Showing papers on "Zero-forcing precoding published in 2000"

Optimal transmit-receiver design in the presence of signal-dependent interference and channel noise

Abstract: Optimal detection of a target return contaminated by signal-dependent interference, as well as additive channel noise, requires the design of a transmit pulse f(t) and a receiver impulse response h(t) jointly maximizing the output signal to interference plus noise ratio (SINR). Despite the highly nonlinear nature of this problem, it has been possible to show that f(t) may always be chosen minimum-phase. A full analysis concludes with the construction of an effective numerical procedure for the determination of optimal pairs (f,h) that appears to converge satisfactorily for most values of input SINR. Extensive simulation reveals that the shape of f(t) can be a critical factor. In particular, the performance of a chirp-like pulse is often unacceptable, especially when clutter and channel noise are low-pass dominant and comparable.

Anti-jamming solution to narrowband CDMA interference problem

Abstract: The main objective of this paper is to describe and simulate an adaptive interference cancelling technique named amplitude domain processing (ADP). The ADP filter will improve the GPS receiver's robustness against all types of interference (coherent CW pulsed or continuous, chirp interference, etc). The ADP filter is designed in Matlab (Simulink) to show its performance and how it can be applied as an adaptive interference canceller to estimate and remove GPS jammers in a real time basis.

Using N-body algorithms for interference computation in wireless cellular simulations

Abstract: A comprehensive simulation model of wireless cellular networks must include the computation of transmitter power levels. In such systems, as time evolves, powers are continuously updated to minimize interference and maintain signal quality. Transmitters operate at the minimum power required to meet a target signal to noise ratio (SNR), which, in the real system, can be promptly estimated since the values involved come front direct measurements. In a simulation model, however, the interference over each receiver is a quantity that must be computed and the associated costs are not low. A system with N pairs of transmitters and receivers requires that O(N/sup 2/) pairwise interactions be computed; it's easy to see how very large the workload is when we consider that, in order to advance simulated time by one second, this large computation may have to be performed hundreds of times. We show that techniques devised for the simulation of systems of self-gravitating bodies (N-body problem) can be successfully applied to reduce the complexity of interference computations in simulations of wireless systems. However, our experiments suggest simple distance-based truncation may be the superior method.

Method and apparatus for interference rejection

Abstract: The invention relates to an apparatus, and an associated method, in a communication system that is tolerant to interference. The received signal is divided into a real and an imaginary part, and the noise and interference is modeled as a filtered process. The invention solves the interference problem by utilizing the inherent signal structure.

Interference estimation in a communications system

Abstract: Estimation of Interference Signal Code Power (ISCP) in a third generation cellular communications system is facilitated by exploiting the known properties of the common pilot channel signal This signal is correlated (4) in a mobile user terminal with a locally generated (5) orthogonal symbol sequence to produce a noise plus interference power estimate This estimate can be used to calculate a signal to interference noise ratio for the purposes of power control

Structured spatial interference rejection combining

Abstract: Modern communication systems are often interference limited. By modeling the co-channel interference as spatially colored, temporally white Gaussian noise, it is straightforward to incorporate interference rejection in the metric of a sequence estimator. In general, estimates of both the channels and the spatial color of the co-channel interference and the noise are needed. In this work, a structured model for the spatial noise covariance matrix is proposed and maximum likelihood estimates of the parameters are derived. The choice of model order is also addressed. Simulation results show large gains due to the use of these structured estimates compared with the conventional, unstructured, approach.

A novel beamformer with multipath signal reception

Abstract: In this paper, a novel beamforming scheme is proposed for reception of coherent signals and suppression of strong interference. An interference-blocking (IB) transformation is first developed for removing the strong interference, while the desired signals and noise are retained. Optimum beamforming is then performed based on the IB transformation data consisting of only the desired signals and noise to produce maximum output signal-to-interference-plus-noise ratio (SINR). Numerical results demonstrate that the proposed interference-blocking maximum signal-to-noise ratio (IB-MSNR) beamformer significantly outperforms the conventional beamformers and can approximately achieve the performance of the optimum beamformer.

Precoding circuit and precoding-multiplexing circuit for realizing very high transmission rate in optical fiber communication

Abstract: A precoding-multiplexing circuit is formed by a precoding circuit for carrying out a precoding with respect to n sets of parallel input binary data signals having a bit rate equal to R/n, to obtain n sets of parallel precoded signals, and a time division multiplexer for time division multiplexing the parallel precoded signals obtained by the precoding circuit, in units of one bit, and outputting time division multiplexed output signal having a bit rate equal to R. In this configuration, the encoding is realized by processing electric signals before the time division multiplexing, so that it becomes possible for the precoding circuit to handle signals which are slower than the transmission rate, and therefore it becomes easier to realize the higher transmission rate.

Block space-time antenna precoding/decoding for generalized multicarrier communications in unknown multipath

Abstract: Transmit antenna diversity has been exploited recently to develop high performance space-time coders and simple maximum-likelihood decoders for transmissions over known at fading channels Relying on block precoding, this paper develops generalized space-time coded multicarrier transceivers appropriate for wireless propagation over frequency-selective (and perhaps unknown) multipath channels Multicarrier precoding maps the frequency-selective channel into a set of at fading sub-channels, whereas space-time encoding/decoding facilitates equalization and achieves performance gains by exploiting the diversity available with transmit (and possibly receive) antennas When unknown, channel status information is acquired blindly based on a deterministic variant of the constant-modulus algorithm that capitalizes on block precoding System performance is evaluated both analytically and with simulations

Interference-resistant LPTV-MMSE equalization

Abstract: The problem of recovering a digital communication signal distorted by a linear time-invariant channel and contaminated by severe co-channel or adjacent-channel digital interference is addressed in this paper. The proposed linear periodically time-varying (LPTV) receiver jointly performs channel equalization and interference suppression, without requiring explicit knowledge or estimation of the interfering channel. Simulation results confirm the effectiveness of the proposed technique, whose performance exhibit a remarkable robustness with respect to varying interference power level.

Blind beamforming for suppression of instantaneously narrowband signals in DS/SS communications using subspace projection techniques

Abstract: This paper proposes a novel blind beamforming method for interference mitigation in direct-sequence spread-spectrum (DS/SS) communications based on subspace projection. Instantaneously narrowband interference signals are considered. The interference signals are highly localized in the time-frequency domain, and their characteristics are different from those of the DS/SS signal. The instantaneous frequencies of the nonstationary interference signals are estimated from the time-frequency domain and used in the temporal domain for interference nulling. We derive the receiver SNRs, which shows improved performance in strong interference environments.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

CA-CDMA: channel adapted CDMA for MAI/ISI free burst transmission

Abstract: In this paper, a new precoding scheme is designed allowing the complete orthogonalization of the users in the uplink of a multiuser CDMA system based on burst transmission. With this channel adapted precoding, all the inter-symbol and inter-user interferences are eliminated thanks to the appropriate linear processing at the receiver. If the received power is fixed, this system minimizes the variance of the symbol estimation error. An infinity of solutions exists to orthogonalize the system. Two objectives are added: a possible recursion in the number of users and a minimization of the average emitted power. The last optimization problem is a complex one. An approximate solution is proposed. It is shown that the system introduced in this paper outperforms burst system using a conventional set of codes.

Narrowband Interference Mitigation in OFDM-Based WLANs

Abstract: We propose two narrowband interference cancellation algorithms for OFDM based Wireless Local Networks. The first consists of adapting the constellation sizes of the carriers to their Signal-to-Interference-plus-Noise Ratio (SINR). The second relies on a spreading sequence to exploit frequency diversity. The BER performance in the indoor multipath channel is evaluated by simulations using a very flexible model of typical narrowband interference. The channel is modeled based on a ray tracing approach. Both interference cancellation algorithms provide an excellent robustness against the frequency selectivity of the multipath fading channel and strong narrowband interference.

Performance of concatenated phase precoding and TCM on frequency selective fading channel

Abstract: In this paper, the concatenated system of phase preceding and trellis coded modulation (TCM) is investigated. Simulations of throughput (Rb) of 2 bits/sec/Hz show that phase precoding gains at BER of 10E-6 by 6.5 dB and 2.5 dB for rate 2/3 8PSK-TCM with four and eight state code respectively, compared to sub-optimum soft output equalization (SSE) at the receiver with the same TCM-codes. This pure precoding is verified on uncoded-QPSK in which more than 30 dB is gained compared to SSE. In addition at Rb of 3, a newly designed multiple-TCM (16PSK-2MTCM, 8 states) with precoding confirms this concatenation system for powerful ISI cancellation by achieving more than 1.5 dB of gain.

Improved performance analysis of spiral curve-phase precoding

Abstract: An efficient method for computing the bit error probability in spiral preceding for M-ary phase shift keying over an intersymbol interference channel is presented, consisting of a simplified single formula. The results show that this method is more effective than previously proposed methods.

Blind channel estimation for precoded variable bit-rate multiuser systems

Abstract: The precoder has been shown to be able to provide source diversity and more freedom in design. In this paper we employ precoding techniques for block transmission based on a multirate filterbank structure. To meet multiuser communication requirements for various high data-rates, different filterbanks are used as precoders with corresponding coefficients and up/down sampling rates. However due to high speed communication in the presence of unknown multipath, different interferences exist in the received data such as multiuser interference, intersymbol interference and interblock interference. To estimate the multipath channel for a desired user we generalize the subspace method by employing all signatures associated with this channel in the current system. In this way a better performance for the channel estimate can be achieved. The delay for that user can also be jointly estimated together with channel estimation.

Data-aided nonlinear filter for narrowband interference rejection in DS-SS systems: closed-form analytical results

Abstract: The performance of the data-aided nonlinear filter (DNF), for combating narrowband interference (NBI) in direct sequence spread spectrum (DS-SS) systems, is analyzed. Closed-form analytical expressions for improvement in signal to interference-plus-noise ratio (SINR) are derived under the condition of single tone interference. Results show that the DNF structure outperforms conventional nonlinear prediction filter.

Advanced signal processing for wireless multimedia communications

Abstract: We present some key advanced signal processing methodologies that have been developed for interference suppression in wireless networks. We focus primarily on the problem of jointly suppressing multiple-access interference (MAI) and intersymbol interference (ISI), which are the limiting sources of interference for the high data-rate wireless systems being proposed for many emerging application areas, such as wireless multimedia. We first present a signal subspace approach to blind joint suppression of MAI and ISI. We then discuss a powerful iterative technique for joint interference suppression and decoding, the so-called turbo multiuser detection, that is especially useful for wireless multimedia packet communications. We also discuss space-time processing methods which employ multiple antennas for interference rejection and signal enhancement. Finally, we touch on the problems of suppressing narrowband interference and impulsive ambient noise, two other sources of radio frequency interference present in wireless multimedia networks.

BER evaluation for optical signals with combined EDFA and interference noise

Abstract: We investigate the effects of combined interference noise and Gaussian noise on the BER evaluation. For the case of one interference source and additional Gaussian noise we propose a method to identify the interference noise and to evaluate the correct BER by the method of modified Chernoff bounds.

Multicarrier transmission system with interference detection and removal

Abstract: The transmission system according to the invention comprises a transmitter (10) and a receiver (12). The transmitter (10) can transmit a multicarrier signal (11) to the receiver (12). The receiver (12) comprises an interference absorption circuit (20), which interference absorption circuit (20) comprises interference detection means (26) for detecting interference components, e.g. impulsive noise components, included in the multicarrier signal (11) and interference removal means (28) for substantially removing the interference components from the multicarrier signal (11). The interference detection means (26) are arranged for generating and supplying to the interference removal means (28) an interference presence signal (27) which is indicative of the presence of the interference components in the multicarrier signal (11). The interference removal means (28) are arranged for substantially removing the interference components from the multicarrier signal (11) in dependence on the interference presence signal (27).

Investigation of multiple access interference within UTRA-TDD

Abstract: This paper highlights inter-cell and inter-operator interference which can occur within a UTRA-TDD system. Interference simulation results show that when the network has frame synchronisation and operates with the same asymmetry in all cells, there will be interference between the base stations and adjacent mobiles only (i.e. MS-BS and BS-MS interference). When synchronisation is lost, or different asymmetries are used, the results indicate the extent of the additional interference between adjacent base stations (BS-BS interference) and between adjacent mobile terminals (MS-MS interference). Further results for interoperator interference shows that the interference at the mobiles caused by synchronised operators is dominated by interference from the base station, whereas for unsynchronised networks the MS-MS interference becomes significant.

Multistage detection of DS-CDMA signals with threshold level comparisons

Abstract: Multiuser detection has been extensively researched as a method of decreasing the interference that occurs when many users simultaneously transmit in a direct sequence code division multiple access (DS-CDMA) system. The multistage detector attempts to estimate the interference that each user causes to every other user. The interference estimate is subtracted from all other signals. This method is computationally complex when there are many users present on the channel. In this paper we propose a multistage detector which only attempts to eliminate the multiple access interference (MAI) from a user's signal if the decision variable falls below a certain threshold level. It is shown that this reduces the computational complexity and improves bit error rate performance compared to the conventional multistage detector.

An adaptive vector quantized flexible precoder for a dynamic continuous frequency selective mobile channel

Abstract: Bandwidth efficient techniques are required to satisfy the demand for future public mobile radio communication systems. Precoding is a nonlinear pre-equalization technique that provides equalization equivalent to a decision-feedback equalizer (DFE) while not being affected by coding. Precoding is shown to be better than conventional equalization over a digital mobile channel that is dynamic in its characteristics. A novel precoding vector quantization scheme is applied to the prediction filter in the precoder and is shown to provide comparable results to the LMS adaptation algorithm while reducing the overheads.

PTV-CMA blind equalization and interference suppression

Abstract: The problem of blindly equalizing a digital communication signal distorted by a linear time-invariant channel, and contaminated by severe co-channel or adjacent-channel digital interference, is considered in this paper. We propose here to adopt a two-stage periodically time-varying (PTV) equalizer; in the first stage, partial interference suppression is achieved by resorting to linear PTV filtering, which allows the second stage, based on a PTV version of the constant modulus algorithm (CMA), to reliably recover the transmitted information symbols. The effectiveness of the new approach is corroborated by the results of computer simulations.

Optimal sequences to suppress the multiuser interference for CDMA systems

Abstract: A joint transmitter-receiver multiuser interference canceling scheme is proposed to suppress the multiuser interference. The idea is to optimize the spreading and despreading waveforms of different users by using the instantaneous channel parameters. The maximum receive signal to interference plus noise ratio criterion is used. An iteration algorithm is given to generate the optimal spreading and despreading waveforms. The proposed scheme can be understood as an adaptive frequency hopping system. The numerical results indicate that, compared with the conventional spreading waveforms such as Gold sequences, the optimal waveforms can greatly decrease the multiaccess interference.

Integrated adaptive spatial-temporal system for controlling interference

Abstract: An integrated adaptive spatial-temporal system (10) and method for controlling narrowband and wideband sources of interference (9). The system includes an N element antenna array (11) which receives a spread spectrum signal and interference signals, each element receiving a different phase shifted version of the spread spectrum and interference signals (9); a spatial filter (12) including an antenna pattern former responsive to the antenna array (11) which combines the phase shifted spread spectrum and interference signals according to controlling weights to null N-1 of the interference signal; an adaptive narrow band, e.g., temporal filter (14), responsive to the spatial filter (12) for filtering any remaining narrowband interference signals from the combined signal; and feedback subsystem (16) responsive to the narrow band filter (14) for adjusting the controlling weights of the antenna pattern former until the operation of the spatial filter (12) is optimized and null wideband interference signals before narrowband interference signals.

Parameter estimation in chaotic interference

Abstract: In many cases signals of interest are submerged by strong chaotic interference, how to extract the weak signal is of great importance and interest. In order to estimate the parameters representing the signal, a novel noise reduction method is proposed in which the chaotic interference is successfully separated from the received data, which is composed of the signal of interest, chaotic interference and measurement noise. The parameters can be precisely estimated from the residual error time series after the novel noise reduction method. Some simulations are given to verify the effectiveness of the estimation and some related discussions are also given.

A novel beamforming for coherent signal reception

Abstract: A novel beamforming scheme for reception of coherent signals is proposed. The scheme first uses estimates of directions-of-arrival (DOAs) of coherent sources to construct a signal-blocking (SE) transformation which removes the desired signal with interference and noise retained. The SE transformed data is then utilized to determine the interference-blocking (IB) subspace for suppressing interference. Finally, an optimum beamforming is performed based on the IB data consisting only of the desired signal and noise to produce maximum output signal-to-interference-plus-noise ratio (SINR). Numerical examples confirm that the proposed scheme can achieve a quite stable output SINR, closer to the optimum one, even in large DOA estimation errors.