Table 2 Vocabulary set considered in our experiments

SUSAS vocabulary set

BRAKE

EIGHTY

GO

NAV

SIX

THIRTY

Change

ENTER

HELLO

NO

SOUTH

THREE

DEGREE

FIFTY

HELP

OH

STAND

WHITE

DESTINATION

FIX

HISTOGRAM

ON

STEER

WIDE

EAST

FREEZE

HOT

OUT

STRAFE

ZERO

EIGHT

GAIN

MARK

POINT

TEN