11-04-2012, 01:10 PM
VLSI Implementation of Auto-Correlation Architecture for Synchronization of MIMO-OFDM WLAN Systems
Year2010Volume10_03_03.pdf (Size: 510.62 KB / Downloads: 60)
INTRODUCTION
Orthogonal frequency division multiplexing (OFDM)
is an effective transmission technique for various
wireless communications such as wireless local area
network (WLAN), for IEEE 802.11a/g/n standards, since
it is robust in multi-path propagation. Also, MIMOOFDM
techniques have been considered the most
promising technique for next generation communications,
since it provides high data rates and spectral efficiency in
multi-path fading channels. However, OFDM and
MIMO-OFDM systems are known to be sensitive to
synchronization errors,
SYSTEM MODEL
To provide both backward compatibility and high
throughput in IEEE 802.11n, three preamble formats are
defined [6]: Non-HT (high throughput) mode (legacy
mode), HT mixed mode that consist of legacy and HT
preamble, and HT Greenfield mode for high data rates.
In this paper, we only consider legacy preamble of IEEE
802.11n standard for the proposed architecture. It is
almost same as a physical layer convergence procedure
(PLCP) preamble of IEEE 802.
Sample Reduction Technique and Analysis forMIMO-OFDM based WLAN
In OFDM system, the auto-correlation is used to
calculate the phase difference between two successive
training symbols to estimate CFO value [1-5]. For
MIMO system, these auto-correlation values can be
simply combined using a maximal-ratio combining
(MRC) which provides better performance because of
improved receiver diversity [1].
Time-Multiplexing Architecture
Fig. 3, we can see that only first 16 samples are
correlated at each RX branch even if the LTS is 64
samples long. It means that the hardware utilization
efficiency of the complex multiplier in auto-correlation
scheme is only 25%. For more efficient implementation,
we propose a folding method, a time-multiplexing
architecture with which we can achieve the hardware
utilization of 100% by sharing the complex multiplier.
CONCLUSIONS
In this paper, the hardware-efficient synchronization
scheme for MIMO-OFDM wireless LAN standard, IEEE
802.11n, is proposed. The features of the proposed
architecture are the use of sample reduction and time
multiplexing techniques which utilize the diversity gain
for the MIMO system. Experimental results show that
our scheme provides smaller area and less power
dissipation compared to the conventional architecture.
Also, the proposed architecture was embedded and
implemented for the synchronization module of WLAN.