Abstract: Systems and methods for controlling subscriber unit power level using power measurements made on access request transmissions. Since a subscriber unit access request typically precedes a subscriber unit data transmission by a relatively short period of time, the data transmission power level will then be based on a recent power measurement. The access request may also trigger a sequence of power control steps including the transmission of special upstream power measurement transmissions which can be used as the basis for even more accurate power control. These power control features are particularly useful in fading environments such as found in a wireless system.

Abstract: Systems and methods for employing digital two-way cable MAC protocols for multi-user wireless communication systems. In one embodiment, a physical layer TDMA framing structure is provided to complement the MAC layer framing. A single MAC layer frame is divided into multiple physical layer frames. The physical layer frames are divided among frames dedicated to transporting data between MAC layer entities and frames dedicated to transporting physical layer control information. Constant delay in transmission through the physical layer is preserved.

Abstract: Systems and methods for appending cyclic prefixes to OFDM bursts while employing minimal additional memory and adding minimal latency are provided. This facilitates lower cost implementations of OFDM communication systems including systems that carry real time traffic such as telephony and video conferencing. The phases of frequency domain symbols are rotated prior to application of the IFFT so that cyclic prefix addition may be implemented as cyclic postfix addition. Cyclic postfix addition requires much less memory and imposes much less latency then cyclic prefix addition.

Abstract: Systems and methods for efficient multiplexing of multiple access requests from disparate sources within a single OFDM burst. Each of multiple subscriber units employ non-overlapping groups of OFDM frequency domain symbols within a single burst for upstream transmission of their access requests. In one embodiment, the OFDM frequency domain symbols are differentially encoded to eliminate the need for transmission of upstream training information. In an alternative embodiment, the group of frequency domain symbols within the burst employed by any particular subscriber unit are contiguous to one another. Channel training for a give subscriber unit need only be performed over the subband occupied by its group of frequency domain symbols. This greatly reduces the number of training symbols required for reception.

Abstract: Systems and methods for converting a baseband OFDM signal to an IF signal while minimizing lengthening of the impulse response duration experienced by the OFDM signal. A conversion technique according to the present invention provides sufficient filtering to limit the effects of spurious frequency domain components caused by transitions between successive OFDM bursts. In one embodiment, the filtering is provided by a combination of a finite impulse response (FIR) filter having non-linear phase characteristics and a cyclic convolution filter. Conversion from the frequency domain into the time domain, upsampling, and cyclic filtering may be combined into one operation.

Abstract: Systems and methods for precisely controlling the amount of redundancy introduced by a turbo encoding process. Bits having predetermined values are introduced into the turbo encoding input stream and then deleted from the turbo encoding output stream. At the receiver end, the bits having predetermined values are reintroduced into the encoded information stream as having been received with a maximum confidence level. Coding rate may be varied by varying the number of bits having predetermined values which are inserted at the encoder input. This scheme permits the amount of redundancy to be varied according to system requirements.

Abstract: A chirp waveform is employed in establishing timing synchronization between nodes of a data communication network. In one embodiment, the chirp waveform is combined with a waveform modulated with data to form a synchronization waveform. The receiver of the synchronization waveform determines an alignment of the chirp waveform to a template chirp waveform to synchronize timing between nodes.

Abstract: A system and method for characterizing a channel used by a digital communication system. In an OFDM system, the number of training symbols used to characterize a channel may be decreased by taking advantage of knowledge of certain channel components, e.g., transmitter and/or receiver digital filters. The number of training symbols used may be less than v, the duration of the impulse response of the overall channel.

Abstract: Systems and methods for providing enhanced subscriber unit power control in a point to multipoint communication system are provided. A central access point may send unsolicited grants of transmission time to individual subscriber units. The subscriber units use the granted transmission time to transmit upstream to the central access point for the purpose of having their output power level measured and regulated. By issuing the unsolicited grants sufficiently frequently, the central access point may maintain optimal subscriber unit transmitter power level. The power control features are particularly useful in fading environments such as found in a wireless system, especially when subscriber units do not transmit data upstream sufficiently frequently for power control to be based on measured power of data transmissions.

Abstract: Systems and methods for estimating channel response in the presence of interference. Interference and/or noise present on received training symbols is estimated. Based on the measured noise and/or interference, a weighting among training symbols is developed. Channel response is then estimated based on a weighted least squares procedure.

Abstract: A space-time signal processing system with advantageously reduced complexity. The system may take advantage of multiple transmitter antenna elements and/or multiple receiver antenna elements, or multiple polarizations of a single transmitter antenna element and/or single receiver antenna element. The system is not restricted to wireless contexts and may exploit any channel having multiple inputs or multiple outputs and certain other characteristics. Multi-path effects in a transmission medium cause a multiplicative increase in capacity.

Abstract: A spatial processor that exploits signals that arrive via multiple outputs of a communication channel to provide soft decision values useful to a trellis or Viterbi decoder. A spatial processor may take into account a statistical characterization of interference as received via the multiple channel outputs. Spatial processor operation may also be optimized to operate in conjunction with orthogonal frequency division multiplexing (OFDM).

Abstract: Systems and methods are provided for transferring physical layer control information from a central access point to individual subscriber units while maintaining transparency to higher layers. Adaptation of wireline MAC protocols to wireless applications is greatly facilitated. Subscriber unit power level may be controlled from the central access point.

Abstract: Improved adjustment of transmission power in a communication system is provided. In one embodiment, in a point to multipoint communication system, transmission power of a subscriber unit is controlled based on power measurements made at a central access point. Power measurement information based on transmissions occurring at irregular intervals may be combined in a beneficial manner to control transmission output power. In one embodiment, a power regulation process determines a series of difference values indicating the differences between desired received power level at the central access point and measured received power level. A smoothing process is applied to the difference values. One or more parameters of the smoothing process vary with elapsed time since a last available power measurement.

Abstract: A space-time signal processing system with advantageously reduced complexity. The system may take advantage of multiple transmitter antenna elements and/or multiple receiver antenna elements, or multiple polarizations of a single transmitter antenna element and/or single receiver antenna element. The system is not restricted to wireless contexts and may exploit any channel having multiple inputs or multiple outputs and certain other characteristics. Multi-path effects in a transmission medium cause a multiplicative increase in capacity.