Tsuyoshi Tamaki

TDOA location system for IEEE 802.11b WLAN

We propose an IEEE 802.11b wireless LAN location system based on the time difference of arrival (TDOA) method. We confirm that IEEE 802.11b, as part of an indoor location system, is potentially highly accurate because of its broad bandwidth. When a location system is implemented in the IEEE 802.11b system, there are two important considerations; system architecture and required positioning accuracy. The accuracy of an indoor location system is apt to be degraded by multipath fading, which is a complex characteristic of indoor propagation. We developed a TDOA location system based on IEEE 802.11b, including several techniques such as access point (APs) synchronization, leading edge timing observations, and averaging with diversity. We experimentally evaluated the proposed system in a storehouse. The positioning accuracy when using ten APs and 3-branch diversity was 2.4 m at the 67/sup th/ percentile.

Downlink MIMO Systems Using Cooperation Among Base Stations in a Slow Fading Channel

To increase the achievable sum rate of downlink MIMO (Multiple Input Multiple Output) systems, the cooperation among Base Stations (BS) is investigated in a slow fading channel. Three levels of BS coordination are considered: full coordination, partial coordination, and no coordination. This paper assumes that the downlink MIMO channel state information (CSI) is sent to the corresponding BS through a feedback link with some delay. In a fully coordinated system, the CSI at each BS needs to be collected at the central coordinator, and this process may result in significant additional delay. In this paper, the achievable throughput of each coordination level is evaluated and compared including the effects of the delay in CSI. A quasi-static fading is considered where the channel is static within one codeword, but it gradually changes over time based on the well-known Jakes model. Also, dirty paper coding (DPC) is applied, which is a transmission method shown to achieve the sum capacity of MIMO broadcast channels (BC). The results show that under certain delay conditions, the partially-coordinated system outperforms the fully-coordinated system. In addition, this paper presents a new partial-coordination method that provides higher throughput than the conventional partial-coordinated system.