443 results about "Multi carrier modulation" patented technology

In a multicarrier modulation communication system, subcarriers are allocated to a plurality of users using a plurality of sets of sequential subcarriers. The plurality of sets of sequential subcarriers may be allocated for transmitting information to the plurality of users or for transmitting information from the plurality of users. A multicarrier modulation communication system and the multicarrier modulation communications device is also discussed.

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 satellite system employing time diversity and a single frequency network of terrestrial re-radiation stations is provided wherein each terrestrial re-radiation station inserts a delay into a terrestrial signal. The delay allows the time of arrival of the early time diversity signal at the center of terrestrial coverage to coincide with the arrival of the corresponding late time diversity signal, thereby improving hand-off between terrestrial and satellite signals at a receiver. The delay also adjusts for distance differences between each terrestrial re-radiation station and the satellite and between each station and the center of the terrestrial coverage region. This adjustment optimizes the TDM-MCM reception by synchronizing at the center of the SFN the phase of the MCM signals re-radiated from the re-radiating stations of the SFN. The delay also compensates for the processing delay encountered when converting a satellite LOS TDM stream into a multicarrier modulated stream for transporting the satellite LOS TDM stream to user receivers and for the diversity delay between the early and late signals.

A system for compensating for in-phase and quadrature (I/Q) imbalances for multiple antenna systems (MAS) with multi-user (MU) transmissions (defined with the acronym MU-MAS), such as distributed-input distributed-output (DIDO) communication systems, comprising multicarrier modulation, such as orthogonal frequency division multiplexing (OFDM). For example, one embodiment of the system comprises one or more coding modulation units to encode and modulate information bits for each of a plurality of wireless client devices to produce encoded and modulated information bits; one or more mapping units to map the encoded and modulated information bits to complex symbols; and a MU-MAS or DIDO IQ-aware precoding unit to exploit channel state information obtained through feedback from the wireless client devices to compute MU-MAS or DIDO IQ-aware precoding weights, the MU-MAS or DIDO IQ-aware preceding unit precoding the complex symbols obtained from the mapping units using the weights to pre-cancel interference due to I/Q gain and phase imbalances and/or inter-user interference.

The invention provides a new approach which is better suited to FFT design as applied to multicarrier modulation systems such as OFDM. The signals are scaled so that overflow, rather than being completely avoided, occurs with low probability throughout the IFFT and FFT structures. The size of the error that results from an overflow depends on how overflow is handled in the DSP. To minimize the degradation, overflow should result in saturation of the value at the maximum positive or negative value option. This is equivalent to clipping the signal. Using the new technique, signals within the FFT structure are scaled to balance the effect of clipping and round-off. Clipping may result in comparatively large errors in a few signal values but because of the spreading effect of the FFT and because OFDM systems typically include error coding/correction, system performance depends on the total error or, in other words the total noise power, across all of the FFT outputs rather than on any individual value.

A broadband local area data network uses coaxial cable wiring for interconnection of terminal devices. Orthogonal frequency division multiplexing (OFDM) with bit loading is used to overcome channel impairments and provide a path for terminal devices to transmit to and receive from other terminal devices. Probe messages are sent between devices to characterize the communication channel and determine optimum bit loading. The data network shares the cable spectrum with other services and uses frequency bands not used by other services. Adaptive power control can be used to maintain signal to noise ratio in a communication between terminal devices. Frequency coordination can be used to avoid interference between the LAN communications and other services transmitted on the cable.

Methods and systems provide an efficient power save mode for multi carrier modems, such as DMT based ADSL and VDSL modems. Fast transitions from power save mode to full operational mode occur, without the overhead of transmitting large quantities of configuration information between the transmitter and receiver. Signal constellation size changes occurring while operating in power save mode to continue to apply once full operational mode is resumed. Multiple power save modes are enabled, each having a different level of power dissipation and crosstalk, both far end crosstalk and near end crosstalk. Power dissipation and crosstalk can thus be graduated on a line, according to a user-requested bit rate.

In an MCM communication system in which one frame includes at least one pilot symbol of a predetermined length and at least one data symbol of the predetermined length, to transmit the pilot symbol for time synchronization and frequency synchronization, a first pilot sequence of a length shorter than the predetermined length is generated, and a second pilot sequence of a length shorter than the predetermined length is generated. Here, the second pilot sequence is different from the first pilot sequence. The first and second pilot sequences are repeated a predetermined number of times. The pilot symbol is generated by combining the repeated first and second pilot sequences, and then transmitted.

The method of transmitting data in the form of symbols sent over an electromagnetic channel is characterized in that a measurement of significance is attributed to each group of data to be transmitted, in that the transmission reliability of the carriers is estimated dynamically, and in that the most significant data are sent over the most reliable carriers at each instant, the other data being sent over the carriers of decreasing reliability, in decreasing order of significance of the data.

A resource block (RB)-based multicarrier modulation (MCM) transmitter and receiver structure for spectral agile systems are disclosed. The transmitter and the receiver are capable of sharing opportunistically available and non-contiguous channels with other users. The RB-MCM partitions the available spectrum, contiguous or non-contiguous, into multiple RBs (same or different sizes), applies a baseband MCM or single carrier modulation, or coded single carrier or multicarrier schemes in each RB with a type of spectral leakage reduction technique, and applies RB modulation for each RB to modulate the signal from baseband to the frequency band of that RB. At the receiver, the received signal may be filtered and RB demodulation may be applied to put each RB signal in baseband and a baseband multicarrier or single carrier or coded single carrier or coded multicarrier demodulation may be applied to each RB signal. Different RBs may use different modulation schemes.

A receiver for receiving a multi-carrier modulated symbol is arranged to suppress a burst noise signal which may have been induced in the symbol. The symbol includes a plurality of pilot carriers as well as a plurality of data bearing carriers. The receiver comprises a burst noise detection processor operable to detect the temporal position of the burst noise signal which may have corrupted the symbol within a period occupied by the symbol, and a channel estimation processor operable to generate a decimated noise signal corresponding to the burst noise, from the recovered pilot carriers. An inverse Fourier transform of the decimated noise signal provides a plurality of estimated versions of the burst noise signal. A noise signal processor is operable to generate an estimate of the burst noise signal by identifying one of the plurality of estimated burst noise versions at the detected temporal location of the burst noise signal. The noise signal processor may be operable to set the signal samples other than the identified estimate of the burst noise signal to zero and to perform a Fourier transform, to provide a frequency domain version of the burst noise signal, thereby interpolating the decimated noise signal. The frequency domain noise signal estimate may be cancelled from the symbol by a noise cancellation processor in the frequency domain, before data is recovered from the symbol. The receiver finds application for Digital Video Broadcasting in which COFDM is employed.

A mixed waveform configuration for wireless communications including a first portion that is modulated according to a single-carrier modulation scheme and a second portion that is modulated according to a multi-carrier modulation scheme. The waveform is specified so that a channel impulse response (CIR) estimate obtainable from the first portion is reusable for acquisition of the second portion. The first portion includes a preamble and header and the second portion typically incorporates the payload.

A modem (10) for transmitting a discrete multitone modulated (DMT) signal over a communications channel (H) is disclosed. In the encoding of an input bitstream, unloaded subchannels in the DMT spectrum are assigned signal values so that a trailing portion of each block or frame of the resulting datastream are forced to a known value, for example zero. The known-valued trailing portion of each block provides the effect of a cyclic prefix, without necessitating the prepending of an actual cyclic prefix and incurring the corresponding data rate loss; alternatively, the effect of a cyclic prefix can be augmented by the forcing of the trailing portion of the blocks to known values.

An object is to generate a pilot signal for estimating transmission characteristic of a transmission channel which is suitable for the OFDM/OQAM multicarrier modulation. A phase reference pilot symbol of which a modulation amplitude is suppressed to zero, and an amplitude reference pilot signal obtained through modulation performed by using an amplitude known to a reception end are transmitted from a transmission end, and the transmission characteristic of the transmission channel is estimated and compensated by using the phase reference pilot signal and the amplitude reference pilot signal at the reception end. Thus, it is possible to simplify frame generation process performed at the transmission end, and reduce transmission power for the phase reference pilot signal.

For one aspect of the invention, a method is described for mitigating power spectral density irregularities in a multi-carrier modulation environment. The method involves identifying at least one carrier of a plurality of carriers that is in a non-data bearing state. Thereafter, that carrier is modulated with random data.

The invention provides a method for reducing peak-to-average power ratio of a filter bank multi-carrier system, and relates to the field of multi-carrier modulation method. The method comprises the following steps: the analysis of main factors affecting the peak-average power ratio of the FBMC system through the establishment of the FBMC system model and the definition of the peak-average power ratio of the FBMC system, the construction of an FSLM method and the check analysis of Monte Carlo simulation experiments, and is characterized in that: a frame selection mapping method is called as the FSLM method, is a signal non-distortion technique, selects sequences for FBMC signal frames and design frames, constructs FBMC carrier frame signals which have the same information and are independent from one another according to the frame selection sequences, and then selects a frame of symbols allowing the time domain signals to have minimum PAPR, and the method can reduce the PAPR of the FBMC system without distortion, and effectively reduce the PAPR of the FBMC system. The invention can ensure that the requirements of the low peak-to-average power ratio of the system, and further optimize the performance of the system. In practice, the invention can provide certain reference value for the application of Beyond3G, 4G, 802.16 and other communications systems.

An improved multicarrier modulation system and method, which has the advantages of both isotropic orthogonal transfer algorithm orthogonal frequency division multiplexing (IOTA OFDM) and scalable advanced modulation (SAM), is introduced. The invention is root raised cosine (RRC) OFDM using the most spectrally efficient RRC filter without sacrificing the compact subchannel spacing of OFDM. The invention further provides an adjacent channel interference (ACI) suppression scheme and a modified RRC for better suppressing ACI of RRC OFDM. The ACI suppression scheme can also be applied to SAM with the modified RRC and to IOTA OFDM with a modified IOTA. The invention greatly improves a major problem of conventional OFDM namely ACI due to the use of a wide subchannel filter. Thus, the invention allows OFDM to meet even the strictest ACI requirements, which was not possible by using a conventional raised cosine windowing method.

The present invention concerns a method and a device for the synchronization of a transmitter (1) and at least one receiver (3) in multi-carrier modulated communication systems in which FFT technology is used for the modulation and demodulation of data transmitted between the transmitter (1) and the receiver (3). According to the invention the transmitter (1) transmits synchronization symbols (15, 16) as training symbols (15, 16) at the beginning of a transmission, until a result is obtained that may indicate where a synchronization symbol starts. The result is used for the adjustment of the symbol rate in the receiver (3). Data symbols may then be transmitted after the synchronization symbols (15, 16).

A communication system includes a receiver having a variable gain module and a baseband processor. The baseband processor measures the power of the signal received and derives a variable gain control setting that is inversely proportional to the power of that signal and sends the variable gain control setting to the variable gain module. The baseband processor generates a channel quality metric that is equivalent to the normalized geometric mean of the squared magnitudes of the gain estimation, divided by the total noise-plus-interference power.

A multiple access system for a network using multicarrier modulation. To contend for service a subscriber station selects an upcoming frame in whose contention window it will contend, selects a contention slot within the window, selects a contention channel corresponding to a subset of the carriers used by the network, and imposes a contention code differentially on the carriers in the contention channel.

Pilot and data transmission schemes for multi-antenna communication systems utilizing multi-carrier modulation are provided. Subband multiplexing is used to avoid interference resulting from transmitting multiple signals simultaneously from multiple antennas. M usable subbands are initially arranged to form multiple groups of subbands, with each group including a different subset of the usable subbands. Each of T transmit antennas is then assigned one or possibly more subband groups for pilot transmission and typically one subband group for data transmission. Pilot and data may then be transmitted from each antenna on the subbands assigned to that antenna for pilot and data transmission. For each transmit antenna, the transmit power for each assigned subband may be scaled higher such that all of the total transmit power available for the antenna is used for transmission. Pilot and/or data may be transmitted simultaneously from all T antennas on all usable subbands without causing mutual interference.