Naoki Fuke

MAP Multiplexing in IEEE 802.16 Mobile Multi-Hop Relay

In this paper, we propose a new scheme called MAP multiplexing for efficient use of the radio resource in IEEE 802.16-based multi-hop wireless networks. Although IEEE 802.16-based multi-hop wireless networks enable expansion of the service area due to the introduction of relay stations, the efficiency of radio resource utilization could be degraded because the radio resource is shared between the base station and relay stations in a time-division or frequency-division manner, and either the base station or one relay station can only use it at one time. MAP multiplexing can improve the efficiency of radio resource utilization. Computer simulation results show that MAP multiplexing reduces the end-to-end delay as well as enhances the radio resource utilization

Long-range oversea wireless network using 2.4 GHz wireless LAN installation and performance

High-quality 2.4 GHz wireless LAN over long-range oversea paths was installed using a space diversity technique. The installed network consists of five wireless links, including a long-range 11.3 km link. To lower the adverse affect of fluctuation in the tidal level, two wireless LAN devices with different antenna heights were installed at one side of the longest link. The antenna heights were suitably determined on the basis of link profile and gained data at the deployment of the equipment. The measured performance indicates that the link with space diversity achieves 100% operating rate in a measured period of time, while the link without space diversity achieves an approximately 90% operating rate in the same time. This method effectively improves the quality of conventional wireless LAN systems.

Multihop Mobile Communications System Adopting Fixed Relay Stations and its Time Slot Allocation Schemes

In this paper, we present a multihop mobile communications system utilizing fixed relay stations to enhance the coverage of the service area. A multihop mobile communications system was originally proposed as a system in which only mobile stations relay communication between other mobile stations and a base station to solve the problem of poor coverage expected in a future cellular system. In the system, however, a probability of a mobile station being able to connect with a base station via their relay functions is governed by a probability of mobile stations existing in its neighborhood. Therefore, we introduce fixed stations as relay stations in addition to relay functions of mobile stations to enhance the probability of link conductivity between a base station and a mobile station. By adopting this multihop architecture, a mobile station which needs relay functions can choose relay stations among fixed relay stations or other mobile stations. Moreover, we also examine its time slot allocation methods. We confirmed that the ratio of successful connection between mobile stations and base stations improved about 0.15 by introducing just 4 fixed relay stations in a certain environment

Simulation evaluation on area extension and system capacity of CDMA packet communication system utilizing multihop connection

The objective of this study is to evaluate effectiveness of multihopping technique applied to CDMA packet communication system. The system model is designed so that mobile stations that have no direct connectivity to any base station setup multi-hopped paths by way of neighbor mobile stations. Two policies are addressed in selecting relay stations based on battery usage, minimized usage on relay station and minimized usage on all stations along multihopped path. With these conditions, system characteristic is evaluated in terms of system capacity and coverage area extension. The result of computer simulation shows that multihopping technique does extend the coverage area with effectively equal performance to the conventional single hop system when the system load is relatively light.

Satellite System with Wideband Spreading Signals overlaid on FDMA Signals within the Same FSS Network

*† We present characteristics of a satellite system with wideband spreading signals overlaid on conventional FDMA signals within the same FSS network. This type of application could enable the transmission of additional information using wideband spreading signals within the same transponder. In particular, it could be suitable for the event of natural disasters and similar emergencies for warning and relief operations, because interference from the same satellite and adjacent satellites is expected to be mitigated by its spreading gain, even if a low-gain antenna is used. We have evaluated the achievable data rate by the link budget analysis, which shows that a data rate of 185 kbit/s is obtainable with a 10 cm dish antenna at the suppressed power level of 20 dB compared to FDMA carriers. Even if spreading signals are overlaid, the number of FDMA carriers can be maintained with adjusting system parameters. We have also evaluated the other model where the dedicated bandwidths are allocated to spreading signals. The result shows that a data rate of several tens of kbit/s can be achieved with a low-gain antenna of 5 dBi under the interference from adjacent satellites. The achieved data rate is considered to be sufficient to deliver low-rate emergency information. Satellite receivers with such low-gain antennas are expected to facilitate installation and maintenance for the purpose of disaster relief communications.

Multihop mobile communications system using MC-CDMA in forward links

This paper proposes a multihop mobile communications system using an MC-CDMA transmission technique in the forward links. In the system, it is assumed henceforth that each mobile station has a relaying function where a frequency band is used both in the 1st and 2nd hops. Then, we examined a radio resource allocation method in the forward links. In this method, an orthogonal codeword is assigned for each group that consists of one or more mobile stations and the resources of time and frequency are distributed to each link within a group. To clarify the characteristics of this method, we compared the proposed system and a conventional one without relaying, in terms of the base station connection rate, throughput, and so on. Simulation results indicate that the proposed system improves the connection rate without further orthogonal codeword consumption, and user throughput in an appropriate mobile station density.

Large-scale CFO-SS (high-speed, long-range 2.4 GHz wireless LAN) network for educational Internet access

A 2.4 GHz wireless LAN network interconnecting schools and educational facilities is constructed employing CFO-SS (carrier frequency offset-spread spectrum) systems. The CFO-SS system provides high-speed (10 or 18 Mbit/s) and long-range transmission without reducing the transmission speed. Parameters of CFO-SS links such as radio channels, antenna polarizations and access modes are selected by considering the CFO-SS network architecture. Changing a radio channel by a network management software, CFO-SS keeps the link quality at a predetermined level under interference from other existing systems using the 2.4 GHz band. The throughput performance is improved with a window control protocol of CFO-SS.