# Johnson-Lindenstrauss Lemma on $S^{d-1}$

Consider the Johnson-Lindenstrauss lemma in the case where we can assume the $n$ input points $x_i$ in $\mathbb{R}^d$ are actually located on the sphere $$S^{d-1}(r):=\{u=(u_1,\ldots,u_{d}): u_1^2+\cdots+u_d^2=r\},$$ for some $r>0.$

How does this impact the conclusion of the theorem? In particular, can the upper and lower bounds $$(1-\varepsilon)\sqrt{k/d}~\left| x_i-x_j\right|^2\leq \left| f(x_i)-f(x_j)\right|^2 \leq (1+\varepsilon)\sqrt{k/d}~\left| x_i-x_j\right|^2,$$ which hold with probability at least $1-\frac{1}{n^{c-2}},$ with $f$ an orthogonal projection on a random $k-$dimensional subspace, where $k=c \log n/\varepsilon^2,$ possibly be strengthened in this case?