Abstract: Various methods and systems efficiently implement broadband multi-carrier communication systems. The invention exploits the structural properties of a frequency-domain channel estimator and transforms it into the time domain. This allows the sharing of certain blocks of hardware (e.g., matched filters otherwise used for timing acquisition) which results in significant reduction of complexity.

Abstract: Equipped with a plurality of mapping blocks 102 and 103 that carry out mappings of different rates, signals subjected to low-speed mapping are placed in the periphery of a band to which a plurality of sub-carriers are assigned at an interval corresponding to the symbol rate. The signal placed on the frequency axis in this way is converted to a time waveform through inverse Fourier transformation block 105, converted to a symbol time series through parallel/serial conversion block 106, then quadrature-modulated and transmitted.

Abstract: A communications system includes a first and second modem coupled together via a communications link. The first modem has at least two user devices coupled thereto, and modulates data generated by the user devices on a plurality of tone carriers for transmission to the second modem. The first modem determines the number of user devices coupled to it. Based upon the number of user devices determined, the first modem divides the plurality of tone carriers into a number of subsets corresponding to the number of user devices based upon a predetermined criterion. The first modem then allocates a subset of tone carriers to a respective user device. In one embodiment, the usage rate of each user device is determined, and the tone carriers are reallocated to different subsets as a function of the usage rate of each respective user device.

Abstract: An orthogonal frequency division multiplexed wideband communication system provides improved time and frequency synchronization by inserting an unevenly spaced pilot sequence within the constellation data. A receive correlates the received data using the unevenly spaced pilot sequence. The pilot sequence is generated with a maximum length pseudo random noise code and inserted into frequency bins having prime numbers.

Abstract: A multicast engine is provided in plurality within a router for replicating and/or modifying packets identified as multicast packets. In preferred embodiments the engine is integrated with one or more ports of a router, particularly with one or more ports of fabric cards. In one implementation the multicast engine is associated with a table having instructions for replicating or modifying multicast packets received, and forwarding the packets accordingly.

Abstract: An OFDM communications system comprises broadcast providers 400, earth stations 100, repeater satellites 200, and receivers 300 (for example mobile receivers). The size of the multiplex can be increased by adding extra channels. Two channels are provided, on the in phase and quadrature components of each subcarrier.

Abstract: A bidirectional telephony (POTS or ISDN) system utilizes RF technology to move the signalling away from the baseband frequency. The method translates baseband telephony signalling into one or more RF signals over twisted pair copper channels, in conjunction with an ADSL or VDSL signal on the same medium.

Abstract: Wireless communication methods and structures are provided that enhance communication robustness while reducing cost. They communicate downstream data with orthogonal frequency division multiplexing (OFDM) transmission processes and upstream data with single carrier transmission processes. This combination of transmission processes is configured with various signal modulations (e.g., quadrature phase shift keying (QPSK), m-ary phase shift keying (MPSK) and n-quadrature amplitude modulation (QAM)) to provide lower cost upstream communication from customer services equipments (CPEs) and more robust downstream communication from headends than has been achieved in conventional communication systems. Signal diversity is enhanced by receiving communication signals with multiple antennas that are spatially separated and have different polarizations to thereby enhance frequency diversity.

Abstract: For example in case of an OFDM multicarrier transmission system the transmission characteristics of subcarriers of a multicarrier transmission system using a plurality of antenna elements (3, 3′) can be adjusted. Particularly the power and the phase of the subcarriers can be adapted. To this object the subcarrier frequency channel (2, 2′) characteristics of the multicarrier transmission are detected (11, 11′) at the side of the transmitter (3). The power of each subcarrier is then distributed by a weighting unit (14, 14′). The subcarriers can be further pre-equalized (1, 1′) by dividing the subcarrier signal respectively by the sum of the squared magnitude of the frequency channel characteristics of all subcarrier signals or a frequency characteristic of the selected antenna element (3, 3′).

Abstract: Method for carrying out simplex transmission of a data message modulated onto a carrier frequency, in particular for simplex radio transmission in a radio access control system, in which the data message is transmitted to increase immunity to interference, whereby the multiple transmission is carried out using at least two different carrier frequencies.

Abstract: A method for automatic frequency control in a wireless communication network having public frequency channels comprises the steps of: scanning the public frequency channels; locking the cellular base station to a signal on one of the public frequency channels; and returning the cellular base station to normal operation.

Abstract: This invention relates to a method and apparatus for channel estimation. A method of determining a maximum likelihood frequency domain estimate of the channel response of a channel between at least one transmitting peer and at least one receiving peer, said method comprising transmitting NU reference tones from said transmitting peer to said receiving peer; capturing said NU reference tones at said receiving peer; and determining at said receiving peer from said NU reference tones said maximum likelihood frequency domain estimate of said channel response at NF predetermined frequencies by directly exploiting the finiteness of the time response of said channel.

Abstract: In the present invention, high speed data is provided by transmitting data on multiple carrier frequencies, multiple code channels and/or from multiple base stations. In a first embodiment of the present invention, multiplexed code symbols are transmitted on a plurality of carrier frequencies from the same base station. In second embodiment, code symbols are transmitted on multiple carrier frequencies with at least one corner frequency providing the code symbols is a multiple code channels. In a third embodiment, a subset of the multiplexed code symbols are redundantly provided on a different carrier from at least one additional base station. In a fourth embodiment, multiplexed symbols as transmitted on different carriers from the same base station and are redundantly transmitted on another set of carriers from a different base station. In a fifth embodiment, code symbols are multiplexed onto carriers from a plurality of base stations for increased throughput.

Abstract: An OFDM communications system comprises broadcast providers 400, earth stations 100, repeater satellites 200, and receivers 300 (for example mobile receivers). The size of the multiplex can be increased by adding extra channels. Two channels are provided, on the in phase and quadrature components of each subcarrier.

Abstract: An improved transmitter apparatus, a receiver apparatus and a base station implemented with the transmitter and receiver apparatuses are described. These apparatuses and the base station serves to establish communication by making use of an orthogonal frequency division demultiplexing demodulation and an inverse spectrum spreading demodulation in combination. The communication coverage thereof can be expaned by making use of an orthogonal frequency division demultiplexing demodulation and an inverse spectrum spreading demodulation in combination.

Abstract: The invention relates to a signal intended to be transmitted towards a plurality of receivers, of the type comprising at least two source signals and consisting of a plurality of independently modulated substantially orthogonal carrier frequencies distributed over a predetermined frequency band. According to the invention, said frequency band (12) is divided into at least two frequency sub-bands (131-134) each comprising a set of said substantially orthogonal carrier frequencies (11), and to each of said sub-bands is allocated one of said source signals, so that a receiver may retrieve from the transmitted signal, by filtration, at least one of said sub-bands and perform demodulation processing only on the carrier frequencies contained in the retrieved sub-bands. The invention also relates to a transmission process as well as to a receiver of such signal.

Abstract: A method and apparatus for simultaneously communicating a first data stream along with a second data stream. A first carrier is modulated with a first data stream and a feature of the modulated first carrier is then imposed under the control of a second independent data stream. The modulated first carrier with the imposed feature is then demodulated to provide the first data stream. The distinguishable feature of the modulated first carrier is then detected to provide the second data stream. The first and the second data streams are clocked at rates which are integer multiples of each other. The distinguishable feature of the modulated first carrier includes the amplitude of the modulated first carrier or the frequency of the modulated first carrier. M-ary information is transmitted by transmitting groups of 3 or more bits simultaneously by using distinguishable amplitude or frequency values of a feature imposed on a first carrier.

Abstract: A block radio design is disclosed that prevents the primary analog-to-digital converter from saturating and thus prevents the introduction of intermodulation products into the multi-carrier signal. The block radio comprises a strong signal suppressor that selectively suppresses any carrier signal in the multi-carrier signal before the multi-carrier signal is digitized by the analog-to-digital converter, thus preventing the possibility that the analog-to-digital converter can be saturated. Furthermore, the strong signal suppressor attenuates the stronger carrier signals without affecting the weaker carrier signals.

Abstract: The establishment of an interactive broadcasting network requires not only a transmission channel from transmitter to receiver but also a transmission channel from receiver to transmitter. A novel method of creating a data feedback channel from receiver to transmitter is implemented in a common frequency network and involves the use of a transmission procedure in conformity with the DAB standard. Each receiver or user is assigned an identifier which is transmitted in the data feedback channel at specially reserved frequencies to request transmission capacity. A computer then allocates transmission capacity to the receiver. The signals received in the forward channel are evaluated using the synchronization symbols they contain in order to synchronize the transmitter component in the receiver. The novel process can be used in all common frequency networks which use data transmission in conformity with the DAB standard and ensures a particularly economical synchronization in the receiver.

Abstract: A multichannel television access control system is disclosed wherein processing of the broadband signal is performed by gated coherent RF injection on a plurality of channels, thereby effecting selective descrambling of an arbitrary subset of channels in a channel group. The system provides for a closed loop injection signal phasor control so as to maintain substantially constant relationship between the television signals and the injected signals. The combined signals are supplied to subscribers enabling the use of their cable ready equipment.

Abstract: The demodulation of data modulated on a set of carriers with equidistant frequencies by a plurality of transmitters (T1 . . . Tn) is executed in the present transmission system (TS) by a discrete multitone receiver (DMT-R). The transmitters (T1 . . . Tn) in the transmission system (TS) modulate their data on subsets of carriers which form part of the set of carriers with equidistant frequencies. These transmitters (T1 . . . Tn) are possibly additionally equipped with a cyclic prefix adder (CPA); synchronization between them is guaranteed if a predefined condition is fulfilled.

Abstract: A transmission system is disclosed which permits the receiving end to demodulate multi-valued modulated symbols successfully under fading conditions and reduces the amount of transmitted reference data to improve data transmission efficiency. At the transmitting end, a multiplexing section, a modulating section, and a transmitting section are provided. In transmitting an OFDM transmission frame, null symbols and reference symbols are placed in the beginning portion of the frame and QPSK symbols are placed in an information symbol data region in the frame with equal spacings in time and frequency. At the receiving end, a receiving section, a demodulation section, an equalizing section, and a demultiplexing section are provided. An error detector detects amplitude and phase errors of each carrier from the reference symbols, and a variation detector detects variations in the amplitude and phase of a received signal from the QPSK symbols.

Abstract: In a multiple access network, signals transmitted by a plurality of secondary stations to a primary station are to be distinguished by the primary station. One method for realizing this is by the use of Sub-Carrier Multiple Access (SCMA). According to the method of SCMA, a transmit signal is modulated on a subcarrier having its own frequency and then amplitude modulated on a main carrier in each secondary station. To reduce a mutual disturbance by the secondary stations in SCMA, according to the present invention, a transmit signal is converted into high-speed bursts of a transmit signal. As a result, fewer secondary stations on average are active, so that the mutual disturbance by the secondary stations will diminish.