Opportunistic Multihop Wireless Communications with Calibrated Channel Model Petros Spachos , Liang Song and Dimitrios Hatzinakos Department of Electrical and Computer Engineering, University of Toronto, Toronto, ON M5S 3G4, Canada Abstract—Opportunistic routing schemes have been studied over the past decade to provide better performance in multihop wireless networks, by taking the advantage of the broadcasting nature of wireless channels. Simulation tools for such study are important and have been investigated to understand the network behavior. In this paper, we use real and simulated channel data to further elaborate the performance of opportunistic networks. In particular, a channel model is built by radio signal strength measurement in an indoor infrastructure, and the output of the channel model is used to feed an opportunistic network simulator. The paper then compares the performance of multihop wireless communications in opportunistic and traditional schemes. I. INTRODUCTION Multihop wireless communications can have important ap- plications in large-scale wireless networks, including wireless mesh networks and wireless sensor networks. The source and destination nodes do not have to be in the direct communi- cation range of each other, where relay nodes in-between the source and destination can relay wireless packets in multiple hops. As such, the coverage of the wireless network can be extended without cabling. Compared to single-hop wireless networks (e.g., star-topology networks), multihop wireless networks also have higher spectrum efficiency and higher energy efficiency, since spectrum resources can be re-used over space, and less transmitting power can be used for conserving energy. Traditional multihop wireless networking requires a prede- termined network topology where routing table can be set up and a predetermined spectrum allocation where point-to- point wireless links can be configured. Both requirements are meeting challenges in engineering practice. Spectrum availability is often volatile due to co-channel interference especially in unlicensed bands; and wireless node availability can be affected by traffic congestions and other factors such as battery and hardware failures. Therefore, in traditional wireless networking, it is often encountered that the communication throughput and latency performances can degrade fast (usually exponentially) with the number of wireless hops. Large-scale cognitive wireless networking [1] has been proposed to tackle the above challenges by an integration of opportunistic routing and opportunistic spectrum access. The performance of wireless communication in an indoor environ- ment with a 3D-ray tracing channel model have been studied in [2]. The contribution of this paper is to compare such schemes with traditional multihop wireless networking under a This work was supported in part by the Natural Sciences and Engineering Research Council of Canada (NSERC), and by the MRI-Ontario under an ORF-RE grant. realistic wireless channel model. Particularly, a channel model is builded by real measurement data in an indoor propagation environment. The model is then used for generating realistic channel parameters in OMNET++ network simulator, where performances of opportunistic and traditional wireless net- works are compared. It is shown that the opportunistic can use dynamics of indoor wireless propagation where the traditional suffers from. In addition, the developed process can also be contributing to indoor wireless network planning in general. The rest of this paper is organized as follows. In Section II, the related works are reviewed. The channel model is described in Section III while the design and the routing protocols are presented in Section IV. In Section V, performance analysis and simulation results are presented, followed by conclusions in Section VI. II. RELATED WORKS The first opportunistic routing method was introduced in Extremely Opportunistic Routing (ExOR), [3]. Next relay node selection process in ExOR is based on a slotted acknowledge (ACK) mechanism. Whenever a node has successfully received a data packet, it has to calculate a priority level which is inversely proportional to the expected transmission count metric (ETX) [4]. ETX is based on the distance between the node an the destination. The shorter the distance the higher the priority. However, this simple priority criteria may lead packets toward the destination through low-quality routes. Opportunistic Any-Path Forwarding (OAPF) [5], overcomes this problem by introducing an expected any-path count (EAX) metric for a pair of nodes with a given set of candidates that captures the expected number of transmissions between them under opportunistic forwarding. According to EAX, a prioritization method for all the candidate nodes is built, which guarantees that each candidate contributes to packet delivery. Although this approach tries to calculate the near- optimal candidate set at each potential relay node to reach the destination, it needs more state information about the network and it has high computational complexity. In ExOR, because of the simple prioritization method, du- plicate packets might occur. MAC-Independent Opportunistic routing and Encoding Protocol (MORE), [6] introduced the concept of innovative packets. In that way it manages to avoid any duplicate packets that might occur in ExOR. A Geographic Random Forwarding (GeRaF), technique was introduced in [7], [8]. In GeRaF each packet carries the loca- tion of the sender and the destination, so that the prioritization of the candidates nodes is based on location information.