Ogawa Masakatsu

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.

The Wi-Fi Direct standard for direct device-to-device communication has been defined by the Wi-Fi Alliance. Wi-Fi Direct defines two types of devices: peer-to-peer (P2P) clients and P2P group owners (GO). A P2P GO acts as an access point, and P2P clients are associated with the P2P GO. Wi-Fi Direct defines a P2P power management for P2P GOs and clients. The P2P power management supports two types of power-saving protocols, Opportunistic Power Save (OppPS) and Notice of Absence (NoA). These protocols allow P2P GOs to be absent to save power. However, an absence period leads to higher delay for P2P clients. The number of CTWindows defined in the OppPS protocol during a beacon interval, which is a presence period in a P2P GO, is one. To reduce delay, we propose a temporary CTWindow to increase the number of CTWindows during the beacon interval. Furthermore, we propose the adaptive control of the number of temporary CTWindows based on the amount of traffic. Simulation results reveal that the proposed method reduces delay compared with the OppPS protocol in a high offered traffic state.

Battery-powered mobile routers must control their power consumption to extend their operating time. The mobile routers have both a wide area network (WAN) interface and a local area network (LAN) interface. Of the two interfaces, the LAN interface operated as a wireless LAN (WLAN) access point (AP) does not have a power-saving function in the IEEE 802.11 standard. Therefore, we focus on reducing power consumption of the AP. The conventional method for saving power in APs concerns the MAC queue status. The mobile routers, however, have Layer 3 functionality. That is, IP frames are transferred from the WAN interface to the LAN interface. To save power, the departure process from the Layer 3 queue to MAC queue needs to be modified. In this paper, we propose a departure control from the Layer 3 queue to save power in the WLAN AP. The numerical analysis and simulation results revealed that the proposed method reduces power compared with the conventional method. © 2014 The Institute of Electrical Engineers of Japan.

Recently, IEEE802.11 wireless LAN devices have been embedded in various portable appliances. Mobile routers are widely used to connect these appliances to the Internet. They have two communication interfaces: one is a terminal for a mobile network, such as 3G, LTE, and WiMAX, and the other is an access point for a wireless LAN. The mobile routers employ power-saving functions for both the mobile network and the wireless LAN. Because each function operates independently, it might be expected that the consumed power could be reduced further through collaborative operation of these two functions. This paper assumes the IEEE802.16m advanced mobile station (AMS) as a terminal of mobile network for mobile routers. In IEEE802.11, the access point (AP) sends buffered packet information to stations (STAs) by means of beacons. Our proposed method exploits this mechanism, and adjusts the traffic indication timing on the IEEE802.16m advanced base station (ABS) side based on the beacon creation time on IEEE802.11 side of the mobile router. Simulation results reveal that power consumption is reduced and delay is reduced except during congestion. © 2014 The Institute of Electrical Engineers of Japan.

The ZigBee has attracted attention as the smart home network. Already the wireless LAN (WLAN) has been introduced in the home network. Both the ZigBee and WLAN use 2.4 GHz frequency band, and the carrier sensing mechanism is used for contentions, but the collisions are occurred because the access control procedure is different. Therefore, it is necessary to improve the transmission success ratio for the sensing data periodically sent by the ZigBee. This paper proposes a media access control for improving the transmission success ratio in coexistence environment between the ZigBee and WLAN. The point of proposal is the collaboration between the ZigBee coordinator and WLAN access point. When the ZigBee coordinator detects the signal for ZigBee, the access parameter, DIFS, for the WLAN is changed. Simulation results show the transmission success ratio is improved by reducing the collisions between the ZigBee and WLAN.

To extend the lifetime for mobile routers, it is necessary to introduce a power saving function. A mobile router has a wide area network (WAN) interface and a local area network (LAN) interface. Of the two interfaces, the LAN interface, which is operating as a wireless LAN (WLAN) access point (AP), does not have a power saving function in the IEEE 802.11 standard. In the conventional method, the AP enters the sleep state to save consumed power only when the Media Access Control (MAC) queue is empty. To reduce consumed power further, the AP has to actively enter the sleep state by creating an empty queue in the MAC layer. Therefore, this paper proposes a queuing control, PSAP/ QC, between the Layer 3 and the MAC queue in a mobile router. The purpose is to create the opportunity of an empty MAC queue, assuming best-effort communication. By controlling dequeuing from the Layer 3 queue adequately, the MAC queue is emptied, and frames stored in the Layer 3 are aggregated. That is, the likelihood of the sleep state is increased by aggregating frames into the Layer 3 queue. The contribution of this paper is the cross-layer queuing control based on the frame arrival rate into the Layer 3 queue, in addition to the small amount of unnecessary delay caused by this control. Numerical analysis and simulation results revealed that the PSAP/QC reduces power consumption compared to the conventional method in a part of the offered traffic, and is low failure rate of dequeuing for frame aggregation.

This paper proposes a new Ad-Hoc network system which comprises the multiple relay access points (APs) with multi channels. Ad-Hoc network systems are recently proposed and incorporated for the communication infrastructure, which relays wireless transmission among access points (APs) in wireless LAN (WLAN) system. System throughput is decreased due to hidden terminal problem when only a single channel is used for the Ad-Hoc network. In order to solve this problem, a new system with multi channels is proposed. However, even if the multi channels are employed, the co- and/or adjacent-channel interference occurs due to hidden terminal problem and multiple APs in a limited space, when considering a simultaneous transmit and reception at the relay AP. In this paper, we develop an Ad-Hoc network testbed which can reduce and avoid co- and/or adjacent-channel interference by using vertically arranged antenna configuration and distributed channel allocation scheme. Moreover, the effectiveness of our testbed is clarified by applying actual WLAN signals.

This paper proposes a power saving control method for battery-powered portable wireless LAN (WLAN) access points (APs) in an overlapping basic service set (OBSS) environment. The IEEE802.11 standard does not support power saving control for APs. Some conventional power saving control methods for APs have been proposed that use the network allocation vector (NAV) to inhibit transmission at stations (STAs) while the AP is sleeping. However, since with these approaches the actual beacon interval in the OBSS environment may be extended due to the NAV as compared to the beacon interval which is set at the AP, the power consumption and delay may be increased as compared to a single BSS unaffected by interference from neighboring APs. To overcome this problem, this paper introduces a new action frame named power saving access point (PSAP) action frame which the AP uses to inform STAs within its BSS about the AP's sleep length. In addition, a function of the PSAP action frame is that STAs enter the sleep state after receiving the PSAP action frame. The proposed control method avoids the postponement of beacon transmission and reduces the power consumption in an OBSS environment, as compared to the conventional control method. Numerical analysis and computer simulation reveal that the newly proposed control method conserves power as compared to the conventional control method. The proposed control method achieves the minimum consumed power ratio at the AP, which is 44% as compared to the standard, when the beacon interval is 100 ms and the sleep length is 60 ms, even if the number of neighboring APs in an OBSS environment is increased.

This paper proposes an interference avoidance technique that allows wireless device with similar frequency bands to be operated adjacent to each other for compact mobile wireless routers (MWRs). This MWR implements two devices of Wireless LAN (WLAN) and Worldwide Interoperability for Microwave Access (WiMAX). The MWR connects WLAN terminals to the backbone network by using WiMAX-WLAN relay. Generally, different frequency channels are assigned for the wireless systems assign in order not to interfere among multiple systems. However, mutual system interference is generated if the space between each device is very close and if the frequency using each system is adjacent. To suppress this interference, this paper proposes a novel interference avoidance technique that leverages IEEE802.1 In Power Save Multi-Poll (PSMP). First, we clarify the conditions that raise the issues of mutual interference by experiment. Simulations are conducted to show that the proposed scheme outperforms the conventional schemes. Finally, the effectiveness of the proposed scheme is shown by the computer simulation.

This paper proposes and investigates a distributed adaptive contention window adjustment algorithm based on the transmission history for wireless LANs called the transmission-history-based distributed adaptive contention window adjustment (THAW) algorithm. The objective of this paper is to reduce the transmission delay and improve the channel throughput compared to conventional algorithms. The feature of THAW is that it adaptively adjusts the initial contention window (CWinit) size in the binary exponential backoff (BEB) algorithm used in the IEEE 802.11 standard according to the transmission history and the automatic rate fallback (ARF) algorithm, which is the most basic algorithm in automatic rate controls. This effect is to keep at a high value in a congested state. Simulation results show that the THAW algorithm outperforms the conventional algorithms in terms of the channel throughput and delay, even if the timer in the ARF is changed.

This paper proposes a power saving control function for battery-powered portable wireless LAN (WLAN) access points (APs) to extend the battery life. The IEEE802.11 standard does not support power control for APs. To enable a sleep state for an AP, the AP forces the stations (STAs) to refrain from transmitting frames using the network allocation vector (NAV) while the AP is sleeping. Thus the sleep state for the AP can be employed without causing frame loss at the STAs. Numerical analysis and Computer simulation reveal that the newly proposed control technique conserve, power compared to the conventional control.

Wireless LAN access is now being offered by small personal terminals in addition to laptops. Since these terminals have very limited battery capacity, wireless LAN interfaces that offer some form of power saving are essential. IEEE802.11. specifies PSM (Power save management) it reduces power consumption by suspending some communications functions. However, since Multicasting and Broadcasting are invariably received by all terminals regardless of PSM, the terminals unnecessarily consume electric power, even if the terminal is not multicast subscriber. This paper clarifies this problem, and proposes a scheme for reducing power consumption. The results of an experiment confirm its excellent performance. Copyright © 2009 The Institute of Electronics, Information and Communication Engineers.

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.

Wireless LAN access is now being offered by small personal terminals in addition to laptops. Since these terminals have very limited battery capacity, wireless LAN interfaces that offer some form of power saving are essential. IEEE802.11. specifies PSM (Power save management) it reduces power consumption by suspending some communications functions. However, since Multicasting and Broadcasting are invariably received by all terminals regardless of PSM, the terminals unnecessarily consume electric power even if the terminal is not engaged in multicasting. This paper clarifies this problem, and proposes a scheme for reducing power consumption and the results of an experiment confirm its excellent performance. © 2009 IEEE.

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.

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.

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 802.11 e 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.

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.

This paper evaluates performance of on demand ad hoc routing protocols to handle unidirectional routing protocols. Ad hoc networks will be 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 effectively 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.

This paper proposes a novel MAC protocol for fair two-way communications. Our protocol achieves fairness in the throughput between the uplink and downlink. under high offered traffic conditions, but the fairness cannot be achieved when using the conventional wireless LAN scheme, CSMA/CA, as the access control method. The proposed scheme introduces a release delay, which is the waiting time to attempt the transmission of the next scheduled packet in the transmission queue. The proposed protocol is evaluated by computer simulation. The results of the simulations that consider high offered traffic verify that the throughput at a station between the uplink and downlink is fair and that the throughput between stations is fair.

Demand for mobile ad hoc networks (MANET) is increasing. In the MANET- mobile stations communicate with, each other by autonomous distributed control. Although flooding is used tor discovering a route from a source to a destination there is the broadcast storm problem that traffic increases rapidly. Besides, there is the hidden terminal problem that packet collisions may be caused in wireless communication. For solving these problems, we propose M-DSMA (MAC protocol using, Dynamic State trarisition of Mobile stations in Ad hoe networks). We define two kinds of states (active state and non-active state) at mobile stations. During active state. Busy Tone is sent as active state station detects that the channel is busy, and Stop Tone is sent is active state station detects packet collisions. BY using two tones, the reachability can be improved.

Recently, demand for multimedia service applicable with wireless ad hoc networks is increasing. Many protocols which support QoS (Quality of Service) defined by ITU H.323 are suitable for the system with a central coordinator (ex. access point), and are not applied to ad hoc networks. Since each mobile station sends a packet randomly in a wireless network, it is necessary to avoid a packet collision which results in the decrement of the channel throughput. IEEE 802.11 is a standard for wireless LANs. The basic access mechanism in its media access control (MAC) protocol is the distributed coordination function (DCF) based on carrier sense multiple access with collision avoidance (CSMA/CA). However, this mechanism does not have QoS control, and packet collision may occur frequently with the increase of the number of mobile stations. In this paper, the two queues, voice over IP (VoIP) queue and DATA queue, are set in each mobile station, and we propose a novel MAC protocol using multiple queues for QoS. Our scheme consists of carrier sensing, packet scheduling and collision avoidance, and improves the contention window in DCF. We use two kinds of packet scheduling. One is the scheduling in a mobile station, and the other is the scheduling among mobile stations. We called the proposed scheduling among mobile stations (DVTS)-V-2 (Distributed Double Virtual Time Scheduling). Simulations are conducted to analyze the proposed scheme. The simulation results show that our scheme is able to carry multimedia traffic with a higher performance compared with the conventional DCF.

Introduction of QoS (Quality of service) control is demanded in wireless network. Reserved MAC protocol with QoS scheduling is necessary in order to satisfy user's demand, because mobile terminals send the packet of the various length at random in uplink (mobile terminal to base station). In this paper, we defined QoS as Allowable Delay Time in uplink and proposed new QoS control scheme for CDMA. The proposed scheme is composed of Distributed Order Queuing and Dynamic Bandwidth Allocation. Simulation results show that the proposed control guarantees delay time and the performance is better than Priority Queuing.

This paper proposed PBMA (Priority Based Multiple Access) and PBMA-TC (Priority Based Multiple Access with Throughput Control) for mobile communication to meet user's demands. We define the priority according to the waiting time, which includes request access time and waiting time at Request Table. We assumed two grades of priority, high priority and low priority. The former is corresponds to time sensitive traffic, and the latter is to cost sensitive traffic. In PBMA, priority is controlled using an admission limitation (admission control) and Request Table. In PBMA-TC, to improve the throughput of a packet of high priority user more, a collision resolution algorithm (throughput control) is added to PBMA. The collision resolution algorithm is a tree algorithm based on priority. These methods were evaluated by computer simulation. As an example, when the value of throughput for Request Access Channel is about 0.32, PBMA-TC is twice as average waiting time of a packet of low priority user as PBMA. In PBMA-TC, probability of loss of a packet of high priority user is zero due to the throughput control.