Commanding Conversation

May 1, 2010 - By

Defense editor Don Jewell is a retired Air Force officer who served for 30 years; many of his former peers and contemporaries are currently senior officers in today’s U.S. Air Force. Don sat down recently with General C. Robert Kehler, Commander of the U.S. Air Force Space Command, whom he has known and worked with for more than 20 years, to discuss GPS from the four-star point of view. read more

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Expert Advice: Quasi-Coherent Delay Lock Loop Tracking and Generalized Binary Coded Symbols in Multipath

May 1, 2010 - By

The original GPS signals, and indeed most GPS signals including L5, utilize conventional pseudonoise (PN) signal code division multiple access (CDMA), some with both in-phase and quadrature-phase modulation. In the late 1990s, I generalized Manchester PN symbol-spreading by defining split-spectrum binary square wave symbol-spreading, in a series of limited-distribution papers for the Air Force GPS Independent Review Team (IRT). These split-spectrum signals have been developed and analyzed much more fully by many others, and they are now termed binary offset carrier (BOC) modulation. The BOC codes can provide a noise-error advantage by placing more of their spectral energy at an offset frequency, thereby increasing the Gabor bandwidth. They can also provide spectral separation from other GNSS signals in the same frequency band, for example, L1. read more

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