| 1. |
- Chaitanya, Tumula, et al.
(författare)
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Adaptive power allocation for HARQ with Chase combining in correlated Rayleigh fading channels
- 2014
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Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 3:2, s. 169-172
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Tidskriftsartikel (refereegranskat)abstract
- We consider the problem of minimizing the packet drop probability (PDP) under an average transmit power constraint for Chase combining (CC)-based hybrid-automatic repeat request (HARQ) schemes in correlated Rayleigh fading channels. We propose a method to find a solution to the non-convex optimization problem using an exact expression of the outage probability. However, the complexity of this method is high. Therefore, we propose an alternative approach in which we use an asymptotically equivalent expression for the outage probability and reformulate it as a geometric programming problem (GPP), which can be efficiently solved using convex optimization algorithms.
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| 2. |
- Fritsche, Carsten, et al.
(författare)
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Bayesian Cramer-Rao Bound for Mobile Terminal Tracking in Mixed LOS/NLOS Environments
- 2013
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Ingår i: IEEE Wireless Communications Letters. - : IEEE. - 2162-2337 .- 2162-2345. ; 2:3, s. 335-338
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Tidskriftsartikel (refereegranskat)abstract
- A computational algorithm is presented for the Bayesian Cramer-Rao lower bound (BCRB) in filtering applications with measurement noise from mixture distributions with jump Markov switching structure. Such mixture distributions are common for radio propagation in mixed line- and non-line-of-sight environments. The newly derived BCRB is tighter than earlier more general bounds proposed in literature, and thus gives a more realistic bound on actual estimation performance. The resulting BCRB can be used to compute a lower bound on root mean square error of position estimates in a large class of radio localization applications. We illustrate this on an archetypical tracking application using a nearly constant velocity model and time of arrival observations.
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| 3. |
- Hussain, Iqbal, et al.
(författare)
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Rateless Codes for the Multiway Relay Channel
- 2014
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Ingår i: IEEE Wireless Communications Letters. - 2162-2337 .- 2162-2345. ; 3:5, s. 457-460
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Tidskriftsartikel (refereegranskat)abstract
- We consider distributed Luby transform (DLT) codes for efficient packet transmission in a multi-way relay network, where the links are modeled as erasure channels. Density evolution is applied for asymptotic performance analysis, and subsequently used in a linear-programming design framework for optimizing the degree distribution at the relay in terms of overhead. Moreover a buffer is introduced at the relay to enable efficient downlink transmission even if packets are lost during uplink transmission. Performance losses in terms of delay and/or erasure rates caused by link erasures during uplink transmission are thus alleviated. The proposed DLT codes provide significant improvements in overhead and decoded erasure rates. Numerical results for finite-length codes follow closely the asymptotic analysis. Our results demonstrate that the proposed buffer-based DLT codes outperform its counterparts for lossy uplink transmission.
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| 4. |
- Jos, S., et al.
(författare)
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Method of generating multiple sets of orthogonal codes with wide choice of spreading factors
- 2012
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Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 1:5, s. 492-495
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a generic method to construct multiple sets of orthogonal codes for application in direct sequence spread spectrum systems. The plurality of orthogonal sets is generated using any single two-level autocorrelation sequence of period one less than the desired spreading factor of the orthogonal codes. The proposed method hence generates orthogonal codes of all spreading factors for which a corresponding two-level autocorrelation sequence exists. The resulting orthogonal sets with wide choice of spreading factors is desirable in synchronous direct sequence spread spectrum systems. The sets can be generated such that they do not contain the codeword with single polarity as in the case of Walsh-Hadamard codes and orthogonal sets generated from cyclic shifts of two-level autocorrelation sequences. This renders all codes in the generated sets with an effective spreading gain. The generation method also encompasses a procedure to generate N-1 sets with low inter-set correlation for application to oversaturated spread spectrum systems.
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| 5. |
- Lindblom, Johannes, 1983-, et al.
(författare)
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Achievable Outage Rate Regions for the MISO Interference Channel
- 2013
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Ingår i: IEEE Wireless Communications Letters. - : IEEE Communications Society. - 2162-2337 .- 2162-2345. ; 2:4, s. 439-442
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Tidskriftsartikel (refereegranskat)abstract
- We consider the slow-fading two-user multiple-input single-output (MISO) interference channel. We want to understand which rate points can be achieved, allowing a non-zero outage probability. We do so by defining four different outage rate regions. The definitions differ on whether the rates are declared in outage jointly or individually and whether the transmitters have instantaneous or statistical channel state information (CSI). The focus is on the instantaneous CSI case with individual outage, where we propose a stochastic mapping from the rate point and the channel realization to the beamforming vectors. A major contribution is that we prove that the stochastic component of this mapping is independent of the actual channel realization.
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| 6. |
- Makki, Behrooz, 1980, et al.
(författare)
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Finite Block-length Analysis of the Incremental Redundancy HARQ
- 2014
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Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 3:5, s. 529-532
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Tidskriftsartikel (refereegranskat)abstract
- This letter studies the power-limited throughput of a communication system utilizing incremental redundancy (INR) hybrid automatic repeat request (HARQ). We use some recent results on the achievable rates of finite-length codes to analyze the system performance. With codewords of finite length, we derive closed-form expressions for the outage probabilities of INR HARQ and study the throughput in the cases with variable-length coding. Moreover, we evaluate the effect of feedback delay on the throughput and derive sufficient conditions for the usefulness of the HARQ protocols, in terms of power-limited throughput. The results show that, for a large range of HARQ feedback delays, the throughput is increased by finite-length coding INR HARQ, if the sub-codeword lengths are properly adapted.
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| 7. |
- Mohammed, S. K., et al.
(författare)
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Constant-Envelope Multi-User Precoding for Frequency-Selective Massive MIMO Systems
- 2013
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Ingår i: IEEE Wireless Communications Letters. - : IEEE. - 2162-2337 .- 2162-2345. ; 2:5, s. 547-550
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Tidskriftsartikel (refereegranskat)abstract
- We consider downlink precoding in a frequency-selective multi-user Massive MIMO system with highly efficient but non-linear power amplifiers at the base station (BS). A low-complexity precoding algorithm is proposed, which generates constant-envelope (CE) signals at each BS antenna. To achieve a desired per-user information rate, the extra total transmit power required under the per-antenna CE constraint when compared to the commonly used less stringent total average transmit power constraint, is small.
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| 8. |
- Ngo, Hien Quoc, et al.
(författare)
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Massive MIMO with Optimal Power and Training Duration Allocation
- 2014
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Ingår i: IEEE Wireless Communications Letters. - : IEEE. - 2162-2337 .- 2162-2345. ; 3:6, s. 605-608
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Tidskriftsartikel (refereegranskat)abstract
- We consider the uplink of massive multicell multiple-input multiple-output systems, where the base stations (BSs), equipped with massive arrays, serve simultaneously several terminals in the same frequency band. We assume that the BS estimates the channel from uplink training, and then uses the maximum ratio combining technique to detect the signals transmitted from all terminals in its own cell. We propose an optimal resource allocation scheme which jointly selects the training duration,training signal power, and data signal power in order to maximize the sum spectral efficiency, for a given total energy budget spent in a coherence interval. Numerical results verify the benets of the optimal resource allocation scheme. Furthermore, we show that more training signal power should be used at low signal-to-noise ratio(SNRs), and vice versa at high SNRs. Interestingly, for the entire SNR regime, the optimal training duration is equal to the number of terminals.
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| 9. |
- Piemontese, Amina, et al.
(författare)
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Frequency Packing and Multiuser Detection for CPMs: How to Improve the Spectral Efficiency of DVB-RCS2 Systems
- 2013
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Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 2:1, s. 74-77
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Tidskriftsartikel (refereegranskat)abstract
- We consider a frequency division multiplexed systemwhere each user adopts a continuous phase modulation (CPM)and multiuser detection is employed at the receiver side. Thespectral efficiency (SE) is used as a performance measure tocompare, from an information-theoretic point of view, differentmodulation formats. More precisely, we consider the newCPM formats recently included in the DVB-RCS2 standard.We describe a framework for computing the information rate(IR) and the SE of such systems, and use it for optimizing thechannel spacing between adjacent users and the CPM phaseresponse. Our analysis reveals that modulation formats adoptedin the DVB-RCS2 standard are suboptimal in terms of SE, whileif we allow multiuser detection excellent performance can beachieved by using simple binary formats and highly frequencypacked signals. Furthermore, we consider practical schemes,where CPMs are serially concatenated with an outer code, and alow-complexity multiuser receiver is employed, showing that thetheoretical limits predicted by the IR analysis can be approached.
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| 10. |
- Pitarokoilis, Antonios, et al.
(författare)
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On the Optimality of Single-Carrier Transmission in Large-Scale Antenna Systems
- 2012
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Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 1:4, s. 276-279
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A single carrier transmission scheme is presentedfor the frequency selective multi-user (MU) multiple-input singleoutput(MISO) Gaussian Broadcast Channel (GBC) with a basestation (BS) having M antennas and K single antenna users.The proposed transmission scheme has low complexity andfor M ≫ K it is shown to achieve near optimal sum-rateperformance at low transmit power to receiver noise power ratio.Additionally, the proposed transmission scheme results in anequalization-free receiver and does not require any MU resourceallocation and associated control signaling overhead. Also, thesum-rate achieved by the proposed transmission scheme is shownto be independent of the channel power delay profile (PDP). Interms of power efficiency, the proposed transmission scheme alsoexhibits an O(M) array power gain. Simulations are used toconfirm analytical observations.
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| 11. |
- Tombaz, Sibel, et al.
(författare)
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On metrics and models for energy-efficient design of wireless access networks
- 2014
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Ingår i: IEEE Wireless Communications Letters. - 2162-2337 .- 2162-2345. ; 3:6, s. 649-652
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Tidskriftsartikel (refereegranskat)abstract
- The energy efficiency of wireless access networks has attracted significant interest, due to escalating energy cost and environmental concerns. How energy efficiency should be measured is, however, still disputed in the literature. In this letter, we discuss the impact of performance metrics and energy consumption models in network dimensioning. We argue that, using a popular metric, the number of bits/Joule may give misleading results, unless the capacity and coverage requirements of the system are carefully defined. We also claim that the energy consumption in the backhaul and the idle power of the base stations have to be taken into account. To support our claims, we demonstrate in a simple example how misleading results can be obtained by using flawed performance metrics.
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| 12. |
- Wang, Zhao, et al.
(författare)
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Secrecy degrees of freedom of the 2 interference channel with delayed CSIT
- 2014
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Ingår i: IEEE Wireless Communications Letters. - 2162-2337 .- 2162-2345. ; 3:4, s. 341-344
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Tidskriftsartikel (refereegranskat)abstract
- We consider the two-hop interference channel with confidential messages (ICC), where each transmitter sends one confidential message to its intended destination through two trusted relays. We study the secrecy degrees of freedom (SDoF) of the considered 2 ?2 ?2 ICC with delayed channel state information at transmitters (CSIT). We settle the optimal SDoF of the considered network to be (1/2, 1/2). Thus, the considered network has a strictly larger sum SDoF than a two-user one-hop ICC with even full CSIT. Moreover, we study the SDoF of the network with limited Shannon feedback, that only one relay can obtain the delayed CSIT and output feedback from the destinations. The optimal SDoF is also shown to be (1/2, 1/2), revealing that only limited feedback can also bring SDoF gain. Our proposed achievable schemes in both cases are integrated forms of the retrospective interference alignment and artificial noise transmission.
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| 13. |
- Yan, Mao, et al.
(författare)
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Outage Probability of Switch and Stay Combining in Two-Way Amplify-and-Forward Relay Networks
- 2012
-
Ingår i: IEEE Wireless Communications Letters. - : IEEE. - 2162-2337 .- 2162-2345. ; 1:4, s. 296-299
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Tidskriftsartikel (refereegranskat)abstract
- In this letter, a switch-and-stay combining (SSC) in two-way amplify-and-forward (AF) networks with two relays is proposed and analyzed. In particular, the closed-form expression of the outage probability for the proposed scheme over Rayleigh fading channels is derived. Asymptotic performance analysis for high signal-to-noise ratio (SNR) is also presented. It is shown that the SSC scheme is capable of realizing full diversity order, and even achieving the same outage performance as the best-relay selection (BRS), when reasonable switching thresholds are set. Simulations are provided to corroborate the theoretical analysis.
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| 14. |
- Butt, M. M., et al.
(författare)
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Maximizing Minimum Throughput Guarantees : The Small Violation Probability Region
- 2013
-
Ingår i: Wireless Communications Letters. - 2162-2337. ; 2:3, s. 271-274
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Tidskriftsartikel (refereegranskat)abstract
- Providing minimum throughput guarantees is one of the goals for radio resource allocation schemes. It is difficult to provide these guarantees without defining violation probability due to limited power budget and rapidly changing conditions of the wireless channel. For every practical scheduling scheme, there is a feasibility region defined by the minimum guaranteed throughput and the corresponding probability that the users fail to get the guaranteed throughput (violation probability). In this work, we focus on minimizing the violation probability specifically in the small probability region. We compare our results with major schedulers available in literature and show that our scheme outperforms them in the small violation probability region.
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| 15. |
- Larsson, Erik G., et al.
(författare)
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Piggybacking an Additional Lonely Bit on Linearly Coded Payload Data
- 2012
-
Ingår i: IEEE Wireless Communications Letters. - : IEEE Communications Society. - 2162-2337. ; 1:4, s. 292-295
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We provide a coding scheme, by which an additional lonely bit can be piggybacked on a payload data packet encoded with a linear channel code, at no essential extra cost in power or bandwidth. The underlying principle is to use the additional bit to select which of two linear codes that should be used for encoding the payload packet, this way effectively creating a nonlinear code. We give a fast algorithm for detecting the additional bit, without decoding the data packet. Applications include control signaling, for example, transmission of ACK/NACK bits
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| 16. |
- Moosavi, Reza, et al.
(författare)
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Optimized Encoding of Scheduling Assignments Using Finite Blocklength Coding Bounds
- 2014
-
Ingår i: Wireless Communications Letters, IEEE. - 2162-2337. ; PP:99, s. 1-4
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Tidskriftsartikel (refereegranskat)abstract
- We provide an analytical framework for optimizing the resources required for signaling of control information in wireless multiple access systems. In doing so, we use recent results in information theory, namely a new bound on the achievable rate in the finite blocklength regime by Polyanskiy. We formulate optimization problems for finding the minimum required number of channel uses such that the overall error probability in decoding the control information is below a given threshold for three different control signaling schemes.
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| 17. |
- Savic, Vladimir, et al.
(författare)
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Reducing Communication Overhead for Cooperative Localization Using Nonparametric Belief Propagation
- 2012
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Ingår i: IEEE Wireless Communication Letters. - 2162-2337. ; 1:4, s. 308-311
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Tidskriftsartikel (refereegranskat)abstract
- A number of methods for cooperative localization has been proposed, but most of them provide only location estimate, without associated uncertainty. On the other hand, nonparametric belief propagation (NBP), which provides approximated posterior distributions of the location estimates, is expensive mostly because of the transmission of the particles. In this paper, we propose a novel approach to reduce communication overhead for cooperative positioning using NBP. It is based on: i) communication of the beliefs (instead of the messages), ii) approximation of the belief with Gaussian mixture of very few components, and iii) censoring. According to our simulations results, these modifications reduce significantly communication overhead while providing the estimates almost as accurate as the transmission of the particles.
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| 18. |
- Vinel, Alexey, 1983-
(författare)
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3GPP LTE Versus IEEE 802.11p/WAVE : Which Technology is Able to Support Cooperative Vehicular Safety Applications?
- 2012
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Ingår i: IEEE Wireless Communications Letters. - Piscataway, NJ : IEEE Communications Society. - 2162-2337. ; 1:2, s. 125-128
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Tidskriftsartikel (refereegranskat)abstract
- The concept of vehicular ad-hoc networks enables the design of emergent automotive safety applications, which are based on the awareness among vehicles. Recently, a suite of 802.11p/WAVE protocols aimed at supporting car-to-car communications was approved by IEEE. Existing cellular infrastructure and, above all 3GPP LTE, is being considered as another communication technology appropriate for vehicular applications. This letter provides a theoretical framework which compares the basic patterns of both the technologies in the context of safety-of-life vehicular scenarios. We present mathematical models for the evaluation of the considered protocols in terms of successful beacon delivery probability.
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| 19. |
- Wang, Zhao, et al.
(författare)
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Degrees of freedom of multi-hop MIMO broadcast networks with delayed CSIT
- 2013
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Ingår i: IEEE Wireless Communications Letters. - 2162-2337. ; 2:2, s. 207-210
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Tidskriftsartikel (refereegranskat)abstract
- We study the sum degrees of freedom (DoF) of a class of multi-layer relay-aided MIMO broadcast networks with delayed channel state information at transmitters (CSIT). In the assumed network a K-antenna source intends to communicate to K single-antenna destinations, with the help of N-2 layers of K full-duplex single-antenna relays. We assume identical and independent fading channels on every hop. Two practical delayed CSIT feedback scenarios are studied. If the source can obtain the CSI feedback signals from all layers, we prove the optimal sum DoF of the network to be K 1+12+...+1K. If the CSI feedback is only within each hop, we show that when K=2 the optimal sum DoF is 4 3, and when K≥ 3 the sum DoF 32 is achieved asymptotically.
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