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Miaowen Wen – One of the best experts on this subject based on the ideXlab platform.

  • Distributed Processing for Multi-Relay Assisted OFDM With Index Modulation
    IEEE Transactions on Wireless Communications, 2019
    Co-Authors: Shuping Dang, Miaowen Wen, Shahid Mumtaz

    Abstract:

    Orthogonal frequency-division multiplexing with index modulation (OFDM-IM) has become a high-profile modulation scheme for the fifth-generation (5G) wireless communications and has thus been extended to multi-hop scenarios in order to improve the network coverage and energy efficiency. However, the extension of OFDM-IM to multi-relay cooperative networks is not trivial, since it is required that a complete OFDM block should be received and decoded as an entity in one node. This requirement prevents the employment of multiple relays to forward fragmented OFDM blocks on individual Subcarriers. In this regard, we propose a distributed processing scheme for multi-relay assisted OFDM-IM, by which multiple relays are selected to forward signals in a per-subcarrier manner to provide optimal error performance for two-hop decode-and-forward (DF) OFDM-IM systems. Specifically, a single selected relay only needs to decode partial information carried on certain Active Subcarriers and forward just as for traditional OFDM systems without IM. After receiving all signals on Active Subcarriers forwarded by different relays, the destination can reconstruct the complete OFDM block and retrieve the full information. We analyze the average block error rate and modulation capacity of the two-hop OFDM-IM system employing the proposed distributed DF protocol and verify the analysis by numerical simulations.

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  • Layered Orthogonal Frequency Division Multiplexing With Index Modulation
    IEEE Systems Journal, 2019
    Co-Authors: Shuping Dang, Miaowen Wen, Xueqin Jiang, Yuyang Peng, Han Hai

    Abstract:

    In this paper, we propose a novel scheme termed layered orthogonal frequency division multiplexing with index modulation (L-OFDM-IM) to increase the spectral efficiency (SE) of OFDM-IM systems. In L-OFDM-IM, all Subcarriers are first divided into multiple layers, each determining the Active Subcarriers and their modulated symbols. The index modulation (IM) bits are carried on the indices of the Active Subcarriers of all layers, which are overlapped and distinguishable with different signal constellations so that the number of the IM bits is larger than that in traditional OFDM-IM. A low-complexity detection is proposed to alleviate the high burden of the optimal maximum-likelihood detection at the receiver side. A closed-form upper bound on the bit error rate, the achievable rate, and diversity order are derived to characterize the performance of L-OFDM-IM. To enhance the diversity performance of L-OFDM-IM, we further propose coordinate interleaving L-OFDM-IM (CI-L-OFDM-IM), which interleaves the real and imaginary parts of the modulated symbols over two different subchannels. Computer simulations verify the theoretical analysis, and results show that L-OFDM-IM outperforms the conventional OFDM-IM scheme. Moreover, it is also confirmed that CI-L-OFDM-IM obtains an additional diversity order in comparison with L-OFDM-IM.

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  • Enhanced Orthogonal Frequency Division Multiplexing With Index Modulation
    IEEE Transactions on Wireless Communications, 2017
    Co-Authors: Miaowen Wen, Ertugrul Basar

    Abstract:

    Index modulation concept has attracted considerable research interest in the past few years. As a realization of index modulation in the frequency domain, orthogonal frequency division multiplexing with index modulation (OFDM-IM) has recently been proposed, which conveys information bits through both the subcarrier activation patterns and the amplitude phase modulation constellation points. This paper proposes two enhanced OFDM-IM schemes aimed at achieving higher spectral efficiency and diversity gain, respectively. The first one, termed OFDM with hybrid in-phase/quadrature index modulation (OFDM-HIQ-IM), explores the I- and Q- dimensions jointly for index modulation, allowing transmission of more index modulation bits in each subcarrier group. The second one, termed linear constellation precoded OFDM-IQ-IM (LP-OFDM-IQ-IM), spreads information symbols across two adjacent Active Subcarriers through linear constellation precoding to harvest additional diversity gain. By maximizing the minimum squared Euclidean distance, two different realizations of LP-OFDM-IQ-IM are derived, which leads to a rotated and a diamond-shaped constellation, respectively. The proposed OFDM-HIQ-IM and LP-OFDM-IQ-IM, as revealed by both theoretical analyses and computer simulations, enable low-complexity detection and exhibit superior error rate performance over the existing OFDM-IM schemes.

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Ertugrul Basar – One of the best experts on this subject based on the ideXlab platform.

  • Fading-aligned OFDM with index modulation for mMTC services
    Physical Communication, 2019
    Co-Authors: Ebubekir Memisoglu, Ertugrul Basar, Huseyin Arslan

    Abstract:

    Abstract 5th generation (5G) of wireless networking is coming with diverse use cases, such as enhanced-Mobile BroadBand (eMBB), Ultra Reliable and Low Latency Communications (URLLC), and massive Machine Type Communications (mMTC). As a result, 5G wireless networks require flexible physical layer solutions through new radio access technologies (RATs). At this point, orthogonal frequency division multiplexing with index modulation (OFDM-IM) appears a flexible solution to satisfy the diverse user demands. Considering the strict requirements of mMTC services, such as low throughput, low power consumption, and low cost design, we propose fading-aligned OFDM-IM for more spectrum- and energy-efficient communication. In the proposed method, inActive Subcarriers in OFDM-IM are cleverly utilized to avoid deep fading sub-channels, because the deep fading of the Active Subcarriers decreases bit error rate (BER) performance significantly. Computer simulation results demonstrate that more than 10 dB gain is obtained for a reference BER value of 1 0 − 4 at the same spectral efficiency with conventional OFDM. Moreover, the proposed method is compared with convolutional coded (CC) OFDM at the same spectral efficiency, and it is shown that the proposed scheme performs better in terms of BER performance. Furthermore, theoretical error performance of the proposed method is investigated to support our computer simulations.

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  • Differential Subcarrier Index Modulation
    IEEE Transactions on Vehicular Technology, 2018
    Co-Authors: Saud Althunibat, Raed Mesleh, Ertugrul Basar

    Abstract:

    One of the main challenges in orthogonal frequency division multiplexing (OFDM)–subcarrier index modulation (SIM) systems is the huge amount of resources required to obtain channel state information at the receiver side. In this paper, a differential subcarrier index modulation (DSIM) scheme is proposed, which entirely avoids the need for any channel knowledge at the receiver side. As such, time and energy resources spent in the channel estimation process are perceived. In DSIM, part of the transmitted block is modulated through ordinary signal modulation, whereas the second part is transmitted by selecting a specific permutation of the Active Subcarriers. The transmitted signals are designed to facilitate differential demodulation at the receiver side. A derivation is conducted for the average bit error probability of DSIM and an upper bound expression is obtained. Derived theoretical expression is substantiated through Monte Carlo simulation results. Reported results reveal that differential demodulation degrades the error performance of coherent SIM by nearly 4 dB in signal-to-noise-ratio.

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  • Adaptive dual-mode OFDM with index modulation
    Physical Communication, 2018
    Co-Authors: Aldirmaz Colak, Yusuf Acar, Ertugrul Basar

    Abstract:

    Abstract With the integration of the index modulation concept, the popular OFDM has gained an appealing new dimension. However, OFDM with index modulation (OFDM-IM) causes a decrease in data rate for higher order modulations due to its unused Subcarriers. Recently, dual-mode OFDM with index modulation (DM-OFDM-IM) has been proposed to prevent this decrease in data rate. The spectral efficiency (SE) of both techniques depends on the selection of different parameters, such as modulation types and number of Active Subcarriers. However, the quality of the wireless channel has not been taken into account yet to increase the data rate. In this paper, we propose a new adaptive DM-OFDM-IM (A-DM-OFDM-IM) system to enhance the bit error probability (BER) performance considering the channel conditions and obtain a substantial increase in SE. Unlike the previous DM-OFDM-IM and the classical OFDM-IM schemes, our proposed system enables the use of different types of modulations for different subblocks in one OFDM signal. We demonstrate that the SE of the proposed system is comparable with that of its OFDM-IM and DM-OFDM-IM counterpart under frequency selective Rayleigh channels. Moreover, computer simulations corroborate that the derived theoretical results are considerably accurate for the SE of A-DM-OFDM-IM systems.

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Mikko Valkama – One of the best experts on this subject based on the ideXlab platform.

  • Frequency-Selective PAPR Reduction for OFDM
    IEEE Transactions on Vehicular Technology, 2019
    Co-Authors: Selahattin Gokceli, Toni Levanen, Taneli Riihonen, Markku Renfors, Mikko Valkama

    Abstract:

    In this correspondence paper, we study the peak-to-average power ratio (PAPR) problem in orthogonal frequency-division multiplexing systems. In conventional clipping and filtering based PAPR reduction techniques, clipping noise is allowed to spread over the whole Active passband, thus degrading the transmit signal quality similarly at all Active Subcarriers. However, since modern radio networks support frequency multiplexing of users and services with highly different quality-of-service expectations, clipping noise from PAPR reduction should be distributed unequally over the corresponding physical resource blocks (PRBs). To facilitate this, we present an efficient PAPR reduction technique, where clipping noise can be flexibly controlled and filtered inside the transmitter passband, allowing to control the transmitted signal quality per PRB. Numerical results are provided in 5G new radio mobile network context, demonstrating the flexibility and efficiency of the proposed method.

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  • Frequency-Selective PAPR Reduction for OFDM.
    arXiv: Signal Processing, 2019
    Co-Authors: Selahattin Gokceli, Toni Levanen, Taneli Riihonen, Markku Renfors, Mikko Valkama

    Abstract:

    We study the peak-to-average power ratio (PAPR) problem in orthogonal frequency-division multiplexing (OFDM) systems. In conventional clipping and filtering based PAPR reduction techniques, clipping noise is allowed to spread over the whole Active passband, thus degrading the transmit signal quality similarly at all Active Subcarriers. However, since modern radio networks support frequency-multiplexing of users and services with highly different quality-of-service expectations, clipping noise from PAPR reduction should be distributed unequally over the corresponding physical resource blocks (PRBs). To facilitate this, we present an efficient PAPR reduction technique, where clipping noise can be flexibly controlled and filtered inside the transmitter passband, allowing to control the transmitted signal quality per PRB. Numerical results are provided in 5G New Radio (NR) mobile network context, demonstrating the flexibility and efficiency of the proposed method.

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  • Compressive Identification of Active OFDM Subcarriers in Presence of Timing Offset
    2015 IEEE Global Communications Conference (GLOBECOM), 2015
    Co-Authors: Alireza Razavi, Mikko Valkama, Danijela Cabric

    Abstract:

    In this paper we study the problem of identifying Active Subcarriers in an OFDM signal from compressive measurements sampled at sub-Nyquist rate. The problem is of importance in Cognitive Radio systems when secondary users (SUs) are looking for available spectrum opportunities to communicate over them while sensing at Nyquist rate sampling can be costly or even impractical in case of very wide bandwidth. We first study the effect of timing offset and derive the necessary and sufficient conditions for signal recovery in the oracle-assisted case when the true Active sub-carriers are assumed known. Then we propose an Orthogonal Matching Pursuit (OMP)- based joint sparse recovery method for identifying Active Subcarriers when the timing offset is known. Finally we extend the problem to the case of unknown timing offset and develop a joint dictionary learning and sparse approximation algorithm, where in the dictionary learning phase the timing offset is estimated and in the sparse approximation phase Active Subcarriers are identified. The obtained results demonstrate that Active subcarrier identification can be carried out reliably, by using the developed framework.

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