1 cdma2000 Radio Access Network Salih Ergut 7/7/2003

2 Outline cdma2000 network architecture Call processing states and call flows CDMA evolution Essential elements in a CDMA system Power Control Mobility management Handoffs Registration Roaming Radio Admission Control

3 Network Architecture Ericsson Black Mountain UCSD MSC BSC PSTN Packet Network PDSN

4 Call Processing - Pilot First MS monitors Pilot channel for Initial acquisition Channel estimation Detection of multipaths for rake receiver Handoffs Pilot Ch

5 Call Processing - Sync Pilot channel is transmitted at all times by the base station. MS uses it to lock to Synch Channel to Synchronize to CDMA system time Obtain configuration parameters such as Protocol Revision (P-REV) Network Identifier (NID) Pilot PN offset Long-code state Paging channel data rate Sync Ch

6 Call Processing - Paging MS decodes the Paging Channel with the information received from the Sync Channel. Paging channel provides Overhead messages: systems parameter, access parameter, neighborlist, channel list Mobile directed messages: page request, SMS Paging Ch

7 Call Processing – Access MS uses Access channel to originate a call or to respond to a page request. Access Channel is used in a random access fashion. Access Ch

8 Call Processing - Traffic Base station assigns a forward and reverse traffic channel to the mobile when it is in conversation Traffic Channel conveys signaling and traffic information When MS is on traffic channel it no longer listens to paging channel or uses the access channel

9 Mobile Station States Power Up Initialization State Access State Traffic State Synchronization Paging Loss Call origination or page response Page response completed End of call Idle State

10 Mobile Originated Voice Call Flow MS BSC MSC Paging Ch. Rev Traffic Ch. Paging Ch. Fwd Traffic Ch. Paging Ch. Access Ch. Fwd Traffic Ch. Rev Traffic Ch. Fwd Traffic Ch. Assignment Complete Overhead Info BS Ack Order Origination Msg Null Frames Channel Assign Msg Preamble BS Ack Order MS Ack Order Service Connect CM Service Request SCCP Connection Cfm Assignment Request Service Conn Cmplt Rev Traffic Ch.

11 CDMA Evolution (1/3) IS-95A (2G) First CDMA protocol, published in May’ /9.6 kbps circuit/packet data IS-95B (2.5G) Most analog information is removed Some technical corrections New Capabilities, such as higher data rate 64 kbps packet data

12 CDMA Evolution (2/3) CDMA2000 1X High speed data (144 kbps packet data with Mobile IP) Coding (Turbo) and Modulation (Hybrid QPSK) New dedicated and common channels Enhanced Power Control Reverse link detection Forward link modulation

13 CDMA Evolution (3/3) 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

14 Multiple Access Methods Dedicated band during entire call Certain frequency, time-slotted Each user transmits at the same time, at the same frequency with a unique code

15 Frequency Re-use Patterns FDMA and TDMAvs.CDMA A A A A A AA A A A A A A D C G B EF E G F B A

16 Channelization Channelization is provided by orthogonal Walsh codes cdma2000 uses variable length Walsh codes for supplemental channel data services Walsh codes can be of length 8, 16, 32, 64, and 128

17 Walsh Codes Walsh codes are orthogonal to each other The shorter the code the higher the data rate since the chip rate is kept constant

18 A Code Channel Example Forward Traffic Channel Generation Encoder and Repetition Block Interleaver Long Code PN Generator Decimator MUX Decimator Power Control bit Wt Mcps 19.2 ksps 800 Hz Mcps

19 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

20 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

21 Near – Far Problem a user near the base station would jam the user far from the base station

22 Power Control – Motivation Overcomes near-far problem CDMA wouldn’t work without it Copes with path loss and fading

23 Power Control – Algorithm Capacity is maximized By having each user transmitting just sufficient SNR to maintain a target FER 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.

24 Mobility management A CDMA system provides mobility: Handoff – continuity of the service across adjacent cells Registration – locating the mobile user Roaming – continuity of the service across different service providers

25 Handoff 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 There are 4 types of handoffs: Idle Handoff Access Handoff Soft/Softer Handoff Hard Handoff

26 Handoff Parameters (1/2) If a pilot strength (P) is greater than T_ADD it will be added into the candidate set If pilot strength is less than T_DROP for T_TDROP, it will be moved from active set to neighbor set If the new pilot strength is T_COMP units greater current pilots a Pilot Strength Measurement Message will be send

27 Handoff Parameters (2/2) T_DROP T_ADD Pilot Strength Time T_TDROP Cell B Cell A

28 Soft Handoff Ericsson Black Mountain UCSD MSC BSC PDSN Both cells have the same frequency

29 Soft Handoff Make-before-break Both cells are at the same 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

30 Soft Handoff Gain Power (dBm) Distance Cell A Cell B Total at MS

31 Hard Handoff Break-before-make Handoff between different frequencies, non- synchronized or disjoint cells which are controlled by different BSCs

32 Registration It is sufficient to know the cell or the region that a MS is active for routing purposes Mobile station identifier, desired paging slot cycle, and registration type is conveyed Cell/LAC based paging is preferred to flood paging

33 Registration Types Autonomous Registration: power-up, power- down, timer-based, distance-based, zone- based registration. Parameter-change registration Ordered registration Implicit registration Traffic channel registration

34 Roaming Users that are outside their home area can receive service from another system by paying some additional charges Mobile station can be: Home state (not roaming) Network roaming System roaming Network 1 Network 2 Network 3 System

35 Radio Admission Control 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

36 Summary (1/2) 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

37 Summary 2/2 Higher data rates: 1x up to kbps and 1x EV-DV up to 3.09 Mbps Battery life is improved Introduction of Turbo codes provides better link quality for supplemental channels