ترجمه مقاله نقش ضروری ارتباطات 6G با چشم انداز صنعت 4.0
- مبلغ: ۸۶,۰۰۰ تومان
ترجمه مقاله پایداری توسعه شهری، تعدیل ساختار صنعتی و کارایی کاربری زمین
- مبلغ: ۹۱,۰۰۰ تومان
Abstract
We consider smoothness properties of the generator of a principal Gabor space on the real line which is invariant under some additional translation–modulation pair. We prove that if a Gabor system on a lattice with rational density is a Riesz basis for its closed linear span, and if the closed linear span, a Gabor space, has any additional translation–modulation invariance, then its generator cannot decay well in time and in frequency simultaneously.
This theorem was originally stated independently by Balian [6] and Low [23] for orthogonal systems, but both of their proofs contained a gap, which was later filled by Coifman et al. [11] who also generalized it to Riesz bases. For general references on the Balian–Low Theorem we refer the reader to [8,19]. In [8], the authors also state and prove the so called Amalgam Balian–Low Theorem, which states that if (ϕ, αZ×βZ) is a Riesz basis for L2(R), then ϕ cannot belong to the Feichtinger algebra S0(R), a class of functions decaying well in time and frequency. For a definition of S0(R) see (2) below. Note that the Amalgam Balian–Low Theorem is seemingly weaker than the Balian–Low Theorem, but is not implied by it.