Multiuser MIMO-OFDM for Next-Generation Wireless Systems

This overview portrays the 40-year evolution of orthogonal frequency division multiplexing (OFDM) research. The amelioration of powerful multicarrier OFDM arrangements with multiple-input multiple-output (MIMO) systems has numerous benefits, which are detailed in this treatise. We continue by highlighting the limitations of conventional detection and channel estimation techniques designed for multiuser MIMO OFDM systems in the so-called rank-deficient scenarios, where the number of users supported or the number of transmit antennas employed exceeds the number of receiver antennas. This is often encountered in practice, unless we limit the number of users granted access in the base station’s or radio port’s coverage area. Following a historical perspective on the associated design problems and their state-of-the-art solutions, the second half of this treatise details a range of classic multiuser detectors (MUDs) designed for MIMO-OFDM systems and characterizes their achievable performance. A further section aims for identifying novel cutting-edge genetic algorithm (GA)-aided detector solutions, which have found numerous applications in wireless communications in recent years. In an effort to stimulate the cross pollination of ideas across the machine learning, optimization, signal processing, and wireless communications research communities, we will review the broadly applicable principles of various GA-assisted optimization techniques, which were recently proposed also for employment inmultiuser MIMO OFDM. In order to stimulate new research, we demonstrate that the family of GA-aided MUDs is capable of achieving a near-optimum performance at the cost of a significantly lower computational complexity than that imposed by their optimum maximum-likelihood (ML) MUD aided counterparts. The paper is concluded by outlining a range of future research options that may find their way into next-generation wireless systems

Performance Investigation of Wireless LAN with Variable Channel Width

Today, mostly the wireless LAN is based on preset static channel widths. Considering unique benefits of adapting channel width, which is a fundamental yet under-explored facet in wireless communication, We carried out investigations on the performance of suggested scenario, which are based on IEEE 802.11 and composed of different number of nodes with different channel width (10MHz, 20 MHz and 40 MHz) associated to one AP. This research work makes a strong case for wireless systems that adapt channel width in WLAN. Adapting channel width offers rich possibilities for improving system performance. This thesis provides an outlook of the aforementioned issues associated with wireless communication for instance, fairness problem among users associated to same AP and hidden terminal problem. Some issues are investigated and analyzed with Matlab tool. We found that the variable channel width increases the range of communication, providing the users with the required spectrum, which offers a natural way to both improve flow fairness and balance the load across the APs. Also the increase in channel width increases the throughput of suggested scenario compare to the fixed channel width. In our future work, we also provide possible solutions to the new problems in WLAN with variable channel width

Indoor infrared wireless PPM systems

Optical wireless communication systems offer several advantages over their radio frequency counter parts. For example, cost, wavelength re-usability and a large unregulated bandwidth are among the advantages. The limitations of this technique include the optical power safety issue, multipath dispersion and interference from ambient light and background radiation. In this project, pulse position modulation is used for receiver sensitivity improvement, and code division multiple access is exploited to provide multiple access facilities. The limitations of an optical wireless system are studied and methods for performance improvement are suggested

Experimental Characterisation and Modelling of Atmospheric Fog and Turbulence in FSO

Free space optical (FSO) communication uses visible or infrared (IR) wavelengths to broadcast high-speed data wirelessly through the atmospheric channel. The performance of FSO communications is mainly dependent on the unpredictable atmospheric channel such as fog, smoke and temperature dependent turbulence. However, as the real outdoor atmosphere (ROA) is time varying and heterogeneous in nature as well as depending on the magnitude and intensity of different weather conditions, carrying out a proper link assessment under specific weather conditions becomes a challenging task. Investigation and modelling the ROA under diverse atmospheric conditions is still a great challenge in FSO communications. Hence a dedicated indoor atmospheric chamber is designed and built to produce controlled atmosphere as necessary to mimic the ROA as closely as possible. The experimental results indicate that the fog attenuation is wavelength dependent for all visibility V ranges, which contradicts the Kim model for V < 0.5 km. The obtained result validates that Kim model needs to be revised for V < 0.5 km in order to correctly predict the wavelength dependent fog attenuation. Also, there are no experimental data and empirical model available for FSO links in diverse smoke conditions, which are common in urban areas. Therefore, a new empirical model is proposed to evaluate the wavelength dependent fog and smoke attenuation by reconsidering the q value as a function of wavelength rather than visibility. The BER performance of an FSO system is theoretically and experimentally evaluated for OOK- NRZ, OOK-RZ and 4-PPM formats for Ethernet line data-rates from light to dense fog conditions. A BER of 10-6 (Q-factor ≈ 4.7) is achieved at dense fog (transmittance, T = 0.33) condition using 4-PPM than OOK-NRZ and OOK-RZ modulation schemes due to its high peak-to-average power ratio albeit at the expense of doubling the bandwidth. The effects of fog on OOK-NRZ, 4-PAM and BPSK are also experimentally investigated. In comparison to 4-PAM and OOK-NRZ signals, the BPSK modulation signalling format is more robust against the effects of fog. Moreover, the effects of using different average transmitted optical communication powers Popton the T and the received Q-factor using the OOK-NRZ modulation scheme are also investigated for light and dense fog conditions. The results show that for an FSO system operating at a Q-factor of 4.7 (for BER = 10-6), the required Q-factor is achieved at T of 48% under the thick fog condition by increasing Popt to 1.07 dBm, whereas the values of T are 55% and ~70% for the transmit power of 0.56 dBm and -0.7 dBm, respectively. The experimental characterisation and investigation of the atmospheric turbulence effect on the Ethernet and Fast-Ethernet FSO link is reported using different modulation schemes. The experiment is carried out in a controlled laboratory environment where turbulence is generated in a dedicated indoor atmospheric chamber. The atmospheric chamber is calibrated to mimic an outdoor turbulence conditions and the measured data are verified against the theoretical predictions. The experiment also demonstrates methods to control the turbulence levels and determine the equivalence between the indoor and outdoor FSO links. The results show that the connectivity of Ethernet and Fast-Ethernet links are highly sensitive to atmospheric turbulence. The results also show that the BPSK and OOK-NRZ modulation signalling formats are more robust against the weak atmospheric turbulence conditions than PAM signal

Multimode Graded-Index Optical Fibers for Next-Generation Broadband Access

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