In this paper, we report on a mobile broadband wireless access (MBWA) system field trial with Fast Low-latency Access with Seamless Handoff Orthogonal Frequency Division Multiplexing (FLASH-OFDM), which was carried out at Sendai city in Japan. This paper describes coverage estimates of an uplink 16 quadrature amplitude modulation (QAM) signal under the condition of constant terminal output power when the bandwidths are from 2.56 MHz to 20.48 MHz. The estimates are based on the field trial results of 1.28 MHz bandwidth. The results show that wider bandwidth yields narrower coverage area. 16 QAM can be used within 55 %, 45 %, 35 %, and 25 % of the field trial area when the signal bandwidths are 2.56 MHz, 5.12 MHz, 10.24 MHz, and 20.48 MHz, respectively. We consider that 16 QAM is useful even if the signal bandwidth is wider than that 10 MHz.