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無線多媒體網路與未來展望

無線多媒體網路與未來展望. 曾宏偉( activebunny@mac.com). Wireless Networking Overview. 9- layer protocol. Mobile Computing( 行動計算). 手機的功能朝多樣化發展 Mobile Computing 的組成. Mobile Wireless System 的演進. First-generation─ 類比訊號 (1)只能傳播聲音 (2)不具有自動漫遊( roaming) 的能力

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無線多媒體網路與未來展望

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  1. 無線多媒體網路與未來展望 曾宏偉(activebunny@mac.com)

  2. Wireless Networking Overview • 9-layer protocol

  3. Mobile Computing(行動計算) • 手機的功能朝多樣化發展 • Mobile Computing的組成

  4. Mobile Wireless System的演進 • First-generation─類比訊號(1)只能傳播聲音(2)不具有自動漫遊(roaming)的能力 • Second Generation(1)WAP(wireless application protocol)(2)2.5G─GPRS(3)Wireless LAN─IEEE 802.11 • Third Generation(1)能傳播各種數位資料─聲音, 影像, 文字, 音樂(2)隨時隨地的數位服務 • Beyond 3-G

  5. 台灣行動電話發展趨勢

  6. 國外行動電話市場概況

  7. 擁擠的無線電波頻道

  8. Wireless Networking Interface

  9. 更貼心的─Location Based App

  10. Ad Hoc.

  11. Infrastructure

  12. Radio Production and Transportation

  13. Radio傳播的issue • Free Space • Land Mobile • Multi-path • Shadow

  14. Free Space • Diffraction(折射) • Reflection(反射) • Scattering(漫射)

  15. Signal Fading • 訊號的衰減：接收者移動，距離遙遠

  16. Link Budget

  17. Direct Sequence Spread Spectrum

  18. Frequency Hopping

  19. Telecom v.s. Datacom • Telecom ─Circuit switch─AMPS ─GSM • Datacom─Packet switch

  20. Multiple Access in Wireless Net

  21. FDMA • FDMA ─Stands for Frequency Division Multiple Access

  22. TDMA • TDMA ─ Time Division Multiple Access • Channel are divided into several different time slots.

  23. ALOHA • ALOHA ─Transmit at any time you like.─If No ACKs, wait a random time, and transmit again─Collision? • Slotted ALOHA─Synchronous each device─Transmission occurs only when slot time arrived

  24. CSMA/CA • CSMA/CA ─ Carrier Sense Multiple Access/Collision Avoidance • Come From CSMA/CD(used in ethernet) • CSMA1. Listen before send2. If channel is free, transmission is allowed.3. If channel is busy, wait a random time and go back to step 1.

  25. Does it really work? • Hidden Terminal

  26. Solution ─ CSMA with “CA” • RTS/CTS/DATA/ACK

  27. More Problems • Exposed Terminal • Near-Far Problem: Fairness?

  28. Bluetooth 2.4GHz的頻帶 資料傳輸率1 Mb/s(64kbps聲音, 721kbps async.,432.6kpbs for sync) 使用TDMA

  29. How PicoNet is created

  30. Network Scenario

  31. IEEE 802.11 • Ad Hoc. • Infrastructure • Access Point • IEEE 802.11a—54Mbps • IEEE 802.11g—36Mbps

  32. Cellular System(細胞系統)

  33. 頻道的分配

  34. HandOff • 發生的原因 進入一個新的cell 電波的衰減 頻道的重新分配 問題：如果新的cell沒有頻道了？ Guard Channel

  35. 誰來決定HandOff? • User自己 • MSC/BS

  36. MacroCell and MicroCell

  37. 蓋台?

  38. 衛星

  39. PCS Architecture

  40. GPRS

  41. GPRS

  42. 3G • 3G 的設計在於能夠： 針對不同市場需求，開發各種應用 • 推動長期以市場為導向的創意服務，建立創新的價值鏈，創造使用者的實際利益，並帶動市場的真正需求。 • 開發技術先進、短小輕薄、容易操作、人性化介面的手機。 • 提供快速即時的多媒體通訊。 • 提供全球行動與漫遊功能。 • 廣泛支援不同行動製造商與系統業者，可供用戶選擇具競爭性的服務與低廉的價格。 • 高速上網及傳送電子郵件。

  43. WCDMA • 可以容納130users, 3db的功率作傳輸.

  44. WLAN

  45. Solution

  46. TCP/UDP • UDP傳資料，什麼也不做。 • TCP

  47. Wireless TCP • 造成封包遺失的原因，不再只是單純的網路擁擠，還有可能是肇因於無線網路連結本身的環境問題。

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