| 1. |
- Fodor, Gábor, et al.
(författare)
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MU-MIMO Receiver Design and Performance Analysis in Time-Varying Rayleigh Fading
- 2022
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Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 70:2, s. 1214-1228
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Tidskriftsartikel (refereegranskat)abstract
- Minimizing the symbol error in the uplink of multi-user multiple input multiple output systems is important, because the symbol error affects the achieved signal-to-interference-plus-noise ratio (SINR) and thereby the spectral efficiency of the system. Despite the vast literature available on minimum mean squared error (MMSE) receivers, previously proposed receivers for block fading channels do not minimize the symbol error in time-varying Rayleigh fading channels. Specifically, we show that the true MMSE receiver structure does not only depend on the statistics of the CSI error, but also on the autocorrelation coefficient of the time-variant channel. It turns out that calculating the average SINR when using the proposed receiver is highly non-trivial. In this paper, we employ a random matrix theoretical approach, which allows us to derive a quasi-closed form for the average SINR, which allows to obtain analytical exact results that give valuable insights into how the SINR depends on the number of antennas, employed pilot and data power and the covariance of the time-varying channel. We benchmark the performance of the proposed receiver against recently proposed receivers and find that the proposed MMSE receiver achieves higher SINR than the previously proposed ones, and this benefit increases with increasing autoregressive coefficient.
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| 2. |
- Fodor, Gabor, 1964-, et al.
(författare)
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Performance Analysis of a Linear MMSE Receiver in Time-Variant Rayleigh Fading Channels
- 2021
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Ingår i: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0090-6778 .- 1558-0857. ; 69:6, s. 4098-4112
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Tidskriftsartikel (refereegranskat)abstract
- The performance of the uplink of single and multiuser multiple input multiple output (MIMO) systems depends crucially on the receiver architecture and the quality of channel state information at the receiver. Therefore, several previous works have developed minimum mean squared error (MMSE) receivers and proposed balancing the resources spent on acquiring channel state information and transmitting the payload of data packets. Somewhat surprisingly, the most popular MIMO linear MMSE receivers do not exploit the correlation structure that is present in autoregressive Rayleigh fading environments. Therefore, in this article we first develop a new linear receiver that not only takes channel state information errors into account in minimizing the MSE of the received data symbols, but it also utilizes that the subsequent noisy channel coefficients are correlated. For this new linear MMSE receiver, we derive the achieved MSE as a function of the number of receive antennas and the pilot-to-data power ratio. Interestingly, we find that the pilot power that minimizes the MSE of the data symbols does not depend on the number of antennas and that the new linear MMSE receiver outperforms previously proposed MIMO receivers when the autocorrelation coefficient of the channel is high.
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| 3. |
- Fodor, Sebastian, et al.
(författare)
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Optimizing Pilot Spacing in MU-MIMO Systems Operating Over Aging Channels
- 2023
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Ingår i: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0090-6778 .- 1558-0857. ; 71:6, s. 3708-3720
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Tidskriftsartikel (refereegranskat)abstract
- In the uplink of multiuser multiple input multiple output (MU-MIMO) systems operating over aging channels, pilot spacing is crucial for acquiring channel state information and achieving high signal-to-interference-plus-noise ratio (SINR). Somewhat surprisingly, very few works examine the impact of pilot spacing on the correlation structure of subsequent channel estimates and the resulting quality of channel state information considering channel aging. In this paper, we consider a fast-fading environment characterized by its exponentially decaying autocorrelation function, and model pilot spacing as a sampling problem to capture the inherent trade-off between the quality of channel state information and the number of symbols available for information carrying data symbols. We first establish a quasi-closed form for the achievable deterministic equivalent SINR when the channel estimation algorithm utilizes multiple pilot signals. Next, we establish upper bounds on the achievable SINR and spectral efficiency, as a function of pilot spacing, which helps to find the optimum pilot spacing within a limited search space. Our key insight is that to maximize the achievable SINR and the spectral efficiency of MU-MIMO systems, proper pilot spacing must be applied to control the impact of the aging channel and to tune the trade-off between pilot and data symbols.
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| 4. |
- Gabor, Fodor
(creator_code:cre_t)
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Method and apparatus for optimizing elastic flows in a multi-path network for a traffic demand
- 2008
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Patent (övrigt vetenskapligt/konstnärligt)abstract
- The present invention provides a method for optimizing elastic flows in a multi-path network for a traffic demand by jointly determining a bandwidth for each flow in a set of flows that realize the traffic demand and an optimized path for the traffic demand by maximizing a fairness utility. The present invention can be implemented as a computer program embodied on a computer readable medium in which the functions or steps of the method are implemented as code segments. In addition, the present invention can be implemented as an apparatus that includes a processor and an interface communicably coupling the processor to the multi-path network. The processor jointly determines a bandwidth for each flow in a set of flows that realize the traffic demand and an optimized path for the traffic demand by maximizing a fairness utility.
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| 5. |
- Malicsko, Gabor, et al.
(författare)
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Link capacity dimensioning and path optimization for networks supporting elastic services
- 2002
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Ingår i: IEEE ICC Proceedings. - New York : IEEE. - 0780374002 ; , s. 2304-2311, s. 2304-2311
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Konferensbidrag (refereegranskat)abstract
- We consider the problem of link capacity dimensioning and routing optimization in networks that support elastic flows and maintain proportional fairness among these flows. We assume that each demand between the origin-destination (O-D) pairs is associated with a minimum and a maximum bandwidth requirement and that a certain allocated bandwidth to a user demand (which must be between these minimum and maximum values) generates revenue for the network operator. On the other hand, the operator is incurred a capacity dependent cost for each link in the network. We then formulate the problem of bandwidth allocation, routing optimization and link capacity dimensioning as an optimization problem where the operator's objective is to maximize profit (under the fairness constraint). We propose computationally efficient algorithms to solve some important variants of this problem.
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| 6. |
- Pioro, Michal, et al.
(författare)
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Optimal link capacity dimensioning in proportionally fair networks
- 2002
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Ingår i: NETWORKING 2002: Networking Technologies, Services, and Protocols; Performance of Computer and Communication Networks; Mobile and Wireless Communications. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 0302-9743. - 3540437096 ; 2345, s. 277-288
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Konferensbidrag (refereegranskat)abstract
- We consider the problem of link capacity dimensioning and bandwidth allocation in networks that support elastic flows and maintain proportional fairness among these flows. We assume that a certain allocated bandwidth to a user demand generates revenue for the network operator. On the other hand, the operator incurs a capacity dependent cost for each link in the network. The operator's profit is the difference between the revenue and the total link cost. Under this assumption, the problem is to determine the bandwidth of the flows and the link capacities such that the profit is maximized. We first show that under fairly general assumptions, the optimum allocation of flows leads to selecting the lowest cost paths between originator-destination pairs. We also derive explicit formulae for the bandwidth allocated to these flows. We distinguish the case when the operator's capacity budget is fixed ("equality budget constraint", in which case the profit is maximized when the revenue is maximized) and the case when the budget is upper-bounded ("inequality budget constraint", in which case the profit can - in general - be maximized by using some portion of the capacity budget). Finally, we show numerical examples to highlight some of the trade-offs between profit maximization, revenue maximization and fairness.
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| 7. |
- Abrardo, A., et al.
(författare)
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A message passing approach for resource allocation in cellular OFDMA communications
- 2012
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Ingår i: Global Communications Conference (GLOBECOM), 2012 IEEE. - : IEEE. - 9781467309219 ; , s. 4583-4588
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Konferensbidrag (refereegranskat)abstract
- This paper proposes a distributed and low-complexity resource allocation scheme for cellular OFDMA networks. In particular, we consider ReMP, a reweighted message passing algorithm that perturbs the standard max-sum algorithm by suitably reweighting messages. In a single-cell scenario, such a scheme allows to achieve convergence to a fixed and provably optimum point without employing any central controller. The ReMP algorithm is then adapted to a multi-cell environment. To this aim, we devise X-ReMP, a ReMP-based algorithm that combines cross-cell signaling and the regular ReMP routine that still runs within each cell. The cross-signaling among cells aids ReMP to deal with the inter-cell multiple-access interference, so that X-ReMP allows convergence to a good working point in terms of system throughput even in presence of strong inter-cell interference.
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| 8. |
- Abrardo, Andrea, et al.
(författare)
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Distributed Digital and Hybrid Beamforming Schemes With MMSE-SIC Receivers for the MIMO Interference Channel
- 2019
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Ingår i: IEEE Transactions on Vehicular Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9545 .- 1939-9359. ; 68:7, s. 6790-6804
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses the problem of weighted sumrate maximization and mean squared error (MSE) minimization for the multiple-input multiple-output (MIMO) interference channel. Specifically, we consider a weighted minimum MSE architecture where each receiver employs successive interference cancellation (SIC) to separate the various received data streams and derive a hybrid beamforming scheme, where the transmitters operate with a number of radio frequency chains smaller than the number of antennas, particularly suited for millimeter-wave channels and 5G applications. To derive our proposed schemes, we first study the relationship between sum-rate maximization and weighted MSE minimization when using SIC receivers, assuming fully digital beamforming. Next, we consider the important-and, as it turns out, highly non-trivial-case where the transmitters employ hybrid digital/analog beamforming, developing a distributed joint hybrid precoding and SIC-based combining algorithm. Moreover, for practical implementation, we propose a signaling scheme that utilizes a common broadcast channel and facilitates the acquisition of channel state information, assuming minimal assistance from a central node such as a cellular base station. Numerical results show that both the proposed weighted MMSE-SIC schemes exhibit great advantages with respect to their linear counterparts in terms of complexity, feedback information, and performance.
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| 9. |
- Abrardo, Andrea, et al.
(författare)
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MMSE Receiver Design and SINR Calculation in MU-MIMO Systems With Imperfect CSI
- 2019
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Ingår i: IEEE Wireless Communications Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-2337 .- 2162-2345. ; 8:1, s. 269-272
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Tidskriftsartikel (refereegranskat)abstract
- The performance of the uplink of multiuser multiple input multiple output systems depends critically on the receiver architecture and on the quality of the acquired channel state information. A popular approach is to design linear receivers that minimize the mean squared error (MSE) of the received data symbols. Unfortunately, most of the literature does not take into account the presence of channel state information errors in the MSE minimization. In this letter we develop a linear minimum MSE (MMSE) receiver that employs the noisy instantaneous channel estimates to minimize the MSE, and highlight the dependence of the receiver performance on the pilot-to-data power ratio. By invoking the theory of random matrices, we calculate the users' signal-to-interference-plus-noise ratio as a function of the number of antennas and the pilot-to-data power ratio of all users. Numerical results indicate that this new linear receiver outperforms the classical mismatched MMSE receiver.
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| 10. |
- Abrardo, A, et al.
(författare)
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Network coding schemes for D2D communications based relaying for cellular coverage extension
- 2015
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Ingår i: European transactions on telecommunications. - : European transactions on Telecommunications. - 1124-318X .- 2161-3915. ; -
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Tidskriftsartikel (refereegranskat)abstract
- Although network-assisted device-to-device (D2D) communications are known to improve the spectral and energy efficiency of proximal communications, the performance of cooperative D2D schemes in licenced spectrum is less understood when employed to extend the coverage of cellular networks. In this paper, we study the performance of D2D-based range extension in terms of sum rate and power efficiency when a relaying user equipment (UE) helps to improve the coverage for cell edge UEs. In our design, the relaying UE may have own traffic to transmit and receive to/from the cellular base station (BS) and can operate either in amplify-and-forward (AF) or decode-and-forward (DF) modes and can make use of either digital or analogue physical (PHY) layer network coding. In this rather general setting, we propose mode selection, resource allocation and power control schemes and study their performance by means of system simulations. We find that the performance of the DF scheme with network coding is superior both to the traditional cellular and the AF-based relaying schemes, including AF with two-slot or three-slot PHY layer network coding.
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