# SACRB-MAC: A High-Capacity MAC Protocol for Cognitive Radio Sensor Networks in Smart Grid
## 1 Introduction  
The legacy electric power grids are facing numerous challenges, such as aging infrastructure, energy inefficiency, frequent transmission congestion and even failures. The next generation of electric grids, termed as smart grids, are expected to supply improved service with higher reliability, efficiency, agility and security [1; 2; 3], due to their capabilities of distributed computing, automated control and advanced bi-directional communications. Electricity providers, distributors and consumers would benefit from real-time awareness of operating environments, requirements and capabilities, since smart grids are capable of gathering information in real time from equipment in different areas and then making intelligent decisions to promote the efficiency and security of electric grids. For the successful operation of a smart grid, an integrated high performance, reliable, efficient, robust and secure communication network is critical [4; 5]  
Recently, the _Cognitive Radio Sensor Network_(CRSN) has gained much attention for electric power networks [6; 7; 8; 9; 10; 11] and is expected to address the unique challenges of communications in a smart grid. In [6; 7], the advantages of CRSNs are introduced, and the potential for the application in smart grids is analyzed. CRSNs can supply low cost, efficient and reliable operation in different parts of a smart grid, such as transmission towers, commercial buildings, distributed power plants, _etc._ The information gathered from sensors can be used for different applications, such as real-time fault detection, smart metering, automated demand response, and so on. Moreover, due to the capability of dynamic spectrum access, CRSNs can reduce congestionand excessive packet loss and thereby make transmissions more reliable. For the realization of CRSNs, literature [8] studies the connectivity of large-scale networks in fading environments under different routing mechanisms; literature [9] studies the coexistence and fairness, when several secondary networks share the same primary user resources; and [10] proposes a receiver-based MAC protocol for CRSNs in a smart grid (_i.e._, Cognitive Receiver-Based (CRB)-MAC), which exploits the broadcast nature of the wireless medium to reduce retransmissions, so as to provide high energy efficiency and reliability. These research works make great contributions to successfully operating CRSNs in a smart grid. However, the high bandwidth requirements is a critical issue for the application of CRSNs in a smart grid, such as in _Advanced Metering Infrastructure_ (AMI) networks [11; 12], which are one of the key elements of a smart grid. Hence, the successful application of CRSN in a smart grid is dependent on the communication capabilities, which brings about enormous challenges for the reliability and throughput of CRSNs. On the other hand, the spectrum aggregation [13] technique has been proposed to meet the increasing bandwidth demands and to overcome the problem of wide continuous spectrum band shortage in the current spectrum resource situation. Recently, a number of studies have been done on spectrum aggregation-based approaches for Cognitive Radio (CR) networks to improve throughput and spectrum efficiency (e.g., see [14; 15; 16; 17; 18; 19; 20; 21; 22]). Especially, in [20], a Spectrum-aware Clustering protocol for Energy-Efficient Multimedia routing (SCEEM) is proposed, in order to improve the routing efficiency and overcome the limitations of energy and spectrum, by using spectrum-aware clustering. In [21], a spectrum-aware and energy-efficient MAC protocol is proposed to improve the energy efficiency of CRSNs. By communications on a _Common Control Channel_ (CCC), the sender and receiver can search the common available channels in subsets of the spectrum band, such that the energy consumption for spectrum sensing is deceased.