This paper introduces the principles of interferometry to multicarrier code division multiple access (MC-CDMA). Specifically, we propose the use of MC-CDMA with novel carrier interferometry (CI) complex spreading codes. The CI/MC-CDMA method, applied to mobile wireless communication systems, offers enhanced performance and flexibility relative to MC-CDMA with conventional spreading codes. Specifically, assuming a frequency selective Rayleigh-fading channel, CI/MC-CDMAs performance matches that of orthogonal MC-CDMA using Hadamard-Walsh codes up to the MC-CDMA user limit; and, CI/MC-CDMA provides the added flexibility of going beyond users, adding up to 1 additional users with pseudo orthogonal positioning. When compared to MC-CDMA schemes capable of supporting greater than users, CI/MC-CDMAs performance exceeds that of MC-CDMA. Additionally, this new system is analyzed in the presence of phase jitters and frequency offsets and is shown to be robust to both cases. Index Terms-Carrier interferometry, complex sequences, frequency diversity, multicarrier code division multiple access (MC-CDMA). I. INTRODUCTION M ULTICARRIER code division multiple access (MC-CDMA) [1] has emerged as a powerful alternative to conventional direct sequence CDMA (DS-CDMA) [2] in mobile wireless communications. In MC-CDMA, each user's data symbol is transmitted simultaneously over narrow-band subcarriers, with each subcarrier encoded with a 1 or 1 (as determined by an assigned spreading code). Multiple users are assigned unique, orthogonal (or pseudo-orthogonal) codes. That is, while DS-CDMA spreads in the time domain, MC-CDMA applies the same spreading sequences in the frequency domain. When perfectly orthogonal code sequences are transmitted over slow, flat fading channels with perfect synchronization, the performance of DS-CDMA and MC-CDMA is equivalent, as the orthogonal multiuser interference vanishes completely. However, in reality, wide-band CDMA signals sent over multipath channels experience more severe channel distortions and the resulting channel dispersion (i.e., frequency selectivity) erodes the orthogonality of CDMA signals. In such cases, it turns out to be far more beneficial to harness the signal energy Manuscript

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The authors present a moltiiarrier platform that is capable of achieving high spectral efficiency by the application of narrow orthogonal carriers, and which enables flexible spectral sharing across different licensed and unlicensed bands via operator borrowing/lending. ABSTRACTIn this article we propose a new multicarrier platform to optimize the efficiency of wireless operators' licensed hands and enable flexible sharing of licensed and unlicensed hands (in different spectral regions). This research, besides introducing a high degree of flexibility of spectrum use for 4G systems, supports a recent FCC proposal that goes beyond suggesting improved spectral efficiency, and instead suggests innovative spectrum management regulations. Specifically, this work presents a multicarrier platform capable of achieving high spectral efficiency by the application of narrow orthogonal carriers, that enables flexible spectral sharing across different licensed and unlicensed bands via operator borrowingilending.

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CO 2 flux measurements are often used to monitor volcanic systems, understand the cause of volcanic unrest, and map sub-surface structures. Currently, such measurements are incomplete at Tarawera (New Zealand), which erupted with little warning in 1886 and produced a ∼17 km long fissure. We combine new soil CO 2 flux and C isotope measurements of Tarawera with previous data from Rotomahana and Waimangu (regions also along the 1886 fissure) to fingerprint the CO 2 source, understand the current pathways for degassing, quantify the CO 2 released along the entire fissure, and provide a baseline survey. The total CO 2 emissions from the fissure are 1227 t•d −1 (742-3398 t•d −1 90 % confidence interval), similar to other regions in the Taupō Volcanic Zone. The CO 2 flux from Waimangu and Rotomahana is far higher than from Tarawera (>549 vs. ∼4 t•d −1 CO 2), likely influenced by a shallow silicic body at depth and Okataina caldera rim faults increasing permeability at the southern end of the fissure. Highly localized regions of elevated CO 2 flux occur along the fissure and are likely caused by cross-cutting faults that focus the flow. One of these areas occurs on Tarawera, which is emitting ∼1 t•d −1 CO 2 with a δ 13 CO 2 of −5.5 ± 0.5 , and comparison with previous observations shows that activity is declining over time. This region highlights the spatial and temporal complexity of degassing pathways at volcanoes and that sub-surface structures exert a primary control on the magnitude of CO 2 flux in comparison to the surface mechanism (i.e., CO 2 released through the soil or lake surface).