Mansor, Z. B., Nix, A. R., & McGeehan, J. P. (2011). PAPR reduction for single carrier FDMA LTE systems using frequency domain spectral shaping. In Proceedings of the 12th Annual Postgraduate Symposium on the Convergence of Telecommunications, Networking and Broadcasting, School of Computing and Mathematical Sciences, Liverpool John Moores University, 2011. Liverpool John Moores University, School of Computing and Mathematical Sciences. Link to publication record in Explore Bristol Research PDF-document University of Bristol - Explore Bristol Research General rights This document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms
PAPR Reduction for Single Carrier FDMA LTE Systems using Frequency Domain Spectral Shaping Zuhanis Mansor, Prof. Andrew Nix and Prof. Joe McGeehan Centre for Communications Research
2 Presentation Outline 3GPP LTE uplink transmission Single-Carrier Frequency Division Multiple Access (SC-FDMA). PAPR comparison of SC-FDMA with distributed and localized subcarrier mapping schemes. Investigate the impact of PAPR through frequency domain spectral shaping with localized sub-carrier mapping.
Introduction Generations of Mobile Networks 1G, 2G, 3G 4G (are currently in development around the world) Mobile phone plays an important roles business or social networking smartphone Limitations network coverage, capacity... Battery life a key parameter that affects all mobile handsets. Even though the battery technology is improving To ensure that mobiles phone use as little energy as possible 3
4G- Wireless & Mobile Technology 4 Wired communication 1G (Analog) 2G (Digital) 3G (W-CDMA) Orthogonal frequency- division multiplexing (OFDM) PAPR??? OFDMA SC-FDMA
5 3GPP LTE (Long-Term Evolution) Scalable Transmission Bandwidth (MHz) 1.4, 3, 5, 10, 15 & 20 Adaptive Modulation QPSK, 16QAM & 64QAM Duplexing FDD and TDD Multiplexing SC-FDMA Scalable Transmission Bandwidth (MHz) 1.4, 3, 5, 10, 15 & 20 Adaptive Modulation QPSK, 16QAM & 64QAM Duplexing FDD and TDD Multiplexing OFDMA
6 SC-FDMA vs OFDMA SC-FDMA OFDMA Data symbols occupy M*15 khz for 1/M SC-FDMA symbol periods Data symbols occupy 15 khz for one OFDMA symbol period shows how a sequence of eight QPSK symbols is presented in frequency and time domain
7 SC-FDMA Transmitter System M s Symbols Serial to Parallel ( ) F 1 x 1 M X ( 1 ) S S ( 1 ) F ( ) m m m N s 1 n M- point FFT Subcarrier Mapping N- point IFFT Parallel to Serial T CP CP Insertion ( ) r 1 CP User 1 User 2 User Q FFT{ x m } X ( k ) 1 m M M 1 n 0 x m e 2 j nm M
PAPR and Power Amplifier Constraints 8 Peak-to-average power ratio (PAPR) problems occur in broadband communications causing power amplifier distortion issues. It also results in received errors as well as reducing power efficiency and battery life. Amplifiers must be specifically designed to cope with this problem, and this increases their cost.
9 PAPR Peak-to-average-power ratio (PAPR) is a performance measurement to indicate the power efficiency of the transmitter. Figure shows the theoretical efficiency limits of linear amplifier. High PAPR degrades the transmit power efficiency performance. 2 max{ xtx( t, i) } t ( i) 10log E[ xtx( t, i) ] PPAPR 2
SC-FDMA Subcarrier Mapping Schemes {x m } 10 LFDMA, DFDMA and IFDMA demonstrating that signals of the four (4) different terminals arriving at a base station occupy mutually exclusive sets of subcarriers. M symbols per block, N subcarriers and Q users. 0 1 M-1 M+1 M {X k }: 2M-1 2M 2M N-1 2M+1 3M-1 3M+1 LFDMA 0 1 2 3 2M-1 2M+1 2M-3 N-2 N-1 DFDMA Subcarrier Subcarrier User 1 User 2 User 3 User 4 0 1 2 3 M M+2 M+1 M+3 IFDMA N-4 N-2 N-3 N-1 Subcarrier
Simulation Parameters/Assumptions 11 Parameter Value Carrier Frequency 2 GHz System bandwidth 5 MHz N-size IFFT 512 M-size FFT 128 Modulation scheme QPSK, 16QAM Cyclic prefix 32 samples (6.4 μs) Antenna scheme SISO
Pr(PAPR>PAPR 0 ) PAPR Comparison of Time 12 Domain Pulse Shaping Filter 10 0 10-1 PAPR CCDF of SC-FDMA and OFDMA (QPSK) IFDMA LFDMA OFDMA LFDMA and IFDMA both have significant PAPR improvement compared to OFDMA. 10-2 LFDMA IFDMA OFDMA OFDMA exhibits a higher PAPR compared to LFDMA and IFDMA. 10-3 10-4 3.3 db 4 5 6 7 8 9 10 11 12 13 14 PAPRo [db] SC-FDMA exhibits a lower PAPR compared to OFDMA because of its single carrier structure.
Pr(PAPR>PAPR 0 ) The Impact of Pulse Shaping on the PAPR of SC-FDMA signals 10 0 10-1 10-2 α = 0.2 LFDMA ( =0.5) LFDMA ( =0.2) LFDMA ( =0.1) LFDMA ( =0) IFDMA ( =0.5) IFDMA ( =0.2) IFDMA ( =0.1) IFDMA ( =0) α = 0 QPSK PAPR decreases as roll-off-factor (α) increases. 13 10-3 α = 0.1 α = 0.5 10-4 3 4 5 6 7 8 9 10 11 PAPRo [db]
Frequency Domain Spectral Shaping (1) 14 What is the difference between the time domain pulse shaping used in traditional single carrier systems and the frequency domain spectral shaping used in SC-FDMA? A traditional time domain pulse shaping filter is used to band limit the transmit signal. However, the frequency domain spectral shaping process is applied to reduce PAPR. The PAPR of SC-FDMA signals with RC frequency domain spectral shaping is now further investigated.
PAPR Reduction via Spectral Shaping 15 The SC-FDMA uplink requires pulse shaping to limit the inter-symbol interference (ISI) between neighboring time symbols Frequency domain spectral shaping can be used in SC-FDMA to achieve PAPR reduction
16 PAPR and Bandwidth Efficiency Comparison of PAPR and bandwidth efficiency using RC frequency domain spectral shaping at α = 0.2 with QPSK modulation. Bandwidth Efficiency 78.1% 85.9% 100% PAPR of LFDMA 6.4dB 6.6dB 7.7dB at CCDF = 10-3 The number of transmit data symbols, M data = 100, 110 and 128. The PAPR of SC-FDMA signals can be reduced at the cost of degraded bandwidth efficiency
Pr(PAPR>PAPR 0 ) 17 10 0 10-1 PAPR Reduction LFDMA Frequency Domain Spectral Shaping LFDMA Time Domain Pulse Shaping PAPR of SC-FDMA for LFDMA employed RC frequency domain spectrum shaping and time domain pulse shaping with QPSK signaling at α = 0.22. 10-2 10-3 1.3 db Results show that a PAPR reduction of 1.3 db can be achieved for QPSK when RC frequency domain spectral shaping is used with roll-off factor of 0.22. 10-4 3 4 5 6 7 8 9 10 11 12 PAPR 0 [db] QPSK Compared to the unfiltered version, the bandwidth efficiency is reduced to 78.1%.
18 Conclusions SC-FDMA is suitable for uplink transmissions as it has a lower PAPR than OFDMA (since it improves the power efficiency of the mobile transmitter). In this paper we have shown that by applying a frequency domain spectral shaping filter, the PAPR of a localized FDMA (LFDMA) signal can be further reduced (1.3 db) at the expense of degraded bandwidth efficiency (78.1%). The resulting PAPR reduction can be used to enhance handset power efficiency, or alternatively to improve uplink throughput and/or operating range.
Thank You Zuhanis Mansor, Prof. Andrew Nix and Prof. Joe McGeehan [Anis.Mansor@bristol.ac.uk] Centre for Communications Research