Transmitting continuously but in receiver side i find the data seems discontinuously transmitted

hello everyone !
i use benchmark_ofdm_tx to tramsmit data continuously .but in the
receiver side ,i get serveral packets ,then a serial of noisy, and then
useful packets again .the packets seem discontinuously transmitted .i
wonder why .
in my program both fusb_nblock and fusb_block_size are zero ,and my
packet size is 320 bytes , i guess maybe the problem lies here. may
somebody give me a clue?