Wireless network characteristics Multiple wireless senders and receivers create additional problems(beyond multiple access): A's signal C's signal strength strength Hidden terminal problem space B,A hear each other Signal fading: ▣B,C hear each other B,A hear each other A,C can not hear each other B,C hear each other means A,C unaware of their A,C can not hear each other interference at B interferring at B 6:Wireless and Mobile Networks 6-11
6: Wireless and Mobile Networks 6-11 Wireless network characteristics Multiple wireless senders and receivers create additional problems (beyond multiple access): A B C Hidden terminal problem B, A hear each other B, C hear each other A, C can not hear each other means A, C unaware of their interference at B A B C A’s signal strength space C’s signal strength Signal fading: B, A hear each other B, C hear each other A, C can not hear each other interferring at B
Code Division Multiple Access (CDMA) used in several wireless broadcast channels (cellular,satellite,etc)standards unique "code"assigned to each user;i.e.,code set partitioning all users share same freguency,but each user has own "chipping"sequence (i.e.,code)to encode data encoded signal (original data)X(chipping sequence) decoding:inner-product of encoded signal and chipping sequence allows multiple users to "coexist"and transmit simultaneously with minimal interference (if codes are "orthogonal") 6:Wireless and Mobile Networks 6-12
6: Wireless and Mobile Networks 6-12 Code Division Multiple Access (CDMA) used in several wireless broadcast channels (cellular, satellite, etc) standards unique “code” assigned to each user; i.e., code set partitioning all users share same frequency, but each user has own “chipping” sequence (i.e., code) to encode data encoded signal = (original data) X (chipping sequence) decoding: inner-product of encoded signal and chipping sequence allows multiple users to “coexist” and transmit simultaneously with minimal interference (if codes are “orthogonal”)
CDMA Encode/Decode channel output Zi.m Zi.m=diCm: data d0=1 1的可 bits d1=-1 sender 时可 5HH code 可可 11日 slot 1 slot 0 channel channel output output slot 1 slot0 D= M received H44 d0=1 input d1=-1 code 11万 1日 slot 1 slot 0 的5 包5 channel channel receiver output output slot 1 slot 0 6:Wireless and Mobile Networks 6-13
6: Wireless and Mobile Networks 6-13 CDMA Encode/Decode slot 1 slot 0 d1 = -1 1 1 1 1 -1 -1 -1 -1 Zi,m= di . cm d0 = 1 1 1 1 1 -1 -1 -1 -1 1 1 1 1 -1 -1 -1 -1 1 1 1 1 -1 -1 -1 -1 slot 0 channel output slot 1 channel output channel output Zi,m sender code data bits slot 1 slot 0 d1 = -1 d0 = 1 1 1 1 1 -1 -1 -1 -1 1 1 1 1 -1 -1 -1 -1 1 1 1 1 -1 -1 -1 -1 1 1 1 1 -1 -1 -1 -1 slot 0 channel output slot 1 channel receiver output code received input Di = S Zi,m . cm m=1 M M
CDMA:two-sender interference senders data =1 d=1 Zim-dfcm bits code 而可 channel,Z data d=1 d6=1 bits code 见匝匝匝匝入 d- slot 1 slot 0 received received input input receiver 1 code匝匝可 币可 6:Wireless and Mobile Networks 6-14
6: Wireless and Mobile Networks 6-14 CDMA: two-sender interference
Chapter 6 outline 6.1 Introduction Mobility ▣6.5 Principles: Wireless addressing and routing ▣6.2 Wireless links, to mobile users characteristics ▣6.6 Mobile IP o CDMA 6.7 Handling mobility in ▣6.3IEEE802.11 cellular networks wireless LANs ("wi-fi") 6.8 Mobility and higher- 6.4 Cellular Internet layer protocols Access o architecture 6.9 Summary o standards(e.g.,GSM) 6:Wireless and Mobile Networks 6-15
6: Wireless and Mobile Networks 6-15 Chapter 6 outline 6.1 Introduction Wireless 6.2 Wireless links, characteristics CDMA 6.3 IEEE 802.11 wireless LANs (“wi-fi”) 6.4 Cellular Internet Access architecture standards (e.g., GSM) Mobility 6.5 Principles: addressing and routing to mobile users 6.6 Mobile IP 6.7 Handling mobility in cellular networks 6.8 Mobility and higherlayer protocols 6.9 Summary