  We report on the realization of a long-haul radio frequency (RF) transfer
scheme by using multiple-access relay stations (MARSs). The proposed scheme
with independent link noise compensation for each fiber sub-link effectively
solves the limitation of compensation bandwidth for long-haul transfer. The
MARS can have the capability to share the same modulated optical signal for the
front and rear fiber sub-links, simplifying the configuration at the repeater
station and enabling the transfer system to have the multiple-access
capability. At the same time, we for the first time theoretically model the
effect of the MARS position on the fractional frequency instability of the
fiber-optic RF transfer, demonstrating that the MARS position has little effect
on system's performance when the ratio of the front and rear fiber sub-links is
around $1:1$. We experimentally demonstrate a 1 GHz signal transfer by using
one MARS connecting 260 and 280 km fiber links with the fractional frequency
instabilities of less than $5.9\times10^{-14}$ at 1 s and $8.5\times10^{-17}$
at 10,000 s at the remote site and of $5.6\times10^{-14}$ and
$6.6\times10^{-17}$ at the integration times of 1 s and 10,000 s at the MARS.
The proposed scalable technique can arbitrarily add the same MARSs in the fiber
link, which has great potential in realizing ultra-long-haul RF transfer.
