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Nagaradjane P.,SSN Institutions | Krishnan L.,University of Maryland University College | Vasan A.S.S.,University of Maryland University College
Computers and Electrical Engineering | Year: 2012

In this paper, we study the performance of co-channel interference (CCI) cancellation technique based on minimum mean square error (MMSE) user-ordered successive interference cancellation (UOSIC) for multi input multi output (MIMO) multicarrier (MC) direct sequence code division multiple access (DS/CDMA) system for multi cell setting. Though MC DS/CDMA possesses several advantages, interference limits the capacity of the system. Mitigating the interference can directly swell the system capacity. In this contribution, we consider K co-channel users arbitrarily distributed in an L cell uplink and downlink communication system with both the base stations (BSs) and the mobile stations (MSs) equipped with two antennas each. Also, we assume that, both the BSs and MSs employ space time block code (STBC) based on the transmission matrix (G2). Our simulation study shows that, MMSE UOSIC provides better achievable bit-error rate (BER) than MMSE maximum likelihood (ML) and MMSE successive interference cancellation (SIC) technique due to optimal ordering among users and iterative interference cancellation (IC). © 2011 Elsevier Ltd. All rights reserved. Source


Ravichandran S.,Georgia Institute of Technology | Nagaradjane P.,SSN Institutions | Paranche Damodaran S.,Eurecom | Srinivasan N.,University of Southern California
Computers and Electrical Engineering | Year: 2013

In this correspondence, we study the performance of cooperative communications with the aid of multi-user transmitter preprocessing (MUTP), both at the base station (BS) and multi-antenna enabled fixed infrastructure based decode and forward relay stations (RSs), for uplink (UL) and downlink (DL) transmissions where, multi-user interference (MUI) and inter-relay interference (IRI) are the domineering channel impairments. MUTP formulated under instantaneous, statistical and imperfect channel state information assumptions at the RSs and BS for UL and DL respectively is based on singular value decomposition and, further at the RSs for DL is based on minimum mean square error principle. Specifically, we investigate the performance of the considered system in the context of weak and dominant MUI at the RSs in UL and dominant IRI at the mobile stations in DL. Our simulation studies show that MUTP aided system achieves better bit error rate than multiuser detection based system. © 2012 Elsevier Ltd. All rights reserved. Source


Nagaradjane P.,SSN Institutions | Ravichandran S.,National Instruments | Srinivasan N.,University of Southern California | Ravichandran S.,Georgia Institute of Technology | Damodaran S.P.,Telecom ParisTech
IET Communications | Year: 2013

In this correspondence, the authors study the performance of multi-user transmitter preprocessing (MUTP)-assisted cooperative downlink (DL) transmission for multi-carrier code division multiple access (MC-CDMA) system, where multiuser interference (MUI) and inter-relay interference (IRI) are the principal channel impairments. Relaying is facilitated with the aid of fixed infrastructure-based relays that perform additional signal processing like formulating the preprocessing matrix for mitigating MUI in addition to forwarding the information they receive from the base station (BS). Specifically, in this study, the authors analyse the performance of cooperative communication-aided DL MC-CDMA system by employing three cooperation strategies: (i) all users supported by a single relay with dominant MUI at the relay and mobile stations (MSs); (ii) each user supported by a single relay where, MUI and IRI are dominant at the relays and MSs, respectively, as well as weak IRI at the MSs; and (iii) all users supported by L relays where MUI is dominant at the relays, and MUI and IRI are dominant at the MSs. Our simulation study shows that MUTP-aided cooperative DL transmission results in better achievable bit error rate than the multi-user detection-aided system as the MUI at the relays and MUI and IRI at the MSs are perfectly eliminated. © The Institution of Engineering and Technology 2013. Source


Nagaradjane P.,SSN Institutions | Rajan Y.A.,Georgia Institute of Technology | Muralidharan P.,Qualcomm | Sarathy S.K.V.,Rutgers University
Physical Communication | Year: 2013

In this contribution we present the performance of a multi-user transmitter preprocessing (MUTP) assisted multiple-input multiple-output (MIMO) space division multiple access (SDMA) system, aided by double space time transmit diversity (DSTTD) and space time block code (STBC) processing for downlink (DL) and uplink (UL) transmissions respectively. The MUTP is invoked by singular value decomposition (SVD) which exploits the channel state information (CSI) of all the users at the base station (BS) and only an individual user's CSI at the mobile station (MS). Specifically, in this contribution, we investigate the performance of multi-user MIMO cellular systems in frequency-selective channels from a transmitter signal processing perspective, where multiple access interference (MAI) is the dominant channel impairment. In particular, the effects of three types of delay spread distributions on MUTP assisted MIMO SDMA systems pertaining to the Long Term Evolution (LTE) channel model are analyzed. The simulation results demonstrate that MUTP can perfectly eliminate MAI in addition to obviating the need for complex multi-user detectors (MUDs) both at the BS and MS. Further, SVD-based MUTP results in better achievable symbol error rate (SER) compared to popularly known precoding schemes such as block diagonalization (BD), dirty paper coding (DPC), Tomlinson-Harashima precoding (THP) and geometric mean decomposition (GMD). Furthermore, when turbo coding is invoked, coded SVD aided MUTP results in better achievable SER than an uncoded system. © 2012 Elsevier B.V. Source


Nagaradjane P.,SSN Institutions | Sarathy S.K.V.,Rutgers University | Muralidharan P.,Qualcomm | Rajan Y.A.,Georgia Institute of Technology
Eurasip Journal on Wireless Communications and Networking | Year: 2012

In this article, we investigate the performance of multiuser transmitter preprocessing (MUTP)-aided multiple-input multiple-output (MIMO) systems in a multi-cell multiuser setting where co-channel interference (CCI) is the major channel impairment, for both uplink (UL) and downlink (DL) transmissions. CCI can considerably reduce data rates resulting in outages in cellular systems, particularly at the cell edges in DL transmission. The MUTP considered in this article is based on singular value decomposition (SVD), which exploits the channel state information (CSI) of all the users at the base stations (BSs) with the aid of BS cooperation, and only the individual users' CSI at the mobile stations (MSs) for both UL and DL transmissions. In particular, in this article, we study the effects of three types of delay spread distributions coupled with different interferer configurations over correlated and uncorrelated frequency-selective channels. Our simulation study shows that SVD-aided MUTP perfectly eliminates CCI with lesser detection complexity under perfect CSI. Also, we provide performance comparisons of SVD-aided MUTP with various precoding techniques widely addressed in literature, and the results show that it provides better achievable symbol error rate (SER) by mitigating multi-stream interference (MSI) and CCI. Further, simulation results demonstrate that compared to equal CCI, the presence of a dominant interferer can lead to more degradation in the system performance in terms of achievable SER while, further degradation results when noise is dominant. Furthermore, this study confirms that imperfect CSI as well as imperfect power control can lead to degradation in the system performance. © 2012 Nagaradjane et al. Source

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