# Mobility-Enhanced Reliable Geographical Forwarding in Cognitive Radio Sensor Networks
## 5 Mror: Mobile Reliable Opportunistic Routing for CRSN
### Channel Selection and Route Request Initiation  
We assume that an event area of radius \(r_{evt}\) meters is to be monitored by the mobile sensors. A typical event can be post-disaster rescue missions or military actions, where the SUs corresponding to mobile robots are strategically deployed to move into difficult and wide terrain to monitor and send their sensory readings to a remote sink. The sensors transmit their data in the form of pictures, low-resolution videos, temperature or a selective combination of these entities to a remote sink. When potential source nodes hit a target area, they contend in initiating a route request by broadcasting a route request (RREQ) packet. Once a node successfully gets through its route request, other nodes will desist route request broadcast and only participate in the implementation of the route request activity. The RREQ packet encapsulates the source's address, the sink's address along with the RREQ tag. After the broadcast, the source node initiates a timer, \(\overline{T_{r}}\). This timer carries the maximum route negotiation time. Within this time, the source node expects to receive a route reply message. If the source node times out without receiving any reply, another RREQ is sent. Depending on the kind of media being transmitted, a quality of service requirement is stipulated by the source node to successfully send the traffic to the sink. This value is also embedded in the route request payload. For this study, the considered QoS metric is the minimum data rate essential to service available packets. This information is captured by the application layer, which is the layer that is in direct contact with the activated sensor. Although the function \(\chi_{i}^{ch}\) can be used to identify an appropriate channel for data transmission, it is pertinent to note that \(\chi_{i}^{ch}\) does not consider the bandwidth and the spectrum sensing error, which are equally important metrics for ensuring QoS. Thus, to be sure a chosen channel can support the traffic at hand, confirming its data rate is essential. While considering mobility, the required data rate will be defined as the achievable spatio-temporal data rate, \(R_{i}\), on any channel based on its spatio-temporal availability, \(\varpi_{i}\), which depends on both the speed and the transmission range of  
Figure 2: MROR channel pool update algorithm. the node \(\frac{v}{\mathbb{R}}\). This defines the sum of the rate, \(R_{s,i}\left(\alpha\right)\), when a channel is detected idle alongside the possibility of PU appearance during the period of packet transmission, \(T_{su,i}\), with the achieved rate, \(R_{f,i}\left(\alpha\right)\), because of false channel availability. Note that interference among SUs, \(I_{su,i}\), is considered in both cases. Hence, the attainable data rate when the PU is inactive and there is no false alarm can be represented as:  
\[b_{s,i}(\varpi)=\beta log_{2}\left(1+\frac{S_{rec}^{su}}{n_{i}+I_{su,i}}\right)\]  
\[R_{s,i}(\varpi)=\left(P_{off,i}-P_{f,j}\right)\frac{T_{su,i}-\overline{T_{s,i}} -\overline{T_{r}}}{T_{su,i}}b_{s,i}(\varpi) \tag{23}\]  
However, a PU can arrive at any time during the time \(T_{su,i}\), which subsequently results to interference that converges to \(\left(1-P_{off,i}\right)T_{su,i}\) with a probability \(1-e^{-\theta\frac{T_{su,i}}{\tau_{un,i}}}\), where \(\theta\) is a scaling factor.