Charge density wave instabilities driven by multiple umklapp scattering
We show that the concept of umklapp-scattering driven instabilities in one-dimensional systems can be generalized to arbitrary multiple umklapp-scattering processes at commensurate fillings given that the system has sufficiently longer range interactions. To this end we study the fundamental model system, namely, interacting spinless fermions on a one-dimensional lattice, via a density-matrix renormalization-group approach. The instabilities are investigated via a method allowing to calculate the ground-state charge stiffness numerically exactly. The method can be used to determine other ground-state susceptibilities in general.
This paper addresses the problem of channel and propagation delay estimation in asynchronous DS/CDMA systems. We consider the uplink connection in DS/CDMA with long spreading codes. The MIMO stochastic gradient algorithm proposed in [6] is estimating a linear combination of the channel impulse responses and the propagation delays. This estimate suffices for the equalization purposes. The propagation delays are estimated with a simple matching scheme.