IND-MAC: A Stratified MAC Protocol for Differentiated Services in IRS-Enhanced Industrial IoT Networks

Industrial internet of things (IIoT) networks face a core challenge in simultaneously managing mission-critical services and massive data streams, compounded by signal blockages from dense machinery. While intelligent reflecting surfaces (IRS) are effective in creating reliable communication links to overcome these blockages, the fundamental task of efficiently allocating these reconfigured resources to services with vastly different requirements falls to the multiple access control (MAC) layer. This paper proposes IND-MAC, an IRS-enhanced non-orthogonal multiple access (NOMA) -based differentiated MAC protocol featuring a stratified access mechanism. The time frame of IND-MAC is logically partitioned into a guaranteed-access period (GAP) for critical services and an efficiency-oriented period (EOP) for routine services. During the GAP, a QoS-aware optimization strategy is employed to jointly optimize IRS phase shifts and transmit power of IIoT devices, whereas during the EOP, an efficiency-driven allocation strategy leverages contention-based NOMA to maximize throughput. Simulation results demonstrate that IND-MAC achieves higher spectral and temporal efficiency than state-of-the-art benchmark protocols. This stratified approach enables IND-MAC to adeptly manage the trade-off between overall system efficiency and guaranteed service quality for heterogeneous IIoT applications.