Abstract: Channel estimation techniques are provided for a receiver of a wireless communication system using orthogonal frequency division multiplexing (OFDM), including legacy 802.11a and various extended rate systems. Training signals are received from one or more receive antennas. An estimated channel impulse response is computed from the received training signals by reference to a training sequence. The estimated channel impulse response is truncated in the time domain based on channel power and noise data. Channel response tracking techniques may also be implemented to correct for variations in channel response over the transmission time of a packet.

Abstract: Soft symbol decoder algorithms for multiple input, multiple output (MIMO) receivers reduce the search complexity by searching over fewer than all possible combinations of transmitted symbols to compute log metrics for each transmitted bit from each transmit antenna. In one algorithm, a sub-optimal set of transmitted symbols is computed and the transmitted symbols are restricted to neighboring constellation points of the sub-optimal set. In another algorithm, all constellation points are searched for every antenna except one. In yet another algorithm, constellation points are searched excluding more than one antenna. The non-searched antenna(s) can be handled by either a bit stuffing or a soft slicing technique.

Abstract: MIMO modulation is supported in a wireless network with at least one degenerate node. A transmitter separates data into multiple streams for modulation. To transmit the modulated data, the transmitter uses a separate antenna for each data stream or coherently combines the modulated data streams prior to transmission via fewer antenna than modulated data streams. In either case, the received signal includes a contribution from each data stream. A receiver is configured for processing multiple signals sent in parallel from multiple transmit antennas; thus, the operation of the receiver is unaffected by whether the multiple data streams of the transmitter were combined in the channel after transmission or in whole or part in the transmitter prior to transmission.

Abstract: Method and apparatus for combining high data rate traffic and low data rate traffic on a common transmission medium while maximizing efficient use of available spectrum. Since spectrum is an economically valuable resource and transport of data generates revenue, the present invention directly leads to more profitable network operation. The disclosed systems are applicable to both wired and wireless transmission media. In one embodiment, a bandwidth reservation scheme provides that data rate may be varied so that when a particular data communication device is allocated a frame, it is also assigned a data rate for use in that frame. Because bandwidth usage varies with data rate, the division of available spectrum into channels for use by individual data communication devices may also vary among frames.

Abstract: Systems and methods for optimally receiving differential encoded OFDM signals via multiple antennas. These techniques may exploit spatial diversity without knowledge of channel characteristics. Further systems and methods are provided for exploiting frequency diversity within an OFDM burst where differentially encoded symbols are repeated to assure optimal performance. The output of differential decoding systems may also be used to provide soft decision values for individual bits of multibit symbols to facilitate use of bitwise channel decoding systems.

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: 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: 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 receiver chain is provided for use in wireless data communication including a plurality of receive antennas and a vector Barker decoder or a CCK decoder. The vector Barker decoder operates on the plurality of received signals, preferably processed through a plurality of channel matched filters. The weightings of the plurality of channels can be done using a slicer variance, a PLL variance or another method.

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: Systems and methods for optimally combining signals from multiple antennas to ameliorate the effects of noise and/or interference on OFDM communications are provided. In one embodiment, an initial spatial statistical characterization of interference and/or noise is based on training symbols received via each antenna. Because the transmitted values of the training symbols are already known, there is no need to estimate their transmitted value to form this initial statistical characterization. The data symbol values received via the multiple antennas are combined based on the initial spatial statistical characterization. The result of this combination step is then used to form a refined spatial statistical characterization of noise and/or interference. The received data symbol values are then recombined based on the refined spatial statistical characterization.

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: 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: Systems and methods for optimally combining signals from multiple antennas to ameliorate the effects of noise and/or interference on OFDM communications are provided. In one embodiment, an initial spatial statistical characterization of interference and/or noise is based on training symbols received via each antenna. Because the transmitted values of the training symbols are already known, there is no need to estimate their transmitted value to form this initial statistical characterization. The data symbol values received via the multiple antennas are combined based on the initial spatial statistical characterization. The result of this combination step is then used to form a refined spatial statistical characterization of noise and/or interference. The received data symbol values are then recombined based on the refined spatial statistical characterization.

Abstract: Systems and methods for wide frequency offset synchronization are provided. A synchronization data sequence is encoded onto a series of OFDM frequency domain bursts as interburst phase differences between training symbols included within the successive bursts. The interburst phase differences may also encode system configuration information. This technique may be used in conjunction with other synchronization techniques to greatly extend the frequency acquisition range achievable with low cost analog components.

Abstract: Systems and methods for sharing a single decoder among data streams originating with multiple sources. Error correction coding techniques are modified to facilitate decoding of data from multiple sources multiplexed in the time domain at the decoder input. A single decoder accommodates multiple sources that have been encoded using disparate code rates. One application is an OFDM point to multipoint system.

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 element 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: Systems and methods for wide offset frequency synchronization in OFDM communications. Frequency domain OFDM bursts include training symbols having known transmitted values in known frequency domain positions. Received values at the known training symbol positions are correlated from burst to burst. The magnitudes are used to establish and correct small integer frequency offsets as measured in frequency domain symbol widths. The phase of the correlation result is used to determine and correct integer frequency offsets that exceed the training tone spacing. Use of the phase to correct large frequency offsets greatly extends the acquisition range required for low cost analog components.

Abstract: Improved receiver automatic gain control for OFDM-based communication systems is provided, thus realizing the full potential of OFDM systems to handle rapid variation in channel characteristics. The improved automatic gain control technique can also accommodate reception of multiple OFDM signals having disparate power levels via the same analog receiver chain and analog to digital converter while minimizing the arithmetic precision necessary for optimal digital processing. By reducing the necessary arithmetic precision, the cost of implementing the receiver with integrated circuit technology is greatly reduced.

Abstract: Systems and methods for efficiently transmitting power level information in a point to multipoint wireless system. Multiple subscriber units may transmit indications of their power level within a shared burst where one or more subchannels are allocated to each subscriber unit. The burst holding the power level information may be understood by the MAC layer to be a data burst. In this way, a wireline MAC protocol may be applied to wireless applications.