1 TENDÊNCIAS EM COMPUTAÇÃO UBÍQUA E MÓVEL Rui Silva Moreira Obectivos do Seminário 2 Sistemas Ubíquos e Móveis Definição e evolução histórica Características e objectivos Exemplos UbiComp Comunicações sem Fios Codificação e Transmissão Multiplexagem & Canais & Células Normas Wi-Fi - 802.11a/b/g/n Bluetooth 802.15.1 ZigBee 802.15.4 Protocolos e Redes Móveis Pilha protocolos Redes ad hoc IP & Integração de Serviços (IMS) Localização e Contextualização Métodos & tecnologias localização Modelização do contexto Adaptação dinâmica local/contexto Requisitos de Sistema Modos/perfis de funcionamento (e.g., poupança de energia) Segurança e privacidade em ambientes móveis
3 Comunicações sem Fios Codificação e Transmissão Multiplexagem & Canais &Células Normas Wi-Fi- 802.11b/g/n Bluetooth- 802.15.1 ZigBee- 802.15.4 Wireless Networks 4 Transmission through common medium (e.g., air, water) using wireless technologies/carriers Carriers (waves that carry information): Radio waves (electromagnetic) Audio waves (ultrasounds) Light waves (IRDa, lasers)
Advantages of Wireless Networks 5 Build flexible data communication systems Mobility: users can roam around Simple instalation: faster/easier to install than wired Extensible: reach places that cannot be wired Flexible: easly adapted to changes in configuration Cost: overall instalation& life-cycle maintenance Scalability: variaty of topologies(e.g., structured, ad hoc) Types of Wireless Networks 6 WBAN (Wireless Body Area Networks) Communication gadgets (RF, Bluetooth) WPAN (Wireless Personal Area Networks) Sync PDA-PC/PC-PC (Bluetooth) WLAN (Wireless Local Area Networks) Workgroups PC-PC (WiFi) WWAN (Wireless Wide Area Networks) Communicate while travelling(3g/umts, WiMAX) WSN (Wireless Sensor Networks) Environment and home monitoring(zigbee)
Information Transmission 7 Transmiter+ Antena = RadioStation/ Cell Sinuswave does not haveinformation needsto be modulated Modulation: process of changing/encoding info into a wave for carrying information use wavesignalsto crosslongdistances(e.g., electromagnetic signals, ultrasound signals, infra-red signals, laser signals, etc.) Basic Analogic Modulation 8 Amplitude Modulation (AM) e.g., used in long distance radio transmissions (country wide) Frequency Modulation (FM) e.g., used in short distance radio transmissions (region wide) Phase Modulation (PM) not widely used for analog radio transmissions, since it requires more complex hardware
Analog Modulation 9 Basic Digital Modulation 10 Amplitude Shift Keying(ASK) e.g., used in long distance radio transmissions(country wide) Frequency Shift Keying(FSK) e.g., used in shorter distance radio transmissions(region wide) Phase Shift Keying(PSK)
Digital Modulation 11 Binary Phase Shif Keying(BPSK) 12 Popular digital modulation where spectral efficiency is 1bit/Hz (i.e., Tx data rate = signal bandwidth) Shifts carrier sine wave 180 for each binary state change
Quadrature PSK 13 Uses 4 unique sine signals shifted by 45 (check constelation diagram below) Each carrier phase represents 2 bits, hence spectral efficiency is 2 bits/hz Shannon-Hartley Law 14 Max theoretical channel Data Rate (bits/s) = Channel capacity (C): C = B log 2 (1 + SNR) C depends on channel bandwidth (B in Hz) and signal-to-noise ratio (SNR) Noise diminishes data rate for a given Bit Error Rate (BER). Baud Rate = number of tx modulation symbols per second Basic binary txuses 1 bit per symbol, hence in such cases baud rate = bit rate With QPSK a bit rate of X Mb/s = baud rate of ½ X symbols/s
Multiple PSK (M-PSK) 15 QPSK = 4-PSK (4 amplitude-phase combinations) Smallerphaseshiftsallowstxmore bits per symbol: 8-PSK (8 symbols with constant carrier amplitude 45 shifts); allows 3 bits/symbol 16-PSK (16 symbols with constant carrier amplitude 22.5 shifts); allows 4 bits/symbol The grater the number of phase shifts, the more difficult is demodulation (in the presence of noise) Quadrature Amplitude Modulation 16 QAM combines amplitude and phase shifts, e.g., 8QAM combines 4 carrier phases & 2 amplitude levels (tx 3 bits/symbol) Figure shows 16QAM which uses 3 amplitudes and 12 phase shifts (4 bits/symbol) Variations: 64QAM (6 bits/symbol) 256QAM (8 bits/symbol)
Amplitude PSK (APSK) 17 QAM is widely used (e.g., cable TV, Wi-Fi LANs, satellites, etc.) but higher levels of QAM are more subject to noise APSK uses fewer amplitude levels, e.g., 16APSK, mostly used in satellites, uses double-ring PSK format-2 amplitude levels and 16 phases (4-12 16APSK) 4 symbols in the center ring 12 symbols in the outer ring Multiplexing 18 Sharingsingle physicalmedium(e.g., air, cable, etc.) between multiple simultaneous tx/rx node pairs
Multiplexing 19 FDMA vstdmavscdma FDMA 20 Frequency Division Multiple Access
FDMA 21 Frequency Division Multiple Access FDMA 22 FDMA Hierarchy
TDMA 23 Synchronous Time Division Multiple Access TDMA 24 Statistical/Asynchronous Time Division Multiple Access
TDMA 25 Digital Data Hierarchy Orthogonal FDM (OFDM) 26 Combines digital modulation + multiplexing techniques to improve spectral efficiency (e.g., IEEE 802.11n, WiMAX, LTE, DSL, PLC, etc.) On WiFi, data rates up to 300 Mbits/s are possible with 64QAM
Radio Technologies 27 Wireless Range vs Bandwidth 28
Broadband Technologies 29 WiFi Channels 30