Jae-In Choi

A Network-Assisted Femto Base Station Management Scheme in IEEE 802.16e System

In the WIMAX (IEEE 802.16e) femtocell environment, serving Base Station (BS) should periodically broadcast neighbor BS information including femtocell to support mobility. As a neighbor list increases, it leads to increasing scanning overheads and wasting air resources. Hence, in this paper we propose a network-assisted femto BS management scheme, using a triangulation mechanism and a femto BS monitoring scheme. The simulation results show that the proposed scheme improves scanning performance and avoids wasting air resources compared with the conventional scheme of IEEE 802.16e system.

Probability-based spray and wait protocol in Delay Tolerant Networks

Delay Tolerant Networks (DTNs) are one of the most interesting evolutions of MANETs. In DTNs which can be characterized by intermittent connectivity, frequent end-to-end path disruption and topology changes, mobile nodes are enabled to communicate with each other even if a route connecting them never exists. When considering routing protocols of DTNs, a forwarding decision and the buffer management scheme are important to improve the opportunity of successful message delivery. In this paper, we propose improved spray and wait routing based on the delivery probability. The simulation results show that the proposed method provides a better delivery ratio and lower communication overhead compared to existing schemes such as epidemic, spray and wait, and PRoPHET routing protocols.

Mobility adaptive hybrid routing for mobile ad hoc networks

Mobile Ad-hoc Networks (MANETs) require a dynamic and efficient routing protocol that can respond quickly to network topology changes. Ad hoc routing protocols for MANETs are classified into: (a) proactive, (b) reactive and (c) hybrid approaches. In general, proactive routing is more suitable for a stationary network, while reactive routing is better for a mobile network with a high mobility. In many applications, a node in a MANET is mobile, yet it can also fluctuate between being mobile and being stationary. Thus, a hybrid routing approach with the ability to adapt to the node mobility could improve the performance of MANETs. In this paper, we propose a Mobility Adaptive Hybrid Routing (MAHR) for MANETs, which varies its routing between reactive approach and proactive approach to adapt to node mobility. The MAHR consists of three parts: (a) calculation of mobility ratio, (b) core node selection, and (c) procedure of hybrid routing. The simulation results showed that MAHR could achieve the advantages of both reactive and proactive routing approaches in performance.

Robust broadcast scheme regardless of vehicle distribution in vehicular ad hoc networks

In vehicular ad hoc networks (VANETs), the efficient and reliable dissemination of emergency messages in a highly mobile environment under a dense or sparse network is a significant challenge. This paper proposes a robust broadcast scheme for VANETs, called the virtual slotted p-persistence scheme, which operates efficiently regardless of the vehicle density and distribution. Via the exchange of hello messages, each vehicle maintains position information on neighbor vehicles in a neighbor table. When a vehicle receives an emergency message, it determines its vehicle group, called a virtual slot, based on the position information in its neighbor table. The proposed scheme guarantees that the vehicles in the farthest group from the broadcaster probabilistically rebroadcast the message first. Simulation results demonstrate that the proposed scheme outperforms the slotted p-persistence scheme in terms of the end-to-end delay, collision ratio, and network overhead, regardless of the vehicle density and distribution.

Neighbor information-based broadcast scheme for VANET

This paper proposes an efficient broadcast scheme based on a neighbor table to mitigate broadcast storms and to reduce the end-to-end delay. To alleviate a broadcast storm in a VANET, it is ideal that the rebroadcasting is performed by the vehicle furthest away from the broadcaster. Thereby the proposed scheme selects the furthest rebroadcasting vehicle based on neighbor tables. Simulation results demonstrate that the proposed scheme outperforms exiting schemes in terms of the end-to-end delay and collision ratio.

Handover decision algorithm based on available data volume in hierarchical macro/femto-cell networks

Hierarchical macro/femto-cell networks are considered a promising technology to increase overall network coverage and bandwidth at a relatively low cost. In these emerging networks, a large number of femtocells are deployed within a macrocell. When a macrocell includes many femtocells, the number of handovers greatly increases because handover from the macrocell to the femtocell is executed frequently. However, frequent handovers increase overhead due to handover management as well as latency due to handover interruption. In this paper, we propose an efficient handover decision algorithm based on available data volume to reduce the unnecessary handovers and increase the throughput. The simulation results show that the proposed algorithm effectively reduces the number of unnecessary handovers while improving the throughput compared to a conventional RSS based algorithm.

An Efficient Femto-cell Scanning Scheme Using Network Assistance in IEEE 802.16e System

The femtocell is a miniaturized Base Station (BS) with low-cost and low-power using general broadband access network as backhaul. It is expected not only to improve indoor coverage but also to reduce a service charge. However, in IEEE 802,16e femtocells, when the Mobile Station (MS) scans neighbor BSs for handover, it takes a long time due to too many number of femto BSs. Also the size of the neighbor advertisement message that will be periodically sent by a serving BS is increased as the number of target femto BSs for scanning increases. In this paper, we proposed an efficient femtocell scanning scheme, using a triangulation mechanism and a femto BS monitoring scheme to reduce the number of scanning operations and the size of the neighbor advertisement messages. The proposed scheme can avoid wasting air resources and reduce scanning overheads by minimal scanning operation. The simulation results showed that the proposed scheme could improve scanning performance and avoid wasting air resources, compared with the conventional scheme of the IEEE 802.16e system.

NAV-based Load Aware Routing protocol in Wireless Mesh Networks

We propose a Network Allocation Vector (NAV) based Load Aware Routing (NA-LAR) protocol for Wireless Mesh Networks. NA-LAR is basically based on the Directional AODV (D-AODV)) to reduce the number of route request packet broadcast by using a restricted directional flooding technique. It also considers network conditions with NAV which indicates the busyness of the medium in IEEE 802.11, and it is used to find load balanced routing path. Thus, NA-LAR can find a less loaded route, and it leads to network performance improvement. Simulation results show that NA-LAR compared with D-AODV could increase the total throughput and reduce the end-to-end delay.

Efficient NEMO support scheme with direct HNP assignment in PMIPv6

This paper proposes an efficient network mobility support scheme with direct home network prefix (HNP) assignment to reduce the location update cost and packet tunneling cost. Since the HNP of a Mobile Network Node (MNN) is directly assigned by the moving mobile access gateway (mMAG), instead of the local mobility anchor (LMA), using a sub-prefix of the mMAGs HNP, the proposed scheme minimizes both the location update and the packet tunneling cost without any additional extension of the PMIPv6 protocol. Numerical results show that the proposed scheme outperforms the existing schemes.

Probability-based spray-and-wait protocol with buffer management in Delay Tolerant Networks

Delay Tolerant Networks (DTNs) are one of the most interesting evolutions of Mobile Ad Hoc Networks (MANETs). DTNs can be characterized by intermittent connectivity, frequent end-to-end path disruption, and topology changes. In these networks, mobile nodes have the ability to communicate with each other, even if a route connecting them does not exist. When considering the routing protocols of DTNs, a forwarding decision and buffer management scheme are both important to improve successful message delivery. Therefore, this paper, proposes an improved spray-and-wait routing protocol based on the delivery probability. Moreover, a buffer management policy is introduced to drop the queued messages with the most replicate copies in the network. Simulation results show that the proposed method provides a better delivery ratio and lower communication overhead, compared to existing schemes.