Mobile and Wireless Networks. Wireless Transmission

Transcription

1 Mobile and Wireless Networks Wireless Transmission

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8 Problems of IP in wireless and mobile networks 1. Low performance in wireless environments No error avoidance, detection or correction 2. Best Effort (no QoS guarantees) No prioritization of traffic 3. No mobility support Routing based on the (static) IP address

9 1. Low performance in wireless environments No error correction in IP Based on anything provided by TCP/UDP or application TCP Designed for non-real-time applications Corrects errors through retransmissions TCP translates loss of packets as congestion to the route UDP Designed for real-time applications No error correction

10 TCP operation Source Destination Source Destination Packet 1 Packet 2 Packet 3 Packet 4 Packet 5 Packet 6 Packet 7 Packet 8 Packet 9 Packet 10 Ack 1 Ack 2 Ack 3 Ack 4 Ack 5 Ack 6 Packet 1 Packet 2 Packet 3 Packet 4 Packet 5 Packet 6 Packet 3 x Ack 1 Ack 2 Ack 4 Ack 5 Ack 6 Ack 4 Packet 7 Packet 8

11 cwnd

12 Loss of packet due to congestion Reduction of cwnd Reduction of data traffic cwnd

13 cwnd

14 cwnd

15 Loss of packet due to the wireless channel TCP translates this as congestion The cwnd is reduced (wrong decision) Lower traffic = lower network utilization cwnd

16 2. «Best Effort» All types of information are formed as IP packets and sent to the network IP does not have mechanism to guarantee quality characteristcs for each traffic flow (delay, packet loss, etc.) Only UDP or TCP traffic is not enough The need for QoS guarantees is much bigger due to the low capacity and high error rate Conclusion: Traditional protocols like Ethernet is insufficient.

17 3. IP does not support mobility Packet routing in based an a static scheme of ΙP addresses A static address depends on the static connection point of the terminal to the network If the connection point changes without change of address the packets are routed to the old connection point But of the address changes how this can be communicated to the rest of the world? Impossible to inform the network each time a terminal changes its connection point

18 IP Header ver. TOS total length IP ID offset TTL protocol checksum 32 bit Source IP address 32 bit Destination IP address Options IP Source Port Destination Port TCP/UDP

19 router *.200 router *

20 IP routing in1 out1 in2 out2 in3 Routing table out x x default out1 out2 out3

21 Wireless and/or Mobile Wireless Mobile Application NO NO Static work stations NO YES Laptop in hotel YES NO Buildings with no cables YES YES Full mobility support

22 Indoor Outdoor Wireless Standards Mobility WAN WLAN Vehicle Walk UMTS LTE-A High performance WLAN Fixed Walk Fixed/ Desktop Bluetooth b a/g Wired LAN 0, Mbps (PHY layer)

23 Basic concepts Global Mobility Zone 4: Global Ζone 3: Suburban Ζone 2: Urban Ζone 1: Buildings MacroCell MicroCell PicoCell

24 Standards organizations and other related bodies have agreed to co-operate for the production of a complete set of globally applicable Technical Specifications for a 3rd Generation Mobile System based on the evolved GSM core networks and the radio access technologies supported by 3GPP partners (i.e., UTRA both FDD and TDD modes). The Project is entitled the Third Generation Partnership Project and may be known by the acronym 3GPP. 3GPP has been established for the preparation and maintenance of the above mentioned Technical Specifications, and is not a legal entity.

25 3GPP comprises of: Partners: Organizational Partners 3GPP is open to all standards organizations irrespective of the geographical location. Market Representation Partners Individual Members

26 3GPP is characterized by the following attributes: Minimum production time for Technical Specifications from conception to approval Fast, electronic based approval process Maximum use of modern (electronic) working methods Minimum number of hierarchical levels with decision making taking place at the lowest appropriate levels

27 Internal structure of 3GPP 3GPP Project Co-ordination Group TSG TSG TSG TSG Radio Access Network Core Network Terminals Service and System Aspects Technical Specifications

28 3GPP meetings

29 ARIB The Association of Radio Industries and Businesses, Japan ATIS The Alliance for Telecommunications Industry Solutions, USA CCSA China Communications Standards Association ETSI The European Telecommunications Standards Institute TTA Telecommunications Technology Association, Korea TTC Telecommunication Technology Committee, Japan

30 Cellular Network Generations It is useful to think of cellular Network/telephony in terms of generations: 0G: Briefcase-size mobile radio telephones 1G: Analog cellular telephony (end 70s) 2G: Digital cellular telephony (beg 90 s) 3G: High-speed digital cellular telephony (including video telephony) (beg 00) 4G: IP-based anytime, anywhere voice, data, and multimedia telephony at faster data rates than 3G (beg 10) 5G: 10-times faster data rates, much more flexible in mobility, Internet of Things (IoT) support (cheap, low energy, massive number of devices) (beg 20)

31 Evolution of Radio Access Technologies LTE (3.9G) : 3GPP release 8~9 LTE-Advanced : 3GPP release 10+

32 Evolution of Cellular Standards 1G 2G 2.5G 3G 4G

33 Εξέλιξη των ψηφιακών συστημάτων κινητών επικοινωνιών Εξέλιξη από 2G σε 4G

34 Global Convergence LTE is the major technology for mobile broadband communications Convergence of 3GPP and 3GPP2 technology tracks Convergence of FDD and TDD into a single technology track D-AMPS PDC 3GPP GSM WCDMA HSPA TD-SCDMA HSPA/TDD LTE FDD and TDD IS-95 cdma2000 EV-DO 3GPP2 WiMAX? IEEE

35 Evolution of terminals and services 2G 3G 4G «Closed», vertical services Telephony Complementary services Fax WAP «Open» horizontal services IP based Added value Java Standard Edition Java Micro Edition ios, Android, full IP TDMA FDD Direct Sequence Frequency Hopping WCDMA TD-CDMA OFDM OFDM TDD

36 Business model evolution 2G 3G 4G GSM Operator Service provider Transport provider Access provider Service provider Content provider UMTS Operator Transport provider Access provider Content Aggregatorr Service provider Access provider Application provider Content provider Transport provider Content Aggregatorr Access provider Subscriber Subscriber Mediator Subscriber User User User

37 A cellular network Cell 1 Cell 2 Mobile Telephone Switching Center (MTSC) Public Switched Telephone Network (PSTN) HLR VLR Mobile User Base Transceiver Station (BTS) Cordless connectionhlr = Home Location Register Wired connection VLR = Visitor Location Register

38 Wireless Transmission Based on the capability of electrons to move creating electromagnetic waves To all directions With the speed of light Even in space Main characteristics of wireless transmission Frequency f = number of oscillations per second (Hertz) Wave length λ = distance between two minimums or two maximums λ*f = c (c=speed of light) The signals behavior depends on its frequency Low frequency = the signal can go through obstacles, its power density is reduced slowly with distance but the information transferred is small High frequency = The information transferred is larger, but the signal cannot go through obstacles so easily and the power density if reduced quickly with distance (path loss).

39 Electromagnetic spectrum f (Hz) f (Hz) Radio Microwave TV Infrared UV X-ray Twisted pair Maritime AM radio Coax FM radio Satellite Visible light Terrestrial microwave Gamma Ray Fiber optics Band LF MF HF VHF UHF SHF EHF THF

40 ISM Band (Industrial Scientific Medical) Can be used without a license Main application in WLANs

41 Problems of radio waves transmission Noise from external electromagnetic sources Attenuation of power density (path loss) multipath fading Interference from systems operating in the same or neighboring frequencies

42 Signal transmission techniques Δf 0 f 0 f Narrow Band: Δf << f 0 most transmission techniques Spread Spectrum Frequency Hopping (FH) Direct Sequence (DS)

43 Narrowband Transmission Each terminal transmits and received in a specific frequency. Uses as less frequency space as possible Interference is avoided through careful assignment of frequences Low cost Low reliability and security

44 Spread Spectrum More expensive system using wider range of frequencies More reliable and secure If the received does not the algorithm of transmission, receives the signal as noise Two main categories: Frequency-Hopping Spread Spectrum (FHSS) Direct-Sequence Spread Spectrum (DSSS)

45 Frequency Slots Time Frequency Hopping Spread Spectrum (FHSS) Requires Large range of frequencies An algorithm of hopping known in sender and receiver Full synchronization of sender and receiver

46 10-chip code word per "1" data bit Inverted 10-chip code word per "0" data bit DSSS

47 Signal Modulation Baseband: Transmission of unmodulated signal Need a wide range of relatively low frequencies Μεγάλη εξασθένιση και περιορισμένη μετάδοση Καλό μόνο για μικρές αποστάσεις και χαμηλές ταχύτητες Modulation: controllable change of one or more factor of a used signal (carrier signal) based on the information it needs to be transmitted Amplitude Frequency Phase Modem: Device for modulation/demodulation

48 Signal Modulation s(t) = A(t) cos(f(t) t + (t)) (a) unmodulated (digital) signal (b) amplitude modulation (AM) s(t) = A(t) cos(f t + ) (c) frequency modulation (FM) s(t) = A cos(f(t) t + ) FSK (frequency shift keying) (d) phase modulation (PM) s(t) = A cos(f t + (t)) phase shift keying (PSK) f : carrier frequency Phase shift 180 o Phase shift 90 o

49 Sample Sample Rate=Samples/sec (Baud Rate) During one Sample one symbol is sent Symbol=piece of information=level of voltage Simpler : 1 symbol = 1 bit (0/1) = voltage/no voltage To increase the data rate we cannot reduce The sample duration indefinitely But we can increase the number of possible Samples (e.g. amplitude levels) This is usually combined with PSK

50 BPSK (Binary Phase Shift Keying) = 2 phase shifts, 1 amplitude level, 1 bit/symbol QPSK (Quadrature Phase Shift Keying) = 4 phase shifts, 1 amplitude level, 2 bits/symbol QAM-16 = 4 phase shifts, 4 amplitude levels, 4 bits/symbol QAM-64 = 4 phase shifts, 16 amplitude levels, 6 bits/symbol QPSK QAM-16 QAM-64

51 Signal Modulation BPSK vs QPSK