Kengo Nagata

A Multi-channel infrastructure based on DCF access mechanism for Wireless LAN Mesh Networks compliant with IEEE 802.11

The mesh topology based on the standard IEEE 802.11 for wireless LANs appears to be a very promising architecture for achieving a ubiquitous wireless Internet access in the future. However, the current IEEE 802.11 protocol is aimed at single access point (AP) environments and many problems related to the wireless meshed interconnection of APs and mobile terminals (MTs) remain to be solved. Some proposed solutions to build such mesh architectures are based on single-channel ad-hoc oriented schemes in which IEEE 802.11 protocol has been modified. The main problem with this type of schemes, however, lies in the very low performance of the single-channel architecture itself. The task group S of IEEE 802.11 is currently working out standards for IEEE 802.11-compliant mesh architectures in a number of usage scenarios including residential, office and campus/community/public access network but a lot of work remains to be done since the group was established just on last year. In this paper we propose a new multi-channel mesh architecture for hot zones which works using a distributed coordination function (DCF)-based technique for interconnecting APs. A major advantage of our proposed scheme is that, putting routing issues aside, it introduces no change into the MAC protocol of IEEE 802.11. Our simulations results obtained in OPNET show a good performance of our proposed scheme in terms of throughput and delay. We also show interesting results related with the size of packets and the mesh architecture itself that could lead to further research in the future

Queuing Scheme for Improved Downlink Throughput on WLANs

A transmission queuing scheme is described that increases downlink throughput on wireless local area networks (WLANs) while also increasing the total throughput. When the amount of uplink traffic increases on a WLAN, the carrier sense multiple access with collision avoidance (CSMA/CA) protocol, which is the prescribed scheme for IEEE 802.11 WLAN channel access, may substantially reduce the rate of downlink data frame transmission. This results in severe throughput degradation for mobile stations with downlink traffic. The proposed scheme comprises a transmission control function based on consecutive transmission, as described in the IEEE 802.11e standard, and a dynamic queue prioritization algorithm. Simulation results demonstrate that the proposed scheme increases the maximum total throughput for uplink and downlink traffic by 17% compared with the conventional distributed coordination function (DCF) scheme and that it reduces the difference between uplink and downlink throughput. In an environment where transmission errors occur, the difference in throughput is reduced by about 50% compared with the conventional schemes.

Multi-channel wireless LAN mesh architecture with DCF-based inter-AP communication and idle channel search packet forwarding

The mesh topology based on the standard IEEE 802.11 for wireless LANs appears to be a very promising architecture for achieving a ubiquitous wireless Internet access in the future. However, the current IEEE 802.11 protocol is aimed at single-AP (access point) environments and many problems related to the wireless meshed interconnection of APs and mobile terminals (MTs) remain to be solved. Some proposed solutions to build such mesh architectures are based on single-channel ad-hoc oriented schemes in which IEEE 802.11 protocol has been modified. The main problem with this type of schemes, however, lies in the very low performance of the single-channel architecture itself. The task group S of IEEE 802.11 is currently working out standards for IEEE 802.11-compliant mesh architectures in a number of usage scenarios including residential, office and campus/community/public access network but a lot of work remains to be done since the group was established just on last year. In this paper we propose a new multi-radio multi-channel mesh architecture for hot zones which works using a distributed coordination function (DCF)-based technique for interconnecting APs and a simple but effective radio routing mechanism. A major advantage of our proposed scheme is that, putting routing issues aside, it introduces no change into the MAC protocol of IEEE 802.11. Our simulations results obtained in OPNET show the great effectiveness of radio routing for balancing the traffic load within the network as well as interesting results related with the size of packets and the mesh architecture itself that could lead to further research in the future. Moreover, the results show the proposed architecture yields a very good performance in terms of total throughput and transmission delay

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.

Enhancement of DCF by multiple data frame transmission scheme based on the number of elapsed contention windows

This paper proposes a new data frame transmission scheme for IEEE 802.11 wireless LAN. IEEE 802.11 wireless LAN employ the binary exponential backoff algorithm to lower the possibility of collisions without reducing efficiency. Unfortunately, it has been shown that the algorithm is, in the short term, highly unfair. To improve the data transmission efficiency, several schemes allow stations to transmit successive frames. Employing these schemes worsens the short-term unfairness. The proposed scheme ties successive transmission to the number of elapsed contention windows to improve the throughput performance without increasing the unfairness. Simulation results show that the proposed scheme achieves high throughput performance while maintaining fairness.

Performance evaluation of the frame bursting method for high speed wireless LAN systems with multirate mechanism

This paper evaluates a novel media access control (MAC) method with multiple frame transmission that increases the throughput performance of high speed wireless local area network (LAN) systems. The current MAC protocol has two problems when used in high speed wireless LAN systems: poor efficiency and the failure to match for a multirate mechanism. The frame bursting method solves these problems by allowing multiple frames to be transmitted within one media access period. The performance evaluations of the frame bursting method are performed by computer simulation. The results demonstrate that the frame bursting method can achieve higher system throughput, 10 Mbit/s, than the system throughput performance of conventional systems. Moreover, the results shows that the frame bursting method works well in the wireless LAN systems that employ the multirate mechanism and can achieve higher throughput performance.