Link Adaptation in Mobile Communication Networks

Transcription

1 Link Adaptation in Mobile Communication Networks Assoc. prof. Vladimír Wieser, PhD. Department of Telecommunication and Multimedia University of Zilina Department of Telecommunications and Multimedia 1

2 Introduction Adaptation system uses the actual information about radio channel state to optimize system parameters (SIR, BER, FER) by changing (adaptation) transceiver parameters. Adaptation automatic control of requested QoS level during communication by changing of: time and target of transmission (Scheduling) transmitted signal parameters (Link adaptation) antenna system parameters Department of Telecommunications and Multimedia 2

3 ADAPTATION METHODS Link adaptation Scheduling Antenna adaptation Power Control Adaptive modulation AMC Adaptive coding Source coding adaptation Channel coding adaptation Department of Telecommunications and Multimedia 3

4 Technical parameters adaptation Transmitter adaptative Modulation Link adaptation SIGNAL SOURCE SOURCE CODING CHANNEL CODING MODULATOR Source coding adaptation Channel coding adaptation Transmitted signal RF TRANSMITTER Radio channel Antenna array adaptation Power control Receiver Received signal signál DEMODULATOR CHANNEL DECODING SOURCE DECODING OUTPUT Antenna array adaptation Department of Telecommunications and Multimedia 4

5 Adaptation criteria 1. Setting of the measurable QoS parameter for specified service (BER, PER, FER, SIR, delay, throughput, jitter) 2. Setting of the parameter threshold level 3. Ensuring the periodical measurement of parameter during communication 4. If the parameter value descends under threshold level during some specified time interval, control system has to change one (or several) parameters Department of Telecommunications and Multimedia 5

6 Throughput maximization Throughput maximization Symbol rate increasing Redundancy decreasing Channel bandwidth increasing Higher order modulation Channel coding with maximum code rate Source coding with minimum transmission rate Department of Telecommunications and Multimedia 6

7 Throughput maximization Throughput maximization methods Number of channels Spreading code parameters Time slots aggregation (TDMA) Variable Spreading factor Spreading codes aggregation (CDMA) Variable chip rate Frequency channels aggregation (FDMA) Department of Telecommunications and Multimedia 7

8 Time Slots Aggregation Frame HSCSD GPRS 1. Constant number of aggregated slots 2. Variable number of aggregated slots Department of Telecommunications and Multimedia 8

9 Number of channels and spreading code parameters CDMA B R ss chip s G p = SF = = = = Bs Rs Tchip T N chip Rchip R s = = N chip R chip SF 1. Variable R chip System with several chip rates 2. Variable SF System with variable spreading factor 3. Variable spreading codes number System with several codes Department of Telecommunications and Multimedia 9

10 Number of channels and spreading code parameters System with several codes k R s = k R chip SF Code Aggregation 1 channel Department of Telecommunications and Multimedia 10

11 Number of channels and spreading code parameters k System with several chip rates R s k = R SF chip for SF = B B ss s = const. SF = N chip = const. T chip = var. R chip = var. B ss = var. Example SF = 4 T s1 R s T chip1 (R chip1 ) Low R s Low R chip wider chips SF = 4 T chip2 = ½ T chip1 R s2 = 2 R s1 Department of Telecommunications and Multimedia 11

12 Number of channels and spreading code parameters System with several chip rates Code Aggregation Several Chip Rates Standard R chip (Mč/s) cdma2000 1,2288 UMTS Multicarrier MC B ss (MHz) N x 1,25 MHz (N = 1,3,6,9,12) Not using 1,25 3,75 7,50 11,25 15,00 Direct Spread DS R c hip (Mchip/s) N x 1,2288 (N = 1,3,6,9,12) 3,84 1 7,68 15,36 1,2288 3,6864 7, , ,7456 B ss (MHz) 1,25 3,75 7,50 11,25 15, Department of Telecommunications and Multimedia 12

13 Number of channels and spreading code parameters System with variable spreading factor R s R SF = = chip const. SF OVSF SF = var. T chip = const. R chip = const. B ss = const. Example R s 2 R s k R s N chip N chip 2 N chip k Problem : E I b 0 r = ( SIR) SF 1. Increasing P 2. Increasing SF r Changing position of MS Changing transmission power of BS r Department of Telecommunications and Multimedia 13

14 OVSF in UMTS N d = 10 Time slot 2560 chips 2560 chips N d = 640 Time slot SF = 256 SF = chips 4 chips Department of Telecommunications and Multimedia 14

15 Link adaptation Link adaptation Power control Rate adaptation AMC (MCS) Adaptive modulation Adaptive coding Department of Telecommunications and Multimedia 15

16 Power control Department of Telecommunications and Multimedia 16

17 Rate adaptation Department of Telecommunications and Multimedia 17

18 Power Control Department of Telecommunications and Multimedia 18

19 Power control Power control aim: 1. Downlink: 2. Uplink: to restrict signal power from BS in cell area (mutual interference decreasing) to provide the minimum UE transmit power requested for required QoS level interference minimization UE battery power consumption decreasing decreasing of possible health hazard Department of Telecommunications and Multimedia 19

20 Power control methods Near-Far problem E I b 0 M 2 = P r 2 P G r1 p < 1 M 1 M 2 Without power control MS 1 MS5 MS2 BS MS4 MS3 Received signal power MS1 MS2 MS3 MS4 MS5 With power control MS1 MS2 MS3 MS4 MS5 Department of Telecommunications and Multimedia 20

21 Without power control Near-Far problem P rx_bs P rx_bs M1 M2 E b G s M2 M1 < 1 I 0 With power control f f P rx_bs M1 M2 P rx_bs E b M4 G s M2 M3 > 1 M1 I 0 f f Department of Telecommunications and Multimedia 21

22 Power control problems 1. Measurement of communication quality: Voice (SIR) Data (BER, PER, FER) QI (BER, FER) RSSI (P rx ) 2. Restrictions : power level number 3. Time delay Department of Telecommunications and Multimedia 22

23 Power control Direction Type Loop Indicator Step Continuity Uplink Central Open Received power Constant Continuous Downlink Distributed Closed SIR Variable Stepped Outer BER, FER, PER Department of Telecommunications and Multimedia 23

24 Direction DOWNLINK UPLINK BS Power control MS Power control Base station (TX) Mobile station (RX) Base station (RX) Mobile station (TX) Department of Telecommunications and Multimedia 24

25 PC Loops Path loss Shadowing Short-term fading TX x(t) A, τ y(t) RX y ( t) = A x( t τ) A = L Path Loss L Shadowing L ST fading e jφ High correlation in UL a DL Low correlation in UL a DL Department of Telecommunications and Multimedia 25

26 Open Loop PC P rx Pilot Pilot signal measurement P pilot Transmitter power P t 1/P pilot BS MS FDD versus TDD quick loop reaction high UL and DL correlation only UL Department of Telecommunications and Multimedia 26

27 Open loop PC (Example) P rx d1 Tx = 0 dbm d2 Rx = -90 dbm Base station P rx = -73 dbm Tx = 17 dbm Tx = -3 dbm Rx = -70 dbm Mobile station 2 Mobile station 1 Department of Telecommunications and Multimedia 27

28 Closed Loop PC UPLINK SIR 2. BS receives usefull signal + interference signals and calculates SIR m. 3. Compares SIR m with SIR r 1. MS transmitts signal 4. BS send PC command 5. MS receives PC command and sets transmission power Interference signals Base station Mobile station Department of Telecommunications and Multimedia 28

29 Closed Loop PC DOWNLINK Base station 1. BS transmitts pilot signal 3. MS sends calculated value Interference signals Mobile station 2. MS receives pilot signal + interference signals and calculates SIR m SIR 4. BS receives SIR m. 5. Compares SIR m with SIR r. 6. BS sets own transmission power Department of Telecommunications and Multimedia 29

30 Outer Loop PC FER 1 FER r FER [%] 10,0 SIR r [db] 0,0 0 9,0 8,0 7,0 6,0 5,0 4,0 increasing SIR r ,0 4,0 5,0 6,0 5,0 frames Department of Telecommunications and Multimedia 30

31 Outer and Closed Loop PC (UL) BASE STATION MOBILE STATION Data Multiplexor PC commands AGC Demultiplexor Decoding setting SIR r Measurement SIR m PC commands FER calculation Power Amplifier Decoding Signal Despreading Data Department of Telecommunications and Multimedia 31

32 Continuity and step PC 1. Continuous PC 2. Stepped PC: Constant step (Up-Down) - algoritmus Variable step (PCM algoritmus) UP-DOWN P tx ( t + 1) = P ( t) tx + if if ( SIR) m < ( SIR) ( SIR) ( SIR) m r r Short-term fading compensation t loop < t coh Example: UMTS: v max = 500 kmph, λ = 15 cm f Dmax = 926 Hz t 9 = = π f coh µ Dmax s Department of Telecommunications and Multimedia 32

33 SIR r Constant step PC command SIR measurement SIR m + Error signal BASE STATION PC command creation PC with algoritmus Uplink Downlink 1, 1, -1, 1, 1, -1, -1, -1, 1, 1, 1 [db] Power setting MOBILE STATION p Command PC command detection m PC command Error signal Error signal Time time n 2,5 1,5 0,5-0,5-1,5-2,5 Error = SIR m SIR r Department of Telecommunications and Multimedia 33

34 Variable step PC command m 3 2 Error signal Chybový signál PC with PCM algoritmus -1, -1, 1, -1, -3, 0, 3, 1, 1, 2, 0 [db] čas time Povel [db] 3 2 m číslo kvantovacej hladiny PC command čas time -3-3 Department of Telecommunications and Multimedia 34

35 PC type Central PC Central Controller Distributed PC Local Controller Local Controller Local Controller Local Controller Department of Telecommunications and Multimedia 35

36 Rate Adaptation Department of Telecommunications and Multimedia 36

37 Modulation adaptation 7 BPSK 1\2 <10 6 Spectral Spektrálna effectivity účinnosť (bps/hz) (b/s/hz) without bez adaptácie link adaptation spoja with s adaptáciou link adaptation spoja 64-QAM 16-QAM QPSK BPSK BPSK QPSK QPSK 16QAM 16QAM 64QAM 64QAM 3\4 1\2 3\4 1\2 3\4 2\3 3\ IEEE g pre kanál bez úniku S/N (db) Rb [Mbps] SNR [db] Department of Telecommunications and Multimedia 37

38 Modulation adaptation Algorithm: 1. Measurement of SNR (BER) in receiver 2. According to BER req to chose MCS scheme for each SNR measurement 3. Information about MCS transmit back to source 10 0 Indicators: SNR, SIR (PHY layer) BER, PER, FER, BLER (link layer) 10-2 BER 10-4 BPSK QPSK 16-QAM 64-QAM Department of Telecommunications and Multimedia S/N (db) 38

39 Modulation adaptation MOBILE STATION Modulator BASE STATION Modulation format estimation Modulation controller Demodulator data traffic information Short-time fading predictor TDD Short-time fading predictor Demodulator Modulation controller data Modulation format estimation Modulator Traffic monitor data Traffic information Department of Telecommunications and Multimedia 39

40 Coding adaptation Source coding adaptation k u = B ss R ( Eb N0 ) r Discontinuous transmission (DTX) cdmaone (QCELP13) Time slot Time slot Time slot Time slot MS 4,8 9,6 kb/s off kb/s 2,4 kb/s off 1,2 kb/s off Time slot Time slot Time slot Time slot BS 9,6 kb/s 4,8 kb/s 4,8 kb/s 2,4 kb/s 2,4 kb/s 2,4 kb/s 2,4 kb/s 1,2 kb/s 1,2 kb/s 1,2 kb/s 1,2 kb/s 1,2 kb/s 1,2 kb/s 1,2 kb/s 1,2 kb/s Department of Telecommunications and Multimedia 40

41 Coding adaptation Channel coding adaptation H-ARQ 1. Without adaptation: FEC is created for the worst channel situation. 2. With adaptation: Code rate changes accordingly channel conditions H-ARQ = ARQ + FEC Joint decoding H-ARQ I P P FEC FEC Chase Combining Department of Telecommunications and Multimedia 41

42 Coding adaptation Channel coding adaptation H-ARQ H-ARQ II. 1. P FEC 2a. P FEC FEC Incremental Redundancy 2b. FEC FEC H-ARQ III. 1. P CPCC individual decoding 2. P CPCC individual decoding Department of Telecommunications and Multimedia 42

43 Coding adaptation H-ARQ II. Incremental redundancy TRANSMITTER RECEIVER k Coder R = k/n n Memmory Channel Decoder Transport control match Next data block CRC? Parity data block non match EGPRS: FEC = 1/3 D D FEC FEC CODER R = 1/3 1. transmission D R = 1 2. transmission 3. transmission FEC R = 1/2 FEC FEC R = 1/3 Department of Telecommunications and Multimedia 43

44 Packet resegmentation Coding schemes Code Rate (FEC) Real throughput (kb/s) CS1 1/2 6.7 CS2 2/ GPRS CS3 3/ CS LLC frame CS CS-3 CS NACK 2, 3 MS MS Department of Telecommunications and Multimedia 44

45 Packet resegmentation EDGE LLC frame MCS-6 MCS Modulation Code Rate MCS MCS-3 Packet Head Code Rate Throuhput (kb/s) Group 1.0 0,35 59,2 A MCS ,35 54,5 A MCS-7 8-PSK ,35 44,8 B MCS /3 29,6 A MCS /3 22,4 B MCS /2 17,6 C MCS-3 GMSK 0.8 1/2 14,8 A MCS /2 11,2 B MCS /2 8,8 C 2 3 MS NACK 2, 3 MS Department of Telecommunications and Multimedia 45