Importance of Physical layer • The most active technologies in wireless communication: RTT • Radio Transmission Technology is composed of 3 layer. In RTT, the basic technology is in Physical layer • Most of market, revenue of mobile equipments, is related to PL (hardware) • The main competition in standard is in RTT L3:RRC L2: RCL MAC PL RF TRx

Base band data processing in CDMA system TX data Multiplexing Channel coding Interleaving Data mapping Spreading Modulation RF Trx TX data Digital combination DAC TX data DAC Signaling PL Control Signaling De-multiplexing De-channel coding De-interleaving De-spreading Demod Rx power estimation Carrier Recovery Synch ADC RX data ADC RX data

Contents in Physical layer • Basic physical layer technologies • Channel mapping • Frame structure • Multiplexing and de-multiplexing • Channel coding and interleaving • Modulation: QPSK • Demodulation, including carrier recovery • Digital combination • Carrier frequency tracking • Power control • Specified PL technologies in TD-SCDMA • Smart antenna • Joint detection • Baton handover • Up-link synchronization • Cell search and Random access

Multiplexing and data mapping • Multiplexing: Service data +high layer signaling +physical layer control signal shall be combined into a common data sequence • De-multiplexing: Opposite procedure of multiplexing • Data mapping: With channel coding and interleaving, the data sequence shall be physical layer frame • Data mapping principle: multiple code or variable SF. • Multiple code: suitable for TD-SCDMA • Variable SF: for FDD signaling data Combine Interleaving Channel coding Rate mapping

Channel coding 10-1 10-2 10-3 10-4 Without coding R=1/2 coding R=1/3 coding • Feature of Channel coding: • Reduce required Eb/(N+I) • Can reach lower BER • Method of coding: • Convolution coding with Viterbe decoding, R=1/2 or 1/3 • Turbo coding • Problem to be solved: • Turbo coding with R=1/2 • Channel coding or ARQ 0 1 2 3 4 5 6 7 8dB Eb/(N+I) 10-0 10-3 10-6 10-9 Without coding With coding

Interleaving In mobile communication environment Fast fading: can not overcome by power control In serious fading period, demodulator could not work, BER will be 50% Interleaving will distribute these error bit to a longer period, then channel coding can take action Interleaving depth 10/20/40/80ms In these cases, BER will be 50%, any coding technology can not solve the problem.

Spreading and Modulation • Spreading code: Walsh code • Walsh code: a complete orthogonal series • Spreading gain=spreading factor (SF) • Based on information theory use bandwidth to higher sensitivity • Other spreading code, LAS code for example, is under studying • Modulation • Basic tech: QPSK • For high data rate for down link packet data, 8PSK, 16QAM, and 64QAM A: data B: spreading code C=A + B

PN code • Function of PN code • Separate cells with same carrier frequency • Flat spectrum in operation band: it is vary important for demodulation, it needs to less than 10dB max for QPSK; 5dB max for 16QAM; and 3dB max for 64QAM • FDD modes • Long code (period far large than SF) • TD-SCDMA • Now, same length as SF (16): to simplify JD algorithm • Lead to very serious amplitude variation in band • Bad performance for use same carrier frequency in adjacent cells • Task: to find efficient algorithm in acceptable complex for long code

Frame Structure Supper frame 720ms Radio frame 10ms 4s SYNC 5ms 8s SYNC1 g Sub-frame g DwPTS UpPTS TS0 TS1 TS2 TS3 TS4 TS5 TS6 G g L1 Data Midamble Data 144chips 864s/675us

General consideration • Why need sub-frame • One radio frame is 10ms, in 120kmph moving speed, the location change will be 0.34m=2λ(2GHz) • In smart antenna system, some algorithm ask high sensitivity of phase (location) • But too short sub-frame can not arrange enough TSs • Why 7 main TSs in a sub-frame • More TSs will be more flexible for asymmetric services • Size of one TS shall capable of supporting a voice channel (8kbps with R=1/2 coding) Up-link beamforming with co-phase of two rays Same down-link beamforming may lead phase opposite Location change

General consideration Total 675us/864 symbols • Why use of midamble and the length of it? • Training sequence, for • QPSK modulation • JD • Up-link synchronization • Different with user and cell • Length of midamble? • Longer is better for JD • Shorter is good for higher efficiency Midamble of 144chips It can overcome delay spreading of 25us Service data area, total 704 chips. It can provide 44 symbols (SF=16) or 17.6kbps data rate in QPSK Guard period of 16 chips for switching point and to avoid overlap because of Multi-path with long delay

Physical layer signaling Total 675us/864chips • L1 signaling field • PC: 2 symbols • SC: 2 symbols • TFCI: 6 symbols • For multiple code services, L1 signaling will be in the first code in one slot • High layer signaling • Multiplexing into data sequence Service data area, total 44 symbols. Take off 10 symbols for L1 signalling, It can provide 13.6kbps data rate in QPSK 2 code can provide 31.2kbps; 4 code can provide 66.4kbps; 8 code can provide 136.8kbps; 16 code can provide 277.6kbps;

Special Time slots • DwPTS: total 75us, 96 chips • 8 bits code, total 32 codes • 32c guard period to separate with TS0 • UpPTS: total 125us, 160 chips • 16 bits code, total 128 codes • 32c guard period to separate with TS1 • G • total 75us, 96 chips, max cell size G TS1 TS0 32c 64c 128c 32c

Power Control • Importance of PC in TD-SCDMA and in FDD is different. In TDD mode, it is more difficulty than FDD if the same control method is used • Open loop: Path loss=Pt-Pr Pt(UE) = EIRP(NB)- Pr(UE) + Preq • In TDD mode, the path loss for UL is the same of DL • In access procedure, UE can get NB’s EIRP in DwPTS/BCCH/average each code ch , and the required receiving power level for the service (10-3 or 10-6) • The initial Pt for UE should be very accuracy • Error will come from power level measurement only, with in 3dB is possible

Power Control (II) • Close loop • As NB received UL signal from UE, it will estimate the power level and Eb/I0, and then send PC in physical layer to control Pt of UE • In worst cases, One UE use higher power will lead to increase power level of other active UE: cocktail party effect. So an outer loop shall be used to limit the level in FDD system • Outer loop • In FDD, power control shall be very complex and critical, so outer loop may a very complex procedure (algorithm) • In TD-SCDMA, outer loop has a function of setting power level of the NB only. Open loop is a more accurate measure. So we can do not use it • General scenario • In FDD system, the rms PC error is 2 to 3dB, which is in the same level of power measurement error • PC can overcome slow fading than fast fading • Conclusion • PC is importance but we can use of open loop to reach good results

Synchronization Control • For a synchronous CDMA system, TD-SCDMA uses both open loop and close loop to guarantee • Open loop for sync establish • In random access and received a paging by UE, UE has to estimate the distance between NB and UE by received power level, or because the cell size could not too big (usually less then 2 to 3km), UE can take half cell radius as initial value is reasonable (max error will be 5us). UE uses the estimated timing to send UpPTS, and the NB can get the UL timing error from the UpPTS, then enter close loop. • Close loop • NB measure the arriving time of UpPTS from the UE, and correct the Tx timing by using of SC in physical layer • NB measures the arriving time of midambles from each active UE, and correct the Tx timing by using of SC in physical layer

Open loop application • To use the advantage of same propagation performance in DL and UL for TD-SCDMA • UE can easily get DL synchronization from DwPTS with higher accuracy than NB gets UL sync from midamble (much less interferences) • After UL sync is reached, UE measured the DwPTS arrive at t, later on, it change to t’=t+5msxN+Δt, the UL timing shall change -2Δt to keep UL sync. • This open loop procedure can be used to check sync error an be used in handover. Δt t t’

Turn-on Procedure • When an UE turn-on, what will happen? • Set Rx frequency in the receive band • When signal is find, record one frame length data • Try to find DwPTS, get down-link sync • Read Tx0 (BCCH), then goes to standby status • If any failure, back to try again Possible location of DwPTS 5ms

The most difficulty scenario • UE located at an location covered by multiple Node_Bs which operated by different operators • All Node_B should synchronous • The DwPTS will close together • UE shall be capable to separate DwPTS from different Node_B • UTRA TDD system can not to find Node_B in much simple scenario • This is the importance of DwPTS in frame design Other operator

How to fasten search procedure • 3GPP asked to search each frequency in 200KHz step • The turn-on procedure should be completed in 3 minutes • In core TDD band (1880-1920, and 2010-2025MHz), there are 55MHz, it means 275 frequency point • In worst case, it no any possibility to search so many frequency • In roaming, especial international roaming, it will take more time. • How solve the problem? • No general solution • In China, may we can search the fixed frequency location only (3 points than 25 points in each 5MHz bandwidth).

General scenario • Handover, a basic feature • Hard handover, loss data • Soft handover, basic IPR of Qualcomm • May we find a way to overcome shortage of soft handover but get its advantage • TD-SCDMA has the possibility of UE location • Easy of synchronization • No more down-link capacity

Procedure of Baton handover Target NB UE Node_B RNC • UE will always measure DwPTS from adjacent cell, record list and report to system • Find target NB, its DwPTS level higher than that in original cell • Get sync to target NB • Open loop sync with target NB • Send HO requirement to system • System makes decision and sends handover signaling • Two NB send the same data at the TS and code(s), UE can receive data from any NB • NB switch to target NB, handover is completed. • Same procedure can be used in DAC Measurement report Find target NB for handover Report Initial sync Sync with target NB Open loop sync HO requirement Handover approval Down-link data from 2 NBs Switch to target NB

Continue Part D: Physical Layer Tech. in TD-SCDMA • Smart antenna • Joint detection • SA + JD • Other anti-multipath technologies

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