This paper discusses results of a MBWA system field trial with Fast Low-latency Access with Seamless Handoff Orthogonal Frequency Division Multiplexing (FLASH-OFDM). The results of the trial show that the downlink throughput performance is significantly impaired by inter-sector interference. To clarify the reasons of the impairment, we carry out a computer simulation on inter-sector interference reduction capability of frequency hopping orthogonal frequency division multiple access (FH-OFDMA), which is used as a multiple access scheme in FLASH-OFDM. The results are summarized as follows: (1) the interference reduction capability of FH-OFDMA is almost the same as that of direct sequence code division multiple access (DS-CDMA), which allocate the same frequency band to all sectors, and (2) in FH-OFDMA, a long hopping-pattern length yields no site diversity effect to reduce inter-sector interference. Additionally, a cumulative distribution of measured signal to noise and interference ratio (SNIR) shows that pilot signals in the neighboring sectors mainly impair the throughput performance. Since a sectored cell layout is mandatory for deployment of the MBWA systems in a high traffic area, inter-sector interference reduction is a key issue for these systems.