MIMO channel modelling for indoor wireless communications

This thesis investigates multiple-input-multiple-output (MIMO) channel modelling for a wideband indoor environment. Initially the theoretical basis of geometric modelling for a typical indoor environment is looked at, and a space-time model is formulated. The transmit and receive antenna correlation is then separated and is expressed in terms of antenna element spacing, the scattering parameter, mean angle of arrival and number of antenna elements employed. These parameters are used to analyze their effect on the capacity for this environment. Then the wideband indoor channel operating at center frequencies of 2.4 GHz and 5.2 GHz is investigated. The concept of MIMO frequency scaling is introduced and applied to the data obtained in the measurement campaign undertaken at the University of Pretoria. Issues of frequency scaling of capacity, spatial correlation and the joint RX/TX double direction channel response for this indoor environment are investigated. The maximum entropy (ME) approach to MIMO channel modelling is investigated and a new basis is developed for the determination of the covariance matrix when only the RX/TX covariance is known. Finally, results comparing this model with the established Kronecker model and its application for the joint RX/TX spatial power spectra, using a beamformer, are evaluated. Conclusions are then drawn and future research opportunities are highlighted.Thesis (PhD)--University of Pretoria, 2008.Electrical, Electronic and Computer Engineeringunrestricte

Towards a bandwidth efficient cognitive positioning system

Presented is an efficient bandwidth determination model for the cognitive positioning system by utilising multiple receive antennas. The performance evaluations of the proposed multiple receive antenna positioning system were carried out using the linear least squares and maximum-likelihood location estimation techniques. Simulated results reveal that in a rural scenario, the 1 × 2 and 1 × 3 singleinput- multiple-output (SIMO) cases display an average bandwidth efficiency with respect to positional accuracy, of 49 and 58%, respectively, over the single-input-single-output (SISO) case. For an urban scenario, the 1 × 2 and 1 × 3 SIMO cases display a higher average bandwidth efficiency of 53 and 62%, respectively, over the SISO case.The Sentech Chair in Broadband Wireless Multimedia Communications at the University of Pretoria and the National Research Foundation.http://www.ietdl.org/ELai201

Prediction based channel allocation performance for cognitive radio

The interdependency, in a cognitive radio (CR) network, of spectrum sensing, occupancy modelling, channel switching and secondary user (SU) performance, is investigated. Achievable SU data throughput and primary user (PU) disruption rate have been examined for both theoretical test data as well as data obtained from real-world spectrum measurements done in Pretoria, South Africa. A channel switching simulator was developed to investigate SU performance, where a hidden Markov model (HMM) was employed to model and predict PU behaviour, from which proactive channel allocations could be made. Results show that CR performance may be improved if PU behaviour is accurately modelled, since accurate prediction allows the SU to make proactive channel switching decisions. It is further shown that a trade-off may exist between achievable SU throughput and average PU disruption rate. When using the prediction model, significant performance improvements, particularly under heavy traffic density conditions, of up to double the SU throughput and half the PU disruption rate were observed. Results obtained from a measurement campaign were comparable with those obtained from theoretical occupancy data, with an average similarity score of 95% for prediction accuracy, 90% for SU throughput and 70% for PU disruption rate.Sentech Chair in Broadband Wireless Multimedia Communication (BWMC), the National Research Foundation (NRF) and the Independent Communications Authority of South Africa (ICASA).http://www.elsevier.com/locate/aeuehb2013ai201

Analysis of an offset modulation transmission

In this article, a method called offset modulation (OM-OFDM) is proposed to control the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) signal. The theoretical bandwidth occupancy of the proposed offset modulated signal is derived. Using these bandwidth occupancy results, a closed-form theoretical bit error rate (BER) expression for an offset modulated transmission is derived and validated. Thereafter, a BER comparison between OM-OFDM and OFDM at a PAPR value of 13 dB shows that both methods offer similar BER characteristics for frequency selective fading channel conditions. The OM-OFDM method in addition is able to accurately control the PAPR of a transmission for a targeted BER. The authors have further proposed a newly applied power performance decision metric, which can be used throughout the PAPR field, in order to compare various methods. By using this power performance decision metric, the authors show that OM-OFDM offers between 4 dB–1.2 dB (60.34%–24.6%) and 4.1 dB–1.2 dB (60.8%–23.6%), net power performance gain (at a BER of 10−4) when compared to a clipped OFDM, OFDM, tone reserved (TR) OFDM and an active constellation extended (ACE) OFDM transmission in a frequency selective fading channel. Finally, by using a complementary cumulative distribution function (CCDF), the OM-OFDM method is shown to offer between 3.2 dB and 2 dB PAPR reduction (at a CCDF of 10−1) when compared to an OFDM, TR, clipped, and ACE OFDM transmission.This work is currently being patented by the University of Pretoria. Both authors are inventors on the patent, with the University of Pretoria holding the patent rights. This paper is based on work, for which the author has been awarded a PhD at the University of Pretoria. The necessary permissions have been obtained to publish such material.http://jwcn.eurasipjournals.com/content/2013/1/19am2013ai201

Capacity-approaching non-binary balanced codes using auxiliary data

It is known that, for large user word lengths, the auxiliary data can be used to recover most of the redundancy losses of Knuth’s simple balancing method compared with the optimal redundancy of balanced codes for the binary case. Here, this important result is extended in a number of ways. First, an upper bound for the amount of auxiliary data is derived that is valid for all codeword lengths. This result is primarily of theoretical interest, as it defines the probability distribution of the number of balancing indices that results in optimal redundancy. This result is equally valid for particular non-binary generalizations of Knuth’s balancing method. Second, an asymptotically exact expression for the amount of auxiliary data for the ternary case of a variable length realization of the modified balanced code construction is derived, that, in all respects, is the analogue of the result obtained for the binary case. The derivation is based on a generalization of the binary random walk to the ternary case and a simple modification of an existing generalization of Knuth’s method for the non-binary balanced codes. Finally, a conjecture is proposed regarding the probability distribution of the number of balancing indices for any alphabet size.The National Research Foundation (NRF) and SENTECH Chair in Broadband Wireless Multimedia Communication.http://ieeexplore.ieee.org/servlet/opac?punumber=18hj2019Electrical, Electronic and Computer Engineerin

Age of information and success probability analysis in hybrid spectrum access-based massive cognitive radio networks

In this paper, we investigate users’ performance under the hybrid spectrum access model in the massive cognitive radio network (CRN), where multiple primary users (PUs) and secondary users (SUs) transmit on the same channel simultaneously. SUs first detect the state of the channel via channel sensing and select an appropriate channel access scheme (either underlay or overlay) for their transmissions based on the outcome of the channel sensing. When at least one PU is active, SUs transmit under the underlay channel access scheme by employing the power control technique to ensure that the interference generated in the primary network is below the pre-defined interference threshold. In the absence of PU, SUs transmit with full transmit power under the overlay channel access scheme, thereby maximizing their throughput. Using the tool of stochastic geometry, we obtained tractable analyses for important metrics such as success probability, throughput, and the average age of information (AoI) in both primary and secondary networks, while capturing the interference between the two networks. The obtained analyses offer an efficient way to understand the metrics of AoI, throughput and success probability in the hybrid spectrum access-based CRN. We further compared users’ performance under the hybrid spectrum access scheme with performances under overlay and underlay spectrum access schemes. The outcome of the numerical simulations shows that the hybrid spectrum access scheme can significantly improve the performance of users in the network, while also capturing more key features of real-life systems.The SENTECH Chair in Broadband Wireless Multimedia Communications (BWMC), Department of Electrical, Electronics, and Computer Engineering, University of Pretoria, South Africa.http://www.mdpi.com/journal/applscipm2021Electrical, Electronic and Computer Engineerin

Transmission scheduling for wireless mesh networks with temporal reuse

Link-assigned transmission schedules with timeslot reuse by multiple links in both the space and time domains are investigated in this study for stationary multihop wireless mesh networks with both rate and power adaptivity. Specifically, cross-layer optimised schedules with proportionally fair end-to-end flow rates and network coding capability are constructed for networks operating under the physical interference model with single-path minimum hop routing. Extending transmission rights in a link-assigned schedule allows for network coding and temporal reuse, which increases timeslot usage efficiency when a scheduled link experiences packet depletion. The schedules that suffer from packet depletion are characterised, and a generic temporal reuse-aware achievable rate region is derived. Extensive computational experiments show improved schedule capacity, quality of service, power efficiency and benefit from network coding accrued with schedules optimised in the proposed temporal reuseaware convex rate region.http://jwcn.eurasipjournals.com/content/2011/1/8

AI meets CRNs : a prospective review on the application of deep architectures in spectrum management

The spectrum low utilization and high demand conundrum created a bottleneck towards ful lling the requirements of next-generation networks. The cognitive radio (CR) technology was advocated as a de facto technology to alleviate the scarcity and under-utilization of spectrum resources by exploiting temporarily vacant spectrum holes of the licensed spectrum bands. As a result, the CR technology became the rst step towards the intelligentization of mobile and wireless networks, and in order to strengthen its intelligent operation, the cognitive engine needs to be enhanced through the exploitation of arti cial intelligence (AI) strategies. Since comprehensive literature reviews covering the integration and application of deep architectures in cognitive radio networks (CRNs) are still lacking, this article aims at lling the gap by presenting a detailed review that addresses the integration of deep architectures into the intricacies of spectrum management. This is a prospective review whose primary objective is to provide an in-depth exploration of the recent trends in AI strategies employed in mobile and wireless communication networks. The existing reviews in this area have not considered the relevance of incorporating the mathematical fundamentals of each AI strategy and how to tailor them to speci c mobile and wireless networking problems. Therefore, this reviewaddresses that problem by detailing howdeep architectures can be integrated into spectrum management problems. Beyond reviewing different ways in which deep architectures can be integrated into spectrum management, model selection strategies and how different deep architectures can be tailored into the CR space to achieve better performance in complex environments are then reported in the context of future research directions.The Sentech Chair in Broadband Wireless Multimedia Communications (BWMC) at the University of Pretoria.http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=6287639am2022Electrical, Electronic and Computer Engineerin

Improving link failure restoration in next-generation wireless sensor networks

Next-generation wireless sensor networks (xWSN) have applications in many emerging wireless technologies, such as fifth-generation, internet-of-things, device-to-device communications, e-health, e-agriculture, etc. For most of these xWSN applications, network reliability and robustness against failures are crucial considerations. In this paper, an appropriate network restoration model is developed to help achieve network protection and/or restoration for xWSN in the event of link failures. In the model, effective network restoration is achieved by investigating efficient pre-configured-cycle (p-cycle)-based restoration solutions for the xWSN. Furthermore, to achieve significant improvement in the capacity efficiency of the p-cycle solutions realised, the concepts of p-cycle selectivity, load redistribution and the use of single p-cycles for double failure restoration are investigated and incorporated in the network restoration design. The restoration model developed, alongside the various improvement concepts incorporated, is shown to achieve better performance in terms of average path length and total capacity cost when compared with similar restoration models for modern wireless communication applications.The SENTECH Chair in Broadband Wireless Multimedia Communications (BWMC), Univerity of Pretoria, South Africa.http://www.elsevier.com/locate/arrayhj2022Electrical, Electronic and Computer Engineerin

Log-domain iterative sphere decoder with symbol sorting

In this paper the authors propose modified branch and pruning metrics for the sphere decoder to facilitate the use of apriori information in the sphere decoder. The proposed sphere decoder operates completely in the log-domain. Additionally the effect of order in which the symbols are decoded on the computational requirements of the decoder are investigated with the authors proposing a modification of the sorted QR decomposition (SQRD) algorithm to incorporate apriori information. The modified SQRD algorithm is shown to reduce the average number of computations by up to 95%. The apriori sphere decoder is tested in an iterative multiple input multiple output (MIMO) decoder and shown to reduce the bit error rate (BER) by an order of magnitude or provide approximately a one decibel improvement.http://www.saiee.org.za/DirectoryDisplay/DirectoryCMSPages.aspx?name=Publications#id=1588&dirname=ARJ&dirid=337am2016Electrical, Electronic and Computer Engineerin