The project contains two parts; one is for the Software-Defined Network (SDN) – based Vehicle to Infrastructure (V2I) offloading scheme from cellular network to 802.11p network and the other one is the Device-to-Device (D2D) Communication–based Wi-Fi offloading using the Software Defined Net-work (SDN) –enabled Wireless Mobile NetNet-work Environment.
For the first part, Vehicular Ad Hoc Network (VANET) is an emergent wireless mobile network [1][2]. In VANET, each vehicle is equipped with an On Board Unit (OBU) and the communication par-adigm can be Vehicle to Vehicle (V2V) or Vehicle to Infrastructure (V2I). This work tackles the problem of the offloading from 3G/3.5G/4G cellular network to IEEE 802.11p network for VANET. The scenario of IEEE 802.11p offloading in VANET that is considered in this work is as follows. Let the OBU of a vehicle X be equipped with a 3G/3.5G/4G cellular network interface and an IEEE 802.11p network interface. X regularly uses the 3G/3.5G/4G cellular network interface of its OBU for V2I (Vehicle to Infrastructure) communication. When X is in the IEEE 802.11p network signal coverage of a RSU, it can offload its V2I communication from the 3G/3.5G/4G cellular network to IEEE 802.11p network.
That is, X’s V2I communication has the handoff from the 3G/3.5G/4G cellular network to the IEEE 802.11p network.
Main concerns that should be considered in VANETs offloading from the 3G/3.5G/4G cellular network to the IEEE 802.11p network of RSU are as follows: 1) Is RSU’s IEEE 802.11p networking situation good enough to allow vehicle X to have the offloading? Since the vehicle is moving, if the networking situation of RSUs 802.11p network is bad, it may need X to handoff back to 3G/3.5G/4G cellular network again after X handoff to RSU’s IEEE 802.11p network for a very short time period or even immediately. That is, it may take longer time overhead for the messaging of handoff processing because RSU’s IEEE 802.11p networking situation is bad and thus the effective time period for offload-ing data transmission through RSU’s IEEE 802.11p network becomes shorter. In the worst/extreme case, it may be out of the signal coverage of RSU’s IEEE 802.11p network before the handoff processing from 3G/3.5G/4G cellular network to RSU’s IEEE 802.11p network is done because the vehicle is moving such that the staying time period inside the signal coverage of the IEEE 802.11p network is limited! 2) Can the handoff decision be made before vehicle X senses the signal of the ahead IEEE 802.11p RSU?
If the offloading can be decided before X enters into the signal coverage of the ahead IEEE 802.11p RSU, i) X can decide not to handoff from 3G/3.5G/4G cellular network to the ahead RSU’s IEEE 802.11p network if the networking situation of the ahead RSU’s IEEE 802.11p network is too bad even if the transmission expense is free and ii) X can save the handoff decision overhead such that X can keep in the 3G/3.5G/4G cellular network without wasting the handoff decision time spent inside RSU’s IEEE 802.11p network when the negative handoff decision is made: It takes some computing time overhead if the handoff decision is made after vehicle X entering into the signal coverage of the corresponding IEEE 802.11p RSU. Figure 1 depicts the abstract architecture of the proposed SDN-based vehicular
network. Figure 2 depicts the configuration for the proposed SDN-based V2I offloading.
Figure 1 The abstract architecture of the proposed SDN-based vehicular network.
Figure 2. The configuration for the proposed SDN-based V2I offloading.
For the second part, with the advance of wireless mobile networks, e.g., 4G cellular network and IEEE 802.11ac and IEEE 802.11ad Wi Fi network, it is feasible to have ubiquitous computing and ubiq-uitous communication at any time and any place using any device. Nevertheless, the increasing subscrib-ers of 3G/3.5G/4G cellular network make the traffic in 3G/3.5G/4G cellular network be higher and higher gradually. Increasing deployment infrastructure might resolve the traffic demand. However, it is too expensive for service providers to solve the problem using this way. Hence, a lot of traffic offloading methods have been proposed to offload part of the traffic from 3G/3.5G/4G cellular network, which uses license spectrum, to 802.11.* Wi Fi network, which uses unlicensed spectrum. In contrast with using licensed spectrum, i.e., the one used in 3G/3.5G/4G cellular network, unlicensed spectrum is less expen-sive. Furthermore, 802.11.* Wi Fi network may have better throughput and consume less power than 3G/3.5G/4G cellular network.
(a)
MN2(b)
Figure 3. The communication configurations of using (a) 3G/3.5G/4G cellular network and (b) the Wi Fi offloading.
Figure 3-(a) shows the communication configuration of using 3G/3.5G/4G cellular network. Two mobile nodes MN1 and MN2 are communicating with each other through 3G/3.5G/4G cellular network.
If MN1 wants to transmit data to MN2, MN1 needs to forward its data to the associated BS, 3G/3.5G/4G core networks, the other BS and then to MN2. It not only consumes licensed bandwidth to transmit data but also results in longer delay time for the data delivery.
Wi Fi offloading is one of the alternative approaches for reducing traffic in 3G/3.5G/4G cellular network. Let the signal coverage of the Wi Fi network be overlapped/inside the signal coverage of 3G/3.5G/4G cellular. Then, a mobile node can switch from the 3G/3.5G/4G cellular network interface to the Wi Fi network interface when the mobile node is inside the overlapped area. Figure 3-(b) is the transmission configuration of traffic offloading from the 3G/3.5G/4G cellular network to the Wi Fi net-work.
Figure 4. The communication configurations of using (a) the Wi Fi infrastructure-based Wi Fi of-floading and (b) the D2D-based Wi Fi ofof-floading.
Wi Fi offloading has the following advantages: (1) Most of currently available user devices have both 3G/3.5G/4G cellular network and Wi Fi network interfaces. Thus, the Wi Fi offloading can be implemented practically without any assumption. (2) Wi Fi offloading runs in the unlicensed spectrum.
The corresponding mobile node can release the 3G/3.5G/4G cellular network to improve spectrum effi-ciency. (3) Wi Fi offloading may result in better throughput than 3G/3.5G/4G cellular network. (4) Using
Wi Fi network can have lower or even free cost comparing with using 3G/3.5G/4G cellular network because of the unlicensed spectrum concern.
Although the 3G/3.5G/4G cellular network's traffic offloading onto the Wi Fi network can improve the throughput of 3G/3.5G/4G cellular network and the energy efficiency of mobile nodes, it still needs to transmit data through the Wi Fi AP when MN1 wants to transmit data to MN2. It may increase the burden of the Wi Fi AP. Moreover, when the peered mobile nodes leave the corresponding Wi Fi AP, Wi Fi offloading becomes useless even if the peered mobile nodes coexist in each other's Wi Fi signal cov-erage. Device-to-Device (D2D) -based Wi Fi offloading, in which the traffic is through the Wi Fi link directly between the peered mobile nodes without going through the Wi Fi AP, is an alternative approach to tackle the aforementioned issue. D2D-based Wi Fi offloading can have better performance than Wi Fi infrastructure-based Wi Fi offloading, in which the traffic goes through the Wi Fi AP and then to the peer mobile node. Figure 4 depicts communication configurations of using (a) the Wi Fi infrastructure-based Wi Fi offloading and (b) the D2D-based Wi Fi offloading.