Browsing by Author "Poor, H. Vincent"

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Citation Count: 2
Flexible LED Index Modulation for MIMO Optical Wireless Communications
(Institute of Electrical and Electronics Engineers Inc., 2020) Yeşilkaya, Anıl; Purwita, Ardimas Andi; Panayırcı, Erdal; Poor, H. Vincent; Haas, Harald
The limited bandwidth of optical wireless communication (OWC) front-end devices motivates the use of multipleinput- multiple-output (MIMO) techniques to enhance data rates. It is known that very high multiplexing gains can be achieved by spatial multiplexing (SMX) at the cost of prohibitive detection complexity. Alternatively, in spatial modulation (SM), a single light emitting diode (LED) is activated per time instance where information is carried by both the signal and the LED index. Since only one LED is active, both the transmitter (TX) and receiver (RX) complexity reduce significantly while retaining the information transmission in the spatial domain. However, this simplified TX utilization approach leads SM to suffer from significant spectral efficiency losses compared to SMX. In this paper, we propose a technique that benefits from the advantages of both systems. Accordingly, the proposed flexible LED index modulation (FLIM) technique harnesses the inactive state of the LEDs as a transmit symbol. Therefore, the number of active LEDs changes in each transmission, unlike conventional techniques. Moreover, the system complexity is reduced by employing a linear minimum mean squared error (MMSE) equalizer and an angle perturbed receiver. Numerical results show that FLIM outperforms the reference systems by at least 6 dB in the low and medium/high spectral efficiency regions.
Citation Count: 1
Joint Channel Estimation and Equalization for OFDM based Broadband Communications in Rapidly Varying Mobile Channels
(IEEE, 2010) Şenol, Habib; Poor, H. Vincent
This paper is concerned with the challenging and timely problem of channel estimation for orthogonal frequency division multiplexing (OFDM) systems in the presence of frequency selective and very rapidly time varying channels. In OFDM systems operating over rapidly time-varying channels the orthogonality between subcarriers is destroyed leading to inter-carrier interference (ICI) and resulting in an irreducible error floor. The band-limited discrete cosine serial expansion of low-dimensionality is employed to represent the time-varying channel. In this way the resulting reduced dimensional channel coefficients are estimated iteratively with tractable complexity and independently of the channel statistics. The algorithm is based on the expectation maximization-maximum a posteriori probability (EM-MAP) technique leading to a receiver structure that also yields the equalized output using the channel estimates. The pilot symbols are employed to estimate the initial coefficients effectively and unknown data symbols are averaged out in the algorithm in a non-data-aided fashion. It is shown that the computational complexity of the proposed algorithm to estimate the channel coefficients and to generate the equalized output as a by-product is similar to O(N) per detected symbol N being the number of OFDM subcarriers. Computational complexity as well as computer simulations carried out for the systems described in WiMAX and LTE standards indicate that it has significant performance and complexity advantages over existing suboptimal channel estimation and equalization algorithms proposed earlier in the literature.
Citation Count: 76
Joint Channel Estimation Equalization and Data Detection for OFDM Systems in the Presence of Very High Mobility
(IEEE-INST Electrical Electronics Engineers Inc, 2010) Şenol, Habib; Şenol, Habib; Poor, H. Vincent
This paper is concerned with the challenging and timely problem of joint channel estimation equalization and data detection for uplink orthogonal frequency division multiplexing (OFDM) systems in the presence of frequency selective and very rapidly time varying channels. The resulting algorithm is based on the space alternating generalized expectation maximization (SAGE) technique which is particularly well suited to multicarrier signal formats leading to a receiver structure that also incorporates interchannel interference (ICI) cancelation. In order to reduce the computational complexity of the algorithm band-limited discrete cosine orthogonal basis functions are employed to represent the rapidly time-varying fading channel by the discrete cosine serial expansion coefficients. It is shown that depending on the normalized Doppler frequency only a small number of expansion coefficients is sufficient to approximate the channel perfectly and there is no need to know the correlation function of the input signal. In this way the resulting reduced dimensional channel coefficients are estimated and the data symbols detected iteratively with tractable complexity. The proposed SAGE joint detection algorithm updates the data sequences serially and the channel parameters are updated in parallel leading to a receiver structure that also incorporates ICI cancelation. Computer simulations show that the cosine transformation represents the time-varying channel very effectively and the proposed algorithm has excellent symbol error rate and channel estimation performance even with a very small number of channel expansion coefficients employed in the algorithm resulting in substantial reduction of the computational complexity.
Citation Count: 0
Joint Data Detection and Channel Estimation for OFDM Systems in the Presence of Very High Mobility
(IEEE, 2009) Şenol, Habib; Şenol, Habib; Poor, H. Vincent
This paper is concerned with the challenging and timely problem of joint channel estimation and data detection for orthogonal frequency division multiplexing (OFDM) systems in the presence of frequency selective and very rapidly time varying channels. The detection and estimation algorithm is based on the space alternating generalized expectation maximization (SAGE) technique which is particularly well-suited to multicarrier signal formats. In order to reduce the computational complexity of the algorithm we apply the cosine orthogonal basis functions to describe the time-varying channel. It is shown that depending on the normalized Doppler frequency only a small number of expansion coefficients is sufficient to approximate the channel perfectly and there is no need to know the correlation function of the input signal. The proposed SAGE joint detection algorithm updates the data sequences in serial and the channel parameters are updated in parallel leading to a receiver structure that also incorporates a partial interference cancelation of the interchannel interference. Computer simulations show that the cosine transformation represents the time-varying channel very effectively and the proposed algorithm has excellent symbol error rate and channel estimation performance even with a very small number of channel expansion coefficients employed in the algorithm resulting in reduction of the computational complexity substantially.
Citation Count: 26
Low-complexity joint data detection and channel equalisation for highly mobile orthogonal frequency division multiplexing systems
(2010) Panayırcı, Erdal; Panayırcı, Erdal; Poor, H. Vincent
This study is concerned with the challenging and timely problem of channel equalisation and data detection for orthogonal frequency division multiplexing (OFDM) systems in the presence of frequency-selective and very rapidly time-varying channels. The algorithm is based on the space alternating generalised expectation-maximisation (SAGE) technique which is particularly well suited to multicarrier signal formats and can be easily extended to multi-input multi-output-OFDM systems. In fast fading channels the orthogonality between subcarriers is destroyed by the time variation of a fading channel over an OFDM symbol duration which causes severe inter-carrier interference (ICI) and in conventional frequency-domain approaches results in an irreducible error floor. The proposed joint data detection and equalisation algorithm updates the data sequences in series leading to a receiver structure that also incorporates ICI cancellation enabling the system to operate at high vehicle speeds. A computational complexity investigation as well as detailed computer simulations indicate that this algorithm has significant performance and complexity advantages over existing suboptimal detection and equalisation algorithms proposed earlier in the literature. © 2010 The Institution of Engineering and Technology.
Citation Count: 24
Low-Complexity MAP-Based Successive Data Detection for Coded OFDM Systems Over Highly Mobile Wireless Channels
(IEEE-INST Electrical Electronics Engineers Inc, 2011) Panayırcı, Erdal; Dogan, Hakan; Poor, H. Vincent
This paper is concerned with the challenging and timely problem of data detection for coded orthogonal frequency-division multiplexing (OFDM) systems in the presence of frequency-selective and very rapidly time varying channels. New low-complexity maximum a posteriori probability (MAP) data detection algorithms are proposed based on sequential detection with optimal ordering (SDOO) and sequential detection with successive cancellation (SDSC). The received signal vector is optimally decomposed into reduced dimensional subobservations by exploiting the banded structure of the frequency-domain channel matrix whose bandwidth is a parameter to be adjusted according to the speed of the mobile terminal. The data symbols are then detected by the proposed algorithms in a computationally efficient way by means of the Markov chain Monte Carlo (MCMC) technique with Gibbs sampling. The impact of the imperfect channel state information (CSI) on the bit error rate (BER) performance of these algorithms is investigated analytically and by computer simulations. A detailed computational complexity investigation and simulation results indicate that particularly the algorithm based on SDSC has significant performance and complexity advantages and is very robust against channel estimation errors compared with existing suboptimal detection and equalization algorithms proposed earlier in the literature.
Citation Count: 2
A Monte Carlo implementation of the SAGE algorithm for joint soft-multiuser decoding channel parameter estimation and code acquisition
(2010) Panayırcı, Erdal; Panayırcı, Erdal; Poor, H. Vincent; Ruggieri, Marina
This paper presents an iterative scheme for joint timing acquisition multi-channel parameter estimation and multiuser soft-data decoding. As an example an asynchronous convolutionally coded direct-sequence code-division multiple-access system is considered. The proposed receiver is derived within the space-alternating generalized expectation-maximization framework implying that convergence in likelihood is guaranteed under appropriate conditions in contrast to many other iterative receiver architectures. The proposed receiver iterates between joint posterior data estimation interference cancellation and single-user channel estimation and timing acquisition. A Markov Chain Monte Carlo technique namely Gibbs sampling is employed to compute the a posteriori probabilities of data symbols in a computationally efficient way. Computer simulations in flat Rayleigh fading show that the proposed algorithm is able to handle high system loads unlike many other iterative receivers. © 2006 IEEE.
Citation Count: 79
New Trellis Code Design for Spatial Modulation
(IEEE-INST Electrical Electronics Engineers Inc, 2011) Panayırcı, Erdal; Aygölü, Ümit; Panayırcı, Erdal; Poor, H. Vincent
Spatial modulation (SM) in which multiple antennas are used to convey information besides the conventional M-ary signal constellations is a new multiple-input multiple-output (MIMO) transmission technique which has recently been proposed as an alternative to V-BLAST (vertical Bell Labs layered space-time). In this paper a novel MIMO transmission scheme called spatial modulation with trellis coding (SM-TC) is proposed. Similar to the conventional trellis coded modulation (TCM) in this scheme a trellis encoder and an SM mapper are jointly designed to take advantage of the benefits of both. A soft decision Viterbi decoder which is fed with the soft information supplied by the optimal SM decoder is used at the receiver. A pairwise error probability (PEP) upper bound is derived for the SM-TC scheme in uncorrelated quasi-static Rayleigh fading channels. From the PEP upper bound code design criteria are given and then used to obtain new 4- 8- and 16-state SM-TC schemes using quadrature phase-shift keying (QPSK) and 8-ary phase-shift keying (8-PSK) modulations for 2 3 and 4 bits/s/Hz spectral efficiencies. It is shown via computer simulations and also supported by a theoretical error performance analysis that the proposed SM-TC schemes achieve significantly better error performance than the classical space-time trellis codes and coded V-BLAST systems at the same spectral efficiency yet with reduced decoding complexity.
Citation Count: 29
Next-Generation Multiple Access Based on NOMA With Power Level Modulation
(IEEE-Inst Electrical Electronics Engineers Inc, 2022) Pei, Xinyue; Chen, Yingyang; Wen, Miaowen; Yu, Hua; Panayırcı, Erdal; Poor, H. Vincent
To cope with the explosive traffic growth expected in next-generation wireless networks, it is necessary to design next-generation multiple access techniques that can provide higher spectral efficiency as well as larger-scale connectivity. As a promising candidate, power-domain non-orthogonal multiple access (NOMA) has been widely studied. In conventional power-domain NOMA, multiple users are multiplexed in the same time and frequency band with different preset power levels, which, however, may limit the spectral efficiency under practical finite alphabet inputs. Inspired by the concept of spatial modulation, we propose to solve this problem by encoding extra information bits into the power levels, and exploiting different signal constellations to help the receiver distinguish between them. To convey this idea, termed power selection (PS)-NOMA, clearly, we consider a simple downlink two-user NOMA system with finite input constellations. Assuming maximum-likelihood detection, we derive closed-form approximate bit error rate (BER) expressions for both users. Moreover, the two-user achievable rate region is also characterized. Simulation results verify the analysis and show that the proposed PS-NOMA can outperform conventional NOMA in terms of BER and achievable rate.
Citation Count: 35
Nondata-aided joint channel estimation and equalization for OFDM systems in very rapidly varying mobile channels
(IEEE-INST Electrical Electronics Engineers Inc, 2012) Şenol, Habib; Panayırcı, Erdal; Poor, H. Vincent
This paper is concerned with the challenging and timely problem of joint channel estimation and equalization for orthogonal frequency division multiplexing (OFDM) systems in the presence of frequency selective and very rapidly time varying channels. The resulting algorithm is based on the space alternating generalized expectation maximization-maximum a posteriori probability (SAGE-MAP) technique which is particularly well suited to multicarrier signal formats. The algorithm is implemented in the time-domain which enables one to use the Gaussian approximation of the transmitted OFDM samples. Consequently the averaging process of the nonpilot data symbols becomes analytically possible resulting in a feasible and computationally efficient channel estimation algorithm leading to a receiver structure that yields also an equalized output from which the data symbols are detected with excellent symbol error rate (SER) performance. Based on this Gaussian approximation the exact Bayesian Cramer Rao lower bound (CRLB) as well as the convergence rate of the algorithm are derived analytically. To reduce the computational complexity of the algorithm discrete Legendre orthogonal basis functions are employed to represent the rapidly time-varying fading channel. It is shown that depending on the normalized Doppler frequency only a small number of expansion coefficients is sufficient to approximate the channel very well and there is no need to know the correlation function of the input signal. The computational complexity of the algorithm is shown to be similar to O(NL) per detected data symbol and per SAGE-MAP algorithm cycle where N is the number of OFDM subcarriers and L is the number of multipath components.
Citation Count: 734
Orthogonal Frequency Division Multiplexing With Index Modulation
(IEEE-INST Electrical Electronics Engineers Inc, 2013) Başar, Ertuğrul; Aygölü, Ümit; Panayırcı, Erdal; Poor, H. Vincent
In this paper a novel orthogonal frequency division multiplexing (OFDM) scheme called OFDM with index modulation (OFDM-IM) is proposed for operation over frequency-selective and rapidly time-varying fading channels. In this scheme the information is conveyed not only by M-ary signal constellations as in classical OFDM but also by the indices of the subcarriers which are activated according to the incoming bit stream. Different low complexity transceiver structures based on maximum likelihood detection or log-likelihood ratio calculation are proposed and a theoretical error performance analysis is provided for the new scheme operating under ideal channel conditions. Then the proposed scheme is adapted to realistic channel conditions such as imperfect channel state information and very high mobility cases by modifying the receiver structure. The approximate pairwise error probability of OFDM-IM is derived under channel estimation errors. For themobility case several interference unaware/aware detection methods are proposed for the new scheme. It is shown via computer simulations that the proposed scheme achieves significantly better error performance than classical OFDM due to the information bits carried by the indices of OFDM subcarriers under both ideal and realistic channel conditions.
Citation Count: 135
Performance of spatial modulation in the presence of channel estimation errors
(IEEE-INST Electrical Electronics Engineers Inc, 2012) Basar, Ertuğrul; Aygölü, Ümit; Panayırcı, Erdal; Poor, H. Vincent
This work investigates the negative effects of channel estimation errors on the performance of spatial modulation (SM) when operating over flat Rayleigh fading channels. The pairwise error probability of the SM scheme is derived in the presence of channel estimation errors and an upper bound on the average bit error probability is evaluated for M-PSK and M-QAM signalling. It is shown via computer simulations that the derived upper bound becomes very tight with increasing signal-to-noise ratio (SNR) and the SM scheme is quite robust to channel estimation errors.
Citation Count: 0
Physical Layer Security With DCO-OFDM-Based VLC Under the Effects of Clipping Noise and Imperfect CSI
(Ieee-inst Electrical Electronics Engineers inc, 2024) Panayirci, Erdal; Panayırcı, Erdal; Bektas, Ekin B.; Poor, H. Vincent
Visible light communications (VLC) and physical-layer security (PLS) are key candidate technologies for 6G wireless communication. This paper combines these two technologies by considering an orthogonal frequency division multiplexing (OFDM) technique called DC-biased optical OFDM (DCO-OFDM) equipped with PLS as applied to indoor VLC systems. First, a novel PLS algorithm is designed to protect the DCO-OFDM transmission of the legitimate user from an eavesdropper. A closed-form expression for the achievable secrecy rate is derived and compared with the conventional DCO-OFDM without security. To analyze the security performance of the PLS algorithm under the effects of the residual clipping noise and the channel estimation errors, a closed-form expression is derived for a Bayesian estimator of the clipping noise induced naturally at the DCO-OFDM systems after estimating the optical channel impulse response (CIR), by a pilot-aided sparse channel estimation algorithm with the compressed sensing approach, in the form of the orthogonal matching pursuit (OMP), and the least-squares (LS). Finally, from the numerical and the computer simulations, it is shown that the proposed PLS algorithm with secret key exchange guarantees the eavesdropper's BER to stay close to 0.5 and that the proposed encryption-based PLS algorithm does not affect the BER performance of the legitimate user in the system.
Citation Count: 27
Physical-Layer Security With Optical Generalized Space Shift Keying
(Ieee-Inst Electrıcal Electronıcs Engıneers Inc, 2020) Panayırcı, Erdal; Yeşilkaya, Anıl; Çoğalan, Tezcan; Poor, H. Vincent; Haas, Harald
Spatial modulation (SM) is a promising technique that reduces inter-channel interference while providing high power efficiency and detection simplicity. In order to ensure the secrecy of SM, precoding and friendly jamming are widely adopted in the literature. However, neither of those methods can take advantage of SM. In this paper, a novel spatial constellation design (SCD) technique is proposed to enhance the physical layer security (PLS) of optical generalized space shift keying (GSSK), which can retain some benefits of SM. Due to the lack of small-scale fading, the quasi-static characteristics of the optical channel is used to tailor the received signal at the legitimate user's (Bob's) side. The PLS of the system is guaranteed by the appropriate selection of the power allocation coefficients for randomly activated light emitting diodes (LEDs). With the aid of Bob's channel state information at the transmitter, the bit error ratio (BER) of Bob is minimized while the BER performance of the potential eavesdroppers (Eves) is significantly degraded. Monte-Carlo simulation results show that the proposed SCD-zero forcing precoding (ZFP) forces Eve to experience a BER of around 0.5 by outperforming both the conventional and ZFP based GSSK for all practical signal-to-noise-ratio regimes and Bob-Eve separations.
Citation Count: 31
Relay-Aided Secure Broadcasting for Visible Light Communications
(IEEE-Inst Electrical Electronics Engineers Inc, 2019) Arafa, Ahmed; Panayırcı, Erdal; Poor, H. Vincent
A visible light communication broadcast channel is considered, in which a transmitter luminaire communicates with two legitimate receivers in the presence of an external eavesdropper. A number of trusted cooperative half-duplex relay luminaires are deployed to aid with securing the transmitted data. Transmitters are equipped with single light fixtures, containing multiple light emitting diodes, and receiving nodes are equipped with single photo-detectors, rendering the considered setting as a single-input single-output system. Transmission is amplitude-constrained to maintain operation within the light emitting diodes' dynamic range. Achievable secrecy rate regions are derived under such amplitude constraints for this multi-receiver wiretap channel, first for direct transmission without the relays, and then for multiple relaying schemes: cooperative jamming, decode-and-forward, and amplify-and-forward. Superposition coding with uniform signaling is used at the transmitter and the relays. Further, for each relaying scheme, secure beamforming vectors are carefully designed at the relay nodes in order to hurt the eavesdropper and/or benefit the legitimate receivers. Superiority of the proposed relaying schemes, with secure beamforming, is shown over direct transmission. It is also shown that the best relaying scheme depends on how far the eavesdropper is located from the transmitter and the relays, the number of relays, and their geometric layout.
Citation Count: 4
Relay-Aided Secure Broadcasting for VLC
(IEEE, 2018) Arafa, Ahmed; Panayırcı, Erdal; Poor, H. Vincent
A visible light communication (VLC) broadcast channel is considered in which a transmitter communicates with two receivers in the presence of an external eavesdropper. Trusted cooperative half-duplex relays are deployed to aid with securing the transmitted data. Transmission is amplitude-constrained to maintain operation within the light emitting diodes (LEDs) dynamic range. Achievable secrecy rate regions are derived under such amplitude constraints for this multi receiver wiretap channel first for direct transmission without the relays and then for cooperative jamming decode-and-forward and amplify-and-forward relaying schemes. Superposition coding with uniform signaling is used for transmission along with secure beamforming at the relays. Superiority of the secure relaying schemes over direct transmission is shown with performance depending on how far the eavesdropper is from the transmitter and the relays.
Citation Count: 11
A Reliable Successive Relaying Protocol
(IEEE-INST Electrical Electronics Engineers Inc, 2014) Panayırcı, Erdal; Aygölü, Ümit; Panayırcı, Erdal; Poor, H. Vincent
Successive relaying has recently emerged as an effective technique for cooperative networks and provides significant improvements in bandwidth efficiency over traditional relaying techniques ;however to achieve full-diversity the available successive relaying protocols generally assume noise-free sourcerelay and interference-free inter-relay channels. In this paper a novel successive relaying protocol is proposed for N-relay wireless networks by removing these optimistic assumptions. The proposed protocol benefits from distributed space-time block codes (STBCs) with coordinate interleaving and relay selection. It achieves a diversity order of two and high transmission rate under realistic network conditions with single-symbol maximum likelihood (ML) detection. A general N-relay signaling protocol is presented and specific design examples are given for N = 2 3 and 4-relay cooperative networks. The average symbol error probability (ASEP) is analytically derived and shown to match with computer simulation results. It is also shown via computer simulations that the proposed scheme achieves significantly better error performance and is more robust to channel estimation errors than its counterparts given in the literature under realistic network conditions.
Citation Count: 2
Reliable two-path successive relaying
(2013) Panayırcı, Erdal; Aygölü, Ümit; Panayırcı, Erdal; Poor, H. Vincent
Emerging two-path successive relaying protocols generally rely on error-free source-relay channels and/or interference-free inter-relay channels to achieve high-rate and full-diversity. In this paper by removing these optimistic assumptions a novel two-path successive relaying scheme that benefits from relay selection and distributed space-time block coding (STBC) and transfers the data from the source to the destination via relays in a reliable fashion is proposed. The proposed scheme can achieve full diversity without the requirement of perfect decoding at relays since not only the destination but also the relays benefit from distributed STBC and relay selection. As the target STBC coordinate interleaved orthogonal design (CIOD) for two transmit antennas is considered. The average symbol error probability of the proposed scheme is derived and its error performance is compared with reference systems. © 2013 IEEE.
Citation Count: 1
Semiblind joint channel estimation and equalization for OFDM systems in rapidly varying channels
(2010) Şenol, Habib; Panayırcı, Erdal; Poor, H. Vincent; Oğuz, Onur; Vandendorpe, Luc
We describe a new joint iterative channel estimation and equalization algorithm for joint channel estimation and data detection for orthogonal frequency division multiplexing (OFDM) systems in the presence of frequency selective and rapidly timevarying channels. The algorithm is based on the expectation maximization-maximum a posteriori (EM-MAP) technique which is very suitable for the multicarrier signal formats. The algorithm leads to a receiver structure that yields the equalized output using the channel estimates. The pilot symbols are employed to estimate the initial channel coefficients effectively and unknown data symbols are averaged out in the algorithm. The band-limited discrete cosine serial expansion of low dimensionality is employed to represent the time-varying fading channel. In this way the resulting reduced dimensional channel coefficients are estimated iteratively with tractable complexity. The extensive computer simulations show that the algorithm has excellent symbol error rate (SER) and mean square error (MSE) performances for very high mobility even during the initialization step. Copyright © ?enol et. al.
Citation Count: 310
Space-Time Block Coded Spatial Modulation
(IEEE-INST Electrical Electronics Engineers Inc, 2011) Başar, Ertuğrul; Aygölü, Ümit; Panayırcı, Erdal; Poor, H. Vincent
A novel multiple-input multiple-output (MIMO) transmission scheme called space-time block coded spatial modulation (STBC-SM) is proposed. It combines spatial modulation (SM) and space-time block coding (STBC) to take advantage of the benefits of both while avoiding their drawbacks. In the STBC-SM scheme the transmitted information symbols are expanded not only to the space and time domains but also to the spatial (antenna) domain which corresponds to the on/off status of the transmit antennas available at the space domain and therefore both core STBC and antenna indices carry information. A general technique is presented for the design of the STBC-SM scheme for any number of transmit antennas. Besides the high spectral efficiency advantage provided by the antenna domain the proposed scheme is also optimized by deriving its diversity and coding gains to exploit the diversity advantage of STBC. A low-complexity maximum likelihood (ML) decoder is given for the new scheme which profits from the orthogonality of the core STBC. The performance advantages of the STBC-SM over simple SM and over V-BLAST are shown by simulation results for various spectral efficiencies and are supported by the derivation of a closed form expression for the union bound on the bit error probability.