無線電技術

A Brief History

RF Signal Propagation

RF Signal Propagation

Propagation Mechanism

頻率與波長

Decibels (dB) and dBm

Gain and Attenuation

Noise, Interference, SNR

最大頻寬 - Shannon理論

Channel Capacity

天線

電波傳播

Radio Frequency (RF) Spectrum

Spectrum Allocation

ITU-R defined ISM Bands

Spectrum Allocation - US

Spectrum Allocation - Singapo

最大頻寬限制

Multipath Interference Problem

Fluctuations of SNR

Multipath Interference Problem

其他干擾

Rain Attenuation

Doppler Effect

FSK

MultiAccess Technology

FDMA

TDMA

TDMA Time Frame

Spread Spectrum

CDMA

雙工 (Full-Duplex)

特性分析

Mobile System

Untitled Document
A Brief History
1834 wired telegraph for manually digitalized data (Gauss & Weber)
1839 first demonstration of telegraph between Washington DC and Baltimore (Morse)
1858 first transoceanic cable for telegraph
1867 manually switched telephone for analog voice (Bell)
1897 wireless telegram (Marconi) SMS service!
1900 transoceanic wireless telegraph (Marconi)
1905 Radio transmission (Fessenden)
1908 idea of TV (Campbell-Swinton)
1915 transcontinental telephone (Bell)
1920 commercial radio broadcast (KDKA), and sampling in comm (Carson)
1926 TV demonstration (Baird, England, and Jenkins)
1933 FM modulation invented (Armstrong)
1941 TV broadcast starts in the US
1946 First computer in U. Pennsylvania
1950 TDM, microwave radio, and voice band modems used in PSTN
1953 Color TV and transoceanic telephone
1957 first satellite (Sputnik I)
1962 Transoceanic satellite TV (Telstar I)
1965 videotape (Sony)
1968 cable TV development
1968 ARPANET started (first node at UCLA)
1971 9600 bps voice band modems (Codex)
1972 Demonstration of cellular systems (Motorola)
1973 Ethernet invented (Metcalfe), also international ARPANET
1980 fiber optic systems applied to PSTN
1995 Netscape, Internet as the first popular data communication networks
Wed Mar 16 00:34:18 CST 2011

Untitled Document
RF Signal Propagation
Wed Mar 16 00:34:18 CST 2011 Untitled Document
RF Signal Propagation
 
What is LOS problem?
 
Case of Signal Differection
   
Case of Lake effect for Cellular System
   
Case of Wireless Link for a Conference
 
Cases of RF signal hopping
   
Ohio Case
   
Circult Board Layout
Wed Mar 16 00:34:20 CST 2011 Untitled Document
Propagation Mechanism
Reflection and transmission
   
Reflection occurs when a propagating electromagnetic wave impinges upon an object which has very large dimensions when compared to the wavelength of the propagating wave.
Diffraction
   
Diffraction occurs when the radio path between the transmitter and receiver is obstructed by a surface that has sharp irregularities (edges).
Scattering
   
Scatters occurs when the medium through which the wave travels consists of objects with dimensions that are small compared to the wavelength, and where the number of obstacles per unit volume is large.
Wed Mar 16 00:34:20 CST 2011 Untitled Document
頻率與波長
c = λf
  c   speed of light, a constant
  λ   wavelength
  f   frequency
   
AM radio with frequency 1710 kHz equal to wavelength 175m
Wed Mar 16 00:34:21 CST 2011 Untitled Document
Decibels (dB) and dBm
Wed Mar 16 00:34:22 CST 2011 Untitled Document
Gain and Attenuation
.FR Wed Mar 16 00:34:23 CST 2011 Untitled Document
Noise, Interference, SNR
Wed Mar 16 00:34:25 CST 2011 Untitled Document
最大頻寬 - Shannon理論
Wed Mar 16 00:34:26 CST 2011 Untitled Document
Channel Capacity
Data rate rate at which data can be communicated (bps)
Bandwidth the bandwidth of the transmitted signal as constrained by the transmitter and the nature of the transmission medium (Hertz)
Noise average level of noise over the communications path
Error rate rate at which errors occur
Error
transmit 1 and receive 0
transmit 0 and receive 1
Wed Mar 16 00:34:27 CST 2011 Untitled Document
天線

Wed Mar 16 00:34:27 CST 2011 Untitled Document
電波傳播
Wed Mar 16 00:34:28 CST 2011 Untitled Document
Radio Frequency (RF) Spectrum
  頻率範圍 波長範圍 傳播特性 代表性用途
特低頻
(VLF) 		3-30 KHz 100,000~10,000公尺 1. 電波沿地球表面行進，可達長距離通信
2. 終年衰減小，可靠性高
3. 利用電離層與地表面形成的導層傳至遠距離
4. 地波與天波並存
5. 使用垂直天線 		1. 極長距離點與點間之通信
2. 航海及助航
3. 感應式室內呼叫系統
低頻
(LF) 		30-300KHz 10,000~1,000公尺 同上 1. 長距離點與點之通信
2. 航海及助航
3. 感應式室內呼叫系統
中頻
(MF) 		300~3000 KHz 1000~100公尺 1. 電波於日間沿地球表面行進，達較短距離
2. 夜間若干電能靠E層反射達較長距離
3. 天波、地波並存
4. 日間及夏季衰減較夜間及冬季為大
5. 使用垂直天線 		1. 中波廣播
2. 航空及航海通
3. 無線電定
4. 固定行動業
5. 海洋浮標
6. 業餘通信
高頻
(HF) 		3-30 MHz 100~10公尺 1. 電波利用電離層(特別是F層)反射 (一次或多次反射)以達遠距離
2. 傳播情況隨季節及每日時間變化頗大
3. 利用天線指向性，可收小功率達長距離之通信效果
4. 通達距離隨頻率及發射角之不同而異
5. 太陽黑子數越多，電離層密度越大，位置較高，最高可用頻率 (MUF)亦加高，通信距離越長，反之相反
6. 地波距發射機不遠即消失
7. 使用水平天線 		1. 長距離點與點通信及廣播
2. 業餘通信
3. 無線電天文
4. 標準頻時信號
5. 航空行動
6. 短波廣播
7. 民用無線電
特高頻
(VHF) 		30-300 MHz 10~1公尺 1. 穿越電離層，較不受其影響
2. 以空間波作視距 (line-of-sight)通信
3. 20-65MHz間利用E層散射達視距外通信
4. 使用垂直及水平天線
(水平天線較多)
5. 接近直線傳輸
中距離通信、雷達、調頻廣播、電視、導航、業餘 、無線電叫人、各種陸地行動通信
超高頻
(UHF) 		3003,000 MHz 100~10公分 1. 視距通信
2. 以空間波接近直線傳輸
3. 1000MHz以上微波：
(1) 使用定向反射面、反射網、喇叭型、 拋物面反射式及平面天線等
(2) 恆向地面彎曲進行
(3) 使用線上保護、熱待接保護及分集式保護等鏈路保護方式
(4) 方向性極高，波束極狹
(5) 發射功率小
(6) 如光波性質，遇阻礙即被吸取
(7) 10GHz以上頻率愈高，受雨點、霧．雪、 雹及空氣中氣體之吸收愈大
(8) 利用對流層散射可達遠距離 		短距離通信、中繼系統、 電視、衛星氣象、天文、業餘無線電定位、 助航太空研究、地球探測、公眾行動電話、 有線電話無線主副機、計程車無線電話
極高頻
(SHF)
至高頻
(EHF) 		3-300 GHz 10~0.1公分 同上 微波中繼、各種雷達、 衛星通信、衛星廣播、 無線電天文
Wed Mar 16 00:34:28 CST 2011 Untitled Document
Spectrum Allocation
RF band for mobile Communication system < 3.5 GHz
Wireless spectrum is regulated by governments
   
Regulation has significant impact on technology advancement and business development
 
Who should use the spectrum? How should it be used?
   
Beauty Contest
   
Auction for licenses (e.g. 3G license)
Regulator
 
NCC (Taiwan)
 
FCC (USA)
Unlicenced Band (ISM)
 
ISM Band (for Industrial, Scientific, and Medical Use)
Wed Mar 16 00:34:29 CST 2011 Untitled Document
ITU-R defined ISM Bands
Frequency range [Hz] Center frequency [Hz] Availability
6.765–6.795 MHz 6.780 MHz Subject to local acceptance
13.553–13.567 MHz 13.560 MHz
26.957–27.283 MHz 27.120 MHz
40.66–40.70 MHz 40.68 MHz
433.05–434.79 MHz 433.92 MHz Region 1 only
902–928 MHz 915 MHz Region 2 only
2.400–2.500 GHz 2.450 GHz
5.725–5.875 GHz 5.800 GHz
24–24.25 GHz 24.125 GHz
61–61.5 GHz 61.25 GHz Subject to local acceptance
122–123 GHz 122.5 GHz Subject to local acceptance
244–246 GHz 245 GHz Subject to local acceptance
 
WLAN
Bluetooth 2450 MHz band
HIPERLAN 5800 MHz band
IEEE 802.11 2450 MHz and 5800 MHz bands
Wed Mar 16 00:34:29 CST 2011 Untitled Document
Spectrum Allocation - US
Wed Mar 16 00:34:30 CST 2011 Untitled Document
Spectrum Allocation - Singapo
Wed Mar 16 00:34:31 CST 2011 Untitled Document
最大頻寬限制
 
Nyquist理論 (沒有雜訊)
   
D bps = 2 B log 2 K
 
Shannon-Hartley Theorem (考慮雜訊)
   
C = B log 2 (1 + S/N)
C the channel capacity in bps
B the bandwidth of the channel, in Hertz
S the total signal power over the bandwidth
N the total noise power over the bandwidth
S/N the signal-to-noise ratio(SNR)
Wed Mar 16 00:34:31 CST 2011 Untitled Document
Multipath Interference Problem
Wed Mar 16 00:34:32 CST 2011 Untitled Document
Fluctuations of SNR
 
Path-Loss
 
Shadow (Slow) fading
 
Fast fading
 
Doppler fading
Wed Mar 16 00:34:33 CST 2011 Untitled Document
Multipath Interference Problem
Wed Mar 16 00:34:34 CST 2011 Untitled Document
其他干擾
ACI (Adjacent Channel Interference)
 
兩個相鄰頻率的使用者，可能因距離不同而基地台收取兩者信號時， 因信號強度大幅起落而導致收訊能力大幅降低
Co-Channel Interference
 
兩個相同頻率但不在同cell的使用者，因對基地台的距離不同，導致 弱信號被強信號蓋台
Wed Mar 16 00:34:35 CST 2011 Untitled Document
Rain Attenuation
雨衰 (降雨衰耗)
 
降雨衰耗為無線電波在穿過雨區時所受到的衰減量。
   
當無線電信號到達天線前，行進的途徑如有烏雲或雨水的阻擋而形成信號衰減， 此種衰減稱為雨衰。
Wed Mar 16 00:34:36 CST 2011 Untitled Document
Doppler Effect
 
Named after the Austrian physicist Christian Doppler.
 
Change in the observed frequency (or wavelength) of waves due to relative motion between the wave source and the observer.
   
The Doppler effect is responsible for the perceived change in pitch of a siren as it approaches and then recedes, and for the red shift of light from distant galaxies.
Wed Mar 16 00:34:36 CST 2011 Untitled Document
FSK
Wed Mar 16 00:34:37 CST 2011 Untitled Document
MultiAccess Technology
   
讓多各使用者共用有限的頻譜，以提高系統容量，避免降低系統效能
Wed Mar 16 00:34:37 CST 2011 Untitled Document
FDMA
每一頻道在任一時刻只能有一個用戶。 如果一個FDMA頻道沒被使用，不能為其他 existing 用戶使用 ，這是一種資源浪費。
FDMA頻道的頻寬為 30kHz。
系統複雜度比TDMA低，所須的額外控制資訊比較少。
為了減小相鄰頻道干擾，FDMA系統對射頻（RF）濾波器要求較高。
Wed Mar 16 00:34:38 CST 2011 Untitled Document
TDMA
Wed Mar 16 00:34:39 CST 2011 Untitled Document
TDMA Time Frame
 
Each channel has 200k Hz
 
Each channel is divided by 8 time slots
Preamble
探測序列 		Information Message
Slot 1 Slot 3 Slot 3
Trail Bits Sync Bits Information Data Guard Bits
----- ----- ----- Slot N
Trail Bits
Wed Mar 16 00:34:40 CST 2011 Untitled Document
Spread Spectrum
 
使用全頻段發射信號
 
FHMA (frequency hopped multiple access)
   
Invented by George Antheil (a composer)
Hedy Lamarr (an actress, 1913–2000)
   
Antheil and Lamarr submitted the idea of a secret communication system in June 1941. On August 11, 1942, U.S. Patent 2,292,387 was granted to Antheil and "Hedy Kiesler Markey", Lamarr's married name at the time. This early version of frequency hopping used a piano roll to change between 88 frequencies and was intended to make radio-guided torpedoes harder for enemies to detect or jam.
 
DSMA (direct sequence multiple access)：又稱為CDMA (code division multiple access)
Wed Mar 16 00:34:40 CST 2011 Untitled Document
CDMA
保密性極高
Qualcomm將CDMA技術商業化
CDMA具備若干優異的特點
UMTS或是cdma2000都以CDMA為核心技術
使用者共用相同頻率，可以採用TDD或FDD。
系統容量限制是軟性的，當使用者數目增加時，雜訊水平(noise
floor)會上升，系統效 能會因而下降。
由於訊號展頻後佔用了相當大的頻段，使得多路徑漸弱效應大減。
Wed Mar 16 00:34:42 CST 2011 Untitled Document
雙工 (Full-Duplex)
 
以 Full-Duplex 方式讓雙方可同時發話
FDD 同時提供兩各單工的頻道，須兩組 Transceiver
TDD 同樣的頻率下提供兩個單工的時槽
Wed Mar 16 00:34:42 CST 2011 Untitled Document
特性分析
  Pedestrian Remote/mobile user
Mobility Low high
User density high hig h/low
Quality , availablity requirements high can compromise
Cost moderate can compromise
Handset size small can be large
Battery life long can be short
Alternative wired access n.a.
Wed Mar 16 00:34:43 CST 2011 Untitled Document
Mobile System
Mobile System Demands BOTH Wireless and Mobility
 
A wireless system may not be a mobile system
Wed Mar 16 00:34:44 CST 2011