Introduction to Hybrid Beamforming Techniques

Transcription

1 Introduction to ybrid Bemforming Techniques Jmes Chen Advisor : Andy Wu Grdute Institute of Electronics Engineering Ntionl Tiwn University Tipei, Tiwn Mr 3, 205

2 2 Outline Introduction of Precoding Why ybrid bemforming? Problem ormultion Existing ybrid Bemforming Technique Summry

3 Introduction of Precoding MIMO System Precoding mitigtes chnnel interference SVD is the optiml method but require higher bndwidth x Precoder V Trnsmit Antenns Receive Antenns Precoding SVD:=UΣV V Chnnel σ σ 4 eedbck link U Trnsmit Bemforming (Precoder Noise Decoder U SVD Trnsmit Antenns RX y Receive Antenns (from RX Receive Bemforming (Combiner = Equivlence Chnnel Reduce the interference mong ntenns Trnsmit Antenns Receive Antenns σ v u u 2 u 3 σ 2 σ 3 v 2 v 3 U Σ V 3

4 Why ybrid bemforming?(/2 In mmwve scenrio, the pthloss is extremely high[3] 30 Gz shows dditionl bout 20 db loss compred to 3 Gz igh pthloss cn be compensted by: Lrge ntenn rry to increse the rry gin Bemforming vi precoding Chnnel is rnk deficient Mximum supportble strems re less then the number of Tx ntenns MS 4

5 Why ybrid bemforming?(2/2 Trditionl Bemforming is done t Requiring one chin per trnsmitting ntenn A chin consists of mixer, PA/LNA nd DAC/ADC ybrid Bemforming relies on precoding to reduce the number of chins[2] Two-stged trnsmitting (, structure 5

6 6 Problem ormultion(/3 Step : The optiml solution of the precoding mtrix, opt,is given by: V opt V is eigenvectors corresponding to N s lrgest eigenvlues of V cn be cquired from performing SVD on Step 2: We further relize opt by hybrid precoder (, (, rg min, Number of chins cn be reduced opt Sptilly Sprse Precoding Bsebnd Precoder Tx Precoding for ybrid Bemformer V AoD SL- SVD CSI Acquisition MIMO Chnnel Bemformer W Bsebnd Equlizer W

7 Problem ormultion(2/3 Step : Get the optiml OPT The chnnel mtrix [3]: (ɵ l is the AOD of ctive pth : L MS MS * lms ( l ( l UV L l 2 2 j d sin( j N d l ( sin( l T ( [, e,, e ] l opt =V cn be formed by liner combintions of (ɵ l N N Tx Precoding for ybrid Bemformer (θ Sptilly Sprse Precoding V AoD SL- SVD CSI Acquisition (θ 2 e e j( N (θ 3 2 j d sin( 3 2 d sin( 3 MS Bsebnd Precoder MIMO Chnnel Bemformer W Bsebnd Equlizer W 7

8 Problem ormultion(3/3 Step 2: Seprte opt into(, ( Due to sptil sprsity, this is equivlent to solve n optimiztion problem Acn, rg min, Choose best Nrf columns to form, nd then ind opt B S T T T T [ (, ( 2, ( L,, ( L N t (θ (θ 2 ] Sptilly Sprse Precoding Bsebnd Precoder Tx Precoding for ybrid Bemformer V V AoD SL- SVD C N t N s CSI Acquisition MIMO Chnnel A cn C N L t Bemformer W Bsebnd Equlizer W ~ C LN s e e j( N 2 j d sin( 3 2 d sin( 3 (θ 3 M S Nt: Number of Tx ntenns Nrf: Number of chins L: Number of Active Pth Ns: Number of Tx dt strems 8

9 9 Existing ybrid Bemforming Technique (I (/2 [3] Use Orthogonl Mtching Pursuit(OMP to clculte (, Perform Nrf itertions of correltion to find Perform pseudo-inverse to fine V C N t N s A cn C N L t ~ C LN s Nt: Number of Tx ntenns Nrf: Number of chins L: Number of Active Pth Ns: Number of Tx dt strems

10 0 Existing ybrid Bemforming Technique (I (2/2 ybrid precoding shows ner optiml sptil efficiency while compred with trditionl bsebnd precoding Sptil efficiency: the dt rte tht cn be trnsmitted over given bndwidth (units: bit/s/z * * * * * ormul: R log ( I R W W W W 2 Ns n R R N s [3]

11 Problem : Imprcticl Cndidte Mtrix Impossible to get ll AOD s informtion Acn N t [ ( T, ( 2 T, ( L T,, Require lrge bndwidth to return ll AOD s informtion from Rx Need cndidte mtrix without the informtion of All AOD ( L T ] (θ V C N t N s A cn C N L t ~ C LN s (θ 2 (θ 3 e e j( N 2 j d sin( 3 2 d sin( 3 MS Nt: Number of Tx ntenns Nrf: Number of chins L: Number of Active Pth Ns: Number of Tx dt strems

12 Problem 2: igh Complexity Optimiztion Algorithm Long computtion time for finding (, OMP need Nrf itertions Need n fster lgorithm with less itertions Pseudo-inverse is not suitble for W implementtion Computtionl complexity:o(n 3 V Need n lgorithm without pseudo-inverse C N t N s A cn C N L t ~ C LN s Nt: Number of Tx ntenns Nrf: Number of chins L: Number of Active Pth Ns: Number of Tx dt strems 2

13 3 B S Existing ybrid Bemforming Technique (II (/3 or problem, DT codebook is used (θ (θ 2 Predefined set: Consist of orthogonl column vectors Don t require ll AOD s informtion Possibly find ll Nrf columns using only itertion Eqully spce 360 degree with Nt ngles to form full rnk mtrix ence Acn hs Nt columns V C N t N s A cn C N t N t ~ C N t N s (θ 3 e j( N e 2 j d sin( 3 2 d sin( 3 M S Acn: DT codebook Nt: Number of Tx ntenns Nrf: Number of chins Ns: Number of Tx dt strems

14 Existing ybrid Bemforming Technique (II (2/3 or problem 2, OBMP with DT codebook is used insted of OMP with Acn Constrints: Acn must be orthogonl Using itertion to find (, No pseudo-inverse V C N t N s A cn C N t N t ~ C Algorithm : Othogonlity-Bsed Mtching Pursuit Require : opt N t Ns : res = OPT * 2: Ψ = A cn res * 3: k = {n n is the lrgest N index of ( l, l} (k 4: = A cn * 5: = opt 6: = Ns opt - 7: return, 4

15 Existing ybrid Bemforming Technique (II (3/3 OBMP s computtion time for finding (, is less then tht of OMP by 896% when Nrf equls 8 896% 5

16 Summry Advntge of hybrid bemforming Reduce the number of chins but remin ner optiml performnce Design gol of hybrid bemforming (, rg min, Method for finding (, opt OMP[3] OBMP Number of itertion Nrf Complexity igh Low Constrints None Orthogonl Acn 6

17 7 Reference [] M Vu nd A Pulrj, MIMO wireless liner precoding, IEEE Signl Process Mg, vol 24, no 5, pp 86 05, Sept 2007 [2] Roh, W; Ji-Yun Seol; Jeongho Prk; Byunghwn Lee; Jekon Lee; Yungsoo Kim; Jeweon Cho; Kyungwhoon Cheun; Arynfr,, "Millimeter-wve bemforming s n enbling technology for 5G cellulr communictions: theoreticl fesibility nd prototype results," Communictions Mgzine, IEEE, vol52, no2, pp06,3, ebrury 204 [3] El Aych, O; Rjgopl, S; Abu-Surr, S; Zhouyue Pi; eth, RW, "Sptilly Sprse Precoding in Millimeter Wve MIMO Systems," Wireless Communictions, IEEE Trnsctions on, vol3, no3, pp499,53, Mrch 204 [4] D P Plomr, J M Cioffi, nd M A Lguns, Joint Tx-Rx bemforming design for multicrrier MIMO chnnels: unified frmework for convex optimiztion, IEEE Trns Signl Process, vol 5, no 9, pp , 2003