| 1. |
- Bencivenni, Carlo, 1986, et al.
(författare)
-
Aperiodic Switched Array for Line-of-Sight MIMO Backhauling
- 2018
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Ingår i: IEEE Antennas and Wireless Propagation Letters. - 1548-5757 .- 1536-1225. ; 17:9, s. 1712-1716
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Tidskriftsartikel (refereegranskat)abstract
- A switchable aperiodic array solution is proposed to increase the minimum channel capacity of a multiple-input-multiple-output (MIMO) backhauling system over an extended line-of-sight communication range. The objective is to propose a low-complexity design solution that is cost-effective in regard to the manufacturing, installation, and its design process. It is shown that by adding only one switch and one auxiliary antenna per base station, a 4 × 4 MIMO system can be realized that is capable of minimizing the capacity loss that both regular and aperiodic arrays suffer from as a function of the link distance.
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| 2. |
- Castaneda, Oscar, et al.
(författare)
-
1-bit Massive MU-MIMO Precoding in VLSI
- 2017
-
Ingår i: IEEE Journal on Emerging and Selected Topics in Circuits and Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 2156-3365 .- 2156-3357. ; 7:4, s. 508-522
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Tidskriftsartikel (refereegranskat)abstract
- Massive multi-user (MU) multiple-input multiple-output (MIMO) will be a core technology in fifth-generation (5G) wireless systems as it offers significant improvements in spectral efficiency compared to existing multi-antenna technologies. The presence of hundreds of antenna elements at the base station (BS), however, results in excessively high hardware costs and power consumption, and requires high interconnect throughput between the baseband-processing unit and the radio unit. Massive MU-MIMO that uses low-resolution analog-to-digital and digital-toanalog converters (DACs) has the potential to address all these issues. In this paper, we focus on downlink precoding for massive MU-MIMO systems with 1-bit DACs at the BS. The objective is to design precoders that simultaneously mitigate MU interference and quantization artifacts. We propose two nonlinear 1-bit precoding algorithms and corresponding very large-scale integration (VLSI) designs. Our algorithms rely on biconvex relaxation, which enables the design of efficient 1-bit precoding algorithms that achieve superior error-rate performance compared with that of linear precoding algorithms followed by quantization. To showcase the efficacy of our algorithms, we design VLSI architectures that enable efficient 1-bit precoding for massive MU-MIMO systems, in which hundreds of antennas serve tens of user equipments. We present corresponding field-programmable gate array (FPGA) reference implementations to demonstrate that 1-bit precoding enables reliable and high-rate downlink data transmission in practical systems.
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| 3. |
- Jacobsson, Sven, 1990, et al.
(författare)
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Massive MU-MIMO-OFDM Downlink with One-Bit DACs and Linear Precoding
- 2018
-
Ingår i: Proceedings - IEEE Global Communications Conference, GLOBECOM. - 2334-0983 .- 2576-6813. ; , s. 1-6
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Konferensbidrag (refereegranskat)abstract
- Massive multiuser (MU) multiple-input multiple- output (MIMO) is foreseen to be a key technology in future wireless communication systems. In this paper, we analyze the downlink performance of an orthogonal frequency division multiplexing (OFDM)-based massive MU-MIMO system in which the base station (BS) is equipped with 1-bit digital-to-analog converters (DACs). Using Bussgang’s theorem, we characterize the performance achievable with linear precoders (such as maximal-ratio transmission and zero forcing) in terms of bit error rate (BER). Our analysis accounts for the possibility of oversampling the time-domain transmit signal before the DACs. We further develop a lower bound on the information-theoretic sum-rate throughput achievable with Gaussian inputs.Our results suggest that the performance achievable with 1-bit DACs in a massive MU-MIMO-OFDM downlink are satisfactory provided that the number of BS antennas is sufficiently large.
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| 4. |
- Jacobsson, Sven, 1990, et al.
(författare)
-
Massive MU-MIMO-OFDM uplink with direct RF-sampling and 1-Bit ADCs
- 2019
-
Ingår i: 2019 IEEE Globecom Workshops, GC Wkshps 2019 - Proceedings.
-
Konferensbidrag (refereegranskat)abstract
- Advances in analog-to-digital converter (ADC) technology have opened up the possibility to directly digitize wideband radio frequency (RF) signals, avoiding the need for analog down- conversion. In this work, we consider an orthogonal frequency- division multiplexing (OFDM)-based massive multi-user (MU) multiple-input multiple-output (MIMO) uplink system that relies on direct RF-sampling at the base station and digitizes the received RF signals with 1-bit ADCs. Using Bussgang's theorem, we provide an analytical expression for the error-vector magnitude (EVM) achieved by digital down-conversion and zero-forcing combining. Our results demonstrate that direct RF-sampling 1-bit ADCs enables low EVM and supports high-order constellations in the massive MU-MIMO- OFDM uplink.
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| 5. |
- Jacobsson, Sven, 1990, et al.
(författare)
-
Massive multiuser MIMO downlink with low- resolution converters
- 2018
-
Ingår i: International Zurich Seminar on Information and Communication (IZS 2018) Proceedings.
-
Konferensbidrag (refereegranskat)abstract
- In this review paper, we analyze the downlink of a massive multiuser multiple-input multiple-output system in which the base station is equipped with low-resolution digital-to-analog converters (DACs). Using Bussgang’s theorem, we characterize the sum-rate achievable with a Gaussian codebook and scaled nearestneighbor decoding at the user equipments (UE). For the case of 1-bit DACs, we show how to evaluate the sum-rate using Van Vleck’s arcsine law. For the case of multi-bit DACs, for which the sum-rate cannot be expressed in closed-form, we present two approximations. The first one, which is obtained by ignoring the overload (or clipping) distortion caused by the DACs, turns out to be accurate provided that one can adapt the dynamic range of the quantizer to the received-signal strength so as to avoid clipping. The second approximation, which is obtained by modeling the distortion noise as a white process, both in time and space, is accurate whenever the resolution of the DACs is sufficiently high and when the oversampling ratio is small. We conclude the paper by discussing extensions to orthogonal frequency-division multiplexing systems; we also touch upon the problem of out-of-band emissions in lowprecision-DAC architectures.
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| 6. |
- Jacobsson, Sven, 1990, et al.
(författare)
-
Nonlinear 1-bit precoding for massive MU-MIMO with higher-order modulation
- 2017
-
Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. ; , s. 763-767
-
Konferensbidrag (refereegranskat)abstract
- Massive multi-user (MU) multiple-input multiple-output (MIMO) is widely believed to be a core technology for the upcoming fifth-generation (5G) wireless communication standards. The use of low-precision digital-to-analog converters (DACs) in MU-MIMO base stations is of interest because it reduces the power consumption, system costs, and raw baseband data rates. In this paper, we develop novel algorithms for downlink precoding in massive MU-MIMO systems with 1-bit DACs that support higher-order modulation schemes such as 8-PSK or 16-QAM. Specifically, we present low-complexity nonlinear precoding algorithms that achieve low error rates when combined with blind or training-based channel-estimation algorithms at the user equipment. These results are in stark contrast to linear-quantized precoding algorithms, which suffer from a high error floor if used with high-order modulation schemes and 1-bit DACs
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| 7. |
- Jacobsson, Sven, 1990, et al.
(författare)
-
On Out-of-Band Emissions of Quantized Precoding in Massive MU-MIMO-OFDM
- 2017
-
Ingår i: Conference Record of the Asilomar Conference on Signals Systems and Computers. - 1058-6393. - 9781538618233 ; , s. 21-26
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Konferensbidrag (refereegranskat)abstract
- We analyze out-of-band (OOB) emissions in the massive multi-user (MU) multiple-input multiple-output (MIMO) downlink. We focus on systems in which the base station (BS) is equipped with low-resolution digital-to-analog converters (DACs) and orthogonal frequency-division multiplexing (OFDM) is used to communicate to the user equipments (UEs) over frequency- selective channels. We demonstrate that analog filtering in combination with simple frequency-domain digital predistortion (DPD) at the BS enables a significant reduction of OOB emissions, but degrades the signal-to-interference-noise-and-distortion ratio (SINDR) at the UEs and increases the peak-to-average power ratio (PAR) at the BS. We use Bussgang’s theorem to characterize the tradeoffs between OOB emissions, SINDR, and PAR, and to study the impact of analog filters and DPD on the error-rate perfor- mance of the massive MU-MIMO-OFDM downlink. Our results show that by carefully tuning the parameters of the analog filters, one can achieve a significant reduction in OOB emissions with only a moderate degradation of error-rate performance and PAR.
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| 8. |
- Jacobsson, Sven, 1990, et al.
(författare)
-
One-Bit Massive MIMO: Channel Estimation and High-Order Modulations
- 2015
-
Ingår i: 2015 IEEE International Conference on Communication Workshop, ICCW 2015. - 9781467363051 ; , s. 1304-1309
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Konferensbidrag (refereegranskat)abstract
- We investigate the information-theoretic throughout achievable on a fading communication link when the receiver is equipped with one-bit analog-to-digital converters (ADCs). The analysis is conducted for the setting where neither the transmitter nor the receiver have a priori information on the realization of the fading channels. This means that channel-state information needs to be acquired at the receiver on the basis of the one-bit quantized channel outputs. We show that least-squares (LS) channel estimation combined with joint pilot and data processing is capacity achieving in the single-user, single-receive-antenna case. We also investigate the achievable uplink throughput in a massive multiple-input multiple-output system where each element of the antenna array at the receiver base-station feeds a one-bit ADC. We show that LS channel estimation and maximum-ratio combining are sufficient to support both multiuser operation and the use of high-order constellations. This holds in spite of the severe nonlinearity introduced by the one-bit ADCs.
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| 9. |
- Jacobsson, Sven, 1990, et al.
(författare)
-
Throughput Analysis of Massive MIMO Uplink With Low-Resolution ADCs
- 2017
-
Ingår i: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 16:6, s. 4038-4051
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the uplink throughput achievable by a multiple-user (MU) massive multiple-input multiple-output (MIMO) system, in which the base station is equipped with a large number of low-resolution analog-to-digital converters (ADCs). Our focus is on the case where neither the transmitter nor the receiver have any a priori channel state information. This implies that the fading realizations have to be learned through pilot transmission followed by channel estimation at the receiver, based on coarsely quantized observations. We propose a novel channel estimator, based on Bussgang's decomposition, and a novel approximation to the rate achievable with finite-resolution ADCs, both for the case of finite-cardinality constellations and of Gaussian inputs, that is accurate for a broad range of system parameters. Through numerical results, we illustrate that, for the 1-bit quantized case, pilot-based channel estimation together with maximal-ratio combing, or zero-forcing detection enables reliable multi-user communication with high-order constellations, in spite of the severe nonlinearity introduced by the ADCs. Furthermore, we show that the rate achievable in the infinite-resolution (no quantization) case can be approached using ADCs with only a few bits of resolution. We finally investigate the robustness of low-ADC-resolution MU-MIMO uplink against receive power imbalances between the different users, caused for example by imperfect power control.
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| 10. |
- Kolomvakis, Nikolaos, 1985, et al.
(författare)
-
Downlink Performance of Regularized ZF in Massive MIMO Systems Subject to IQ Imbalance
- 2017
-
Ingår i: IEEE International Conference on Communications. - 1550-3607.
-
Konferensbidrag (refereegranskat)abstract
- This paper studies the impact of in-phase and quadrature imbalance (IQI) on the downlink of a single-cell multiuser multiple-input multiple-output (MU-MIMO) system with large antenna arrays. Moreover, we consider a time-division duplex (TDD) system where we assume uplink/downlink channel reciprocity in the downlink precoding design and study the impact of uplink/downlink channel mismatch on the downlink rate caused by different IQI on the base station (BS) and users equipment (UEs). A tractable analytical expression to predict the achievable downlink rates is derived for the regularized zero-forcing (RZF) and based on this expression, we prove that, as the number of BS antennas grow large, the achievable downlink rate of each UE is limited either by the RX IQI at the UEs or by the simultaneous presence of the transmit/receive IQI at the BS and TX IQI at the UEs, when there is uplink/downlink channel mismatch.
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| 11. |
- Kolomvakis, Nikolaos, 1985, et al.
(författare)
-
IQ Imbalance in Multiuser Systems: Channel Estimation and Compensation
- 2016
-
Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 64:7, s. 3039-3051
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we consider the uplink of a single-cell multi-user single-input multiple-output (MU-SIMO) system with in-phase and quadrature-phase imbalance (IQI). Particularly, we investigate the effect of receive (RX) IQI on the performance of MU-SIMO systems with large antenna arrays employing maximum-ratio combining (MRC) receivers. In order to study how IQI affects channel estimation, we derive a new channel estimator for the IQI-impaired model and show that the higher the value of signal-to-noise ratio (SNR) the higher the impact of IQI on the spectral efficiency (SE) of MRC receivers. Moreover, a novel pilot-based joint estimator of the augmented MIMO channel matrix and IQI coefficients is described and then, a low-complexity IQI compensation scheme is proposed which is based on the IQI coefficients' estimation and it is independent of the channel gain. The performance of the proposed compensation scheme is analytically evaluated by deriving a tractable approximation of the ergodic SE assuming transmission over Rayleigh fading channels with large-scale fading.Furthermore, we investigate how many MSs should be scheduled in massive MIMO systems with IQI and show that the highest SE loss occurs at the optimal operating point.Finally, by deriving asymptotic power scaling laws, and proving that the SE loss due to IQI is asymptotically independent of the number of BS antennas, we show that massive multiple-input multiple-output (MIMO) is resilient to the effect of RX IQI.
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| 12. |
- Kolomvakis, Nikolaos, 1985, et al.
(författare)
-
Massive MIMO Systems with IQ Imbalance: Channel Estimation and Sum Rate Limits
- 2017
-
Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 65:6, s. 2382 - 2396
-
Tidskriftsartikel (refereegranskat)abstract
- This paper studies the impact of in-phase and quadrature imbalance (IQI) on single-cell multiuser multiple-input multiple-output (MU-MIMO) systems with large antenna arrays. Moreover, we consider a time-division duplex (TDD) system where we assume uplink/downlink channel reciprocity in the downlink precoding design. First, we investigate the effect of transceiver IQI on the uplink channel estimation by deriving the linear minimum-mean-square-error (LMMSE) estimator for the IQ-impaired model and prove that only the receiver IQI at the base station (BS) limits the estimation accuracy. Then, we study the impact of uplink/downlink channel mismatch on the downlink rate caused by different IQI on the BS and user equipments (UEs). We prove that the achievable downlink rate of each UE is limited either by the receiver IQI at the UEs or jointly by the transmit and receive IQI at the BS, when there is mismatch between the uplink and downlink channels.
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| 13. |
- Kolomvakis, Nikolaos, 1985, et al.
(författare)
-
Massive MIMO with IQ Imbalance: Performance analysis and compensation
- 2015
-
Ingår i: IEEE International Conference on Communications. - 1550-3607. - 9781467364324 ; , s. 1703-1709
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we consider the uplink of a single-cell massive multiple-input multiple-output (MIMO) system with inphase and quadrature-phase imbalance (IQI). This scenario is of particular importance in massive MIMO systems, where the deployment of lower-cost, lower-quality components is desirable to make massive MIMO a viable technology. Particularly, we investigate the effect of IQI on the performance of massive MIMO employing maximum-ratio combining (MRC) receivers. In order to study how IQI affects channel estimation, we derive a new channel estimator for the IQI-impaired model and show that IQI can substantially downgrade the performance of MRC receivers. Moreover, a low-complexity IQI compensation scheme, suitable for massive MIMO, is proposed which is based on the IQI coefficients' estimation and it is independent of the channel gain. The performance of the proposed compensation scheme is analytically evaluated by deriving a tractable approximation of the ergodic achievable rate and providing the asymptotic power scaling laws assuming transmission over Rayleigh fading channels with log-normal large-scale fading. Finally, we show that massive MIMO effectively suppresses the residual IQI effects, as long as, the compensation scheme is applied.
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| 14. |
- Makki, Behrooz, 1980, et al.
(författare)
-
Finite Block-length Analysis of Large-but-finite MIMO Systems
- 2019
-
Ingår i: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 8:1, s. 113-116
-
Tidskriftsartikel (refereegranskat)abstract
- This letter studies the performance of point-to-point multiple-input-multiple-output (MIMO) systems in the presence of large but finite numbers of transmit and receive antennas. We use some recent results on the achievable rates of finite-length codes to analyze the system performance in the cases with short packets. The results are presented for different fading models. With codewords of finite length, we derive closed-form expressions for the error probability/throughput and determine the minimum number of antennas which are required to satisfy different error probability/throughput requirements. As we show, while the error-constrained required number of antennas is sensitive to the length of short codewords, its effect is negligible for codewords of moderate/long length.
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| 15. |
- Seifi, Nima, 1981, et al.
(författare)
-
Adaptive Multicell 3-D Beamforming in Multiantenna Cellular Networks
- 2016
-
Ingår i: IEEE Transactions on Vehicular Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9545 .- 1939-9359. ; 65:8, s. 6217-6231
-
Tidskriftsartikel (refereegranskat)abstract
- We consider a cellular network with multiantenna base stations (BSs) and single-antenna users, multicell cooperation, imperfect channel state information (CSI), and directional antennas, each with a vertically adjustable beam. We investigate the impact of the elevation angle of the BS antenna pattern, which is denoted as tilt, on the performance of the considered network when employing either a traditional single-cell transmission or a fully cooperative multicell transmission. Using the results of this investigation, we propose a novel hybrid multicell cooperation technique in which the intercell interference is controlled via either cooperative beamforming in the horizontal plane or coordinated beamforming in the vertical plane of the wireless channel, which is denoted as adaptive multicell 3-D beamforming. The main idea is to divide the coverage area into two disjoint vertical regions and adapt the multicell cooperation strategy at the BSs when serving each region. A fair scheduler is used to share the time slots between the vertical regions. It is shown that the proposed technique can achieve performance comparable with that of a fully cooperative transmission but with significantly lower complexity and signaling requirements. To facilitate computationally efficient simulation and design space exploration, accurate approximations of the user ergodic rate are proposed for different transmission strategies under imperfect CSI.
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| 16. |
- Seifi, Nima, 1981, et al.
(författare)
-
Elevation plane spatial multicell interference mitigation with No CSI sharing
- 2015
-
Ingår i: IEEE Globecom Workshops, GC Wkshps 2015, San Diego, United States, 6-10 December 2015. - 9781467395267
-
Konferensbidrag (refereegranskat)abstract
- We study downlink transmission in a cellular network with multi-antenna base stations (BSs) and single-antenna users. We propose a novel coordinated transmission strategy that controls the intercell interference (ICI) via exploiting the elevation plane of the wireless channel. The key idea is to divide the area of each cell into two disjoint vertical regions and to serve the non-adjacent vertical regions in the neighboring cells according to a set of pre-determined coordinated transmission patterns. A scheduler is used to dynamically allocate the available time-slots among transmission patterns. By appropriately adapting the elevation angle of the antenna main beam, denoted as tilt, at the BSs in each pattern, ICI can be effectively suppressed. Unlike the state-of-the-art coordinated transmission schemes, the proposed technique requires no channel state information sharing among BSs and/or infeasible BS tilting capabilities, but achieves comparable performance.
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| 17. |
- Sezgin, Ibrahim Can, 1992, et al.
(författare)
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A Low-Complexity Distributed-MIMO Testbed Based on High-Speed Sigma-Delta-Over-Fiber
- 2019
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 67:7, s. 2861-2872
-
Tidskriftsartikel (refereegranskat)abstract
- Distributed multiple-input-multiple-output (D-MIMO) is a very promising technique to improve capacity and quality of service for emerging 5G systems. In this paper, we propose a flexible and low-cost testbed for D-MIMO systems, where a sigma-delta over fiber (SDoF) solution is proposed to address the fundamental challenge of phase-coherent transmission between multiple distributed access points (APs) from a central unit (CU). Employing low-cost standardized optical data interconnects, SDoF, brings a very flexible and software controlled transmission of RF signals over optical fiber. An SDoF-based D-MIMO testbed with a CU feeding 12 distributed APs has been realized and experimentally evaluated. Initial experiments of D-MIMO and conventional colocated MIMO systems at 2.365 GHz have been performed to demonstrate the flexibility and potential of the proposed testbed as a new powerful tool in the design and analysis of emerging communication system concepts.
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| 18. |
- Zhang, Xinlin, 1986, et al.
(författare)
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Hybrid beamforming in uplink massive MIMO systems in the presence of blockers
- 2017
-
Ingår i: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - 1520-6149. ; , s. 6503-6507
-
Konferensbidrag (refereegranskat)abstract
- Hybrid beamforming (HBF) is a potential solution to reduce the baseband hardware cost in massive multiple-input multiple-output (MIMO) systems that has drawn considerable attention recently. In this paper, we consider the uplink of a multiuser massive MIMO system in the presence of blockers. Such blockers, which arise from, for example, users served by other non-cooperative base stations (BSs), can limit the system performance if not handled properly. We propose a HBF scheme that can remove the impact of blockers, while preserving signals from intended users. Specifically, in our two-step receive beamforming scheme, the analog beamformer (ABF) is designed based on channel covariance matrices to minimize the powers of blockers, while the digital beamformer (DBF) deals with inter-user interference. We propose an iterative algorithm that efficiently gives a good sub-optimal solution to the NP-hard problem in the ABF design. Moreover, we consider a more complete BS architecture by incorporating automatic gain control (AGC) and analog-to-digital converter (ADC). As we show in the simulations, for a system with full-precision ADCs, our scheme approaches the sum rate of an ideal fully-digital system. Interestingly, for a system with low-resolution ADCs, our HBF scheme can even outperform a fully-digital system.
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| 19. |
- Zhang, Xinlin, 1986, et al.
(författare)
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Impact of Residual Transmit RF Impairments on Training-Based MIMO Systems
- 2015
-
Ingår i: IEEE Transactions on Communications. - : Institute of Electrical and Electronics Engineers (IEEE). - 0090-6778 .- 1558-0857. ; 63:8, s. 2899-2911
-
Tidskriftsartikel (refereegranskat)abstract
- Radio-frequency (RF) impairments, which intimately exist in wireless communication systems, can severely limit the performance of multiple-input-multiple-output (MIMO) systems. Although we can resort to compensation schemes to mitigate some of these impairments, a certain amount of residual impairments always persists. In this paper, we consider a training-based point-to-point MIMO system with residual transmit RF impairments (RTRI) using spatial multiplexing transmission. Specifically, we derive a new linear channel estimator for the proposed model, and show that RTRI create an estimation error floor in the high signal-to-noise ratio (SNR) regime. Moreover, we derive closed-form expressions for the signal-to-noise-plus-interference ratio (SINR) distributions, along with analytical expressions for the ergodic achievable rates of zero-forcing, maximum ratio combining, and minimum mean-squared error receivers, respectively. In addition, we optimize the ergodic achievable rates with respect to the training sequence length and demonstrate that finite dimensional systems with RTRI generally require more training at high SNRs than those with ideal hardware. Finally, we extend our analysis to large-scale MIMO configurations, and derive deterministic equivalents of the ergodic achievable rates. It is shown that, by deploying large receive antenna arrays, the extra training requirements due to RTRI can be eliminated. In fact, with a sufficiently large number of receive antennas, systems with RTRI may even need less training than systems with ideal hardware.
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