Browsing by Author "Pillay, Narushan."

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Differential spatial modulation : low complexity detection and improved error performance.
(2016) Kadathlal, Kavish.; Xu, Hongjun.; Pillay, Narushan.
Multiple-input multiple-output (MIMO) systems utilize multiple transmit and receive antennas in order to achieve a high spectral efficiency and improved reliability for wireless links. However, MIMO systems suffer from high system complexity and costs, due to inter-channel interference (ICI) at the receiver, the requirement of transmit-antenna synchronization (TAS), and the need for multiple radio frequency (RF) chains. Spatial modulation (SM) is a MIMO system which maintains a high spectral efficiency without suffering from ICI or TAS, while utilizing a single RF chain. However, the SM receiver requires full knowledge of the channel state information (CSI) to achieve optimal error performance, thereby increasing the receiver detection complexity. To overcome this, differential SM (DSM) has been developed which does not require CSI to perform detection. However, the maximum-likelihood (ML) detection for DSM results in excessive computational complexity when the number of transmit antennas is large, and suffers from a 3 dB signal-to-noise ratio (SNR) penalty compared to coherent SM. This dissertation aims to reduce the computational complexity of DSM, and mitigate the 3 dB SNR penalty. A generalized differential scheme based on SM (GD-SM) is proposed, which employs optimal power allocation to reduce the 3 dB SNR penalty. GD-SM divides a frame into a reference part and normal part. The reference part is transmitted at a higher power than the normal part, and is used to encode and decode the information in the normal part. Optimal power allocation is applied to the system, and the results demonstrate that at a bit error rate (BER) of 10−5 and for a frame length of 400, GD-SM is only 0.5 dB behind coherent SM. The frame structure of GD-SM and optimal power allocation is extended to conventional DSM (C-DSM). At a BER of 10−5, a 2.5 dB gain is achieved over C-DSM for a frame length of 400. Furthermore, the frame structure allows for easy implementation of quadrature amplitude modulation (QAM), which yields an additional gain in error performance. The use of QAM constellations is not possible in C-DSM. A simple, near-ML, low-complexity detector (L-CD) is proposed for DSM. The L-CD exploits the features of the phase shift keying, and amplitude phase shift keying constellations to achieve near-ML error performance, and at least a 98% reduction in computational complexity. The proposed detector is independent of the constellation size, and demonstrates a significantly lower complexity than that of current L-CDs.
Double spatial media based modulation.
(2019) Tsvaki, Ronald Tafireyi.; Pillay, Narushan.; Xu, Hongjun.
Multiple-input multiple-out (MIMO) systems have become an increasingly popular technology in wireless communications due to their high data rates and increased reliability. However, several drawbacks degrade the performance of MIMO systems. Inter-channel interference, inter- antenna synchronization, low energy e ciency, and relatively high-complexity receive algorithms are several of the challenges that MIMO systems face. As such, spatial modulation (SM) was introduced as a scheme that is capable of exploiting the advantages of MIMO systems, while simultaneously mitigating its drawbacks. SM provided an excellent method of exploiting spatial diversity, which eventually replaced MIMO systems. However, as the use of SM became more prominent, its drawbacks became more apparent. The spectral e ciency of SM is limited by the logarithmic relationship between spectral efficiency and the number of transmit antennas. Several SM-based transmission schemes, such as quadrature spatial modulation and double spatial modulation (DSM), were introduced with the prospect of improving the spectral efficiency of SM. These schemes have a single radio frequency (RF) chain; therefore, relatively low-complexity receive algorithms are employed. Conventional transmission techniques are referred to as source-based modulation (SBM). Media-based modulation (MBM) is a new attractive transmission scheme that has been recently receiving increased research attention. MBM employs the use of RF mirrors to vastly improve the error performance and/or spectral efficiency of modulation schemes. It has been demonstrated that MBM, coupled with SBM techniques, vastly improves the error performance and can potentially increase the spectral efficiency of these systems. In this dissertation, DSM is extended to employ MBM, such as to improve error performance. The proposed transmission scheme is called double spatial media-based modulation (DSMBM). The theoretical average bit error probability (ABEP) of DSMBM over an independent and identically distributed Rayleigh frequency- at fading channel in the presence of additive white Gaussian noise is formulated. The theoretical ABEP of DSMBM is validated by Monte Carlo simulations, where the error performance matches the theoretical ABEP at high signal-to-noise ratios (SNRs). Lastly, coded channels are investigated. Typically soft-output detection coupled with soft-input channel decoding yields a signicant SNR gain. Motivated by this, this dissertation further proposes a soft-output maximum-likelihood detector for the DSM and DSMBM schemes.
Index modulation for next generation radio communications.
(2021) Oso, Oluwabukunmi Williams.; Pillay, Narushan.; Xu, Hongjun.
Man’s insatiable desire for swift and more efficient internet service, a wide range of connectivity and increased data rate of transmission necessitated the need for further research to improve the efficiency of the existing systems. The development and evolution of the next-generation communication systems can be ascribed to the multiple-input multiple-output (MIMO) techniques implemented. The fundamental founding block of the MIMO systems is the spatial modulation (SM) which interestingly was able to attain high spectral efficiency as the receiver maintained significantly lower complexity. However, even with the feat achieved by the SM scheme, there was still a need improve on the performance of the SM scheme which meant an increase in the spectral efficiency was required, this prompted further research and a new scheme was introduced. The quadrature SM (QSM) scheme was introduced to better the performance of the conventional SM. QSM retains all the good benefits the SM scheme offers, while still enhancing the spectral efficiency and improving overall throughput. However, the demand for increased reliability, i.e., improving the QSM scheme’s error performance led to a new scheme being introduced. Space-time QSM (ST-QSM) improves the QSM scheme’s error performance by achieving second-order diversity gain for QSM. This scheme combines both the spatial dimension and diversity to the QSM scheme, bringing about a new and improved scheme. In this dissertation, a scheme was introduced to fix the high computational complexity (CC) that affects MIMO systems transmitting at high data rates. Signal orthogonal projection (OP) was employed to decrease the CC of the space-time block coded spatial modulation (STBC-SM). The proposed scheme is called STBC-SM-OP and its results were investigated by comparing it with the STBC-SM with maximum likelihood detection (STBC-SM-ML). The proposed STBC-SM-OP scheme’s error performance matched that of STBC-SM-ML tightly down to low BER whilst maintaining a low CC.
Index modulation for next generation wireless communications.
(2018) Adejumobi, Babatunde Segun.; Pillay, Narushan.; Mneney, Stanley Henry.
A multicarrier index modulation technique in the form of quadrature spatial modulation (QSM) orthogonal frequency division multiplexing (QSM-OFDM) is proposed, in which transmit antenna indices are employed to transmit additional bits. Monte Carlo simulation results demonstrates a 5 dB gain in signal-to-noise ratio (SNR) over other OFDM schemes. Furthermore, an analysis of the receiver computational complexity is presented. A low-complexity near-ML detector for space-time block coded (STBC) spatial modulation (STBC-SM) with cyclic structure (STBC-CSM), which demonstrate near-ML error performance and yields significant reduction in computational complexity is proposed. In addition, the union-bound theoretical framework to quantify the average bit-error probability (ABEP) of STBC-CSM is formulated and validates the Monte Carlo simulation results. The application of media-based modulation (MBM), to STBC-SM and STBC-CSM employing radio frequency (RF) mirrors, in the form of MBSTBC-SM and MBSTBC-CSM is proposed to improve the error performance. Numerical results of the proposed schemes demonstrate significant improvement in error performance when compared with STBC-CSM and STBC-SM. In addition, the analytical framework of the union-bound on the ABEP of MBSTBC-SM and MBSTBC-CSM for the ML detector is formulated and agrees well with Monte Carlo simulations. Furthermore, a low-complexity near-ML detector for MBSTBC-SM and MBSTBC-CSM is proposed, and achieves a near-ML error performance. Monte Carlo simulation results demonstrate a trade-off between the error performance and the resolution of the detector that is employed. Finally, the application of MBM, an index modulated system to spatial modulation, in the form of spatial MBM (SMBM) is investigated. SMBM employs RF mirrors located around the transmit antenna units to create distinct channel paths to the receiver. This thesis presents an easy to evaluate theoretical bound for the error performance of SMBM, which is validated by Monte Carlo simulation results. Lastly, two low-complexity suboptimal mirror activation pattern (MAP) optimization techniques are proposed, which improve the error performance of SMBM significantly.
Index modulation for next-generation wireless networks.
(2020) Oladoyinbo, Segun Emmanuel.; Pillay, Narushan.; Xu, Hongjun.
The desirability of high throughput and superior system performance for multimedia services requires schemes that can achieve high spectral efficiency. However, this imposes high system/hardware complexity due to the large number of antennas required at the transmitter. This led to the development of several innovative multiple-input multiple-output (MIMO) techniques in the research community, such as generalized spatial modulation (GSM). GSM is a spatial modulation (SM) based scheme, which employs transmit antenna combinations coupled with identical symbols to convey additional information. This made the use of multiple transmit antennas possible in index modulation, improving the setback/limitation of hardware complexity experienced in the conventional MIMO and SM schemes. Furthermore, in the literature, an improved spectral efficient quadrature spatial modulation (QSM) based scheme termed generalized quadrature spatial modulation (GQSM) is proposed. In GQSM, the antennas at the transmitter are divided into groups and a unique symbol is employed across multi-active transmit antenna groups. Hence, GQSM requires less transmit antennas to achieve a high data rate when compared to its counterparts. However, GQSM requires multiple radio frequency (RF) chains, considering unique symbols are employed in each transmit antenna group. This motivates us to investigate single-symbol GQSM (SS-GQSM), which employs identical symbols across each group requiring a single RF chain. Recently, the application of RF mirrors termed media-based modulation (MBM) was introduced to the research community as a technique to enhance the spectral efficiency at a reduced hardware complexity. This motivates us to investigate MBM with single-symbol GSM to enhance its error performance and to mitigate the drawback of the requirement of multiple RF chains. In addition, link adaptation has been stated in literature as a technique, which can enhance the performance of a single-input multiple-output (SIMO)/MIMO scheme. MBM achieves a high data rate coupled with enhanced system performance. However, to the author's best knowledge, link adaptation has not been investigated with MBM. This motivates us to propose an adaptive algorithm that employs different candidate transmission modes to enhance the reliability of the SIMO system. The proposed scheme is called adaptive SIMOMBM (ASIMOMBM). Lately, two-way cooperative relaying has been proven as a spectral efficient relaying system. This technique employs two or more source nodes, which transmit information to the relay node simultaneously. Considering the advantages of GQSM stated earlier, this motivates us to investigate two-way decode-and-forward relaying for the GQSM scheme to improve the error performance of the conventional GQSM system.
Link adaptation for quadrature spatial modulation.
(2016) Oladoyinbo, Segun Emmanuel.; Pillay, Narushan.; Xu, Hongjun.
Abstract available in PDF file.
Repeat--punctured turbo codes and superorthogonal convolutional turbo codes.
(2007) Pillay, Narushan.; Xu, Hongjun.; Takawira, Fambirai.
The use of error-correction coding techniques in communication systems has become extremely imperative. Due to the heavy constraints faced by systems engineers more attention has been given to developing codes that converge closer to the Shannon theoretical limit. Turbo codes exhibit a performance a few tenths of a decibel from the theoretical limit and has motivated a lot of good research in the channel coding area in recent years. In the under-mentioned dissertation, motivated by turbo codes, we study the use of three new error-correction coding schemes: Repeat-Punctured Superorthogonal Convolutional Turbo Codes, Dual-Repeat-Punctured Turbo Codes and Dual-Repeat-Punctured Superorthogonal Convolutional Turbo Codes, applied to the additive white Gaussian noise channel and the frequency non-selective or flat Rayleigh fading channel. The performance of turbo codes has been shown to be near the theoretical limit in the AWGN channel. By using orthogonal signaling, which allows for bandwidth expansion, the performance of the turbo coding scheme can be improved even further. Since the resultant is a low-rate code, the code is mainly suitable for spread-spectrum modulation applications. In conventional turbo codes the frame length is set equal to the interleaver size; however, the codeword distance spectrum of turbo codes improves with an increasing interleaver size. It has been reported that the performance of turbo codes can be improved by using repetition and puncturing. Repeat-punctured turbo codes have shown a significant increase in performance at moderate to high signal-to-noise ratios. In this thesis, we study the use of orthogonal signaling and parallel concatenation together with repetition (dual and single) and puncturing, to improve the performance of the superorthogonal convolutional turbo code and the conventional turbo code for reliable and effective communications. During this research, three new coding schemes were adapted from the conventional turbo code; a method to evaluate the union bounds for the AWGN channel and flat Rayleigh fading channel was also established together with a technique for the weight-spectrum evaluation.
Soft-output detection for transit antenna index modulation-based schemes.
(2016) Tijani, Abdulmajeed Adekilekun.; Pillay, Narushan.; Xu, Hongjun.
Abstract available in PDF file.
Transmit antenna selection algorithms for quadrature spatial modulation.
(2016) Naidu, Suvigya.; Pillay, Narushan.
The use of multiple-input multiple-output (MIMO) systems has become increasingly popular due to the demand for high data rate transmissions. One such attractive MIMO system is spatial modulation (SM). SM is an ideal candidate for high data rate transmission as it is able to achieve a high spectral efficiency, whilst maintaining a relatively low receiver complexity. SM completely avoids inter-channel interference and the need for inter-antenna synchronisation. Furthermore, SM requires the existence of only one radio frequency chain. However, the need to increase the spectral efficiency achieved by SM is a topic which continues to garner interest. Quadrature spatial modulation (QSM) was introduced as an innovative SM-based MIMO system. QSM maintains the aforementioned advantages of SM, whilst further increasing the spectral efficiency of SM. However, similar to SM, the need to improve the reliability (error performance) of QSM still exists. One such strategy is the application of a closed-loop technique, such as transmit antenna selection (TAS). In this dissertation, Euclidean distance-based antenna selection for QSM (EDAS-QSM) is proposed. A substantial improvement in the average error performance is demonstrated. However, this is at the expense of a relatively high computational complexity. To address this, we formulate an algorithm in the form of reduced-complexity Euclidean distance-based antenna selection for QSM (RCEDAS-QSM) that is used for the computation of EDAS-QSM. RCEDAS-QSM yields a significant reduction in the computational complexity, whilst preserving the error performance. To further address computational complexity, four sub-optimal, low-complexity, TAS schemes for QSM are investigated, viz. capacity optimised antenna selection for QSM (COASQSM), TAS for QSM based on amplitude and antenna correlation (TAS-A-C-QSM), lowcomplexity TAS for QSM based on amplitude and antenna correlation using the splitting technique (LCTAS-A-C-QSM) and TAS based on amplitude, antenna correlation and Euclidean distance for QSM (A-C-ED-QSM). Amongst the sub-optimal algorithms, A-C-ED-QSM provides superior error performance. While the computational complexity of A-C-ED-QSM is higher than the other sub-optimal, lowcomplexity schemes, there is a significant reduction in the computational complexity compared to the optimal RCEDAS-QSM. However, this is at the expense of error performance. Hence, clearly a trade-off exists between error performance and computational complexity, and is investigated in detail in this dissertation.