Digital wireless communications systems that eliminates intersymbol interference (ISI) and multipath cancellation using a plurality of optimal ambiguity resistant precoders
A digital wireless communications system which eliminates intersymbol interference in a transmitted signal using a plurality of precoders in a transmitter thereof and a method of using the same. The digital wireless communications system includes a receiver having an antenna array for receiving transmitted digitally-encoded signals, and a transmitter for transmitting the digitally-encoded signals. The transmitter has a plurality of precoders which eliminate intersymbol interference in the transmitted signals such that the receiver recovers digital information from the transmitted signals which is free from intersymbol interference. Ambiguity resistant (AR) precoding has been recently proposed in intersymbol interference (ISI) and multipath cancellations, where the ISI/multipath channel may have frequency-selective fading characteristics and its knowledge is not necessarily known. With the AR precoding, no diversity is necessary at the receiver. In the precoding, the AR property for a precoder plays an important rule. In this paper. more families and properties of AR precoders are presented and characterized. In particular. all systematic AR precoders are characterized. More importantly, the concepts of precoder distance and optimal precoders are introduced and characterized, enabling construction of all optimal systematic AR precoders when additive channel random noise is concerned. A necessary and sufficient condition for an AR precoder to be optimal is provided which is easy to check. Numerical examples are also presented to show the improved performance over the known AR precoders in ISI cancellation applications.
A precoded orthogonal frequency division multiplexer (OFDM) system that improves the preformance of OFDM systems for spectral null channels, and size K.times.1 vector OFDM systems that reduce the cyclic prefix length by K times compared to conventional OFDM systems. The precoding scheme comprises inserting one or more zeros between each of the two sets of K consecutive information symbols, although it can be generalized to a general form. This precoding scheme removes the spectral nulls of an ISI channel without knowing the ISI channel. When no zero is inserts between each of the two sets of K consecutive information symbols and only K consecutive symbols are blocked together, vector OFDM systems are obtained. The bit error rate performance of the vector OFDM systems of the present invention is much improved over conventional OFDM systems.
A power-based hardware antenna diversity method for a wireless transceiver with multiple antennas is disclosed. The method is characterized in the steps of setting the transceiver gain at a maximum level to establish a first story of dynamic power range above a noise floor level, using a high-resolution ADC at a large back-off level relative to the noise floor to detect weak signals within the first story of the dynamic power range, switching antennas and measuring power level for each antenna during signal onset, and selecting an antenna having a largest power level.
A wireless communications device for a multiple input multiple output wireless communications system includes a radio frequency transceiver that includes at least two antennae and a medium access control device that includes a link adaptation module. The link adaptation module dynamically adjusts a bandwidth of the wireless communications device based on a transmission error rate and a correlation measurement at a remote wireless communications device. A transmission error module receives the transmission error rate from the remote wireless communications device and generates a transmission error control signal. A signal correlation module receives the correlation measurement from the remote wireless communication device and generates a signal correlation control signal. The link adaptation module adjusts at least one of the bandwidth and an amount of spatial multiplexing that is executed by a space-time processor based on the transmission error control signal and the signal correlation control signal.
A rate-adaptive method of communicating over a multipath wireless communication system uses multiple links such that each end of a link uses multiple transmit and receive antennas. A number of independent streams that are to be transmitted for each link is determined based on an overall system performance measure. In addition, the system may also jointly determine the best modulation, coding, power control, and frequency assignment for each link, based on an overall system performance measure. In OFDM systems, the number of independent streams, as well as the modulation, coding, and power control, may be determined on a tone-by-tone basis based on an overall system performance measure.
In order to provide a magneto-resistive angle sensor (100) comprising a sensor device for detecting an angle (.alpha.) of an external magnetic field relative to a reference axis of the sensor device, which allows measurement of the angle (.alpha.) without the measurement result being affected by manufacturing errors, it is proposed that the sensor device comprises a flat AMR layer (14, 15) with one electrical contact (K.sub.0) for applying a current (I) and a plurality of electrical contacts (K.sub.i) for measuring a flow of current through the AMR layer (14,15).
