Abstract: Techniques for supporting fault tolerance in communications systems, e.g., cellular communications networks with mobile wireless user devices, are described. In various embodiments end nodes, e.g., mobile devices, store information indicating which other nodes are critical to their operation, e.g., critical to messages and/or signals being properly routed to the individual end node. Different network nodes may be critical to different end nodes. Critical node information stored by an end node may be statically preprogrammed or dynamically generated, or may include a combination of both and static and dynamic information. In some embodiments at least a portion of the information used to determine which nodes are critical to a particular end node is generated dynamically from signaling information, e.g., session control signaling, transmitted and/or received during normal operation of the end node. Faults, failures and/or scheduled outages in various network nodes are detected and/or reported.

Abstract: A communications system includes a transmitter that generates symbols in a plurality of bins using a first timing signal and generates a reference signal by using the first timing signal. The transmitter transmits the symbols and the reference signal carried by a first signal, which is frequency multiplexed with a second signal from another transmission source. A demultiplexer frequency demultiplexes the first signal, which is downconverted in response to a control signal to generate a frequency downconverted signal, and a processing circuit is responsive to the frequency downconverted signal to identify the predetermined bin and to generate the control signal in response to the identification of the predetermined bin.

Abstract: A method and apparatus for providing uplink macro-diversity in packet-switched networks that allows packets and/or portions of packets, e.g., frames, to be selectively sent from an end node, e.g., wireless communication device or mobile terminal, over a set of multiple communication connections, e.g., physical-layer or link-layer connections, to one or more access nodes, e.g., base stations. Uplink macro-diversity is achieved in part through intelligent selective forwarding over multiple communication connections, where the forwarding decision is controlled by the end node based on a variety of factors, e.g., physical-layer channel conditions and/or higher layer policy. The forwarding decision is executed on a rapid timescale, e.g., on a per packet basis, to adapt to the dynamically varying conditions of the set of communication connections.

Abstract: A method and apparatus for allocating bits to subchannels in a discrete multitone environment. The method employs the use of precalculated and prestored look-up tables which take into account a desired bit error rate, signal-to-noise ratio gap for a particular coding scheme, and gain scaling factor. This eliminates the need for the communication device to conduct complex and time consuming calculations. During the training sequence portion of data communication channel establishment, the measured signal-to-noise ratio for each subchannel is compared with values in the precalculated look-up tables to determine the bit allocation for that subchannel. The bit allocation value is stored in a data structure in the communication device. A gain scaling factor for each subchannel is then determined and stored as a data structure. The bit allocation and gain scaling data can then be transmitted to a partner communication device in order to instruct the transmitter how to load each subchannel.

Abstract: A method and apparatus for interference suppression in wireless communication systems, especially Orthogonal Frequency Division Multiplexed (OFDM) systems. The array apparatus includes a two-tier adaptive array system which provides for both spatial diversity and beamforming at the uplink. The adaptive array is comprised of sub-arrays spaced at a distance sufficient to provide spatial diversity, ideally 5 to 15 wavelengths at the frequency of operation. Each sub-array is composed of at least two antenna elements spaced in proximity sufficient to provide effective beamforming or scanning, ideally less then one-half of one wavelength at the frequency of operation. The Direction of Arrival (DOA) of signals impinging upon the array can be calculated by comparing signals from sub-array elements.

Abstract: An apparatus for receiving a discrete multi-tone signal over a communications channel having an impulse response h(n), energy of the impulse response being substantially concentrated in a first band of samples, the apparatus including: a receiver for receiving the discrete multi-tone signal; and a T coefficient finite impulse response time-domain equalizer included in the receiver, the time-domain equalizer having an output additive noise signal, the T coefficients of the time-domain equalizer being provided such that: (a) energy of an effective impulse response heff(n) of at least the communications channel combined with the time-domain equalizer is substantially concentrated in a second band of V+1 samples, whereby the second band of samples is shorter than the first band of samples; and (b) a variance in a frequency spectrum of the output additive noise signal of the time-domain equalizer is controlled.

Abstract: A multi-point communications system is set forth herein. The communications system comprises a head end unit disposed at a primary site and a plurality of receivers disposed at remote sites. The head end unit includes a transmitter for transmitting OFDM/DMT symbols over a predetermined number of bins across a transmission medium. The OFDM/DMT symbols are transmitted in periodically occurring formatted symbol frames. The cyclic prefix includes a predetermined periodic signal superimposed thereon. The receivers receive the OFDM/DMT symbols over a subset of the predetermined number of bins from the transmission medium and use the superimposed signals to attain symbol alignment. Preferably, the superimposed signal is an impulse signal that varies in polarity throughout the transmission cycle and which is superimposed on one or more symbols occurring during a cyclic prefix of the formatted symbol frames.

Abstract: A multi-point communications system that comprises a head end unit disposed at a primary site and a plurality of receivers disposed at remote sites. The head end unit includes a transmitter for transmitting OFDM/DMT symbols over a predetermined number of bins across a transmission medium. The OFDM/DMT symbols are transmitted in periodically occurring formatted symbol frames. The cyclic prefix includes a predetermined periodic signal superimposed thereon. The receivers receive the OFDM/DMT symbols over a subset of the predetermined number of bins from the transmission medium and use the superimposed signals to attain symbol alignment. In accordance with a further aspect of the present invention, the receivers apply a predetermined incremental phase shift to received samples corresponding to the received OFDM/DMT symbols to thereby compensate for phase shifts. The multi-point communications system may include a similar system for aligning symbols transmissions from a remote service unit having a transmitter.

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: 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 communications system is set forth comprising a plurality of remote receivers numbering M for receiving and demodulating respective PSK symbols received from a transmission medium. A central transmitter transmits periodically occurring frames of data to the plurality of receivers over the transmission medium. Each frame of data contains L total symbols including a subset of X.sub.m symbols designated for each one of the M plurality of remote receivers. The transmitter interleaves the X.sub.m symbols in a given frame into a plurality of periodic, non-consecutive groups of R symbols per group, wherein R<X.sub.m. In accordance with one embodiment of the invention, each of the remote receivers includes an equalizer implemented as a digital filter having N taps. In such instances, the transmitter interleaves the X.sub.m symbols in a given frame into a plurality of periodic, non-consecutive groups of R symbols per group, wherein R.ltoreq.N.