## 1 Introduction  
In smart cities the availability of ubiquitous sensor communications is essential, but the use of a flexible and portable network for transporting the sensed data is also key. A Wireless Mesh Network (WMN) [1; 2] is a key technology in current wireless communications which fulfils this aim. It is arranged into a set of devices (user terminals or linking interfaces) whose interconnections are wireless and organized in a lattice structure. The International Electrical and Electronic Engineering (IEEE) association has developed different standards, especially IEEE 802.11 for Wireless Fidelity (WiFi) or IEEE 802.15 for Wireless Sensor Networks (WSNs), among others. They are generally deployed in an ad-hoc mode, depending on the requirements, and can be used as a means of transport for data from end users and specially for interconnection of subnetworks whose distance or difficult access require wireless connectivity. Often communication sources can be directly linked to mesh nodes, e.g., user smartphones cooperating in a shared task. In some solutions for smart cities there already exist different proposals for facilitating both mobile collaborative sensing and sensed data access, so the collected information can be processed and shared by all the users. As stated above,typical sensed data are generated by smartphone sensors (such as Global Positioning System (GPS) receivers, accelerometers, cameras and several others) but also from different sources like presence sensors (those which usually activate lighting). Whatever mission a WMN has (a traditional transport network, a network for sensing capable stations, or a sensor network), it entails multiple challenges such as routing, throughput, range of operation, power saving, adaptability, stability, and robustness, among others. Some technologies at the link level have been proposed to implement WMNs [3] in different environments. The IEEE 802.11s [4] standard is normally used in wide area WMNs deployed in cities or places of similar area. WiFi routers and Access Points (APs) have been proposed to implement such WMNs [5]. We will call them hereafter Mesh Access Points (MAPs). WMNs can be deployed in very large numbers in different domains [6], e.g., a smart city [7] in which the WMN is configured as a backbone that transports a variety of traffic including sensor data [8], and multimedia [9], among others, but there are still several challenges to convert them into a suitable infrastructure in some domain applications. Next we review some of them. An efficient channel assignment in WMN [10] improves its throughput considerably. The optimal assignment is not efficient or impossible when there will be uncontrolled external aspects present around the WMN, e.g., the interferences caused by external APs and other wireless devices owned by a third party. Those devices can be commonly deployed statically or sometimes dynamically (e.g., massive usage of mobile telephones with tethering technology as in [11]). Channel interferences or collisions in current cities [12], where dense WiFi networks are deployed, could be a hard problem for IEEE 802.11s- or WiFi-based WMNs. WiFi interferences penalize greatly data communication due to the fact wireless channels would be busy communicating signalling. The routing is a key parameter to obtain the connectivity among MAPs [13]. Optimized Link State Routing (OLSR) [14] is a routing protocol used in Mobile Ad Hoc NETworks (MANETs), but it also can be used in WMNs, as well as Hierarchical OLSR (HOLSR) [15]. When a strong pattern of collisions or interferences, signal or packet loss, connection drops, or even service disruptions [16] occur in a MAP, its suitability for relaying the packets of any route will be compromised. In that case, the routing protocol must rapidly set up a new route in order to maintain the connectivity of the network. Energy saving in WMNs is another important challenge [17] as recognized in [18], but it is also a driving force behind sustainable solutions for smart cities [19; 20; 21; 22; 23; 24].