摘要 :
One problem with channel quality measurement in Long-Term Evolution (LTE) is how to define channel quality. Another is how to report it. We present a new framework for calculating the Channel Quality Indicator (CQI) and describe m...
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One problem with channel quality measurement in Long-Term Evolution (LTE) is how to define channel quality. Another is how to report it. We present a new framework for calculating the Channel Quality Indicator (CQI) and describe methods for efficient CQI reports that comply with LTE signaling schemes.
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摘要 :
One problem with channel quality measurement in Long-Term Evolution (LTE) is how to define channel quality. Another is how to report it. We present a new framework for calculating the Channel Quality Indicator (CQI) and describe m...
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One problem with channel quality measurement in Long-Term Evolution (LTE) is how to define channel quality. Another is how to report it. We present a new framework for calculating the Channel Quality Indicator (CQI) and describe methods for efficient CQI reports that comply with LTE signaling schemes.
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摘要 :
Codebook based multiple-input multiple-output (MIMO) precoding can significantly improve the system spectral efficiency with limited feedback and has been accepted as one of the most promising techniques for the Evolved UTRA (E-UT...
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Codebook based multiple-input multiple-output (MIMO) precoding can significantly improve the system spectral efficiency with limited feedback and has been accepted as one of the most promising techniques for the Evolved UTRA (E-UTRA). Compared with single-user (SU) MIMO, multi-user (MU) MIMO can further improve the system spectral efficiency due to increased multi-user diversity gain. MU-MIMO is preferred for the case of a large number of users,when the total feedback overhead will become a problem. In order to reduce the feedback overhead, feedback of single channel quality indicator (CQI), e.g. rank 1 CQI, is required in E-UTRA currently. The main challenge is how to obtain CQIs of other ranks at Node B for rank adaptation with single CQI feedback. In this paper, an adaptive CQI update scheme at Node B based on statistical characteristics of CQI of various ranks is proposed. To further increase the accuracy of CQI at Node B for data transmission, an adaptive CQI feedback scheme is then proposed in which single CQI with the rank same as previously scheduled is fed back. Simulation results show that our proposed CQI update scheme can achieve 2.5-5% gain compared with the conventional method with fixed backoff. Moreover, with the proposed adaptive feedback scheme, 20-40% performance gain can be obtained and the performance can approach the upper bound.
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Small cells with wireless backhaul are promising, whereas challenges of severe overlapping coverage and strong interference are yet to be addressed. Coordinating small cells could resolve the challenges; however, existing multicel...
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Small cells with wireless backhaul are promising, whereas challenges of severe overlapping coverage and strong interference are yet to be addressed. Coordinating small cells could resolve the challenges; however, existing multicell coordinated beamforming techniques involve high cost of communication overhead, synchronization and backhaul. Such problems may deteriorate in practical cellular applications, where there could be many users, each generating high channel feedback overhead to compete for an opportunity of being scheduled, and the downlink data signals of the coordinated cells need to be precisely synchronized at each of the users. We propose a new scheme, which cuts the overhead by 80% and enables the coordination to be practically implemented in a decentralized manner. Our scheme is a user-centric downlink scheduling approach, where mobile terminals trigger and participate in the scheduling decisions of small cells. We also develop a new recursive algorithm to optimize the quantization levels of mobile terminals' feedback, minimizing the feedback requirement. Analysis, confirmed by simulations, shows that our scheme is able to achieve 94.4% of the sum-rate upper-bound which can only be approached by idealized centralized coordination. In terms of throughput, given the 80% reduced overhead, our scheme is 139.5% better than the idealized centralized coordination approach.
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This paper considers the best-M channel-quality-indicator (CQI) reporting scheme for multi-carrier and multi-user systems. The perfect knowledge of CQIs is crucial for efficient resource allocation. Using outdated (which occurs du...
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This paper considers the best-M channel-quality-indicator (CQI) reporting scheme for multi-carrier and multi-user systems. The perfect knowledge of CQIs is crucial for efficient resource allocation. Using outdated (which occurs due to feedback delay) and imperfectly estimated CQIs for resource allocation can severely degrade the system performance. The conventional approach of dealing with the imperfections in CQIs at the base station (BS) is not efficient for multi-carrier systems as the BS has a small number of CQIs and therefore, does not know the distribution of the imperfections for all subcarriers. Approaching this problem more realistically, we model the CQI variations as a discrete-time linear dynamic system where the distribution of the imperfections is unknown, and propose a novel best-M scheme that accounts for feedback delay and imperfect CQI estimation at the CQI reporting level. Instead of reporting the estimated CQIs (i.e., the conventional approach), in our scheme, each user reports so-called adapted CQIs computed by using an H~∞-controller based approach. Unlike the conventional approaches, the H~∞ -controller does not require information on the probability distribution of the imperfections, and it guarantees robust performance in scenarios where the conventional approaches fail. The impact of feedback delay and imperfect CQI estimation on resource allocation is taken into account in the computation of adapted CQIs. That is adapted CQIs are computed such that if they are used for resource allocation, the deviation between the allocated rate by the BS and the actual channel rate is reduced. Results show that our scheme outperforms the schemes used in the current wireless standards.
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We consider channel state information (CSI) feedback in 3GPP Long Term Evolution (LTE)-Advanced context. In LTE-Advanced, switching between single user and multiuser transmission schemes is possible without higher layer signaling,...
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We consider channel state information (CSI) feedback in 3GPP Long Term Evolution (LTE)-Advanced context. In LTE-Advanced, switching between single user and multiuser transmission schemes is possible without higher layer signaling, which means that the feedback should support both single user and multiuser transmissions. Typically, the CSI feedback consists of a precoding matrix index (PMI) and channel quality indication(s) (CQI). For PMI feedback, we consider different PMI selection schemes and study whether there is a tradeoff between single user and multiuser specific codeword selection metrics. For multiuser CQI, we consider different CQI estimation strategies for two paired users, which is the primary case in LTE-Advanced. The schemes include single user single stream and two stream CQIs and several multiuser specific CQI estimation options. We find that estimating the multiuser CQI as an average over unitary pairs or as the minimum of the signal-to-interference and noise ratios of the unitary pairs offers a stable, well-performing options for different signal-to-noise ratio (SNR) ranges and antenna correlation values.
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We consider channel state information (CSI) feedback in 3GPP Long Term Evolution (LTE)-Advanced context. In LTE-Advanced, switching between single user and multiuser transmission schemes is possible without higher layer signaling,...
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We consider channel state information (CSI) feedback in 3GPP Long Term Evolution (LTE)-Advanced context. In LTE-Advanced, switching between single user and multiuser transmission schemes is possible without higher layer signaling, which means that the feedback should support both single user and multiuser transmissions. Typically, the CSI feedback consists of a precoding matrix index (PMI) and channel quality indication(s) (CQI). For PMI feedback, we consider different PMI selection schemes and study whether there is a tradeoff between single user and multiuser specific codeword selection metrics. For multiuser CQI, we consider different CQI estimation strategies for two paired users, which is the primary case in LTE-Advanced. The schemes include single user single stream and two stream CQIs and several multiuser specific CQI estimation options. We find that estimating the multiuser CQI as an average over unitary pairs or as the minimum of the signal-to-interference and noise ratios of the unitary pairs offers a stable, well-performing options for different signal-to-noise ratio (SNR) ranges and antenna correlation values.
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In previous literature on adaptive transmission in multiuser OFDMA systems, only uncoded case or capacity (coded with infinite length of codeword) has been considered. In this paper, an adaptive transmission algorithm for coded OF...
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In previous literature on adaptive transmission in multiuser OFDMA systems, only uncoded case or capacity (coded with infinite length of codeword) has been considered. In this paper, an adaptive transmission algorithm for coded OFDMA systems with practical codeword lengths is investigated. Also, in order to keep the feedback overhead within a practical range, a two-step partial CQI scheme is adopted, which has both better performance and reduced feedback overhead compared to conventional partial CQI schemes. By allowing a long codeword block across all allocated sub-bands with appropriate power and modulation order allocation rather than using short codeword blocks to each sub-band, high coding gain can be obtained, which leads to performance improvement.
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