Analysis of the Multistage CM Array/Signal Canceler for Digital Communication Signals
A.V. Keerthi, John J. Shynk · IETE Journal of Research · 2000
The multistage constant modulus (CM) array is a blind adaptive beamformer that can separate cochannel digital communication signals. It consists of several identical stages connected in a cascade structure. Each stage is composed of a multichannel linear equalizer (MCLE) and a multichannel signal canceler (MCSC). The MCLE generates a linear estimate of one cochannel signal impinging on the antenna array. This captured source is removed from the input by the MCSC, which is a parallel connection of adaptive FIR filters, one for each antenna element. In this paper, we describe the architecture of the multistage CM array/signal canceler, and derive the Wiener weights for the MCLE and the MCSC. A discrete-time channel model with fractional sampling at the antenna array is employed. It is demonstrated that the power of the source captured by the first stage is reduced to the noise floor at the input of the next stage, whereas the other sources pass through essentially unchanged. Computer simulations are presented to illustrate the capture behavior of the multistage system.