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Anti-jamming techniques are critical to maintain the integrity and functionality of GPS systems in various applications. One of the major problems with existing array-based antijamming GPS receivers is the errors introduced in the carrier phase, affecting the GPS solution. In this letter, we propose a novel anti-jamming GPS receiver structure that preserves the GPS signal phase continuity. The effectiveness of the proposed technique is verified by simulation results.

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This paper proposes a new relay selection method based on local channel state information (CSI) for a system consisting of a source, a destination and an arbitrary number of amplify-and-forward relay nodes. A set of candidate relays, whose source-relay (S-R) links are not in outage, is formed. An S-R link is in outage if its signal-to-noise ratio (SNR) is below the predefined threshold value of the destination SNR plus some adjustable margin. The candidate relay that yields the maximum second-hop SNR is then selected at the destination. Unlike the opportunistic relaying (OR) based on full CSI (F-CSI), the proposed method requires to equip the destination node with the instantaneous CSI of the S-R channel corresponding to only the selected relay. It is qualitatively shown that the training overhead of the proposed relay selection is less than or comparable to that of the partial relay selection (PRS) but can be much smaller than that of the OR with F-CSI. However, the proposed scheme requires to estimate a higher number of single-input single-output (SISO) channels than in the PRS scheme. The exact and asymptotic expressions of outage probability are derived and it is shown that the proposed method achieves full diversity. Simulation results verify theoretical analysis, and show that, for the optimized margin, the proposed scheme provides performance which is comparable to the method having F-CSI. The results also show that the proposed method significantly This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. 2 outperforms PRS, which may justify the linear order of the computational complexity associated with the estimation of the additional SISO channels and the low-cost one-dimensional line search used for optimizing the margin. Index TermsRelay selection, cooperative communications, amplify-and-forward relay, outage probability, diversity gain. I. INTRODUCTIONCooperative communication [1]-[2] is an emerging technique that improves spatial diversity 1 , coverage range and system throughput in cellular communications [4]. A key component of cooperation is relaying in which a source (base station) seeks the assistance of user terminals (dedicated relay terminals) in its coverage area to relay the source signal to the destination (user equipment). Among different relay protocols [2], the amplify-and-forward (AF) protocol is often used due to its simplicity. However, in systems with multiple relays, the feedback requirements and the overall implementation become complicated and can prove costly. System complexity and cost rise in multi-antenna cooperative systems that employ beamformers over the set of nodes (source, relays, destinations)[5]- [6]. In this context, relay selection is key to reducing signaling overhead and system design complexity while maintaining the diversity gain [7]-[9].The relay selection method for AF relays is often based on the end-to-end SNR, which is commonly referred to as opportunist...

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