1785 results about "Cyclic prefix" patented technology

A method and apparatus provides OFDM signal compression for transfer over serial data links in a base transceiver system (BTS) of a wireless communication network. For the uplink, an RF unit of the BTS applies OFDM cyclic prefix removal and OFDM frequency transformation of the baseband signal samples followed by frequency domain compression of the baseband signal samples, resulting from analog to digital conversion of received analog signals followed by digital downconversion, forming compressed coefficients. After transfer over the serial data link, the baseband processor applies frequency domain decompression to the compressed coefficients prior to further signal processing. For the downlink, the RF unit performs frequency domain decompression of the compressed coefficients and applies OFDM inverse frequency transformation of the decompressed coefficients and OFDM cyclic prefix insertion prior to digital upconversion and digital to analog conversion, generating the analog signal for transmission over the antenna.

Embodiments are provided for supporting variable sub-carrier spacing and symbol duration for transmitting OFDM or other waveform symbols and associated cyclic prefixes. The symbol duration includes the useful symbol length and its associated cyclic prefix length. The variable sub-carrier spacing and symbol duration is determined via parameters indicating the sub-carrier spacing, useful symbol length, and cyclic prefix length. An embodiment method, by a network or a network controller, includes establishing a plurality of multiple access block (MAB) types defining different combinations of sub-carrier spacing and symbol duration for waveform transmissions. The method further includes partitioning a frequency and time plane of a carrier spectrum band into a plurality of MAB regions comprising frequency-time slots for the waveform transmissions. The MAB types are then selected for the MAB regions, wherein one MAB type is assigned to one corresponding MAB region.

Disclosed is a method, a computer program product and a device that includes a receiver for receiving a downlink signal transmitted into a cell. The receiver is operable to obtain time, carrier frequency and cell-specific preamble synchronization to the received signal and includes a plurality of synchronization units that include a first detector to detect a frame boundary using preamble delay correlation; a second detector to detect the frame boundary with greater precision using a conjugate symmetry property over a region identified by the first detector; a cyclic prefix correlator to resolve symbol boundary repetition; an estimator, using the cyclic prefix, to estimate and correct a fractional carrier frequency offset; an operator to perform a Fast Fourier Transform of an identified preamble symbol and a frequency domain cross-correlator to identify cell-specific preamble sequences and an integer frequency offset in sub-carrier spacing. The transmitted signal may be a downlink signal transmitted into the cell from a base station that is compatible with IEEE 802.16e (WiMAX).

Signal construction, detection and estimation techniques for use in uplink timing synchronization and access control in an orthogonal frequency division multiplexed (OFDM) wireless system or other type of wireless communication system. In accordance with an illustrative embodiment of the invention, timing and access signals to be transmitted in designated timing and access intervals are constructed from orthogonal multitone signals. The multitone signals may be similar to multitone signals used in OFDM data transmission, except that a cyclic prefix associated with reception of the signals in a base station is extended to cover the timing errors of mobile stations not yet synchronized. The invention also provides design techniques which optimize the time resolvability and peak-to-average ratio of the multitone signals, an efficient fast Fourier transform (FFT) based technique for maximum likelihood timing estimation, and a robust linear filtering technique for averaging timing estimates from different synchronizations.

In an OFDMA-based cellular system, a frame of a downlink signal includes a common slot and traffic slots. The common slot includes a synchronization preamble and a cell search preamble. The synchronization preamble has a structure for synchronizing time and frequency, and the cell search preamble has a cell search structure. The traffic slot includes pilot symbols provided on the time and frequency axes. A cyclic prefix is used to estimate initial symbol synchronization, and the initial symbol synchronization and the synchronization preamble are used to synchronize the frame. The synchronization frame and the cell search preamble are used to estimate time and frequency synchronization. The cell search preamble is used to search cells. When the initial synchronization is performed, the cyclic prefix is used to track the frequency, the synchronization preamble is used to track symbol synchronization, and the cell search preamble is used to track fine frequency synchronization.

A precoded orthogonal frequency division multiplexer (OFDM) system that improves the preformance of OFDM systems for spectral null channels, and size K×1 vector OFDM systems that reduce the cyclic prefix length by K times compared to conventional OFDM systems. The precoding scheme comprises inserting one or more zeros between each of the two sets of K consecutive information symbols, although it can be generalized to a general form. This precoding scheme removes the spectral nulls of an ISI channel without knowing the ISI channel. When no zero is inserts between each of the two sets of K consecutive information symbols and only K consecutive symbols are blocked together, vector OFDM systems are obtained. The bit error rate performance of the vector OFDM systems of the present invention is much improved over conventional OFDM systems.

An OFDM/OFDMA frame structure technology for communication systems is disclosed. The OFDM/OFDMA frame structure technology comprises a variable length sub-frame structure with efficiently sized cyclic prefixes and efficient transition gap durations operable to effectively utilize OFDM/OFDMA bandwidth. Furthermore, the frame structure provides compatibility with multiple wireless communication systems. An uplink frame structure and a downlink frame structure are provided.

Access to a wireless communication system (100) by a subscriber station (101-103) is facilitated by selecting (705) an access sequence from a set of sequences that have been identified to have a low average of peak-to-average-power-ratios of access signals generated by the set of sequences and also based on a good cross-correlation of the access signals; forming (714) the access waveform by generating an access signal using the access sequence and appending in the time domain a cyclic prefix to the access signal; and transmitting (715) the access waveform. In some implementations, the access waveform is cyclically shifted (820) before the cyclic prefix is appended, and in some implementations, the signal is transmitted (710, 810) in a randomly selected sub-band of an access 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 method and system for communication of information in OFDM format are disclosed. The method employs multi-symbol encapsulation (MSE), wherein multiple OFDM symbols are grouped together in cyclic frames having a single cyclic guard portion, for example a cyclic prefix, with multiple OFDM symbols sandwiched between each two consecutive cyclic guard portions. All OFDM symbols of one frame are equalized together at the receiver in a frequency domain using a single DFT/IDFT operation sequence. Embodiments of the MSE OFDM system are disclosed enabling high bandwidth efficiency, high tolerance to carrier frequency offset and low peak-to-average power ratio.

A method for transmitting/processing data in a wireless communication system, and a transmitter are disclosed. A method processing method for data transmission at a transmitting side of a wireless communication system employing multiple carriers comprises performing a symbol mapping process on a binary data sequence, and generating a symbol sequence, converting the symbol sequence into a time-domain symbol using a plurality of sub-carriers having a variable sub-carrier spacing therebetween, and adding a cyclic prefix to the time-domain symbol.

In a wireless telecommunications network, a Code Division Multiple Access (CDMA) scheme is applied to data to encode it. The encoded data transmitted in the uplink using an Orthogonal Frequency Division Multiplexing (OFDM) frame structure including a cyclic prefix (CP). The CDMA encoded data may be time multiplexed with Single Carrier-Frequency Division Multiple Access (SC-FDMA) transmissions. The CDMA transmissions may be used for relatively small payloads, such as those associated with voice traffic and control signals, and the SC-FDMA transmissions used for higher date rate transmissions. This enables autonomous transmission, without scheduling, for smaller payloads. A transmitter includes a selector 3 for performing time multiplexing in the uplink, the required mode being indicated by the Hybrid Automatic Repeat Request (HARQ) ID. A first branch 1 carries SC-FDMA data and a second branch 2 carries data to be transmitted as a CDMA scheme. A CAZAC code may be used in encoding the CDMA data.

According to various embodiments of the disclosed method and apparatus, nodes on a network are programmed to generate a probe transmission in response to a request from the node that will be receiving the probe. The receiving node may generate a probe request that specifies a plurality of parameters, such as a modulation profile for the probe; the payload content of the probe; the number of times to transmit the probe; a number of symbols for the payload of the probe; a preamble type for the probe; a cyclic-prefix length for the payload of the probe; a transmit power for the probe; and a transmit power scaling factor for the payload of the probe.

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.

The present invention relates to a method and an apparatus for transmitting a reference signal by a base station in a wireless communication system. The base station generates a channel state information (CSI) reference signal (RS) for each of a plurality of layers, performs mapping the plurality of CSI-RSs to a resource element set constituted by a plurality of resource elements(REs) in a subframe and transmits the subframe with the plurality of mapped CSI-RSs. The plurality of resource elements constituting the resource element set are resource elements that are arranged with constant subcarrier spacing in two neighboring orthogonal frequency division multiplexing (OFDM) symbols, and the subframe has an extended cyclic prefix (CP) structure including 12 OFDM symbols.

A method for transmitting high rate data within a multiple input multiple output (MIMO) wireless local area network (WLAN) begins by determining a data transmission rate. The method continues by, when the data transmission rate is between a first data rate and a second data rate, enabling two transmission paths. The method continues by, for each of the two transmission paths, determining at least one of: level of constellation, number of data subcarriers, rate code, and cyclic prefix duration.

A transceiver includes a receive unit and a transmit unit. The receive unit is adapted to receive a prefix width parameter. The transmit unit includes a modulator and a cyclic prefix unit. The modulator is adapted to receive digital data and generate an output symbol based on the digital data. The output symbol includes a plurality of waveform samples. The cyclic prefix unit is adapted to receive the output symbol and the prefix width parameter. The cyclic prefix unit generate a cyclic prefix based on a subset of the plurality of waveform samples and prepends the cyclic prefix to the output symbol to generate a transmit symbol. The size of the subset is based on the prefix width parameter. A method for adjusting the symbol rate of a transceiver includes receiving a prefix width parameter and receiving digital data. An output symbol is generated based on the digital data. The output symbol includes a plurality of waveform samples. A cyclic prefix is generated based on a subset of the plurality of waveform samples. The cyclic prefix is prepended to the output symbol to generate a transmit symbol. The size of the subset is based on the prefix width parameter.

A coherent optical receiver for a data-frame format in which a data frame has two or more pilot-symbol blocks, each having a cyclic prefix or suffix, and one or more payload-symbol blocks, each of which is concatenated with at least one adjacent block without a guard interval between them. The receiver uses optical signals corresponding to the pilot-symbol blocks to perform data-frame synchronization, frequency-offset correction, and channel-estimation procedures, which are robust even in the presence of certain transmission impairments. The receiver applies block-overlap processing with a sliding window to recover the payload data in a manner that substantially cancels the adverse effects of inter-block interference caused by the absence of guard intervals in the payload portion of the data frame. In one embodiment, the receiver performs channel-estimation and block-overlap processing for polarization-division-multiplexed signals in a manner that enables a combined, intertwined application of channel-response-compensation and polarization-demultiplexing procedures.

A system and method for effectively providing an adaptive modulation scheme and known-cyclic prefix (CP) technology in an orthogonal frequency division multiplexing (OFDM) communication system. An OFDM transmission system variably generates a known CP while considering a channel state. Pilot subcarrier position information for generating the known CP is sent to a transmitter. Pilot subcarriers are selected on the basis of a channel state of an OFDM symbol through which data is transmitted and the known CP is generated, such that data transmission is provided efficiently.

The present invention relates to a transmitting apparatus of an OFDMA system and a method thereof. The transmitting apparatus includes an encoder for modulating data to be transmitted into data or a preamble by using a desired modulation scheme; an S/P converter for converting serial data output from the encoder to parallel data; a preamble or pilot generator for generating a pilot or preamble; a multiplexer for multiplexing the data or preamble output from the preamble or pilot generator and the parallel data; an antenna selection controller for dividing an entire band of a signal output from the multiplexer into groups formed of neighboring symbols in time domain and neighboring subcarriers in frequency domain, and selecting a transmit antenna for each group; an IFFT unit for turning off subcarriers in groups selected by the antenna selection controller and subcarriers in unselected groups by the antenna selection controller and performing IFFT; for each antenna, a P/S converter for converting parallel signals transmitted from the IFFT unit into serial signals and inserting a cyclic prefix; and for each antenna, a D/A converter and filter for converting a digital signal transmitted from the P/S into an analog signal and filtering the analog signal, and transmitting the filtered analog signal through an antenna of an R/F end. Accordingly, when a transmitting end does not know a channel state of a transmit antenna, a transmit antenna is selected for an allocation unit and data is transmitted through the selected transmit antenna when a transmitting end of an OFDMA system using multiple antennas does not know a channel state, and accordingly a diversity gain can be acquired without making any changes in allocation of subcarriers according to the number of antennas, a transmission structure of a pilot of the transmitting end, an allocation structure of the transmitting end, and a receiving end. In addition, when the transmitting end does know the channel state, an antenna having the best channel state is selected for each group, and accordingly, performance degradation due to feedback delay of channel state information and inter-antenna interference due to an increase of mobility of the terminal can be prevented.