| 1. |
- Al-Salihi, Hayder, et al.
(författare)
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A Successive Optimization Approach to Pilot Design for Multi-Cell Massive MIMO Systems
- 2018
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Ingår i: IEEE Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1089-7798 .- 1558-2558. ; 22:5, s. 1086-1089
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Tidskriftsartikel (refereegranskat)abstract
- In this letter, we introduce a novel pilot designapproach that minimizes the total mean square errors of theminimum mean square error estimators of all base stations (BSs)subject to the transmit power constraints of individual users inthe network, while tackling the pilot contamination in multicellmassive MIMO systems. First, we decompose the originalnon-convex problem into distributed optimization sub-problemsat individual BSs, where each BS can optimize its own pilotsignals given the knowledge of pilot signals from the remainingBSs. We then introduce a successive optimization approach totransform each optimization sub-problem into a linear matrixinequality form, which is convex and can be solved by availableoptimization packages. Simulation results confirm the fast convergenceof the proposed approach and prevails a benchmarkscheme in terms of providing higher accuracy.
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| 2. |
- Amani, Navid, 1985, et al.
(författare)
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Per-Antenna Power Distribution of a Zero-Forcing Beamformed ULA in pure LOS MU-MIMO
- 2018
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Ingår i: IEEE Communications Letters. - 1558-2558 .- 1089-7798. ; 22:12, s. 2515-2518
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Tidskriftsartikel (refereegranskat)abstract
- An analytical model is presented to determine the per-antenna power distribution of a beamformed M-element uniform linear array (ULA) as a base station antenna (BSA). The analysis assumes a single sector cell serving two user equipments (UEs) in a downlink multiuser multiple-input multiple-output (MU-MIMO) system employing zeroforcing (ZF) transmission. Determinative design parameters of the BSA configuration are identified. Afterwards, their effects on the power spread across the array are investigated when the positions of the users are random and they are uniformly distributed over the cell. It is shown that the power distribution across the ULA antenna aperture is a periodic function whose characteristics mainly depend on the angular separation of two UEs and the number of BSA elements. A significant variation between ULA input powers is seen to occur if the number of elements in the ULA is smaller than one period of this power distribution function. In order to mitigate the dynamic range of the power variation across the array, an upper bound for the inter-element spacing, depending on the field-of-view (FoV) of the BSA, is defined. It is shown that, in a 20-element ULA, increasing the inter-element spacing from 0.5-wavelength to 1.4-wavelength reduces the power variation from 19 dB to 10 dB for differentiating two close-by UEs with 1 degree angular separation.
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| 3. |
- Campolo, Claudia, et al.
(författare)
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On Latency and Reliability of Road Hazard Warnings over the Cellular V2X Sidelink Interface
- 2019
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Ingår i: IEEE Communications Letters. - Piscataway, NJ : IEEE. - 1089-7798 .- 1558-2558. ; 23:11, s. 2135-2138
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Tidskriftsartikel (refereegranskat)abstract
- Decentralized Environmental Notification Messages (DENMs) are generated by a vehicle upon detection of an accident or other hazards on the road, and need to be promptly and reliably transmitted. Delayed or lost messages may have fatal consequences, especially in critical driving situations, such as automated overtake and emergency braking, when vehicles can be very close to each other. In this letter, the DENM latency and reliability performances are characterized over the Cellular Vehicle-to-everything (C-V2X) sidelink (PC5 interface). The conducted study uses analytical tools, among which stochastic geometry, to derive performance results, then validated by simulations. Results are applied to the case of DENMs for emergency electronic brake lights, and helpful insights are provided for this crucial case and for other more general DENM-assisted V2X use cases.
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| 4. |
- Cao, Le Phuong, et al.
(författare)
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Transmit Beamforming for Single-User Large-Scale MISO Systems With Sub-Connected Architecture and Power Constraints
- 2018
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Ingår i: IEEE Communications Letters. - : IEEE. - 1089-7798 .- 1558-2558. ; 22:10, s. 2096-2099
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Tidskriftsartikel (refereegranskat)abstract
- This letter considers optimal transmit beamforming for a sub-connected large-scale MISO system with RF chain and per-antenna power constraints. The system is configured such that each RF chain serves a group of antennas. For the hybrid scheme, necessary and sufficient conditions to design the optimal digital and analog precoders are provided. It is shown that, in the optimum, the optimal phase shift at each antenna has to match the channel coefficient and the phase of the digital precoder. In addition, an iterative algorithm is provided to find the optimal power allocation. We study the case where the power constraint on each RF chain is smaller than the sum of the corresponding per-antenna power constraints. Then, the optimal power is allocated based on two properties: each RF chain uses full power and if the optimal power allocation of the unconstraint problem violates a per-antenna power constraint then it is optimal to allocate the maximal power for that antenna.
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| 5. |
- Charalambous, Themistoklis, et al.
(författare)
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Modeling Buffer-Aided Relay Selection in Networks With Direct Transmission Capability
- 2015
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Ingår i: IEEE Communications Letters. - 1089-7798 .- 1558-2558. ; 19:4, s. 649-652
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Tidskriftsartikel (refereegranskat)abstract
- We consider a wireless relay network that consists of a source, half-duplex decode-and-forward buffer-aided relays and a destination. While the majority of previous works on relay selection assume no direct transmission between source and destination in such a setting, we lift this assumption and propose a link selection policy that exploits both the buffering ability and the opportunity for successful reception of a packet directly from the source. The proposed relay selection scheme incorporates the instantaneous strength of the wireless links and adapts the relay selection decision based on the strongest available link. The evolution of the network as a whole is modeled by means of a Markov chain and thus, the outage probability is associated with the steady state of the Markov chain. It is deduced that even if the link between the source and the destination is in principle a very unreliable link, it is always beneficial for the source to multicast a packet to both the relay with the strongest available link and the destination.
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| 6. |
- Chen, Bolin, et al.
(författare)
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Resource Optimization for Joint LWA and LTE-U in Load-Coupled and Multi-Cell Networks
- 2019
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Ingår i: IEEE Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1089-7798 .- 1558-2558. ; 23:2, s. 330-333
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Tidskriftsartikel (refereegranskat)abstract
- We consider the performance optimization of multi-cell networks with LTE and Wi-Fi aggregation (LWA) and LTE-unlicensed (LTE-U) with sharing of the unlicensed band. Theoretical results are derived to enable an algorithm to approach the optimum. Numerical results show the algorithm's effectiveness and benefits of joint use of LWA and LTE-U.
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| 7. |
- Chen, Zheng, et al.
(författare)
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Probabilistic Caching in Wireless D2D Networks: Cache Hit Optimal Versus Throughput Optimal
- 2017
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Ingår i: IEEE Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1089-7798 .- 1558-2558. ; 21:3, s. 584-587
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Tidskriftsartikel (refereegranskat)abstract
- Departing from the conventional cache hit optimization in cache-enabled wireless networks, we consider an alternative optimization approach for the probabilistic caching placement in stochastic wireless D2D caching networks taking into account the reliability of D2D transmissions. Using tools from stochastic geometry, we provide a closed-form approximation of cache-aided throughput, which measures the density of successfully served requests by local device caches, and we obtain the optimal caching probabilities via numerical optimization. Compared with the cache-hit-optimal case, the optimal caching probabilities obtained by cache-aided throughput optimization show notable gain in terms of the density of successfully served user requests, particularly in dense user environments.
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| 8. |
- Cheng, Yuxin, et al.
(författare)
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Reliable and Cost Efficient Passive Optical Interconnects for Data Centers
- 2015
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Ingår i: IEEE Communications Letters. - : IEEE Communications Society. - 1089-7798 .- 1558-2558. ; 19:11, s. 1913-1916
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Tidskriftsartikel (refereegranskat)abstract
- To address the sustainability, scalability, and reliability problems that data centers are currently facing, we propose three passive optical interconnect (POI) architectures on top of the rack. The evaluation results show that all three architectures offer high reliability performance (connection availability for intra-rack interconnections higher than 99.999%) in a cost-efficient way.
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| 9. |
- Chu, Thi My Chinh, et al.
(författare)
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Performance of a Non-orthogonal Multiple Access System with Full-Duplex Relaying
- 2018
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Ingår i: IEEE Communications Letters. - : Institute of Electrical and Electronics Engineers Inc.. - 1089-7798 .- 1558-2558. ; 22:10, s. 2084-2087
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we study a power-domain nonorthogonal multiple access (NOMA) system in which a base station (BS) superimposes the transmit signals to the users. To enhance spectral efficiency and link reliability for the far-distance user, a full-duplex (FD) relay assists the BS while the neardistance user is reached over the direct link. For this setting, we analyze outage probability and sum rate of the NOMA system over Nakagami-m fading with integer fading severity parameter m. Numerical results are provided for outage probability and sum rate to show the effect of system parameters on the performance of the FD NOMA system over Nakagami-m fading. IEEE
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| 10. |
- Duc Ho, Chung, et al.
(författare)
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On the Performance of Zero-Forcing Processing in Multi-Way Massive MIMO Relay Networks
- 2017
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Ingår i: IEEE Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1089-7798 .- 1558-2558. ; 21:4, s. 849-852
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Tidskriftsartikel (refereegranskat)abstract
- We consider a multi-way massive multiple-input multiple-output relay network with zero-forcing processing at the relay. By considering the time-division duplex protocol with channel estimation, we derive an analytical approximation of the spectral efficiency. This approximation is very tight and simple, which enables us to analyze the system performance, as well as to compare the spectral efficiency with zero-forcing and maximum-ratio processing. Our results show that by using a very large number of relay antennas and with the zero-forcing technique, we can simultaneously serve many active users in the same time-frequency resource, each with high spectral efficiency.
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