AbstractâResearch on non-coherent detection for cooperative communications is at an early stage and many fundamental problems are still open. We will be ...
Efficient NonCoherent Detection Techniques for Broadband Cooperative Networks Sara Al Maeeni Advisors: Sami Muhaidat and Ibrahim Abualhaol Electrical and Computer Engineering Department, Khalifa University Email:{sara.almaeeni,sami.muhaidat,ibrahim.aboalhaol}@kustar.ac.ae
based on converting the operating wideband channel char acterized by frequency selectivity into a number of paral lel frequencyat narrowband subcarriers resulting in a low complexity solution. Due to its significant advantages, OFDM has been adopted for several wired and wireless standards and applications such as the IEEE802.11a WLAN standard, HIPERLAN2 [3], digital audio broadcasting (DAB), and ter restrial transmission standard for digital video broadcasting (DVBT). The goal of this research is to develop and analyze non coherent OFDM systems for broadband cooperative networks over frequency selective channels. The objective is to realize the diversity potentials that broadband cooperative wireless networks can achieve in high mobility scenarios, while main taining practical low complexity. Moreover, there have been considerable research efforts on differential spacetime block coding (STBC) for frequency at fading channels, however only a few isolated results have been reported on differential STBC for frequency selective channels in the context of co operative transmission. This research aims to fill this research gap and investigates noncoherent detection for broadband cooperative networks. Currently we are adopting the maximum likelihood (ML) criterion as a possible noncoherent method for broadband cooperative networks [4]. We are aware that the distributed structure of the underlying problem, together with the under lying channel model assumption, makes the implementation of a noncoherent receiver practically infeasible. Therefore, a special emphasis will be imposed on distributed space time block coded systems carefully exploiting their inherent orthogonal structure to maintain lowdecoding complexity.
Abstract—Research on noncoherent detection for cooperative communications is at an early stage and many fundamental problems are still open. We will be working on an important open problems in broadband cooperative wireless communications. A novel noncoherent detection scheme for a multirelay cooperative orthogonal frequency division multiplexing (OFDM) wireless system is investigated. We consider a distributed spacetime block code (STBC) system over timevarying fading channels, in which sourcerelay, relaydestination, and sourcedestination links experience different Doppler spreads. Simulation results demonstrate that the recursive decoder achieves sufficient results even under quasistatic fading assumption.
I. I NTRODUCTION Multiple Input Multiple Output (MIMO) systems have demonstrated that the deployment of multiple antennas at the transmitter and/or receiver results in a great improvement in spectrum efficiency and reliability of a pointtopoint wireless link [1]. However, in some scenarios, the use of multiple antennas at the receiver is not feasible because of additional hardware complexity and the market acceptability of MIMO systems. Recently, cooperative diversity has been proposed as effective techniques to overcome these limitations [2]. The basic idea of cooperative communication is form a virtual antenna array to exploit the benefits of MIMO systems and improve the overall performance such as power efficiency, network coverage, and reduce the outage probability. This communication paradigm, which is considered as one of diversity techniques, has proved to be quite attractive for deployment in the cellular applications at the mobile terminals and has been already included in some of modern wireless technologies. Most of the work related to diversity cooperative communi cation consider coherent detection and assume full knowledge of the channel coefficients. However in practice, these coef ficients are unknown which causes degradation in the system performance. Moreover, previous related researches have only considered the at fading environment, which yields systems suitable for narrowband cooperative but not the highspeed broadband applications. A major design challenge for high speed broadband applications is to handle the interference among consecutive transmitted symbols known as intersymbol interference (ISI). Orthogonal frequency division multiplexing (OFDM) is an effective approach used to mitigate ISI. It is
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II. P RELIMINARY RESULTS Extensive Monte Carlo simulations have been conducted to examine the performance of the proposed noncoherent detection for cooperative OFDM wireless network over two tap Rayleigh fading channels. All simulations are based on Protocol III [5] and modulated using binary phase shift keying (BPSK). Furthermore, the channels between the three elements are experienced different path loss and shadowing effects. The performance of the proposed system is simulated over timevarying channel for different normalized Doppler (fdT) values. Table I shows the cases used in Fig. 1. As expected,
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TABLE I L IST OF CASES APPLIED TO DIFFERENT COFDM WIRELESS NETWORKS
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I II III IV V
fdT: = 002 = 001 and = 0015 fdT: = 001 = 002 and = 0015 fdT: = 001 = 001 and = 001 Case III with the assistance of 5 relays Case IV, = 20 dB
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Bit Error Rate
Case Case Case Case Case
Static Case I Case II Case III
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Bit Error Rate
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Static Case III Case IV Case V
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Fig. 2.
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10 E /N (dB) SD
Fig. 1.
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the BER performance is degraded as the Doppler value is increased. However, reducing the Doppler value in ! link will improve the BER performance by more than 3 dB. This is due to the fact that in AaF relaying technique, the noise accumulated in the received signal is amplified at the transmission. Multirelay assisted system for Case III is evaluated and simulated as shown in Fig. 2. The relay selection is based on selecting the relay with maximum energy at the destination, which is considered as one of the most simplest selection’s technique. Consequently, having more assisted terminals in the network can improve the BER performance significantly and with a negligible complexity. AND
SD
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BER performance using 5 relays
important guidelines and benchmarks for the evaluation and improvement of practical systems. In this research we will consider both distributed differen tial STBC and coded multicarrier modulation for broadband cooperative networks. Due to the block modulation format of multicarrier modulation, the scheme is limited to block fading. Therefore, we will seek alternative modulation strategies that support fast modulation and fast noncoherent detection in cooperative networks. Novel relaying strategies will also be developed to match the underlying modulation and detection strategies. Moreover, the analytical tools will be used to involve the derivations of pairwise error probability (PEP) expressions to demonstrate the achievable diversity order for intervehicular cooperative networks. Derivation of PEP also leads to the computation of BER, which are widely used as performance measures in digital communication systems.
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BER performance using different normalized Doppler values
III. C ONCLUSION
10 /N (dB)
REFERENCES [1] D. Gesbert, M. Shafi, S. Dashan; P. Smith, and A. Naguib, “From theory to practice: an overview of MIMO spacetime coded wireless systems,” IEEE Journal on Selected Areas in Communications, vol.21, no.3, pp.281 302, April 2003. [2] J. N. Laneman and G. W. Wornell, “Distributed SpaceTime Coded Protocols for Exploiting Cooperative Diversity in Wireless Networks,” IEEE Trans. Inf. Theory, vol. 49, no. 10, pp. 24152525, Oct. 2003. [3] ETSI: Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; System Overview; 2000. TR 101 683 V1.1.1. [4] H. Mheidat and M. Uysal, “NonCoherent and MismatchedCoherent Receivers for Distributed STBCs with AmplifyandForward Relaying,” IEEE Trans. Wireless Commun., vol. 6, no. 11, pp.4060–4070, 2007. [5] R. U. Nabar, H. Bölcskei, and F. W. Kneubühler, “Fading relay channels: Performance limits and spacetime signal design,” IEEE J. Sel. Areas Commun., vol. 22, no. 6, pp. 10991109, August 2004.
F UTURE W ORK
Although there have been considerable research efforts on noncoherent STBC over timevarying fading channel, only a few isolated results have been reported in the context of cooperative transmission. This research aims to fill this research gap and investigate noncoherent detection for broad band cooperative networks. It is anticipated that the developed algorithms by the proposed research will not only advance our knowledge in cooperative networks, but also provide
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