The Company's intangible assets at December 31, 2015 include patents with estimated remaining economic useful lives ranging from 0.5 to 5.75 years.  For all periods presented, all of the Company's patents were subject to amortization.  The gross carrying amounts and accumulated amortization related to acquired intangible assets as of December 31, 2015 and 2014 are as follows:

Amortization expense for the years ended December 31, 2015 and 2014 was $1,655,000 and $1,650,000, respectively.  Future amortization of current intangible assets, net is as follows:

On February 28, 2013, the Company acquired the Cox Patent Portfolio consisting of four U.S. patents and a pending patent application from Dr. Ingemar Cox which the Company valued at $1,725,000 (see Note H[2]).  Since the acquisition of the Cox Patent Portfolio, the Company has been issued seven additional patents resulting in eleven patents comprising the Cox Patent Portfolio.  On May 21, 2013, the Company's wholly-owned subsidiary acquired  the Mirror Worlds Patent Portfolio consisting of nine U.S. patents and five pending patent applications from Mirror Worlds, LLC which the Company valued at $4,354,000 (see Note H[2]).

The Company's Remote Power Patent expires in March 2020. The expiration dates of the patents within the Company's Mirror Worlds Patent Portfolio range from June 2016 to February 2020. The expiration dates of the patents within the Cox Patent Portfolio range from September 2021 to November 2023 and the expiration date of patents within the Company's QoS patents is June 2019.