The Experts below are selected from a list of 49353 Experts worldwide ranked by ideXlab platform
Peter Willett - One of the best experts on this subject based on the ideXlab platform.
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recursive and trellis based feedback reduction for mimo ofdm with rate limited feedback
IEEE Transactions on Wireless Communications, 2006Co-Authors: Shengli Zhou, Baosheng Li, Peter WillettAbstract:We investigate an adaptive MIMO-OFDM system with a feedback link that can only convey a finite number of bits. We consider three different transmitter configurations: i) beamforming applied per OFDM Subcarrier, ii) precoded spatial multiplexing applied per Subcarrier, and iii) precoded orthogonal space time block coding applied per Subcarrier. Depending on the channel realization, the receiver selects the optimal beamforming vector or precoding matrix from a finite-size codebook on each Subcarrier, and informs the transmitter through finite-rate feedback. Exploiting the fact that the channel responses across OFDM Subcarriers are correlated, we propose two methods to reduce the amount of feedback. One is recursive feedback encoding that selects the optimal beamforming/precoding choices sequentially across the Subcarriers, and adopts a smaller-size time-varying codebook per Subcarrier depending on prior decisions. The other is trellis-based feedback encoding that selects the optimal decisions for all Subcarriers at once along a trellis structure via the Viterbi algorithm. Our methods are applicable to different transmitter configurations in a unified fashion. Simulation results demonstrate that the trellis-based approach outperforms the recursive method as well as an existing interpolation-based alternative at high signal-to-noise-ratio, as the latter suffers from "diversity loss"
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GLOBECOM - Recursive and trellis-based feedback reduction for MIMO-OFDM with transmit beamforming
GLOBECOM '05. IEEE Global Telecommunications Conference 2005., 2005Co-Authors: Shengli Zhou, Peter WillettAbstract:We consider a MIMO-OFDM system with transmit beamforming applied on each OFDM Subcarrier, where each beamforming vector is drawn from a codebook with finite size. Depending on the channel realization, the receiver decides the optimal beamforming vector on each Subcarrier, and informs the transmitter through a rate-limited feedback link. Exploiting the fact that the channel responses across OFDM Subcarriers are correlated, we propose two methods to reduce the amount of needed feedback. One is recursive feedback encoding that selects the optimal beamforming vectors sequentially across the Subcarriers, and adopts a smaller-size time-varying codebook per Subcarrier depending on prior decisions. The other is trellis-based feedback encoding that selects the optimal beamforming vectors for all Subcarriers at once along a trellis structure via the A. The trellis-based feedback encoding outperforms the recursive feedback encoding at the expense of encoding complexity at the receiver. Simulation results demonstrate that our trellis-based approach outperforms an existing interpolation-based alternative, as the latter incurs diversity loss at high SNR
Yuhong Dai - One of the best experts on this subject based on the ideXlab platform.
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on the complexity of joint Subcarrier and power allocation for multi user ofdma systems
IEEE Transactions on Signal Processing, 2014Co-Authors: Yafeng Liu, Yuhong DaiAbstract:Consider a multi-user orthogonal frequency division multiple access (OFDMA) system where multiple users share multiple discrete Subcarriers, but at most one user is allowed to transmit power on each Subcarrier. To adapt fast traffic and channel fluctuations and improve the spectrum efficiency, the system should have the ability to dynamically allocate Subcarriers and power resources to users. Assuming perfect channel knowledge, two formulations for the joint Subcarrier and power allocation problem are considered in this paper: the first is to minimize the total transmission power subject to the quality of service constraints and the OFDMA constraint, and the second is to maximize some system utility function subject to the total transmission power constraint per user and the OFDMA constraint. In spite of the existence of various heuristics approaches, little is known about the computational complexity status of the above problem. This paper aims at filling this theoretical gap, i.e., characterizing the complexity of the joint Subcarrier and power allocation problem for the multi-user OFDMA system. It is shown in this paper that both formulations of the joint Subcarrier and power allocation problem are strongly NP-hard. Several subclasses of the problem which can be solved efficiently in polynomial time are also identified. These complexity results suggest that there are not polynomial time algorithms that are able to solve the general joint Subcarrier and power allocation problem to global optimality (unless P=NP), and determining an approximately optimal Subcarrier and power allocation strategy is more realistic in practice.
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on the complexity of joint Subcarrier and power allocation for multi user ofdma systems
arXiv: Information Theory, 2012Co-Authors: Yafeng Liu, Yuhong DaiAbstract:Consider a multi-user Orthogonal Frequency Division Multiple Access (OFDMA) system where multiple users share multiple discrete Subcarriers, but at most one user is allowed to transmit power on each Subcarrier. To adapt fast traffic and channel fluctuations and improve the spectrum efficiency, the system should have the ability to dynamically allocate Subcarriers and power resources to users. Assuming perfect channel knowledge, two formulations for the joint Subcarrier and power allocation problem are considered in this paper: the first is to minimize the total transmission power subject to quality of service constraints and the OFDMA constraint, and the second is to maximize some system utility function (including the sum-rate utility, the proportional fairness utility, the harmonic mean utility, and the min-rate utility) subject to the total transmission power constraint per user and the OFDMA constraint. In spite of the existence of various heuristics approaches, little is known about the computational complexity status of the above problem. This paper aims to fill this theoretical gap, i.e., characterizing the complexity of the joint Subcarrier and power allocation problem for the multi-user OFDMA system. It is shown in this paper that both formulations of the joint Subcarrier and power allocation problem are strongly NP-hard. The proof is based on a polynomial time transformation from the so-called 3-dimensional matching problem. Several subclasses of the problem which can be solved to global optimality or $\epsilon$-global optimality in polynomial time are also identified. These complexity results suggest that there are not polynomial time algorithms which are able to solve the general joint Subcarrier and power allocation problem to global optimality (unless P$=$NP), and determining an approximately optimal Subcarrier and power allocation strategy is more realistic in practice.
Huseyin Arslan - One of the best experts on this subject based on the ideXlab platform.
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OFDM with Index Modulation for Asynchronous mMTC Networks.
Sensors (Basel Switzerland), 2018Co-Authors: Seda Dogan, Armed Tusha, Huseyin ArslanAbstract:One of the critical missions for next-generation wireless communication systems is to fulfill the high demand for massive Machine-Type Communications (mMTC). In mMTC systems, a sporadic transmission is performed between machine users and base station (BS). Lack of coordination between the users and BS in time destroys orthogonality between the Subcarriers, and causes inter-carrier interference (ICI). Therefore, providing services to asynchronous massive machine users is a major challenge for Orthogonal Frequency Division Multiplexing (OFDM). In this study, OFDM with index modulation (OFDM-IM) is proposed as an eligible solution to alleviate ICI caused by asynchronous transmission in uncoordinated mMTC networks. In OFDM-IM, data transmission is performed not only by modulated Subcarriers but also by the indices of active Subcarriers. Unlike classical OFDM, fractional Subcarrier activation leads to less ICI in OFDM-IM technology. A novel Subcarrier mapping scheme (SMS) named as Inner Subcarrier Activation is proposed to further alleviate adjacent user interference in asynchronous OFDM-IM-based systems. ISA reduces inter-user interference since it gives more activation priority to inner Subcarriers compared with the existing SMS-s. The superiority of the proposed SMS is shown through both theoretical analysis and computer-based simulations in comparison to existing mapping schemes for asynchronous systems.
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OFDM With Subcarrier Number Modulation
IEEE Wireless Communications Letters, 2018Co-Authors: Ahmad M. Jaradat, Jehad M. Hamamreh, Huseyin ArslanAbstract:A new modulation technique, named orthogonal frequency division multiplexing (OFDM) with Subcarrier number modulation, is proposed for efficient data transmission. In this scheme, the information bits are conveyed by changing the number of active Subcarriers in each OFDM subblock. The idea behind this scheme is inspired from the integration of OFDM with pulse width modulation, where the width of the pulse represents the number of active Subcarriers corresponding to specific information bits. This is different from OFDM with index modulation (OFDM-IM), where the information bits are sent by the indices of the Subcarriers instead of their number. The scheme is shown to provide better spectral efficiency than that of OFDM-IM at comparable bit error rate performances. Another key merit of the proposed scheme over OFDM-IM is that the active Subcarriers can be located in any position within the subblock, thus enabling channel-dependent optimal Subcarrier selection that can further enhance the system performance.
Shengli Zhou - One of the best experts on this subject based on the ideXlab platform.
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recursive and trellis based feedback reduction for mimo ofdm with rate limited feedback
IEEE Transactions on Wireless Communications, 2006Co-Authors: Shengli Zhou, Baosheng Li, Peter WillettAbstract:We investigate an adaptive MIMO-OFDM system with a feedback link that can only convey a finite number of bits. We consider three different transmitter configurations: i) beamforming applied per OFDM Subcarrier, ii) precoded spatial multiplexing applied per Subcarrier, and iii) precoded orthogonal space time block coding applied per Subcarrier. Depending on the channel realization, the receiver selects the optimal beamforming vector or precoding matrix from a finite-size codebook on each Subcarrier, and informs the transmitter through finite-rate feedback. Exploiting the fact that the channel responses across OFDM Subcarriers are correlated, we propose two methods to reduce the amount of feedback. One is recursive feedback encoding that selects the optimal beamforming/precoding choices sequentially across the Subcarriers, and adopts a smaller-size time-varying codebook per Subcarrier depending on prior decisions. The other is trellis-based feedback encoding that selects the optimal decisions for all Subcarriers at once along a trellis structure via the Viterbi algorithm. Our methods are applicable to different transmitter configurations in a unified fashion. Simulation results demonstrate that the trellis-based approach outperforms the recursive method as well as an existing interpolation-based alternative at high signal-to-noise-ratio, as the latter suffers from "diversity loss"
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GLOBECOM - Recursive and trellis-based feedback reduction for MIMO-OFDM with transmit beamforming
GLOBECOM '05. IEEE Global Telecommunications Conference 2005., 2005Co-Authors: Shengli Zhou, Peter WillettAbstract:We consider a MIMO-OFDM system with transmit beamforming applied on each OFDM Subcarrier, where each beamforming vector is drawn from a codebook with finite size. Depending on the channel realization, the receiver decides the optimal beamforming vector on each Subcarrier, and informs the transmitter through a rate-limited feedback link. Exploiting the fact that the channel responses across OFDM Subcarriers are correlated, we propose two methods to reduce the amount of needed feedback. One is recursive feedback encoding that selects the optimal beamforming vectors sequentially across the Subcarriers, and adopts a smaller-size time-varying codebook per Subcarrier depending on prior decisions. The other is trellis-based feedback encoding that selects the optimal beamforming vectors for all Subcarriers at once along a trellis structure via the A. The trellis-based feedback encoding outperforms the recursive feedback encoding at the expense of encoding complexity at the receiver. Simulation results demonstrate that our trellis-based approach outperforms an existing interpolation-based alternative, as the latter incurs diversity loss at high SNR
Lieliang Yang - One of the best experts on this subject based on the ideXlab platform.
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Subcarrier-allocation in downlink multicarrier DS-CDMA systems
2013 IEEE CIC International Conference on Communications in China (ICCC), 2013Co-Authors: Jia Shi, Lieliang YangAbstract:In LTE/LTE-A orthogonal frequency-division multiple-access (OFDMA) systems, the number of Subcarriers is usually very high, upto 2048, and the number of simultaneously supported users may also be very high. These characteristics of OFDMA systems not only result in the severe peak-to-average power ratio (PAPR) problem, but also prevent schedulers from employing the optimum or near-optimum Subcarrier-allocation algorithms, due to their relatively high-complexity when the number of Subcarriers and the number of users are high. Multicarrier direct-sequence code-division multiple-access (MC DS-CDMA) is one of high-flexibility communication schemes. Owing to the DS spreading, the number of Subcarriers in MC DS-CDMA can be significantly lower than that in OFDMA, and can be configurated according to the frequency-selectivity of wireless channels, so that each Subcarrier experiences independent fading. Therefore, the relatively high-complexity optimum or near-optimum Subcarrier-allocation algorithms may be employed by MC DS-CDMA for achieving the best possible performance. In this contribution, we study the Subcarrier-allocation issue in MC DS-CDMA. Specifically, three representative Subcarrier algorithms, namely the greedy algorithm, worst Subcarrier avoiding (WSA) algorithm and the optimum Hungarian algorithm, are introduced to and studied associated with the MC DS-CDMA. Furthermore, according to the characteristics of the MC DS-CDMA, a Subcarrier-allocation algorithm, named as the parallel Hungarian algorithm, is proposed. The achievable performance of these Subcarrier-allocation algorithms are compared in terms of complexity and bit error rate (BER).
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a low complexity Subcarrier power allocation scheme for frequency division multiple access systems
IEEE Transactions on Wireless Communications, 2010Co-Authors: Tingting Liu, Chenyang Yang, Lieliang YangAbstract:This letter aims to design a low-complexity Subcarrier-power allocation scheme to improve the communication reliability of various types of frequency-division multiple-access (FDMA) systems. Both uplink and downlink are considered. Specifically, a low-complexity worst Subcarrier avoiding (WSA) Subcarrier-allocation scheme is proposed, in order to avoid assigning users the Subcarriers experiencing severe fading. After the Subcarrier-allocation, channel-inversion assisted power-allocation is employed to assign the Subcarriers the corresponding power. Our studies and simulation results show that the achievable error performance of the FDMA systems employing the proposed Subcarrier-power allocation algorithm is independent of the multiplexing method. The proposed algorithm outperforms the existing Subcarrier-power allocation algorithms that have a similar complexity as the proposed one.
