A Comparison Study of 3G System Proposals: cdma2000 vs. WCDMA

1. A Comparison Study of 3G System Proposals: cdma2000 vs. WCDMA Emre A. Yavuz and Dr. Victor C. M. Leung University of British Colombia Vancouver, BC

2. Objective • To discuss the similarities and the differences between the two radio interface proposals, ARIB/ETSI’s WCDMA and TIA’s cdma2000, for future mobile multimedia communications (IMT-2000) by comparing the technical features of each proposal.

3. Agenda • The motives behind the efforts to increase capacity and the data rates, the standardization efforts of ITU and other bodies. • The similarities between the two proposals. • The differences that are affecting the performance of the systems. • The main issues in detail to find out the benefits or the drawbacks that those issues bring to each proposal.

4. Motives • To extend 2nd generation capabilities (voice and low/medium rate data) to introduce multimedia and new supported services such as support for high bit rates and introduction of packet data/IP access into mobile communications. • To find standards and recommendations to develop a mobile communication network with a service quality similar to fixed network.

5. Similarities (1) • Coherent downlink and uplink. • Fast power control on downlink as well as uplink. • Variable length orthogonal Walsh sequences for downlink and uplink channelization in order to separate users. • Variable spreading factor to achieve higher rates and to support blind rate estimation for simple services (e.g. voice).

6. Similarities (2) • Turbo codes for higher data rates. • Convolutional codes used as baseline. • Complex QPSK spreading on downlink. • Soft handoff and mobile assisted inter-frequency hard handoff procedures.

7. Differences (1) • Achieves the same type of system performance that a conventional signal carrier would provide. • Allows backward compatibility with IS-95. 1. Downlink RF Channel Structure - while the DS technique is used for both channel structures, cdma2000 also uses multicarrier cdma technique. The advs. are: Although DS is more spectrally efficient in the vehicular environment than MS method, it’s only slightly better or comparable in the pedestrian and indoor environments.

8. Service Environment Spectrum Efficiency (RL/FL) (users/MHz/cell) for voice (Mbps/MHz/cell) for data Multicarrier (MC) Direct Spread (DS) Voice 9.6 kbps 1% FER Vehicular 29 / 28.2 29 / 45.1 Pedestrian 42.1 / 45.8 43.2 / 45.3 Indoor 38.9 / 32.5 34.7 / 33.6 Mixed 34.1 / 34.6 35.7 / 46.1 Packet Data 76.8 kbps 10% FER Vehicular 0.176 / 0.094 0.209 / 0.138 Pedestrian 0.253 / 0.099 0.264 / 0.111 Indoor 0.218 / 0.064 0.226 / 0.070 Differences (2)

9. Differences (3) 2. Chip Rates - Rates of 3.84 Mbps and 3.6864 Mbps are assigned for WCDMA and cdma2000, respectively. 3. Power control - both systems have similar open and fast closed loops other than the rates they are using: 1.6 kHz for WCDMA vs. 800 Hz in cdma2000.

10. Differences (4) 4. Frame lengths - 10ms/20ms (opt.) for WCDMA, 20ms for data and control / 5ms for control information on control channels for cdma2000. • 5 & 10ms frame lengths are appropriate for cont. messages and low-delay data applications. • End-to-end delay is less for 10ms, but it reduces time diversity and increases SNR requirement. • 20ms based frame length is considered as the basis for voice and data applications and provides better overhead percentage. (11% as opposed to 20%)

11. Time and code muxed pilot symbols in the downlink and uplink, respectively. Primary and Secondary pilot channels . Downlink (F-PICH) & common auxiliary pilot (F-CAPICH) channels. Additional channels; downlink dedicated aux. (F-DAICH), transmit (F-TDPICH) and aux. transmit diversity pilot(F-ATDPICH) channels. Differences (4) 5. Coherent detection - no common pilot for downlink in WCDMA, common continuous and auxiliary pilot channels for downlink in cdma2000.

12. Combined IQ and code mux. solution (dual channel QPSK) in uplink to avoid EMC problems with DTX. Time muxed dedicated channels (DPDCH and DPCCH) in the downlink. Code muxed control, pilot, fundamental & supplemental channels in both uplink and downlink. Differences (5) 6. Channel multiplexing in uplink and downlink

13. Var. length orthogonal sequence for ch. separation and Gold seq. 218 for cell and user separation in downlink. Var. length orthogonal sequence and Gold sequences 241 for user separation. Var. length Walsh seq. for channel separation andM-sequence 215 in downlink. Var. length orthogonal sequences, M-sequence 215 and 241 for user separation. Differences (6) 7. Spreading for both downlink and uplink

14. Differences (7) 8. Base station synchronization - Asynchronous and synchronous base stations are used synchronously in WCDMA and cdma2000, respectively. • quick in acquisition and neighbor detection. • Suits better for battery saving techniques. • permit the operation of common overhead and signaling channels into soft handoff. • requires highly stable timing references. • needs higher complexity. • performance issues for hard, inter-frequency handoff.

15. Differences (8) • Sync. channels - two subchannels for WCDMA limits the search of long codes to a subset of all the codes. • Broadcasting channels - the frame structure for cdma2000 reduces battery consumption. • Paging channels - cdma2000 has a quick paging channel for informing mobiles to listen to the paging. • Others in downlink - DPCCH and DPDCH to F-DCCH and F-FCH, channels that can not be corresponded to each other, PDSCH, F-PCCH, F-CACH. • Others in uplink - DPDCH to R-FCH and R-SCH, DPCCH to R-PICH and RDCCH etc.

16. Overview and Conclusion • The motives and the standardization efforts of ITU and other bodies. • The similarities between the proposals. • The differences that are affecting the performance. • The main issues in detail to find out the benefits or the drawbacks that those issues bring to each proposal.

17. THANKS !