Cdma2000 Radio Access Network

1. 1 cdma2000 Radio Access Network Salih Ergut 7/7/2003 Salih Ergut is a full-time employee at Ericsson Wireless Communication Inc. (San Diego, CA) and pursuing his PhD part-time at ECE Department of UCSD. E-mails: Salih.Ergut@Ericsson.com sergut@ucsd.edu Salih Ergut is a full-time employee at Ericsson Wireless Communication Inc. (San Diego, CA) and pursuing his PhD part-time at ECE Department of UCSD. E-mails: Salih.Ergut@Ericsson.com sergut@ucsd.edu

2. 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. 3 Network Architecture A CDMA Network architecture consists of the following components: Mobile station Radio Base Station (RBS) Base Station Controller (BSC) Mobile Switching Center (MSC) Public Switch Telephone Network PDSN as an IP Gateway A CDMA Network architecture consists of the following components: Mobile station Radio Base Station (RBS) Base Station Controller (BSC) Mobile Switching Center (MSC) Public Switch Telephone Network PDSN as an IP Gateway

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

5. 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 offsetLong-code state Paging channel data rate In addition following information is also conveyed in synch channel message: Local time offset Daylight saving indicator In addition following information is also conveyed in synch channel message: Local time offset Daylight saving indicator

6. 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

7. 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.

8. 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. 9 Mobile Station States Initialization: Acquire pilot channel of the selected CDMA system within 20 secs (not standardized) Process synch channel for synchronization (long code and CDMA timing) Idle: Monitor paging channel for overhead and mobile directed messages Move to access state to originate a call or respond to a page request Access: MS sends messages to the base station and gets responses in the paging channel This can be a call origination or a page response Traffic: MS communicates with the base station using forward and reverse traffic channels Paging and access channels are no longer monitored Alert with info is used for order messageInitialization: Acquire pilot channel of the selected CDMA system within 20 secs (not standardized) Process synch channel for synchronization (long code and CDMA timing) Idle: Monitor paging channel for overhead and mobile directed messages Move to access state to originate a call or respond to a page request Access: MS sends messages to the base station and gets responses in the paging channel This can be a call origination or a page response Traffic: MS communicates with the base station using forward and reverse traffic channels Paging and access channels are no longer monitored Alert with info is used for order message

10. 10 Mobile Originated Voice Call Flow

11. 11 CDMA Evolution (1/3) IS-95A (2G) First CDMA protocol, published in May’99 14.4/9.6 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 In IS-95B, 64 kbps packet data is achieved by combining code channels In IS-95B, 64 kbps packet data is achieved by combining code channels

12. 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. 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 RTT : Radio Transmission Technology. An RTT reflects the combination of technical design choices and concepts allowing for the provision of a radio subsystem (air interface) to the telecommunication system. RTT : Radio Transmission Technology. An RTT reflects the combination of technical design choices and concepts allowing for the provision of a radio subsystem (air interface) to the telecommunication system.

14. 14 Multiple Access Methods

15. 15 Frequency Re-use Patterns FDMA and TDMA vs. CDMA

16. 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. 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 A Walsh codes is orthogonal to all different length Walsh codes which do not share the same root If a short Walsh function is assigned to a high data rate user descendants of that long Walsh code cannot be used A Walsh codes is orthogonal to all different length Walsh codes which do not share the same root If a short Walsh function is assigned to a high data rate user descendants of that long Walsh code cannot be used

18. 18 A Code Channel Example Forward Traffic Channel Generation Encoder is always convolutional encoder for voice. However supplemental channel can use Turbo codes for a better performance. Turbo codes results in a higher delay measure.Encoder is always convolutional encoder for voice. However supplemental channel can use Turbo codes for a better performance. Turbo codes results in a higher delay measure.

19. 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 Length of PN offset is 2^15 Length of PN offset is 2^15

20. 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. 21 Near – Far Problem a user near the base station would jam the user far from the base station

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

23. 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. 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. 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. 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. 27 Handoff Parameters (2/2) Pilot Strength = Ec / IoPilot Strength = Ec / Io

28. 28 Soft Handoff

29. 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. 30 Soft Handoff Gain

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

32. 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. 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. 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

35. 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. 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. 37 Summary 2/2 Higher data rates: 1x up to 153.6 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 Increased Battery LifeCDMA2000 significantly enhances battery performance. Benefits include: Quick paging channel operation Improved reverse link performance New common channel structure and operation Reverse link gated transmission New MAC states for efficient and ubiquitous idle time operation Increased Battery LifeCDMA2000 significantly enhances battery performance. Benefits include: Quick paging channel operation Improved reverse link performance New common channel structure and operation Reverse link gated transmission New MAC states for efficient and ubiquitous idle time operation