| 1. |
- 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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| 2. |
- Fodor, Gabor, et al.
(författare)
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A recursive formula to calculate the steady state of CDMA networks
- 2005
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Ingår i: Performance Challenges for Efficient Next Generation Networks. - Beijing : International Teletraffic Congress. ; , s. 1285-1294
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Several previous contributions have proposed calculation methods that can be used to calculate the steady state (and from it the blocking probabilities) in CDMA systems. To our best knowledge, this present work is the first one that extends the classical Kaufman-Roberts formula such that it becomes applicable in CDMA where elastic services (with state dependent instantaneous bit rate and average bit rate dependent residency time) are supported. The core of this method is to approximate the original irreversible Markov chain with a reversible one and to assign a proper blocking measure to the macro states of the system.
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| 3. |
- Fodor, Gabor, et al.
(författare)
-
Link capacity sharing for throughput-blocking optimally in a mixed rigid-elastic traffic environment by dividing the bandwidth into common and dedicated parts
- 1999
-
Patent (populärvet., debatt m.m.)abstract
- The invention concerns an efficient strategy for sharing link bandwidth in a mixed rigid-elastic traffic environment, as well as a strategy for sharing bandwidth among elastic traffic flows. The idea according to the invention is to sharing the link bandwidth among rigid and elastic traffic by dividing the link bandwidth into a first common part CCOM for elastic as well as rigid traffic and a second part CELA dedicated for elastic traffic. Subsequently, one or more admission control parameters for the elastic traffic are determined in order to restrict the number of elastic traffic flows simultaneously present on the link. In particular, by formulating a call-level model for elastic traffic and determining a maximum number NELA of admissible elastic traffic flows based on call-level constraints for the elastic traffic related to throughput and/or blocking, the so-called throughput-to-blocking trade-off for elastic traffic can be fully considered.
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| 4. |
- 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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| 5. |
- Fodor, Gabor, et al.
(författare)
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On Minimizing the MSE in the Presence of Channel State Information Errors
- 2015
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Ingår i: IEEE Communications Letters. - : IEEE Press. - 1089-7798 .- 1558-2558. ; 19:9, s. 1604-1607
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Tidskriftsartikel (refereegranskat)abstract
- We consider the uplink of a multiuser multiple input multiple output (MU MIMO) system, in which the base station acquires channel state information (CSI) for which the estimation error depends on the resources assigned to the uplink pilot symbols. For this system, we first derive the receiver that minimizes the mean square error (MSE) of the uplink detected data symbols, as opposed to the naïve receiver that does not minimize the MSE in the presence of CSI errors. We then derive a closed form expression for the MSE as a function of the employed pilot-to-data power ratio, number of antennas and the MU MIMO interference power. This expression allows us to gain the insight that the gain of using the actual MMSE receiver as opposed to the naïve receiver becomes particularly important when the number of BS antennas is large.
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| 6. |
- Fodor, Gabor, et al.
(författare)
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On the Impact of Antenna Correlation and CSI Errors on the Pilot-to-Data Power Ratio
- 2016
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Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 64:6, s. 2622-2633
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Tidskriftsartikel (refereegranskat)abstract
- In systems employing pilot-symbol aided channel estimation, the pilot-to-data power ratio is known to have a large impact on performance. Therefore, previous works proposed methods setting the pilot power such that either the weighted sum of the mean squared error (MSE) of the estimated data symbols is minimized or the overall spectral efficiency (SE) is maximized. However, previous works did not take into account the impact of correlated antennas and channel state information (CSI) errors on the optimal pilot power setting. In this paper, we consider the uplink of a multiuser multiple-input multiple-output (MU MIMO) system employing a receiver that minimizes the MSE of the received data symbols in the presence of CSI errors and derive closed-form expressions for theMSE and the achievable SE. These expressions take into account the impact of antenna correlation and CSI errors, and are a function of pilot power and the number of receive antennas. The analytical and numerical results can help set the pilot power, minimizing the MSE in multiple antenna systems.
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| 7. |
- Fodor, Gabor, 1964-, et al.
(författare)
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On the Impact of Antenna Correlation on the Pilot-Data Balance in Multiple Antenna Systems
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We consider the uplink of a single cell single input multiple output (SIMO) system, in which the mobile stations use intra-cell orthogonal pilots to facilitate uplink channel estimation. In such systems, the problem of pilot-data transmission power balancing is known to have a large impact on the performance on the achievable uplink data rates. In this paper we derive a closed form expression for the mean square error (MSE) as a function of the pilot and data power levels under a per-user sum pilot-data power constraint. Our major contribution is the derivation of the MSE formula for Gaussian channels under arbitrary channel covariance matrices. For example, our model readily allows to study the MSE as a function of the number of antennas and antenna correlation structures, including the popular spatial channel model (SCM). Numerical results suggest that the impact of antenna spacing on the MSE is limited, but the angle of arrival (AoA) and angular spread have a more articulated impact on the MSE performance. We also find that as the number of antennas at the base station grows large, a higher percentage of the power budget should be allocated to pilot signals than with a low number of antennas.
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| 8. |
- Fodor, Gábor, 1964-, et al.
(författare)
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On the Pilot-Data Power Trade Off in Single Input Multiple Output Systems
- 2014
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Ingår i: 20th European Wireless Conference, EW 2014. - 9783800736218 ; , s. 485-492
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Konferensbidrag (refereegranskat)abstract
- We consider a single cell single input multiple output (SIMO) system employing orthogonal frequencydivision multiplexing (OFDM). In such systems, setting the pilot-to-data power ratio (PDPR)has a large impact on the spectral and energy efficiency. In this paper we provide a closedform solution for the mean square error (MSE) of the received data as a function of thePDPR assuming Gaussian channels and minimum mean square error (MMSE) equalization.In numerical experiments we find that the MSE is a convex function of the PDPRand study the optimal PDPR as the number of antennas at the base station (BS) grows large.We find that the optimal PDPR heavilydepends on the number of antennas and the path loss between the mobile station and theBS. Specifically, as the number of antennas grows large, a larger portionof the total power budget needs to be allocated for pilot signals, especially for low pathloss users.
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| 9. |
- Fodor, Gabor, et al.
(författare)
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On the tradeoff between blocking and dropping probabilities in CDMA networks supporting elastic services
- 2006
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Ingår i: Lecture Notes in Computer Science. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 0302-9743 .- 1611-3349. ; 3976, s. 954-965
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Tidskriftsartikel (refereegranskat)abstract
- This paper is a sequel of previous work, in which we proposed a model and computational technique to calculate the Erlang capacity of a single CDMA cell that supports elastic services. The present paper extends that base model by taking into account two important features of CDMA. First, we capture the impact of soft blocking by modeling the neighbor cell interference as a lognormally distributed random variable. Secondly, we model the impact of the outage by taking into account that in-progress sessions can be dropped with a probability that depends on the current load in the system. We then consider a system with elastic and rigid service classes and analyze the trade-off between the total (soft and hard) blocking probabilities on the one hand and the throughput and the session drop probabilities on the other.
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| 10. |
- Fodor, Gabor, et al.
(författare)
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Optimal Pilot-to-Data Power Ratio for Massive SIMO Systems
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We consider a single cell single input multiple output (SIMO) system employing orthogonal frequencydivision multiplexing (OFDM). In such systems, setting the pilot-to-data power ratio (PDPR)has a large impact on the spectral and energy efficiency. In this paper we provide a closedform solution for the mean square error (MSE) of the received data as a function of thePDPR assuming Gaussian channels and minimum mean square error (MMSE) equalization.In numerical experiments we find that the MSE is a convex function of the PDPRand study the optimal PDPR as the number of antennas at the base station (BS) grows large.We find that the optimal PDPR heavilydepends on the number of antennas and the path loss between the mobile station and theBS. Specifically, as the number of antennas grows large, a larger portionof the total power budget needs to be allocated for pilot signals, especially for low pathloss users.
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