Statistical Power Grid Observability under NOMA-based Communication Constraints

This paper studies the observability of the power grid by jointly considering the power system with the wireless communication system under the strict latency requirements of Phasor Measurement Units (PMUs), which is characterized via the theory of effective capacity. In order to meet the quality of service (QoS) requirements and save communication bandwidth at the same time, the technique of non-orthogonal multiple access (NOMA) is adopted. For practical purposes, we consider the case where each NOMA group consists of at most two PMUs. The problem is formulated as minimizing the required communication bandwidth while satisfying the observability constraint of the power grid, over all possible NOMA user pairing strategies, bandwidth allocation among NOMA groups, power allocation within each NOMA group and the normalized QoS exponents of each PMU. In order to solve this problem, we first derive the closed-form expressions of the effective capacity of the two-PMU NOMA pair, then the problem is solved by first fixing the NOMA user pairing strategy and the probability of successful transmission of each PMU, and finding the optimal bandwidth allocation among NOMA groups, power allocation within each NOMA group and the normalized QoS exponents of each PMU via the bisection search method. Then, the probability of successful transmission of each PMU is found via the simulated annealing algorithm for a fixed NOMA user pairing strategy. Finally, we discuss the benefit of using uniform channel gain difference (UCGD) pairing as the PMU-pairing strategy. Numerical results on the IEEE 14-bus power system demonstrate the significant bandwidth savings of the proposed algorithm compared with the orthogonal multiple access (OMA) method and the NOMA method with equal bandwidth and power allocation.