Real-Time Implementation of a Sphere Decoder-Based MIMO Wireless System 14th EURASIP European Signal Processing Conference, EUSIPCO 4-8th September 2006, Florence, Italy Institute for Digital Communications School of Engineering and Electronics University of Edinburgh Communications and Digital Signal Processing Area Mondragon Goi Eskola Politeknikoa University of Mondragon
Introduction Background The Sphere Decoder is considered the most promising approach to Maximum Likelihood MIMO detection [Viterbo99][Damen03]. Several interesting real-time implementations of the SD algorithm:
However, the integration of the Sphere Decoder in a real-time system needs to be further analyzed to evaluate BER and throughput degradation due to:
Non-ideal parameter estimation and channel preprocessing.
Introduction Motivation Sphere Decoder Univ. of Edinburgh
Flat Rayleigh channel
HW in the loop.
Perfect Ch. Est.
Offline inv., Chol.
Real-Time Prototyping Platform Univ. of Mondragon
Flat MIMO channel emulator
Basic linear detectors
12-bits ADC resolution
Introduction Objectives 1.- Integration of the sphere decoder algorithm in the complete MIMO platform: a.- Platform for validating and comparing different implementations of the Sphere Decoder algorithm. b.- Complexity analysis. 2.- Evaluation of the BER and throughput degradation due to: a.- Fixed point resolution. b.- Estimation and synchronization errors. c.- Validation maintaining the flat channel assumption: c1.- Low-rate real burst transmissions. c2.- High-rate channel emulator.
Sample-time synchronization : basic ML approach. [Naguib98]
Frequency offset estimation : reduced complexity implementation. [Simoens04]
Channel emulator : channels (random numbers) stored in large RAM blocks
MIMO detection – Sphere Decoder algorithm . Adaptation of [Barbero05].
Real-Time Implementation Task partitioning 2x2 16-QAM MIMO System PCI-based communication with host software
Real-Time Implementation Co-simulation Flexible system to allow step-by-step validation of algorithm implementation: any algorithm can be chosen to run in Matlab, in the FPGA (may not be real-time) or both. Main setups:
Ideal simulation : Perfect synchronization, channel estimation and inverse calculation.
Estimated parameters : Channel, real-time calculated inverse and Cholesky.
Complete system : All algorithms running in the FPGAs.
References [Barbero05] L. G. Barbero and J. S. Thompson, “Rapid prototyping of the sphere decoder for MIMO systems,” in Proc. IEE/EURASIP Conference on DSP Enabled Radio (DSPeR ’05) , vol. 1, Southampton, UK, Sept. 2005, pp. 41–47. [Burg05] A. Burg, M. Borgmann, M.Wenk, M. Zellweger, W. Fichtner, and H. Bölcskei, “VLSI implementation of MIMO detection using the sphere decoding algorithm,” IEEE J. Solid-State Circuits , vol. 40, no. 7, pp. 1566–1577, July 2005. [Damen03] M. O. Damen, H. E. Gamal, and G. Caire, “On maximumlikelihood detection and the search for the closest lattice point,” IEEE Trans. Inform. Theory , vol. 49, no. 10, pp. 2389–2402, Oct. 2003. [Heiskala02] J. Heiskala and J. Terry, OFDM Wireless LANs: A Theoretical and Practical Guide . Indiana, USA: Sams Publishing, 2002. [Naguib98] A. F. Naguib, V. Tarokh, N. Seshadri, and A. R. Calderbank, “A space-time coding modem for high-data-rate wireless communications,” IEEE J. Solid-State Circuits , vol. 16, no. 8, pp. 1459–1478, Oct. 1998. [Schnorr94] C. P. Schnorr and M. Euchner, “Lattice basis reduction: Improved practical algorithms and solving subset sum problems,” Mathematical Programming , vol. 66, pp. 181–199, 1994. [Simoens04] F. Simoens and M. Moeneclaey, “A reduced complexity frequency offset estimation technique for flat fading mimo channels,” in Proc. IEEE CAS Symposium on Emerging Technologies , vol. 2, Shanghai, China, June 2004, pp. 705–708. [Viterbo99] E. Viterbo and J. Boutros, “A universal lattice code decoder for fading channels,” IEEE Trans. Inform. Theory , vol. 45, no. 5, pp. 1639–1642, July 1999. [Wong02] K. Wong, C. Tsiu, R. S. Cheng, and W. Mow, “A VLSI architecture of a K-best lattice decoding algorithm for MIMO channels,” in Proc. IEEE International Symposium on Circuits and Systems (ISCAS ’02) , vol. 3, Scottsdale, AZ, May 2002, pp. 273–276.
Real-Time Implementation of a Sphere Decoder-Based MIMO Wireless System 14th EURASIP European Signal Processing Conference, EUSIPCO 4-8th September 2006, Florence, Italy L. G. Barbero, J. S. Thompson Institute for Digital Communications School of Engineering and Electronics University of Edinburgh M. Mendicute, G. Landaburu, J. Altuna, V. Atxa Communications and Digital Signal Processing Area Mondragon Goi Eskola Politeknikoa University of Mondragon