Introduction to OFDM and GFDM Systems for 4G to 5G Transition
Explore the transition from 4G to 5G with an introduction to Orthogonal Frequency Division Multiplexing (OFDM) and Generalized Frequency Division Multiplexing (GFDM) systems. Understand the key advantages and disadvantages of OFDM, and learn how GFDM offers a solution with lower out-of-band radiation and improved synchronization, catering to the needs of IoT and machine-to-machine communications in the evolving network landscape.
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Presentation Transcript
From 4G to 5G: Intro to OFDM and GFDM System B03901048 EE3 Ching-Lun Tai 2017.4.28
Outline 4G: OFDM System Overview 5G: GFDM System Overview GFDM System: Properties GFDM System: Performance Figure credits: http://www.25pp.com/android/detail_273393/ https://fon.com/5g-future-of-wifi-network/
1. 4G: OFDM System Overview
OFDM System OrthogonalFrequency Division Multiplexing A kind of multicarrier system with orthogonality between subcarriers Figure Credit: http://www.wirelesscommunication.nl/reference/chaptr05/ofdm/ofdmmath.htm
Why 4G adopts OFDM? The orthogonality between subcarriers Low inter-symbol interference (ISI) More subcarriers can be used (save bandwidth) Easier equalization Figure Credit: http://www.2cm.com.tw/technologyshow_content.asp?sn=1403210010 http://s1.z9x9.com/archives/66613
But... There are several disadvantages about OFDM. 1. Sensitive to frequency shift The transmitter and receiver need strict frequency synchronization. Why does it take time to turn on the cellphone? Figure Credit: https://www.mobile01.com/topicdetail.php?f=566&t=4870296
But (cont.) There are several disadvantages about OFDM. 2. Large out-of-band (OOB) radiation Power leakage affects the user in the near band! Figure Credit: https://www.mathworks.com/help/comm/examples/ufmc-vs-ofdm-modulation.html http://health.takungpao.com.hk/illness/q/2015/0916/3167956_print.html
2. 5G: GFDM System Overview
GFDM System GeneralizedFrequency Division Multiplexing A kind of multicarrier system with circular pulse-shaping toward data The transmitter matrix is constructed with the prototype filter
GFDM System (cont.) Advantages over OFDM 1. Lower OOB radiation 2. Relaxation of frequency synchronization - Internet of things (IoT) - machine-to-machine communications (M2M) Figure Credit: http://www.huffingtonpost.com/sam-cohen/internet-of-things-as-the_b_10937956.html http://www.toy-people.com/?p=33819
Notations Wp: normalized p-point DFT matrix sincp(x): periodic sinc function
GFDM Transceiver Transceiver block diagram K subcarriers, and each subcarrier transmits M subsymbols total: D=KM symbols Data vector: dl(D X 1 vector) [dl]k+mK: mth subsymbol on kth subcarrier
GFDM Transceiver (cont.) Transmitter matrix A=[g0,0...gK-1,0g0,1...gK-1,1...gK-1,M-1] Prototype filterg=g0,0 constructor of A Frequency domain prototype filter Figure Credit: http://game.ettoday.net/article/552284.htm
GFDM System (cont.) Transmitted samples: xl=Adl - passed through a parallel-to-serial (P/S) converter - added a cyclic prefix (CP) of length L Digital baseband transmit signal D =D+L
GFDM System (cont.) Zero-forcing (ZF) Receiver c[n]: channel impulse response q[n]: complex AWGN with variance N0 Define C as a circulant matrix whose 1stcolumn is c[n] Estimated data vector: BZF=A-1C-1
Classic Prototype Filter OFDM(K=D, M=1) [g]l=1, l=0, 1, , D-1 Dirichlet pulse Raised-cosine [gf]l=0.5[1-cos(?lin (l/M))] lin (x)=min(1, max(0,(1+ )/2 +|x|/ ))
3. GFDM System: Properties
Matrix Characterization Characteristic matrixof A (K X M matrix) [reshape(g, K, M)]k,m=gk+mK Noise enhancement factor (NEF) NEF=1 minimized MSE for the ZF receiver under AWGN channel (EX. OFDM, Dirichlet pulse)
Power Spectral Density (PSD) Define a D/A converter - sampling interval: Ts - interpolation filter: p(t) Assumption -Data symbols are zero-mean and i.i.d. -L=0
4. GFDM System: Performance
Filter Optimization of Out-of-Band Radiation with Performance Constraint for GFDM Systems (P.-C. Chen and B. Su, 2017)
Intro Design a GFDM prototype filter with - NEF=1 - minimized OOB radiation Define S=vec(G)vec(G)H
Parameter Setting CP length: L=0 Symbol energy: Es=1 Sampling interval: Ts=1 s Subcarrier index Subsymbol index OOB frequencies
Iterative Algorithm Initialization: is a zero D X D matrix Iteration: Find the optimal point of with the optimal point of Termination: |si-si-1|/si < 5 X 10-5
Summary OFDM system has several drawback such as large OOB radiation. GFDM system performs better in terms of OOB radiation. SER performance of GFDM and OFDM can be the same.
Reference J. Bingham, Multicarrier modulation for data transmission: an idea whose time has come, IEEE Commun. Mag., vol. 28, no. 5, pp. 5 14, May 1990. G. Fettweis, M. Krondorf, and S. Bittner, GFDM -generalized frequency division multiplexing, in Veh. Technol. Conf., 2009. VTC Spring 2009. IEEE 69th, Apr. 2009, pp. 1 4. N.Michailow,M.Matth,I.Gaspar,A.Caldevilla,L.Mendes,A.Festag, and G. Fettweis, Generalized frequency division multiplexing for 5th generation cellular networks, IEEE Trans. Commun., vol. 62, no. 9, pp. 3045 3061, Sep. 2014. P.-C. Chen, B. Su, and Y. Huang, Matrix characterization for GFDM systems: Low-complexity MMSE receivers and optimal prototype filters, IEEE Trans. Signal Process., in revision. [Online]. Available: http://arxiv.org/abs/1611.04429v3 M. Matth e, N. Michailow, I. Gaspar, and G. Fettweis, Influence of pulse shaping on bit error rate performance and out of band radiation of generalized frequency division multiplexing, in Proc. IEEE ICC Workshop, 2014, pp. 43 48. S. Haykin, Communication Systems, 4th ed. Wiley Publishing, 2001.
