I. Altunbas

Istanbul Technical University, İstanbul, Istanbul, Turkey

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Publications (36)10.62 Total impact

  • A. Karademir, I. Altunbas
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    ABSTRACT: In this paper, error performance of a cooperative communication system with one relay is analyzed over composite fading and shadowing channels modeled by generalized-K distribution. At the relay, variable-gain amplify and forward and at the destination, maximal ratio combining and selection combining methods are used. The symbol error rate expressions are derived analytically by using the Padé approximation of the moment generating function of the signal-to-noise ratio at the receiver. The theoretical results are verified by Monte-Carlo simulations.
    Signal Processing and Communications Applications Conference (SIU), 2013 21st; 01/2013
  • Mustafa Yagimli, Ibrahim Altunbas
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    ABSTRACT: In this paper, two different physical layer network coding (PLNC) systems that apply antenna selection technique at the relay, consisting of two single-antenna terminals and a multi-antenna relay are proposed. The bound expressions of symbol error rate (SER) of the systems over frequency non-selective and slowly Rayleigh fading channels for M-PSK modulation are derived by using the moment generating function (MGF) method. In addition, Monte Carlo SER simulation results are given for both systems. According to the obtained theoretical and simulation results, diversity order of the systems is equal to the number of total antennas at the relay, and thus it is shown that error performance of the conventional PLNC system is significantly improved by the proposed systems. Also, SER performances of the proposed systems are compared with each other.
  • M.C. Ilter, I. Altunbas
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    ABSTRACT: Although there has been a growing literature on physical layer network coding (PLNC) technique, to the best of our knowledge, performance analysis of the PLNC systems over the generalized shadowed fading channels modelled by independent but not necessarily identically distributed generalized-K distribution has not been reported so far. Generalized-K channel is versatile model which is capable of representing different levels of shadowing and multipath fading effects in the wireless environment. In this paper, we investigate outage and symbol error rate performance of the PLNC system consisting of two sources and one relay with one transmit/receive antenna in each node. Amplify and forward relaying method is used at the relay. More specifically, we utilize the moment generating function of the SNR which is obtained by the Padé approximation to evaluate the system performance. We also investigate the energy allocation problem to improve the system error performance by allocating the total energy optimally among the sources and the relay in different channel conditions. The analytical results are verified by Monte Carlo simulations.
    Wireless Communication Systems (ISWCS), 2012 International Symposium on; 01/2012
  • M.C. Ilter, I. Altunbas
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    ABSTRACT: In this paper, performance of a physical layer network coding system consisting of two users and one relay with one transmit/receive antenna is analyzed in the presence of composite fading/shadowing effects modeled by generalized-K distribution. Amplify and forward method is used at the relay. The outage probability and symbol error rate of the system are analyzed based on the Padé approximation of the moment generating function. The analytical results are verified by computer simulations.
    Signal Processing and Communications Applications Conference (SIU), 2012 20th; 01/2012
  • Haci Ilhan, Ibrahim Altunbas
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    ABSTRACT: In this paper, error performances of distributed parallel con- catenated (turbo) coded relay/cooperative systems, whose com- ponent codes are recursive space-time trellis codes are inves- tigated over cascaded fading channels. Two seperate systems with one and two relays are considered. In the first system, the relay uses "decode and forward" method while in the second one, the relays use "amplify and forward" and decode and for- ward methods. Computer simulations are performed under the double Rayleigh fading channel assumption and the superiority of the distributed turbo coded systems is presented. 1. Giris¸
  • Source
    H. İlhan, Ibrahim Altunbas, Murat Uysal
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    ABSTRACT: In this letter, we consider the deployment of distributed space-time trellis codes (STTCs) for user cooperation. We derive a pairwise error probability (PEP) expression for distributed STTCs over cascaded Rayleigh fading channels. Using the derived PEP expression, we determine a code design criterion and propose novel 4-/8-/16-state 4-PSK and 8-/16-state 8-PSK distributed STTCs through a systematic code search. We confirm the superiority of the proposed codes through extensive Monte-Carlo simulations.
    IEEE Communications Letters 01/2011; 14(12-14):1140 - 1142. DOI:10.1109/LCOMM.2010.102610.101133 · 1.46 Impact Factor
  • Yasemin Sitti, Ibrahim Altunbas
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    ABSTRACT: In this paper, a cooperative system with more than one receive antenna at relay and destination is considered. Amplify and forward method is used at the relay and maximal ratio combiners are employed at the receivers. It is assumed that source-relay and relay-destination channels have Nakagami-m fading and source-destination channels have composite shadowing/fading modeled by Generalized-K distribution. The bit error performance of the system under consideration is analyzed based on the moment generating function technique and the analytical results are verified by computer simulations.
  • Source
    O. Özdemir, I. Altunbaş, M. Bayrak
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    ABSTRACT: Super-orthogonal space-time trellis (SOSTT) codes provide a significant coding gain with respect to the conventional space-time trellis (STT) codes without increasing the decoding complexity at the receiver. Transmit antenna selection (TAS) is an important technique to solve the implementation complexity problems of multiple-antenna systems that arise from employing a separate RF chain for each antenna. This study treats a scheme combining SOSTT coding with TAS in order to exploit performance improvements provided by SOSTT codes while realising the promises made by the TAS technique. In the proposed scheme, transmit antennas that maximise the signal-to-noise ratio at the receiver are chosen and activated out of all available transmit antennas for transmission of the baseline SOSTT code, whereas all other transmit antennas are silent. The error performance of the proposed structure is investigated by deriving moment generating function (MGF)-based upper bound expressions on the pairwise error probability in quasi-static flat Rayleigh fading channels for both perfect and imperfect antenna subset selection. The performance analysis demonstrates that the proposed scheme provides full diversity order as if all transmit antennas were used when antennas are perfectly selected. Moreover, it is shown that this structure provides better error performance almost at the same decoding complexity compared to the previous STT coding structures with TAS in the literature.
    IET Communications 12/2010; 4(16-4):1942 - 1951. DOI:10.1049/iet-com.2009.0698 · 0.74 Impact Factor
  • Deniz Çelik, Ibrahim Altunbas, Aygölü
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    ABSTRACT: In this paper, coded user cooperation systems are integrated with combined frequency and phase modulation. Frequency/phase shift keying modulation defined over a signal set varying in both frequency and phase is a nonlinear constant envelope multidimensional modulation technique. Error performance of the proposed scheme is evaluated by computer simulations in quasi-static Rayleigh fading channels, for both full and selective cooperation cases. The selective cooperation is performed first by cyclic redundant check code control and then by threshold signal-to-noise control. Simulation results show that in all cases, frequency/phase shift keying modulation provides much better error performance than the conventional phase shift keying modulation in coded cooperation systems.
  • A.F. Coskun, O. Kucur, I. Altunbas
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    ABSTRACT: In this work, bit/symbol error rate (BER/SER) performances of multiple-input multiple-output (MIMO) systems that employ Alamouti coded transmission with transmit antenna selection (TAS) are examined for independent but non-identical flat Nakagami-m fading channels. Exact BER/SER expressions are derived by using the moment generating function (MGF)-based analysis method for binary phase shift keying (BPSK), binary frequency shift keying (BFSK), M-ary phase shift keying (M-PSK) and M-ary quadrature amplitude modulation (M-QAM) signals. Also, upper bound expressions have been obtained in order to examine the asymptotic diversity order of TAS/Alamouti scheme. Monte Carlo simulations have validated the theoretical SER performance results derived for different numbers of transmit and receive antennas.
    Signal Processing and Communications Applications Conference (SIU), 2010 IEEE 18th; 05/2010
  • I. Altunbaş, M. Uysal
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    ABSTRACT: In this paper, error performance of a coded cooperative relay system is investigated when channels have cascaded Nakagami distribution. By using general pairwise error probability upper bound of the system, code design criterion for the distributed space-time code is derived and using this criterion, 8-state distributed space-time trellis codes for 4-PSK and 8-PSK modulations are designed. The error performances of the new codes are evaluated by computer simulations and compared those of the corresponding codes.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Continuous phase frequency shift keying is a power/bandwidth efficient modulation technique, hence, attractive for use in relay/cooperative systems employing inexpensive nonlinear power amplifiers. We investigate optimum distributed space-time 4-ary continuous phase frequency shift keying trellis codes for amplify & forward relaying method and propose novel codes for relay transmission systems. The error performances of the classical and novel codes are investigated for one and two-relay systems using various transmission protocols.
    Communication Theory, Reliability, and Quality of Service (CTRQ), 2010 Third International Conference on; 01/2010
  • Source
    H. Ilhan, M. Uysal, I. Altunbas
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    ABSTRACT: Although there has been a growing literature on cooperative diversity, the current literature is mainly limited to the Rayleigh fading channel model, which typically assumes a wireless communication scenario with a stationary base station antenna above rooftop level and a mobile station at street level. In this paper, we investigate cooperative diversity for intervehicular communication based on cascaded Nakagami fading. This channel model provides a realistic description of an intervehicular channel where two or more independent Nakagami fading processes are assumed to be generated by independent groups of scatterers around the two mobile terminals. We investigate the performance of amplify-and-forward relaying for an intervehicular cooperative scheme assisted by either a roadside access point or another vehicle that acts as a relay. Our diversity analysis reveals that the cooperative scheme is able to extract the full distributed spatial diversity. We further formulate a power-allocation problem for the considered scheme to optimize the power allocated to the broadcasting and relaying phases. Performance gains up to 3 dB are obtained through optimum power allocation, depending on the relay location.
    IEEE Transactions on Vehicular Technology 10/2009; DOI:10.1109/TVT.2009.2014685 · 2.64 Impact Factor
  • H. Ilhan, I. Altunbas, M. Uysal
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    ABSTRACT: In this paper, error performance of a cooperative relay system using amplify and forward method is investigated when channels between source, relay and destination have cascaded Nakagami distribution. General pairwise error probability of the system is derived and effective and asymptotic diversity orders are investigated for some special cases. Bit error probability curves are obtained by computer simulations.
    Signal Processing and Communications Applications Conference, 2009. SIU 2009. IEEE 17th; 05/2009
  • Deniz Çelik, I. Altunbas, U. Aygolu
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    ABSTRACT: In this paper, coded user cooperation systems are integrated with combined frequency and phase modulation FSK/PSK. Bit error performance of the proposed scheme is evaluated by computer simulations in quasistatic Rayleigh fading channels. Simulation results show that the FSK/PSK modulation provides much better error performance than the classical MPSK modulation in coded cooperation systems.
  • H. Ilhan, I. Altunbas, M. Uysal
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    ABSTRACT: Cooperative communication techniques promise the advantages of MIMO (multi-input multi-output) communications for wireless scenarios with single-antenna terminals. In this paper, we investigate the performance of a vehicle-to-vehicle cooperative scheme where another vehicle in the vicinity of the source vehicle acts as a relay. The underlying source-to-relay, relay-to-destination, and source-to-destination links are modeled as cascaded (double) Rayleigh fading. This statistical model provides a realistic description of inter-vehicular channel where two or more independent Rayleigh fading processes are assumed to be generated by independent groups of scatterers around the two mobile terminals. We derive a pairwise error probability (PEP) expression for the inter-vehicular cooperative scheme under consideration and show that the full distributed spatial diversity is extracted. Based on the derived PEP expressions, we obtain union bounds on the bit error rate performance which are then minimized to optimally allocate power between broadcasting and relaying phases. Optimum power allocation brings performance gains up to 3dB depending on the relay location and deployed modulation scheme.
    Vehicular Technology Conference, 2008. VTC 2008-Fall. IEEE 68th; 10/2008
  • Source
    H. Ilhan, I. Altunbas, M. Uysal
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    ABSTRACT: Although there has been a growing literature on cooperative diversity, the current literature is mainly limited to Rayleigh fading channel model which typically assumes a wireless communication scenario with a stationary base station antenna above roof-top level and a mobile station at street level. In this paper, we investigate cooperative diversity for inter-vehicular communication based on cascaded Rayleigh fading. This channel model provides a realistic description of inter-vehicular channel where two or more independent Rayleigh fading processes are assumed to be generated by independent groups of scatterers around the two mobile terminals. We investigate the performance of amplify-and-forward relaying for an inter-vehicular cooperative scheme assisted by a road-side access point which acts as a relay. Our diversity analysis reveals that the cooperative scheme is able to extract the full distributed spatial diversity. We further formulate a power allocation problem for the considered scheme to optimize the power allocated to broadcasting and relaying phases. Performance gains up to 2.8 dB are observed through optimum power allocation depending on the relay location.
    Vehicular Technology Conference, 2008. VTC Spring 2008. IEEE; 06/2008
  • H. Ilhan, I. Altunbas, M. Uysal
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    ABSTRACT: In this paper, we investigate performance of cooperative diversity techniques for inter-vehicular communication. The channel model used in this system is cascaded Rayleigh which provides a realistic description of inter-vehicular channel where two or more independent Rayleigh processes are assumed to be generated by independent groups of scatterers around the two mobile terminals. In this paper, we investigate the performance of amplify-and-forward relaying for an inter-vehicular cooperative scheme assisted by a road-side access point which acts as a relay. Our diversity analysis shows that the cooperative scheme is able to extract the full distributed spatial diversity. We further formulate a power allocation problem for the considered scheme to optimize the power allocated to considered system. Performance gains up to nearly 3 dB are observed through optimum power allocation depending on the relay location.
    Signal Processing, Communication and Applications Conference, 2008. SIU 2008. IEEE 16th; 05/2008
  • H. Ilhan, I. Altunbas
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    ABSTRACT: Cooperative diversity is an effective method of improving power efficiency of wireless communication systems without using additional transmit antennas on the mobile device. In this paper, error performance of the improved super-orthogonal space-time trellis codes in the relay cooperative diversity system using amplify and forward method is investigated for different channel combinations. It is shown by computer simulations that the improved super-orthogonal space-time trellis codes provide the best error performance for the evaluated system.
    Signal Processing and Communications Applications, 2007. SIU 2007. IEEE 15th; 07/2007
  • E. Aydm, I. Altunbas
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    ABSTRACT: In this paper, a serial concatenation scheme comprising of low-density parity-check (LDPC) and space-time trellis codes (STTC) with transmit antenna selection (TAS) is considered. We analyze the frame error rate (FER) performance of this scheme over quasi-static and fast Rayleigh fading channels by computer simulations. It is shown that applying TAS further improves the performance of the serial concatenation LDPC-STTC. In particular, TAS provides diversity gain over quasi-static fading and coding gain over fast fading channels. Diversity gain over fast fading is improved by the LDPC decoding iterations
    Electrotechnical Conference, 2006. MELECON 2006. IEEE Mediterranean; 06/2006

Publication Stats

127 Citations
10.62 Total Impact Points

Institutions

  • 1994–2012
    • Istanbul Technical University
      • • Department of Electronics and Communication Engineering
      • • Faculty of Electrical and Electronic Engineering
      • • Department of Electrical Engineering
      İstanbul, Istanbul, Turkey
  • 2008
    • University of Waterloo
      • Department of Electrical & Computer Engineering
      Ватерлоо, Ontario, Canada
  • 2006
    • Yeditepe University
      • Department of Electrical and Electronics Engineering
      İstanbul, Istanbul, Turkey
  • 2005
    • Gebze Institute of Technology
      • Department of Electronics Engineering
      Gebze, Kocaeli, Turkey
  • 2001
    • Texas A&M University
      • Department of Electrical and Computer Engineering
      College Station, Texas, United States