6: Wireless and Mobile Networks6-1 hub or switch AP 2 AP 1 H1 BBS 2 BBS : mobility within same subnet router r H1 remains in same IP subnet: IP address can remain same r switch: which AP is associated with H1? m self-learning (Ch. 5): switch will see frame from H1 and “remember” which switch port can be used to reach H1 m AP2 broadcast H1’s MAC to switch

6: Wireless and Mobile Networks6-2 CDMA Principle (6.2.1) r Code Division Multiple Access m Wide spectrum technique m All users use the full spectrum m Users with different codings not interfere r Each bit is encoded by much high rate signal (code) m Receiver can recover the bit with the corresponding code

6: Wireless and Mobile Networks6-3 CDMA example

6: Wireless and Mobile Networks6-4 Working with multiple users r How to extract data when multiple users transmit at the same time? r Assumptions: m Interfering signals are additive m Signal (-1) = 2 r New signals in the air (N senders): Same decoding formula!

6: Wireless and Mobile Networks6-5 Why extract correctly By each user? A: user codes are orthogonal

6: Wireless and Mobile Networks MAC and Bluetooth r MAC m 11 Mbps – 54 Mbps m Up to 100 meters range r MAC m Wireless personal area network (WPAN) m < 10 meters range m Simple (cheap) device, low power assumption m Cable, wire replacement E.g., mouse, keyboard, headphone m Example: Bluetooth

6: Wireless and Mobile Networks6-7 Bluetooth r Physical layer properties: m 2.4GHz unlicensed spectrum m Frequency-hopping spread spectrum 79 channels with different frequencies TDM transmit: jump among channels with preset sequences (coding) m Up to 721bps ( is 11 Mbps to 54 Mbps)

6: Wireless and Mobile Networks6-8 Bluetooth r Ad hoc network structure r One master, <=7 slaves m Odd time slot: master m Even time: slaves r Parked: inactive devices r Problem: slow speed can be achieved by RF device m Much cheaper, simpler