Chikara Ohta

Delay Guarantee and Service Interval Optimization for HCCA in IEEE 802.11e WLANs

IEEE 802.11e medium access control (MAC) is a supplement to the IEEE 802.11 wireless network (WLAN) standard to support quality of service (QoS). The 802.11e MAC defines a new coordination function, namely hybrid coordination function (HCF), which takes the QoS requirements of flows into account and allocates transmission opportunity (TXOP) to stations. On the basis of mean sending rate, delay of variable bit rate (VBR) traffic cannot be bounded with the reference HCF scheduling algorithm proposed in this supplement. In this paper, the authors propose a new scheduling algorithm that utilizes the token bucket and a modified latency-rate (LR) scheduling algorithm to guarantee a bounded delay for HCF controlled channel access (HCCA). The new service interval (SI) is calculated to optimize the number of stations accommodated and takes into account delay bound and token bucket parameters. The authors show that is possible to obtain worst-case performance guarantees on delay. First, the authors analyze the behavior of the proposed scheduler with a loss free wireless channel model and after this, with a burst loss model and the authors explain how it is possible to extend this scheduler for a multi-rate scheme. Properties of the proposal are investigated both theoretically and using ns-2 simulations. The authors present a set of simulations with both constant bit rate (CBR) and VBR flows and performance comparisons with HCF scheduling algorithm. The results show that the delay upper bound can be achieved for a large range of networks load with bandwidth optimization.

Isochronous MAC using Long-Wave Standard Time Code for Wireless Sensor Networks

This paper proposes isochronous-MAC (I-MAC), which utilizes low-frequency radio waves time synchronization for sensor networks. Using IMAC, based on the low power listening (LPL), all sensor nodes wake and listen channel periodically and synchronously. Since a sender can easily predict wakeup time of an intended receiver, it can shorten the length of preamble to make the receiver prepare for reception of the following data packet. This saves power consumption for the sender to rendezvous with the receiver. In the paper, we use an analytical model to investigate the impact of the data transmission frequency, the number of neighboring nodes, the wakeup period, the clock drift, and the time-synchronization frequency on the power consumption for consideration of the power overhead to perform the time synchronization. Those results demonstrate that I-MAC allows determination of any arbitrary wakeup period without much difficulty, whereas LPL requires a much more careful setting of the wakeup period because its optimum wakeup period is sensitive to the frequency of data transmission as well as to the number of neighboring nodes. Therefore, IMAC has a great potential to reduce the power consumption in most situations compared with LPL, in spite of the overhead to perform time synchronization.

Aggregation efficiency-aware greedy incremental tree routing for wireless sensor networks

SUMMARY In most research work for sensor network routings, perfect aggregation has been assumed. Such an assumption might limit the application of the wireless sensor networks. We address the impact of aggregation efficiency on energy consumption in the context of GIT routing. Our questions are how the most efficient aggregation point changes according to aggregation efficiency and the extent to which energy consumption can decrease compared to the original GIT routing and opportunistic routing. To answer these questions, we analyze a two-source model, which yields results that lend insight into the impact of aggregation efficiency. Based on analytical results, we propose an improved GIT: “aggregation efficiency-aware GIT,” or AGIT. We also consider a suppression scheme for exploratory messages: “hop exploratory.” Our simulation results show that the AGIT routing saves the energy consumption of the data transmission compared to the original GIT routing and opportunistic routing.

A single-chip sensor node LSI with synchronous MAC protocol and divided data-buffer SRAM

This paper presents an ultra-low-power singlechip sensor-node VLSI with a synchronous MAC protocol and divided data-buffer SRAM for wireless-sensor-network applications. One of the most challenging issues in wireless sensor networks is extension of the overall network lifetime. So a communication centric design approach has been introduced to reduce the power consumption of the RF circuits and the entire sensor network system, through a vertical cooperative design among circuits, architecture, and communication protocols. A transceiver, i8051 microcontroller, and dedicated MAC processor with divided SRAM are integrated in a single chip. The test chip occupies 3.0 × 1.7 mm2 in a 180-nm CMOS process, including 0.63 M transistors. Divided data-buffer reduces 18.6% of average power and the LSI consumes 6.34µW under a network environment.

Peak rate regulation scheme for ATM networks and its performance

Using the rate control to restrict the peak cell rate of traffic is addressed. The asynchronous transfer mode (ATM) environment is considered as a discrete-time environment in which one slot is equal to one cell transmission time. A rate control that can restrict the number of cells during any fixed-length time interval in a discrete-time environment is studied. The scheme is realized by means of simple counter accumulation per slot, and it is easy to synchronize with slots. The simplicity of this scheme may make possible the flexible restriction of the peak cell rate according to network conditions. The scheme is analyzed, using matrix analytic techniques, in order to investigate the smoothing effect of bursty traffic and the queue length required to satisfy a certain quality of cell loss probability. Numerical results show the effect of restricting the peak cell rate of bursty traffic and the tradeoff between the smoothing effect and the required queue length.<<ETX>>

Traffic control scheme for interconnection of FDDI networks through ATM network

A traffic control scheme for FDDI (fiber distributed data interface) interconnection through an ATM (asynchronous transfer mode) network is presented. The scheme consists of two parts, a VP (virtual path) bandwidth allocation algorithm and a feedback type buffer protection flow control. Both use the acknowledge for the frame of FDDI as a control unit. Simulation results show that VP bandwidth allocated by the scheme increases according to arrival traffic when the destination FDDI has enough capacity and allocated bandwidth is not increased when its capacity is less than arrival traffic. Thus, the scheme has desirable VP bandwidth allocation characteristics. Simulation results also show that the scheme prevents cell loss at a destination gateway completely.<<ETX>>

Index-server optimization for P2P file sharing in mobile ad hoc networks

In this paper, we compare two basic approaches towards providing peer-to-peer file-sharing (or more generally, information search) in mobile ad-hoc networks (MANET). The flooding approach broadcasts a query (e.g., to locate a node holding a given file) to all network nodes. The index-server approach adds additional servers (known as index servers) that cache directory information about which nodes have which files. With index servers, a node wishing to locate a file first queries its local index server, which then queries other index servers, as needed. The use of index servers presents the possibility of locating a file index quickly in an index server cache, but requires additional overhead to maintain cache consistency. We compare the performance of the flooding approach to two index-server caching approaches: consistent caching and local caching. We quantify the reduction in search overhead using the index-server scheme rather than flooding in MANET, and study how the optimal number of index servers varies according to network size, query rate, and index generation rate. We compare the flooding scheme and the consistent caching and local caching schemes, for two types of queries: history queries and latest queries. Numerical results show how one can choose between the alternatives of consistent caching and local caching depending on network size, index generation rate and query rate.

Cell loss properties for multiplexing of MPEG video sources considering picture coding types in ATM networks

In MPEG coding, there are three types of encoded pictures. Since these picture coding types have different importance of data content, the cell loss of each picture coding type affects the video quality differently in MPEG video transmission through ATM networks. This paper analyzed the per-session cell loss properties of MPEG video traffic in an ATM switching node in both the steady-state case and the transient case considering each picture type. In the analysis, a 3-state Markov modulated Bernoulli process (MMBP) is proposed as a traffic model for MPEG video which is tractable analytically. Numerical results revealed the influence of the picture transmission pattern on the cell loss properties of each picture coding type.

Finding good combinations of initial phases for periodic sources in discrete-time queues

Our study aims to construct the framework to accommodate periodic and bursty sources into ATM networks effectively. For this purpose, we develop two effective algorithms which can find a good combination of the initial phases of periodic sources in a short time. We then consider a call admission control (CAC) scheme which controls phase combinations of the periodic sources and decides whether a new call is accepted or not by taking account of the controlled phase combinations. Our CAC scheme is applicable to real-time MPEG video traffic which will be the major traffic in ATM networks. Simulation results show that our algorithms can find a better combination of initial phases than those chosen randomly in any our trials under both homogeneous and heterogeneous traffic environments.

Quasi-STM transmission method based on ATM network

In the ATM network, various kinds of traffic will be supported. This includes traffic which requires high quality of service. For example, coded HDTV requires no cell loss because of high compression and no possibility of retransmission. CBR (constant bit rate) services require no delay jitter. Thus, it will be required to support some class of services with no cell loss and no delay jitter. This paper proposes a new transmission method Q-STM, with which no cell loss and no delay jitter can be supported in the ATM network. The Q-STM introduces two new concepts into the ATM networks; frame structure and time slot reservation. A frame structure itself is similar to the framed ATM. However, in the Q-STM, a frame is divided into some subframes and each subframe is a unit of time switching in intermediate switching nodes. This leads to smaller end-to-end delay than that of the framed ATM. Time slots in a frame are reserved for each Q-STM call in a call setup phase and this leads to no delay jitter and no cell loss. Ordinary ATM service class is also supported and this kind of cell uses an empty slot which is not reserved or is not used because of fluctuation of Q-STM call transmission rate.