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Submitted on: 28 February 2008.
Revised on: 28 May 2008.
Accepted on: 09 June 2008.
___________________IEEE Vehicular Technology Magazine
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Submitted on: 23 January 2002.
Revised on: 14 April 2002.
Accepted on: 18 May 2002.
___________________IEEE Vehicular Technology Magazine
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