| 1. |
- Zhang, Jiayi, et al.
(författare)
-
Achievable Rate of Rician Large-Scale MIMO Channels With Transceiver Hardware Impairments
- 2016
-
Ingår i: IEEE Transactions on Vehicular Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9545 .- 1939-9359. ; 65:10, s. 8800-8806
-
Tidskriftsartikel (refereegranskat)abstract
- Transceiver hardware impairments (e.g., phase noise, inphase/quadrature-phase imbalance, amplifier nonlinearities, and quantization errors) have obvious degradation effects on the performance of wireless communications. While prior works have improved our knowledge of the influence of hardware impairments of single-user multiple-input multiple-output ( MIMO) systems over Rayleigh fading channels, an analysis encompassing the Rician fading channel is not yet available. In this paper, we pursue a detailed analysis of regular and large-scale (LS) MIMO systems over Rician fading channels by deriving new closed-form expressions for the achievable rate to provide several important insights for practical system design. More specifically, for regular MIMO systems with hardware impairments, there is always a finite achievable rate ceiling, which is irrespective of the transmit power and fading conditions. For LS-MIMO systems, it is interesting to find that the achievable rate loss depends on the Rician K-factor, which reveals that the favorable propagation in LS-MIMO systems can remove the influence of hardware impairments. However, we show that the nonideal LS-MIMO system can still achieve high spectral efficiency due to its huge degrees of freedom.
|
|
| 2. |
- Yang, Xi, et al.
(författare)
-
Power Scaling Laws for Massive MIMO Relay Systems with Linear Transceivers
- 2016
-
Ingår i: 2015 IEEE Global Conference on Signal and Information Processing, GlobalSIP 2015. Orlando; United States; 13-16 December 2015. - 9781479975914 ; , s. 7416932, Pages 38-42
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we study the uplink of a relay- assisted multiuser massive MIMO system. The relay station (RS) equipped with M1 antennas processes the received signal from K single-antenna users, using maximum ratio combining (MRC)/zero-forcing (ZF) detection, and then forwards the post- processed signal to the base station (BS) with M2 antennas, according to the all-pass relay protocol. In particular, we derive closed-form approximations of the ergodic achievable rate lower bounds, assuming that MRC/ZF combining is performed at the BS. Furthermore, we examine the power scaling law of the proposed system, and find that the transmit powers of relay or users can be reduced in proportion to M1 or M2, respectively, without any loss in the achievable rate.
|
|
| 3. |
- Zhang, Xinlin, 1986, et al.
(författare)
-
Energy Efficiency Optimization in Hardware-Constrained Large-Scale MIMO Systems
- 2014
-
Ingår i: 2014 11th International Symposium on Wireless Communications Systems, ISWCS 2014 - Proceedings. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781479958634 ; , s. 992-996
-
Konferensbidrag (refereegranskat)abstract
- Large-scale multiple-input multiple-output (MIMO) communication systems can bring substantial improvement in spectral efficiency and/or energy efficiency, due to the excessive degrees-of-freedom and huge array gain. However, large-scale MINI is expected to deploy lower-cost radio frequency (RF) components, which are particularly prone to hardware impairments. Unfortunately, compensation schemes are not able to remove the impact of hardware impairments completely, such that a certain amount of residual impairments always exists. In this paper, we investigate the impact of residual transmit RF impairments (RTRI) on the spectral and energy efficiency of training-based point-to-point large-scale MIMO systems, and seek to determine the optimal training length and number of antennas which maximize the energy efficiency. We derive deterministic equivalents of the signal-to-noise-and-interference ratio (SINR) with zero-forcing (ZF) receivers, as well as the corresponding spectral and energy efficiency, which are shown to be accurate even for small number of antennas. Through an iterative sequential optimization, we find that the optimal training length of systems with RTRI can be smaller compared to ideal hardware systems in the moderate SNR regime, while larger in the high SNR regime. Moreover, it is observed that RTRI can significantly decrease the optimal number of transmit and receive antennas.
|
|
| 4. |
- Zhang, Xinlin, 1986, et al.
(författare)
-
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.
|
|
| 5. |
- Zhang, Xinlin, 1986, et al.
(författare)
-
Impact of residual transmit RF impairments on training-based MIMO systems
- 2014
-
Ingår i: 2014 IEEE International Conference on Communications, ICC 2014. - : IEEE. - 9781479920037 ; , s. 4741-4746
-
Konferensbidrag (refereegranskat)abstract
- Radio-frequency (RF) impairments, that exist intimately in wireless communications systems, can severely degrade the performance of traditional multiple-input multiple-output (MIMO) systems. Although compensation schemes can cancel out part of these RF impairments, there still remains a certain amount of impairments. These residual impairments have fundamental impact on the MIMO system performance. However, most of the previous works have neglected this factor. In this paper, a training-based MIMO system with residual transmit RF impairments (RTRI) is considered. In particular, we derive a new channel estimator for the proposed model, and find that RTRI can create an irreducible estimation error floor. Moreover, we show that, in the presence of RTRI, the optimal training sequence length can be larger than the number of transmit antennas, especially in the low and high signal-to-noise ratio (SNR) regimes. An increase in the proposed approximated achievable rate is also observed by adopting the optimal training sequence length. When the training and data symbol powers are required to be equal, we demonstrate that, at high SNRs, systems with RTRI demand more training, whereas at low SNRs, such demands are nearly the same for all practical levels of RTRI.
|
|
| 6. |
- Zhang, Xinlin, 1986, et al.
(författare)
-
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.
|
|
| 7. |
- Zhang, Xinlin, 1986
(författare)
-
MIMO Systems with Residual Hardware Impairments
- 2014
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recent years have witnessed an unprecedented explosion in mobile data traffic, due to the expansion of numerous types of wireless devices, which have enabled a plethora of data-hungry applications. Novel techniques, such as large-scale multiple-input multiple-output (MIMO) systems, represent potential candidates to support the ever-growing demands. However, large-scale MIMO systems will be a viable solution only if low-cost and energy-efficient hardware is deployed, which is particularly prone to impairments. Previous works have reported effective calibration schemes and compensation algorithms to mitigate individual hardware impairments, such as I/Q imbalance, phase noise and amplifier nonlinearities. However, a certain amount of residual hardware impairments always persist.In this thesis, we aim at exploring the fundamental limits that residual hardware impairments have imposed on MIMO systems, and more interestingly, on large-scale MIMO systems. We consider both the cases whereof the receiver has perfect channel state information (CSI) and estimated CSI. Important insights are gained through the analysis of system performance indicators, such as ergodic channel capacity and achievable rates, channel estimation accuracy and energy efficiency.Paper A characterizes the ergodic channel capacity of Rayleigh fading channels in the presence of transceiver residual hardware impairments. Closed-form capacity formulas for MIMO systems with arbitrary number of antennas and signal-to-noise ratio (SNR) values are derived, while approximations at low and high SNRs are also presented. We further extend our results to large-scale MIMO systems, and derive the channel capacity in the asymptotic regime.Paper B, which is a journal version of Paper D, considers a training-based MIMO system with transmit residual hardware impairments. The impact of residual hardware impairments on channel estimation accuracy and achievable rates with different linear receivers is theoretically analyzed. The achievable-rate-maximizing training lengths are thereafter presented. For large-scale MIMO systems, we derive deterministic equivalents of the achievable rates, and the corresponding optimal training lengths.In paper C, we assess residual hardware impairments from an energy-efficiency perspective. Assuming estimated CSI and zero-forcing (ZF) receivers, we find the optimal training lengths, as well as, the number of transmit and receive antennas that maximize the system energy efficiency at any given SNR, through a proposed iterative sequential optimization algorithm.
|
|
| 8. |
- Zhang, Xinlin, 1986, et al.
(författare)
-
On the MIMO Capacity with Residual Transceiver Hardware Impairments
- 2014
-
Ingår i: IEEE International Conference on Communications, ICC 2014, Sydney, Australia. - : IEEE. - 9781479920037 ; , s. 5299-5305
-
Konferensbidrag (refereegranskat)abstract
- Radio-frequency (RF) impairments in the transceiver hardware of communication systems (e.g., phase noise (PN), high power amplifier (HPA) nonlinearities, or in- phase/quadrature-phase (I/Q) imbalance) can severely degrade the performance of traditional multiple-input multiple-output (MIMO) systems. Although calibration algorithms can partially compensate these impairments, the remaining distortion still has substantial impact. Despite this, most prior works have not analyzed this type of distortion. In this paper, we investigate the impact of residual transceiver hardware impairments on the MIMO system performance. In particular, we consider a transceiver impairment model, which has been experimentally validated, and derive analytical ergodic capacity expressions for both exact and high signal-to-noise ratios (SNRs). We demonstrate that the capacity saturates in the high-SNR regime, thereby creating a finite capacity ceiling. We also present a linear approximation for the ergodic capacity in the low-SNR regime, and show that impairments have only a second-order impact on the capacity. Furthermore, we analyze the effect of transceiver impairments on large-scale MIMO systems; interestingly, we prove that if one increases the number of antennas at one side only, the capacity behaves similar to the finite-dimensional case. On the contrary, if the number of antennas on both sides increases with a fixed ratio, the capacity ceiling vanishes; thus, impairments cause only a bounded offset in the capacity compared to the ideal transceiver hardware case.
|
|
