Traces of fractional Sobolev spaces $W^{s,p}$ with $0<s<1/p$

Question

I've stumbled upon a problem involving the trace of a function in a fractional Sobolev space of the form $W^{s,2}(H)$, where $H$ is a half-plane in $\mathbb{R}^2$. Would it be possible to define a notion of trace, in the case in which $0<s<\frac{1}{2}$ ? If yes, is there a characterization of the space of such traces? Are the traces locally integrable? Are you aware of any reference where such information could be found?