FPGA Implementation of Gaussian Multicarrier. Receiver with Iterative. Interference. Canceller. Tokyo Institute of Technology

Transcription

1 FPGA Implementation of Gaussian Multicarrier Receiver with Iterative Interference Canceller Tetsuou Ohori,, Satoshi Suyama, Hiroshi Suzuki, and Kazuhiko Fukawa Tokyo Institute of Technology This work was presented in Int. OFDM workshop 2008.

2 Outline - Background - Design of Gaussian Multicarrier (GMC) - GMC receiver with iterative interference canceller - FPGA implementation - Performance evaluation - Conclusion 2

3 Background Future wireless communication More sophisticated spectrum management by multicarrier transmission is one of the most promising techniques (Example : Cognitive radio) Multicarrier transmission scheme should satisfy the following items; 1. Feasibility to control the signal spectrum 2. Sharp spectral attenuation 3. Deep spectral dip 3

4 Multicarrier (MC) Transmission Single-carriers with spectrum shaping OFDM 4

5 OFDM vs GS-OFDM OFDM Considerable amount of sidelobes Large guard band Orthogonality OFDM with windowing (IEEE802.11a) GMC Gaussian multicarrier(gmc) Sharp spectral attenuation High spectral efficiency Non-orthogonality 5

6 Gaussian Pulse Time domain Frequency domain Frequency Interference in time domain Interference in frequency domain σ is large Large Small σ is small Small Large 6

7 Subcarrier Arrangement Rectangular Rectangular Honeycomb Honeycomb = 0.275Ts minimizes interference power 7

8 Which is Best Pulse Shaping Waveform? Pulse Waveform 8

9 Interference in GMC GMC cannot maintain complete orthogonality among symbols and subcarriers : Inter-symbol Interference Inter-carrier Interference : Subcarrier spacing : Symbol duration GMC receiver requires interference canceller. Objective Feasibility study of Iterative Interference Canceller (IIC) FPGA implementation of GMC transceiver, and evaluation of its performance and circuit size 9

10 Configuration of GMC Transmitter Transmitted Signal : Modulation signal at n-th subcarrier Gaussian pulse IFFT GMC transmission can be realized by adding the Gaussian pulse shaping to IFFT Information Bit OFDM Modulator Gaussian Pulse Multiplier Transmitted Signal 10

11 GMC Transmitter with Truncated Gaussian Pulse Convolutional code Truncation of Gaussian pulse Gaussian pulse shaping ( Truncation : M ) 11

12 Principle of GMC Modulation Using IFFT Transmitted Signal In case of M = 3 IFFT output Truncation of Gaussian pulse M = 3 12

13 Block Diagram of GMC Receiver FFT output Desired Signal Leakage Coefficient Interference Interference cancellation by generating the interference replicas from decoded bits 13

14 Specification of GS-OFDM Transceiver Max. 90 MHz Max. 135 Mbps 3 OFDM x 5/4 (24 Mbps) 14

15 Implementation of IIC Signal A energy of Gaussian pulse attenuates exponentially Interference Consider only 8 adjacent subcarriers Simplified Interference Canceller 15

16 Implementation of GMC Receiver Pipelined process for each iteration Processing Delay << Packet Length 16

17 FPGA Board Implementation Virtex-4 (XC4VLX100) x 8 DAC 8ch ADC 4ch 14 bit, 125MHz IIC+DET(1) DET Fading Noise Spectrum Analyzer 2GHz Signal Generator I Q IIC+DET(2) Transmitter Circuit size:about 10% of the total system-gate 17

18 Measured Spectrum 40 db One subcarrier hole Three subcarrier holes Achieved 40 db spectral dip with three subcarrier holes Five subcarrier holes 18

19 Packet Error Rate (PER) Performance QPSK FPGA (fixed point) Computer Simulation (floating point) Considering adjacent interference only Computer Simulation (floating point, Ideal IIC) Considering all interference, Ideal transmission signal replica 19

20 PER Performance with 16QAM 20

21 Effect of Iterative Interference Canceller (IIC) (16QAM) FFT output Coherent detector output without IIC with IIC (1 iteration) with IIC (2 iterations) 21

22 Conclusion GMC can realize sharp spectral attenuation. Implementation GMC transmitter and receiver Iterative interference canceller (IIC) with 3 iterations Real-time evaluation on on FPGA Board Measured PER results agree with those of computer simulation. IIC with 2 iterations can almost cancel interference with QPSK. Real-time performance up to 135 Mbps (16QAM) Special Thanks to Mr. Terao, Mr. Onodera, and Mr. Goto 22