| 1. |
- Chatzinotas, S., et al.
(författare)
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Energy-efficient MMSE beamforming and power allocation in multibeam satellite systems
- 2011
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Ingår i: Signals, Systems and Computers (ASILOMAR), 2011 Conference Record of the Forty Fifth Asilomar Conference on. - : IEEE. ; , s. 1081-1085
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Konferensbidrag (refereegranskat)abstract
- In current satellite communication systems, energy efficiency is of paramount importance since it strongly affects the satellite size and lifetime. In this paper, the energy efficiency of a multibeam downlink system is investigated in terms of maximizing the ratio of system throughput over consumed power. More specifically, the consumed power comprises both operating power which is needed for running the network equipment and transmit power which is needed for forwarding the information to the end users. Regarding the employed transmission technique, Minimum Mean Square Error (MMSE) beamforming together with power optimization for satellite downlink channel is used while full frequency reuse is assumed. By varying the ratio of operating and transmit power, we study the performance of the forward link in terms of spectral and energy efficiency.
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| 2. |
- Chatzinotas, Symeon, et al.
(författare)
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Joint Precoding with Flexible Power Constraints in Multibeam Satellite Systems
- 2011
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Ingår i: Proceedings Global Communications Conference (GLOBECOM). - 9781424492688
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Konferensbidrag (refereegranskat)abstract
- In conventional multibeam satellite systems, frequencyand polarization orthogonalization have been traditionallyemployed for mitigating interbeam interference. However, theparadigm of multibeam joint precoding allows for full frequencyreuse while assisting beam-edge users. In this paper, the performanceof linear beamforming is investigated in terms of meetingtraffic demands. More importantly, generic linear constraints areconsidered over the transmit covariance matrix in order to modelthe power pooling effect which can be implemented throughflexible traveling wave tube amplifiers (TWTAS) or multiportamplifiers. The performance of this scheme is compared againstconventional spotbeam systems based on the rate-balancingobjective. In this context, it is shown that significantly higherspectral efficiency can be achieved through beamforming, whileflexible power constraint offers better rate-balancing.
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| 3. |
- Gerbracht, Sabrina, et al.
(författare)
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Non-regenerative two-hop wiretap channels using interference neutralization
- 2012
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this paper, we analyze the achievable secrecy rates in the two-hop wiretap channel with four nodes, where the transmitter and the receiver have multiple antennas while the relay and the eavesdropper have only a single antenna each. The relay is operating in amplify-and-forward mode and all the channels between the nodes are known perfectly by the transmitter. We discuss different transmission and protection schemes like artificial noise (AN). Furthermore, we introduce interference neutralization (IN) as a new protection scheme. We compare the different schemes regarding the high-SNR slope and the high-SNR power offset and illustrate the performance by simulation results. It is shown analytically as well as by numerical simulations that the high SNR performance of the proposed IN scheme is better than the one of AN.
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| 4. |
- Huang, Yongming, et al.
(författare)
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Distributed Multicell Beamforming With Limited Intercell Coordination
- 2011
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Ingår i: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 59:2, s. 728-738
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies distributed optimization schemes for multicell joint beamforming and power allocation in time-division-duplex (TDD) multicell downlink systems where only limited-capacity intercell information exchange is permitted. With an aim to maximize the worst-user signal-to-interference-and-noise ratio (SINR), we devise a hierarchical iterative algorithm to optimize downlink beamforming and intercell power allocation jointly in a distributed manner. The proposed scheme is proved to converge to the global optimum. For fast convergence and to reduce the burden of intercell parameter exchange, we further propose to exploit previous iterations adaptively. Results illustrate that the proposed scheme can achieve near-optimal performance even with a few iterations, hence providing a good tradeoff between performance and backhaul consumption. The performance under quantized parameter exchange is also examined.
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| 5. |
- Kapetanovic, Dzevdan, et al.
(författare)
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Detection of pilot contamination attack using random training and massive MIMO
- 2013
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Ingår i: Personal Indoor and Mobile Radio Communications (PIMRC), 2013 IEEE 24th International Symposium on. ; , s. 13-18
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Konferensbidrag (refereegranskat)abstract
- Channel estimation attacks can degrade the performance of the legitimate system and facilitate eavesdropping. It is known that pilot contamination can alter the legitimate transmit precoder design and strengthen the quality of the received signal at the eavesdropper, without being detected. In this paper, we devise a technique which employs random pilots chosen from a known set of phase-shift keying (PSK) symbols to detect pilot contamination. The scheme only requires two training periods without any prior channel knowledge. Our analysis demonstrates that using the proposed technique in a massive MIMO system, the detection probability of pilot contamination attacks can be made arbitrarily close to 1. Simulation results reveal that the proposed technique can significantly increase the detection probability and is robust to noise power as well as the eavesdropper's power.
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| 6. |
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| 7. |
- Zheng, Gan, et al.
(författare)
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Collaborative-Relay Beamforming with Perfect CSI : Optimum and Distributed Implementation
- 2009
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Ingår i: IEEE Signal Processing Letters. - : IEEE. - 1070-9908 .- 1558-2361. ; 16:4, s. 257-260
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Tidskriftsartikel (refereegranskat)abstract
- This letter studies the collaborative use of amplify-and-forward (AF) relays to form a virtual multiple-input single-output (MISO) beamforming system with the aid of perfect channel state information (CSI) in a flat-fading channel. In particular, we optimize the relay weights jointly to maximize the received signal-to-noise ratio (SNR) at the destination terminal with both individual and total power constraints at the relays. We show that the optimal collaborative-relay beamforming (CRB) solution achieves the full diversity of a MISO antenna system. Another main contribution of this letter is a distributed algorithm that allows each individual relay to learn its own weight, based on the Karush-Kuhn-Tucker (KKT) analysis.
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| 8. |
- Zheng, Gan, et al.
(författare)
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Cooperative Cognitive Networks : Optimal, Distributed and Low-Complexity Algorithms
- 2013
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Ingår i: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 61:11, s. 2778-2790
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers the cooperation between a cognitive system and a primary system where multiple cognitive base stations (CBSs) relay the primary user's (PU) signals in exchange for more opportunity to transmit their own signals. The CBSs use amplify-and-forward (AF) relaying and coordinated beamforming to relay the primary signals and transmit their own signals. The objective is to minimize the overall transmit power of the CBSs given the rate requirements of the PU and the cognitive users (CUs). We show that the relaying matrices have unity rank and perform two functions: Matched filter receive beamforming and transmit beamforming. We then develop two efficient algorithms to find the optimal solution. The first one has a linear convergence rate and is suitable for distributed implementation, while the second one enjoys superlinear convergence but requires centralized processing. Further, we derive the beamforming vectors for the linear conventional zero-forcing (CZF) and prior zero-forcing (PZF) schemes, which provide much simpler solutions. Simulation results demonstrate the improvement in terms of outage performance due to the cooperation between the primary and cognitive systems.
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| 9. |
- Zheng, Gan, et al.
(författare)
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Cooperative Communications against Jamming with Half-Duplex and Full-Duplex Relaying
- 2013
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Ingår i: Proceedings of IEEE 77th Vehicular Technology Conference. - : IEEE. - 9781467363372 ; , s. 6692490-
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Konferensbidrag (refereegranskat)abstract
- This paper studies the impact of jamming on the design of three-node two-hop cooperative amplify-and-forward (AF) communications with both half-duplex and full-duplex relaying. For the half-duplex relaying, the jammer is smart such that it can optimally allocate jamming power between listening and forwarding phases. Given separate source and relay power constraints, we derive the optimal jamming power allocation; with a total source and relay power constraint, we model the interaction between the legitimate system and the jammer as a noncooperative game and prove the existence and uniqueness of the Nash Equilibrium (NE). It is found that due to the fact that the end performance is limited by the weaker phase, the legitimate systems tries to balance the performance of two phases while the jammer attacks the system by making the two hops imbalanced. While for the full-duplex relaying, we show that if the self-interference can be properly controlled, it can bring substantial performance gain. Simulation results verify our analysis.
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| 10. |
- Zheng, Gan, et al.
(författare)
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Improving Physical Layer Secrecy Using Full-Duplex Jamming Receivers
- 2013
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Ingår i: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 61:20, s. 4962-4974
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies secrecy rate optimization in a wireless network with a single-antenna source, a multi-antenna destination and a multi-antenna eavesdropper. This is an unfavorable scenario for secrecy performance as the system is interference-limited. In the literature, assuming that the receiver operates in half duplex (HD) mode, the aforementioned problem has been addressed via use of cooperating nodes who act as jammers to confound the eavesdropper. This paper investigates an alternative solution, which assumes the availability of a full duplex (FD) receiver. In particular, while receiving data, the receiver transmits jamming noise to degrade the eavesdropper channel. The proposed self-protection scheme eliminates the need for external helpers and provides system robustness. For the case in which global channel state information is available, we aim to design the optimal jamming covariance matrix that maximizes the secrecy rate and mitigates loop interference associated with the FD operation. We consider both fixed and optimal linear receiver design at the destination, and show that the optimal jamming covariance matrix is rank-1, and can be found via an efficient 1-D search. For the case in which only statistical information on the eavesdropper channel is available, the optimal power allocation is studied in terms of ergodic and outage secrecy rates. Simulation results verify the analysis and demonstrate substantial performance gain over conventional HD operation at the destination.
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