TD-SCDMA History, Current Standard, and Future Directions.

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