Masakatsu Ogawa

Unidirectional Ad Hoc Routing Protocol with Area-controlled Flooding Using Overheard Neighbor Node Information

In ad hoc networks, wireless links can be unidirectional due to the difference of transmission range of each node. Particularly for temporally formed ad hoc networks, routing protocols should support route construction using unidirectional links to provide high connectivity in various network configurations. Although existing DSR have a mode of two way flooding to support route construction using unidirectional links, it involves substantial control traffic and should be avoided in the high node density environment. This paper proposes a novel routing protocol supporting unidirectional links called FOCUS2 (flooding based ad hoc routing protocol controlled with overheard control information to support unidirectional links). FOCUS2 employs an area-controlled two way flooding that adaptively limiting flooding area. Performance evaluation by simulation shows that FOCUS2 reduces the number of control packets by approximately 50 % as compared with existing two way flooding DSR and that the degradation of route construction performance is small

AD HOC Routing Protocol with Flooding Control using Unidirectional Links

In ad hoc networks, unidirectional links between nodes exist due to differing propagation patterns or wireless interferences. Routing protocols for bidirectional links must cause the decline of connectivity. In recent years, some routing protocols considering unidirectional links have been proposed. However, these protocols have a problem: the broadcast traffic for backward path discovery increases. This paper proposes a novel routing protocol for ad hoc networks that positively uses unidirectional links and that drastically reduces the number of control packets. Our protocol improves network connectivity and reduces the number of control traffic.

Proposal and Evaluation of a Mesh Wireless Local Area Network Architecture with Dual DCF-HCCA Channel Access Scheme in the Vicinity of Gateway Access Points

The gateway access point (AP) in a wireless mesh network becomes the natural bottleneck node around which all the traffic relayed by APs that is exchanged among the terminals and the Internet tend to concentrate. So far most of the practical deployments of mesh wireless local area networks (WLANs) focused on public safety and public access have taken place in rural or suburban areas where the low density of users and the low data-rate applications in use do not impose stringent traffic conditions, making the conventional single-radio DCF-based system defined by IEEE 802.11 a feasible implementation option. However, under relatively high traffic-load conditions, the large number of packet collisions produced by the accumulation of traffic in the vicinity of gateway APs may greatly reduce the overall network throughput and largely increase the delay, especially in case of packets that traverse several hops, thus affecting real-time applications like voice over IP (VoIP). To cope with this problem a polling mechanism compliant with the IEEE 802.11e hybrid-coordination-function controlled channel access (HCCA) which operates in a single network interface card (NIC) in the vicinity of gateway APs has been proposed in this paper. The polling scheme is complemented with a Distributed Coordination Function (DCF) channel access that also operates in the vicinity of gateway APs in a different NIC and on a different channel. The HCCA NIC allows any gateway AP to exchange data frames with its surrounding APs in a scheduled and bidirectional way while the DCF NIC provides gateway APs a contention-based way to receive data frames from their respective surrounding APs. Computer simulations carried out in OPNET version 10.0 to evaluate the combination of both contention-based and contention-free access schemes in the area surrounding gateway APs show that the proposed mechanism can largely increase the total throughput while providing low transmission delay. As no changes to the IEEE 802.11 related protocols are required, the proposed scheme represents an attractive option to implement a mesh WLAN.

Ad hoc unidirectional routing protocol based on relay control of route requests

In ad hoc networks where mobile nodes form networks autonomously, many unidirectional links can be generated due to the diversity of transmission range of each node In order to achieve high connectivity in such networks, routing protocols should construct routes by aggressively using unidirectional links. Typical existing routing protocols such as DSR (dynamic source routing) are basically designed assuming links are bidirectional, and they generate substantial control traffic in the unidirectional routing since their optimization schemes are not effective for unidirectional links. This paper presents a novel on-demand ad hoc routing method called FOCUS (controlled-flooding-based ad hoc routing protocol using overheard hop count information to support unidirectional links). FOCUS reduces control traffic of route reconstruction as compared with conventional method by issuing route request in the restricted region around the broken route. The results of performance evaluation by simulation show FOCUS reduces the number of RREQ (route request) packets by about 60 % and reduces packet transmission delay by about 30% compared to DSR.

Unidirectional ad hoc routing with efficient route reconstruction using relay control of route requests

This paper evaluates performance of on demand ad hoc routing protocols to handle unidirectional routing protocols. Ad hoc networks are consisted of nodes of various transmission range in many cases. Thus routing protocols should support route construction using unidirectional links to provide high connectivity and high routing performance with low control overhead. Among existing routing protocols, DSR is typical protocol to support unidirectional routing, but its optimization mechanism is not effective for unidirectional links and generates substantial control traffic. We have previously proposed a new on demand ad hoc routing method for unidirectional routing called FOCUS. In this paper, FOCUS is evaluated and compared with DSR. Results of simulation show that FOCUS outperforms DSR in the number of transmitted RREQ packets and data packet transmission delay while maintaining route construction performance, and that it is especially effective in high density network.

Experimental Evaluation of Coexistence Method for ZigBee under WLAN Interference

ZigBee has attracted attention for constructing the sensor network such as home energy management system. Both ZigBee and wireless LAN (WLAN) use a 2.4GHz band, called the industrial, scientific, and medical unlicensed band; therefore, ZigBee faces severe interference problems in the presence of WLAN. Frame collisions are serious problems between ZigBee and WLAN. Both employ a carrier sense mechanism to avoid collision, but both use different channel access mechanisms. The primary problem is the competition that exists between WLAN data frames and ZigBee ACK frames, i.e., because of WLAN interference, ZigBee may not receive any given ACK frame; therefore, the ZigBee transmission success ratio is degraded. To overcome this problem, the authors propose an interference avoidance method that improves ZigBee and WLAN coexistence and utilizes actual equipment to present the experimental evaluation. The experimental results reveal that the ZigBee transmission success ratio increases as the WLAN transmission rate increases. In addition, we clarified the distance in which the proposed method can effectively operate. Index Terms—Wireless LAN, ZigBee, CSMA, interference, frame collisions

A novel interference avoidance technique on MAC protocol for Wireless LAN-WIMAX relay

To use WLAN (wireless LAN) terminals anywhere, mobile wireless routers (MWRs) that can connect WLAN terminals to the backbone network by using WLAN-WiMAX (Worldwide Interoperability for Microwave Access) relay are receiving a lot of attention. These MWRs have small chassises because of their mobility. Therefore, the WLAN device and WiMAX device are adjacent to each other in these MWRs. Moreover, the assigned frequency bands of WLAN (2.4GHz) and WiMAX (2.5GHz) are close. Under this situation, the two wireless devices suffer mutual system interference, which greatly degrades system throughput of the wireless relay. To suppress this interference, this paper proposes a novel interference avoidance technique for the MAC protocol of WLAN-WIMAX relays; it is comparatively easy to implement in small terminals. Simulations show that the proposed method outperforms the conventional methods.

Fair Wireless Access Control with Error Compensation Based on Retry Count

Fairness in the number of effective opportunities for wireless access between the uplink and downlink and that between stations cannot be achieved in wireless packet communications such as wireless LANs due to the packet error caused by packet collisions or received power degradation. In this paper, we propose fair wireless access control with error compensation (FWAC/EC) to achieve fairness over an unstable link. The key features of the proposal are release delay control and packet compensation control. The point of the release delay control is to control the waiting time for attempting a subsequent transmission after an ongoing transmission. The point of the packet compensation control is continuous transmission based on the number of retries. Simulation results show that FWAC/EC achieves fairness in the number of effective opportunities for wireless access between the uplink and downlink and that between stations over an unstable link.