Communication Systems and Different Research Topics Presented by: Ahmed Ahmedin University of California, Davis
A-wireless communication aspects. 1-Modulation is the key 2-analog and digital transmission 3-bit rate 4-signal to noise ratio 5-jamming 6-interference 7-distortion 8-capacity
Base band signal • Features: • -Low frequency range is occupied. • -no modulation is done. • -may be analog or digital.
Base band signal (cont.) Analog: t
Base band signal (cont.) Analog: Power spectral density power f BW
Base band signal (cont.) Digital:
Base band signal (cont.) Digital: 1 1 1 1 1 1 0 0 0 0 Tb Rb
Transmission medium 1- Twisted-pair: It is very low bandwidth and it is easily tapped either physically or by monitoring its electromagnetic radiation 2- Coaxial cable: It is greater bandwidth than twisted-pair but it is very expensive. 3- optical fibers: It is very high bandwidth , very high bit rate and inherently transmission medium.
Pass band transmission • Why wireless? 1- Long distance & less cost than wires. 2- mobility. • Why modulation? • Higher freq. lead to lower noise (no flicker !!!) • Antenna length proportional to wave length.
3-Modulation techniques. • Analog (AM,FM) • Digital (ASK,FSK,PSK) (on square wave !!!)
2-Multiple access techniques • 1-FDMA • 2-TDMA • 3-CDMA
Strength f1 f2f3 FDMA
B-multiple access techniques 1-FDMA
B-multiple access techniques 2-TDMA
Strength Frequency CDMA
B-multiple access techniques 3-CDMA
Noise Received info. Transmitted signal Received signal Info. Source User Transmitter Receiver Channel SOURCE Source Source encoder Channel encoder Modulator Destination Source decoder Channel decoder Demodulator Introduction Communication system consists of :- Transmitter Receiver
D-Wireless different systems and mobile generations. Radio AMPS (Advanced mobile phone sys. Or Cordless) [1G] analog GSM [2G] digital GPRS [2.5G] EDGE [2.75G] UMTS [3G] then 3.5 & 3.75G LTE or WiMAX [4G] Wi-Fi Bluetooth Ultra wide band (UWB) [low dist. But high rates] Zigbee [low rate and low power consumption specially in industry] …..etc
Nile University Zweil University
Some Research Directions in NU • Cognitive Radio Network • Wireless Sensor Network (WSN) • Wireless Security
Cognitive Radio Networks Research problems include: • Efficient and robust spectrum sensing. • Cognitive transmitter-receiver synchronization. • Exploration-vs-exploitation tradeoff. • Collaboration and competition among cognitive users. • Interference management in cognitive networks. • Centralized and decentralized scheduling in cognitive networks.
Wireless Sensor Networks • Secure sensor networks • Location determination • Cross-layer optimization • Clustering algorithms
Wireless Security • Practical secrecy capacity-achieving codes. • Secure broadcasting and multicasting. • Secrecy without transmit-CSI (channel state information). • Secrecy of MIMO channels. Authentication. • Cooperation for secrecy.
My Work Femtocells Interference Mitigation: