Algorithm and VLSI Architecture for Linear MMSE Detection in MIMO-OFDM Systems A. Burg, S. Haene, D. Perels, P. Luethi, N. Felber and W. Fichtner Integrated Systems Laboratory, ETH Zurich, Switzerland { apburg,haene,perels,luethi,felber,fw } @iis.ee.ethz.ch Data frame Abstract- The paper describes an algorithm and a correspond- ing VLSI architecture for the implementation of linear MMSE Idle Dtat Idle detection in packet-based MIMO-OFDM communication sys- tems. The advantages of the presented receiver architecture are low latency, high-throughput, and efficient resource utilization, MIMO detectioni since the hardware required for the computation of the MMSE Detection latency estimators is reused for the detection. The algorithm also supports the extraction of soft information for channel decoding. Fig. 1. Timing diagram of MIMO detection process in packet-based MIMO- I. INTRODUCTION OFDM systems. Multiple-input multiple-output (MIMO) wireless communi- cation systems [1] employ multiple antennas at the transmitter time index t on the kth tone of the OFDM signal. After proper and at the receiver to increase system capacity and to achieve OFDM modulation at the transmitter and demodulation at the better quality of service. In spatial multiplexing mode, MIMO receiver, the corresponding received vector y[k, t] is given by systems reach higher peak data rates without increasing the y[k, t]= H[k]s[k, t] + n[k, t], (1) bandwidth of the system by transmitting multiple data streams in parallel in the same frequency band. Orthogonal frequency where the MR X MT-dimensional matrix H[k] describes the division multiplexing (OFDM) is a modulation scheme that is effective MIMO channel for the kth tone and the vector n[k, t] robust against interference arising from multipath propagation. models the thermal noise in the system as i.i.d. proper complex Consequently, many upcoming standards for high throughput Gaussian with variance (Y per complex dimension. Assuming wireless communication such as IEEE 802.1 in and IEEE knowledge of the channel matrices, the linear MMSE estimator 802.16 rely on a combination of MIMO with OFDM. Unfor- for each tone is given by tunately, the performance improvements of MIMO technol- G[k] = (HH [k]H[k] +MT 2I) l HH[k] (2) ogy also entail a considerable increase in signal processing complexity, in particular for the separation of the parallel and linear MIMO detection corresponds to a straightforward data streams. Hence, a major challenge associated with the matrix-vector multiplication according to implementation of future wireless communication systems is in the design of low-complexity MIMO detection algorithms s[k,t] G[k]y[k,t] (3) and corresponding VLSI architectures. followed by quantization of the entries of s[k, t] to the nearest In this work, we consider the VLSI implementation of constellation point. linear MMSE detection for wideband MIMO-OFDM systems. The difficulty in the implementation of linear receivers for A suboptimal linear detection scheme is contemplated since packet-based MIMO-OFDM systems arises from the frame the implementation of algorithms with better performance structure because the initial training phase, during which the (e.g., [2], [3], [4]) either do not meet the high throughput receiver obtains knowledge of H[k], is immediately followed requirements for MIMO-WLAN (especially not on FPGAs) by data. Since the detection of the data according to (3) only or lack the ability to provide soft-information for channel starts when the MMSE estimators for all K data carrying tones decoding with low hardware complexity. have been computed, the delay incurred by the preprocessing according to (2) translates directly into detection latency as A. System Model and Requirements illustrated in Fig. 1. In MIMO-OFDM receiver implementa- The system under consideration is a packet-based MIMO- tions [5], this latency is responsible for considerable memory requirements to buffer the received vectors and can cause prob- OFDM system wtth MT transmit and MR recetve antennas. par than th-eA 0-7803-9390-2/06/$20.00~~~lem ©2006 IEEEn 4102emnt ISCA 2006du acsscnto Authorized licensed use limited to: Texas A M University. Downloaded on March 24, 2009 at 03:08 from IEEE Xplore. Restrictions apply.