1. Shahzad A. Malik, Ph.D. smalik@comsats.edu.pk EEE464 Wireless Communications

2. CDMA Cellular Networks

3. Shahzad MalikLecture 83Wireless Communications CDMA IS-95 CDMA – Code Division Multiple Access  A digital wireless technology that allow multiple users to share radio frequencies at the same time without interfering with each other IS-95  Second generation CDMA scheme  Primarily deployed in North America  Transmission structures different on forward and reverse links

4. Shahzad MalikLecture 84Wireless Communications CDMA Evolution  IS-95A (2G)  First CDMA protocol, published in May’99  14.4/9.6 kbps circuit/packet data  IS-95B (2.5G)  Some technical corrections  New Capabilities, such as higher data rate  64 kbps packet data  CDMA2000 1X/3X  High speed data (144 kbps packet data with Mobile IP)  Coding (Turbo) and Modulation (Hybrid QPSK)  New dedicated and common channels  Enhanced Power Control

5. Shahzad MalikLecture 85Wireless Communications CDMA Evolution  1X EV-DO  (1xRTT Evolution for high-speed integrated Data Only)  The objective is to provide the largest practical number of users to run high-speed packet data applications  2.4 Mbps packet data  1X EV-DV  (1xRTT Evolution for high-speed integrated Data and Voice)  Voice and High Speed Data mixed on one carrier  Backward-compatible with CDMA2000 1X  3.1 Mbps packet data

6. IS-95 (CdmaOne)

7. Shahzad MalikLecture 87Wireless Communications IS-95 CDMA  Direct Sequence Spread Spectrum Signaling on Reverse and Forward Links  Each channel occupies 1.25 MHz  Fixed chip rate 1.2288 Mcps Reverse CHForward CH 847.74 MHz892.74 MHz 45 MHz

8. Shahzad MalikLecture 88Wireless Communications Spreading Codes in IS-95  Orthogonal Walsh Codes  To separate channels from one another on forward link  Used for 64-ary orthogonal modulation on reverse link.  PN Codes  Decimated version of long PN codes for scrambling on forward link  Long PN codes to identify users on reverse link  Short PN codes have different code phases for different base stations

9. Shahzad MalikLecture 89Wireless Communications IS-95 Channel Structure

10. Shahzad MalikLecture 810Wireless Communications IS-95 Forward Link  Up to 64 logical CDMA channels each occupying the same 1.25 MHz bandwidth (Chip rate = 1.2288 Mcps)  Four types of channels:  Pilot (channel 0)  Continuous signal on a single channel  Allows mobile unit to acquire timing information  Provides phase reference for demodulation process  Provides signal strength comparison for handoff determination  Consists of all zeros  Synchronization (channel 32)  1200-bps channel used by mobile station to obtain identification information about the cellular system  System time, long code state, protocol revision, etc.

11. Shahzad MalikLecture 811Wireless Communications IS-95 Forward Link  Paging (channels 1 to 7)  Contain messages for one or more mobile stations  Traffic (channels 8 to 31 and 33 to 63)  55 traffic channels  Original specification supported data rates of up to 9600 bps  Revision added rates up to 14,400 bps  All channels use same bandwidth  Chipping code distinguishes among channels  Chipping codes are the orthogonal 64-bit Walsh codes derived from 64  64 Hadamard matrix

12. Shahzad MalikLecture 812Wireless Communications Forward Link Transmission

13. Shahzad MalikLecture 813Wireless Communications Cell Separation  Walsh code spreading is followed by quadrature spreading using PN chips with time offsets  Adjacent cells have different PN offsets.  This prevents interference since time shifted PN sequences are orthogonal to each other I-PN Q-PN Wt Baseband Filter Baseband Filter sin wot cos wot

14. Shahzad MalikLecture 814Wireless Communications IS-95 Reverse Link  Up to 94 logical CDMA channels  Each occupying same 1.25 MHz bandwidth (1.2288 Mcps)  Supports up to 32 access channels and 62 traffic channels  Traffic channels mobile unique  Each station has unique long code mask based on serial number  42-bit number, 2 42 – 1 different masks  Access channel used by mobile to initiate call, respond to paging channel message, and for location update  One of the logical channel is permanently and uniquely associated with each MS. The channel does not change upon handoff.

15. Shahzad MalikLecture 815Wireless Communications Reverse Link Transmission

16. Shahzad MalikLecture 816Wireless Communications Power Control Near-Far Problem: a user near the base station would jam the user far from the base station  Power Control - Motivation  Overcomes near-far problem  CDMA wouldn’t work without it  Copes with path loss and fading  Capacity is maximized  By having each user transmitting just sufficient SNR to maintain a target FER  Power Control - Algorithm  Open Loop Estimate  Initial transmit power level for the mobile is determined by the received pilot strength  Closed Loop Power Control  Base station controls the power level on the mobile by the received quality information.

17. Shahzad MalikLecture 817Wireless Communications Use of Multipath in CDMA Systems  FDMA/TDMA (narrow-band)  multipath hurts  equalizers are used to cancel multipath  CDMA (wide-band)  can discriminate between the multipath arrivals  Rake receivers are used to combine multipath signals to reduce error rate at the receiver RAKE Receiver Concept  Multi-path diversity channels (micro-diversity)  Problem is how to isolate various multi-path signals?  If the maximal delay spread (due to multi-path) is T m seconds and if the chip rate 1/Tc = W >> 1/Tm, then individual multi-path signal components can be isolated  Amplitudes and phases of the multipath components are found by correlating the received waveform with delayed versions of the signal  Multi-path with delays less than T c can’t be resolved

18. Shahzad MalikLecture 818Wireless Communications Rake Receiver in IS-95  Rake Receiver is used in Mobile receiver for combining  Multi-path components  Signal from different base stations (resolve multi-path signals and different base station signals)  3 Parallel Demodulator (RAKE Fingers)  For tracking and isolating particular multi-path components (up to 3 different multi-path signals on FL)  1 Searcher  Searches and estimates signal strength of  multi-path pilot signals from same cell site  pilot signals from other cell sites

19. Shahzad MalikLecture 819Wireless Communications Handoff in CDMA System  CDMA is specifically designed not only to reduce handoff failures but also to provide seamless service  Handoffs between cells are supported while the mobile is in traffic or idle  MS continuously keeps searching for new cells as it moves across the network  MS maintains active set, neighbor set, and remaining set as well as candidate set  Soft Handoff (macro-diversity)  Mobile commences Communication with a new BS without interrupting communication with old BS  same frequency assignment between old and new BS  provides different site selection diversity  Softer Handoff  Handoff between sectors in a cell  CDMA to CDMA hard handoff  Mobile transmits between two base stations with different frequency assignment

20. Shahzad MalikLecture 820Wireless Communications Soft Handoff Advantages  Contact with new base station is made before the call is switched  Diversity combining is used between multiple cell sites  additional resistance to fading  If the new cell is loaded to capacity, handoff can still be performed for a small increase in BER  Neither the mobile nor the base station is required to change frequency  Reduces number of call drops  Increases the overall capacity  Mobile transmit power is reduced  Voice quality near the cell boundaries are improved  MS reports the SNR of the candidate sets A unique feature of CDMA Mobile

21. Shahzad MalikLecture 821Wireless Communications Soft Handoff Architecture MSC BSC BTS BSC BTS R new link old link R R- handoff request sent to the old cell energy measurements are made at the mobile R

22. Shahzad MalikLecture 822Wireless Communications Soft Handoff Gain Power (dBm) Distance Cell A Cell B Total at MS

23. cdma2000

24. Shahzad MalikLecture 824Wireless Communications cdma2000  cdma2000 supports both voice and data services in the same carrier  provides enhanced voice capacity  Forward link  Fast power control in forward/reverse links  Lower code rates  New code channels  Reverse Link  Coherent detection  Higher data rates: 1x up to 153.6 kbps and 1x EV-DV up to 3.09 Mbps  Battery life is improved – efficient power control  Introduction of Turbo codes provides better link quality for supplemental channels

25. Shahzad MalikLecture 825Wireless Communications cdma2000  cdma2000 allocates resources dynamically  Admission control is important to ensure quality of service for the existing users when new resources are requested  A new request can be call setup, supplemental channel set-up, handoff, data rate change  Available Walsh codes, residual power in the forward and reverse links are considered before granting a request

26. Third Generation (3G) Mobile Cellular Systems

27. Shahzad MalikLecture 827Wireless Communications Third Generation Systems  Objective to provide fairly high-speed wireless communications to support multimedia, data, and video in addition to voice  ITU ’ s International Mobile Telecommunications for the year 2000 (IMT-2000) initiative defined ITU ’ s view of third-generation capabilities as:  Voice quality comparable to PSTN  144 kbps available to users in vehicles over large areas  384 kbps available to pedestrians over small areas  Support for 2.048 Mbps for office use  Symmetrical and asymmetrical data rates  Support for packet-switched and circuit-switched services  Adaptive interface to Internet  More efficient use of available spectrum  Support for variety of mobile equipment  Flexibility to allow introduction of new services and technologies

28. Shahzad MalikLecture 828Wireless Communications UMTS and IMT-2000  Proposals for IMT-2000 (International Mobile Telecommunications)  UWC-136, cdma2000, W-CDMA  UMTS (Universal Mobile Telecommunications System) from ETSI  UMTS  UTRA (was: UMTS, now: Universal Terrestrial Radio Access)  enhancements of GSM  EDGE (Enhanced Data rates for GSM Evolution): GSM up to 384 kbit/s  CAMEL (Customized Application for Mobile Enhanced Logic)  VHE (virtual Home Environment)  fits into GMM (Global Multimedia Mobility) initiative from ETSI requirements  min. 144 kbit/s rural (goal: 384 kbit/s)  min. 384 kbit/s suburban (goal: 512 kbit/s)  up to 2 Mbit/s urban

29. Shahzad MalikLecture 829Wireless Communications Frequencies for IMT-2000 IMT-2000 18501900195020002050210021502200MHz MSS  ITU allocation (WRC 1992) IMT-2000 MSS  Europe China Japan North America UTRA FDD  UTRA FDD  TDDTDD TDDTDD MSS  MSS  DE CT GSM 1800 18501900195020002050210021502200 MHz IMT-2000 MSS  IMT-2000 MSS  GSM 1800 cdma2000 W-CDMA MSS  MSS  MSS  MSS  cdma2000 W-CDMA PHS PCS rsv.

30. Shahzad MalikLecture 830Wireless Communications IMT-2000 family IMT-DS (Direct Spread) UTRA FDD (W-CDMA) 3GPP IMT-TC (Time Code) UTRA TDD (TD-CDMA); TD-SCDMA 3GPP IMT-MC (Multi Carrier) cdma2000 3GPP2 IMT-SC (Single Carrier) UWC-136 (EDGE) UWCC/3GPP IMT-FT (Freq. Time) DECT ETSI GSM (MAP) ANSI-41 (IS-634) IP-Network IMT-2000 Core Network ITU-T IMT-2000 Radio Access ITU-R Interface for Internetworking Flexible assignment of Core Network and Radio Access Initial UMTS (R99 w/ FDD)

31. Shahzad MalikLecture 831Wireless Communications UMTS services  Data transmission service profiles  Virtual Home Environment (VHE)  Enables access to personalized data independent of location, access network, and device  Network operators may offer new services without changing the network  Service providers may offer services based on components which allow the automatic adaptation to new networks and devices  Integration of existing IN services Circuit switched16 kbit/sVoice SMS successor, E-MailPacket switched14.4 kbit/sSimple Messaging Circuit switched14.4 kbit/sSwitched Data asymmetrical, MM, downloadsCircuit switched384 kbit/sMedium MM Low coverage, max. 6 km/hPacket switched2 Mbit/sHigh MM Bidirectional, video telephoneCircuit switched128 kbit/sHigh Interactive MM Transport modeBandwidthService Profile

32. Shahzad MalikLecture 832Wireless Communications UMTS Architecture (Release 99) UTRANUECN IuIu UuUu  UTRAN (UTRA Network)  Cell level mobility  Radio Network Subsystem (RNS)  Encapsulation of all radio specific tasks  UE (User Equipment)  CN (Core Network)  Inter system handover  Location management if there is no dedicated connection between UE and UTRAN

33. Shahzad MalikLecture 833Wireless Communications UMTS domains and interfaces  User Equipment Domain  Assigned to a single user in order to access UMTS services  Infrastructure Domain  Shared among all users  Offers UMTS services to all accepted users USIM Domain Mobile Equipment Domain Access Network Domain Serving Network Domain Transit Network Domain Home Network Domain CuCu UuUu IuIu User Equipment Domain ZuZu YuYu Core Network Domain Infrastructure Domain

34. Shahzad MalikLecture 834Wireless Communications UMTS domains and interfaces  Universal Subscriber Identity Module (USIM)  Functions for encryption and authentication of users  Located on a SIM inserted into a mobile device  Mobile Equipment Domain  Functions for radio transmission  User interface for establishing/maintaining end-to-end connections  Access Network Domain  Access network dependent functions  Core Network Domain  Access network independent functions  Serving Network Domain  Network currently responsible for communication  Home Network Domain  Location and access network independent functions

35. Shahzad MalikLecture 835Wireless Communications UTRAN architecture  UTRAN comprises several RNSs  Node B can support FDD or TDD or both  RNC is responsible for handover decisions requiring signalingto the UE  Cell offers FDD or TDD RNC: Radio Network Controller RNS: Radio Network Subsystem Node B RNC I ub Node B UE 1 RNS CN Node B RNC I ub Node B RNS I ur Node B UE 2 UE 3 IuIu

36. Shahzad MalikLecture 836Wireless Communications UTRAN functions  Admission control  Congestion control  System information broadcasting  Radio channel encryption  Handover  SRNS moving  Radio network configuration  Channel quality measurements  Macro diversity  Radio carrier control  Radio resource control  Data transmission over the radio interface  Outer loop power control (FDD and TDD)  Channel coding  Access control

37. Shahzad MalikLecture 837Wireless Communications Core network  The Core Network (CN) and thus the Interface I u, too, are separated into two logical domains:  Circuit Switched Domain (CSD)  Circuit switched service incl. signaling  Resource reservation at connection setup  GSM components (MSC, GMSC, VLR)  I u CS  Packet Switched Domain (PSD)  GPRS components (SGSN, GGSN)  I u PS  Release 99 uses the GSM/GPRS network and adds a new radio access!  Helps to save a lot of money …  Much faster deployment  Not as flexible as newer releases (5, 6)

38. Shahzad MalikLecture 838Wireless Communications Core network: architecture BTS Node B BSC A bis BTS BSS MSC Node B RNC I ub Node B RNS Node B SGSNGGSN GMSC HLR VLR I u PS I u CS IuIu CN EIR GnGn GiGi PSTN AuC GR

39. Shahzad MalikLecture 839Wireless Communications Core network: protocols MSC RNS SGSNGGSN GMSC HLR VLR RNS Layer 1: PDH, SDH, SONET Layer 2: ATM Layer 3: IP GPRS backbone (IP) SS 7 GSM-CS backbone PSTN/ ISDN PDN (X.25), Internet (IP) UTRANCN

40. Shahzad MalikLecture 840Wireless Communications UMTS protocol stacks (user plane) apps. & protocols MAC radio MAC radio RLC SAR UuUu I u CS UE UTRAN3G MSC RLC AAL2 ATM AAL2 ATM SAR apps. & protocols MAC radio MAC radio PDCP GTP UuUu I u PSUEUTRAN3G SGSN RLC AAL5 ATM AAL5 ATM UDP/IP PDCP RLCUDP/IP GnGn GTP L2 L1 UDP/IP L2 L1 GTP 3G GGSN IP, PPP, … IP, PPP, … IP tunnel Circuit switched Packet switched

41. Shahzad MalikLecture 841Wireless Communications Support of mobility: macro diversity  Multicasting of data via several physical channels  Enables soft handover  FDD mode only  Uplink  simultaneous reception of UE data at several Node Bs  Reconstruction of data at Node B, SRNC or DRNC  Downlink  Simultaneous transmission of data via different cells  Different spreading codes in different cells CNNode BRNC Node B UE

42. Shahzad MalikLecture 842Wireless Communications Support of mobility: handoff  From and to other systems (e.g., UMTS to GSM)  This is a must as UMTS coverage will be poor in the beginning  RNS controlling the connection is called SRNS (Serving RNS)  RNS offering additional resources (e.g., for soft handover) is called Drift RNS (DRNS)  End-to-end connections between UE and CN only via I u at the SRNS  Change of SRNS requires change of I u  Initiated by the SRNS  Controlled by the RNC and CN SRNC UE DRNC I ur CN IuIu Node B I ub Node B I ub

43. Shahzad MalikLecture 843Wireless Communications Spreading and scrambling of user data  Constant chipping rate of 3.84 Mchip/s  Different user data rates supported via different spreading factors  higher data rate: less chips per bit and vice versa  User separation via unique, quasi orthogonal scrambling codes  users are not separated via orthogonal spreading codes  much simpler management of codes: each station can use the same orthogonal spreading codes  precise synchronisation not necessary as the scrambling codes stay quasi-orthogonal data 1 data 2 data 3 scrambling code 1 spr. code 3 spr. code 2 spr. code 1 data 4 data 5 scrambling code 2 spr. code 4 spr. code 1 sender 1 sender 2

44. Shahzad MalikLecture 844Wireless Communications OSVF Coding 1 1,1 1,-1 1,1,1,1 1,1,-1,-1 X X,X X,-X 1,-1,1,-1 1,-1,-1,1 1,-1,-1,1,1,-1,-1,1 1,-1,-1,1,-1,1,1,-1 1,-1,1,-1,1,-1,1,-1 1,-1,1,-1,-1,1,-1,1 1,1,-1,-1,1,1,-1,-1 1,1,-1,-1,-1,-1,1,1 1,1,1,1,1,1,1,1 1,1,1,1,-1,-1,-1,-1 SF=1SF=2SF=4SF=8 SF=n SF=2n... OVSF - Orthogonal Variable Spreading Factor

45. Shahzad MalikLecture 845Wireless Communications UMTS FDD frame structure W-CDMA 1920-1980 MHz uplink 2110-2170 MHz downlink chipping rate: 3.840 Mchip/s soft handover QPSK complex power control (1500 power control cycles/s) spreading: UL: 4-256; DL:4-512 012121213131414... Radio frame PilotFBITPC Time slot 666.7 µs 10 ms Data Data 1 uplink DPDCH uplink DPCCH downlink DPCH TPCTFCIPilot 666.7 µs DPCCHDPDCH 2560 chips, 10 bits 2560 chips, 10*2 k bits (k = 0...6) TFCI 2560 chips, 10*2 k bits (k = 0...7) Data 2 DPDCHDPCCH FBI: Feedback Information TPC: Transmit Power Control TFCI: Transport Format Combination Indicator DPCCH: Dedicated Physical Control Channel DPDCH: Dedicated Physical Data Channel DPCH: Dedicated Physical Channel Slot structure NOT for user separation but synchronisation for periodic functions!

46. Shahzad MalikLecture 846Wireless Communications Typical UTRA-FDD uplink data rates User data rate [kbit/s] 12.2 (voice) 64144384 DPDCH [kbit/s]60240480960 DPCCH [kbit/s]15 Spreading641684

47. Shahzad MalikLecture 847Wireless Communications UMTS TDD frame structure TD-CDMA 2560 chips per slot spreading: 1-16 symmetric or asymmetric slot assignment to UL/DL (min. 1 per direction) tight synchronisation needed simpler power control (100-800 power control cycles/s) 012121213131414... Radio frame Data 1104 chips Midample 256 chips Data 1104 chips Time slot 666.7 µs 10 ms Traffic burst GP GP: guard period 96 chips 2560 chips