TD-SCDMA
History, Current Standard, and
Future Directions
History of TD-SCDMA
Qualcomm Dominated IP in 3G
Ownership of Declared IPR in 3GPP2
(IS-95/CDMA2000)
Ownership of Declared IPR in 3GPP
(GSM/GPRS/EDGE/WCMDA/UMTS)
Source: “3G Cellular Standards and Patents”, David J. Goodman and Robert A. Meyers
Qualcomm charges licensees an estimated ~4.6% to 6% of HS ASP
~$500M / quarter from licensing, ~35% of it’s revenue
32% of lic rev from WCDMA and growing (up from 12% 1 yr. ago)
Unique position with IPR, strong chipset biz, and other key ingredients
China’s Perspective
Massive rapidly growing captive market ~ 1 billion customers
Source: TDSCIA
• Previously languishing telecom industry
– Looking to jump start
• Wanted to limit payments for “Western IP”
(read as Qualcomm)
TD-SCDMA History
An Early Projected TD-SCDMA Timeline
Roll-out Has Not Gone As Expected
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Was going to roll out in 2004
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Then 2005
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http://news.zdnet.com/2110-1035_22-6207356.html
Delays make Chinese state-owned service providers unhappy
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http://www.theage.com.au/news/Technology/China-Mobile-to-launch-3G-mobile-servicesend2007/2007/02/12/1171128898337.html
Now will reportedly issues licenses in 2008
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http://www.accessmylibrary.com/premium/0286/0286-9623636.html
Then 2007
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http://www.chinadaily.com.cn/english/doc/2004-06/23/content_341749.htm
Then 2006
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http://www.commsdesign.com/news/market_news/OEG20030102S0009
Grumblings about forgoing TD-SCDMA from ChinaMobile (1 of 3 to get licenses)
http://www.forbes.com/markets/feeds/afx/2006/01/31/afx2489964.html
However, China has made it a point of national pride to have the network running for
the 2008 Olympics
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http://www.highbeam.com/doc/1G1-150687033.html
Is already being tested in 10 cities (includes the Olympic cities) but nationwide licenses may
not even be issued by the Olympics
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http://www.thestandard.com.hk/news_detail.asp?pp_cat=1&art_id=54099&sid=15557306&con_type=1
Some of The Problems
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Government interference
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http://www.telecom.globalsources.com/gsol/I/Mobile-wireless/a/9000000090209.htm
Mandating
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WCDMA and cdma2000 and WiMAX’s big lead and broader deployment base has moved them
further down cost/unit curves
Feature creep while keeping up with 3GPP releases
Global roaming now impractical
Local roaming not that good either
Limited range (though claimed coverage up to 40 km)
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Trying to develop as much IP as possible “in-house” but industry was previously virtually
nonexistent
Relative lack of incentives for experienced players to help along the process as contracts
are preferentially given to state companies
Compounding effects
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Very slow to license
Always problems moving from laboratory to field
Lack of expertise
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Licensees provide wireline service as well
Base-station site-sharing arrangements as well as Radio Access Network (RAN) and core-network sharing
Tight timing requirements limits coverage
Requires more base stations, increases costs for widescale deployment
Developed a bad reputation
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http://homepage.mac.com/dwbmbeijing/iblog/SiHu/C520534961/E20060302210839/index.html
Unnamed China Mobile engineer – “you GIVE me a TD-SCDMA network, and I wouldn't take it."
Other Interesting TD-SCDMA
Factoids
• Selected # of Papers on IEEE Explore (9/29/07)
– TD-SCDMA
135
• That’s 15 papers/yr dating back to 1999
– WCDMA 2100
– cdma2000 558
– 802.11 = 4741
• Claims that TDIA holds 70% of IP
– http://www.tdscdma-alliance.org/english/news/list.asp?id=4420
• Disputed by Qualcomm (and others) due to dependence
on WCDMA network
– http://www.theregister.co.uk/2006/02/15/china_3g_royalties/
– Actually a significant trade issue between China and the US
Overview of TD-SCDMA
Standard and Key Algorithms
TD-SCDMA Standard Overview
• Part of 3GPP Family and officially
designated as 3G
• Very similar to WCDMA
TD-SCDMA Characteristics
http://www.tdscdmaforum.org/EN/pdfword/200511817463050335.pdf
– Sometimes referred to as “low chip
rate version of UMTS-TDD”, e.g.,
Yuhong Wang
• Designated as a National Standard
in China
• Available for download
– http://www.tdscdmaforum.org/EN/resources/detail.asp?l
=3
• Key technologies
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TDMA/CDMA
OVSF codes
Multiuser detection
Antenna Arrays
Dynamic Channel Assignment
L. Huang, K. Zheng, X. Wang, G. Decarreau, “Timing Performance
Analysis in an Open Software Radio System,” ChinaCom06, pp. 1-5
Relative Complexity
Comparison to Other 3G Standards
B. Li, D. Xie, S.Cheng, J. Chen, P. Zhang, W.Zhu, B. Li; “Recent advances on TD-SCDMA in
China,” IEEE Comm. Mag, vol 43, pp 30-37, Jan 2005
TDMA/CDMA/FDMA
• TD-SCDMA permits adaptation of time,
code, and frequency (for 1.6 MHz
bandwidth)
• Permits exploitation of multi-user diversity
– Varying conditions and requirements by user
B. Li, D. Xie, S.Cheng, J. Chen, P. Zhang,
W.Zhu, B. Li; “Recent advances on TDSCDMA in China,” IEEE Comm. Mag, vol 43,
pp 30-37, Jan 2005
TDMA Structure
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5 ms frames (technically called
“sub-frames”)
7 time slots
Timeslot assignment to uplink and
downlink function of traffic
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symmetric used during telephone
and video calls (multimedia
applications), where the same
amount of data is transmitted in
both directions, the time slots are
split equally between the downlink
and uplink.
asymmetric services used with
Internet access (download), where
high data volumes are transmitted
from the base station to the
terminal, more time slots are used
for the downlink than the uplink.
Each time slot contains a midamble
of 144 chips used as a pilot
sequence and a guard period (16
chips) to simplify timing
requirements
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Unique midamble per user
OVSF Codes
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A hierarchical set of Walsh codes
Codes across branches are
orthogonal
Codes down from a node are not
orthogonal
Users can be assigned different
rates by picking different
spreading factors
TD-SCDMA uses up to SF=16
– 1,2,4,8,16
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Multipath and timing variances
can significantly damage
orthogonality
Interference will arrive from
adjacent cells
Thus in a practical TD-SCDMA
system, MUD techniques still need
to be employed
• Common issue with MUD is
sudden power level changes in
urban areas as users move into
and out of LOS conditions
– Large power level change
• TD-SCDMA gets large change in
power levels + loss of timing
synch
Synchronization Impact
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Uniform distribution of timing error
Relatively small impact if kept within
a chip (781 ns)
92% of capacity under worse case
Can be problems with high-speed
mobility
W. Zizhou, L. Jinpei, W. Peng, Y. Dacheng, “Uplink
Performance Analysis for TD-SCDMA System,” WiCOM2006,
Sept 06, pp. 1-4.
Joint Detection (MUD)
Uplink
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Because of multipath, timing issues, and
inter-cell interference, received signals
cannot be demodulated interference free
Multi-user techniques frequently used
In general, this allows higher CDMA loading
factors (not unique to TD-SCDMA)
Greatly aided by unique training sequence
for each user (midamble)
Typically used techniques
– Zero Forcing Block Linear Equalizer (BLE)
– Minimum Mean Square Error BLE
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Downlink
In general, MMSE-BLE is better, but ZFBLE is lower complexity
Very close on uplink
MMSE-BLE performance is dependent on
quality of noise power estimation
S. Kang, Z. Qiu, S. Li, “Comparison of ZF-BLE
and MMSE-BLE in TD-SCDMA system,”
ICII2001, vol 2, pp 297-302.
Antenna Arrays
• Smart antennas are a
commonly cited feature of TDSCDMA
– Shorter codes reported to be
especially good for TD-SCDMA
• Standard might not even be
feasible without smart antennas
• Brief study
– 4 users
– Average 2 chip timing error
– Arrays
• No array
• Switched beam (9 beams)
• LMS Smart Antenna
– Unstable
• Software radio technique that
combines the two based on
SINR
X. Ze-ming, “Software antenna using algorithm diversity in TD-SCDMA,”
Antennas and Propagation Society International Symposium 2006, pp.
2529 - 2532
Dynamic Channel Assignment
Downlink
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Implements both fast (intra-cell) and
slow (inter-cell) DCA
Time Domain DCA (TDMA
operation)
– Traffic is dynamically allocated to
the least interfered timeslots.
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Frequency Domain DCA (FDMA
operation)
– Traffic is dynamically allocated to
the least interfered radio carrier (3
available 1.6 MHz radio carriers in
5MHz band).
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Uplink
Space Domain DCA (SDMA
operation)
– Adaptive smart antennas select the
most favorable directional decoupling on a per-users basis.
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Code Domain DCA (CDMA
operation)
– Traffic is dynamically allocated to
the least interfered codes (16 codes
per timeslot per radio carrier).
C.Rui; C. Yong-yu, Y. Da-cheng, “Research on Fast DCA
Algorithms in TD-SCDMA Systems,”WiCOM06, pp. 1-4.
Spectral Efficiency Under Different
Operating Conditions
TD-SCDMA Spectrum
• Minimum frequency band required:
– 5MHz (3.84 Mcps)
– 1.6MHz with 1.28 Mcps
• Frequency re-use: 1
K. Zheng, L. Huang, W. Wang, G. Yang,
“TD-CDM-OFDM: Evolution of TD-SCDMA
toward 4G,” IEEE Comm Mag, Vol 43,
Issue 1 pp. 45-52, Jan 2005.
Other Benefits of TD-SCDMA
• Idle timeslots allow mobiles when non actively receiving or
transmitting to perform measurements of the radio link quality of the
neighboring base stations.
– This results in reduced search times for handover searching (both intraand inter-frequency searching), which produces a significant
improvement in standby time.
• No soft handoff
– Allows service provider to claw back some spectrum lost to softhandoffs
– Uses a procedure called “baton handoff”, a hard handoff variation which
permits handoffs across base stations and across carriers
• Does require very precise location information
• No cell-breathing
– Capacity not a function of power as multiple access drawn from predefined code sets and time slots
– Should make site planning much easier
– Should make network management easier
– Should make call reliability better
TD-SCDMA Evolution
TD-SCDMA Evolution Path
• 3GPP
LCR TDD
（R4）
LTE TDD
LCR TDD
（R5）
LCR TDD
(R6)
LCR TDD
(R7)
• CCSA
N Frequency
Bands Cell
MC-CDMA
TDD
OFDMA
TDD
SC-FDMA
/OFDMA TDD
TD-SCDMA
Stage III
（R6/R7）
TD-SCDMA
Stage II
（R5）
TD-SCDMA
Stage I
（R4 2003/03）
TD-SOFDMA
Multi-carrier
Current status
Short Term Evolution
2005
ZTE Corporation, “3GPP Specification Evolution”
2007
Long Term Evolution
Projected Data Rates and Key
Technologies
G. Liu, J. Zhang, P. Zhang, “The vision on future TDSCDMA,” ConTEL05, vol 1, pp. 83-90.
Short Term Evolution for TDSCDMA
• Hybrid ARQ
• RRM Problems:
– Handover (synch to two systems on single frequency)
– Cell search
• Multiple frequencies per cell
– Simplifies multiple synch
– Permits Multi-carrier HSPA
• Add Multimedia Broadcast and Multicast Services (MBMS)
• Higher Order Modulation (16, 64-QAM)
• Adaptive Modulation
MBMS example
Longer Term Evolution
TD-CDM-OFDM Proposal
• Want to preserve TDD
features
• OFDMA, MIMO
• Want to support hot
spots and wide-area
networks
• Backwards compatible?
K. Zheng, L. Huang, W. Wang, G. Yang, “TD-CDMOFDM: Evolution of TD-SCDMA toward 4G,” IEEE
Comm Mag, Vol 43, Issue 1 pp. 45-52, Jan 2005.
Downlink Rates
TD-SCDMA Summary
TD-SCDMA Summary
• Similar to WCDMA
• Synchronous Time-slotted CDMA
– Asymmetric UL/DL TDD
• Significant opportunities to exploit multi-user
diversity
• Short term evolution will adopt 3GPP advances
• Evolving to exploit OFDM and MIMO long term
• Significantly delayed roll-out
– Nationwide may miss the Olympics, though fall back
to just test systems is viable
TD-SCDMA Links
• Standard
– http://www.tdscdmaforum.org/EN/resources/detail.asp?l=3
• TD-SCDMA Forum
– http://www.tdscdma-forum.org/
• TD-SCDMA Industry Alliance
– http://www.tdscdmaalliance.org/english/index.asp