Abstract: An OFDM receiver includes a demodulator for receiving a passband signal having multiple symbols, one or more of the symbols being a reference symbol, and for converting the passband signal to a baseband signal, a CFO compensation circuit for receiving the baseband signal and modifying a phase of the baseband signal in response to a first control signal, a transformation circuit for translating the baseband signal from the CFO compensation circuit into a frequency domain constellation, an equalizer for receiving the frequency domain constellation and modifying the frequency domain constellation based at least in part on the reference symbol, and a CFO estimation circuit coupled between an output of the equalizer and the CFO compensation circuit in a feedback configuration. The CFO estimation circuit is capable of measuring a difference in phase error between multiple symbols received from the equalizer and generating the first control signal, which is representative of the measured phase error difference.

Abstract: The invention relates to a method of canceling noise in a signal generated by discrete multi-tone modulation. The noise is caused primarily by the transient of a transmission channel via which the signal is transmitted. The signal comprises a plurality of symbols each of which is preceded by a cyclic prefix. According to the invention, a plurality of parameters is calculated from the digitized sample values of the signal and the approximate transient of the transmission channel is calculated from said plurality of parameters. To cancel the noise the approximately calculated transient is subtracted from the digitized sample values.

Abstract: An example spread spectrum communication system is provided in which a transmission signal is separated into an I-phase component and a Q-phase component. In a complex spreading portion, spreading is performed by using multipliers and adders together with a sequence pattern of 1 and ?1 appearing alternately. The outputs from the complex spreading portion are modulated in multipliers using pseudo-random sequences PN(k)(x) allotted for individual users. The baseband signal undergoes waveform shaping by roll-off filters and is modulated through a carrier modulator, then sent to a power amplifier, where it is amplified and transmitted via an antenna.

Abstract: Communication systems employing subchannel communication such as OFDM or multicode CDMA have a disadvantage of power variation of the transmitted signal. The present invention provides reduced power variation without compromising performance or bandwidth. Information symbols to be transmitted on the individual subchannel are fed to encoders which map the information symbols into channel symbols by increasing their order. The encoding in response to a forward error correction scheme and includes selection between redundant symbol values to reduce power variation. Preferably the encoder includes a trellis coder jointly encoding the symbols and a compensation data set to reduce power variation.

Abstract: A frequency tracking loop (100) includes: a mixer (122) for correcting frequency offset of an input radio signal that includes bursts of known data; a frequency offset estimator (134), for providing an estimate of frequency offset; a variable bandwidth filter (142), for providing a filtered signal; an oscillator (146) for supplying a second input of the mixer with a signal whose frequency depends on the filtered signal; the frequency tracking loop (100) is adapted to change the bandwidth of the variable bandwidth filter (142) in dependence on at least one characteristic of the currently received burst of known data.

Abstract: A digital transmission method with error correcting coding includes a coding procedure and a decoding procedure in order to correct transmission errors. The coding procedure includes a plurality of elementary coding steps operating in parallel or in series. The decoding procedure is iterative and includes, for each iteration, a plurality of elementary decoding steps which correspond to the plurality of elementary coding steps. Each elementary decoding step generates at least one weighted output information item. A characteristic quantity is generated directly from a set of weighted output information items generated by each elementary decoding step for processing a decoding sequence. A comparison step is adapted to compare the characteristic quantity with a threshold quantity determined by a threshold quantity determination step. An interrupt step interrupts the iterative decoding procedure at the elementary decoding step when the characteristic quantity reaches the threshold quantity.

Abstract: The present invention, generally speaking, provides a digital circuit and method for forming number streams for frequency and/or phase comparison of digital or digitized signals, referred to herein as clock signals, where typically one of the clock signals is a known clock signal and another of the clock signal is an unknown clock signal. The unknown clock signal may be derived from a communications signal, for example. The rate of the unknown clock signal may exceed the rate of the known clock signal. In an exemplary embodiment, an “alias” value (e.g., an integer 1, 2, 3, etc.) is applied to the circuit as an indication of the expected frequency range of the unknown clock signal. The number stream is formed accordingly.

Abstract: A method for reliably transmitting signaling information is provided. One type of signaling information is transmitted over a primary control channel. The signaling information that is to be transmitted over the primary control channel is defined as a set of particular information. Other signaling information are conveyed over a secondary control channel. Prior to transmission, the information to be conveyed over the secondary channel is scrambled in accordance with a particular scrambling procedure that indicates the information that is to be sent over the primary control channel. The scrambling is thus used to encode the information content of the primary control channel into the information of the secondary control channel thereby further protecting the integrity of the information being conveyed over both control channels.

Abstract: A method and circuit arrangement for transmission of messages in which a number of L components (m0, . . . , mL-1) are coded by means of orthogonal functions to a signal (s(t)), and in which approximations of hermitic functions are used as orthogonal functions. A Fourier transform is performed on the received signal and subsequently decoded with the aid of the orthogonal functions.

Abstract: A transmitter for sending signals over wireless channels and a method of sending signals over wireless channels are described. The transmitter and the method are used to determine a transfer characteristic of an amplifier (8) in the transmitter. Test signals are input at preset times into OFDM signals to be transmitted, and then test signals amplified by the amplifier (8) are compared with test signals buffered in a measurement module (12) to determine the transfer characteristic of the amplifier (8). This transfer characteristic of the amplifier (8) is used by a predistorter (4) to predistort the signals according to this transfer characteristic. The test signal generated by a signal generator (13) is input into a synchronization symbol, with the amplitude of the test signal being increased incrementally or being large enough to determine the transfer properties of the amplifier (8). The test signal has an envelope which is not dependent on time.

Abstract: A convolutional encoder (112) comprises a controller (201), having a transmission rate (e.g. frame rate) as an input. The controller (201) initializes the encoder (112) to an initial state based on a transmission rate currently being utilized. When decoding, a decoder (300) utilizes a Trellis diagram having an initial and final state based upon the frame rate.

Abstract: A method of transmitting a data bit stream on a multi-carrier transmission system is provided. The steps include estimating a signal to noise ratio for each carrier for a known transmit power for each carrier, allocating a quantity of bits for each carrier within limits imposed by a target bit error rate and the estimated signal to noise ratio, computing a total excess power available for a current allocation of bits, computing additional power that would be required by each carrier to carry additional bits, and allocating the total excess power based on the computation of additional power required by each carrier to carry additional bits. The computation of additional power needed may be performed by computing the additional gain necessary to carry additional bits or by computing the additional excess power necessary to carry additional bits.

Abstract: A multiplier device for multiplying one of a discrete set of digital level values with a filter coefficient in a filter device implemented in a decision feedback equalizer including (i) a decoder device for receiving a discrete digital level value to be multiplied and for generating control signals according to the digital level value, (ii) an inverter circuit providing two parallel operations, each operation including multiplying the determined number by either +1/?1 in accordance with the control signals for generating two intermediate results, (iii) a multiplier circuit receiving the two intermediate results and providing respective parallel operations for multiplying a corresponding intermediate result by +1 or zero (0) in accordance with a control signal and generating further intermediate results, (iv) a logic circuit for shifting bits of one further intermediate result to effect a multiplication of one of the further intermediate output result with a discrete digital level value different than any of t

Abstract: Frame configuration determination section 101 judges a communication situation based on the transmission path information indicating the level of fluctuations of the transmission path due to fading and data transmission speed information indicating the transmission speed of the transmission data based on the level of the reception signal and determines the interval of inserting a known pilot symbol and the modulation system of a transmission digital signal. Quadrature baseband modulation section 102 modulates the transmission digital signal to a quadrature baseband signal according to the modulation system indicated from frame configuration determination section 101. Pilot symbol generation section 103 generates a pilot symbol known between the transmitting and receiving sides. Frame configuration section 104 inserts the known pilot symbol output from pilot symbol generation section 103 at the insertion interval instructed from frame configuration determination section 101 to configure a frame.

Abstract: A method of determining a start of a transmitted frame at a receiver on a frame-based communications network. A received transmitted frame is filtered using filter coefficients matched to a preamble symbol sequence to provide a correlation sequence. The correlation sequence is low-pass filtered and delayed to provide a delayed low-pass filtered correlation signal. The delayed low-pass filtered correlation signal is compared with the low-pass filtered correlation signal and a fixed predetermined threshold to provide a correlation difference indicator. Energy of the received transmitted frame is detected and the energy is low-pass filtered to provide a low-pass filtered energy signal. The low-pass filtered correlation signal is compared with the low-pass filtered energy signal to provide a correlation peak indicator. A logical-AND of the correlation difference indicator and the correlation peak indicator is formed to determine a match/no match comparison indicative of the start of a transmitted frame.

Abstract: A method and apparatus provide coarse frequency synchronization compensating for a carrier frequency deviation from an oscillator frequency in a demodulation system capable of demodulating a signal having a frame structure with at least one useful symbol and a reference symbol which is an amplitude-modulated sequence. A received and down-converted signal undergoes amplitude-demodulation to generate an envelope that is correlated with a predetermined reference pattern to determine the carrier frequency deviation. Finally, the oscillator frequency is controlled based on the carrier frequency deviation. The reference symbol may comprise two identical sequences. In this case, the envelope obtained by the amplitude-demodulation has two portions which are based on the identical sequences. One of the portions of the envelope is correlated with the other one of the portions in order to determine the carrier frequency deviation.

Abstract: A correlator which detects correlation for data having a certain length includes a plurality of sub-correlators, each of the sub-correlators having a length equal to a divisor of the certain length and each of the sub-correlators having such a length that a product of all lengths of the sub-correlators is equal to the certain length. A correlation value output from one of the sub-correlators is input into a sub-correlator located immediately downstream of one of the sub-correlators.

Abstract: A variable-gain digital filter includes a selector and multiplier arranged inside the digital filter for regulating gain whereby the number of bits of filter input is X, the number of flip-flops inside the filter is X×n bits, and a (Y×n bit) reduction in the number of flip-flops is enabled. The gain regulation circuit incorporated within the digital filter enables a reduction in circuit scale.

Abstract: A system for providing an accurate interference value signal received over a channel and transmitted by an external transceiver. The system includes a first receiver section for receiving the signal, which has a desired signal component and an interference component. A signal extracting circuit extracts an estimate of the desired signal component from the received signal. A noise estimation circuit provides the accurate interference value based on the estimate of the desired signal component and the received signal. A look-up table transforms the accurate noise and/or interference value to a normalization factor. A carrier signal-to interference ratio circuit employs the normalization factor and the received signal to compute an accurate carrier signal-to-interference ratio estimate. Path-combining circuitry generates optimal path-combining weights based on the received signal and the normalization factor.

Abstract: A new method makes the most efficient use of the scarce spectral bandwidth in a wireless discrete multitone spread spectrum communications system by updating the spectral and/or spatial spreading weights at a rate that is determined by the measured quality of the link. Low quality links require more frequent updates of the spreading weights than do higher quality links. Spreading weights and despreading weights for a station are adaptively updated, depending on the error in received signals. If the error value is less than a threshold error value, then the method maintains the existing spreading weights as the current spreading weights to apply to an outgoing data signal. Alternately, if the error value is greater than the threshold error value, then the method adaptively calculates updated despreading weights at the base station from the first spread signal and calculates updated spreading weights as the current spreading weights from the updated despreading weights to apply to the outgoing data signal.