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
Macrodiversity Effect Using ROF Ubiquitous Antenna Architecture in Wireless CDMA System
This paper proposes an ROF ubiquitous antenna architecture for the wireless CDMA system. The proposed system separates each component of independent signals passing through the multipath in radio and optical links, which are gathered at passive double star link, by using RAKE reception and the macrodiversity effect is obtained. Theoretical analysis shows that the proposed system improves BER performance by 22 dB and reduces the transmission power and its control range by 19 dB. key words: ROF, ubiquitous antenna system, macrodiversity, RAKE reception
Convergence Anatomization of Aquaculture Production in Leading Fish-Producing Countries During the Period of 1997-2013
Growth and national importance of aquaculture production is empirically assessed as an important indicator of development. The present article aims to test whether the major aquaculture producing countries of the world are converging over time. The authors have applied the absolute and conditional beta convergence and sigma convergence approaches on the data of FAO for the period 1997-2013. The results show that there is an absolute beta convergence and sigma convergence among 25 major aquaculture producing countries; negative sign of coefficient of conditional beta convergence with per capita income is also noticed. It implies, the growth rates of aquaculture for developed nations are declining with rise in per capita income and backward fish-intensive countries are catching up with the giant producers like China and India. The cross-country variations are also going down which means that the countries' development gaps are getting narrowed by means of growth of aquaculture resources.