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

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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

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Objective

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

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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.

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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.

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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).

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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.

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Differences (1)
1. Downlink RF Channel Structure - while the DS
technique is used for both channel structures,
cdma2000 also uses multicarrier cdma technique.
The advs. are

• Achieves the same type of system performance that
  a conventional signal carrier would provide.
• Allows backward compatibility with IS-95.

Although DS is more spectrally efficient in the
vehicular environment than MS method, its only
slightly better or comparable in the pedestrian
and indoor environments.
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Differences (2)
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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.
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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)

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Differences (4)
5. Coherent detection - no common pilot for
downlink in WCDMA, common continuous and
auxiliary pilot channels for downlink in cdma2000.

• 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.

• Time and code muxed pilot symbols in the downlink
  and uplink, respectively.
• Primary and Secondary pilot channels .

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Differences (5)
6. Channel multiplexing in uplink and downlink

• Code muxed control, pilot, fundamental
  supplemental channels in both uplink and downlink.

• 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.

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Differences (6)
7. Spreading for both downlink and uplink

• Var. length Walsh seq. for channel separation
  andM-sequence 215 in downlink.
• Var. length orthogonal sequences, M-sequence 215
  and 241 for user separation.

• 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.

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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.

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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.

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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.

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THANKS !