On the Adaptivity in Down- and Upink MC- Systems Ivan Cosovic German Aerospace Center (DLR) Institute of Comm. and Navigation Oberpfaffenhofen, Germany Stefan Kaiser DoCoMo Euro-Labs Wireess Soution Laboratory Munich, Germany IEEE Communication Theory Workshop 2005 Park City, USA, June 15, 2005 Introduction Adaptivity in MC- Concept of Adaptivity in Upink MC- Concept of Adaptivity in Downink MC- Concusions 2
Adaptivity in MC- SNR MAI MC- transmitter channe MC- receiver 3 Adaptivity in MC- MC- transmitter channe MC- receiver 4
Adaptivity in MC- MC- transmitter channe MC- receiver 5 Adaptivity in MC- MC- transmitter channe MC- receiver Adapt transmission signa to : 1) Eiminate MAI Zero-forcing (ZF) 2) Maimize SNR Maimum ratio transmission (MRT) 3) Trade-off between ZF and MRT MMSE 6
Adaptivity in MC- MC- transmitter channe MC- receiver 7 Adaptivity in MC- MC- transmitter channe MC- receiver at T and R more degrees of freedom Mobie station - ow compeity Base station - higher compeity 8
Adaptivity in Upink MC- Avaiabe Ony at T Input/output reation: K r = k = 1 G c d w ( k ) ( k ) ( k ) ( k ) ( ) pre T channe R Pre-equaization Technique Coefficients ZF (eiminates MAI) G ( k ) pre, = ( k ) ( k ) 2 W MRT (maimizes SNR) G ( k ) pre, = ( k ) W MMSE (trade-off between ZF and MRT) G ( k ) pre, = K L ( k ) 1 ( k ) 2 2 n W σ 9 Adaptivity in Upink MC- Avaiabe at T and R Concept of combined-equaization equaization Aim at maimizing SNR at T and suppressing MAI at R New improved MC- singe-user bounds Cosey approached even in a fuy-oaded system T channe R Compeity Low compeity at T one-tap pre-equaization igher compeity at R non-inear parae interference canceation (PIC) Optimization agorithm Cosed form soution not avaiabe in a muti-user case A simpe and effective approach; A singe optimization parameter - parameter p of the generaized pre-equaization equaization used to trade SNR and MAI G ( k ) pre, = ( k ) p ( k ) Contros power distribution over subcarriers W 10
Adaptivity in Upink MC- Avaiabe at T and R 10 0 10-1 AWGN channe MF bound, L=16 (state of the art) Uncoded system QPSK Uncorreated Rayeigh Spreading ength L=16 Singe-user Idea BER 10-2 10-3 P MF L L = 1 1 γ L 1 1 γ 2 = 0 2 γ = Et N0 L E N t 0 10-4 0 2 4 6 8 10 12 MF matched fiter SNR in db 11 Combined-Equaization Frequency Domain Singe-User Transmission System T c 1 G pre,1 1 n1 G post,1 c 1 R c 2 G pre,2 G post,2 channe 2 n2 c 2 d dˆ c L G pre,l L n L G post,l c L G post, = f ( Gpre, ) 12
Combined-Equaization Seection Diversity (SD) Combined-Equaization T c 1 0 channe 1 n1 0 c 1 R d c L c L n 1 Best propagation conditions 0 L n L 0 c c L dˆ 13 Adaptivity in Upink MC- Avaiabe at T and R BER 10 0 10-1 10-2 10-3 AWGN channe MF bound, L=16 (state of the art) Uncoded system QPSK Uncorreated Rayeigh Spreading ength L=16 Singe-user Idea SD bound, L=16 (new MC- bounds) L L = 1 1 γ L 1 1 γ PMF 2 = 0 2 γ = Et N0 L E N t 0 10-4 4.5 db 0 2 4 6 8 10 12 SNR in db P SD L = 1 L L 1 ( 1) Et N0 1 2 = 0 1 1 Et N0 SD seection diversity MF matched fiter 14
Combined-Equaization Drawback of seection diversity: Not suitabe for the muti-user user case Requirements: Appropriate for appication in muti-user user upink MC- Capabe to cosey approach seection diversity bound Preferaby feibe Soution: Generaized pre-equaization equaization (G-pre pre-eq) 15 Combined-Equaization in Muti-User MC- As p grows singe-user bounds are better, but more MAI is induced Optimization probem reduced to determination of parameter p 10 0 10-1 10-2 SNR = 1.5 db, G-pre-eq PIC (1 iter.) SNR = 0.0 db, G-pre-eq PIC (3 iter.) SNR = 0.0 db, G-pre-eq PIC (5 iter.) Convo. coded system (R=1/2) QPSK Uncorreated Rayeigh Spreading ength L=16 Number of active users K=16 Idea BER 10-3 10-4 10-5 10-6 0 1 2 3 4 5 6 7 8 9 p 16
Concept of Adaptivity in Upink MC- Numerica Resuts 10 0 10-1 Convo. coded R=1/2 QPSK Uncoreated Rayeigh Spreading ength L=16 Number of active users K=16 Idea BER 10-2 10-3 10-4 10-5 pre-eq ma SINR, pre-eq ony PIC (3 iter.), post-eq ony MF bound, L=16 AWGN channe G-pre-eq (p=3) PIC (3 iter.) G-pre-eq-MRC bound, L=16, p=3 SD comb-eq bound, L=16-8 -7-6 -5-4 -3-2 -1 0 1 2 3 4 5 6 SNR in db 4 db Pre-eq ony ( at T) Post-eq ony ( at R no adaptivity) Comb-eq ( at T and R) 17 Concept of Adaptivity in Downink MC- Avaiabe Ony at T Input/output reation: z = F Ud w Fading & despreading F = ( 1) (1) ( K ) ( K ) ( ) c K ( ) c ) Pre-equaization (& spreading) T channe R Pre-equaization Technique ZF (eiminates MAI) Pre-equaization matri ( ) 1 W U = F F F MRT (maimizes SNR) U = FW MMSE (trade-off between ZF and MRT) 2 1 ( F σ ) W U = F F I n 18
Adaptivity in Downink MC- Avaiabe Ony at T Non-inear interference pre-canceation: z = F Ub w F = RQ R QR-decomposition; ower trianguar; unitary matri Q T channe R ( QQ = I) U = Q b = d R 1 ( R R) b R diagona matri - contains diagona eements of R 1 z = RQQ R Rd w = Rd w MAI is competey eiminated 19 Adaptivity in Downink MC- Avaiabe at T and R Compeity igher compeity at T non-inear interference pre-canceation Low compeity at R one-tap post-equaization, i.e., singe-user detection (SUD) T channe R Optimization agorithm Cosed form soution is given by a compicated iterative procedure Simpe and effective approach Pre-equaization equaization is performed assuming that a certain SUD is empoyed at the receiver pre-equaization, SUD & despreading SUD U = f (F) F = ( 1) (1) ( K ) ( K ) ( ) g K ( ) g ) k ) g = f ( ( ( k ) ) 20
Adaptivity in Downink MC- Numerica Resuts 10 0 10-1 Uncoded system QPSK Uncoreated Rayeigh Spreading ength L=16 Number of active users K=16 Idea Bit Error Rate 10-2 10-3 10-4 S&G S&M MMSE detection non-inear precoding PD non-inear precoding MRC non-inear precoding EGC AWGN 10-5 0 2 4 6 8 10 12 14 16 SNR in db 21 Concusions Combined equaization can propery be designed for upink and downink, aowing ow compeity termina stations and higher compeity base stations. Optimization based on generaized pre-equaization equaization. Simuation resuts show that in muti-user scenarios combined equaization significanty outperforms systems with ony pre- or post- equaization. Prerequisite is to have channe knowedge avaiabe at the transmitter and the receiver. 22
5th Internationa Muti-Carrier Spread Spectrum Workshop (MC-SS 2005) September 14-16, 2005 Oberpfaffenhofen, Germany www.mcss2005.org 23