Post on 26-Mar-2015
TD-SCDMA
History, Current Standard, and Future Directions
History of TD-SCDMA
Qualcomm Dominated IP in 3GOwnership of Declared IPR in 3GPP (GSM/GPRS/EDGE/WCMDA/UMTS)
Ownership of Declared IPR in 3GPP2 (IS-95/CDMA2000)
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
• Previously languishing telecom industry– Looking to jump start
• Wanted to limit payments for “Western IP” (read as Qualcomm)
Massive rapidly growing captive market ~ 1 billion customers
Source: TDSCIA
TD-SCDMA History
An Early Projected TD-SCDMA Timeline
Roll-out Has Not Gone As Expected
• Was going to roll out in 2004– http://www.commsdesign.com/news/market_news/OEG20030102S0009
• Then 2005– http://www.chinadaily.com.cn/english/doc/2004-06/23/content_341749.htm
• Then 2006– http://www.accessmylibrary.com/premium/0286/0286-9623636.html
• Then 2007– http://www.theage.com.au/news/Technology/China-Mobile-to-launch-3G-mobile-services-en
d2007/2007/02/12/1171128898337.html
• Now will reportedly issues licenses in 2008– http://news.zdnet.com/2110-1035_22-6207356.html
• Delays make Chinese state-owned service providers unhappy– 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
– 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• http://www.thestandard.com.hk/news_detail.asp?pp_cat=1&art_id=54099&sid=15557306&con_type=
1
Some of The Problems• Government interference
– http://www.telecom.globalsources.com/gsol/I/Mobile-wireless/a/9000000090209.htm– Mandating
• Licensees provide wireline service as well• Base-station site-sharing arrangements as well as Radio Access Network (RAN) and core-network sharing
– Very slow to license • Always problems moving from laboratory to field• Lack of expertise
– 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– 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)– Tight timing requirements limits coverage– Requires more base stations, increases costs for widescale deployment
• Developed a bad reputation– 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
– 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.tdscdma-forum.org/EN/
resources/detail.asp?l=3• Key technologies
– TDMA/CDMA– OVSF codes– Multiuser detection– Antenna Arrays– Dynamic Channel Assignment
http://www.tdscdma-forum.org/EN/pdfword/200511817463050335.pdf
TD-SCDMA Characteristics
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 TD-SCDMA in China,” IEEE Comm. Mag, vol 43, pp 30-37, Jan 2005
TDMA Structure• 5 ms frames (technically called
“sub-frames”)• 7 time slots• Timeslot assignment to uplink and
downlink function of traffic– 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
– Unique midamble per user
OVSF Codes• 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
• 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• 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)
• 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
• In general, MMSE-BLE is better, but ZF-BLE is lower complexity
• Very close on uplink• MMSE-BLE performance is dependent on
quality of noise power estimation
Uplink
Downlink
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 TD-SCDMA– 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• Implements both fast (intra-cell) and
slow (inter-cell) DCA• Time Domain DCA (TDMA operation)
– Traffic is dynamically allocated to the least interfered timeslots.
• 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).
• Space Domain DCA (SDMA operation)
– Adaptive smart antennas select the most favorable directional de-coupling on a per-users basis.
• 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.
Downlink
Uplink
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 intra-
and inter-frequency searching), which produces a significant improvement in standby time.
• No soft handoff – Allows service provider to claw back some spectrum lost to soft-
handoffs– 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 pre-
defined code sets and time slots– Should make site planning much easier– Should make network management easier– Should make call reliability better
TD-SCDMA Evolution
• 3GPP
LCR TDD( R4)
LCR TDD( R5)
LCR TDD(R6)
• CCSA
Multi-carrier
TD-SCDMA Stage I
( R4 2003/03)
N Frequency Bands Cell
TD-SCDMAStage II( R5) TD-SOFDMA
MC-CDMA TDD
TD-SCDMAStage III
( R6/R7)
Current status Short Term Evolution Long Term Evolution
OFDMA TDD
SC-FDMA /OFDMA TDD
LTE TDD
LCR TDD(R7)
2005 2007
ZTE Corporation, “3GPP Specification Evolution”
TD-SCDMA Evolution Path
Projected Data Rates and Key Technologies
G. Liu, J. Zhang, P. Zhang, “The vision on future TD-SCDMA,” ConTEL05, vol 1, pp. 83-90.
Short Term Evolution for TD-SCDMA
• 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
• 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-CDM-OFDM: Evolution of TD-SCDMA toward 4G,” IEEE Comm Mag, Vol 43, Issue 1 pp. 45-52, Jan 2005.
TD-CDM-OFDM Proposal
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.tdscdma-forum.org/EN/resources/
detail.asp?l=3
• TD-SCDMA Forum– http://www.tdscdma-forum.org/
• TD-SCDMA Industry Alliance– http://www.tdscdma-alliance.org/english/
index.asp