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hub or switch

H1 remains in same IP subnet: IP address can remain same switch: which AP is associated with H1? self-learning (Ch. 5): switch will see frame from H1 and “remember” which switch port can be used to reach H1 AP2 broadcast H1’s MAC to switch. router. 802.11: mobility within same subnet.

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hub or switch

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  1. H1 remains in same IP subnet: IP address can remain same switch: which AP is associated with H1? self-learning (Ch. 5): switch will see frame from H1 and “remember” which switch port can be used to reach H1 AP2 broadcast H1’s MAC to switch router 802.11: mobility within same subnet hub or switch BBS 1 AP 1 AP 2 H1 BBS 2 6: Wireless and Mobile Networks

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

  3. CDMA example 6: Wireless and Mobile Networks

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

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

  6. 802.15 MAC and Bluetooth • 802.11 MAC • 11 Mbps – 54 Mbps • Up to 100 meters range • 802.15 MAC • Wireless personal area network (WPAN) • < 10 meters range • Simple (cheap) device, low power assumption • Cable, wire replacement • E.g., mouse, keyboard, headphone • Example: Bluetooth 6: Wireless and Mobile Networks

  7. Bluetooth • Physical layer properties: • 2.4GHz unlicensed spectrum • Frequency-hopping spread spectrum • 79 channels with different frequencies • TDM transmit: jump among channels with preset sequences (coding) • Up to 721bps (802.11 is 11 Mbps to 54 Mbps) 6: Wireless and Mobile Networks

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

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