Introduction to WCDMA and WCDMA Dimensioning for UMTS

Transcription

1 Introduction to WCDMA and WCDMA Dimensioning for UMTS 1

2 internet Third generation services 2M 384K video conference video conference remote medical service video catalogue shopping video on demand mobile TV 64K 32K 16K 9.6K 2.4K telephone conference telephone pager electronic newspaper voice mail electronic publishing ISDN FAX distribution services (voice) distribution services (data) mobile radio 1.2K bidirectional unidirectional multicast point to point multipoint 2

3 UTRAN (UMTS Terrestrial Radio Access Net) Architecture Core Network I u I u UTRAN RNS RNC I u r RNS RNC I ub I ub B-node B-node B-node B-node I ub I ub Site Contr Site Contr Site Contr Site Contr BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS 4

4 Access techniques for mobile communications FDMA (TACS) P T F TDMA,FDMA (GSM) P F T CDMA (UMTS) P - Power T - Time F - Frequency P T F 5

5 W-CDMA (Wide Band CDMA) Key features Improved capacity and coverage (over second generation); thus, backward compatible High degree of service flexibility: multiple, parallel services per connection; efficient pkt access 6

6 Basics of Spread Spectrum and CDMA 7

7 Overview Why consider Spread Spectrum? What is Spread Spectrum & CDMA? Frequency Hopping Spread Spectrum Impact of channel Current systems Direct Sequence Spread Spectrum Spreading Codes Analytical Performance Model Rake Processing Near Far Effect (Power Control) Handover 8

8 Why Consider Spread Spectrum? Spread Spectrum has been adopted as the air interface standard for 3rd Generation Mobile Systems (IMT2000): Europe (ETSI): UMTS (W- CDMA ) Japan (ARIB): Wideband CDMA USA (TIA TR45. 5) CDMA nd Generation standard deployed in US and Korea IS95 (Qualcomm CDMA) 9

9 What is spread spectrum? Narrow Band Message Narrow Band Message Wideband Message 10

10 Frequency Hopping Spread Spectrum 11

11 Classification of Spread Spectrum Systems Frequency Hopping (FH) Narrow band message signal is modulated with a carrier frequency which is rapidly shifted. The hop frequency is indicated by a spreading function. This spreading function is also available at the receiver and enables it to retune to the correct channel for each hop. 12

12 Hop rates in an FH system Fast frequency hopping Data symbol spread over several hop frequencies Symbol diversity Very resistant to jamming and interference, often used in military systems Slow frequency hopping Several data symbols on each hop frequency Codeword diversity with interleaving Less complex 13

13 Direct Sequence Spread Spectrum 14

14 Classification of Spread Spectrum Direct Sequence (DS) Systems Secondary modulation in the form of pseudonoise is applied to an already modulated narrowband message, thereby spreading the spectrum. At the receiver, the incoming waveform is multiplied by an identical synchronized spreading waveform in order to recover the message. 15

15 Direct sequence spread spectrum Narrow Band Message D(t) S(t) Narrow Band Message C(t) Wide Band Pseudo Random Noise fc fc C(t) Up conversion To fixed carrier frequency Down conversion Wide Band Pseudo Random Noise 16

16 Data Signal Code Signal Multiplication 17

17 Spreading codes Maximal length sequences good auto- and cross- correlation Gold codes and Kasami sequences are derived from M- sequences with similar correlation properties, and a larger code set. 18

18 Orthogonal spreading Codes Walsh and Hadamard sequences zero correlation between codes when aligned cross- correlation non- zero when time shifted fixed spreading factor (codes of different length are not orthogonal) Orthogonal Variable Spreading Factor (OVSF) codes permit orthogonal codes for different rate services Both types of code lose orthogonality when shifted due to channel dispersion e. g. 40% loss of orthogonality in a large macrocell 19

19 Orthogonal Variable Spreading Factor c 2,1 = (1,1) c 4,1 = (1,1,1,1) c 4,2 = (1,1,-1,-1) c 4,3 = (1,-1,1,-1) c 2,2 = (1,-1) c4,4 = (1,-1,-1,1)

20 21

21 22

22 23

23 DS-SS Application for CDMA S1(t) S2(t)g2(t) X1(t) Mod. S1(t)g1(t) Coswt g1(t) g1(t) SN(t)gN(t) 24

24 Theoretical CDMA capacity DS- CDMA capacity is inversely proportional to the energy per bit per noise power density which is tolerated A standard DS- CDMA system is interference limited by - intra- cell interference - Therefore increase capacity by: - voice activity detection - antenna sectorisation - adaptive antennas - interference cancellation 25

25 The Multipath Environment The received signal is made up of a sum of attenuated, phaseshifted and time delayed versions of the transmitted signal. Propagation modes include diffraction, transmission and reflection. 26

26 Path diversity in the multipath Path diversity Path diversity can be exploited by separating out the multipath components, co- phasing and summing them. Number of paths resolved (Lm) depends on the total multipath delay (Tm) and the chip period (Tc) Lm< Tm/Tc +1 27

27 RAKE Receiver tc tc tc C(t) C(t-tc) C(t-LTc) Int. Int Int Diversity Combiner One method of realising path diversity is with a RAKE and a bank of correlators Out Put 28

28 Diversity and diversity combinig Diversity: providing multiple versions of the transmitted signal. Commonly: multiple antennas multiple paths Diversity combining selection: best branch is chosen equal gain: equal combining: all branch summed maximal ratio: branches summed and weighted depending on their quality 29

29 The near-far effect in CDMA Everyone on same frequency at the same time. A MS close to the BS will drown out other MSs unless it reduces it s power. Power control is required. 30

30 CDMA Power Control Power control required on uplink, desired on downlink. Open loop control can be used to remove shadowing (as the channel is reciprocal). Closed loop control is required to remove the fast fading BS receives MS signal and calculates the SIR BS sends MS a transmit power control (TPC) signal to increase or decrease its power TPC issues include rate and step size 31

31 Uplink closed loop power control algorithms Sigma- delta scheme used Command rate must be sufficient to track channel changes Trade- off in step size between tracking and accuracy 32

32 Handover and Mobility BS1 BS2 33

33 W-CDMA in UMTS W- CDMA is used in FDD mode in UMTS On the downlink it is possible to use orthogonal reading codes to reduce interference. A scrambling code is used to separate the cells On the uplink, low cross correlation codes are used to separate the mobiles. A single mobile can use multi-code transmission: each service is mapped onto several bearers, each of which is spread by an orthogonal code. 34

34 WCDMA Air Interface 35

35 Radio Interface - protocol L3 architecture C-plane U-plane RRC L2/LAC L2/MAC RLC LAC LAC RLC LAC RLC RLC Logical channels L1 MAC Physical Layer Transport channels 36

36 Layer 1 - up link physical channels (W-CDMA example) Data Dedicated Physical Data Channel ms Pilot Feedback indicator Transmit power control Transport format ind. Dedicated Physical Control Channel Slot#1Slot#2 Slot#i Slot#15 Frame#1Frame#2 Frame#i Frame#72 10 ms 37

37 Layer 1 - down link physical channels (W-CDMA example) DPCCH Pilot TPC TFI DPDCH Data ms Slot#1Slot#2 Slot#i Slot#15 frame Frame#1Frame#2 Frame#i Frame#72 superframe 10 ms 38

38 Transport channels (example) Dedicated Channel (DCH): fast change of bit rate (10ms) fast power control inherent MS addressing Random Access Channel (RACH) - up link: Broadcast Control Channel (BCH) - down link Forward Access Channel (FACH) - down link: collision open loop power control explicit MS addressing slow power control explicit MS addressing Paging Channel (PCH) - down link: use of sleep modes 39

39 coding interleaving rate matching interleaving multiplexing rate matching interleaving coding interleaving rate matching interleaving Multiplexing transport channels onto physical channels DCH trasport channels multiplexing DCH DCH DCH dynamic (up link) intra frame interleaving static inter frame interleaving 40

40 MAC Services and Functions set-up, release of logical channels data transfer service on logical channels allocation/re-allocation of radio resources measurement report Functions Selection of the transport format Handling of priority within one user/between users Scheduling of control messages (broadcast, paging, notification) Multiplexing/de-multiplexing of higher layers PDUs DCH DCH DCH Coding and multiplexing mapping DCHDCH Coding and multiplexing mapping on/from common or dedicated transport channels phy ch phy ch phy ch Contention control on the random access channel 41

41 Radio Network planning And Dimensioning Procedures Preparation Estimation No. of Cells Detailed Planning 42

42 Preparation 1-Targets of Capacity and Coverage 2-Strategy of Network Planning 43

43 Estimation No. of Cells Population of Region Influence percentage Traffic/User No of Users Offered Traffic Capacity/Cell Cell Rangr No of Cells 44

44 Estimation Capacity of Cell Principle Factors : 1. Data Rate 2. Traffic characteristics (variation Rates,..) 3. Requirements (delays, BER) 4. Disconnect Probability 5. Sectorized Effect 6. Load Effect 45

45 Cell Range Link Budget A Chip Rate 3.84 Mchip/s B Information Rate 12.2 Kbit/s C Processing Gain (10log(A/B)) db 46

46 D Mobile transmit power 21.0 dbm E Mobile antenna gain 2.0 dbi F Body Loss 3.0 db G Mobile EIRP (D+E-F) 20.0 dbm 47

47 H Base Station antenna Gain 14.0 dbi I Thermal noise density dbm/hz J Base Station Noise density dbm K Base Station Noise Figure 5.0 db L Target Eb/N0 5.5 db M Base Station Sensivity dbm 48

48 N Cable Loss 3.0 db O Lognormal shadowing margin 9.0 db P Noise Rise (intracell) 3.0 db Q Noise Rise (intercell) 2.0 db R Soft handoff gain 4.0 db Maximum path loss=g+h-m-n-o-p-q+r= db 49

49 UMTS Dimensioning Operators required (QOS,Capacity, Coverage) Condition of Radio Propagaiton Estimation The Number of users Available Techniques Dimensioning Process Estimation of required equipments and arrangment of network array Optimization 50

50 UMTS RAN Dimensioning Process Node B Dimensioning RNC Dimensioning Interface Dimensioning Offering prepare topology for RAN 51

51 Required Data for each phase of Network development 1. Radio coverage (regions, subregions, region classifications) 2. Traffic ( Frequency spectrum, customers Density in each region, customers profile) 3. QOS (coverage probability, Blocking prob., service level in each region) 52

52 Node B Dimensioning Up Link 1. Considering a radius for cell r1 2. Estimation average traffic inside cell 3. Estimation no. of channels for peak traffic service 4. Considering a Statistical method for calculating accumulated noise 53

53 Up Link 5. Calculating Maximum path loss then cell range r2 6. Continuing till r1 = r2 7. Cell bar test 54

54 Down Link 1. Considering a cell range r1 2. From input traffic, estimate average cell traffic 3. Estimation no. of channels for peak traffic service 4. Calculation of One user required power for each service 5. Calculating transmit accumulated power in Node B 55

55 Down Link Calculating Cell range r2 Continue till r1=r2 56

56 RNC Dimensioning Process Steps 1. Knowing No. of Node Bs then By Considering Management Limitations,Estimate minimum RNC, RNC1 2. By considering input average traffic and traffic limitations, Estimate minimum RNC that needs for traffic handling, RNC2 3. Average traffic for each RNC is known, then peak traffic for each RNC must be calculated 4. Max(RNC1,RNC2)=No. of RNC 57

57 RNC Dimensioning Process Efficient factors for RNC Dimensioning Process are: 1. Traffic Limitations 2. Management Limitations 3. Communications Limitations 58