Field measurements of an indoor high-speed QAM wireless system using decision feedback equalization and smart antenna array

This paper reports on field measurements of point-to-point indoor high-speed (10 Mbit/s to 30 Mbit/s at 5 Mbaud) wireless communications realized using a flexible multilevel quadrature amplitude modulation (M-QAM) testbed that features real-time equalization and smart antenna-array technology. The results from an extensive set of measurements, 59262 trials in all, performed without cochannel interference under various receiver configurations and wireless environments are presented and analyzed. The results underscore the dramatic potential for a system that optimally combines equalization and a smart antenna array. For example, using only 10 mW of transmit power, the system delivered 30 Mbit/s at an uncoded bit error rate (BER) of 10(-3) with 5% outage at a coverage radius of 20 m. For a lower data rate of 10 Mbit/s, the coverage radius was increased to 32 m, the uncoded BER dropped below 10(-7), and the outage improved to 1%. The field measurements indicate that a 4-tap feedforward-filter decision-feedback equalizer with eight feedback-filter taps is sufficient-to mitigate the intersymbol interference for typical indoor environments. They. also show a significant gain when using a smart antenna array. For example, when transmitting between rooms at a 2% outage probability, the signal-to-noise ratio (SNR) improves by 8.3 dB when using two antennas instead of one antenna. Doubling the number of antennas to four provided an additional SNR improvement of 5.2 dB. The paper also presents simulation results that confirm the performance trends observed from the field measurements.