This paper presents the concept, principles, and analysis of maximum ratio transmission for wireless communications where multiple antennas are used for both transmission and reception. The principles and analysis are applicable to general cases, including maximum ratio combining. Simulation results agree with the analysis. The analysis shows that the average overall SNR is proportional to the cross-correlation between channel vectors and that error probability decreases inversely with the (L/spl times/K)th power of the average SNR.

Maximum ratio transmission

Disclosed herein are methods and systems for encoding digital watermarks into content signals. Also disclosed are systems and methods for detecting and/or verifying digital watermarks in content signals. According to one embodiment, a system for encoding of digital watermark information includes: a window identifier for identifying a sample window in the signal; an interval calculator for determining a quantization interval of the sample window; and a sampler for normalizing the sample window to provide normalized samples. According to another embodiment, a system for pre-analyzing a digital signal for encoding at least one digital watermark using a digital filter is disclosed. According to another embodiment, a method for pre-analyzing a digital signal for encoding digital watermarks comprises: (1) providing a digital signal; (2) providing a digital filter to be applied to the digital signal; and (3) identifying an area of the digital signal that will be affected by the digital filter based on at least one measurable difference between the digital signal and a counterpart of the digital signal selected from the group consisting of the digital signal as transmitted, the digital signal as stored in a medium, and the digital signal as played backed. According to another embodiment, a method for encoding a watermark in a content signal includes the steps of (1) splitting a watermark bit stream; and (2) encoding at least half of the watermark bit stream in the content signal using inverted instances of the watermark bit stream. Other methods and systems for encoding/decoding digital watermarks are also disclosed.

Optimization methods for the insertion, protection, and detection of digital watermarks in digitized data

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.

Spatio-temporal processing for communication

A simple block coding arrangement is created with symbols transmitted over a plurality of transmit channels, in connection with coding that comprises only of simple arithmetic operations, such as negation and conjugation. The diversity created by the transmitter utilizes space diversity and either time or frequency diversity. Space diversity is effected by redundantly transmitting over a plurality of antennas, time diversity is effected by redundantly transmitting at different times, and frequency diversity is effected by redundantly transmitting at different frequencies. Illustratively, using two transmit antennas and a single receive antenna, one of the disclosed embodiments provides the same diversity gain as the maximal-ratio receiver combining (MRRC) scheme with one transmit antenna and two receive antennas. The principles of this invention are applicable to arrangements with more than two antennas, and an illustrative embodiment is disclosed using the same space block code with two transmit and two receive antennas.

Transmitter diversity technique for wireless communications

A dual-band antenna matching system and a method for dual-band impedance matching are provided. The method comprises: accepting a frequency-dependent impedance from an antenna; and, selectively supplying a conjugate impedance match for the antenna at either a first and a second communication band, or a third and a fourth communication band. More specifically, the method comprises: tuning a first tuning circuit to a first frequency; and, simultaneously tuning a second tuning circuit to a second frequency. In response, a conjugate match is supplied to the antenna in the first communication band in response to the first frequency. Simultaneously, the antenna is matched in the second communication band in response to the second frequency. When the first tuning circuit is tuned to a third frequency, and the second tuning circuit is tuned to a fourth frequency, then conjugate matches are supplied for the third and fourth communication bands, responsive to the third and fourth frequencies, respectively.

System and method for dual-band antenna matching

A center tap of a transversal filter, which forms part of a forward equalizer, is shifted by at least one symbol interval. An error signal is generated using a decision output and tap outputs of the forward and backward equalizers. An impulse response estimation circuit is provided to receive the decision output of the predetermined tap signals of the forward equalizer. The forward equalizer is controlled in accordance with the channel response to effectively achieve adaptive equalization.

Decision feedback equalizer including forward part whose signal reference point is shiftable depending on channel response

A sidelobe canceler includes a main antenna, an array of sub-antennas, a subtractor having a first input connected to the main antenna, a main-array processor and M sub-array processors. The main-array processor multiplies the outputs of the sub-antennas with weight coefficients using correlations between the sub-antenna outputs and the subtractor output and combines the multiplied signals into a signal, which is coupled to the second input of the subtractor. The signal-to-noise ratio of the subtractor output is maximized by an adaptive matched filter. Each sub-array processor multiplies the sub-antenna outputs with weight coefficients using correlations between the sub-antenna outputs and a decision signal. The multiplied signals are summed to produce an output of each sub-array processor, which is combined with the outputs of the other sub-array processors into a first diversity-combined signal, the latter being combined with the matched filter output to produce a second diversity-combined signal. Intersymbol interference is removed by an adaptive equalizer from the second diversity-combined signal according to a decision error so that the decision signal is produced and applied to the sub-array processors. Different amounts of delay are introduced to the outputs of (M - 1) of the sub-array processors so that the output of the i-th sub-array processor is delayed by (i - 1) T , where i = 2, 3, ....., M, and different amounts of delay are introduced to the decision signals applied to (M - 1) of the sub-array processors so that the decision signal applied to the j-th sub-array processor is delayed by (M - j) T , where j = 1, 2, ....., M-1. The total amounts of delay associated with each of the M sub-array processors is equal to (M-1)τ.

Maximal diversity combining interference cancellation using sub-array processors and respective delay elements

A time diversity transmission-reception system has, on transmit side, at least one delay of a predetermined delay for providing at least a pair of delayed and undelayed data symbol sequences, at least a pair of modulators for modulating the data symbol sequences into modulated intermediate frequency signals, and at least a pair of spread spectrum signal generators employing mutually different pseudo-random code sequences for code division multiplexing On receive side, the received signals are subjected to code division demultiplexing, demodulation, and delaying to restore at least a pair of timed demodulated signals These signals are then subjected to adaptive matched filtering, whose outputs are combined and applied to adaptive equalization to provide diversity reception signal The present system provides a plurality of diversity branches without employing a plurality of frequencies, planes of polarization of a carrier wave or receiving antennas Also, principal part of the system of the present invention can be readily integrated into LSI's, contributing to the reduction of manufacturing cost

Time diversity transmission-reception system

At a transmitter side, signals are providcd with a delay difference with a plurality of branches, coded multiplexed by spectrum spreaders and a combination unit, and transmitted by single antenna. At a receiver side, the signals are received by a single antenna, and diversity branches are extracted and separated by first and second spectrum de-spreaders. They are subject to linear combination so that the mean square of the decision error signals is minimized. The output passes through an adaptive matched filter and an adaptive equalizer so as to provide an output from which interference waves are eliminated. Thus, interference is eliminated and diversity gain for a signal is ensured, while reducing the scale and cost of a system without using a plurality of antennae.

Method and apparatus for eliminating interference using transmission delay and code multiplexing in digital radio system

In a time diversity radio communications system, quadrature-modulated spread spectrum signals of different mutual time delay are combined into a code division multiplex signal and up-converted to a radio-frequency signal and transmitted. At a receive site, the signal is received by an antenna and down-converted to recover the code division multiplex signal. Quadrature-modulated component signals contained in the recovered code division multiplex signal are converted to baseband signals which are then time-aligned with each other. The time-aligned baseband signals are multiplied respectively by complex weighting factors and are combined together to produce an input signal for an adaptive equalizer. This input signal is also applied to an AGC amplifier where it is amplified and applied to correlation detectors where correlations between the amplified signal and the baseband signals are detected and the complex weighting factors are derived respectively from the correlations. In a modified embodiment, the quadrature-modulated component signals are fed into an adaptive RAKE matched filter where the output of the AGC amplifier is used for detecting the correlations.

Spread spectrum time diversity communications system

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