Wireless and Mobile Networks Background: # wireless (mobile) phone - PowerPoint PPT Presentation

Wireless and Mobile Networks Background:  # wireless (mobile) phone subscribers now exceeds # wired phone subscribers (5-to-1)!  # wireless Internet-connected devices equals # wireline Internet-connected devices  laptops, Internet-enabled phones promise anytime untethered Internet access  two important (but different) challenges  wireless: communication over wireless link  mobility: handling the mobile user who changes point of attachment to network 1

Outline 1 Introduction Mobility 5 Principles: addressing and Wireless routing to mobile users 2 Wireless links, 6 Mobile IP characteristics 7 Handling mobility in cellular  CDMA networks 3 IEEE 802.11 wireless LANs 8 Mobility and higher-layer ( “ Wi-Fi ” ) protocols 4 Cellular Internet Access  architecture 9 Summary  standards (e.g., GSM) 2

Elements of a wireless network network infrastructure 3

Elements of a wireless network wireless hosts  laptop, smartphone  run applications  may be stationary (non- mobile) or mobile network  wireless does not always infrastructure mean mobility 4

Elements of a wireless network base station  typically connected to wired network  relay - responsible for sending packets between wired network and network wireless host(s) in its infrastructure “ area ”  e.g., cell towers, 802.11 access points 5

Elements of a wireless network wireless link  typically used to connect mobile(s) to base station  also used as backbone link  multiple access protocol network coordinates link access infrastructure  various data rates, transmission distance 6

Characteristics of selected wireless links 200 802.11n 54 802.11a,g 802.11a,g point-to-point Data rate (Mbps) 5-11 802.11b 4G: LTWE WIMAX 4 3G: UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO 1 802.15 .384 2.5G: UMTS/WCDMA, CDMA2000 .056 2G: IS-95, CDMA, GSM Indoor Outdoor Mid-range Long-range 10-30m 50-200m outdoor outdoor 200m – 4 Km 5Km – 20 Km 7

Elements of a wireless network infrastructure mode  base station connects mobiles into wired network  handoff: mobile changes base station providing network connection into wired infrastructure network 8

Elements of a wireless network ad hoc mode  no base stations  nodes can only transmit to other nodes within link coverage  nodes organize themselves into a network: route among themselves 9

Wireless network taxonomy multiple hops single hop host may have to host connects to relay through several infrastructure base station (WiFi, wireless nodes to WiMAX, cellular) (e.g., APs) connect to larger which connects to Internet: mesh net larger Internet no base station, no connection to larger no no base station, no Internet. May have to connection to larger infrastructure relay to reach other Internet (Bluetooth, a given wireless node ad hoc nets) MANET, VANET 10

IoT architecture IEEE 802.16e IEEE 802.3, (WiMAX) IP-based network (ethernet) with wide-area IEEE 802.11 (WiFi) 3G, 4G …… coverage, wireless or wired and powerful servers IoT infrastructure: static ambient nodes AN attaching to clusters in lowest layer AN AN Moving clusters of MN nodes with sensing MN capability but often with MN limited resources MN MN MN = mobile node /network AN = ambient node / network e.g. single person moving around with sensors 10

Taxonomy Middle layer Multi hop Single hop (no hop) (ambient infrastructure) (access points) Bottom layer • Multi hop Most general case: Moving clusters connecting to access • moving clusters points through ambient • infrastructure ad-hoc networks • ad-hoc networks Single hop (no hop) Moving nodes Moving nodes connecting to ambient connecting to access infrastructure points 11

Examples Middle layer Multi hop Single hop (no hop) (ambient infrastructure) (access points) Bottom layer • • Multi hop vehicle to vehicle vehicle to infra structure • vehicle to infra structure • user wearing • user wearing cluster of sensors connected sensors connected to to phone phone • • Single hop (no hop) laptop / wifi phone • sensor in low power mesh network 12

Outline 1 Introduction Mobility 5 Principles: addressing and Wireless routing to mobile users 2 Wireless links, 6 Mobile IP characteristics 7 Handling mobility in cellular  CDMA networks 3 IEEE 802.11 wireless LANs 8 Mobility and higher-layer ( “ Wi-Fi ” ) protocols 4 Cellular Internet Access  architecture 9 Summary  standards (e.g., GSM) 14

Wireless Link Characteristics (1) important differences from wired link ….  decreased signal strength: radio signal attenuates as it propagates through matter (path loss)  interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as well  multipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times …. make communication across (even a point to point) wireless link much more “ difficult ” 15

Wireless Link Characteristics (2)  SNR: signal-to-noise ratio 10 -1  larger SNR – easier to 10 -2 extract signal from noise (a 10 -3 “ good thing ” ) BER 10 -4  SNR versus BER tradeoffs 10 -5  given physical layer: increase power -> increase SNR- 10 -6 >decrease bit error rate (BER)  given SNR: choose physical layer 10 -7 10 20 30 40 that meets BER requirement, SNR(dB) giving highest throughput QAM256 (8 Mbps) • SNR may change with QAM16 (4 Mbps) mobility: dynamically adapt physical layer (modulation BPSK (1 Mbps) technique, rate) 16

Wireless network characteristics Multiple wireless senders and receivers create additional problems (beyond multiple access): A B C C C ’ s signal A ’ s signal strength B strength A Hidden terminal problem space Signal attenuation:  B, A hear each other  B, A hear each other  B, C hear each other  B, C hear each other  A, C can not hear each other  A, C can not hear each other means A, C unaware of their interfering at B interference at B 17

Characteristics of Wireless Networks  Multiplexing : in a mobile and wireless network, the wireless medium is shared by many nodes.  Hence, multiple use of a shared medium is a major challenge in wireless networking.  Most decisions for accessing the wireless medium is made in the MAC layer.

Multiplexing  The wireless channels can be multiplexed in four dimensions:  Time(t): A channel gets the whole frequency spectrum for a certain amount of time.  Space(s): Same frequency can be reused when the base stations are separated in space.  Frequency(f): The whole spectrum is separated into smaller frequency bands.  Code(c): Each channel uses a unique code for transmitting.

Time Division Multiplex (TDM)  A channel gets the whole frequency spectrum for a certain amount of time. f  Only one user for the medium at a time.  Usually the throughput is high even with many users.  However, no two users should use the medium at the same time. Precise t synchronization is needed.

Space multiplexing : Cellular Networks  Same frequency can be reused when the base stations are separated in space.  The reuse of frequencies depend on signal propagation range.  Example : fixed frequency assignment for reuse with distance 2.

Frequency Division Multiplex (FDM)  The whole spectrum is separated into smaller frequency bands.  A band is allocated to a f channel for the whole time.  This is somewhat inflexible if the traffic is non-uniform.  An example is radio or TV broadcast. The bandwidth is wasted if a t station is off the air.

Code Division Multiplex (CDM)  Each channel uses a c unique code for transmitting.  All channels use the same frequency spectrum at the same time. t f  However, signal regeneration is very complex and requires complex HW/SW support.

Code Division Multiplexing  CDMA has ben adopted for the 3G mobile phone technology.  CDMA is not very suitable for ad hoc networking as we cannot expect specialized hardware/software support at the nodes.  TDMA and its variations are most suitable for ad hoc networking.

Code Division Multiple Access (CDMA)  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  allows multiple users to “ coexist ” and transmit simultaneously with minimal interference (if codes are “ orthogonal ” )  encoded signal = (original data) X (chipping sequence)  decoding: inner-product of encoded signal and chipping sequence 25

CDMA encode/decode channel output Z i,m Z i,m = d i . c m d 0 = 1 data 1 1 1 1 1 1 1 1 d 1 = -1 bits - - - 1 - - - - - 1 1 1 1 1 1 1 sender slot 0 slot 1 1 1 1 1 1 1 1 1 code channel channel - 1 - 1 - 1 - 1 - - 1 - 1 - 1 1 output output slot 1 slot 0 M D i = S Z i,m . c m m=1 M received 1 1 1 1 1 1 1 1 d 0 = 1 - - input - 1 - 1 1 - 1 - 1 - 1 - 1 1 d 1 = -1 slot 0 slot 1 1 1 1 1 1 1 1 1 code channel channel - 1 - 1 - 1 - 1 - - 1 - 1 - 1 1 output output receiver slot 1 slot 0 26