Wireless network characteristics Multiple wireless senders and receivers create additional problems(beyond multiple access): C C A's signal S sig streng th strength Hidden terminal problem space dB. A hear each other Signal fading 口B. C hear each other 口B. a hear each other d Ac can not hear each other gB. C hear each other means a, C unaware of their g AC 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) D used in several wireless broadcast channels (cellular, satellite, etc)standards O unique " code"assigned to each user i. e. code set partitioning o all users share same frequency, but each user has own" chipping"sequence(i.e, code) to encode data D encoded signal=(original data)X(chipping sequence o decoding: inner-product of encoded signal and chipping sequence O 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 Zim= d:c m data do 1 bits d1=-1 sender 回F slot 1 slot o code channel channel slot 1 slot o output output ∑ M received 1111 input FilL d1=-1 slot 1 code channel channel receiver output output slot 1 slot o 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 bits L dE-1 code D10A-FI channelZ m ) data bits c吧吧呼F d2=22 slot 1I slot O received[ received nput input receiver code Li 01111 甘甘 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 口65 Principles: Wireless addressing and routing 06.2 Wireless links to mobile users characteristics 066 Mobile ip O CDMA 06.7 Handling mobility in 6.3IEEE802.11 cellular networks wireless LANs(wi-fi")D6.8 Mobility and higher 06.4 Cellular Internet yer proToco ls 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