Abstract: A wireless broadband communications system that provides increased reliability in environments in which portions of the available operating frequency band are subject to interference. The system determines whether the operating frequency band is being subjected to interference. If so, then the system determines whether such interference is affecting one or more portions of the band. If interference is affecting just portions of the band, then the system reduces the data rate and the number of sub-carriers used to transmit data. Next, the system allocates the data to be transmitted to the sub-carriers currently being subjected to the lowest levels of interference, while allocating no data to the sub-carriers currently being subjected to the highest levels of interference. In this way, the system allocates the data to be transmitted to the sub-carriers occupying optimal portions of the operating frequency band, in response to detected changes in the interference environment.

Abstract: A wireless broadband communications system and method that achieves reduced latency for high priority data when multiplexed with lower priority data for transmission over a TDD point-to-point radio link. The system prepares multiple data streams for transmission over a TDD radio link by buffering multiple data streams containing high and low priority packets in separate queues based upon their corresponding priority level. Each packet in the higher priority queues has a specified size, and a header defining the type of service provided and the packet destination. Next, the packets in the lower priority queues are fragmented to a reduced size based upon the data capacity of the link. The high priority packets and the fragmented, low priority packets are arranged in a sequence such that the high priority packets are transmitted first, and the low priority packets are transmitted when no data is buffered in any high priority queue.

Abstract: A method is provided for implementing a coding and adaptive modulation scheme for application to a point-to-point orthogonal frequency division multiplexed radio communications link. The method determines estimates of the likelihood of the two least significant bits of the digital representation of an input amplitude being a predetermined logical level. The likelihood estimates are input to a Forward Error Correction decoder, which produces a decision as to the state of the bits taking into account previous samples. Once the decision has been made, it is known what the ideal input amplitude would have been in the absence of noise and distortion, on the assumption that the decision was correct, and hence the contribution due to noise and distortion can be estimated. This knowledge can be used to assist the decoding of the most significant bits.

Abstract: A wireless broadband communication system that operates with high efficiency and reduced latency in long range point-to-point and point-to-multipoint applications. The system includes multiple transceivers and multiple antennas for transmitting and receiving wireless signals using TDD techniques over multiple channels, which include a control channel for setting both the size of the transmit bursts and the modulation threshold level. By determining the size of the transmit bursts for a subsequent data transmission based upon the number of filler packets detected in a specified number of previously received bursts, and adjusting the modulation threshold level for the subsequent transmission based upon the transmit burst size, the system provides increased data throughput, while maintaining the packet error rate at an acceptable level. As the throughput requirements of the system are relaxed, the modulation threshold levels can be adjusted to provide reduced packet error rates.

Abstract: The channel estimation technique employs a set of pilot tones to determine channel state information. Because some of the pilot tones contained in the OFDM symbols may be missing after transmission, the disclosed technique employs a set of known pilot tones to compute an estimate of the channel impulse response, which may exhibit a level of distortion. Non-zero terms of the estimated channel impulse response that fall outside of a prescribed time window are regarded as artifacts of a set of missing or unknown pilot tones. Information relating to the known pilot tones and the artifacts of the unknown pilot tones are employed for mathematically reconstructing and deriving values of the unknown tones. Then, the values of the known pilot tones and the derived values of the unknown pilot tones are employed to recompute the channel impulse response, thereby obtaining the channel estimate with a reduced level of distortion.