  Reconfigurable intelligent surface (RIS) is a promising reflective radio
technology for improving the coverage and rate of future wireless systems by
reconfiguring the wireless propagation environment. The current work mainly
focuses on the physical layer design of RIS. However, enabling multiple devices
to communicate with the assistance of RIS is a crucial challenging problem.
Motivated by this, we explore RIS-assisted communications at the medium access
control (MAC) layer and propose an RIS-assisted MAC framework. In particular,
RISassisted transmissions are implemented by pre-negotiation and a
multi-dimension reservation (MDR) scheme. Based on this, we investigate
RIS-assisted single-channel multi-user (SCMU) communications. Wherein the RIS
regarded as a whole unity can be reserved by one user to support the multiple
data transmissions, thus achieving high efficient RIS-assisted connections at
the user. Moreover, under frequency-selective channels, implementing the MDR
scheme on the RIS group division, RISassisted multi-channel multi-user (MCMU)
communications are further explored to improve the service efficiency of the
RIS and decrease the computation complexity. Besides, a Markov chain is built
based on the proposed RIS-assisted MAC framework to analyze the system
performance of SCMU/MCMU. Then the optimization problem is formulated to
maximize the overall system capacity of SCMU/MCMU with energy-efficient
constraint. The performance evaluations demonstrate the feasibility and
effectiveness of each
