Multi-Cell Communication Systems Using Radio over Fiber Technology
あらまし 光無線融合技術(ROF:radio over fiber)は,光ファイバ伝送の低損失性と無線伝送の柔軟性を 組み合わせた通信システムの構築を可能にする.更に分岐が容易となる光ファイバ伝送路の特徴を生かすこと で,マルチセル型の無線システムが効果的に構成できる.しかし,光–電気変換部の付加に伴うコスト増や,マ ルチセル構成時のセル間干渉が課題となる.また光ファイバ区間を長くして長距離伝送に対応する場合,遅延が 大きくなるために通信プロトコルでのタイムアウトを考慮する必要がある.本文ではこれに対し,光–電気変換 部に FP-LD(fabry-perot laser diode)を採用した BIDI(bi-directional)モジュールを適用し,特に公衆無線 LANを対象としてシステムを経済化する方策を示す.セル間干渉に対しては,公衆無線 LANに限らず,CDMA (code division multiple access),切換ダイバーシチ,MIMO(multi-input multi-output)など,マルチパス を積極的に活用する無線技術に基づく対策を示す.特に MIMO の場合,異なるアンテナ出力を隣接セルに接続 すれば,セル端の干渉が生じる部分の方が条件によってはセルの中央より伝送品質が高くなる可能性を指摘する. また,長距離伝送時の遅延に対する留意点を説明する. キーワード 光無線融合技術,FP-LD,BIDI,ダイバーシチ,無線 LAN
Experimental evaluation of combined effect of coherent RAKE combining and SIR-based fast transmit power control for reverse link of DS-CDMA mobile radio
The combined effect of coherent RAKE combining using the weighted multislot averaging (WMSA) channel estimation filter and closed-loop fast transmit power control (TPC) in the 4.096 Mchip/s direct sequence code division multiple access (DS-CDMA) mobile radio reverse link is experimentally evaluated. The WMSA channel estimation filter utilizes periodically transmitted pilot symbols (four pilot symbols are time-multiplexed in each 40-symbol time slot). Its observation period is extended to 2-K slots in order to improve the accuracy of the channel estimation. The fast TPC is based on the measurement of signal-to-interference plus background noise ratio (SIR) using pilot symbols. Laboratory experiments show that the use of the K=2 WMSA channel estimation filter reduces the required E/sub b//I/sub 0/ at the average BER of 10/sup -3/ by approximately 0.5 dB compared to use of the linear interpolation filter, and that the required E/sub b//I/sub 0/ is minimized when the SIR measurement interval is M=10 symbols (one slot TPC delay). It was also clarified that SIR-based TPC works satisfactorily when two users with different information data rates, i.e., SF, independently employ fast TPC. Field experimental results obtained in an area nearby Tokyo showed that the average BER of 10/sup -3/ is achieved at the target E/sub b//I/sub 0/ per antenna of approximately 2.5 dB by using four-finger branch RAKE and two-branch antenna diversity. Although the target E/sub b//I/sub 0/ to achieve same BER, when there is one interfering user with a fourfold greater transmit power than that of the desired user that independently employs fast TPC, is almost the same as that in the single-user case, the mobile transmit power is increased by 1.0-2.0 dB due to the increased MAI. These results indicate that the combination of coherent RAKE combining and fast TPC works well in practical multipath fading channels.
Mechanics of deformable directed surfaces
Abstract The paper develops a simple, yet complete and consistent non-linear dynamic thermo-elastic shell theory based on the concepts of a two-dimensional directed continuum. The constitutive equations are postulated in a general form. Stress-strain relations are derived using the equation of energy balance and the two entropy production inequalities, which are rewritten in a special form. The linear theory is discussed in detail. The structure of the stress-strain relations is presented in the most general form and then specialized to concrete examples, in particular, to the classical shell theory, using their invariance properties with respective to certain symmetry groups. The elastic moduli are determined by demanding the coincidence of the frequency dispersion surfaces obtained using the two-dimensional theory with the lowest foils of the corresponding surfaces resulting from the three-dimensional theory of elasticity.