| 21. |
- Ingason, Tryggvi, 1983, et al.
(författare)
-
Impact of frequency selective channels on a line-of-sight MIMO microwave radio link
- 2010
-
Ingår i: IEEE Vehicular Technology Conference. - 1550-2252. - 9781424425198
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Two line-of-sight (LoS) multiple-input multipleoutput (MIMO) systems for point-to-point microwave radio links are simulated and analyzed. Both 2×2 spatially-separated, singlepolarized and 4×4 spatially-separated, dual-polarized systems are considered in the presence of a frequency selective and time varying channel. Time dependence is introduced by moving the antennas during the simulation and thereby introducing the need for an adaptive space-time-equalizer (STE). Our results indicate that a time-varying frequency selective LoS MIMO channel puts higher requirements on the STE and introduces a higher SNR penalty compared to a single-input single-output (SISO) system. © 2010 IEEE.
|
|
| 22. |
- Jacobsson, Sven, 1990, et al.
(författare)
-
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
-
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.
|
|
| 23. |
- 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.
|
|
| 24. |
- 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.
|
|
| 25. |
- 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
|
|
| 26. |
- 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
-
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.
|
|
| 27. |
- 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
-
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.
|
|
| 28. |
- 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.
|
|
| 29. |
- 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.
|
|
| 30. |
- 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.
|
|
