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EEE464 Wireless Communications Shahzad A. Malik, Ph.D. [email protected] CDMA Cellular Networks 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 Shahzad Malik Wireless Communications Lecture 8 3 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 Shahzad Malik Wireless Communications Lecture 8 4 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 Shahzad Malik Wireless Communications Lecture 8 5 IS-95 (CdmaOne) 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 CH Forward CH 45 MHz 847.74 MHz Shahzad Malik Wireless Communications 892.74 MHz Lecture 8 7 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 Shahzad Malik Wireless Communications Lecture 8 8 IS-95 Channel Structure Shahzad Malik Wireless Communications Lecture 8 9 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. Shahzad Malik Wireless Communications Lecture 8 10 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 Shahzad Malik Wireless Communications Lecture 8 11 Forward Link Transmission Shahzad Malik Wireless Communications Lecture 8 12 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 Wt cos wot Baseband Filter Baseband Filter Q-PN Shahzad Malik Wireless Communications sin wot Lecture 8 13 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, 242 – 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. Shahzad Malik Wireless Communications Lecture 8 14 Reverse Link Transmission Shahzad Malik Wireless Communications Lecture 8 15 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. Shahzad Malik Wireless Communications Lecture 8 16 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 Tm 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 Tc can’t be resolved Shahzad Malik Wireless Communications Lecture 8 17 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 Shahzad Malik Wireless Communications Lecture 8 18 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 Shahzad Malik Wireless Communications Lecture 8 19 Soft Handoff A unique feature of CDMA Mobile 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 Shahzad Malik Wireless Communications Lecture 8 20 Soft Handoff Architecture MSC R BSC BSC old link R BTS BTS R R- handoff request sent to the old cell Shahzad Malik Wireless Communications BTS BTS energy measurements are made at the mobile Lecture 8 21 Soft Handoff Gain Power (dBm) Cell A Cell B Total at MS Distance Shahzad Malik Wireless Communications Lecture 8 22 cdma2000 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 Shahzad Malik Wireless Communications Lecture 8 24 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 Shahzad Malik Wireless Communications Lecture 8 25 Third Generation (3G) Mobile Cellular Systems 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 Shahzad Malik Wireless Communications Lecture 8 27 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 Shahzad Malik Wireless Communications Lecture 8 28 Frequencies for IMT-2000 1850 1900 ITU allocation (WRC 1992) Europe China IMT-2000 GSM DE 1800 CT GSM 1800 Japan T D D 2000 1900 T D D IMT-2000 Wireless Communications MHz MSS MSS cdma2000 MSS W-CDMA MSS 2000 2200 UTRA MSS FDD cdma2000 MSS W-CDMA 1950 2100 2150 IMT-2000 MSS PCS 1850 2050 MSS UTRA MSS FDD IMT-2000 PHS North America Shahzad Malik 1950 rsv. 2050 2100 2150 MSS 2200 Lecture 8 MHz 29 IMT-2000 family Interface for Internetworking IMT-2000 Core Network ITU-T GSM (MAP) Shahzad Malik IP-Network Flexible assignment of Core Network and Radio Access Initial UMTS (R99 w/ FDD) IMT-2000 Radio Access ITU-R ANSI-41 (IS-634) IMT-DS IMT-TC IMT-MC IMT-SC IMT-FT (Direct Spread) (Time Code) (Multi Carrier) (Single Carrier) (Freq. Time) UTRA FDD (W-CDMA) 3GPP UTRA TDD (TD-CDMA); TD-SCDMA 3GPP cdma2000 UWC-136 (EDGE) UWCC/3GPP DECT Wireless Communications 3GPP2 Lecture 8 ETSI 30 UMTS services Data transmission service profiles Service Profile High Interactive MM High MM Bandwidth Transport mode 128 kbit/s Circuit switched 2 Mbit/s Packet switched Medium MM 384 kbit/s Circuit switched Switched Data 14.4 kbit/s Circuit switched Simple Messaging 14.4 kbit/s Packet switched Voice Bidirectional, video telephone Low coverage, max. 6 km/h asymmetrical, MM, downloads SMS successor, E-Mail 16 kbit/s Circuit switched 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 Shahzad Malik Wireless Communications Lecture 8 31 UMTS Architecture (Release 99) 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 Uu UE Shahzad Malik Iu UTRAN Wireless Communications CN Lecture 8 32 UMTS domains and interfaces Home Network Domain Zu Cu USIM Domain Mobile Equipment Domain Uu Access Network Domain Iu Yu Serving Network Domain Transit Network Domain Core Network Domain User Equipment Domain Infrastructure Domain 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 Shahzad Malik Wireless Communications Lecture 8 33 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 Shahzad Malik Wireless Communications Lecture 8 34 UTRAN architecture RNS RNC: Radio Network Controller RNS: Radio Network Subsystem UE1 Node B Iub Iu RNC CN UE2 Node B UE3 Iur Node B Iub Node B RNC Node B 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 RNS Shahzad Malik Wireless Communications Lecture 8 35 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 Shahzad Malik Wireless Communications Lecture 8 36 Core network The Core Network (CN) and thus the Interface Iu, 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) IuCS Packet Switched Domain (PSD) GPRS components (SGSN, GGSN) IuPS 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) Shahzad Malik Wireless Communications Lecture 8 37 Core network: architecture VLR BTS Abis BSS Iu BSC MSC GMSC PSTN Node BTSB IuCS AuC EIR HLR GR Node B Iub Node B RNC SGSN GGSN Gn Node B RNS Shahzad Malik Gi IuPS Wireless Communications CN Lecture 8 38 Core network: protocols VLR MSC GSM-CS backbone RNS GMSC PSTN/ ISDN GGSN PDN (X.25), Internet (IP) HLR RNS SGSN Layer 3: IP Layer 2: ATM Layer 1: PDH, SDH, SONET UTRAN Shahzad Malik GPRS backbone (IP) SS 7 CN Wireless Communications Lecture 8 39 UMTS protocol stacks (user plane) UE Uu UTRAN IuCS 3G MSC apps. & protocols Circuit switched RLC MAC RLC MAC radio radio UE Packet switched Shahzad Malik apps. & protocols IP, PPP, … PDCP Uu SAR SAR AAL2 AAL2 ATM ATM UTRAN IuPS 3G SGSN Gn IP tunnel 3G GGSN IP, PPP, … GTP RLC RLC GTP UDP/IP MAC MAC AAL5 AAL5 L2 L2 radio radio ATM ATM L1 L1 PDCP Wireless Communications GTP UDP/IP UDP/IP GTP UDP/IP Lecture 8 40 Support of mobility: macro diversity UE Node B Shahzad Malik Node B RNC CN Wireless Communications 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 Lecture 8 41 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 Iu at the SRNS Change of SRNS requires change of Iu Initiated by the SRNS Controlled by the RNC and CN Node B Iub UE CN SRNC Node B Iur Iu DRNC Iub Shahzad Malik Wireless Communications Lecture 8 42 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 data1 data2 data3 data4 data5 spr. code1 spr. code2 spr. code3 spr. code1 spr. code4 scrambling code1 sender1 Shahzad Malik Wireless Communications scrambling code2 sender2 Lecture 8 43 OSVF Coding OVSF - Orthogonal Variable Spreading Factor 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 X,X 1,1,-1,-1,-1,-1,1,1 1 X ... 1,1,-1,-1 1,-1,1,-1,1,-1,1,-1 X,-X ... 1,-1,1,-1 1,-1,1,-1,-1,1,-1,1 SF=n SF=2n 1,-1 1,-1,-1,1,1,-1,-1,1 ... 1,-1,-1,1 1,-1,-1,1,-1,1,1,-1 SF=1 SF=2 Shahzad Malik Wireless Communications SF=4 SF=8 Lecture 8 44 UMTS FDD frame structure W-CDMA Radio frame 10 ms 0 1 2 ... 12 13 14 Time slot 666.7 µs Pilot TFCI FBI TPC uplink DPCCH 2560 chips, 10 bits 666.7 µs uplink DPDCH Data 2560 chips, 10*2k bits (k = 0...6) 666.7 µs Data1 TPC TFCI Data2 Pilot DPDCH DPCCH DPDCH DPCCH 2560 chips, 10*2k bits (k = 0...7) Slot structure NOT for user separation but synchronisation for periodic functions! Shahzad Malik downlink DPCH 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 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 Wireless Communications Lecture 8 45 Typical UTRA-FDD uplink data rates User data rate [kbit/s] 12.2 (voice) 64 144 384 DPDCH [kbit/s] 60 240 480 960 DPCCH [kbit/s] 15 15 15 15 Spreading 64 16 8 4 Shahzad Malik Wireless Communications Lecture 8 46 UMTS TDD frame structure Radio frame 10 ms 666.7 µs 0 1 2 Time slot Data Midample 1104 chips 256 chips 2560 chips ... Data GP 1104 chips 12 13 14 Traffic burst GP: guard period 96 chips 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) Shahzad Malik Wireless Communications Lecture 8 47