Showing papers by "Ananthanarayanan Chockalingam published in 2015"
TL;DR: In this article, an average bit error probability (ABEP) analysis for maximum likelihood detection in multiuser GSM-MIMO on the uplink, where an upper bound on the ABEP was derived, and low-complexity algorithms for signal detection and channel estimation at the base station receiver based on message passing were proposed.
Abstract: Generalized spatial modulation (GSM) uses $n_{t} $ transmit antenna elements but fewer transmit radio frequency (RF) chains, $n_{rf} $ . Spatial modulation (SM) and spatial multiplexing are special cases of GSM with $n_{rf}=1$ and $n_{rf}=n_{t} $ , respectively. In GSM, in addition to conveying information bits through $n_{rf} $ conventional modulation symbols (for example, QAM), the indices of the $n_{rf} $ active transmit antennas also convey information bits. In this paper, we investigate GSM for large-scale multiuser MIMO communications on the uplink. Our contributions in this paper include: 1) an average bit error probability (ABEP) analysis for maximum-likelihood detection in multiuser GSM-MIMO on the uplink, where we derive an upper bound on the ABEP, and 2) low-complexity algorithms for GSM-MIMO signal detection and channel estimation at the base station receiver based on message passing. The analytical upper bounds on the ABEP are found to be tight at moderate to high signal-to-noise ratios (SNR) . The proposed receiver algorithms are found to scale very well in complexity while achieving near-optimal performance in large dimensions. Simulation results show that, for the same spectral efficiency, multiuser GSM-MIMO can outperform multiuser SM-MIMO as well as conventional multiuser MIMO, by about 2 to 9 dB at a bit error rate of $10^{-3} $ . Such SNR gains in GSM-MIMO compared to SM-MIMO and conventional MIMO can be attributed to the fact that, because of a larger number of spatial index bits, GSM-MIMO can use a lower-order QAM alphabet which is more power efficient.
144 citations
TL;DR: The comparison of the BERs of SSK and conventional phase-shift keying (PSK) are shown and also show the instances where SSK outperforms PSK and the diversity analyses for SSK in systems I and II, which predict the achievable diversity orders as a function of system parameters.
Abstract: In this paper, space-shift keying (SSK) is considered for multihop multiple-input-multiple-output (MIMO) networks. In SSK, only one among $n_{s} = \hbox{2}^{m}$ available transmit antennas, chosen on the basis of $m$ information bits, is activated during transmission. We consider two different systems of multihop cooperation, where each node has multiple antennas and employs SSK. In system I, a multihop diversity relaying scheme is considered. In system II, a multihop multibranch relaying scheme is considered. In both systems, we adopt decode-and-forward (DF) relaying, where each relay forwards the signal only when it correctly decodes. We analyze the end-to-end bit error rate (BER) and diversity order of both the systems with SSK. For binary SSK $(n_{s} = \hbox{2})$ , our analytical BER expression is exact, and our numerical results show that the BERs evaluated through the analytical expression overlap with those obtained through Monte Carlo simulations. For nonbinary SSK $(n_{s} > \hbox{2})$ , we derive an approximate BER expression, where the analytically evaluated BER results closely follow the simulated BER results. We show the comparison of the BERs of SSK and conventional phase-shift keying (PSK) and also show the instances where SSK outperforms PSK. We also present the diversity analyses for SSK in systems I and II, which predict the achievable diversity orders as a function of system parameters.
44 citations
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TL;DR: Analysis and simulation results show that GSM in VLC outperforms the other considered MIMO schemes at moderate to high SNRs; for example, for 8 bits per channel use, GSM outperforms SMP and GSSK by about 21 dB, and SM by about 10 dB at $10^{-4}$ BER.
Abstract: In this paper, we investigate the performance of generalized spatial modulation (GSM) in indoor wireless visible light communication (VLC) systems. GSM uses $N_t$ light emitting diodes (LED), but activates only $N_a$ of them at a given time. Spatial modulation and spatial multiplexing are special cases of GSM with $N_{a}=1$ and $N_{a}=N_t$, respectively. We first derive an analytical upper bound on the bit error rate (BER) for maximum likelihood (ML) detection of GSM in VLC systems. Analysis and simulation results show that the derived upper bound is very tight at medium to high signal-to-noise ratios (SNR). The channel gains and channel correlations influence the GSM performance such that the best BER is achieved at an optimum LED spacing. Also, for a fixed transmission efficiency, the performance of GSM in VLC improves as the half-power semi-angle of the LEDs is decreased. We then compare the performance of GSM in VLC systems with those of other MIMO schemes such as spatial multiplexing (SMP), space shift keying (SSK), generalized space shift keying (GSSK), and spatial modulation (SM). Analysis and simulation results show that GSM in VLC outperforms the other considered MIMO schemes at moderate to high SNRs; for example, for 8 bits per channel use, GSM outperforms SMP and GSSK by about 21 dB, and SM by about 10 dB at $10^{-4}$ BER.
41 citations
01 Dec 2015
TL;DR: The proposed encoding procedure exploits the low complexity computation of combinadics in combinatorial number system and allows `on-the-fly' computation of GSFIM encoding maps, and a low complexity detection algorithm based on a multi-stage message passing approach is proposed.
Abstract: This paper is concerned with an attractive multi-antenna multi-carrier modulation scheme, termed as {\em generalized space-frequency index modulation (GSFIM)}, which is a promising modulation scheme for next generation wireless systems. GSFIM uses both spatial domain and frequency domain to encode bits through {\em indexing}. In GSFIM, information bits are mapped through antenna indexing in the spatial domain, subcarrier indexing in the frequency domain, and M-ary modulation. GSFIM can offer higher rates using fewer transmit radio frequency (RF) chains and better performance compared to conventional MIMO-OFDM. In this paper, we address the problem of low-complexity encoding and detection of large-dimensional GSFIM signals. The proposed encoding procedure exploits the low complexity computation of {\em combinadics} in combinatorial number system. This allows `on-the-fly' computation of GSFIM encoding maps. For detecting GSFIM signals, we propose a low complexity detection algorithm based on a {\em multi-stage message passing} approach. The proposed low complexity encoding/detection algorithms allow practical implementation of large-dimension GSFIM systems.
16 citations
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TL;DR: The proposed QCM module can serve as a basic building block to bring in the benefits of complex modulation to VLC and achieve improved bit error performance.
Abstract: In this paper, we propose a simple and novel complex modulation scheme for multiple-LED wireless communication, termed as {\em quad-LED complex modulation (QCM)}. The proposed QCM scheme uses four LEDs (hence the name `quad-LED'), one LED each to map positive real, negative real, positive imaginary, and negative imaginary parts of complex modulation symbols like QAM/PSK symbols. The QCM scheme does not need Hermitian symmetry operation to generate LED compatible positive real transmit signals. Instead it exploits spatial indexing of LEDs to convey sign information. The proposed QCM module can serve as a basic building block to bring in the benefits of complex modulation to VLC. For example, QCM with phase rotation (QAM-PR) where the complex modulation symbols are rotated in phase before mapping the signals to the LEDs achieves improved bit error performance. We also find that the proposed QCM when used along with OFDM, termed as QCM-OFDM, achieves very good performance.
13 citations
TL;DR: An average bit error probability (ABEP) analysis for maximum-likelihood detection in multiuser GSM-MIMO on the uplink, where the analytical upper bounds on the ABEP are found to be tight at moderate to high signal-to-noise ratios (SNR), and low-complexity algorithms for G SM-M IMO signal detection and channel estimation at the base station receiver based on message passing.
Abstract: Generalized spatial modulation (GSM) uses $n_t$ transmit antenna elements but fewer transmit radio frequency (RF) chains, $n_{rf}$. Spatial modulation (SM) and spatial multiplexing are special cases of GSM with $n_{rf}=1$ and $n_{rf}=n_t$, respectively. In GSM, in addition to conveying information bits through $n_{rf}$ conventional modulation symbols (for example, QAM), the indices of the $n_{rf}$ active transmit antennas also convey information bits. In this paper, we investigate {\em GSM for large-scale multiuser MIMO communications on the uplink}. Our contributions in this paper include: ($i$) an average bit error probability (ABEP) analysis for maximum-likelihood detection in multiuser GSM-MIMO on the uplink, where we derive an upper bound on the ABEP, and ($ii$) low-complexity algorithms for GSM-MIMO signal detection and channel estimation at the base station receiver based on message passing. The analytical upper bounds on the ABEP are found to be tight at moderate to high signal-to-noise ratios (SNR). The proposed receiver algorithms are found to scale very well in complexity while achieving near-optimal performance in large dimensions. Simulation results show that, for the same spectral efficiency, multiuser GSM-MIMO can outperform multiuser SM-MIMO as well as conventional multiuser MIMO, by about 2 to 9 dB at a bit error rate of $10^{-3}$. Such SNR gains in GSM-MIMO compared to SM-MIMO and conventional MIMO can be attributed to the fact that, because of a larger number of spatial index bits, GSM-MIMO can use a lower-order QAM alphabet which is more power efficient.
11 citations
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TL;DR: Simulation results show that, for the same spectral efficiency, CI-NDC OFDM that uses coding on the index bits performs better than NDC OFDM.
Abstract: Use of multiple light emitting diodes (LED) is an attractive way to increase spectral efficiency in visible light communications (VLC). A non-DC-biased OFDM (NDC OFDM) scheme that uses two LEDs has been proposed in the literature recently. NDC OFDM has been shown to perform better than other OFDM schemes for VLC like DC-biased OFDM (DCO OFDM) and asymmetrically clipped OFDM (ACO OFDM) in multiple LEDs settings. In this paper, we propose an efficient multiple LED OFDM scheme for VLC which uses {\em coded index modulation}. The proposed scheme uses two transmitter blocks, each having a pair of LEDs. Within each block, NDC OFDM signaling is done. The selection of which block is activated in a signaling interval is decided by information bits (i.e., index bits). In order to improve the reliability of the index bits at the receiver (which is critical because of high channel correlation in multiple LEDs settings), we propose to use coding on the index bits alone. We call the proposed scheme as CI-NDC OFDM (coded index NDC OFDM) scheme. Simulation results show that, for the same spectral efficiency, CI-NDC OFDM that uses LDPC coding on the index bits performs better than NDC OFDM.
10 citations
TL;DR: The numerical results suggest that the proposed sum-rate capacity upper bounds for the MIMO XC are tighter than existing bounds.
Abstract: In this paper, we study the Gaussian MIMO Z channel and the Gaussian MIMO X channel. The MIMO X channel (XC) consists of two multiple antenna transmit-receive pairs, where each transmitter communicates with both receivers. The MIMO Z channel (ZC) is obtained from the MIMO X channel by eliminating one of the links and its corresponding message. First, we derive a sum-rate upper bound for the MIMO Z channel and compare it with an existing bound in literature. Next, we consider the MIMO X channel and propose a new sum-rate upper bound by utilizing the sum-rate upper bound for the MIMO ZC. Subsequently, we derive another upper bound for the MIMO XC by assuming receiver cooperation and deriving the worst noise covariance matrix for the resulting two-user MAC. We compare the above two upper bounds for the MIMO XC with the MaddahAli-Motahari-Khandani (MMK) scheme. Then, we consider some consequences of the above results for the MIMO interference channel. Finally, we present some numerical results. The numerical results suggest that the proposed sum-rate capacity upper bounds are tighter than existing bounds.
10 citations
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TL;DR: Using tight analytical BER upper bounds and spatial distribution of the received signal-to-noise ratios, the achievable rate contours for a given target BER in QCM, DCM, and SM-DCM are plotted.
Abstract: In this paper, we propose simple and novel complex modulation techniques that exploit the spatial domain to transmit complex-valued modulation symbols in visible light wireless communication. The idea is to use multiple light emitting diodes (LEDs) to convey the real and imaginary parts of a complex modulation symbol and their sign information, or, alternately, to convey the magnitude and phase of a complex symbol. The proposed techniques are termed as {\em quad-LED complex modulation (QCM)} and {\em dual-LED complex modulation (DCM)}. The proposed QCM scheme uses four LEDs (hence the name `quad-LED'); while the magnitudes of the real and imaginary parts are conveyed through intensity modulation of LEDs, the sign information is conveyed through spatial indexing of LEDs. The proposed DCM scheme, on the other hand, exploits the polar representation of a complex symbol; it uses only two LEDs (hence the name `dual-LED'), one LED to map the magnitude and another LED to map the phase of a complex modulation symbol. These techniques do not need Hermitian symmetry operation to generate LED compatible positive real transmit signals. We present zero-forcing and minimum distance detectors and their performance for QCM-OFDM and DCM-OFDM. We further propose another modulation scheme, termed as SM-DCM {\em (spatial modulation-DCM)} scheme, which brings in the advantage of spatial modulation (SM) to DCM. The proposed SM-DCM scheme uses two DCM BLOCKs with two LEDs in each BLOCK, and an index bit decides which among the two BLOCKs will be used in a given channel use. We study the bit error rate (BER) performance of the proposed schemes through analysis and simulations. Using tight analytical BER upper bounds and spatial distribution of the received signal-to-noise ratios, we compute and plot the achievable rate contours for a given target BER in QCM, DCM, and SM-DCM.
10 citations
01 Dec 2015
TL;DR: The achievable perfect secrecy rate region is obtained by maximizing the worst case sum secrecy rate and obtaining the corresponding transmit covariance matrices associated with the message signals and the jamming signals.
Abstract: In this paper, we consider the achievable sum secrecy rate in MISO (multiple-input-single-output) {\em full-duplex} wiretap channel in the presence of a passive eavesdropper and imperfect channel state information (CSI). We assume that the users participating in full-duplex communication have multiple transmit antennas, and that the users and the eavesdropper have single receive antenna each. The users have individual transmit power constraints. They also transmit jamming signals to improve the secrecy rates. We obtain the achievable perfect secrecy rate region by maximizing the worst case sum secrecy rate. We also obtain the corresponding transmit covariance matrices associated with the message signals and the jamming signals. Numerical results that show the impact of imperfect CSI on the achievable secrecy rate region are presented.
4 citations
TL;DR: In this article, generalized space and frequency index modulation (GSIM) was proposed to achieve higher bit error rate (BER) than spatial multiplexing, where the indices of active transmit antennas and subcarriers convey information bits.
Abstract: Unlike in conventional modulation where information bits are conveyed only through symbols from modulation alphabets defined in the complex plane (e.g., quadrature amplitude modulation (QAM), phase shift keying (PSK)), in index modulation (IM), additional information bits are conveyed through indices of certain transmit entities that get involved in the transmission. Transmit antennas in multi-antenna systems and subcarriers in multi-carrier systems are examples of such transmit entities that can be used to convey additional information bits through indexing. In this paper, we introduce {\em generalized space and frequency index modulation}, where the indices of active transmit antennas and subcarriers convey information bits. We first introduce index modulation in the spatial domain, referred to as generalized spatial index modulation (GSIM). For GSIM, where bits are indexed only in the spatial domain, we derive the expression for achievable rate as well as easy-to-compute upper and lower bounds on this rate. We show that the achievable rate in GSIM can be more than that in spatial multiplexing, and analytically establish the condition under which this can happen. It is noted that GSIM achieves this higher rate using fewer transmit radio frequency (RF) chains compared to spatial multiplexing. We also propose a Gibbs sampling based detection algorithm for GSIM and show that GSIM can achieve better bit error rate (BER) performance than spatial multiplexing. For generalized space-frequency index modulation (GSFIM), where bits are encoded through indexing in both active antennas as well as subcarriers, we derive the achievable rate expression. Numerical results show that GSFIM can achieve higher rates compared to conventional MIMO-OFDM. Also, BER results show the potential for GSFIM performing better than MIMO-OFDM.
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TL;DR: This paper considers decode-and-forward (DF) relay beamforming with imperfect channel state information (CSI), cooperative artificial noise (AN) injection, and finite-alphabet input in the presence of an user and non-colluding eavesdroppers, and numerical results showing the effect of perfect/imperfect CSI, presence/absence of AN with finite- Ralphabet input on the secrecy rate are presented.
Abstract: In this paper, we consider decode-and-forward (DF) relay beamforming with imperfect channel state information (CSI), cooperative artificial noise (AN) injection, and finite-alphabet input in the presence of an user and $J$ non-colluding eavesdroppers. The communication between the source and the user is aided by a multiple-input-multiple-output (MIMO) DF relay. We use the fact that a wiretap code consists of two parts: i) common message (non-secret), and ii) secret message. The source transmits two independent messages: i) common message (non-secret), and ii) secret message. The common message is transmitted at a fixed rate $R_{0}$, and it is intended for the user. The secret message is also intended for the user but it should be kept secret from the $J$ eavesdroppers. The source and the MIMO DF relay operate under individual power constraints. In order to improve the secrecy rate, the MIMO relay also injects artificial noise. The CSI on all the links are assumed to be imperfect and CSI errors are assumed to be norm bounded. In order to maximize the worst case secrecy rate, we maximize the worst case link information rate to the user subject to: i) the individual power constraints on the source and the MIMO relay, and ii) the best case link information rates to $J$ eavesdroppers be less than or equal to $R_{0}$ in order to support a fixed common message rate $R_{0}$. Numerical results showing the effect of perfect/imperfect CSI, presence/absence of AN with finite-alphabet input on the secrecy rate are presented.