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TD-SCDMA Principle and Development Dr. Shihe Li e-mail: lish@pub
TD-SCDMA Principle and Development Dr. Shihe Li Datang MobileCo
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Contents Back ground Principle of TD-SCDMA Developing Conclusion
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History of Mobile Communication
Early period: from early 50’s: Military application Without system concept Analog voice and signaling Single BS operation Concept of cellular in 70’s Cellular concept Frequency Reuse The 1 G: Analog system in 80’s Different standard in each country The 2G: Digital system in 90’s GSM/CDMA(IS-95) Universal standard Duplex is 1G/2G: FDD Cellular Concept
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Mobile Network ___1st generation
OAM BS PSTN Mobile SW HS or MS
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Mobile Network ___2nd generation
OAM ACU BS PSTN Mobile SW With data HS or MS PDN BSC
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Mobile Network ___3rd generation
OAM ACU Node_B PSTN Mobile SW Circuit and Packet UE PDN RNC Internet
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CN and Radio Access Network: Radio Access:
Slow progress, from 1G to 3G, circuit switch take the same technology Need longer period to stable Low revenue and high profit (3% of market in mobile, but high margin) Radio Access: Fast change technologies Key issue in mobile system and user terminals Main part in equipment market, mobile communications IMT-2000 asked proposal for RTT 3 main stream standards are 3 different Radio Transmission Technology
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Basic Requirement for RTT
Contents of Physical layer Multiple access technology Duplexing Frame structure Data multiplexing Modulation Channel coding/Interleaving Signal detection Antenna technologies Random access Cell search Handover Other key technologies Q&S BER requirement for different service in different environment Spectrum efficiency Quantities of services provided in unit bandwidth Complexity – cost E&M compatibility Interference to other system Reject interference from other systems
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One Generation per 10 years
Widely application Standard 4G? Product Development R/D 3G(CDMA) 2G(TDMA) 1G (FDMA)
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What is Multiplex means
Multiple users share a same frequency band Possible way for multiple access Frequency Division Multiple Access (FDMA) Separating user by different carrier frequency Most popular way to be used in all mobile system Time Division Multiple Access (TDMA) Separating user by different time slot in same carrier frequency Common used in digital system Code Division Multiple Access (CDMA) Separating user by different code in same time and carrier frequency Wide adopted in 3G technology Space Division Multiple Access (SDMA) Separating user by different location (direction) in same time, code, and carrier frequency Future technology based on smart antenna
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Frequency Plan Both FDMA and TDMA need frequency plan__Interference in adjacent carrier Frequency re-use factor FDMA: same carrier shall be separated by two cells: re-use factor = 11 TDMA: same carrier shall be separated by one cells: re-use factor = 7 CDMA: Adjacent cell can use same carrier, re-use factor = 1
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Spectrum Efficiency for voice services in 1/2G systems
1G FDMA(TACS) 2 x 25kHz for 1 voice ch., frequency re-use factor=11 Spectrum efficiency=1/0.05/11=1.8ch/cell/MHz 2G TDMA(GSM) 2 x 200kHz for 8 voice ch., frequency re-use factor=7 Spectrum efficiency=8/0.4/7=2.8ch/cell/MHz 2G CDMA(IS-95) 2 x 1.25MHz for 20 voice ch., frequency re-use factor=1 Spectrum efficiency=20/2.5/1=8ch/cell/MHz Theoretically, if all code can be used, the spectrum efficiency may reach 64/2.5/1=25.8ch/cell/MHz, which is nearly 14 times of FDMA and 8 times of TDMA.
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Basic CDMA concept Spectrum Spreading is a technology used in military communication since 60’s Basic concept Spreading code: Walsh code, it is an orthogonal code when synchronized CDMA is a self-interference system: Multiplex interference: between code channels Multi-path and Doppler Interference from other system and users in adjacent cell Near-far effect Capacity of a CDMA system is limited by total interference level
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Basic CDMA IS-95 concept IS-95 is a FDD CDMA system
Operated in AMPS frequency band (taking BW of 41 AMPS carriers) Chiprate Mcps Carrier separation 1.23MHz Channel code and interleaving Spreading factor: 64 Studying in late 80’ for public mobile communication, the mainly contributions by Qualcomm are as follows Two sets of code: short code (Walsh) for distinguish user in the cell and long code (PN code) for distinguish cell Strict up-link power control: to overcome near-far effect Receiver: Rake receiver to overcome multi-path Macro-diversity and soft-handover: to enhance capacity and handover without interrupt (suitable for data transmission) Variable rate voice coder to enhance capacity
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Capacity in CDMA system: General situation
Basic consumption: Ideal power control, received power level from each active UE is the same: Eb User distribution: uniform When N users are active, then the interference from the same cell will be (N-1)Eb. The total interference from the adjacent cells (1st and 2nd layers) will be the same as that from the same cell. required Eb/N0≤lg(SF)+Eb/(N0+2*(N-1)Eb)~ lg(SF)-lg(2N) N≤(10lg(SF)-Eb/N0)/2 Reduce interference
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Technologies related to capacity
Macro diversity UE get down-link from 2 to 3 BSs Each BS may transmit less power, less interference to enhance down-link capacity about 2 dB Power control Power control error: usually 2 to 3 dB Because of fast fading and multi-path Capacity loss: 2dB
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The possible way to improve CDMA system
Variable code rate (by Qualcom in IS-95) Based on voice performance, reduce coding rate. May double capacity (half interference) for CDMA Key IPR for Qualcom Useless in Data service Smart Antenna (by TD-SCDMA) Most efficient tech Capacity enhance by N times (N is the number of antenna elements)
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Basic concept of Duplex
Fdown Fup Duplex: communication between UE and BS simultaneously Traditional tech: divided by frequency: FDD Time Division Duplex (TDD) is from data communication From end of 80’s, TDD started to use in voice communication (CT2, DECT, etc.) From 3G, TDD become one duplex in RTT t Down link data Up link data TSdown TSup t
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Comparison between FDD & TDD
Items FDD TDD Transmission Ppeak/ave Continuous, low Burst, high Receiving sensitivity high (BW=datarate) low (BW>datarate) Comm distance in same Pmax Long Short Number of carrier f 2, down and up separation by frequency 1, down and up separation by time Wave propagation in down- and up-link different Same at the same time Need duplexer in transceiver Yes in UE Two antennas in BS None in UE One antenna in BS Asymmetric data Some spectrum resource may not be used All spectrum resource can be used
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Main Feature in TDD Duplex
Spectrum flexibility: do not need paired frequency Same carrier frequency in both Down- and Up-link, symmetric propagation performance suitable for smart antenna, pre-Rake, open loop power control and other technologies Support asymmetric data services, by adjusting different numbers of slots in up- and/or down-link It may use of different bandwidth for asymmetric services in FDD, but it could not be flexible Low cost: Do not ask high isolation between Tx and Rx path, one may design single IC for RF transceiver in UE
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Main Shortage for TDD t Higher peak/average tx power ratio for UE
FDD: continuous transmit TDD: only one TS work, the extra ratio will be 10lgM, M is the number of TS Higher requirement for transmitter and PA. Lower sensitivity for receiver Bandwidth: the total chiprate Data rate: limited by number of TS Sensitivity loss: 10lgM. Discontinue operation Less communication distance, half nearly Difficult for high speed moving. t
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How to overcome the shortages?
The shortage of TDD leads to: TDD can only be used in Micro- and Pico-cell TDD can only support slow moving Possible way to overcome the shortages Smart antenna: increase sensitivity and EPRI Smart antenna plus Joint detection: improve performance in fast fading (multi-path in high speed moving)
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Wave Propagation Loss ITU Model Indoor: L= 30lgd + 54.35 (n=1)
Loos (dB) 100 110 120 130 140 150 160 170 180 Pedestrian Vehicular 2GHz 900MHz ITU Model Indoor: L= 30lgd (n=1) 30lgd (n=2) 30lgd (n=3) dB where n is the number of floors d is the distance in meter Pedestrian: L=40lgd +30lgf + 49 =40lgd + 148dB Vehicular: L= 40( h)lgd- 18lgh +21lgf +80 =35.2lgd+122.7dB where f is frequency in MHz (2GHz); h is the hight of BS antenna over average roof level in meter(30m); d is the distance in kilometer. D= k 3k 10km
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Radio Resource f code t
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Capacity in CDMA system: General situation
Basic consumption: Ideal power control, received power level from each active UE is the same: Eb User distribution: uniform When N users are active, then the interference from the same cell will be (N-1)Eb. The total interference from the adjacent cells (1st and 2nd layers) will be the same as that from the same cell. Itotal = 2(N-1)Eb>>N0, N0is thermal noise Required Eb/(Itotal +N0)≈ Eb/(Itotal ) ≤lg(SF)-lg(2N) N≤(10lg(SF)-Eb/ (Itotal + N0))/2 For QPSK modulation and R=1/3 coding, Required Eb/(Itotal +N0)≈ 3.1dB(0.3) for BER of 1x10-3 Or N≈SF/4
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Capacity in CDMA system: General situation
Basic consumption: Ideal power control, received power level from each active UE is the same: Eb User distribution: uniform When N users are active, then the interference from the same cell will be (N-1)Eb. The total interference from the adjacent cells (1st and 2nd layers) will be the same as that from the same cell. If the antenna of BS with beamformed pattern, then only a part of interference will be inter demodulator. Eb/N0≤lg(SF)+Eb/(N0+(2*(N-1)Eb)/m)~ lg(SF)-lg(2N/m) N≤m(10lg(SF)-Eb/N0)/2 m means coverage anger/beam width
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Basic concept of Smart Antenna
When the main incident ray from a user k has an incident anger of , then the received signal at the i-th element will be alejl , l means the l-th ray Then the total received signal will be wi(ejdicos alejl ) Separate it by code Find receiving weight W Get DOA Combine received signal (up-link beamforming Down-link beamforming di
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Features of Smart Antenna
Increase receiving sensitivity Increase EIRP Reduce Interference Increase Capacity of system Reduce cost of BS Increase reliability of BS
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Up-link synchronization
Establish of synchronization Open loop estimate the distance to BS. Send UpPTS Find error Adjustment Tx timing Maintenance of synchronization Close loop Open loop
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Features of synchronous CDMA
In multi-path condition, ideal synchronization can not be reached One can do is synch for the main ray, and takes the other ray as interference or noise The main feature is to sync all up-link signals in the same time slot, simplify data procession
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Basic concept of SR Antenna and Feed cable Multi- band and multi-standard in mobile communication Each standard ask different equipment design Compose of a radio equipment: Antenna and cable: wideband RF transceiver: different bandwidth BB digital signal processor Ctrl and I/O: switch and MCU The most active technology: in BB DSP Software radio (SR): by using SW in general DSP/FPGA to replace ASICs Advantages of SR: Save developing time and cost, reduce risk Easy to up-grade of technology, upgrade SW only Suitable for using new technologies RF sub-system BB digital signal processing Ctrl and interface
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Key point in SR design BB DSP complexity: technologies to be used (Rack receiver or Joint detection?) Present capacity of DSP/FPGS: For BS, the most powerful DSP is less than 1000MIPS, and FPGA is about 200gates For UE, DSP will be 3/400MIPS only (power consumption limitation) Sampling rate and accuracy: Single antenna or multiple antenna Bandwidth (chip-rate) This is why TD-SCDMA takes 1/3 of chip-rate for WCDMA Algorithm to be developed Suitable for DSP or FPGA? Complexity and accuracy? Low cost consideration: have to lower than developing and using ASIC
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Why do not use Soft-handover
Points to considering Advantage of Soft-handover All code channel is used for services, have no more DL channel for macro-diversity Overcome shortages of Soft handover Do not need macro-diversity for capacity Difficult to use two receivers for macro diversity Possibility Smart antenna for UE location Synchronous CDMA RNC
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Baton Handover Measurement: Find target BS:
DwPTS only List strength of measured pilot and report to BS until one reaches HO threshold Find target BS: Send UpPTS Enter close loop synch with the target BS Record new timing for UL synch with the target BS Open-loop synch with target BS Find the change of DL timing of target BS Renew UL timing Excuse HO System decision DL transmission by two BS Switch to target BS Excuse measurement
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Narrow Bandwidth Flexible for allocation Suitable for software radio
Especial for private network Suitable for software radio Smart antanna Joint detection Synchronous CDMA Future development: wide-band TD-SCDMA for different applications 5MHz MHz 1.6MHz
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Single carrier frequency
Wave Propagation Fading; Multi-path; Doppler; etc. Wave Propagation depends on frequency, environment, time, and etc. In mobile communication, it is varied. In TDD, up-link and down-link takes the same carrier frequency, the wave propagation performance will be nearly the same if the TDD period is short enough. Advantages of one carrier frequency: BS can get the up-link propagation from the received signal from one user Then BS can assume down-link has the same performance as up-link, and some technologies are easy to use such as Beamforming for smart antenna Pre-rack receiver For UE, the open-loop power control will has much higher accuracy
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Highest spectrum efficiency
Spectrum efficiency is one of most important issue in 3G TD-SCDMA can use all code channel, reaches wolsh limitation. For data services, TD-SCDMA can provide 3x16 pairs of symmetric channels When voice coding is 12.2kbps, 3GPP asks to provide one voice channel by using of 2 code channels, the spectrum efficiency is 3x8/1.6=15/MHz/cell When voice coding is 8kbps, the spectrum efficiency is 3x16/1.6=30/MHz/cell For WCDMA, (3 for 12.2kbps and 6 for 8kbps coding rate) its spreading efficient is the lowest one in 3G standards. For data services, the calculation and definition is varied, but TD-SCDMA is always the highest one. The spectrum efficiency will double when smart antenna is used in FDD modes
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All environment In traditional understanding, TDD can only use in micro- or pico-cell environment TD-SCDMA has overcome the shortage in TDD mode, by using of smart antenna technology, it can be used in all environment system Sensitivity Max comm. distance Operation level Max cell radius WCDMA -117dBm(voice) -99dBm(384kbps) 3.7km 2.1km -111dBm(Voice) -93dBm(384kbps) 2.5km 1.4km TD-SCDMA -113dBm(Voice) -110dBm(384kbps) 4.5km 3.8/5.9 km -107dBm(Voice) -104dBm(384kbps) 3.0km 2.6/4km
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Low cost solution Cost for 3G equipment Smart antenna reduce cost
CN/RNC/UE will be nearly the same for each standard Cost for Node_B is varied with technology Smart antenna reduce cost ACU and etc. will be the same cost The most expensive part is linear power amplifier Smart antenna can use a group small PA to replace the expensive HPA Now BS for IS-95 and WCDMA is much expensive than GSM, but we’ll provide BS with lower price than GSM.
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Contents Back ground Principle of TD-SCDMA Development Conclusion
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Development Face to next generation : Beyond 3G or 4G IP network
TDD, narrow and wide band TDD, 1.6MHz to 5MHz to 10/20MHz of band width Smart antenna, much efficient algorithm/FDD application/Smart antenna for UE Software Defined Radio Hardware platform/System structure/Algorithm High speed package data transmission Higher modulation scheme Other coding technologies IP network
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Products From standard to commercial products TD-SCDMA products team
Core Network: Siemens; Putian; ZTE; Huawei; etc Radio Access Network RNC: Datang Mobile; UT starcom; Huawei; etc Node_B: Siemens; Putian; Datang Mobile; etc UE Chipset: Commit; T3G; etc UE: many companies TD-SCDMA Industrial Alliance
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Development: system 2004 Products for large scope commercial trial
2003 Field Trial Commercial products development System integration test Node_B tester 2004 Products for large scope commercial trial 2001 First call between FTMS And Node_B 2000 Field Trial MS 2002 Demo TD-SCDMA System integration test Field trial 1999 Coop with Siemens Node_B based on GSM network
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Development: Chipset for UE
End 2003: first chipset Mid 2004: Multiple UE providers ready 2003 T3G (TDM/Philips/Sumsong) 2002 Commit (TDM/Putian/TI/ Dbtel/Nokia/LG/etc) 2003 Other companies: RTX National Semiconductor Spreadtrum ……….. 02-03 ST Micro 2000- DTM Field trial MS
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Conclusion TD-SCDMA RTT is now accepted by more and more people
Strong supported by government 155MHz spectrum TD-SCDMA Industrial Alliance Key project in 10th 5 year plan In 2003, standard will become products In 2004, Commercial trial After 2005, world wide application
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Thanks
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