A video streaming user is usually interested in some semantically-important scenes of a video content, e.g. goal scene in a football game. If the user could watch the video segments consisting that scene with high quality, the quality of experience (QoE) of the user would be substantially improved more than ever. Although Adaptive Bitrate (ABR) algorithm considering this aspect can achieve better QoE, design of current approach has been limited only inside the application layer. It is expected that higher QoE could be achieved when the underlying transport layer also handle these semantics information for its congestion control mechanism. In this paper, we propose a new concept for quality of service (QoS) control with differentiated explicit congestion notification (ECN) to improve QoE and reveal that throughput differentiation by ECN considering video semantics can improve QoE of a video streaming user. Evaluation results show that throughput differentiation by congestion control conducted inside the network improves the QoE of the user up to 57.9%.

In this demonstration, we propose a calculation method for the focus distance of a depth of field blur effect that incorporates the convergence distance with the aim of improving the sense of photorealism and interactive experience for virtual reality (VR) media using a head-mounted display (HMD). The proposed method considers the convergence distance in the calculation of focal distance to avoid misfocusing on unintended objects. In addition, a calibration of the convergence distance for filling the gap between the measured convergence distance and the intention of the user is introduced. This demonstration using a laptop PC and an HMD with an eye tracker can provide a photorealistic experience.

In adaptive streaming, consumers set video segment quality levels based on the estimated throughput. However, in named data networking (NDN), the consumer 's throughput estimation is not always accurate due to cache segments. As a result, in situations where bottlenecks exist between the consumer and the router, requested -higher quality segments arrive at the consumer after their designated playback time, which means the downloaded data cannot be used for playback. In this paper, we propose an interest packet control method to reduce unused data packets in scalable video coding (SVC)-based adaptive streaming in NDN. In our proposed method, when receiving an interest packet, the router determines if the requested data packet can be expected to arrive at the consumer in time for playback. If the router determines that the data requested will not arrive in time, it discards the interest packet. Through computer simulation-based performance evaluations, we show that our proposed method reduces the transmission of unused data packets.

In Adaptive Bit Rate (ABR) utilized in MPEG-DASH (MPEG Dynamic Adaptive Streaming over HTTP), there have been proposed three representative algorithms, rate-based, buffer-based and hybrid-based ones. In the information centric networks, which have been widely studied as a network architecture for efficient content distribution including video streaming, routers are generally equipped with cache storage. When some segments of a required content is occasionally downloaded from cache storage in a router, content download from a router might be faster than segment retrieval from the original content server. This inaccurate throughput estimation might lead to inappropriate bitrate selection of ABR algorithm running on the user's application and significant degradation of QoE (Quality of Experience) performance. In this paper, from the viewpoint of QoE, we evaluate the influence of in-network caches on three types of ABR algorithm in video streaming.

Earth observation satellites obtain various data from the Earth and its surrounding environment. The amount of data handled by Earth observation satellites has increased in step with the improved performance of observation equipment. By using free-space optics (FSO) for satellite communication, much faster data transmission becomes possible. However, FSO is influenced by atmospheric conditions, which can disrupt the optical link between a satellite and ground station (GS). In contrast, a radio-frequency (RF) link is hardly ever influenced by atmospheric conditions, and communication can continue even when clouds pass between the satellite and GS. In this paper, we propose RF/FSO hybrid routing for satellite constellations. In the proposed method, when the FSO link between a satellite and GS is disrupted due to atmospheric phenomena, a detour path through other satellites with a functioning FSO link to the GS is established to increase the total amount of data transmitted to the GS. Using numerical calculations, we show that the proposed method is effective for increasing the total amount of data transmitted from a satellite to its GS compared to the conventional method.

Due to their limited functionality, ubiquitous connected devices in the Internet of Things rely heavily on the computational and storage resources of the cloud. However, mainstream cloud systems always require high network bandwidth and cannot satisfy the delay requirement of real-time applications. Therefore, a new paradigm called multiaccess edge computing has emerged to offload the computation and storage needs of end user devices to the edge cloud servers located in the radio access networks of 5G mobile networks. In this paper, we study and compare three load sharing schemes, namely, no sharing, random sharing, and least loaded sharing, which exploit the collaboration between clustered servers in different degrees. We develop computationally efficient analytical models to evaluate the performance of these schemes. These models are validated by simulation, and then used to compare the performances of the three load sharing schemes under various system parameters. Comparison results show that the least loaded sharing scheme is most suitable to fully exploit the collaboration between the servers and achieve load balance among them. It contributes to reducing the blocking probability and waiting time experienced by users.

Congestion control is a hot topic in named data networking (NDN). Congestion control methods for NDN are classified into two approaches: the rate-based approach and the window-based approach. In the window-based approach, the optimum window size cannot be determined due to the largely changing round-trip time. Therefore, the rate-based approach is considered to be suitable for NDN and has been studied actively. However, there is still room for improvement in the window-based approach because hop-by-hop control in this approach has not been explored. In this paper, we propose a hop-by-hop widow-based congestion control method for NDN, which resolves these problems. The proposed method introduces a window-size control for per-hop Interest transmission using hop-by-hop acknowledgment. The simulation results show that the proposed method achieves high throughput performance, as well as the max-min fairness, while effectively avoiding congestion.

This paper proposes a flickerless screen-camera communication method using interframe difference to reduce the bit error rate (BER) when the distance between the screen and the smartphone camera becomes long in screen-camera communications. The proposed method uses interframe difference to decode embedded information without interfering with the user's view. Through performance evaluation using an actual screen and a smartphone camera, we show that the proposed method reduces the BER when the communication distance becomes long.

Resource Pooling concept has been proposed as fair sharing of total network resources among all users sharing a network so that a whole network is treated as a single pooled resource. MPTCP (Multipath TCP) has been proposed as one of the most promising congestion controls which realize the Resource Pooling in the situation that each user can utilize multiple paths. In CCN (Content-Centric Networking), several multipath/multisource congestion control methods have been proposed. A fundamental difference between CCN congestion control and MPTCP where single source is assumed, is multisource and the Resource Pooling in multipath/multisource situation is quite a new research issue. In this paper, we discuss congestion control for CCN from the viewpoint of the Resource Pooling and show that our previously proposed congestion control satisfies the Resource Pooling concept. Our simulation results also show that our proposed congestion control achieves macroscopic fairness among users, which means the Resource Pooling concept is satisfied.

This paper proposes a new congestion control method based on a hop-by-hop rate control in named data networking (NDN). The proposed method suppresses the excessive reduction of Interest sending rate due to continuous negative acknowledgement (NACK) packets caused by the propagation delay. The proposed method limits the rate reduction to once per congestion. The point of our method is not to change Interest sending rate for NACK packets after the rate reduction for a congestion until the rate reduction becomes effective. Through the performance evaluation by computer simulations, we show that the proposed method improves the throughput performance compared to the conventional method.

In this paper, we have proposed an extended version of MPTCP with heterogeneous communication links to solve the out-of-order packet problem. We have confirmed that the proposed method can improve the end-to-end throughput performance up to 72.7% when RTTs of subflows are different. In addition, we have also confirmed that the proposed method does not affect the end-to-end throughput performance in the situation when RTTs of subflows are almost the same.

In this paper, we propose a quality of experience (QoE) aware quality-level switching algorithm for adaptive video streaming. The proposed algorithm is a quality- level switching algorithm which works on the controller of dynamic adaptive streaming over HTTP (DASH) system. The proposed algorithm has two features: insertion of intermediate quality level and limitation of quality-level switching. The proposed algorithm uses these two features adaptively for improving QoE based on network-throughput estimations. We implement the proposed algorithm on a real DASH system and evaluate QoE via subjective evaluations of users. As a result, we show that the proposed algorithm is effective to improve QoE when network throughput fluctuates. Note that the proposed algorithm realizes a high applicability to the existing web-based streaming because the proposed algorithm works on the client computer, and does not need any modifications on the server side.

Mobile Peer-to-peer (P2P) realizes communications between mobile nodes without any access points. In general, Mobile P2P utilizes IEEE 802.11 Wireless LANs. However, IEEE 802.11 Wireless LANs do not support intelligent energy management schemes. Therefore, nodes should appropriately switch on and off its WLAN interface for reducing energy consumptions. In this paper, we propose energy efficient mobile P2P communications based on context information of users. We propose two models: Server-based model and Client-based model. In both models, nodes collect their context information such as location acquired by GPS. Server-based model uses a server to handle users' context information. In Server-based model, mobile nodes transmit the acquired context information to the server periodically. The server determines if the user should wake up or sleep, and transmits the decision to the user. Client-based model does not use any server. In Client-based model, each node decides to wake up or sleep by itself. We evaluate the performance of the proposed models via Nexus S smartphone. As results, we confirm that the proposed models can reduce energy consumption compared with the conventional IEEE 802.11 WLANs without energy management. In addition, we implement an audio streaming application using the proposed mobile P2P communications.

No abstract available.

In this paper, we propose a routing protocol for directional full-duplex wireless (D-FDW) to reduce hidden terminal problems in multi-hop networks. The proposed routing protocol is an on-demand detour routing protocol, which reduces number of cross points among traffic flows. In general, the throughput of a detour route degrades excessively due to increase of the number of hops between source and destination nodes. However, D-FDW has a remarkable benefit that throughput does not degrade excessively as the number of hops between source and destination nodes becomes large. Thus, the proposed detour routing can bring out the potential of D-FDW effectively. We evaluate the performance of the proposed routing protocol via ns-3 computer simulations, and show that the proposed routing protocol can reduce hidden terminal problems and improve end-to-end throughput performance up to 86.4% compared with the conventional AODV in a grid multi-hop network. To the best of our knowledge, this is the first routing protocol for D-FDW.

Wireless full-duplexing enables a transmission and a reception on the same frequency channel at the same time, and has the potential to improve the end-to-end throughput of wireless multi-hop networks. In the present paper, we propose a media access control (MAC) protocol for wireless full- duplex and multi-hop networks called Relay Full- Duplex MAC (RFD-MAC). The RFD-MAC is an asynchronous full-duplex MAC protocol, which consists of a primary transmission and a secondary transmission. The RFD-MAC increases the full-duplex links by overhearing frames, which include 1-bit information concerning the existence of a successive frame, and selecting a secondary transmission node using the gathered information. The gathered information is also used to avoid a collision between the primary and secondary transmission. Simulation results reveal that the proposed RFD-MAC improves up to 68%, 49% and 56% of end-to-end throughput compared to CSMA/CA, FD-MAC and MFD-MAC, respectively.

Multi-view video consists of multiple video sequences captured simultaneously by multiple closely spaced cameras from different angles. It allows the users to change their viewpoints by playing different video sequence. However, the transmission of multi-view video is much larger than conventional media and increases with increasing number of views, which brings much more increment in the bandwidth requirement. In our previous works, we have proposed a live-encoding scheme call UDMVT [1][2] to reduce the transmission bitrate for multi-view video transmission. In UDMVT, the periodic feedback containing the position and switching speed of user is used to predict a triangle area. Frames in this triangle area are possible to be displayed in next period of time. Only these specific frames are transmitted instead of all the frames to reduce the transmission bitrate. Even though, UDMVT hasn't effectively solve the “out of triangle” problem in which the user may switch to the outside of the triangle during the playback in the triangle area. In this paper, we propose a layered scheme called Layered User dependent Multi-view video Streaming (LUMS) to solve the “out of triangle” problem for UDMVT. In LUMS each triangle is layered into several layers according to the minimum and maximum switching speed. The corresponding layers are transmitted according to the current switching speed each time received from feedback. If the “out of triangle” occurs, the higher layers will be retransmitted. All the frames in high layers are encoded into B-frame predicted from the basic and lower layers, so the retransmission bitrate is low. Performance evaluation proves that LUMS reduce transmission bitrate by 44.9% compared to UDMVT.

In this paper, we propose a novel node architecture introducing directional antennas into full duplex wireless (FDW) technology. In the proposed architecture, each element of switched-beam antenna is connected to a software switch for directional antenna selection. A node needs only one set of digital and analog cancellation circuits, which is almost the same circuit scale and complexity of the conventional omnidirectional FDW node. In addition, we propose a MAC protocol for the proposed node architecture with FDW and directional antennas for avoiding collisions and obtaining the advantages of both techniques. We evaluate the performance of the proposed protocol via computer simulations, and show that the proposed protocol can improve end-to-end throughput performance up to 114 percent in a line-type multihop network. Moreover, we extend the proposed MAC protocol for mitigating the performance degradation in two-way traffic in line-type multihop networks, and confirm its effectiveness. To the best of our knowledge, this is the first work that attempts to use directional antennas in FDW networks.

Multi-view video consists of multiple views which are taken by multiple cameras from different positions and angles. It allows the users to freely change their viewpoints. Typical applications of multi-view video include Free Viewpoint TV, remote medical surgery, wireless multimedia sensor networks and so on. However, the traffic of multi-view video is also several times larger than traditional multimedia, which brings much more increment in the bandwidth requirement. To overcome this problem, Simulcast and MVC (Multi-view Video Coding) can be used to decrease the traffic for multi-view video. However, although Simulcast removes redundant information within each view, it still contains a large amount of inter-view redundant information. MVC further removes the correlation between the views, but all the views should be encoded and transmitted. So the bit-rates are still too high in these schemes. In this paper, in order to reduce the bit-rate for multi-view video transmission, we analyze the user's motion which is classified into random access model and successive motion model. We find that in the successive motion model only part of frames are possible to be displayed in a period of time. According to the analytical result, we propose a user dependent system to decrease the bit-rate of multi-view video transmission. The proposed system only encodes and transmits those frames that are possible to be displayed according to the user's motion. Further, in order to support the proposed system, we also propose a prediction structure as a substitute of the prediction structure in MVC. Performance evaluation proves that the proposed system reduces the average bit-rate for the transmission of multi-view video and is to be more effective when the number of views is large.

The traffic of multi-view video is several times larger than traditional multimedia, which brings much more increment in the bandwidth requirement. To overcome this problem, Simulcast and MVC (Multi-view Video Coding) can be used to decrease the traffic for multi-view video. However, although Simulcast removes redundant information within each view, it still contains a large amount of inter-view redundant information. MVC further removes the correlation between the views, but all the views should be encoded and transmitted. So the bit-rates are still too high in these schemes. In this paper, in order to reduce the bit-rate for multi-view video transmission, we analyze the user's motion which is classified into random access model and successive motion model. We find that in the successive motion model only part of frames are possible to be displayed in a period of time. According to the analytical result, we propose a user dependent scheme to decrease the bit-rate of multi-view video transmission. The proposed scheme only encodes and transmits those frames that are possible to be displayed according to the user's motion. Further, in order to support the proposed scheme, we also propose a prediction structure as a substitute of the prediction structure in MVC. Performance evaluation proves that this proposed scheme reduces the average bit-rate for the transmission of multi-view video.

Energy harvesting has been studied as a candidate for powering next generation wireless sensor networks. The technologies that can harvest electric power from ambient energy sources include solar, vibration, heat and wind. However, sensor nodes powered by energy harvesting devices cannot always communicate with other nodes because the energy harvesting devices cannot provide a stable supply power. A node cannot know whether its neighboring nodes have enough energy to receive a data packet that it has transmitted. During the process of relaying the packet, each additional hop increases the overall probability of losing the packet. In this paper, we propose two data collection protocols for the energy harvesting wireless sensor networks called Probabilistic ReTransmission protocol (PRT) and PRT with Collision Consideration (PRT-CC). The idea is to derive the number of times to retransmit a packet based on the reception probability and the active intervals computed by the receivers themselves. In PRT-CC, each node computes the reception probability with packet collision consideration. The simulation results show that the proposed protocols achieve higher delivery ratio than the previous works (GR-DD and GR DD-RT).

Opportunistic spectrum access (OSA) is a suitable approach to increase spectrum efficiency for the current spectrum management. This paper considers the temporal aspect of 802.11-based OSA scenario. Firstly, we investigate the secondary users (SU) multi-rate transmission and number of hops effects to the SU performance when exploiting primary users (PU) idle duration. Numerical analysis and simulation results show that, during limited PU idle duration, higher data rate transmission is essential even though it results in more hops but as the SU source traffic is getting busier, the balance between the data rate and number of hops is required. Secondly, according to the multi-rate multi-hop investigation, we propose a rate adaption scheme with PU activity consideration, called Auto Rate Increase (ARI). ARI is based on the Auto Rate Fallback (ARF) scheme with the difference that ARI aims to increase the SU data rate whenever it detects PU interruption failure. ARI also adopts ARF simplicity, hence, there is no need for any prior nor additional knowledge of the networks environment. Simulation results show, under tight OSA environment, ARI scheme can increase the SU performance up to 56% compared with the original ARF scheme.

Due to the Recent development in wireless technology, wireless sensor networks attract researchers' attention because of their applicability in many fields for effective collection of sensing data with low cost. Wireless sensor networks have many applications; some of the applications are military application, environmental application and flood detection. For example, in an environmental application for forest fire detection, the sensor nodes sense the fire information, then transmit or relay the information to base station in a multi-hop way. In wireless sensor networks, energy saving is critical issue as sensor nodes are battery-powered. Here we propose, partial data aggregation as one of the energy saving technique. In this paper, we analyze the tradeoffs among communication delay, energy consumption, and data accuracy of the partial data aggregation technique and discuss the results. First, we analyze the partial data aggregation with Markovian chain; analytical result shows that, non-aggregation method suffers large energy consumption while full aggregation suffers long transmission delay. From the analysis results, we find that the proposed partial aggregation method WRP (Waterfalls Random partial aggregation) can trade off energy consumption and transmission delay. Thus, we discuss the tradeoffs among data accuracy, transmission delay and energy consumption with different criteria and parameters. The results show that we could control the significance of transmission delay, energy consumption and data accuracy by tradeoffs index (TOI). We also analyze the several applications of wireless sensor networks with different significance based on the TOI. From the observed results, we found that we could set the significance of transmission delay, energy consumption and data accuracy for different applications based on different criteria TOI. Thus, by evaluating and comparing the criteria with different data generation rate as well as aggregation factor, we get the least TOI value, which denotes the desired tradeoffs among them.

In this paper, a novel medium access control (MAC) protocol with transmission power and transmission rate control in multi-rate ad hoc networks is proposed to realize high energy efficient data transmission. In the proposed protocol, each node prepares a table that includes energy efficiency in all combinations of transmission power and rate. By exchanging of control frames and looking up the transmission power and rate table, direct and relay transmission sequences are used arbitrarily. When relay transmission by intermediate node between sender and receiver is more effective in terms of power consumption, relay sequence is adopted instead of direct transmission. We show that the proposed protocol can realize high energy efficient data transmission via computer simulations.

Directional antennas are expected to provide significant improvements over omni-directional antennas in wireless ad hoc networks. Directional MAC protocols, however, introduce new kinds of problems arising from directivity. One major problem is deafness, caused by a lack of state information from neighbor nodes (i.e., idle or busy). This paper proposes DMAC/DA (Directional MAC with Deafness Avoidance) to overcome the deafness problem. In DMAC/DA, WTS (Wait To Send) frames are transmitted by the transmitter and the receiver after the successful exchange of directional RTS (Request To Send) and CTS (Clear To Send) to notify the on-going communication to potential transmitters that may experience deafness. Furthermore, DMAC/DA is enhanced by the next packet notification to distinguish transmitters from neighbors. We evaluate our protocol through extensive simulation study with different values of parameters such as the number of flows, data size and beamwidth. The experimental results show that DMAC/DA outperforms existing directional MAC protocols, such as DMAC (Directional MAC) and MDA (MAC protocol for Directional Antennas), in terms of throughput, RTS failure ratio, and control overhead.

Recent studies on directional media access control (MAC) protocols using smart antennas for wireless ad hoc networks have shown that directional MAC protocols outperform traditional omni-directional MAC protocols. Those studies evaluate performance primarily based on a simulations, where antenna beam is assumed to be ideal, i.e., with neither side-lobes nor back-lobes. Propagation conditions are also assumed to be based on a mathematical model without realistic fading. However, for the real application of ad hoc networks those optimistic assumptions do not hold anytime. In this paper, we develop at first a testbed for directional MAC protocols which enables investigation of the performance of MAC protocols in a real environment. It incorporates ESPAR as a practical smart antenna, IEEE802.15.4/ZigBee, GPS and gyro modules to allow easy installation of different MAC protocols. To our knowledge, it is the first compact testbed with a practical smart antenna for directional MAC protocols. We implement a directional MAC protocol called SWAMP to evaluate it in a real environment. The empirical discussion based on the experimental results shows the degradation of the protocol with ideal antennas, and it shows that the protocol still achieves the SDMA effect of spatial reuse and the effect of communication range extension.

Recently, several MAC protocols using directional antennas, typically referred to as directional MAC protocols, have been proposed for wireless ad hoc networks. However, the MAC protocols in the previous studies were evaluated using simulation with ideal antenna forms. When using practical antenna beam forms, side lobes and back lobes exist which may cause new problems. In this paper, we evaluate the performance of the directional MAC protocol in the previous studies with practical antenna beam forms. In addition, we propose a directional MAC protocol that assumes practical antenna beam forms. The proposed MAC protocol mitigates data collisions due to the effects of minor lobes by the following two schemes. First, the nodes rotate directional receiving antenna beams in an idle state. Second, nodes transmit NAV (Network Allocation Vector) request frames to avoid collisions from neighboring nodes. By controlling the transmitting power, our protocol allows nodes to communicate with nodes beyond the omni-directional transmission range. The simulation results show that the proposed directional MAC protocol improves throughput performance compared to existing directional MAC protocol when using practical antenna beam forms.

Recently, several MAC protocols using directional antennas, typically referred to as directional MAC protocols, have been proposed for wireless ad hoc networks. Although directional transmissions are expected to provide significant improvements, directional MAC protocols introduce new kinds of problems. One such problem is deafness. Deafness is caused when a transmitter repeatedly attempts to communicate with its intended receiver, but it fails because the receiver has its beam pointed towards a direction away from the transmitter. This paper proposes RI-DMAC (Receiver-Initiated Directional MAC) to address the issue of deafness in directional MAC protocols. RI-DMAC is a combination of sender-initiated and receiver-initiated operations. The sender-initiated mode is the default mode and the receiverinitiated mode is triggered when the transmitter experiences deafness. In RI-DMAC, each node maintains a polling table and polls a potential deafness node using the RTR (Ready To Receive) frame after the completion of every dialog. The experimental results show that RI-DMAC improves throughput and fairness performance compared to existing directional MAC protocols.

This paper proposes two schemes for wireless sensor networks with multiple sinks in order to save battery energy and to improve network lifetime performance. In these schemes, each sensor node transmits sensing data to randomly chosen sink according to the sending rates. These schemes are referred to as DispersiveCast. The first decentralized scheme called B-DOP scheme (basic DispersiveCast of packet), enables each sensor node to derive locally the sending rate by the number of hops to sinks. The second one is O-DOP scheme (optimal DispersiveCast of packet) that is partially centralized than B-DOP. In O-DOP, sinks send the information to nodes so as for them to calculate the optimal sending rates. DispersiveCast is effective when the generate rate of sensing data at every sensor node geographical nonuniformity. In such a situation, batteries of nodes in the specific area deplete fast and others late, which causes partial depletion of the entire network. As a result, network lifetime can not be extended sufficiently. We evaluate the DispersiveCast schemes by simulations for several network topologies and show that DispersiveCast scheme prolongs the network lifetime compared with the conventional nearest sink scheme, especially O-DOP can achieve 1.5 times longer

In this paper, we propose a novel energy efficient route construction scheme with transmission power control in ad hoc sensor networks. The proposed scheme is very simple and can improve energy consumption performance without any information of neighbor nodes. In the proposed scheme, when a node receives a route request (RREQ), the node calculates the standby time inversely proportional to the received power of the RREQ. The node relays the RREQ with full power when the standby time expires in order to construct the least energy consumption route. After the route construction, source and intermediate nodes transmit packets with power controlled medium access control (MAC) protocol. In addition, we propose the extended version of the proposed scheme to construct energy efficient route in discrete power control environment. Simulation results show the proposed scheme can construct more energy efficient route than the conventional schemes in both continuous and discrete power control environment.

In this paper, in order to realize the consecutive long-term operations of sensor networks, we propose a novel sustainable sensor network routing protocol considering easy node exchangeability. In the proposed routing protocol, in order to exchange nodes easily, power consumption of nodes is biased intentionally. We focus on a routing protocolfor the sustainable sensor networks. In the proposed routing protocol, the power consumption of nodes in a specific zone becomes larger than that in other zones. Battery of Nodes in the specific zone is emptied earlier. As restricting the geographical area of the node exchange, node exchangeability improves. We evaluate the proposed routing protocol by means of computer simulations to show the effectiveness of the proposed routing protocol.

Smart antennas are expected to enhance scalability in ad hoc networks. This paper describes the evaluations of three directional MAC protocols, DMAC, MMAC, and SWAMP, as well as the IEEE 802.11 DCF omni-directional protocol in a multi-hop transmission environment. These evaluations address the problem that performance strongly depends on the route topology between the source and destination, referred to as the directional hidden terminal problem. After analyzing this problem, we propose three MAC level solutions. The MAC solutions are NAV indicators, i.e. HCTS, BRTS, and RCTS, which indicate on-going communications to a directional hidden terminal to set NAV. Based on simulated results, we show that all the proposed MAC solutions could improve the throughput performance

In this paper, we propose split multi-path routing protocol with load balancing policy (SMR-LB) to improve TCP performance in mobile ad hoc networks. In SMR-LB, each intermediate node records how many primary paths are attempted to construct as well as the source ID which attempts to construct the primary path. Each intermediate node decides which primary path should be constructed by using the primary path and the source ID information. As a result, SMR-LB can utilize the load balancing policy to reduce the probability of congestion and avoid the continuous link breakages between the specific source and destination pair. We show that SMR-LB can improve TCP performance compared with the conventional protocols by computer simulation.

The next generation (NG) wireless system, called beyond 3G, is envisioned as a seamless worldwide wireless system. Handover latency is an important metric for the NG wireless system. This paper analyzes the handover latency of mobility support schemes including mobile Ethernet. We compare various mobility support schemes from multiple viewpoints. For the quantitative evaluation, we introduce an analytical network model through a Markovian model. The sequence of location update frames in four schemes, i.e., mobile Ethernet, a scheme using MPLS, a scheme using VLAN tag, and mobile IPv6, formulates the handover latency and handover costs. The combination of the latency of each switch, router, and link defines handover latency. The feature of this analysis is that it evaluates the latency of four schemes within the same model. Numerical results show mobile Ethernet achieves small handover latency. By means of analytical results concerning handover latency and handover costs, we consider the benefit of each scheme.

In this paper, in order to avoid disconnection of a multicast path caused by the hand off of a mobile host (MH), we propose a multicast protocol in mobile Internet protocol (IP) environment. In the proposed protocol, when MH which receives multicast packets via mobile multicast gateway (MMG) from correspondent host (CH) hands off to other networks, MMG exchanges the multicast path to reduce disconnected time without increasing utilization of bandwidth. The simulation results show that the proposed protocol can reduce both utilization of bandwidth and disconnected time compared with the conventional protocols.

In order to realize low handoff latency without increasing overhead in wired channel, we propose a handoff scheme using positional information for mobile IP based networks. In the proposed scheme, foreign agents (FA) exchange IP addresses and positional information. When a distance between FA and mobile host (MH) exceeds a threshold, FA copies packets and forwards them only to MH's next FA. Moreover, in order for MH to receive first advertisement (ADV) message earlier, the transmission interval of ADV message is shortened in next FA. By shortening transmission interval of ADV message, MH can receive forwarded packets earlier. In addition, when new FA receives registration request (REQ) message from MH, FA replies tentative registration (TREG) message to MH. Adding tentative registration, MH can begin receiving forwarded packets without waiting for receiving registration reply (REP) message from home agent (HA). By performance evaluation using both theoretical analysis and computer simulations, we show that the proposed scheme can realize low handoff latency without increasing overhead in both wired and wireless channel.

In order to reduce the number of binding updates (BU) when the number of connecting mobile hosts (MH) is limited for higher level mobility anchor point (MAP), a scheme adopting distributed location management (DLM) to multilevel hierarchical mobile IPv6 (M-HMIPv6) is proposed. In the proposed scheme, to avoid extreme load for higher level MAP, a threshold of the number of connecting MHs is set. When a MAP receives a BU and the number of connecting MHs exceeds the threshold, the MAP forwards the BU to the next MAP candidate. In addition, to reduce the number of BUs and extend a MAP domain, DLM is adopted in M-HMIPv6. The usage of the distance field in MAP option is modified to distinguish the route redundancy and keep transparency to HMIPv6. Moreover, to realize load balancing when mobility deviation exists, a load balancing by average BU interval in both access router (AR) and MH is adopted. By classifying MHs roughly by the average BU interval in AR, relatively faster MHs select higher MAPs. By performance evaluation using computer simulations, we show that the proposed scheme transparent to HMIPv6 can reduce the number of BUs and realize load balancing without excessive route redundancy.