal sampling point sequence of a frame header symbol period and the frequency offset, the amplitude and the initial phase of the verified bit sequence are estimated; a demodulation signal is recovered on the basis of frequency offset, amplitude and initial phase estimation values; the recovered strong signal is subtracted from the separated mixed baseband signals.

The present invention relates to a new parallel interference cancellation (PIC) configuration where the PIC is implemented after the rake reception and multipath combining. In the invention disclosed, the regenerated interference contributions (functions of signature sequence cross-correlations) for multiuser detection (MUD) in a multipath radio channel are explicitly filtered through the estimated multipath channels, and stored. These stored quantities already contain the effect of the channel, and only need updating according to the rate of change of channel dynamics, and not the symbol period. During each symbol period, interference is computed from each interfering user to each desired user using current estimates of symbol decisions and the aforementioned interference contributions. The precomputation of the interference contributions, which are valid for a sequence of symbols, allows for extremely low complexity baseband processing in the receiver.

The invention relates to the mobile communication field, disclosing a space frequency coding based multi-antenna transmission diversity method and the system thereof. When the number of transmission antenna is over 2, a coding can be accomplished within an OFDM symbol period and meanwhile a diversity gain similar to STTD+CSD can be obtained. The invention uses space frequency coding to obtain the diversity gain and at the same time introduces phase offset in the frequency-domain to obtain extra frequency diversity similar to CSD through the channel of the frequency-domain data. The phase offset satisfies: the frequency-domain data loaded in the sub-carrier wave set used in SFTD on the same antenna possesses the same phase offset and the frequency-domain data loaded between the sub-carrier wave sets possesses different phase offsets. Moreover, the frequency-domain data loaded on the same sub-carrier wave on different antenna in the same antenna stack possesses different phase offsets.

An OFDM receiver 1 receives an OFDM signal. The OFDM signal is composed of a useful symbol period for transmitting a signal relating to data and a guard interval period for transmitting a signal that is the same as part of the signal transmitted in the useful symbol period. An interference wave cancel circuit 18 cancels a narrow-band interference wave component relating to a narrow-band interference wave from the OFDM signal, and outputs the OFDM signal from which the narrow-band interference wave component has been canceled, as a cancel signal. The correlation detection circuit 20 calculates a correlation between a cancel signal output from the interference wave cancel circuit 18 and a cancel signal which has been delayed by the useful symbol period delay circuit 19 by the useful symbol period.

A mobile communication system 1 according to the present invention comprises base station 30 and mobile station 10. The base station 30 sends a pilot symbol sequence known to the mobile station 10, to the mobile station 10, using a plurality of carriers for downward channels, and performs communication with the mobile station 10 while multiplying the channels by frequencywise same scrambling codes every symbol period. The mobile station 10 is provided with a peak detector 17 for calculating cross correlation allowing for a phase difference of the scrambling codes, between frequencywise pilot symbol sequences received from the base station 30, thereby detecting a radio frame boundary.

The transmit diversity and symbol rate in a wireless mobile system are increased by allocating the complex symbols to be transmitted in accordance with a time-space slot format that incorporates non-orthogonal-based matrices, defined as matrices whose format is such that the product of the matrix and its Hermitian transpose is other than the identity matrix times a real number other than unity. The non-orthogonal-based matrices are indexed by antenna and by symbol period. Copies and complex conjugates (or negative complex conjugates) of the same symbol that are transmitted from different antennas are mutually separated into non-adjacent parts of the slot. Each non-orthogonal-based "space-time" matrix is composed of orthogonal-based matrices, i.e., matrices other than non-orthogonal-based matrices. Preferably, sequences of complex conjugates are time-reversed in the slot.

Techniques are described for wireless communication. A first method includes winning a contention for access to an unlicensed radio frequency spectrum band, and transmitting at least a portion of a channel usage beacon signal (CUBS) over the unlicensed radio frequency spectrum band. The at least portion of the CUBS is transmitted in a number of frequency interlaces of the unlicensed radio frequency spectrum band. A second method includes winning a contention for access to an unlicensed radio frequency spectrum band; determining whether the contention is won within a threshold time before a next symbol period boundary; and transmitting at least a portion of a CUBS over the unlicensed radio frequency spectrum band. The at least portion of the CUBS is transmitted during a preamble including a fractional period of a first symbol period. The at least portion of the CUBS may be based at least in part on the determining.

In a wireless transmitter having a plurality of spatial streams differentiable at a receiver, wherein data is encoded and transmitted over a communication channel with pilot tones to provide the receiver with information about the effects of the communication channel and / or transmitter impairments and / or receiver impairments on the spatial streams transmitted, the benefits can be provided by identifying a plurality of symbol periods within which symbols representing some of the encoded data are to be transmitted, identifying pilot tone values for the plurality of symbol periods, wherein the identified pilot tone values are such that the receiver, when receiving at least some of the pilot tones having the identified pilot tone values, is provided with signals enabling the receiver to characterize the communication channel and / or transmitter impairments and / or receiver impairments to obtain transmit stream diversity gain, and transmitting the symbols and the pilot tones over the plurality of spatial streams for the plurality of symbol periods. In some embodiments, the pilot tones are orthogonal over space and time or over space and time and frequency, while in others they are semi-orthogonal. Pilot tone values might be of a constant amplitude and phase shifted, or might also have amplitude variations wherein at least two pilot tones are nonzero for spatial streams for a given symbol period.

Techniques for managing re-contention on a shared communication medium are disclosed. In order to facilitate re-contending for access to the communication medium, an access point may adjust one or more uplink transmission parameters associated with a triggering condition for invoking a contention timer. In addition or as an alternative, the access point may mute transmission on the communication medium during one or more symbol periods designated for transmission. In addition or as an alternative, the access point may configure a timing advance to create a re-contention gap.