Toshikazu Kodama

Local predictive resource reservation for handoff in multimedia wireless IP networks

This paper presents two new methods that use local information alone to predict the resource demands of and determine resource reservation levels for future handoff calls in multimedia wireless IP networks. The proposed methods model the instantaneous resource demand directly. This differs from most existing methods that derive the demands from modeling the factors that impact the demands. As a result, the proposed methods allow new and handoff calls to: (1) follow non-Poisson and/or nonstationary arrival processes; (2) have arbitrary per-call resource demands; and (3) have arbitrarily distributed call and channel holding times. The first method is based on the Wiener prediction theory and the second method is based on time series analysis. Our simulations show that they perform well even for non-Poisson and nonstationary handoff call arrivals, arbitrary per-call bandwidth demands, and nonexponentially distributed call and channel holding times. They generate closely comparable performance with an existing local method and an existing collaborative method that uses information about mobiles in neighboring cells, under assumptions for which these other methods are optimized. The proposed methods are much simpler to implement than most other existing methods with fewer capabilities.

Voice capacity of IEEE 802.11b, 802.11a and 802.11g wireless LANs

IEEE 802.11 based wireless local area networks (WLANs) are becoming popular in home, enterprise and public access areas primarily due to their low cost, simplicity of installation and high data rates. While WLANs continue to be predominantly data centric, there is growing interest in using WLANs for voice, especially in enterprise markets. This paper presents new analytical and simulation results for the conversational speech capacity of WLANs and compares the different WLAN technologies in that regard. Specifically, we consider IEEE 802.11b, 802.11a and 802.11g systems in the infrastructure mode and find that voice capacity is a strong function of the channel bandwidth, codec packetization interval, data traffic and the packet size used by data. For the IEEE 802.11g system, we find that capacity depends on the CTS-to-self and RTS-CTS legacy protection mechanisms, with the RTS-CTS mechanism achieving lower capacity. We show that the analytical results are in close agreement with those from simulations and conclude the paper by highlighting some key factors that dictate the capacity of WLANs.

Voice performance in WLAN networks - an experimental study

In this work, we measure wireless local area network (WLAN) voice performance and capacity. While most WLAN applications today are data centric, the growing popularity of Voice over IP (VoIP) applications and the escalating trend towards convergence with cellular networks will catalyze an increased mix of voice traffic. Since voice applications must compete with each other and with simultaneous data applications for WLAN bandwidth, quantifying voice performance and capacity in the presence of background data traffic is an important issue. We offer a practical investigation into the ability of 802.11b MAC layer to support simultaneous voice and data. We quantify VoIP capacity for standard WLAN networks, indicative of those already in the field, as well as evaluate the practical benefits of implementing backoff control and priority queuing at the access point. Conclusions are drawn based on an extensive set of real-world measurements conducted using off-the-shelf equipment in a commercial testbed.

Seamless proactive handover across heterogeneous access networks

Dual-mode handsets and multimode terminals are generating demand for solutions that enable convergence and seamless handover across heterogeneous access networks. The IEEE 802.21 working group is creating a framework that defines a Media Independent Handover Function (MIHF), facilitates handover across heterogeneous access networks, and helps mobile users experience better performance during mobility events. In this paper, we describe this 802.21 framework and also summarize a Media-independent Pre-Authentication (MPA) mechanism currently under discussion within the IRTF that can further optimize handover performance. We discuss how the 802.21 framework and the MPA technique can be integrated to improve handover performance. Finally, we describe a test-bed implementation and validate experimental performance results of the combined mobility technique.

Bluetooth: channel coding considerations

We have noted that several papers that address the performance of Bluetooth (BT) over a fading channel implicitly assume a perfectly interleaved channel and neglect the bursty nature of a fading channel. The paper analyzes the effects of this incorrect assumption on BTs performance over a frequency-flat Rayleigh block fading channel. Despite the simplicity of the analysis, we obtain interesting results not previously published. We show that neglecting the burst nature of the channel leads to overly-pessimistic conclusions about the performance of Bluetooth in the low SNR region and, thus, that many reported results on the coexistence of Bluetooth and 802.11 are overly-pessimistic. Moreover, we also conclude that the coding strategy used in Bluetooth has little or no effect on a frequency-flat Rayleigh block fading channel.

Saw IF Filter on LITaO3 for Color TV Receivers

More than eight years have passed since DeVries et al. reported the first attempt at installing SAW (Surface Acoustic Wave) filters in a TV set(1). In Japan, SAW IF filter development has been continued by several companies and TV receivers incorporating SAW filter have been placed on the market since 1977.

Improving WLAN voice capacity through dynamic priority access

The most commonly deployed wireless local area network (WLAN) standard, IEEE 802.11b, provides no inherent quality of service (QoS) mechanisms to support delay sensitive applications. In particular, 802.11b WLANs exhibit poor voice capacity. This problem stems from limitations in the mandatory medium access control (MAC) protocol, called the distributed coordination function (DCF). WLANs commonly comprise an access point (AP) that must deliver all downlink packets, yet is afforded no special privileges under the DCF. This disparity leads to high downlink packet delays, which is the limiting factor in WLAN voice capacity. We believe that the main mechanism to improve capacity is to enable the AP to acquire the medium with a higher priority than the stations. This method is espoused in the forthcoming QoS-extension, IEEE 802.11e. In addition to the technique itself, knowing when and how long to apply it is critical for voice capacity improvement. We present such a technique, named aggrementing, for legacy 802.11b APs, as well as a generic approach that relates real-time system performance with the dynamics of such priority medium access techniques. We demonstrate that intelligently applying these techniques can improve WLAN voice capacity by as much as 25%.

Dynamic Buffering Control Scheme for Mobile Handoff

In a mobile environment, as a mobile node moves from one point of attachment to another during an ongoing application session it is subjected to packet loss due to network and link layer transition. Such packet loss affects the quality of ongoing communication session such as interactive VoIP traffic and streaming media. We provide a solution to this scenario by buffering packets for the mobile node at an access router or network node near the edge of the network where mobile may be moving away from or moving towards. The buffered packets are then forwarded to the mobile node once the handoff process completes. The buffering scheme is used in conjunction with existing mobility protocols, access protocols or as an independent network or link layer mechanism. Ability to control the buffer dynamically provides a reasonable trade-off between delay and packet loss which is within the threshold limit for real-time communication. The overview and mechanisms of such schemes are described and comparisons on existing buffering schemes are also provided

Voice capacity of IEEE 802.11b and 802.11a wireless LANs in the presence of channel errors and different user data rates

IEEE 802.11 based wireless local area networks (WLANs) are becoming popular in home, enterprise and public access areas primarily due to their low cost, simplicity of installation and high data rates. While WLANs continue to be predominantly data centric, there is growing interest in using WLANs for voice, especially in enterprise and hot spot scenarios. The paper presents new results for the conversational speech capacity of 802.11b and 802.11a WLANs by specifically considering channel errors and different user rates. Our results show that both systems suffer a significant loss in capacity for packet error rates (PER) greater than 5%. We also show link adaptation can prove to be invaluable in coping with higher PERs. Finally, we show that even a limited presence of low data rate users severely limits the overall voice capacity of WLANs.

Realizing mobile wireless Internet telephony and streaming multimedia testbed

Streaming real-time multimedia content over the Internet is gaining momentum in the communications, entertainment, music and interactive game industries as well as in the military. In general, streaming applications include IP telephony, multimedia broadcasts and various interactive applications such as multi-party conferences, collaborations and multiplayer games. Successfully realizing such applications in a highly mobile environment, however, presents many research challenges. In order to investigate such challenges and demonstrate viable solutions, we have developed an experimental indoor and outdoor testbed laboratory. By implementing standard IETF protocols into this testbed, we have demonstrated the basic functionalities required of the mobile wireless Internet to successfully support mobile multimedia access. These requirements include signaling, registration, dynamic configuration, mobility binding, location management, Authentication Authorization and Accounting (AAA), and quality of service over a variety of radio access network (RAN) technologies (e.g. 802.11b, CDMA/GPRS). In this paper, we describe this testbed and discuss important design issues and tradeoffs. We detail the incorporation and inter-relation of a wide catalog of IETF protocols-such as SIP, SAP, SDP, RTP/RTCP/RTSP, MGCP, variants of Mobile-IP, DRCP, HMMP, PANA, and DSNP-to achieve our goals. We believe that the results and experiences obtained from this experimental testbed will advance the understanding of the pertinent deployment issues for a Mobile Wireless Internet.