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Such a system can be independent , but often can be connected to other fixed systems such as the public switched telephone network ( PSTN ) or cellular network s. Military use The land mobile radio system is also the United States Department of Defense 's new state-of-the-art communication system .
 United States Department of Defense
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 United States Department of Defense