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Research Publications (Engineering and Built Environment)

Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/215

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Author: search.filters.author.Quazi, TahmidSubject: search.filters.subject.Labelling diversity

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    Optimal antenna spacings for uncoded space-time labelling diversity systems with linear and non-linear antenna configurations
    (2018-09-05) Patel, Sulaiman Saleem; Quazi, Tahmid; Xu, Hongjun; Lewis, John; Ndlela, Zamandlela
    —Uncoded Space-Time Labelling Diversity (USTLD) is a recent technique that has been applied to multiple-input, multiple-output (MIMO) systems to improve their error performance. However, the presence of multiple antennas leads to correlation, resulting in a performance degradation. Given that 5G systems aim to operate with large-scale antenna arrays and in the millimetre-wave frequency spectrum, antenna correlation is highly likely in next-generation MIMO systems. It is thus insightful to predict the optimal antenna spacing required to balance robustness to correlation with small form factor in USTLD systems. This paper investigates the cases of densely arranged, linearly arranged and equispaced antenna configurations to propose an optimal antenna spacing for each configuration. The results presented indicate that the optimal spacings are 0.3λ for dense antenna arrays, 0.4λ for linearly arranged antenna arrays and 0.3λ for equispaced antennas, where λ is the transmission carrier wavelength.
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    A genetic algorithm for designing encoded space-time labelling diversity mappers
    (IEEE, 2018-10) Patel, Sulaiman Saleem; Quazi, Tahmid; Xu, Hongjun
    The extent to which Uncoded Space-Time Labelling Diversity is able to improve the error performance of spacetime block coded (STBC) systems is dependent on the binary mappers used to encode information. Existing design techniques are limited; as they either rely on symmetry-based heuristics, or constrain the size of the constellation due to high computational costs. This paper proposes a new genetic algorithm for labelling diversity (LD) mapper design which is applicable to constellations of any shape or size. The proposed algorithm is tested using 16QAM, 64QAM, 32PSK and three 16APSK constellations that do not display diagonal symmetry. The proposed LD mappers match the best heuristic designs for 16QAM and 64QAM. The 32PSK LD mapper produced achieves a diversity gain of ≈ 8dB when compared to the available heuristic-based LD mapper. In addition, the 16APSK mappers achieve a diversity gain of approximately 3 to 8dB compared to Alamouti-coded STBC systems for the three non-symmetric constellations considered.
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    Performance of uncoded space-time labelling diversity over dual-correlated Rayleigh-fading channels
    (2017-09-09) Patel, Sulaiman Saleem; Quazi, Tahmid; Xu, Hongjun; van Loggerenberg, Samuel; Laureles, Jonabelle
    Uncoded Space-Time Labelling Diversity (USTLD) is a recent technique to improve error performance in multiple-input, multiple-output (MIMO) systems. Standard MIMO systems assume that channels between transmit and receive antennas are independent and identically distributed (i.i.d.), and thus, uncorrelated. This assumption is also made in previous works on USTLD. However, in practice, if antennas are spaced closer than half a transmission wavelength to each other, channels become correlated. This motivates the study in this paper of the performance of USTLD under correlated channel conditions. An analytical expression for the upper bound of the average bit error rate (BER) in the presence of correlated fading is derived. This expression is validated using results from Monte Carlo simulations, which show a tight fit in the high signal-to-noise ratio (SNR) region. Results presented confirm that channel correlation adversely affects the BER of USTLD for both 16QAM and 64QAM. Interestingly, results also indicate that USTLD is more sensitive to channel correlation than comparable standard MIMO schemes.
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    Error performance of uncoded space time labelling diversity in spatially correlated Nakagami-q channels
    (Wiley, 2018-08) Patel, Sulaiman Saleem; Quazi, Tahmid; Xu, Hongjun
    Greater spectral efficiency has recently been achieved for Uncoded Space Time Labelling Diversity (USTLD) systems by increasing the number of antennas in the transmit antenna array. However, due to constrained physical space in hardware, the use of more antennas can lead to degradation in error performance due to correlation. Thus, this paper studies the effects of spatial correlation on the error performance of USTLD systems. The union bound approach, along with the Kronecker correlation model, is used to derive an analytical expression for the average bit error probability (ABEP) in the presence of Nakagami‐q fading. This expression is validated by the results of Monte Carlo simulations, which shows a tight fit in the high signal‐to‐noise ratio (SNR) region. The degradation in error performance due to transmit and receive antenna correlation is investigated independently. Results indicate that transmit antenna correlation in the USTLD systems investigated (3 × 3 8PSK, 2 × 4 16PSK, 2 × 4 16QAM, and 2 × 4 64QAM) causes a greater degradation in error performance than receive antenna correlation. It is also shown that 2 × 4 USTLD systems are more susceptible to correlation than comparable space‐time block coded systems for 8PSK, 16PSK, 16QAM, and 64QAM.
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    High-rate uncoded space-time labelling diversity with low-complexity detection
    (Wiley, 2020-09-25) Patel, Sulaiman Saleem; Quazi, Tahmid; Xu, Hongjun
    Uncoded space-time labelling diversity (USTLD) is a recent scheme that improved the error performance compared to conventional multiple-input, multiple-output systems. Thus far, USTLD has suffered from limited achievable data rates, as the original model uses only two transmit antennas. This motivates for the work in this paper, where the USTLD model is extended to allow for any desired number of transmit antennas. An analytical bound for the average bit error probability of this high-rate USTLD (HR-USTLD) system is derived. This expression is verified using the results of Monte Carlo simulations, which show a tight fit in the high signal-to-noise ratio region. The increased data rates associated with larger transmit antenna arrays in HRUSTLD systems come at the cost of increased detection complexity. Therefore, this paper studies the application of low-complexity detection algorithms based on the popular QR decomposition technique and proposes a new algorithm specifically designed for HR-USTLD systems. Analysis of this algorithm in terms of accuracy and computational complexity is also provided and benchmarked against maximum-likelihood detection (MLD). It is shown that the proposed algorithm achieves near-MLD accuracy, while reducing complexity by 79.75% and 92.53% for the respective 4 × 4 16QAM and 4 × 5 16PSK HR-USTLD systems investigated.