Multistage Constant Modulus Array Research Articles

A Multistage Hybrid Constant Modulus Array With Constrained Adaptation for Correlated Sources

The multistage constant modulus (CM) array was previously proposed for capturing multiple received signals in a cochannel signal environment. It consists of a cascade of individual CM array stages combined with adaptive signal cancelers that remove the various signals captured across the stages. However, when the received signals are mutually correlated, the signals captured by the CM array stages are not completely canceled, and previous parallel extensions of the system do not guarantee that different signals will be captured across the stages. In this paper, we present a hybrid implementation of the multistage CM array for separating correlated signals where the canceler weights in the cascade structure provide estimates of the direction vectors of the captured signals. These estimates are then used in a parallel implementation of the linearly constrained CM (LCCM) array leading to the hybrid structure. Since the direction vectors are obtained directly from the canceler weights, the hybrid implementation does not require prior knowledge of the array response matrix and is independent of the type of antennas used in the receiver. The effect of a bias in the direction vector estimates for closely-spaced signals is analyzed, and the steady-state performance of the hybrid structure is compared to that of a conventional constrained implementation for correlated sources. Computer simulations for example cochannel scenarios are provided to illustrate various properties of the system. Mean-square-error (MSE) learning curves indicate that the proposed hybrid LCCM algorithm converges faster and has lower MSE than previous implementations

Simultaneous estimation of source number and directions-of-arrival via blind beamforming

Blind beamforming algorithms have the ability to recover the desired signals from sensor array outputs without any prior knowledge of the direction-of-arrivals (DOAs). Non-Gaussian signals with negative kurtosis can be automatically captured by the multistage constant modulus (CM) array, which is the most striking blind beamforming algorithm and has been widely discussed in literatures. However, the sources number must be pre-determined in all kinds of blind beamforming algorithms. Based on the multistage CM array, we present a new method in this paper. It is designed to recover the desired signals and automatically determine the number of sources simultaneously. If the array geometry is known, the DOAs of all sources also can be estimated at the same time. The performance of the new method was analyzed via computer simulations and water tank experiments, and compared with that of other DOA estimation algorithms including “non-blind” and “blind” ones under the assumption of knowing the sources number. The new method shows better results in all considered situations.

Minimum-span constant modulus array for a smart antenna testbed

The realisation of an efficient algorithm for a real-time smart antenna testbed based on DECT technology is considered. The testbed is based on a multistage constant modulus array, a blind adaptive beamformer and an adaptive signal canceller that removes the captured signal from the input signals. Based on the Wiener model of convergence, a reduced form of the CM array has been developed that takes advantage of the reduced rank of the input correlation matrix for additional stages. Computer simulations confirm the functionality of this algorithm, and convergence and sensitivity to fading are also discussed.

A variable step-size CM array algorithm for fast fading channels

A new constant modulus (CM) array algorithm with a time-varying step size is presented. It is designed for use in a cascade multistage system where each beamformer stage recovers one cochannel source. We assume that each source has a small angular spread and that the antenna elements are closely spaced. For this scenario, the new algorithm ensures that a stage tracks the same source during fast fading conditions, thus yielding reliable source estimation in a nonstationary environment. We present the cost function associated with the algorithm and compare it with that of the original CM array. Computer simulations for Rayleigh fading channels are presented to illustrate the improved tracking behavior of the multistage CM array.