Experimental broadband OFDM system: field results for OFDM and OFDM with frequency domain spreading

The paper presents link performance results of a series of field experiments conducted for OFDM and spread-OFDM/MC-CDMA in the context of a fourth-generation cellular system (4G) downlink. The experimental system is a 20 MHz 2×2 MIMO-OFDM system operating at a carrier frequency of 3.676 GHz. Measurements were conducted in a moderate density urban and suburban setting outside Chicago, Illinois, which exhibits varying degrees of delay spread and signal-to-noise ratio, with vehicle speeds ranging from 0 to 65 miles per hour. Coded performance (r=1/2 64-state convolutional coding) is compared for various link configurations: no receive diversity, 2-branch diversity, Alamouti transmit diversity, and 2×2 MIMO for QPSK, 16-QAM, and 64-QAM constellations. Results indicate that OFDM typically outperforms spread-OFDM, especially for higher order modulations. Moreover, the performance of dual-stream MIMO is sensitive to the channel condition number.