I have checked OWB esm in FOMM, loaded my save game and waited for around an hour, but neither radio signal nor any message about OWB is show up.

My load order is new vegas -> dead money -> honest heart -> old world blues

Do anyone know what is the problem?

whats the game version?

From the main menu, hit "Downloadable Content" and see if OWB shows up. If it doesn't, you might not have the patch installed, or the files are corrupt. Try deleting the DLC and re installing.

Also, make sure you have the appropriate box checked under 'Data Files', if it isn't the game may not recognize the DLC as being there despite it being installed.