This paper presents the developed orthogonal frequency division multiplexing (OFDM) baseband processor employing adaptive modulations to grouped subcarriers, and its demonstration in millimeter-wave wireless indoor links. Channel measurements and characterizations are performed in line-of-sight (LOS) office environments where the developed OFDM system is supposed to be used. The OFDM baseband processor utilizes 192 data subcarriers among 256 FFT numbers. To minimize bit-error-rate (BER) performance in frequency selective channels of millimeter-wave wireless indoor links, these 192 data subcarriers are grouped into 24 subcarrier groups and independently modulated according to channel characteristics in each subcarrier group. We demonstrate it incorporating with the developed 70 GHz self-heterodyne transceiver. BER measurements and maximum TCP throughput test are performed in practical millimeterwave indoor environments. The results verify the advantages of the proposed adaptive modulation in OFDM and show better BER performance as well as higher throughput performance than a typical OFDM system.