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Reciprocity calibration techniques, implementation on the OpenAirInterface platform
- in 4th International Conf. on Cognitive Radio and Advanced Spectrum Management (COGART
, 2011
"... The channel reciprocity is an advantageous hypothesis in cognitive radio (CR) technologies, however it is not practically exploitable due to miscellaneous discrepancies including the radio frequency (RF) impairments. Consequently, previousstudiesproposedcalibration solutions tosolve these RF impairm ..."
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Cited by 6 (4 self)
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The channel reciprocity is an advantageous hypothesis in cognitive radio (CR) technologies, however it is not practically exploitable due to miscellaneous discrepancies including the radio frequency (RF) impairments. Consequently, previousstudiesproposedcalibration solutions tosolve these RF impairments. This paper is a step ahead in the implementation of calibration algorithms through the EURE-COM’s experimental OpenAirInterface (OAI) platform. It proposes to implement and evaluate a less computationally intensive multiple-input multiple-output (MIMO) calibration algorithm, according to a realistic scenario based on long term evolution-time division duplex (LTE-TDD) specification. The result from OAI simulator shows that it is feasible to restore the reciprocity after calibration in a non reciprocal channel, and provides an overview of the challenges in the channel estimation in a real time case. Categories andSubject Descriptors
Hermitian precoding for distributed MIMO systems with individual channel state information
"... Abstract—In this paper, we consider a distributed MIMO communication network in which multiple transmitters cooperatively send common messages to a single receiver. In this scenario, it is usually costly to acquire full channel state information at the transmitters (CSIT), i.e., every transmitter pe ..."
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Abstract—In this paper, we consider a distributed MIMO communication network in which multiple transmitters cooperatively send common messages to a single receiver. In this scenario, it is usually costly to acquire full channel state information at the transmitters (CSIT), i.e., every transmitter perfectly knows the overall channel state information (CSI) of the network. Hence, we assume individual CSIT (I-CSIT), i.e., each transmitter only knows its own CSI. We propose a novel precoding technique, named Hermitian precoding, to enhance the system performance under the constraint of I-CSIT. We show that the proposed scheme can perform close to the system capacity with full CSIT. This reveals that the amount of CSI required at the transmitters can be significantly reduced without considerably compromising performance. I.
Hardware-Impairment Compensation for Enabling Distributed Large-Scale MIMO
"... Abstract—Distributed large-scale MIMO is a promising option for coping with the projected explosion in mobile traffic. It involves multiple Access Points (APs) that are connected to a central server via wired backhaul and act as a distributed MIMO transmitter, serving multiple users via spatial prec ..."
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Abstract—Distributed large-scale MIMO is a promising option for coping with the projected explosion in mobile traffic. It involves multiple Access Points (APs) that are connected to a central server via wired backhaul and act as a distributed MIMO transmitter, serving multiple users via spatial precoding. As is well known, large downlink (DL) spectral efficiencies can be achieved with TDD operation, pilots sent in the uplink (UL), and DL-UL channel reciprocity. With APs made of inexpensive hardware and connected via, e.g., Ethernet, synchronization and reciprocity calibration are the main hurdle for implementing a truly distributed MU-MIMO system. This work studies mechanisms for RF calibration that can enable distributed high-performing large-scale MIMO operation. We propose methods for relative calibration of the APs in order to ensure TDD reciprocity while not relying on an explicitly self-calibrating RF design. As our analysis and simulations suggest, the proposed methods significantly outperform existing self calibration methods without requiring additional signaling overhead and can enable TDD reciprocity for calibration of noncolocated networks. I.
Design and implementation of spatial interweave lte-tdd cognitive radio communication on an experimental platform
- IEEE Wireless Communications Magazine
, 2013
"... Abstract—Cognitive radio, which enables smart use of wireless resources, is a key ingredient to achieve high spectral efficiency. LTE, the latest evolution of cellular standards, is widely adopted and also targets high spectral efficiency. Hence, to enable wide adoption of cognitive radio, using LTE ..."
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Abstract—Cognitive radio, which enables smart use of wireless resources, is a key ingredient to achieve high spectral efficiency. LTE, the latest evolution of cellular standards, is widely adopted and also targets high spectral efficiency. Hence, to enable wide adoption of cognitive radio, using LTE as the physical layer is a natural choice. Targeting a real-time implementation of LTEbased cognitive radio, we focus on spatial interweave cognitive radio, in which a secondary user uses an antenna array to perform null-beamforming in the primary user’s direction, hence reusing the spectrum spatially. To allow this, without any help from the primary system, we use the time division duplex (TDD) mode and take advantage of the channel reciprocity. However, this reciprocity is jeopardized by the mismatch between the RF front-ends. Hence, we design a calibration protocol to restore it. The whole system is implementedand evaluated on EURECOM’s experimental OpenAirInterface platform. Performance results are presented, showing the feasibility of spatial interweave cognitive radio on a real-time platform. Index Terms—Spatial interweave cognitive radio, beamforming, channel estimation, reciprocity calibration, LTE-TDD platform. I.
Author manuscript, published in "CROWNCOM 2012, Stockholm: Sweden (2012)" DOI: 10.4108/icst.crowncom.2012.248472 Estimation of Time-Domain Calibration Parameters to Restore MIMO-TDD Channel Reciprocity
, 2012
"... Abstract—Spatial interweave cognitive radio opportunistically exploitsspatial holestoenabletransmissionofsecondary systems. The latter form carefully aligned spatial beams so that there is no interference to the primary system. This requires acquisition of the (spatio-temporal) channel state (CS) be ..."
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Abstract—Spatial interweave cognitive radio opportunistically exploitsspatial holestoenabletransmissionofsecondary systems. The latter form carefully aligned spatial beams so that there is no interference to the primary system. This requires acquisition of the (spatio-temporal) channel state (CS) between the secondary emitter and the primary receiver. CS can be acquired by using a multi-input multi-output time-division-duplex (MIMO-TDD) setup thanks to channel reciprocity inherent in such systems. Unfortunately, global reciprocity is often jeopardized by the nonreciprocal radio frequency front-ends (RF) at the two ends of the link.Restoration of reciprocity to compensate for the RF calls for on-line (and hence low complexity) calibration parameters estimation. In this paper, we propose an approach to estimate the space-time-domain parameters restoring the channel reciprocity in a frequency selective MIMO-TDD context. Accounting for antenna coupling effects, we find accurate space-time-domain calibration parameters and demonstrate real-time calibration process in an OFDM system 1. Index Terms—Interweave cognitive radio, reciprocity calibration, MIMO/TDD, beamforming, frequency selective channel estimate, precoding. I.
On the Performance of Calibration Techniques for Cognitive . . .
- THE 14TH INTERNATIONAL SYMPOSIUM ON WIRELESS PERSONAL MULTIMEDIA COMMUNICATIONS (WPMC'11)
, 2011
"... In Cognitive Radio (CR) systems, primary licensed and secondary unlicensed users share the same spectrum. To minimize the interference caused by secondary users to primary users, we use Beamforming (BF). To perform BF in time division duplex (TDD), we acquire Channel State Information (CSI) with th ..."
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In Cognitive Radio (CR) systems, primary licensed and secondary unlicensed users share the same spectrum. To minimize the interference caused by secondary users to primary users, we use Beamforming (BF). To perform BF in time division duplex (TDD), we acquire Channel State Information (CSI) with the help of channel reciprocity. This reciprocity is in practice not perfect due to non reciprocal Radio Frequency (RF) frontends, this non reciprocity can be compensated by calibration algorithms, using only CSI, pilots and signalling. This paper compares the performance of three calibration algorithms in OFDM-MIMO (Orthogonal Frequency Division Multiplexing Multiple-Input Multiple-Output) context, namely a M × N SISO and two full MIMO techniques (Alternating Total Least-Squares MIMO: Alt TLS MIMO and TLS MIMO). Simulations performed on synthetic and measured channels show that the TLS MIMO successfully performs full calibration, whereas the less complex SISO method fails to compensate antenna mutual coupling. They also give an approximation of the required CSI to achieve calibration. The final objective is to implement a proper calibration scheme in an existing CR scenario on the EURECOM OpenAirInterface platform.
<10.1145/2093256.2093282>. <hal-00742987>
, 2012
"... HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte p ..."
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HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et a ̀ la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Reciprocity Calibration Techniques, Implementation on the
