The Experts below are selected from a list of 4371 Experts worldwide ranked by ideXlab platform
Mikko Valkama - One of the best experts on this subject based on the ideXlab platform.
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Digital Cancellation of Passive Intermodulation in FDD Transceivers
arXiv: Signal Processing, 2018Co-Authors: Muhammad Zeeshan Waheed, Pablo Pascual Campo, Adnan Kiayani, Dani Korpi, Lauri Anttila, Mikko ValkamaAbstract:Modern radio systems and transceivers utilize carrier aggregation (CA) to meet the demands for higher and higher data rates. However, the adoption of CA in the existing Long Term Evolution (LTE)-Advanced and emerging 5G New Radio (NR) mobile networks, in case of Frequency Division Duplexing (FDD), may incur self-interference challenges with certain band combinations. More specifically, the nonlinear distortion products of the transmit signals or component carriers (CCs), stemming from the passive radio Frequency (RF) front-end components of the transceiver, can appear in one or more of the configured receiver bands, potentially leading to the receiver desensitization. In this paper, we present advanced baseband equivalent signal models for such passive intermodulation (PIM) distortion viewed from the RX point of view, considering also potential memory effects in the PIM generation. Then, building on these signal models, a digital self-interference cancellation technique operating in the transceiver digital front-end is presented. The performance of the proposed solution is evaluated with real-life RF measurements for LTE-Advanced type user equipment (UE) with dual CC inter-band CA, demonstrating excellent suppression properties. The findings in this work indicate that digital cancellation is a feasible approach for improving the receiver sensitivity of mobile devices that may be prone to RF front-end induced PIM challenges.
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ACSSC - Digital Cancellation of Passive Intermodulation in FDD Transceivers
2018 52nd Asilomar Conference on Signals Systems and Computers, 2018Co-Authors: Muhammad Zeeshan Waheed, Pablo Pascual Campo, Adnan Kiayani, Dani Korpi, Lauri Anttila, Mikko ValkamaAbstract:Modern radio systems and transceivers utilize carrier aggregation (CA) to meet the demands for higher and higher data rates. However, the adoption of CA in the existing Long Term Evolution (LTE)-Advanced and emerging 5G New Radio (NR) mobile networks, in case of Frequency Division Duplexing (FDD), may incur self-interference challenges with certain band combinations. More specifically, the nonlinear distortion products of the transmit signals or component carriers (CCs), stemming from the passive radio Frequency (RF) front-end components of the transceiver, can appear in one or more of the configured receiver bands, potentially leading to the receiver desensitization. In this paper, we present advanced baseband equivalent signal models for such passive intermodulation (PIM) distortion viewed from the RX point of view, considering also potential memory effects in the PIM generation. Then, building on these signal models, a digital self-interference cancellation technique operating in the transceiver digital front-end is presented. The performance of the proposed solution is evaluated with real-life RF measurements for LTE-Advanced type user equipment (UE) with dual CC interband CA, demonstrating excellent suppression properties. The findings in this work indicate that digital cancellation is a feasible approach for improving the receiver sensitivity of mobile devices that may be prone to RF front-end induced PIM challenges.
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low complexity subband digital predistortion for spurious emission suppression in noncontiguous spectrum access
IEEE Transactions on Microwave Theory and Techniques, 2016Co-Authors: Mahmoud Abdelaziz, Lauri Anttila, Chance Tarver, Kaipeng Li, Joseph R Cavallaro, Mikko ValkamaAbstract:Noncontiguous transmission schemes combined with high power-efficiency requirements pose big challenges for radio transmitter and power amplifier (PA) design and implementation. Due to the nonlinear nature of the PA, severe unwanted emissions can occur, which can potentially interfere with neighboring channel signals or even desensitize the own receiver in Frequency Division Duplexing transceivers. In this paper, to suppress such unwanted emissions, a low-complexity subband digital predistortion solution, specifically tailored for spectrally noncontiguous transmission schemes in low-cost devices, is proposed. The proposed technique aims at mitigating only the selected spurious intermodulation distortion components at the PA output, hence allowing for substantially reduced processing complexity compared with classical linearization solutions. Furthermore, novel decorrelation-based parameter learning solutions are also proposed and formulated, which offer reduced computing complexity in parameter estimation as well as the ability to track time-varying features adaptively. Comprehensive simulation and RF measurement results are provided, using a commercial LTE-Advanced mobile PA, to evaluate and validate the effectiveness of the proposed solution in real-world scenarios. The obtained results demonstrate that highly efficient spurious component suppression can be obtained using the proposed solutions.
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digital mitigation of transmitter induced receiver desensitization in carrier aggregation fdd transceivers
IEEE Transactions on Microwave Theory and Techniques, 2015Co-Authors: Adnan Kiayani, Lauri Anttila, Mahmoud Abdelaziz, Vesa Lehtinen, Mikko ValkamaAbstract:Carrier aggregation transmissions in Frequency Division Duplexing devices reduce the Duplexing distance between the transmitter (TX) and receiver (RX) bands. As a consequence, the spurious intermodulation distortion products created by the nonlinear RF front-end of the TX may easily extend over to the RX band, potentially causing own RX desensitization. In this paper, we propose an efficient and computationally feasible adaptive digital identification and cancellation technique to mitigate the RX desensitization. We first show that the spurious leakage signal at own RX band depends on an equivalent leakage channel that models the overall signal leakage path including the TX nonlinearities, duplexer filter responses, and RX path. The parameters of the equivalent leakage channel can be efficiently estimated with the least squares or the recursive least squares algorithm, using the actual digital transmit data as a reference, and then used to regenerate and cancel the leakage interference from the received signal. The performance of the proposed technique is evaluated with extensive computer simulations, as well as with practical real-world RF measurements, demonstrating excellent calibration properties with up to 19-dB improvement in singal-to-interference plus noise ratio of the desired received signal.
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Digital suppression of power amplifier spurious emissions at receiver band in FDD transceivers
IEEE Signal Processing Letters, 2014Co-Authors: Adnan Kiayani, Lauri Anttila, Mikko ValkamaAbstract:As the Duplexing distances in emerging wireless systems are getting more and more narrow, achieving sufficient isolation between transmit and receive chains using radio Frequency (RF) filtering alone becomes increasingly complex. Particularly challenging problem in this context is the spectral regrowth of nonlinear power amplifiers (PAs) in the transmit chain, and other transmitter out-of-band (OOB) emissions, which can heavily desensitize the receiver chain. In this letter, we first carry out detailed modeling of transmitter OOB emissions due to practical wideband PAs with memory effects. Stemming from this modeling, and using the known digital transmit data inside the transceiver as reference, we then propose an efficient nonlinear digital cancellation technique to suppress the transmitter OOB emissions in the receiver path. The proposed technique is verified and analyzed using extensive computer simulations, rendering excellent suppression properties, hence enabling sufficient TX-RX isolation in Frequency Division Duplexing (FDD) transceivers without any extra analog/RF filtering or PA linearization.
Robert W. Heath - One of the best experts on this subject based on the ideXlab platform.
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channel feedback based on aod adaptive subspace codebook in fdd massive mimo systems
IEEE Transactions on Communications, 2018Co-Authors: Wenqian Shen, Byonghyo Shim, Linglong Dai, Zhaocheng Wang, Robert W. HeathAbstract:Channel feedback is essential in Frequency Division Duplexing (FDD) massive multiple-input multiple-output (MIMO) systems. Unfortunately, prior work on multiuser MIMO has shown that the feedback overhead scales linearly with the number of base station (BS) antennas, which is large in massive MIMO systems. To reduce the feedback overhead, we propose an angle-of-departure (AoD) adaptive subspace codebook for channel feedback in FDD massive MIMO systems. Our key insight is to leverage the observation that path AoDs vary more slowly than the path gains. Within the angle coherence time, by utilizing the constant AoD information, the proposed AoD-adaptive subspace codebook is able to quantize the channel vector in a more accurate way. From the performance analysis, we show that the feedback overhead of the proposed codebook only scales linearly with a small number of dominant (path) AoDs instead of the large number of BS antennas. Moreover, we compare the proposed quantized feedback technique using the AoD-adaptive subspace codebook with a comparable analog feedback method. Extensive simulations show that the proposed AoD-adaptive subspace codebook achieves good channel feedback quality, while requiring low overhead.
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Two-Dimensional AoD and AoA Acquisition for Wideband Millimeter-Wave Systems With Dual-Polarized MIMO
IEEE Transactions on Wireless Communications, 2017Co-Authors: Dalin Zhu, Junil Choi, Robert W. HeathAbstract:In this paper, a novel two-dimensional super-resolution angle-of-departure (AoD) and angle-of-arrival (AoA) estimation technique is proposed for wideband millimeter-wave multiple-input multiple-output systems with dual-polarized antenna elements. The key ingredient of the proposed method is the custom designed beam pairs, from which there exists an invertible function of the AoD/AoA. A new multi-layer reference signal structure is developed for the proposed method to facilitate angle estimation for wideband channels with dual-polarized antenna elements. To reduce feedback in closed-loop Frequency Division Duplexing systems, a novel differential feedback strategy is proposed to feedback the estimated angle pairs. Numerical results demonstrate that good azimuth/elevation AoD and AoA estimation performance can be achieved under different levels of signal-to-noise ratio, channel conditions, and antenna array configurations.
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Limited feedback power loading for OFDM
IEEE MILCOM 2004. Military Communications Conference 2004., 2004Co-Authors: David James Love, Robert W. HeathAbstract:Orthogonal Frequency Division multiplexing (OFDM) is a practical technique for communicating over broadband channels in multi-path fading environments. It is well known that varying the power allocation from Frequency tone-to-Frequency tone, commonly called power loading, can improve capacity or error rate performance. Unfortunately, the implementation of power loading is complicated by the fact that the transmitter must have knowledge of the forwardlink channel. This assumption is often unrealistic, particularly in systems using Frequency Division Duplexing (FDD). In this paper we present a limited feedback approach for power loading OFDM symbols. In this approach, the receiver, which is assumed to have full forwardlink channel knowledge, designs a power loading vector and conveys it to the transmitter over a limited rate feedback channel. The technique uses a codebook of power loading vectors known to both the transmitter and receiver. We design limited feedback schemes for error rate optimized and capacity optimized power loading. We show how to design quantizers using iterative optimization techniques from the theory of vector quantization for the case of error rate selection. In the capacity case, we characterize optimal feedback schemes for asymptotic signal-to-noise ratio (SNR) scenarios and present a simple method called multi-mode power loading that uses a codebook that switches subcarriers off and on. Simulation results show that the limited feedback techniques provide performance close to perfect channel knowledge power loading.
Lauri Anttila - One of the best experts on this subject based on the ideXlab platform.
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Digital Cancellation of Passive Intermodulation in FDD Transceivers
arXiv: Signal Processing, 2018Co-Authors: Muhammad Zeeshan Waheed, Pablo Pascual Campo, Adnan Kiayani, Dani Korpi, Lauri Anttila, Mikko ValkamaAbstract:Modern radio systems and transceivers utilize carrier aggregation (CA) to meet the demands for higher and higher data rates. However, the adoption of CA in the existing Long Term Evolution (LTE)-Advanced and emerging 5G New Radio (NR) mobile networks, in case of Frequency Division Duplexing (FDD), may incur self-interference challenges with certain band combinations. More specifically, the nonlinear distortion products of the transmit signals or component carriers (CCs), stemming from the passive radio Frequency (RF) front-end components of the transceiver, can appear in one or more of the configured receiver bands, potentially leading to the receiver desensitization. In this paper, we present advanced baseband equivalent signal models for such passive intermodulation (PIM) distortion viewed from the RX point of view, considering also potential memory effects in the PIM generation. Then, building on these signal models, a digital self-interference cancellation technique operating in the transceiver digital front-end is presented. The performance of the proposed solution is evaluated with real-life RF measurements for LTE-Advanced type user equipment (UE) with dual CC inter-band CA, demonstrating excellent suppression properties. The findings in this work indicate that digital cancellation is a feasible approach for improving the receiver sensitivity of mobile devices that may be prone to RF front-end induced PIM challenges.
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ACSSC - Digital Cancellation of Passive Intermodulation in FDD Transceivers
2018 52nd Asilomar Conference on Signals Systems and Computers, 2018Co-Authors: Muhammad Zeeshan Waheed, Pablo Pascual Campo, Adnan Kiayani, Dani Korpi, Lauri Anttila, Mikko ValkamaAbstract:Modern radio systems and transceivers utilize carrier aggregation (CA) to meet the demands for higher and higher data rates. However, the adoption of CA in the existing Long Term Evolution (LTE)-Advanced and emerging 5G New Radio (NR) mobile networks, in case of Frequency Division Duplexing (FDD), may incur self-interference challenges with certain band combinations. More specifically, the nonlinear distortion products of the transmit signals or component carriers (CCs), stemming from the passive radio Frequency (RF) front-end components of the transceiver, can appear in one or more of the configured receiver bands, potentially leading to the receiver desensitization. In this paper, we present advanced baseband equivalent signal models for such passive intermodulation (PIM) distortion viewed from the RX point of view, considering also potential memory effects in the PIM generation. Then, building on these signal models, a digital self-interference cancellation technique operating in the transceiver digital front-end is presented. The performance of the proposed solution is evaluated with real-life RF measurements for LTE-Advanced type user equipment (UE) with dual CC interband CA, demonstrating excellent suppression properties. The findings in this work indicate that digital cancellation is a feasible approach for improving the receiver sensitivity of mobile devices that may be prone to RF front-end induced PIM challenges.
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low complexity subband digital predistortion for spurious emission suppression in noncontiguous spectrum access
IEEE Transactions on Microwave Theory and Techniques, 2016Co-Authors: Mahmoud Abdelaziz, Lauri Anttila, Chance Tarver, Kaipeng Li, Joseph R Cavallaro, Mikko ValkamaAbstract:Noncontiguous transmission schemes combined with high power-efficiency requirements pose big challenges for radio transmitter and power amplifier (PA) design and implementation. Due to the nonlinear nature of the PA, severe unwanted emissions can occur, which can potentially interfere with neighboring channel signals or even desensitize the own receiver in Frequency Division Duplexing transceivers. In this paper, to suppress such unwanted emissions, a low-complexity subband digital predistortion solution, specifically tailored for spectrally noncontiguous transmission schemes in low-cost devices, is proposed. The proposed technique aims at mitigating only the selected spurious intermodulation distortion components at the PA output, hence allowing for substantially reduced processing complexity compared with classical linearization solutions. Furthermore, novel decorrelation-based parameter learning solutions are also proposed and formulated, which offer reduced computing complexity in parameter estimation as well as the ability to track time-varying features adaptively. Comprehensive simulation and RF measurement results are provided, using a commercial LTE-Advanced mobile PA, to evaluate and validate the effectiveness of the proposed solution in real-world scenarios. The obtained results demonstrate that highly efficient spurious component suppression can be obtained using the proposed solutions.
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digital mitigation of transmitter induced receiver desensitization in carrier aggregation fdd transceivers
IEEE Transactions on Microwave Theory and Techniques, 2015Co-Authors: Adnan Kiayani, Lauri Anttila, Mahmoud Abdelaziz, Vesa Lehtinen, Mikko ValkamaAbstract:Carrier aggregation transmissions in Frequency Division Duplexing devices reduce the Duplexing distance between the transmitter (TX) and receiver (RX) bands. As a consequence, the spurious intermodulation distortion products created by the nonlinear RF front-end of the TX may easily extend over to the RX band, potentially causing own RX desensitization. In this paper, we propose an efficient and computationally feasible adaptive digital identification and cancellation technique to mitigate the RX desensitization. We first show that the spurious leakage signal at own RX band depends on an equivalent leakage channel that models the overall signal leakage path including the TX nonlinearities, duplexer filter responses, and RX path. The parameters of the equivalent leakage channel can be efficiently estimated with the least squares or the recursive least squares algorithm, using the actual digital transmit data as a reference, and then used to regenerate and cancel the leakage interference from the received signal. The performance of the proposed technique is evaluated with extensive computer simulations, as well as with practical real-world RF measurements, demonstrating excellent calibration properties with up to 19-dB improvement in singal-to-interference plus noise ratio of the desired received signal.
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Digital suppression of power amplifier spurious emissions at receiver band in FDD transceivers
IEEE Signal Processing Letters, 2014Co-Authors: Adnan Kiayani, Lauri Anttila, Mikko ValkamaAbstract:As the Duplexing distances in emerging wireless systems are getting more and more narrow, achieving sufficient isolation between transmit and receive chains using radio Frequency (RF) filtering alone becomes increasingly complex. Particularly challenging problem in this context is the spectral regrowth of nonlinear power amplifiers (PAs) in the transmit chain, and other transmitter out-of-band (OOB) emissions, which can heavily desensitize the receiver chain. In this letter, we first carry out detailed modeling of transmitter OOB emissions due to practical wideband PAs with memory effects. Stemming from this modeling, and using the known digital transmit data inside the transceiver as reference, we then propose an efficient nonlinear digital cancellation technique to suppress the transmitter OOB emissions in the receiver path. The proposed technique is verified and analyzed using extensive computer simulations, rendering excellent suppression properties, hence enabling sufficient TX-RX isolation in Frequency Division Duplexing (FDD) transceivers without any extra analog/RF filtering or PA linearization.
Wenqian Shen - One of the best experts on this subject based on the ideXlab platform.
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channel feedback based on aod adaptive subspace codebook in fdd massive mimo systems
IEEE Transactions on Communications, 2018Co-Authors: Wenqian Shen, Byonghyo Shim, Linglong Dai, Zhaocheng Wang, Robert W. HeathAbstract:Channel feedback is essential in Frequency Division Duplexing (FDD) massive multiple-input multiple-output (MIMO) systems. Unfortunately, prior work on multiuser MIMO has shown that the feedback overhead scales linearly with the number of base station (BS) antennas, which is large in massive MIMO systems. To reduce the feedback overhead, we propose an angle-of-departure (AoD) adaptive subspace codebook for channel feedback in FDD massive MIMO systems. Our key insight is to leverage the observation that path AoDs vary more slowly than the path gains. Within the angle coherence time, by utilizing the constant AoD information, the proposed AoD-adaptive subspace codebook is able to quantize the channel vector in a more accurate way. From the performance analysis, we show that the feedback overhead of the proposed codebook only scales linearly with a small number of dominant (path) AoDs instead of the large number of BS antennas. Moreover, we compare the proposed quantized feedback technique using the AoD-adaptive subspace codebook with a comparable analog feedback method. Extensive simulations show that the proposed AoD-adaptive subspace codebook achieves good channel feedback quality, while requiring low overhead.
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channel feedback codebook design for millimeter wave massive mimo systems relying on lens antenna array
IEEE Wireless Communications Letters, 2018Co-Authors: Wenqian Shen, Linglong Dai, Zhaocheng Wang, Lajos HanzoAbstract:The recently proposed millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) system relying on a lens antenna array (LAA) significantly reduces the number of radio Frequency chains using beam selection. A high data rate can be achieved based on the reduced-dimensional equivalent channel after beam selection. In Frequency Division Duplexing systems, the equivalent channel has to be fed back to the base station (BS) via a feedback channel based on a codebook. However, no dedicated codebook has been proposed for LAA-aided mmWave systems. To fill this gap, in this letter, we propose a reduced-dimensional subspace codebook (RDSC) for such systems. Specifically, under the recently proposed concept of angle coherence time , we first generate the large-dimensional vectors in the channel subspace , which is determined by the angles-of-departure of the dominant paths. Then, based on these vectors in the channel subspace, we create the RDSC by considering both the lens and the beam selector. Finally, the equivalent channel is quantized using the proposed RDSC and fed back to the BS. Finally, we carry out mathematical performance analysis of the proposed RDSC and show that its feedback overhead is rendered proportional to the relatively small number of dominant paths per user. The analytical results are verified by our simulations.
Byonghyo Shim - One of the best experts on this subject based on the ideXlab platform.
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Downlink Pilot Precoding and Compressed Channel Feedback for FDD-Based Cell-Free Systems
IEEE Transactions on Wireless Communications, 2020Co-Authors: Seungnyun Kim, Jun Won Choi, Byonghyo ShimAbstract:Cell-free system where a group of base stations (BSs) cooperatively serves users has received much attention as a promising technology for the future wireless systems. In order to maximize the cooperation gain in the cell-free systems, acquisition of downlink channel state information (CSI) at the BSs is crucial. While this task is relatively easy for the time Division Duplexing (TDD) systems due to the channel reciprocity, it is not easy for the Frequency Division Duplexing (FDD) systems due to the CSI feedback overhead. This issue is even more pronounced in the cell-free systems since the user needs to feed back the CSIs of multiple BSs. In this paper, we propose a novel feedback reduction technique for the FDD-based cell-free systems. Key feature of the proposed technique is to choose a few dominating paths and then feed back the path gain information (PGI) of the chosen paths. By exploiting the property that the angles of departure (AoDs) are quite similar in the uplink and downlink channels (this property is referred to as angle reciprocity ), the BSs obtain the AoDs directly from the uplink pilot signal. From the extensive simulations, we observe that the proposed technique can achieve more than 60% reduction in feedback overhead over the conventional CSI feedback scheme.
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channel feedback based on aod adaptive subspace codebook in fdd massive mimo systems
IEEE Transactions on Communications, 2018Co-Authors: Wenqian Shen, Byonghyo Shim, Linglong Dai, Zhaocheng Wang, Robert W. HeathAbstract:Channel feedback is essential in Frequency Division Duplexing (FDD) massive multiple-input multiple-output (MIMO) systems. Unfortunately, prior work on multiuser MIMO has shown that the feedback overhead scales linearly with the number of base station (BS) antennas, which is large in massive MIMO systems. To reduce the feedback overhead, we propose an angle-of-departure (AoD) adaptive subspace codebook for channel feedback in FDD massive MIMO systems. Our key insight is to leverage the observation that path AoDs vary more slowly than the path gains. Within the angle coherence time, by utilizing the constant AoD information, the proposed AoD-adaptive subspace codebook is able to quantize the channel vector in a more accurate way. From the performance analysis, we show that the feedback overhead of the proposed codebook only scales linearly with a small number of dominant (path) AoDs instead of the large number of BS antennas. Moreover, we compare the proposed quantized feedback technique using the AoD-adaptive subspace codebook with a comparable analog feedback method. Extensive simulations show that the proposed AoD-adaptive subspace codebook achieves good channel feedback quality, while requiring low overhead.
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SPAWC - FDD-Based Cell-Free Massive MIMO Systems
2018 IEEE 19th International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), 2018Co-Authors: Seungnyun Kim, Byonghyo ShimAbstract:Cell-free massive MIMO system is a promising technology of 5G wireless communications that provide a user-centric coverage to the user by the basestation cooperation. Most prior works on the cell-free massive MIMO systems assume the time Division Duplexing (TDD) systems, although the Frequency Division Duplexing (FDD) systems dominate the current wireless communications. In the FDD systems, CSI acquisition and feedback overhead are serious concerns when the number of antennas is large. To address these problems, we use the property that the uplink and downlink multipath components are similar, so-called angle reciprocity. By exploiting the angle reciprocity, basestation can directly acquire multipath component information from the uplink pilot signal. In this paper, we propose multipath component estimation technique and basestation cooperation scheme based on the multipath components for the FDD-based cell-free massive MIMO systems. Simulation results show that the proposed multipath component estimation technique outperforms the conventional subspace-based technique. Also, we show that the FDD-based cell-free massive MIMO systems substantially improve energy efficiency over the cellular systems.
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Antenna Grouping Based Feedback Compression for FDD-Based Massive MIMO Systems
IEEE Transactions on Communications, 2015Co-Authors: Byungju Lee, David James Love, Junil Choi, Ji-yun Seol, Byonghyo ShimAbstract:—Recent works on massive multiple-input multiple-output (MIMO) have shown that a potential breakthrough in capacity gains can be achieved by deploying a very large number of antennas at the basestation. In order to achieve the perfor-mance that massive MIMO systems promise, accurate transmit-side channel state information (CSI) should be available at the basestation. While transmit-side CSI can be obtained by employ-ing channel reciprocity in time Division Duplexing (TDD) systems, explicit feedback of CSI from the user terminal to the basestation is needed for Frequency Division Duplexing (FDD) systems. In this paper, we propose an antenna grouping based feedback reduction technique for FDD-based massive MIMO systems. The proposed algorithm, dubbed antenna group beamforming (AGB), maps multiple correlated antenna elements to a single representative value using pre-designed patterns. The proposed method modifies the feedback packet by introducing the concept of a header to select a suitable group pattern and a payload to quantize the reduced dimension channel vector. Simulation results show that the proposed method achieves significant feedback overhead reduction over conventional approach performing the vector quantization of whole channel vector under the same target sum rate requirement.