A New Approach for Simple Cooperative Relaying Ugljesa Urosevic #1 , Zoran Veljovic #2 , Milica Pejanovic-Djurisic #3 , Dina Simunic *4 # Faculty of Electrical Engineering, University of Montenegro 1 ugljesa@ac.me, Montenegro 2 veljovic@ac.me, Montenegro 3 milica@ac.me, Montenegro * Faculty of Electrical Engineering and Computing, University of Zagreb 4 dina.simunic@fer.hr, Croatia Abstract—In this paper we present a new simple cooperative scheme for achieving 4th order diversity. The proposed scheme is compared with simple cooperative schemes with virtual orthogonal space time block coding (OSTBC) and quasi orthogonal space time block coding (QOSTBC). Every of these three schemes includes one base station with two antennas, two relay stations with a single antenna and one mobile station with a single antenna. The aim of the proposed scheme is to preserve, as much as it is possible, bit error rate (BER) performance of the cooperative scheme with virtual OSTBC, but with increased code rate. It is shown that the presented scheme obviously outperforms simple cooperative scheme with virtual QOSTBC, while in comparison with simple cooperative scheme with virtual OSTBC has very similar BER performance and greater code rate. Keywords: BER, Cooperative diversity, OSTBC, QOSTBC I. INTRODUCTION With ever increasing demands for multimedia services and web-related content, a high data rate is becoming one of the major features in the next generation of wireless communication systems. However, channel fading, an inherent property of wireless communication links, severely limits the increase of the data rate. Among many diversity techniques that can be used for improving communication performances and combat channel fading, spatial diversity techniques are particularly attractive since they provide diversity gain without incurring extra costs of transmission time and bandwidth. Traditionally, spatial diversity is achieved by using multiple antennas at the transmitter and/or receiver, where the spacing among antennas is with the order of a half of wavelength. These multiple-input multiple-output (MIMO) systems are known as collocated MIMO. Because of the diversity gain, collocated MIMO architectures are effective in improving bit error rate (BER), system capacity, spectrum efficiency, energy efficiency, etc [1], [2]. Apart from being employed in a point-to-point communication link between mobile station (MS) and base station (BS), MIMO systems are also implemented in a distributed mode, with a goal to improve performance in cooperative and relay networks, where every node can be equipped with only one antenna, [3]. Further, the benefits of the collocated MIMO technique can be improved with a distributed or virtual MIMO. Problem with nodes size limitation, i.e. problem with providing sufficient space separation between antennas with a purpose to achieving uncorrelated channels can be overcome with virtual MIMO. The major difference between the virtual and collocated MIMO is that multiple antennas are distributed among widely separated nodes. In a virtual MIMO system, each node may be only equipped with one antenna. In this paper, we present a new approach for simple cooperative relaying for achieving 4th order diversity. This new scheme is compared with simple cooperative relaying with virtual orthogonal space time block coding (OSTBC) and quasi orthogonal space time block coding (QOSTBC), [4]. We provide a detailed description of the distributed coding procedure for all three schemes. Every of the previously mentioned schemes assumes one BS with two antennas, two relay stations (RS) with a single antenna and one MS with a single antenna. In these 2-hop schemes, the procedure in the RSs is reduced due to omitting the coding process. None of the RSs need detection and space-time coding. Their procedure is just permutation andforwarding of the signal sequences. The main QOSTBC advantage in comparison with OSTBC for more than 2nd order diversity is its code rate. For 4th order diversity QOSTBC has greater code rate, but with BER performance degradation a consequence. Our goal was to propose a new simple cooperative relaying scheme similar BER performance as simple cooperative relaying scheme with virtual OSTBC, but with greater code rate. We present a new simple cooperative scheme that has greater code rate than cooperative scheme with virtual OSTBC, i.e. it needs half of time slots between BS and RSs in comparison with simple cooperative scheme with virtual OSTBC. These free time slots can be used for other BS-MS, BS-RS communications, for better channel estimation, etc. The simulation results show that the new scheme has similar BER performance with cooperative scheme with virtual OSTBC. Also it has evidently better BER performance than cooperative scheme with virtual QOSTBC. This paper is composed in the following order. In Sect. 2 the simple cooperative relaying with virtual QOSTBC and OSTBC is described. The proposed simple cooperative scheme is presented in Sect. 3, while the simulation results are presented in Sect. 4. Conclusions are drawn in Sect. 5. EuroCon 2013 • 1-4 July 2013 • Zagreb, Croatia 514 978-1-4673-2232-4/13/$31.00 ©2013 IEEE