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Swap-Based frequency-domain Packet scheduling Algorithm for Small-Queue Condition in OFDMA

IEEE COMMUNICATIONS LETTERS 2013年第5期17卷 1028-1031页

作者： Lee, Suk-Bok Hanyang Univ Dept Comp Sci & Engn Ansan South Korea

We propose an efficient frequency-domain packet scheduling (FDPS) for situations where some of the queues have a small amount of data available for transmission in downlink OFDMA-based systems. Under such small-queue condition, we first show that current FDPS proposals result in sub-optimal outcome, suffering from their isolated resource-assignment strategies. With our simple algorithmic solution, we demonstrate that better performance is achieved in terms of system throughput as well as fairness perspective, which is evaluated using 3GPP LTE system model simulations.

关键词： scheduling algorithm frequency-domain scheduling OFDMA LTE cellular networks

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scheduling for Virtual MIMO in Single Carrier FDMA (SC-FDMA) System

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JOURNAL OF COMMUNICATIONS AND NETWORKS 2015年第1期17卷 27-33页

作者： Kim, Jinwoo Hwang, In Seok Kang, Chung Gu Korea Univ Res Inst Informat & Commun Technol Seoul South Korea Samsung Elect Suwon South Korea Korea Univ Dept Elect Engn Seoul South Korea

In this paper, we consider a joint frequency-domain scheduling and user-pairing problem for virtual MIMO in the single carrier frequency division multiple access (SC-FDMA) system, e.g., the uplink transmission for third generation partnership project-long term evolution (3GPP-LTE) standard. Due to the subcarrier adjacency constraint inherent to SC-FDMA, its complexity becomes unmanageable. We propose a greedy heuristic algorithm for PF scheduling so as to deal with the complexity issue in this joint problem. It has been shown that its performance can reach up to 90% of its upper bound.

关键词： frequency-domain scheduling proportional fair single carrier frequency division multiple access (SC-FDMA) virtual MIMO

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Interference management for LTE-Advanced Het-Nets: stochastic scheduling approach in frequency domain

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TRANSACTIONS ON EMERGING TELECOMMUNICATIONS TECHNOLOGIES 2013年第1期24卷 4-17页

作者： Zheng, Zhong Dowhuszko, Alexis A. Hamalainen, Jyri Aalto Univ Dept Commun & Networking Comnet FI-00076 Aalto Finland Ericsson R&D Ctr FI-90590 Oulu Finland

Heterogeneous networks represent a practical way to face high traffic demands in densely populated areas. Nevertheless, to achieve these advertised data rates, advanced interference management techniques are required. Trying to tackle this problem, this paper presents a stochastic scheduling approach for two-layer LTE-Advanced networks. The proposed stochastic frequency-domain scheduling?(SFDS) algorithm seeks the avoidance of cross-layer and colayer interference, and is based on allocating different portions of the transmission bandwidth probabilistically. The SFDS algorithm is first presented as an interference management solution for an orthogonal frequency-division multiple access system (i.e. LTE-Advanced downlink). Later on, the SFDS algorithm is extended to be compatible with single-carrier frequency-division multiple access transmissions, and its performance is evaluated when combined with open-loop power control techniques (i.e. LTE-Advanced uplink). Extensive system level simulations are carried out to evaluate the performance of SFDS algorithm in a predefined LTE-Advanced scenario that combines both macrolayer and femtolayer. Results show that the proposed algorithm allows to balance the cross-layer and colayer interferences, extending the performance trade-offs that well-known full-range spectrum allocation and orthogonal spectrum allocation approaches provide. Copyright (c) 2012 John Wiley & Sons, Ltd.

关键词： heterogeneous networks interference management cross-layer interference femtocells frequency-domain scheduling LTE-Advanced

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Throughput Analysis of Best-m Feedback in OFDM Systems with Uniformly Correlated Subchannels

Throughput Analysis of Best-<i>m</i> Feedback in OFDM System...

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20th National Conference on Communications (NCC)

作者： Ananya, S. N. Mehta, Neelesh B. Indian Inst Sci IISc Dept Elect Commun Engn Bangalore Karnataka India

ISBN: (纸本)9781479923618

Practical orthogonal frequency division multiplexing (OFDM) systems, such as Long Term Evolution (LTE), exploit multi-user diversity using very limited feedback. The best-m feedback scheme is one such limited feedback scheme, in which users report only the gains of their m best subchannels (SCs) and their indices. While the scheme has been extensively studied and adopted in standards such as LTE, an analysis of its throughput for the practically important case in which the SCs are correlated has received less attention. We derive new closed-form expressions for the throughput when the SC gains of a user are uniformly correlated. We analyze the performance of the greedy but unfair frequency-domain scheduler and the fair round-robin scheduler for the general case in which the users see statistically non-identical SCs. An asymptotic analysis is then developed to gain further insights. The analysis and extensive numerical results bring out how correlation reduces throughput.

关键词： Orthogonal frequency division multiplexing (OFDM) Correlation Channel quality feedback Best-m frequency-domain scheduling Adaptive modulation and coding

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Joint Evaluation of Channel Feedback Schemes, Rate Adaptation, and scheduling in OFDMA Downlinks With Feedback Delays

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IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 2013年第4期62卷 1719-1731页

作者： Guharoy, Subhojit Mehta, Neelesh B. Qualcom India Pvt Ltd Hyderabad Andhra Pradesh India Indian Inst Sci Dept Elect Commun Engn Bangalore 560012 Karnataka India

Orthogonal frequency-division multiple access (OFDMA) systems divide the available bandwidth into orthogonal subchannels and exploit multiuser diversity and frequency selectivity to achieve high spectral efficiencies. However, they require a significant amount of channel state feedback for scheduling and rate adaptation and are sensitive to feedback delays. We develop a comprehensive analysis for OFDMA system throughput in the presence of feedback delays as a function of the feedback scheme, frequency-domain scheduler, and rate adaptation rule. Also derived are expressions for the outage probability, which captures the inability of a subchannel to successfully carry data due to the feedback scheme or feedback delays. Our model encompasses the popular best-n and threshold-based feedback schemes and the greedy, proportional fair, and round-robin schedulers that cover a wide range of throughput versus fairness tradeoff. It helps quantify the different robustness of the schedulers to feedback overhead and delays. Even at low vehicular speeds, it shows that small feedback delays markedly degrade the throughput and increase the outage probability. Further, given the feedback delay, the throughput degradation depends primarily on the feedback overhead and not on the feedback scheme itself. We also show how to optimize the rate adaptation thresholds as a function of feedback delay.

关键词： Channel quality feedback feedback delays frequency-domain scheduling orthogonal frequency-division multiple access (OFDMA) rate adaptation

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An Opportunistic, Fast, and Distributed Subchannel and User-Pairing Algorithm for OFDMA

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IEEE TRANSACTIONS ON COMMUNICATIONS 2012年第3期60卷 767-778页

作者： Karthik, A. Mehta, Neelesh B. Indian Inst Sci IISc Dept Elect Commun Engn Bangalore Karnataka India

Channel-aware assignment of subchannels to users in the downlink of an OFDMA system requires extensive feedback of channel state information (CSI) to the base station. Since bandwidth is scarce, schemes that limit feedback are necessary. We develop a novel, low feedback, distributed splitting-based algorithm called SplitSelect to opportunistically assign each subchannel to its most suitable user. SplitSelect explicitly handles multiple access control aspects associated with CSI feedback, and scales well with the number of users. In it, according to a scheduling criterion, each user locally maintains a scheduling metric for each subchannel. The goal is to select, for each subchannel, the user with the highest scheduling metric. At any time, each user contends for the subchannel for which it has the largest scheduling metric among the unallocated subchannels. A tractable asymptotic analysis of a system with many users is central to SplitSelect's simple design. Extensive simulation results demonstrate the speed with which subchannels and users are paired. The net data throughput, when the time overhead of selection is accounted for, is shown to be substantially better than several schemes proposed in the literature. We also show how fairness and user prioritization can be ensured by suitably defining the scheduling metric.

关键词： OFDMA subcarrier allocation downlink fading channels distributed algorithms splitting algorithm multiuser diversity frequency-domain scheduling feedback

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An Accurate Model for EESM and its Application to Analysis of CQI Feedback Schemes and scheduling in LTE

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IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2011年第10期10卷 3436-3448页

作者： Donthi, Sushruth N. Mehta, Neelesh B. IISc Dept Elect Commun Eng Bangalore Karnataka India

The Effective Exponential SNR Mapping (EESM) is an indispensable tool for analyzing and simulating next generation orthogonal frequency division multiplexing (OFDM) based wireless systems. It converts the different gains of multiple subchannels, over which a codeword is transmitted, into a single effective flat-fading gain with the same codeword error rate. It facilitates link adaptation by helping each user to compute an accurate channel quality indicator (CQI), which is fed back to the base station to enable downlink rate adaptation and scheduling. However, the highly non-linear nature of EESM makes a performance analysis of adaptation and scheduling difficult;even the probability distribution of EESM is not known in closed-form. This paper shows that EESM can be accurately modeled as a lognormal random variable when the subchannel gains are Rayleigh distributed. The model is also valid when the subchannel gains are correlated in frequency or space. With some simplifying assumptions, the paper then develops a novel analysis of the performance of LTE's two CQI feedback schemes that use EESM to generate CQI. The comprehensive model and analysis quantify the joint effect of several critical components such as scheduler, multiple antenna mode, CQI feedback scheme, and EESM-based feedback averaging on the overall system throughput.

关键词： Effective exponential SNR mapping (EESM) long term evolution (LTE) orthogonal frequency division multiplexing (OFDM) channel quality feedback multiple antenna diversity frequency-domain scheduling adaptive modulation and coding lognormal random variable

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Performance Analysis of User Selected Subband Channel Quality Indicator Feedback Scheme of LTE

Performance Analysis of User Selected Subband Channel Qualit...

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IEEE Global Telecommunications Conference (GLOBECOM 2010)

作者： Donthi, Sushruth N. Mehta, Neelesh B. Indian Inst Sci Dept Elect Commun Engn Bangalore 560012 Karnataka India

ISBN: (纸本)9781424456383

frequency-domain scheduling and rate adaptation have helped next generation orthogonal frequency division multiple access (OFDMA) based wireless cellular systems such as Long Term Evolution (LTE) achieve significantly higher spectral efficiencies. To overcome the severe uplink feedback bandwidth constraints, LTE uses several techniques to reduce the feedback required by a frequency-domain scheduler about the channel state information of all subcarriers of all users. In this paper, we analyze the throughput achieved by the User Selected Subband feedback scheme of LTE. In it, a user feeds back only the indices of the best M subbands and a single 4-bit estimate of the average rate achievable over all selected M subbands. In addition, we compare the performance with the subband-level feedback scheme of LTE, and highlight the role of the scheduler by comparing the performances of the unfair greedy scheduler and the proportional fair (PF) scheduler. Our analysis sheds several insights into the working of the feedback reduction techniques used in LTE.

关键词： LTE Long Term Evolution Long Term Evolution OFDM modulation OFDMA PF scheduler cellular radio channel state information feedback feedback reduction techniques frequency division multiple access frequency-domain analysis frequency-domain scheduling greedy

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