Abstract: A receiver, an integrated circuit chip and a method are provided for estimating the power of a digitally modulated signal received by the receiver in a communication system. The method comprises determining in-phase and quadrature-phase values of a phase constellation system relating to the received signal, calculating at least one modified in-phase value and at least one modified quadrature-phase value relating to the phase constellation system rotated by a predetermined angle, and determining absolute values of the in-phase and quadrature-phase values and the modified in-phase and quadrature-phase values. The method further comprises identifying the maximum of the absolute values, and determining a power estimate of the received signal based on the identified maximum value. The provided technique may allow for estimating the power of a digitally modulated signal in a simple and less complex implementation.

Abstract: A mobile communication system is provided for use in communication. The mobile communication system may include a radio control station (CS), a base station (BS), and a mobile station (MS). The BS is connected to the CS, and the MS may perform, with the BS, data communication in a parallel combinatory spread-spectrum (PCSS) scheme. The CS comprises at least a storage storing a plurality of communication parameters corresponding to the BS and a transmitter transmitting a determined parameter to the BS. The BS comprises a receiver receiving a determined parameter from the CS, a determining unit for determining transmitting power and a transmitter transmitting data generated by using the determined parameter and performing spreading processing to the MS. Further, the MS comprises a reproduction unit reproducing data by using the determined parameter and performing despreading processing.

Abstract: An ultra wide bandwidth, high speed, spread spectrum communications system uses short wavelets of electromagnetic energy to transmit information through objects such as walls or earth. The communication system uses baseband codes formed from time shifted and inverted wavelets to encode data on a RF signal. Typical wavelet pulse durations are on the order of 100 to 1000 picoseconds with a bandwidth of approximately 8 GHz to 1 GHz, respectively. The combination of short duration wavelets and encoding techniques are used to spread the signal energy over a an ultra wide frequency band such that the energy is not concentrated in any particular narrow band (e.g. VHF: 30-300 MHz or UHF: 300-1000 MHz) and is not detected by conventional narrow band receivers so it does not interfere with those communication systems.

Abstract: A device of dynamic communication of information allows, on the average, non-integer bits per symbol transmission, using a compact code set or a partial response decoding receiver. A stream of selectable predetermined integer bits, e.g., k or k+1 data bits, is grouped into a selectable integer number of bit vectors which then are mapped onto corresponding signal constellations forming transmission symbols. Two or more symbols can be grouped and further encoded, so that a symbol is spread across the two or more symbols being communicated. Sequence estimation using, for example, maximum likelihood techniques, as informed by noise estimates relative to the received signal. Each branch metric in computing the path metric of a considered sequence at the receiver is weighted by the inverse of the noise power. It is desirable that the constellation selection, sequence estimation and noise estimation be performed continuously and dynamically.

Abstract: The present invention involves a method for transmitting data using an orthogonal frequency division multiplex (OFDM) transmission system, such as over a terrestrial network used in satellite digital audio radio. A OFDM signal is generated based on first input data. A variation is introduced in the OFDM signal based on second input data to generate a modified OFDM signal which is transmitted. The modified OFDM signal is decoded by performing a demodulation of the modified OFDM signal then a first and second detection to obtain the first input data and the second input data. The introduction of a variance may include introducing an additional phase offset across adjacent OFDM sub-carriers, across adjacent OFDM symbols, an additional phase offset in the OFDM signal, an additional amplitude offset in the OFDM signal, an additional amplitude augmentation in the OFDM signal, and/or a second variation in the first OFDM signal based on third input data.

Abstract: A digital communication system (20) in which a signal constellation (30) of a dimensionality of at least four is used, with distance properties chosen to reduce the bit error rate compared to that of digital communication systems using signal constellations of half the dimensionality. A symbol generator (21) uses the higher dimensional signal constellation (30), or any orthogonal transformation of the higher dimensional signal constellation (30), to translate a bit stream into a stream of higher dimensional symbols, which it then provides to a modulator (22). The modulator (22) transmits each higher dimensional symbol in at least two parts, using a modulation scheme according to the prior art, such as QAM or QPSK.

Abstract: An impairment compensation sequence for use in a communications system susceptible to one or more potential impairments each periodic in an integer number of symbols includes N phases, wherein N is selected such that each potential impairment, if present, is periodic therein, and a sequence of symbols, the sequence organized to place at least one instance of each symbol from a predetermined set of symbols in each phase to allow detection of the potential impairments in each of the N phases. The potential impairments may include robbed-bit signaling and padding. Using estimates prepared based on such an impairment compensation sequence, individual phase intervals may be grouped according to similarity of apparent aggregate effect of the impairments thereon without identification of individual impairments active in the particular phases. Constellation points may then be assigned based on group characteristics corresponding to phase intervals.

Abstract: A transmitting/receiving apparatus includes a packet construction section for dividing continuous data into a plurality of subpackets, and constructing a packet by concatenating the plurality of subpackets; a modulation transmission section for modulating the constructed packet, and transmitting the modulated packet to another apparatus; a training session execution section for checking channel conditions, when a predetermined condition is satisfied, and changing a modulation rule; and a subpacket transmission confirmation section for confirming whether or not a subpacket included in the transmitted packet is transmitted successfully to the transmission destination apparatus.

Abstract: An orthogonal frequency division multiplexed signal transmitting apparatus executes a time-division multiplexing process that inserts a reference signal at a predetermined interval based on reference signal position information into an information signal to be transmitted. The transmitting apparatus generates an orthogonal frequency division multiplexed signal by digital-modulating the time-division multiplexed signal to radiate into a spatial transmission line. An orthogonal frequency division multiplexed signal receiving apparatus receives the signal from the transmitting apparatus to get the reference signal by demodulating the signal.

Abstract: A frequency and symbol timing synchronization apparatus for orthogonal frequency division multiplexed (OFDM) signals, and a method performed by the apparatus are provided. This apparatus includes an autocorrelation unit, a comparator, a peak flat detector, a frequency offset estimator, a frequency offset compensation unit, a cross correlation unit and a symbol timing synchronization unit. The autocorrelation unit receives data including a synchronizing symbol made up of at least three identical synchronizing signals, delays the received data by a predetermined delay amount, performs autocorrelation between the received data and the delayed data, normalizes an autocorrelated value, and outputs a normalized autocorrelated value. The comparator compares the normalized autocorrelated value with a predetermined threshold value. The peak flat detector detects as a flat section a section where the normalized autocorrelated value is equal to or greater than the threshold value.

Abstract: A receiving apparatus includes a demodulation circuit which estimates a transfer function of a reception signal in which a time domain has been converted into a frequency domain and demodulates the reception signal according to a demodulation method corresponding to the estimated transfer function, a reliability determining circuit which determines the reliability of the demodulation signal based on the transfer function estimated by the demodulation circuit, a variation detecting circuit which detects a variation amount of the demodulation signal on a frequency base, time base, a de-mapping circuit which subjects the demodulation signal to a de-mapping process and in which the contents of the de-mapping process are changed according to the result of determination in the reliability determining circuit and the result of detection in the variation detecting circuit, an error correction circuit which makes error correction based on the signal subjected to the de-mapping process.

Abstract: Techniques to estimate the frequency response of a wireless channel in an OFDM system. In one method, an initial estimate of the frequency response of the wireless channel is obtained for a first group of subbands based on a pilot transmission received via the subbands in the first group. An estimate of the impulse response of the wireless channel is then derived based on the initial frequency response estimate. An enhanced estimate of the frequency response of the wireless channel is then derived for a second group of subbands based on the impulse response estimate. The first and second groups may each include all or only a subset of the usable subbands. Subband multiplexing may be used to allow simultaneous pilot transmissions by multiple terminals on their associated groups of subbands.

Abstract: Signalling information is conveyed from a transmitting device (101) to a receiving device (102) in a cellular radio network where user data transmission takes place on a traffic channel in discrete transmission bursts (111–120; 211–220; 310–313) consisting of consecutive symbols. A piece of signalling information is formatted into symbols which are transmitted as a block of consecutive symbols (FACCH) in a certain transmission burst of a traffic channel. It is also indicated within said certain transmission burst that it contains symbols carrying signalling information.

Abstract: The aim of the invention is to determine the user data constellation of a multi-carrier signal at the receiving end. Said signal is QAM modulated in the 2K mode according to the DVB-T standard and is provided with a central carrier that is situated I the centre of the individual carriers and is temporarily modulated with user data and temporarily represents a distributed pilot. To resolve the aim of the invention, the appearance frequency of all I/Q values pertaining to the portion of user data belonging to the central carrier is detected and the centre of said user data constellation is then detected.

Abstract: Methods and systems for communicating on a wireless channel are provided which enable subscribers that share the channel to transmit using different modulation schemes. The modulation scheme used by each subscriber is assigned to the subscriber by a wireless access termination system. The modulation scheme assigned to a subscriber by the wireless access termination system is determined based on measurements of the quality of signals received from that subscriber. In one embodiment, the invention includes a transmitter and a receiver. The receiver is capable of transmitting data using one of a number of encoding and symbol constellation configurations. The receiver is also capable of receiving a first signal. Receiving the first signal causes the transmitter to transmit a second signal using a specified encoding and symbol constellation configuration.

Abstract: A reception synchronization apparatus capable of achieving precise synchronization of an OFDM signal including a frame guard added to the OFDM signal includes a multiplier for calculating the correlation between a received OFDM signal and an OFDM signal delayed by a delay circuit; a moving integration circuit for adding a signal from the multiplier over a guard period; n frame guard removing circuits, which respectively receive a signal from the moving integration circuit, remove the frame guard period from the received signal, and output a resultant signal; n interval integrators for cumulatively adding signals outputted from the frame guard removing circuits; and a detection circuit for detecting a maximum peak from the results from the n interval integrators and generating a detection signal indicating a synchronization timing position corresponding to the detected maximum peak position.

Abstract: A method and a circuit arrangement for efficient use of multistage modulation methods using orthogonal base functions for the representation of a signal to be transmitted. Signal points of a signal constellation are selected according to a respective predetermined and/or selected probabilities so as to optimize a respective signal energy and/or a respective signal data rate, the selected signal points each having a defined respective energy. A 16-QAM signal constellation can be used, for example, for transmitting at low data rates. In the circuit arrangement, a source (1) which supplies a data stream (2) and is connected to a code converter (3) for converting the data stream. The output of the code converter (3) is connected to a modulator (4) in which the corresponding signal points are selected according to the respective probabilities. The data stream (2) is then transmitted over a channel (5), and a demodulator (6) situated downstream from a code converter (7) carries out the inverse operation.

Abstract: A communication band is divided into a plurality of allocation channels (202, 204, 206, 208). At least one allocation channel (204) is transferred to a transform domain. The behavior of the at least one allocation channel is monitored in the transform domain in order to derive a set of statistics. The set of statistics are used to determine a channel category for the at least one allocation channel.

Abstract: Disclosed is a method of adjusting a supplementary data signal (wm(n)) to be embedded in an information signal (x(n)), for example an audio signal. The method comprises the steps of determining (301) a position where a predetermined property of the information signal exceeds a predetermined threshold, e.g. an attack position, and suppressing (302) the supplementary data signal in a predetermined neighbourhood of the determined position.

Abstract: A system and method for synchronising data for use in a powerline communications network.

Abstract: Data is distributed among the channels of an asymmetric data subscriber loop (ADSL) communications system in accordance with an adaptive algorithm which from time to time measures the signal to noise ratio of the various channels and finds a margin for each channel dependent on achievement (where possible) of a given bit error rate and a desired data transmission rate. The margin distribution is achieved by augmenting the constellation signal to noise ratio to enhance computational efficiency and allow redetermination of bit allocation tables during transmission as necessary. Pairs of bit allocation tables are maintained at the transmitter and receiver and one table of each pair at the transmitter and receiver is updated while the other pair is in use for controlling communication.

Abstract: A multi-point communications system is set forth herein. The communications system comprises a transmitter for transmitting OFDM/DMT symbols over a predetermined number of bins across a transmission medium. The OFDM/DMT symbols are generated using at least one timing signal. At least one of the predetermined number of bins includes a pilot tone sub-symbol having a frequency corresponding to the clock signal. The communications system also includes a receiver for receiving the OFDM/DMT symbols from the transmission medium. The receiver demodulates the received symbols using at least one timing signal. The receiver has a first pilot tone search mode of operation in which the receiver adjusts its timing signal to scan the frequency range of the predetermined number of bins looking for the pilot tone sub-symbol and identifies the bin including the pilot tone sub-symbol.

Abstract: In general, joint error-control coding and linear precoding techniques are proposed for fading-resilient transmissions over frequency- at and frequency-selective fading channels encountered with high-rate wireless OFDM transmissions. For example, a wireless communication system includes a transmitter that applies non-linear codes and a linear precoder to a data stream to produce a joint coded-precoded waveform. A receiver receives the joint coded-precoded waveform from the transmitter via a wireless communication channel, and demodulates the joint-coded precoded waveform to produce estimated data. The combination offers a multiplicative benefit to the diversity achievable by the wireless communication system.

Abstract: A method and apparatus for performing an operability test on a communications system device such as a cable modem is provided. The testing method comprises the steps of providing a set of output test data to the communications system device being tested, and generating an output signal with the device in a manner that is responsive to the output test data. In the case of a cable modem, the output signal is generated by the modem's modulator. The output signal is then provided as an input to a reflective mixer which generates a reflected signal in response to the output signal and directs it back into the communications system device being tested. The communications device can then use the reflected signal to generate a set of input test data that can be compared to the output test data to check the accuracy of the device's operation.

Abstract: Access is provided in a wireless communications system including at least one base station operative to communicate with one or more terminals over a forward control channel and a reverse control channel. A high-penetration channel reservation status is transmitted indicator from a base station in a plurality of slots assigned to a high-penetration forward control channel, such that the high-penetration channel reservation status indicator has a redundancy greater than that of a channel reservation status indicator transmitted over the forward control channel. Transmission of the high-penetration channel reservation status may be preceded by transmission of a high-penetration access request from a terminal in a plurality of slots assigned to a high-penetration reverse control channel, such that the high-penetration access request has a redundancy greater than that of an access request transmitted over the reverse control channel, and reception of the high-penetration access request at the base station.

Abstract: The known signal that is transmission data for the pilot carrier is output to multiplier 103 to be subjected to amplitude adjustment (gain control) using a predetermined coefficient. The coefficient is set as appropriate in the range that makes an amplitude of the known signal larger than the amplitude of a message signal in consideration of, for example, error rate deterioration and increment of peak power in the entire transmission power. In addition, since the number of pilot carriers is small as compared to the number of all carriers, the increment of the gain of the pilot carrier does not generally have a large effect on the increment of the peak power.

Abstract: A hyperspectral image encoder (10) for compressing hyperspectral imagery includes a differential pulse code modulation (DPCM) loop (26) to perform data decorrelation in the spectral domain and a discrete wavelet transform (DWT) processing means (28) to perform decorrelation in the spatial domain. The DPCM loop (26) determines an error image between a present image at the input of the encoder (10) and a predicted image. The DWT processing means (28) then divides the error image into a plurality of frequency subbands and quantizes information within the subbands in accordance with a plurality of predetermined quantization states to provide a coded output signal. In one embodiment, an interband predictor (24) is provided to predict an image, for use in calculating the error image, using the coded output signal.

Abstract: A transmission system using nQAM. A control channel is superimposed on a nQAM data channel. It is desirable to separate control channel data from user data without using a higher level protocol layer. In multi-carrier systems with variable bit-loading it is particularly desirable that the control channel data be separable from user data when the value of n. that is the bit-loading, or constellation identifier are unknown. Binary data is transmitted using nQAM modulation. The binary data includes both user data and control data. This means that a control channel is superimposed on a user data channel within the same nQAM constellation. Separation of the control data is facilitated by arranging control data points to have either a unique phase or unique amplitude values. These unique values are not employed for user data points.

Abstract: A multi-carrier communications system with a programmable interleaver and de-interleaver that can change the interleaving rate for data transmitted and received in the communications system is presented. The programmable interleaver and de-interleaver permits a level of flexibility in determining the immunity of the communications system to errors and sources of interference. The multi-carrier communications system is able to vary the interleaving rate based on input from a user or from data that it maintains from actual network performance. The multi-carrier communications system can change the interleaving rate during the initial installation of the multi-carrier communications system or whenever the system is reset or restarted or on any individual transmission unit.

Abstract: A method and apparatus that differentially encodes and decodes data symbols in dual domains is taught. Data packets are encoded, transmitted, and decoded during a plurality of symbol intervals on a plurality of sub-carriers. Encoding and decoding are accomplished across both the time and frequency domains such that the minimum number of carrier states are employed as reference only states that do not encode a symbol of data in and of themselves. A rule of adjacency is followed, both across time and frequency, so that decorrelation is minimized. Any modulation scheme that is applicable to differential encoding and decoding can be utilized. Communication systems that couple via radio waves, through metallic conductors, or over fiber optic paths can be employed.

Abstract: A wireless communications system includes a plurality of base stations that communicate control information with terminals at a first redundancy level over regular control channels. A subset of the plurality of base stations also communicate control information with terminals at a second redundancy level greater than the first redundancy level over high-penetration control channels. The subset of base stations may be distributed to efficiently provide service without using an inordinate amount of channel capacity. In one embodiment, cells served by the plurality of base stations may be grouped into a plurality of groups, e.g., frequency or code reuse groups, such that a respective group of base stations serves a respective group of cells. The subset of base stations may include at least one base station from each group of base stations. The subset of base stations may be geographically distributed with a greater density than the groups of cells to provide improved service to obstructed locations.

Abstract: In a wireless communications system, information is communicated over one of a first communications channel having a first redundancy level or a second communications channel having a second redundancy level based on a determination of communications quality for at least one of the channels. In embodiments of the present invention, communications occur over a first channel, e.g., a “standard” channel until a measure of communications quality for that channel, such as bit error rate or frame error rate, meets a predetermined criterion. When the communications quality meets the predetermined criterion, communications shifts to a “robust” high-penetration channel that utilizes substantially the same amount of spectral resource as the first channel but provides significantly increased redundancy. In other embodiments, a terminal, e.g.

Abstract: The present invention provides low complexity methods and apparatus for improving the performance of conventional QAM modulations. These methods provide (a) larger noise margins than conventional constellations and/or (b) improved labeling schemes. Additionally, the invention provides fixed-point approximations of these constellations to allow for low complexity VLSI implementations of these schemes.

Abstract: A transmission system for transmitting a data signal with an analog passband signal through a analog transmission line. The data signal is transformed to a signal representing a descrete data signal point in a vector signal space. The analog passband signal is transformed to a base band signal, and the base band signal is superimposed on the signal representing a descrete data signal point. A signal representing the superimposed data signal point is modulated and transmitted through the analog transmission line. In a receiver, the data signal point is decided from the signal representing the superimposed data signal point, and the superimposed bass band signal is extracted by subtracting the decided result from the signal representing the superimposed data signal point. The base band signal is transformed to the analog passband signal. A portion of information carried by the analog passband signal may be converted to a digital signal, and the digital signal is multiplexed with the data signal.

Abstract: The invention concerns a multicarrier signal designed to be transmitted to digital receivers, especially in a non-stationary transmission channel, corresponding to the frequency multiplexing of several elementary carriers each corresponding to a series of symbols, two consecutive symbols being separated by a symbol time &tgr;0, a signal in which, firstly, the spacing &ngr;0 between two neighboring carriers is equal to half of the reverse of the symbol time &tgr;0 and, secondly, each carrier undergoes an operation of filtering for the shaping of its spectrum having a bandwidth strictly greater than twice said spacing between carriers &ngr;0 and is spectrum is chosen so that each symbol element is highly concentrated in the temporal domain and in the frequency domain. The invention also concerns the methods for the transmission and reception of such a signal.

Abstract: To simultaneously transmit data related to two channels using code division data related to a first channel (DTCH) are spread parallely using a first spreading code (CI) and a second spreading code (CQ), data related to a second channel (PCCH) are spread parallely using a first spreading code (CI) and a second spreading code (CQ), the power level of a signal representing said data related to the second channel (PCCH) after the spreading is changed (G) with respect to the power level of a signal representing the data related to the first channel (DTCH) after the spreading, and a transmission is compiled from spread data related to the first channel and spread data related to the second channel the power level of which has been changed.

Abstract: In the phase modulation multiplexing transmission unit 1, a digital input signal is divided by a signal division unit, each of the resultant division signal is output to multiplication units 3a and 3b, respectively. The multiplication units 3a and 3b multiply the division signals by spread code signals output from spread code generators 2a and 2b, respectively. A multiplication signal Sb output from the multiplication unit 3b is shifted by &pgr;/2 radian through a phase shifter 4, which is added to a multiplexing signal Sa output from the multiplication unit 3a through an adder 5. A synthetic signal Se(n) output from the adder 5 is BPSK modulated through a modulator 6, which is transmitted through a transmission amplifier 7 and an antenna 8.

Abstract: A multi-carrier transmission system using DMT. It is known to recover a receiver sample and clock from a reserved carrier, a pilot carrier having a fixed phase. A sampling clock oscillator in a receiver is then phase locked to the pilot carrier. Multi-carrier receivers, such as DMT receivers, are normally equipped with an FFT processor. A complex number representing the pilot carrier is then available from the FFT processor output. If an FFT processor is not available, a one frequency DFT processor can be provided to produce a complex estimate of the pilot carrier. In a DMT system, frame synchronization is handled separately from sampling clock synchronization, although the two processes are intimately related and frame synchronization must be acquired before sampling clock synchronization.

Abstract: A multi-point communications system having an allocated total bandwidth is set forth. The system comprises a head end unit disposed at a primary site. The head end unit includes a receiver for receiving OFDM/DMT modulated data from a plurality of remote transceivers over a predetermined number of bins from a transmission medium. The receiver of the head end unit receives OFDM/DMT modulated data corresponding to a first data stream from a first one of the plurality of remote transceivers over one or more bins of a first subset of the predetermined number of bins and OFDM/DMT data corresponding to a second data stream from a second one of the plurality of remote transceivers over one or more bins of a second subset of the predetermined number of bins. The head end unit and each of the first and second transceivers can receive and/or transmit in at least a given X QAM mode or Y QAM mode.

Abstract: A system and method for the transmission of additional special marker symbols in a circular signal space constellation allows the communication of additional control information without requiring any additional power to transmit the additional symbol. Additional symbols can include "Start of Message", "End of File", "End of Transmission", "Increase Data Rate", "Decrease Data Rate", "Save State" or "Clear", or any additional command signal desired to be transmitted.

Abstract: An adaptive gain algorithm allows the maximization of gain of an audio signal that is transmitted with a digital data signal by allowing a trellis decoder to compensate for occasional excursions of the audio and noise signal across a signal space boundary. By measuring the short term energy present in an audio signal, the algorithm of the present invention allows the maximum power to be used to transmit an analog signal without overloading the trellis decoder.

Abstract: In accord with the transmission system, encoded signals may be processed in intermediate stations and at receiving stations in an order different from the order of the original encoding process for transmission. In particular, the recovery of CDMA encoded signals does not require application of spreading/despreading codes in the original scheme or sequence of application of spreading codes. In one embodiment, code applications may be permuted without losing the original signal which has been encoded. In such applications, not all of the encoding spreading functions results in an increased spreading rate.

Abstract: A synchronizing apparatus for a differential OFDM receiver that simultaneously adjust the radio frequency and sample clock frequency using a voltage controlled crystal oscillator to generate a common reference frequency. Timing errors are found by constellation rotation. Subcarrier signals are weighted by using complex multiplication to find the phase differentials and then the timing errors. The reference oscillator is adjusted using the timing errors. Slow frequency drift may be compensated using an integral of the timing error. Frequency offset is found using the time required for the timing offset to drift from one value to another.

Abstract: An RF phase and/or amplitude control device (40) has a digitally controlled attenuator (41) at it input to adjust the overall output level of the output. The device includes an in-phase power divider (43) for splitting up the input signals over two paths (I and Q). The power divided signals in the two paths are further power divided and shifted in relative phase at 180.degree. hybrids (49 and 50). The power divided and phases shifted signals in each path I and Q are selectively switched using switches (51 and 53). The selected and switched output is quadrative combined at a 90.degree. hybrid (55). This provides a single inexpensive device which can provide digitally controlled output signals which are either phase controlled or amplitude controlled or both.

Abstract: In a discrete multitone spread spectrum system, a base station distinguishes between normal collisions and noise bursts when receiving access request signals from remote units on a common access channel. The base station is then able to reply to the remote units with information about the quality of the common access channel and why their transmissions were not successful. The remote units then use this information to adapt their retry processes to the channel's quality, depending on whether there was a noise burst, a normal collision, or a successful transmission on the channel.

Abstract: A multi-point communications system is set forth herein. The communications system includes a transmitter for transmitting OFDM/DMT symbols over a predetermined number of bins across a transmission medium. The OFDM/DMT symbols are generated using at least one timing signal. At least one of the predetermined number of bins includes pilot tone sub-symbols generated from a pilot tone having a frequency corresponding to the at least one timing signal. The communications system also includes a receiver for receiving the OFDM/DMT symbols from the transmission medium. At least one frequency multiplexer is disposed along the transmission medium that frequency multiplexers the OFDM/DMT symbols and a transmission from at least one other transmission source. A mixer is disposed along the transmission medium between the frequency multiplexer and the receiver for mixing the OFDM/DMT symbols for receipt within a passband of the receiver.

Abstract: A Mobile Switching Center (MSC) includes a cellular modem pool that comprises a number of pairs of modems in which the data terminal equipment (DTE) ports of each modem pair are cross-connected in a "back-to-back" fashion. This allows the two modems of each pair to interchange data via their DTE ports and thereby isolate that portion of the cellular fax call over the cellular communications channel from that portion of the cellular fax call through the public-switched telephone network (PSTN). Fax information is transmitted over both the PSTN-portion of the cellular fax call and the cellular portion of the cellular fax call using standard fax modulation techniques. The cellular-side modem of each modem pair is adapted to recover fax handshaking and data signaling from the received--fax modulated--signal and translate the recovered fax information into non-modulated signals (e.g. AT commands) for application to the corresponding PSTN-side modem of the modem pair.

Abstract: Data to be transmitted is converted into symbols using a plurality of data-to-symbol conversion processes. The symbols from these processes are then time-division multiplexed. Advantageously, at least one of these conversion processes incorporate coding in a manner which provides the same degree of error protection for each process. In the disclosed embodiments, the data originates from two independent sources and the data from each source is converted into symbols using a different data-to-symbol conversion process.

Abstract: A synchronizing apparatus for a differential OFDM receiver that simultaneously adjust the radio frequency and sample clock frequency using a voltage controlled crystal oscillator to generate a common reference frequency. Timing errors are found by constellation rotation. Subcarrier signals are weighted by using complex multiplication to find the phase differentials and then the timing errors. The reference oscillator is adjusted using the timing errors. Slow frequency drift may be compensated using an integral of the timing error. Frequency offset is found using the time required for the timing offset to drift from one value to another.

Abstract: A first phase change is introduced to an analog signal based on a symbol specified by a data signal, where the symbol is one of a plurality of symbols in a symbol constellation. The analog signal is added to the data signal to form a combined signal which is transmitted over a communication channel that introduces a channel phase change to the analog and data signals. After transmission through the communication channel, the combined signal comprises a phase changed analog signal and a phase changed data signal. A received symbol is specified by the phase changed data signal, and a phase shift is introduced to the phase changed analog signal based on the identity of the received symbol.