Mobile Communications: Technology and QoS

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Mobile Communications: Technology and QoS Course Overview! Marc Kuhn, Yahia Hassan kuhn@nari.ee.ethz.

1 Mobile Communications: Technology and QoS Course Overview! Marc Kuhn, Yahia Hassan / Institut für Kommunikationstechnik (IKT) Wireless Communications Group ETH Zürich 1

MCTQ: Overview of the Course (a few selected slides per chapter)! Dr.- Ing. Marc Kuhn! kuhn@nari.

2 MCTQ: Overview of the Course (a few selected slides per chapter)! Dr.- Ing. Marc Kuhn! Institut für Kommunikationstechnik (IKT),! Wireless Communications Group! ETH Zürich!! 2

3 Contents Introduction! Wireless Channel! Mobile Communication! Wireless Networks! Quality of Service QoS! Future Technologies 3

4 Contents Introduction! Wireless Channel! Mobile Communication! Wireless Networks! Quality of Service QoS! Future Technologies 4

5 Wireless Channel Propagation Channel! Maxwell equations, system functions of wireless channels! Multipath Propagation! Path loss! Doppler Effect! Channel Characterization, Channel Models! Fading, delay spread, Doppler spread, coherence time and bandwidth, channel models! Antennas 5

6 Wireless Channel: Observations Channel strength (attenuation) and thus SNR at Rx varies! depending on the location (space-selective fading)! over time (time-selective fading)! over frequency (frequency-selective fading)! Bandwidth limited! Shared medium! interference 6

7 Basic Propagation Mechanisms Reflection! Propagating electromagnetic wave impinges on object with very large dimension compared to wavelength! Reflection e.g. from buildings and walls (or from surface of earth)! Diffraction! Radio path between Tx and Rx obstructed by a surface that has sharp irregularities! Scattering! Between Tx and Rx: objects with dimensions small compared to the wavelength 7

8 Multipath Propagation: Location- Dependent Fading Position A r2 r3 rtx [db] at a given frequency f1 Position B r1 r2 r1 rtx 8 location x rtx r4

9 Wireless Channel Large-scale fading! Relevant to cell-site planning Received power decreases with distance r! e.g. free space: 1/r²!! can even be faster due to shadowing and scattering effects! Small-scale fading! Relevant to design of communication systems Variation of signal strength over distances of the order of the carrier wavelength, due to constructive and destructive interference of multi-paths! Doppler spread, coherence time (e.g. due to velocity of mobile)! Delay spread, coherence bandwidth (lengths of shortest and longest path) 9

10 Narrowband System Narrowband system H c (f ) H s (f ) H(f ) X = 1/ t max f f f h c (t ) h s (t ) h(t ) = t max t t t [Molisch, Wireless Communications ] 10

11 Wideband (or Broadband) System Wideband system H c (f ) H s (f ) H(f ) X = 1/ t max f f f h c (t ) h s (t ) h(t ) = t max t t t [Molisch, Wireless Communications ] 11

12 Quasi-Static CIR Quasi-static, h(t, τ) varies only slowly over time:! Variable t parameterizes the impulse response: which (out of a large ensemble) impulse response h(τ) is currently valid From [ Wireless Communications: Principles & Practice T. Rappaport] 12

13 Multipath Propagation, Narrowband Fading Multipath propagation:! constructive and destructive interference! random fluctuations of receive power (small-scale) Fading! strong influence on quality of the transmission mean 13

14 Contents Introduction! Wireless Channel! Mobile Communication! Wireless Networks! Quality of Service QoS! Future Technologies 14

15 Mobile Communication PHY Layer! OFDM! MIMO! Receiver structures! MAC Layer! MAC: IEEE ,.11e 15

16 OFDM Continuous-time vs. discrete-time model! Transmitter Channel Receiver Data source S/P conversion c 0, i c 1, i e j0 e j2π(w/n)t s(t) Hs(t) H e j0 e j2π(w/n)t c 0, i c 1, i P/S conversion Data sink c N 1, i c N 1, i e j2π(n 1) (W/N)t e j2π(n 1) (W/N)t c 0, i c 0, i Data source S/P conversion c 1, i s(t) Hs(t) IFFT P/S H S/P FFT c 1, i P/S conversion Data sink c N 1, i c N 1, i [A. Molisch, Wireless Communications] 16

17 OFDMA Distributed OFDMA mode User OFDM sub-carriers Localized OFDMA mode 17

18 Diversity Techniques Tx Diversity: Alamouti Code (ST-Code) h 1,1! Vectors: elements in spatial domain s 1 s 2 h 1,2 r 1 s 1 = s 1 * s 2 s 2 = s 2 * s 1 Assume channel const. for 2 time slots: r 1 (1) = h 1,1 s 1 h 1,2 s 2 * + w 1 (1) r 1 (2) = h 1,2 s * 1 + h 1,1 s 2 + w 1 (2) r * 1 (2) = h * 1,2 s 1 + h * 1,1 s * 2 + w * 1 (2)! Matrix S: 2 vectors in 2 time-slots S = s 1 s 2 = s 1 s 2 * s 2 s 1 * d(1) = h * 1,1 r 1 (1) + h 1,2 r * (2) = h s1 1,1 + h s1 1,2 + n 1 d(2) = h * 1,2 r 1 (1) + h 1,1 r * 2 1 (2) = h * 2 s2 1,1 + h * s2 1,2 + m 1! Orthogonalize decision variables! Two-fold diversity!! One symbol per time slot (more efficient!) Diversity, MIMO Marc Kuhn 22 18

19 MIMO Multiple Input Multiple Output MIMO TX RX Telatar, Foschini: C = E log 2 det I MR + E S HH H M T N 0 M T : number of TX antennas, M R : number of RX antennas. Diversity, MIMO Marc Kuhn 33 19

20 Capacity of MIMO Channels: Perfect CSIT! With perfect CSIT: - Tx combining to orthogonalize MIMO channel (multiply with unitary matrix V) Tx signal: s = Vs - Tx power per Eigenvalue has to be optimized (Water-filling algorithm) => choose optimal γ i (energy allocated to sub-channel i) to maximize capacity γ i = E s i 2 where H = USV H N ( ), for i = 1, 2,..., N γ i i=1 w i! = M T s i!! y i! C pcsit = max N γ i 1 = M T λ i +! N i=1 log 2 1+ E S λ M T N i { HH H } γ i 0 y i = E S M T λ i s i + n i Diversity, MIMO Marc Kuhn 41 20

21 Multi-User MIMO Uplink: Multiple Access Channel (MIMO-MAC)!!!! Downlink: Broadcast Channel (MIMO-BC) 21

22 WLAN IEEE MAC Sublayer: DCF transmit, if medium is free >= DIFS DIFS Medium busy Defer access DIFS PIFS SIFS Contention Window Backoff-Window Slot time Decrement Backoff Timer as long as medium idle Next Frame CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance):! Channel access:! If WM seems to be free for a time >= DIFS, STA transmits immediately! If WM busy, STA waits until the end of the ongoing transmission and starts Backoff Procedure! After this the status of the channel is checked again MCTQ: Wireless Networks, Wireless Networks, Marc Kuhn! ! 50 22

23 Contents Introduction! Wireless Channel! Mobile Communication! Wireless Networks! Quality of Service QoS! Future Technologies 23

24 Wireless Networks Current (and future) wireless networks:! How do they work?! For which services are they used?! Cellular Networks! GSM! UMTS! LTE, LTE-Advanced! WLAN IEEE n 24

25 Cellular Networks Mobile Communication! Omnipresent! 9.9 Mio. SIM cards in CH (2012)! 99.9 % of Swiss population covered! Exponential increase in data traffic! Different standards (GSM, UMTS, LTE,... ) (2G, 3G, 4G) Cellular Networks 11 25

26 Cellular Networks Cellular Wireless: max. Downlink Rates Peak data rate [Mbit/s] GSM CSD HSCSD GPRS EDGE UMTS HSDPA HSPA+ LTE LTE-Advanced! Techniques to achieve this almost exponential growth in peak rate! Closer look on LTE and LTE-Advanced Cellular Networks 12 26

2e+09 1e+09 8e+08 1000 6e+08 4e+08 y Position [m] 500 200 Mbit/s 2e+08 0 500

27 Cellular Networks Structure of Cellular Networks Mean Rate Rmean(SINR), DL, with BS interference 22e+09 Gbit/s 1.8e e e e+09 1e+09 8e e+08 4e+08 y Position [m] Mbit/s 2e Mbit/s 1e+07 x Position [m] Cellular Networks 16 27

28 Coordinated Multi Point - CoMP 28

29 Contents Introduction! Wireless Channel! Mobile Communication! Wireless Networks! Quality of Service QoS! Future Technologies 29

30 Quality of Service - QoS What does QoS mean?! How is QoS support implemented in wireless networks?! Which problems do occur?! Theoretical analysis of QoS at PHY and MAC of wireless systems! How can we measure QoS?! End-to-End QoS Measurements! Statistical evaluation of QoS measurements! Benchmarking (drive tests, methods) 30

31 PHY QoS KPIs 10 0 MIMO: Outage Probability for Outage Rate (2x2) MIMO P out (3x3) MIMO (2x3) MIMO (3x2) MIMO S / N [db] Cumulative Distribution Function SISO: CDF of channel capacity ; Rayleigh fading SNR = [0, 5, 10, 15, 20] db Capacity [bit/channel use] Outage Rate: 2 bit/ channel use! 31

32 MAC QoS KPIs Example: IEEE MAC 32

33 Quality of Service - QoS What does QoS mean?! How is QoS support implemented in wireless networks?! Which problems do occur?! Theoretical analysis of QoS at PHY and MAC of wireless systems! How can we measure QoS?! End-to-End QoS Measurements! Statistical evaluation of QoS measurements! Benchmarking (drive tests, methods) 33

34 E2E QoS Measurements Call Stability ( Comparison of the last 4 quarters) 8,0% 7,0% 6,0% 5,0% Call Drop Rate [%] 4,0% 3,0% 2,0% 1,0% 0,0% -1,0% Module 1 Module 2 Module 3 Module 4 A Q2/04 0,6% 2,1% 0,4% 0,7% A Q3/04 0,3% 1,9% 0,2% 0,5% A Q4/04 0,4% 2,0% 0,2% 0,6% A Q1/05 0,4% 1,6% 0,1% 0,8% B Q2/04 0,2% 1,3% 0,1% 0,2% B Q3/04 0,3% 1,1% 0,2% 0,5% B Q4/04 0,4% 1,2% 0,1% 0,4% B Q1/05 0,5% 0,9% 0,1% 0,4% C Q2/04 1,4% 5,9% 0,7% 0,5% C Q3/04 1,8% 3,9% 0,4% 0,5% C Q4/04 0,9% 3,1% 0,4% 0,4% C Q1/05 1,2% 3,2% 0,2% 0,2% D Q2/04 1,5% 4,0% 0,8% 0,5% D Q3/04 1,8% 2,8% 0,4% 0,2% D Q4/04 1,5% 4,0% 0,2% 0,5% D Q1/05 1,4% 2,5% 0,0% 0,4% 34

35 Call Stability ( all Modules) 4.5% Call Drop Rate [%] 4.0% 3.5% 3.0% 2.5% 2.0% 1.5% 1.0% 0.5% 0.0% -0.5% Module 1 Module 2 Module 3 Module 4 A 0.4% 1.6% 0.1% 0.8% B 0.5% 0.9% 0.1% 0.4% C 1.2% 3.2% 0.2% 0.2% D 1.4% 2.5% 0.0% 0.4% Won Pairwise comparisons: Coverage Quality () Won Pairwise comparisons: Call Setup Success Rate Module 1 Module 2 Module 3 Module 4 All Modules A B C D

36 Contents Introduction! Wireless Channel! Mobile Communication! Wireless Networks! Quality of Service QoS! Future Technologies 36

37 Future Technologies Base station or user cooperation! Relaying! Interference alignment!... 37

The Radio Channel. COS 463: Wireless Networks Lecture 14 Kyle Jamieson. [Parts adapted from I. Darwazeh, A. Goldsmith, T. Rappaport, P.

The Radio Channel. COS 463: Wireless Networks Lecture 14 Kyle Jamieson. [Parts adapted from I. Darwazeh, A. Goldsmith, T. Rappaport, P. The Radio Channel COS 463: Wireless Networks Lecture 14 Kyle Jamieson [Parts adapted from I. Darwazeh, A. Goldsmith, T. Rappaport, P. Steenkiste] Motivation The radio channel is what limits most radio