Browsing by Author "Doğan, Hakan"

Now showing 1 - 16 of 16

Citation Count: 4
Channel Estimation for Spatial Modulation Orthogonal Frequency Division Multiplexing Systems
(IEEE, 2015) Acar, Yusuf; Doğan, Hakan; Panayırcı, Erdal
A combination of spatial modulation and orthogonal frequency division multiplexing (SM-OFDM) has been recently proposed for multicarrier systems while assuming the perfect channel state information (P-CSI) available at the receiver. But in practical scenarios the estimation of CSI is crucial in order to detect the transmitted data coherently. In this work(1) a new frame structure and pilot symbol aided channel estimation (PSA-CE) technique with a piecewise linear interpolation is proposed for the SM-OFDM systems operating in the presence of frequency selective channel. Bit error rate (BER) performance of the proposed channel estimation technique is then investigated with different channel models such as Typical Urban ( TU) and Rural Urban (RU) for 4-quadrature amplitude modulation (QAM). In particular it is shown that the performance with estimated channel came close to that with known channel within 2.3 dB in SNR for BER = 10(-4) for TU channels.
Citation Count: 5
An efficient joint channel estimation and decoding algorithm for turbo-coded space-time orthogonal frequency division multiplexing receivers
(Inst Engineering Technology-IET, 2008) Doğan, Hakan; Çırpan, Hakan Ali; Panayırcı, Erdal
The challenging problem in the design of digital receivers of today's and future high-speed high data-rate wireless communication systems is to implement the optimal decoding and channel estimation processes jointly in a computationally feasible way. Without realising such a critical function perfectly at receiver the whole system will not work properly within the desired performance limits. Unfortunately direct implementation of such optimal algorithms is not possible mainly due to their mathematically intractable and computationally prohibitive nature. A novel algorithm that reaches the performance of the optimal maximum a posteriori (MAP) algorithm with a feasible computational complexity is proposed. The algorithm makes use of a powerful statistical signal processing tool called the expectation-maximisation (EM) technique. It iteratively executes the MAP joint channel estimation and decoding for space-time block-coded orthogonal frequency division multiplexing systems with turbo channel coding in the presence of unknown wireless dispersive channels. The main novelty of the work comes from the facts that the proposed algorithm estimates the channel in a non-data-aided fashion and therefore except a small number of pilot symbols required for initialisation no training sequence is necessary. Also the approach employs a convenient representation of the discrete multipath fading channel based on the Karhunen-Loeve (KL) orthogonal expansion and finds MAP estimates of the uncorrelated KL series expansion coefficients. Based on such an expansion no matrix inversion is required in the proposed MAP estimator. Moreover optimal rank reduction is achieved by exploiting the optimal truncation property of the KL expansion resulting in a smaller computational load on the iterative estimation approach.
Citation Count: 0
An efficient joint data detection and channel estimation technique for uplink MC-CDMA systems based on SAGE algorithm
(IEEE, 2007) Panayırcı, Erdal; Doğan, Hakan; Çırpan, Hakan Ali; Fleury, Bernard Henri
This paper is concerned with joint channel estimation and data detection for uplink multicarrier code-division multiple-access (MC-CDMA) systems in the presence of frequency fading channel. The detection and estimation algorithm implemented at the receiver is based on a version of the expectation maximization (EM) technique called the spece-alternating-generalized-expectation-maximization (SAGE) algorithm which is very suitable for the the multicarrier signal formats. Application of the SAGE algorithm to the problem of iterative data detection and channel estimation leads to a receiver structure that also incorporates a partial interference cancelation. Computer simulations show that the proposed algorithm has excellent BER end estimation performance.
Citation Count: 0
EM-based joint data detection and channel estimation for uplink MC-CDMA systems over frequency selective channels
(IEEE, 2007) Doğan, Hakan; Panayırcı, Erdal; Çırpan, Hakan Ali; Fleury, Bernard Henri
This paper is concerned with joint channel estimation and data detection for uplink multicarrier code-division multiple-access (MC-CDMA) systems in the presence of frequency fading channel. The detection and estimation algorithm implemented at the receiver is based on a version of the expectation maximization (EM) technique which is very suitable for the multicarrier signal formats. Application of the EM-based algorithm to the problem of iterative data detection and channel estimation leads to a receiver structure that also incorporates a partial interference cancelation. Computer simulations show that the proposed algorithm has excellent BER end estimation performance.
Citation Count: 2
EM-Based MAP channel estimation and data detection for downlink MCC-CDMA systems
(IEEE, 2007) Doğan, Hakan; Panayırcı, Erdal; Çırpan, Hakan Ali
In this work we propose a joint MAP channel estimation and data detection technique based on the Expectation Maximization (EM) method with paralel interference cancelation(PIC) for downlink multi-carrier (MC) code division multiple access (CDMA) systems in the presence of frequency selective channels. The EM algorithm derived estimates the complex channel parameters of each subcarriers iteratively and generates the soft information representing the data a posterior probabilities. The soft information is then employed in a PIC module to detect the symbols efficiently. Moreover the MAP-EM approach considers the channel variations as random processes and applies the Karhunen-Loeve (KL) orthogonal series expansion. The performance of the proposed approach are studied in terms of bit-error rate (BER) and mean square error (MSE). Throughout the simulations extensive comparisons with previous works in literature are performed showing that the new scheme can offer superior performance.
Citation Count: 0
EM-MAP based initialization of PIC receiver for downlink MC-CDMA systems
(IEEE, 2007) Panayırcı, Erdal; Cirpan, Hakan Ali; Panayırcı, Erdal
The quality of multiple access interference (MAI) which can be improved by using channel estimation and data estimation of all active users effects considerably the performance of PIC detector. Therefore data and channel estimation performance is obtained in the initial stage has a significant relationship with the performance of PIC. So obviously it is necessary to make excellent joint data and channel estimation for initialization of PIC detector. In this work to initiate PIC module efficiently a joint MAP channel estimation and data detection technique based on the Expectation Maximization (EM) method has been proposed. Moreover the MAP-EM approach considers the channel variations as random processes and applies the Karhunen-Loeve (KL) orthogonal series expansion. The performance of the proposed approach are studied in terms of bit-error rate (BER). Throughout the simulations extensive comparisons with previous works in literature are performed showing that the new scheme can offer superior performance.
Citation Count: 19
Iterative channel estimation and decoding of turbo coded SFBC-OFDM systems
(IEEE, 2007) Doğan, Hakan; Çırpan, Hakan Ali; Panayırcı, Erdal
We consider the design of turbo receiver structures for space-frequency block coded orthogonal frequency division multiplexing (SFBC-OFDM) systems in the presence of unknown frequency and time selective fading channels. The Turbo receiver structures for SFBC-OFDM systems under consideration consists of an iterative MAP Expectation/Maximization (EM) channel estimation algorithm soft MMSE-SFBC decoder and a soft MAP outer-channel-code decoder. MAP-EM employs iterative channel estimation and it improves receiver performance by re-estimating the channel after each decoder iteration. Moreover the MAP-EM approach considers the channel variations as random processes and applies the Karhunen-Loeve (KL) orthogonal series expansion. The optimal truncation property of the KL expansion can reduce computational load on the iterative estimation approach. The performance of the proposed approaches are studied in terms of mean square error and bit-error rate. Through computer simulations the effect of a pilot spacing on the channel estimator performance and sensitivity of turbo receiver structures on channel estimation error are studied. Simulation results illustrate that receivers with turbo coding are very sensitive to channel estimation errors compared to receivers with convolutional codes. Moreover superiority of the turbo coded SFBC-OFDM systems over the turbo coded STBC-OFDM systems is observed especially for high Doppler frequencies.
Citation Count: 1
Iterative channel estimation for spatial modulation systems over fast fading channels
(IEEE, 2014) Acar, Yusuf; Doğan, Hakan; Panayırcı, Erdal
Spatial Modulation (SM) based on the use of antenna indices to transmit information in addition to the conventional signal constellations has been recently proposed to solve practical problems encountered in MIMO systems. In the literature estimation of CSI for SM systems is simply investigated by RLS for slow fading channels. However iterative receivers that offer significant performance gains over a non- iterative when the total number of pilot is not sufficient and the channel is fast fading have not been investigated for SM based systems. In this paper it shown that the RLS based receiver has a performance degradation for fast fading channels and a new iterative channel estimation techniques is proposed with the necessary signal model to enhance receiver performance for fast fading channels. Computer simulation results indicate that proposed iterative receiver has a significant performance advantage over the RLS based receiver for time-varying Rayleigh channels.
Citation Count: 0
Iterative channel estimation techniques for uplink MC-CDMA systems
(IEEE, 2007) Doğan, Hakan; Panayırcı, Erdal; Çırpan, Hakan Ali
In this work maximum likelihood (ML) channel estimation for uplink multicarrier code-division multiple-access (MC-CDMA) systems is considered in the presence of frequency fading channel. The expectation-maximization (EM)- and a space-alternating generalized expectation-maximization (SAGE) algorithm are introduced to avoid matrix inversion for the ML channel estimation problem. We compare the both algorithms in terms of the number of used iteration and show that the proposed algorithms converge the same performance of the ML estimator as the increasing number of iterations.
Citation Count: 0
Iterative Receiver for DS-CDMA Systems in the Presence of Time-Varying Channels
(IEEE, 2008) Doğan, Hakan; Panayırcı, Erdal; Çırpan, Hakan Ali; Cam, Gökhan
In this paper we present an efficient iterative receiver structure of tractable complexity for joint multiuser detection and multichannel estimation (JDE) of direct-sequence code-division multiple-access systems operating in the presence of time-varying flat fading channel. The time-varying channel is assumed to be modeled according to a piece-wise constant channel. An optimality criterion is defined and analytical expressions for the corresponding optimized weight coefficients are given. Monte-Carlo simulations of a synchronous scenario show that the proposed JDE receiver have excellent multiuser efficiency and are robust against errors in the estimation of the channel parameters.
Citation Count: 0
Joint data detection and channel estimation for uplink MC-CDMA systems over frequency selective channels
(Springer, 2007) Panayırcı, Erdal; Doğan, Hakan; Çırpan, Hakan Ali; Fleury, Bernard Henri
This paper is concerned with joint channel estimation and data detection for uplink multicarrier code-division multiple-access (MC-CDMA) systems ill the presence of frequency fading channel. The detection and estimation implemented at the receiver are based on a version of the expectation maximization (EM) algorithm which is very suitable for the the multicarrier signal formats. Application of the EM-based algorithm to the problem of iterative data detection and channel estimation leads to a receiver structure that also incorporates a partial interference cancelation. Computer simulations show that the proposed algorithm has excellent BER end estimation performance.
Citation Count: 5
MAP channel-estimation-based PIC receiver for downlink MC-CDMA systems
(Hindawi Publishing Corporation, 2008) Doğan, Hakan; Panayırcı, Erdal; Çırpan, Hakan Ali; Fleury, Bernard Henri
We propose a joint MAP channel estimation and data detection technique based on the expectation maximization (EM) method with paralel interference cancelation (PIC) for downlink multicarrier (MC) code division multiple access (CDMA) systems in the presence of frequency selective channels. The quality of multiple access interference (MAI) which can be improved by using channel estimation and data estimation of all active users affects considerably the performance of PIC detector. Therefore data and channel estimation performance obtained in the initial stage has a significant relationship with the performance of PIC. So obviously it is necessary to make excellent joint data and channel estimation for initialization of PIC detector. The EM algorithm derived estimates the complex channel parameters of each subcarrier iteratively and generates the soft information representing the data a posterior probabilities. The soft information is then employed in a PIC module to detect the symbols efficiently. Moreover the MAP-EM approach considers the channel variations as random processes and applies the Karhunen-Loeve (KL) orthogonal series expansion. The performance of the proposed approach is studied in terms of bit-error rate (BER) and mean square error (MSE). Throughout the simulations extensive comparisons with previous works in literature are performed showing that the new scheme can offer superior performance.
Citation Count: 10
On channel estimation for spatial modulated systems over time-varying channels
(Academic Press Inc Elsevier Science, 2015) Acar, Yusuf; Doğan, Hakan; Panayırcı, Erdal
Spatial Modulation (SM) has been proposed recently for multiple-input multiple-output (MIMO) systems to cope with the interchannel interference and to reduce the detection complexity as compared to the conventional MIMO systems. In SM system the data symbols are transmitted by a randomly selected active antenna of a MIMO transmitter to the receiver through a wireless channel. The information is carried both by the data symbol from any signal constellation such as M-ary phase shift keying (M-PSK) or M-ary quadrature amplitude modulation (M-QAM) by the index of the selected antenna. The channel estimation is a critical process at the receiver during the coherent detection of the transmitted symbol and the antenna index randomly selected. Recently the channel estimation of channel for SM systems has been investigated by the recursive least square (RLS) algorithm for only quasi-static fading channels. In this paper a novel channel estimation is proposed for SM systems in the presence of rapidly time-varying channels. The Bayesian mean square error (MSE) bound has been derived as a benchmark and the performance of the proposed approaches is studied in terms of MSE and bit-error rate (BER). Computer simulation results have confirmed that the proposed iterative channel estimation technique has significant BER/MSE performance advantages compared with existing channel estimation algorithm proposed earlier in the literature. (C) 2014 Elsevier Inc. All rights reserved.
Citation Count: 12
Pilot Symbol Aided Channel Estimation for Spatial Modulation-OFDM Systems and its Performance Analysis with Different Types of Interpolations
(Springer, 2017) Acar, Yusuf; Doğan, Hakan; Panayırcı, Erdal
Spatial modulation orthogonal frequency division multiplexing (SM-OFDM) system has been recently proposed as an alternative for multiple-input multiple-output (MIMO)-OFDM systems to increase spectral efficiency by keeping a low-complexity implementation. In the literature SM-OFDM systems assume a perfect channel state information (P-CSI) available at the receiver for coherent detection and the channel estimation problem is not considered. It is clear that the channel estimation is a critical issue on the performance of SM-OFDM systems. In this paper a frame structure where pilot symbols are typically interspersed with data symbols among the sub-carriers to aid the channel estimation is considered. Then the pilot symbol aided channel estimation (PSA-CE) technique with different interpolations is proposed for the SM-OFDM systems. It is shown that in the proposed PSA-CE equidistantly spaced pilot symbols allow to reconstruct the channel response by means of interpolation if the spacing of the pilots is sufficiently close to satisfy the sampling theorem. Linear nearest neighbor piecewise cubic Hermite and the low-pass interpolations are investigated to explore trade-off between complexity and performances. We show that the low pass interpolator yields better performance than the other interpolation techniques for selected cases such as higher order modulations. The results validate the potential of the proposed PSA-CE estimation applying to SM-OFDM systems.
Citation Count: 0
Pilot Symbol Assisted Channel Estimation for 4x4 Space Time Block Coded Spatial Modulation Systems
(IEEE, 2015) Acar, Yusuf; Doğan, Hakan; Panayırcı, Erdal
Recently spatial modulation (SM) and space-time block coding (STBC) are combined to take advantage of the benefits of both while avoiding their drawbacks for multiple-input and multiple-output (MIMO) systems. The pioneering works on STBC-SM assume that perfect knowledge of the channel fading coefficients is available at the receiver. This work(1) addresses the challenging and timely problem of channel estimation for 4 x 4 STBC-SM systems in the presence of time-varying channels. In this paper the estimation of channel at pilot durations is done by least square (LS) method and then the channel interpolation is performed by linear interpolation or nearest neighbor interpolation algorithms. Simulation results have demonstrated that the proposed channel estimation based on the linear interpolation offer substantial performance gains over the channel estimation based on the nearest neighbor interpolation. In particular a savings of about 5dB is obtained at BER = 10(-5) as compared with the nearest interpolation based receiver at 120km/h for 4 x 4 STBC-SM systems with the binary phase shift keying (BPSK) modulation.
Citation Count: 4
Spline Based Channel Estimation for STBC-SM Systems over Fast-Varying Rician Fading Channels
(IEEE, 2015) Acar, Yusuf; Doğan, Hakan; Panayırcı, Erdal
In the STBC-SM systems the information is carried both by STBC symbols and indices of the transmit antennas from which these symbols are transmitted. Channel estimation is a critical process at the receiver during the coherent detection of the transmitted STBC symbols and indices of the transmit antennas. In this paper a spline interpolation and pilot symbols based channel estimation has been proposed for the space-time block coded spatial modulation (STBC-SM) systems to track the channel variations in the presence of Rician fading channels. The estimation of channel at pilot durations is done by least squares (LS) method and then the spline based channel interpolation is performed. It has been shown via computer simulations that the proposed spline based channel estimation channel estimation outperforms the piecewise linear interpolation (PLI) and the nearest neighbor interpolation (NNI) based channel estimations.