Hi!
The Plancerel-Polya inequality can be stated as follows:
Let $0 < p\le \infty$ and $ \nu \in \mathbb{Z}$. Suppose that $g$ is a (smooth) function satisfying $\mbox{supp }\hat g \subset \lbrace\xi: |\xi| \le 2^{\nu + 1}\rbrace$. Then $$ \sum_{k\in\mathbb{Z}} \sup_{x\in [k2^{-\nu},(k+1)2^{-\nu}]} |g(x)|^p \lesssim 2^{\nu} \|g\|_p^p. $$
Question: Does an analogous inequality hold if the support condition on $\hat g$ is relaxed? Say, if we assume that $g_\nu = \varphi\left(2^{\nu}\cdot\right)$ (EDIT: This definition of $g$ is modulo a scaling factor in order for the $p$ norms to scale properly with $\nu$ e.g. so that $\|g_\nu\|_p = 1$ for all $\nu$), 2^{-\nu}\varphi\left(2^{\nu}\cdot\right)$, where $\varphi$ is some smooth function? I am mainly interested in the case $p<1$.
EDIT: I will try a concrete example which is in the same spirit: Assume that $\varphi$ is some nice function (but not with compact frequency support). When does an inequality of the form $$ \sum_{k\in \mathbb{Z}} |c_k|^p \lesssim \|\sum_{k\in \mathbb{Z}}c_k\varphi(\cdot - k)\|_p^p ? $$
hold? Certainly if $\hat \varphi$ has compact frequency support, this follows from the PP inequality. But also if e.g. $\varphi$ is a B-spline, so compact frequency support of $\varphi$ is not necessary.
