Showing papers on "Zero-forcing precoding published in 1990"
TL;DR: A technique for characterizing multiuser interference and background noise in a direct-sequence spread-spectrum network is introduced, and packet error probabilities are calculated and modifications to the basic direct- sequence scheme that improve performance in the case of one strong interferer are suggested.
Abstract: A technique for characterizing multiuser interference and background noise in a direct-sequence spread-spectrum network is introduced, and packet error probabilities are calculated. The multiuser interference over a packet in the network is modeled as a compound Gaussian multivariate random variable for moderate to large values of the processing gain. The conditional variance is dependent on the number of users and their interference powers. The method works for any interference with statistics of the block interference having a spherically symmetric distribution. The best performance results, in terms of the expected total interference power, are obtained for the case of a large number of interferers with comparable interference powers. As the number of interferers approaches infinity, the performance is the same as that for Gaussian noise. For a small number of interferers, the block error probability curve is broader than that for Gaussian noise. For small values of SNR, the probability of error is smaller than that corresponding to Gaussian noise, and for large values of SNR it is larger. Modifications to the basic direct-sequence scheme that improve performance in the case of one strong interferer are suggested. >
95 citations
Patent•
10 Sep 1990
TL;DR: In this article, a closed-loop control is used to reverse the polarity and to adjust the amplitude and phase of the cancelling interference until the sum of the synthesized interference, and that to be reduced in the transmission line, becomes a minimum.
Abstract: Devices and methods for selectively reducing an electromagnetic or acoustic interference present in a transmission line by an active adaptive means, are described. For the electromagnetic interference, the transmission line may include a waveguide carrying a desired signal along with an undesired interference, the objective of the invention being to reduce the interference selectively at the output of the transmission line without affecting the desired signal substantially. Similarly, for an acoustic interference, the transmission line may include an exhaust pipe of an auto or Diesel engine carrying an undesired acoustic interference or noise, the objective of the invention being to reduce this noise at the output of the pipe. The selective interference reduction in this invention is achieved by sampling the interference almost exclusively from the transmission line, and automatically synthesizing a cancelling interference which, when summed with the interference present in the transmission line, cancels or substantially reduces the interference at the transmission line output. A closed-loop control is used to reverse the polarity and to adjust the amplitude and phase of the cancelling interference until the sum of the synthesized cancelling interference, and that to be reduced in the transmission line, becomes a minimum.
16 citations
23 Jul 1990
TL;DR: This signal processing technique can enhance the performance of broadband (3 kHz) HF radio systems subject to narrowband interference, and an example of this is presented.
Abstract: Describes a system for identifying narrowband interference (e.g. CW and FEK) in a 3 kHz HF radio channel. The system is able to detect and eliminate such interference under severe HF channel conditions of frequency selective fading and noise. This signal processing technique can enhance the performance of broadband (3 kHz) HF radio systems subject to narrowband interference, and an example of this is presented. The performance of the currently implemented algorithm is outlined and the application of the technique to different signal formats is discussed. The system uses a programmable finite impulse response (FIR) filter implemented on a digital signal processor to remove unwanted interference. The signal processor also performs the spectrum analysis of the baseband 3 kHz radio channel and makes the decisions on the structure of the interference to enable rejection to take place. >
5 citations
30 Sep 1990
TL;DR: The measured data upon which this model is based are described, and analyses performed on the data and results obtained using the model for noise/interference simulations are discussed.
Abstract: The development of a wideband HF noise/interference model that is based on measured data and is suitable for implementation in a wideband HF channel simulator is reviewed. The measured data upon which this model is based are described, and analyses performed on the data and results obtained using the model for noise/interference simulations are discussed. >
3 citations
TL;DR: It is found that different angular locations may correspond to the same processing gain and interference immunity of adaptive narrowband linear beamformers, but the former varies from unity to a maximum value which under certain conditions is independent of both the array geometry and the number of interference sources.
Abstract: The dependence of processing gain and interference immunity of adaptive narrowband linear beamformers on angular locations of single, double, and L interference sources is investigated. Corresponding expressions of these figures of merit are derived. It is found that different angular locations may correspond to the same processing gain and interference immunity. The former varies from unity to a maximum value which under certain conditions is independent of both the array geometry and the number of interference sources. The null directions of the quiescent beam correspond to unity processing gain and 100% interference immunity. However, there are always other directions where the processing gain is unity but the interference immunity is extremely small. The maximum processing gain is always associated with 50% immunity. >
1 citations