Wireless network coding (WNC) has been considered as a promising solution with its capability of improving the overall performance of wireless mesh networks. A problem caused when WNC is employed in multi-rate wireless networks is that the link status between the relay node and intended receivers of a coded packet is mutually different. Even though there are links that support higher transmission rates, the relay node must transmit the coded packet at the lowest transmission rate among intended links' rates for the successful reception at all intended receivers. In this paper, we propose a WNC scheme that is combined with Forward Error Correction (FEC) to alleviate the problem explained above. The proposed scheme tries to transmit coded packets with a transmission rate higher than the lowest transmission rate so that the time required to transmit coded packets is reduced. However, it may increase the error rate. To compensate for the increased error rate, we use adaptively controlled FEC code. Our simulation study results show that the proposed scheme can increase the network coding gain compared to existing schemes.

To provide Internet connectivity to mobile ad hoc networks, several solutions have been proposed. Most of the proposals focus on the suitable and optimal gateway selection and handover schemes in accordance with the network status and node mobility. However, since an integration of the Internet and ad hoc networks is a function of the network layer, they do not consider characteristics of lower layers such as a multichannel capability. If the operating channels of each gateway are different, mobile nodes connecting to one gateway cannot receive any messages from other gateways, and thus they cannot perform handovers to other gateways. In this paper, we propose a new handover scheme for hybrid ad hoc networks in multi-channel environments. We revise and extend the previously proposed handover schemes namely the forced handover and optimized handover. We also studied the performance of the proposed two schemes through ns-2 simulations.

In this paper, we define a resource allocation problem focusing on the scheme minimizing energy consumption of subscribers in uplink subframe of the IEEE 802.16 OFDMA systems. In order to clearly formulate the relation between the uplink resource allocation and energy efficiency of subscribers, we use the multiple choice knapsack (MCK) problem, which is proved to be an NP-hard problem. Instead of finding an optimal solution, we seek a suboptimal solution. Based on the problem formulation, we adopt the existing solution of the Multiple Choice Knapsack problem to solve the resource allocation problem. The suboptimal solution adaptively uses the modulation and coding scheme defined in the IEEE 802.16 systems to minimize the required transmission power while guaranteeing QoS. Our simulation results show that the suboptimal algorithm can reduce the energy consumption up to 53% compared to the channel state information (CSI) scheme, which determines the modulation and coding level only considering the channel state information.

There has been much research effort to exploit the multi-rate capability of WLANs to improve performance. While these approaches focused on exploiting good channel conditions for direct transmission between stations, there are no considerations of performance degradation by low rate transmissions due to poor channel conditions. Thus, we propose a frame relay based MAC protocol, termed FR-MAC, to tackle this issue and to improve network performance. The key idea of FR-MAC is that the time required to transmit a frame using an intermediate station as a relay can be much smaller than the direct transmission at a lower rate, if the intermediate station between the source and the receiver can relay the frame at higher rates. Simulation results show that the proposed protocol improves network performance and the amount of improvement significantly increases as the number of relayed stations and the payload size are increased.

In ad hoc networks, broadcasting is one of the important communications patterns frequently used. Straight-forward broadcast is usually known to be very expensive and results in serious redundancy, contentions, and collisions. The phenomenon is referred to as broadcast storm problem. In this paper, we propose a forwarding set selection scheme and efficient schemes to broadcast with transmission power control in multi-hop ad hoc networks. Our simulation study shows that the proposed schemes reduce the broadcast latency, the number of collisions, average power consumption, etc.

Recently, many on-demand routing protocols for ad-hoc networks have been proposed, but most of these works have been done on the basis of the IEEE 802.11 standard that supports a single transmission rate. In ad hoc networks supporting the multi-rate transmission scheme, which is referred to as dynamic rate shifting in the IEEE 802.11 standard, few performance studies on ad-hoc routing protocols have been performed. In this paper, we extensively study the impact of dynamic rate shifting on the performance of ad-hoc routing protocols in various situations in multi-rate WLANs environments. Our question is whether the dynamic rate shifting scheme supported by the IEEE 802.11 standard affects the relative performance of the routing protocols being studied. We have extended the ns-2 network simulator to accurately model the IEEE 802.11b wireless LAN standard, and simulated the performance of two ad hoc routing protocols over each of networks supporting single rate and multi-rate transmissions.

In this paper, we propose an efficient multicast routing protocol based on mobile IP standard in wireless mobile networks. A mobile host that is located in a foreign network receives a tunneled multicast datagram from a multicast agent, which is located in a remote network or local network. While receiving a tunneled multicast datagram from a remote multicast agent, the local multicast agent starts a multicast tree join operation if the mobile host is expected to remain the network relatively long period of time, while it does not start multicast tree join operation if the mobile host is expected to remain the network relatively short period of time. The proposed protocol tries to maximize the number of unnecessary multicast tree join operations. We examined performance of the proposed protocol by simulation under various environments and we got good performance results.