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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.


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.


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.


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.


Nagaradjane P.,SSN Institutions | Muthu T.,Pondicherry Engineering College
Computers and Electrical Engineering | Year: 2016

In this paper, we consider the performance of a cellular uplink (UL) multi-user feedback multiple-input multiple-output (MIMO) system assisted by joint transmitter-receiver (Tx-Rx) design and polarization-multiplexing (PM). PM is realized with the aid of dual and triply-polarized antennas. At the transmitter, we take advantage of only the individual user's channel impulse responses (CIRs) obtained through feedback channels that endure noise, fading and delay to construct the preprocessing matrix, while at the receiver the post-processing matrix construction relies on the perfect CIRs of all the users. In multi-user UL-MIMO transmissions, multiple-access interference (MAI) and inter-antenna interference (IAI) can severely degrade the system's performance. Our study shows that the joint Tx-Rx is capable of completely eliminating the IAI as well as the MAI when it employs perfect CIRs based preprocessing and post-processing. On the other hand, noise, fading and delay tainted quantized-CIRs based preprocessing results in noticeable performance degradation due to imperfect removal of IAI. Nevertheless, our results demonstrate that, when the preprocessing is based on the quantized-CIRs obtained through ideal feedback channels, the resultant achievable symbol-error-rate and sum-capacity remain close to that obtained with the perfect CIRs based design. © 2016 Elsevier Ltd.


Nagaradjane P.,SSN Institutions | Muthu T.,Pondicherry Engineering College
Wireless Personal Communications | Year: 2015

The achievable bit-error-rate (BER) performance of a relay-aided downlink (DL) multi-carrier code division multiple access (MC-CDMA) cellular system, where multi-user interference (MUI) and inter-relay interference (IRI) are the dominant channel impairments is investigated in this paper, principally from a transmitter signal processing perspective. Specifically, in this paper, we investigate the considered system by employing three cooperation strategies. The MUI and IRI are mitigated with the aid of the transmitter preprocessing (TP) operated at the base station (BS) and relays, respectively. The TP operated at the BS that suppresses the MUI at the relays is based on the maximum-signal-to-interference-plus-noise ratio approach, while that operated at the relays that mitigates the IRI relies on the classical transmit minimum-mean-square-error principle. Further, the TP in our work is constructed with the aid of vector-quantized channel state information (VQ-CSI) acquired via feedback channels. Our simulation study shows that relay-aided cooperative DL MC-CDMA system employing TP, results in better achievable BER, as the TP helps in achieving the relay-diversity by mitigating the DL-MUI and IRI at the relays and DMSs, respectively. Furthermore, our study demonstrates that the resultant BER performance of the VQ-CSI based TP remains close to that achieved with the perfect CSI based TP. Hence, we advocate that the feedback of the VQ-CSI to the transmitter for conceiving the preprocessing can be considered as an efficient approach, particularly in a frequency division duplex type wireless system. © 2015, Springer Science+Business Media New York.


Nagaradjane P.,SSN Institutions | Muthu T.,Pondicherry Engineering College
2015 International Conference on Communication and Signal Processing, ICCSP 2015 | Year: 2015

In this paper, we revisit the performance of a joint transmitter-receiver (Tx-Rx) design for a multi-input multi-output (MIMO) uplink (UL) transmission when aided by polarization multiplexing (PM). At the transmitter, we exploit only the individual user's channel state information (CSI) to concoct the preprocessing matrix while at the receiver, the CSIs of all the users are invoked to formulate the post-processing matrix. In a multi-user UL transmission, multi-user interference (MUI) can severely degrade the system performance. It is demonstrated through simulation that the joint-Tx-Rx is capable of mitigating the inter-antenna interference (IAI) as well as the MUI. © 2015 IEEE.


Nagaradjane P.,SSN Institutions | Muthu T.,Pondicherry Engineering College
IET Communications | Year: 2015

In this study, the authors investigate the performance of a multi-user downlink (DL) multiple-input-multiple-output (MIMO) system aided by polarisation multiplexing (PM) and multi-user transmitter pre-processing (MUTP). Dual- and triply-polarised antennas that are called on to establish PM offer the advantage of replacing uni-polarised antennas that impose space constraints. In a multi-user scenario, users conflict multi-user interference (MUI). In this contribution, the DL-MUI is suppressed with the aid of pre-processing operated at the base station. To be specific, two pre-processing approaches are considered in their study which are based on singular value decomposition. Both the approaches exploit the channel impulse responses (CIRs) of all the users to formulate the pre-processing matrix and that the second approach which is a joint multi-user transmission and detection technique exploits only user specific CIRs to formulate the post-processing matrix. In their contribution, the required CIRs for formulating the pre-processing matrix are acquired via noisy feedback channels that endure fading as well as delay. Simulation results demonstrate that noise and fading tainted CIRs based MUTP results in performance degradation in terms of the attainable symbol-error-rate (SER) and sum-capacity. Moreover, it is inferred that further degradation results when the feedback channels experience delay. However, their study shows that the application of dual or triply-polarised antennas in conjunction with MUTP can serve as an efficient approach for the DL of the feedback MIMO system, as the achievable sum-capacity and SER under ideal feedback remain close to that attained with the perfect CIRs hypothesis. Furthermore, it is observed that the considered MUTP techniques result in superior SER performance compared with their multi-user detection counterpart and other widely known pre-processing techniques. © 2015. The Institution of Engineering and Technology.


Nagaradjane P.,SSN Institutions | Muthu T.,Pondicherry Engineering College
Computers and Electrical Engineering | Year: 2015

In this paper, we investigate the achievable bit-error-rate performance (BER) of a transmitter preprocessing (TP)-aided cooperative downlink (DL) multi-carrier code division multiple access system by employing three cooperation strategies. In a multi-user cooperative DL communication, multi-user interference at the relays, which prevents the achievement of relay diversity, is suppressed with the aid of the TP operated at the base station (BS). In addition, inter-relay interference at the destination mobile station is mitigated by the TP employed at the relays. Furthermore, the channel impulse responses (CIRs) required for formulating the TP at the BS is based on the quantized CIRs feedback in contrast to the perfect CIRs (PCIRs) assumption at the relays. Our study shows that the resultant BER performance of the quantized CIRs feedback-based TP at the BS, coupled with the PCIR-based TP at the relays, remains close to that attained with the PCIRs knowledge at the BS and relays. © 2015 Elsevier Ltd.


Vishvaksenan K.S.,SSN Institutions | Kalaiarasan R.,SSN Institutions
Proceedings of the 2016 IEEE International Conference on Wireless Communications, Signal Processing and Networking, WiSPNET 2016 | Year: 2016

A double space-time transmit diversity (DSTTD) system achieves higher throughput by employing four transmit antennas and four receive antennas. In this correspondence, we explicate the bit error rate (BER) performance of DSTTD aided interleave division multiple access (IDMA) with the aid of multi-user transmitter pre-processing (MUTP) technique for downlink(DL) communication. We realize MUTP using singular value decomposition (SVD) technique to mitigate the effects of co-channel interference (CCI) in addition to the Multi-user Interference (MUI). The MUTP which is considered in our work exploits the signals space of all the active users channel state matrix (CSM) at the base station (BS) and an individual users CSM at the mobile station (MS) for the downlink communication. To be specific, we study the effects of two types of delay spread distributions on MUTP assisted DSTTD-IDMA system using Stanford University Interim channel model. Our computer simulation results explicate that SVD based MUTP techniques provides better BER with power efficient signal to noise ratio (SNR) for our considered system by combating the effects of CCI and MUI the context of DL transmission. © 2016 IEEE.

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