# mDARAL: A Multi-Radio Version for the DARAL Routing Algorithm
## 1 Introduction  
The rapid growth of Smart Cities among academics and public organizations is leading to numerous research projects [1; 2; 3]. Its rise involves the development of embedded devices, powering techniques and communication technologies. This work focuses on the challenge that communication technologies represent. This challenge has been intensively studied, as it is a large area of knowledge, which covers every aspect of the communication itself, such as traffic, collision reduction, data ratesincrease, number of nodes, compatibility, convergence time or even energy used by the different network protocols. Previous works of the authors focused on some of these aspects like the convergence time, energy used and control messages used by network protocols, proposing a new one, Dynamic and Adaptive Radio Protocol (DARP) [4; 5], focused on the optimization of these parameters during the forming phase of the network.  
The analysis of Smart City projects [6; 7] and the increment in terms of number of nodes and density present in networks [8; 9; 10; 11] have led to new challenges. The number of collisions and the saturation of the channels are problems that need new solutions and proposals. The study of multi-channel or even multi-radio approaches is a major trend today [12] for solving those issues. In [13], [PERSON] et al. demonstrate that a multi-radio system can provide high data rates with low energy consumption. [PERSON] et al. [14] analyzed how network reliability can be significantly improved with dual radio communication without having a significant impact on energy consumption. Following these works, the development of a new version of _DARP_ with multi-radio support is a logical development in order to face the above-mentioned new challenges.  
_mDARAL_ proposes a multi-radio routing algorithm based on the Dynamic and Adaptive Radio Algorithm (_DARAL_). It uses the main functionality of _DARAL_[5], adding the capability of selecting the communication frequency for each sub-network, regarding the use of each channel. It intends to maximize the performance through the distribution of the traffic into unoccupied frequencies. Therefore, the algorithm offers a better load distribution, minimizing the overall collisions. Since _DARAL_ organized the nodes in virtual sub-networks, each sub-network will adapt its frequency independently. _mDARAL_ is designed to be used in multi-radio devices, using one radio only for relevant communications on a fixed channel. In order to reduce the power consumption, the use of the radios is optimized, disabling inactive radios in nodes without routing requirements.  
The rest of the paper is organized as follows: Section 2 provides an overview of different previous works in the area of multi-radio based routing algorithms techniques for Wireless Sensor Networks (WSN). Section 3 describes _mDARAL_, the proposed algorithm designed for a better use of the available channels, increasing the delivery ratio in the network. The simulation procedure and the obtained results are shown in Sections 4 and 5. Section 6 presents the conclusions of this paper.