ECE6604 PERSONAL & MOBILE COMMUNICATIONS

Transcription

1 ECE6604 PERSONAL & MOBILE COMMUNICATIONS GORDON L. STÜBER School of Electrical and Computer Engineering Georgia Institute of Technology Atlanta, Georgia, Ph: (404) Fax: (404) URL: 1

2 COURSE OBJECTIVES To study the fundamental principles of physical wireless communication systems. Focus is on the Physical Layer or PHY Layer Concentrate on the digital baseband signal processing as opposed to RF devices. The course stresses the underlying principles of mobile communications that are applicable to a wide variety of wireless systems and standards for cellular and wireless local applications. Mathematical modeling and statistical characterization of wireless channels, signals, noise and interference. Geometrically based stochastic models are often used for wireless channel simulation. Design of digital waveforms and associated receiver structures for recovering channel corrupted message waveforms. Single, multi-carrier and spread spectrum physical layer performance analysis on wireless channels. Methods for mitigating wireless channel impairments and cochannel interference. 2

3 3G Cellular cdma2000 EV-DO Rev. A Stack Default Signaling Application Signaling Network Signaling Link Default Packet Application Radio Link Flow Control Location Update Application Layer Stream Stream Layer Session Management Address Management Session Configuration Session Layer Air Link Management Packet Consolidation Initialization State Route Update Idle State Connected State Overhead Messages Connection Layer Security Key Exchange Authentication Encryption Security Layer Control Channel MAC Forward Traffic Channel MAC Access Channel MAC Reverse Traffic Channel MAC MAC Layer Physical Layer Physical Layer 1 3

4 Quad-band EGPRS (GSM) Chipset A p p l i c a t i o n E x a m p l e Q u a d - B a n d E G P R S S o l u t i o n P r o d u c t B r i e f I 2 C Interface Power Bus Peripherals Power Bus Baseband AC-Adaptor I 2 C V USB Host V Memory V BB I/O Hi V BB USB Charger SM-POWER (PMB 6811) V DD Pre-Charge Amp Motor Driver LED Driver NiMH/LiIon Battery M V BB Analog V RTC Control V BT BB Power Bus Bluetooth FLASH/SDRAM V BB1 V RF3 (BT) S-GOLD2 (PMB 8876) I 2 S I 2 S / DAI SSC GPTU IR-Memory V BB2 BB (LR)/Mem/Copro Step down 600 ma On-chip Reference V RF Main V RF VCXO Power Bus RF Headset Ringer Earpiece Car Kit * 0 # MUX D D A A A D USB FS OTG Keypad GPIOs Speech and Channel Decoding Speech and Channel Encoding DMAC TEAKLite SRAM Equalizer 8 PSK/GMSK Modulator ICU GSM Cipher Unit D A D A A D A D GEA-1/2/3 CAPCOM GPTU RF Control AFC AUX ADC I 2 C CGU GSM Timer SCCU I Q CLK DAT ENA AFC 26 MHz SMARTi DC+ (PMB 6258) GSM 900/1800 Atomatic Offset Compensation Control Logic SAM Fast PLL GSM 850/ Rx/Tx USIM Fast IrDA ARM 926 EJ-S MOVE Copro RTC JTAG Multimedia IC IF EBU RF Control Multi Mode PA MMC/SD IF USIF SSC USARTs Camera IF Display IF FCDP MMC SDC 4

5 TOPICAL OUTLINE 1. INTRODUCTION TO CELLULAR RADIO SYSTEMS 2. MULTIPATH-FADING CHANNEL MODELLING AND SIMULATION 3. SHADOWING AND PATH LOSS 4. CO-CHANNEL INTERFERENCE AND OUTAGE 5. SINGLE- AND MULTI-CARRIER MODULATION TECHNIQUES AND THEIR POWER SPECTRUM 6. DIGITAL SIGNALING ON FLAT FADING CHANNELS 7. MULTI-ANTENNA TECHNIQUES 8. ADVANCED TOPICS MULTI-CARRIER TECHNIQUES SPREAD SPECTRUM TECHNIQUES 5

6 ECE6604 PERSONAL & MOBILE COMMUNICATIONS Week 1 Introduction, Path Loss, Co-channel Interference 6

7 1G Cellular Technologies 1979 Nippon Telephone and Telegraph (NTT) introduces the first cellular system in Japan Nordic Mobile Telephone (NMT) 900 system introduced by Ericsson Radio Systems AB and deployed in Scandinavia Advanced Mobile Telephone Service (AMPS) introduced by AT&T in North America. Feature NTT NMT AMPS Frequency Band / RL/FL a / (MHz) / Carrier Spacing 25/ b 30 (khz) Number of 600/ Channels Modulation analog FM analog FM analog FM a RL = reverse link, FL = forward link b frequency interleaving using overlapping channels, where the channel spacing is half the nominal channel bandwidth. 7

8 2G Cellular Technologies 1990 Interim Standard IS-54 (USDC) adopted by TIA Japanese Ministry of Posts and Telecommunications standardized Personal Digital Cellular (PDC) 1992 Phase I GSM system is operational (September 1) Interim Standard IS-95A (CDMA) adopted by TIA Interim Standard IS-136 adopted by TIA IS-95B standard is approved GSM is available in 219 countries, 6.5 billion subscribers. Roaming everywhere except Korea and Japan. IS-95A/B is deployed in 121 countries, IS-54/136 is extinct, PDC only ever existed in Japan is likely extinct. 8

9 2G Cellular Technologies Feature GSM/DCS1800/PCS1900 IS-54/136 Frequency Band GSM: / / RL/FL a /894 (MHz) DCS1800: / / PCS1900: / Multiple Access F/TDMA F/TDMA Carrier Spacing (khz) Modulation GMSK π/4-dqpsk Baud Rate (kb/s) Frame Size (ms) Slots/Frame 8/16 3/6 Voice Coding (kb/s) VSELP(HR 6.5) VSELP (FR 7.95) RPE-LTP (FR 13) ACELP (EFR 7.4) ACELP (EFR 12.2) ACELP (12.2) Channel Coding Rate-1/2 CC rate-1/2 CC Frequency Hopping yes no Handoff hard hard 9

10 2G Cellular Technologies Feature PDC IS-95 Frequency Band / / RL/FL a (MHz) / / Multiple Access F/TDMA F/CDMA Carrier Spacing (khz) Modulation π/4-dqpsk QPSK Baud Rate (kb/s) Mchips/s Frame Size (ms) Slots/Frame 3/6 1 Voice Coding (kb/s) PSI-CELP (HR 3.45) QCELP (8,4,2,1) VSELP (FR 6.7) RCELP (EVRC) Channel Coding rate-1/2 BCH FL: rate-1/2 CC RL: rate-1/3 CC Frequency Hopping no N/A Handoff hard soft 10

11 3G Cellular Technologies 1998 A group called 3GPP (Third Generation Partnership Project) is created to] produce a common 3G standard based on WCDMA The group 3GPP2 is created to harmonize the use of multicarrier cdma South-Korean Telecom (SKT) launches cdma2000-1x network (DL/UL: 153 kbps) 2001 NTT DoCoMo deploys commercial UMTS network in Japan 2002 cdma2000 1xEV-DO (UL: 153 kbps, DL: 2.4 Mb/s) 2003 WCDMA (UL/DL: 384 kbps) 2006 HSPA (UL: 384 kbps, DL: 7.2 Mbps) 2007 cdma2000 1xEV-DO Rev A (UL: 1.8 Mbps, DL: 3.1 Mbps) 2010 HSPA (UL: 5.8 Mbps, DL: 14.0 Mbps), cdma2000 1xEV- DO Rev A (UL: 1.8 Mbps, DL: 3.1 Mbps) HSPA networks in 203 countries, 365 commercial HSPA+ networks in 157 countries (most UL: 22 Mbps, DL: 168 Mbps) 175 commercial 1xEV-DO Rev A networks 11

12 3G Cellular Technologies Feature W-CDMA cdma2000 Multiple Access DS-CDMA DS-CDMA Chip Rate (Mcps) Carrier Spacing (MHz) Frame Length (ms) 10 5/20 Modulation FL: QPSK FL: BPSK/QPSK RL: BPSK RL: BPSK 64-ary orthogonal Coding rate-1/2, 1/3 rate-1/2, 1/3, 1/4, K = 9 conv. code 1/6 K = 9 conv. code rate-1/3 rate-1/2, 1/3, 1/4, K = 4 turbo code 1/5, K = 4 turbo code Interleaving inter/intraframe intraframe Spreading FL: BPSK complex RL: QPSK Inter BS asynchronous synchronous synchronization 12

13 4G Cellular Technologies LTE and WiMAX are sometimes branded as 4G cellular technologies. LTE: Currently seeing rapid deployment There are 318 LTE networks in 111 countries. 170 million subscribers worldwide. LTE-A: seeing initial deployment. There are 17 LTE-A networks in 12 countries. WiMAX: Currently seeing less rapid deployment: There are 580 commercial WiMax networks in 149 countries million subscribers worldwide. 13

14 Cellular subscriber growth rates. 14

15 WIRELESS LANs (WiFi) IEEE Direct Sequence Spread Spectrum (1-and-2 Mb/s, 2.4GHz) IEEE b Complimentary Code Keying (CCK) (5.5-and-11 Mb/s, 2.4GHz) IEEE g/a Orthogonal Frequency Division Multiplexing (OFDM) (6-to-54 Mb/s, 2.4/5GHz) IEEE e MAC enhancements for Quality of Service (QoS) IEEE i Security IEEE n MIMO physical layer Femtocells: integrate WiFi with cellular. Benefits: Frees up cellular capacity and reduces BS power consumption. Drawbacks: MS power drain due to femtocell searching. Fast femtocell-to-cellular handoff is needed to prevent dropped calls. 15

16 WIRELESS PANs IEEE Std Mb/s WPAN/Bluetooth v1.x derivative work - uses frequency hop spread spectrum. Today Bluetooth is managed by the Bluetooth Special Interest Group. P Recommended Practice for Coexistence in Unlicensed Bands P Mb/s High Rate WPAN for Multimedia and Digital Imaging P a Mb/s Higher Rate Alternative PHY for Ultra wideband (UWB) P kb/s max for interactive toys, sensor and automation needs Applications include (mobile) ad hoc networks, sensor networks 16

17 FREQUENCY RE-USE AND THE CELLULAR CONCEPT A C B A C B D D E C A F B G 3-Cell 4-Cell 7-Cell Commonly used hexagonal cellular reuse clusters. Tessellating hexagonal cluster sizes, N, satisfy N = i 2 +ij +j 2 where i, j are non-negative integers and i j. hence N = 1, 3, 4, 7, 9, 12,... are allowable. 17

18 B G F G D B C G A F B G D E C A E C A F B A F G D D E C A F G B Cellular layout using 7-cell reuse clusters. Real cells are not hexagonal, but irregular and overlapping. Frequency reuse introduces co-channel interference and adjacent channel interference. 18

19 CO-CHANNEL REUSE FACTOR A A R D Frequency reuse distance for 7-cell reuse clusters. For hexagonal cells, the co-channel reuse factor is D R = 3N 19

20 RADIO PROPAGATION MECHANISMS Radio propagation is by three mechanisms: Reflections off of objects larger than a wavelength, sometimes called scatterers. Diffractions around the edges of objects Scattering by objects smaller than a wavelength A mobile radio environment is characterized by three nearly independent propagation factors: Path loss attenuation with distance. Shadowing caused by large obstructions such as buildings, hills and valleys. Multipath-fading caused by the combination of multipath propagation and transmitter, receiver and/or scatterer movement. 20

21 FREE SPACE PATH LOSS (FSPL) Equation for free-space path loss is ( ) 2 4πd L FS =. and encapsulates two effects. 1. The first effect is that spreading out of electromagnetic energy in free space is determined by the inverse square law, i.e., where Ω t is the total transmit power λ c µ Ωr (d) = Ω t 1 4πd 2, µ Ωr (d) is the received power per unit area or power spatial density (in watts per meter-squared) at distance d. Note that this term is not frequency dependent. 21

22 FREE SPACE PATH LOSS (FSPL) Second effect 2. The second effect is due to aperture, which determines how well an antenna picks up power from an incoming electromagnetic wave. For an isotropic antenna, we have µ Ωp (d) = µ Ωr (d) λ2 c 4π = Ω t ( λc 4πd ) 2, where µ Ωp (d) is the received power. Note that aperature is entirely dependent on wavelength, λ c, which is how the frequencydependent behavior arises in the free space path loss. For free space, the propagation path loss is { } { (4πd ) } 2 Ωt L FS (db) = 10log 10 = 10log 10 µ Ωp (d) λ c { (4πd ) } 2 = 10log 10 c/f c = 20log 10 f c +20log 10 d db. 22

23 PROPAGATION OVER A FLAT SPECULAR SURFACE BS h b d 1 d 2 d MS h m 1

24 The length of the direct path is d 1 = d 2 +(h b h m ) 2 and the length of the reflected path is d 2 = d 2 +(h b +h m ) 2 d = distance between mobile and base stations h b = base station antenna height h m = mobile station antenna height Given that d h b h m, we have d 1 d and d 2 d. However, since the wavelength is small, the direct and reflected paths may add constructively or destructively over small distances. The carrier phase difference between the direct and reflected paths is φ 2 φ 1 = 2π λ c (d 2 d 1 ) 2

25 Taking into account the phase difference, the received signal power is ( ) λc 2 1+ae µ Ωp (d) = Ω jb t e j(φ 2 φ 1 ) 2, 4πd where a and b are the amplitude attenuation and phase change introduced by the flat reflecting surface. If we assume a perfect specular reflection, then a = 1 and b = π for small θ. Then ( ) λc 2 µ Ωp (d) = Ω t 1 e j(2π d) λc 2 4πd ( ) 2 ( ) ( ) λc 2π 2π 2 = Ω t 1 cos d jsin d 4πd λ c λ c ( ) 2 [ ( )] λc 2π = Ω t 2 2cos d 4πd λ c ( ) 2 ( ) λc π = 4Ω t sin 2 d ) 4πd λ c where d = (d 2 d 1 ). 3

26 Given that d h b and d h m, and applying the approximation 1+x 1+x/2 for small x, we have d d (1+ (h ) b +h m ) 2 d (1+ (h ) b h m ) 2 2d 2 2d 2 Finally, the received envelope power is ( ) 2 ( ) λc µ Ωp (d) 4Ω t sin 2 2πhb h m 4πd λ c d = 2h bh m d. Under the condition that d h b h m, the above reduces to µ Ωp (d) Ω t ( hb h m d 2 where we have invoked the small angle approximation sinx x for small x. Propagation over a flat specular surface differs from free space propagation in two respects it is not frequency dependent signal strength decays with the with the fourth power of the distance, rather than the square of the distance. ) 2 4

27 1000 Path Loss (db) Path Length, d (m) Propagation path loss L p (db) with distance over a flat reflecting surface; h b = 7.5 m, h m = 1.5 m, f c = 1800 MHz. L FE (db) = [ ( ) 2 ( ) ] 1 λc 4sin 2 2πhb h m 4πd λ c d 5

28 In reality, the earth s surface is curved and rough, and the signal strength typically decays with the inverse β power of the distance, and the received power at distance d is µ Ωp (d) = µ Ω p (d o ) (d/d o ) β where µ Ωp (d o ) is the received power at a reference distance d o. Expressed in units of dbm, the received power is µ Ωp (dbm) (d) = µ Ωp (dbm) (d o ) 10βlog 10 (d/d o ) (dbm) β is called the path loss exponent. Typical values of µ Ωp (dbm) (d o ) and β have been determined by empirical measurements for a variety of areas Terrain µ Ωp (dbm) (d o = 1.6 km) β Free Space Open Area North American Suburban North American Urban (Philadelphia) North American Urban (Newark) Japanese Urban (Tokyo)

29 Co-channel Interference Worst case co-channel interference on the forward channel. 7

30 Worst Case Co-Channel Interference For N = 7, there are six first-tier co-channel BSs, located at distances { 13R,4R, 19R,5R, 28R, 31R} from the MS. Assuming that the BS antennas are all the same height and all BSs transmit with the same power, the worst case carrier-to-interference ratio, Λ, is Λ = = R β ( 13R) β +(4R) β +( 19R) β +(5R) β +( 28R) β +( 31R) β 1 ( 13) β +(4) β +( 19) β +(5) β +( 28) β +( 31). β With a path loss exponent β = 3.5, the worst case Λ is db for N = 7 Λ (db) = 9.98 db for N = db for N = 3 Shadows will introduce variations in the worst case Λ. 8

31 Cell Sectoring Worst case co-channel interference on the forward channel with 120 o cell sectoring. 9

32 120 o cell sectoring reduces the number of co-channel base stations from six to two. For N = 7, the two first tier interferers are located at distances 19R, 28R from the MS. The carrier-to-interference ratio becomes Λ = = R β ( 19R) β +( 28R) β 1 ( 19) β +( 28). β Hence Λ (db) = db for N = db for N = db for N = 3. For N = 7, 120 o cell sectoring yields a 6.04 db C/I improvement over omni-cells. The minimum allowable cluster size is determined by the threshold Λ, Λ th, of the radio receiver. For example, if the radio receiver has Λ th = 15.0 db, then a 4/12 reuse cluster can be used (4/12 means 4 cells or 12 sectors per cluster). 10