Automatic meter reading in the smart grid using contention based random access over the free cellular spectrum

Real-time transmission of smart meter measurement data is investigated. A contention based approach exploiting the unused cellular spectrum, e.g. of 4G Long Term Evolution (LTE), is proposed. The proposed approach uses subsets of LTE resource blocks (RBs) as allocation units. It is based on channel aware reservation slotted Aloha over orthogonal frequency division multiple access (OFDMA) using time/frequency slots, which leads to a reduction of collision probability, prevents collisions in the transmission phase, and allows detecting these collisions at the reservation phase. The proposed method relies on an access point (AP) that indicates the "available" OFDMA subcarriers to the contending devices after receiving this information through coordination with the cellular base station (BS): The BS informs the AP of the LTE RBs that it intends to keep free for a certain time period (e.g., because the current load on the network does not mandate their allocation to primary cellular users). Then, with the proposed approach, the AP transmits pilot signals on the free channels so that they can be used by the contending devices. Simulation results show that a large number of smart meters can be successfully accommodated within a limited coverage area with the proposed approach, while transmitting their measurement data in real-time.