On an approach to provide space diversity to an ultra wideband time hopping pulse position modulated wireless communication system

The hypothesis question, which is addressed in this PhD dissertation, is how to use two transmission antennas in an Ultra Wide Band Time Hopping Pulse Position Modulation system to take advantage of space diversity in such a way as to not significantly degrade the communication link compared to using only one transmit antenna. In answering the hypothesis question, this dissertation proposes a novel technique, based on Space Time Spreading, to allow an Ultra Wideband Time Hopping Pulse Position Modulation system to obtain full advantage from space diversity using two transmit antennas and one receive antenna, showing how such a Multiple Input Multiple Output system is designed. This is achieved with the added advantage of transmitting the same two symbols simultaneously on each antenna link. This means that for the proposed system, should a fade occur on one of the two antenna links, the two symbols transmitted will still be received with a slight increased cost in average Bit Error Rate (BER) performance as Signal to Noise Ratio (SNR) or measured Eb/No is increased. Results are first provided for wideband Space Time Spreading in the presence of Multiple Access Interference when using two, four and eight transmit antennas. A system is developed in simulation using modules provided by MATLABs Simulink program. It is then shown that using low correlation Wysocki spreading code set results in an improved BER performance compared to the more often used Walsh Hadamard spreading code set. A Simulink Ultra Wide Band Pulse Position Modulation Single Input Single Output system is developed and validated against published peer reviewed material. This is then modified to consider the use of Space Time Spreading in a Single Input Single Output system and it is shown that improved performance over an Ultra Wide Band Pulse Position Modulated Single Input Single Output is possible. It is also shown that this improvement allows the transmission of two symbols in the same time that the original system only transmits one symbol. The thesis also investigates a system which uses two transmit antennas but a hard decision is made on a chip by chip basis. Its performance, compared to an equivalent Single Input Single Output comparable system, is suboptimal. It does, however, have the advantage that it sends two symbols in the same time that the equivalent Single Input Single output Ultra Wide Band Pulse Position Modulation system sends one, and its implementation is simpler to codify. Also, it has the feature that both symbols are sent simultaneously on each antenna link. The simulator is then modified to make a hard decision after all chips of a spreading sequence for two antennas are received and it is shown that this system, in simulation and analysis, has a similar performance to that for a comparable Single Input Single Output system with the added advantage that both antenna links send the same two symbols simultaneously. It is further demonstrated in simulation and analysis that such systems can be affected by Multiple Access Interference. In addition, it is shown, using simulation, that the choice of spreading sequence set does have an impact on the average BER performance of the proposed Space Time Spreading Time Hopping Ultra Wideband Pulse Position Modulation system. The thesis finally proposes some extensions using the developed simulator which are outlined in future work

Adaptive Space-Time-Spreading-Assisted Wideband CDMA Systems Communicating over Dispersive Nakagami-m Fading Channels

In this contribution, the performance of wideband code-division multiple-access (W-CDMA) systems using space-timespreading-(STS-) based transmit diversity is investigated, when frequency-selective Nakagami-m fading channels, multiuser interference, and background noise are considered. The analysis and numerical results suggest that the achievable diversity order is the product of the frequency-selective diversity order and the transmit diversity order. Furthermore, both the transmit diversity and the frequency-selective diversity have the same order of importance. Since W-CDMA signals are subjected to frequency-selective fading, the number of resolvable paths at the receiver may vary over a wide range depending on the transmission environment encountered. It can be shown that, for wireless channels where the frequency selectivity is sufficiently high, transmit diversity may be not necessitated. Under this case, multiple transmission antennas can be leveraged into an increased bitrate. Therefore, an adaptive STS-based transmission scheme is then proposed for improving the throughput ofW-CDMA systems. Our numerical results demonstrate that this adaptive STS-based transmission scheme is capable of significantly improving the effective throughput of W-CDMA systems. Specifically, the studied W-CDMA system’s bitrate can be increased by a factor of three at the modest cost of requiring an extra 0.4 dB or 1.2 dB transmitted power in the context of the investigated urban or suburban areas, respectively

Initial synchronisation of wideband and UWB direct sequence systems: single- and multiple-antenna aided solutions

This survey guides the reader through the open literature on the principle of initial synchronisation in single-antenna-assisted single- and multi-carrier Code Division Multiple Access (CDMA) as well as Direct Sequence-Ultra WideBand (DS-UWB) systems, with special emphasis on the DownLink (DL). There is a paucity of up-to-date surveys and review articles on initial synchronization solutions for MIMO-aided and cooperative systems - even though there is a plethora of papers on both MIMOs and on cooperative systems, which assume perfect synchronization. Hence this paper aims to ?ll the related gap in the literature

Terahertz Communications and Sensing for 6G and Beyond: A Comprehensive View

The next-generation wireless technologies, commonly referred to as the sixth generation (6G), are envisioned to support extreme communications capacity and in particular disruption in the network sensing capabilities. The terahertz (THz) band is one potential enabler for those due to the enormous unused frequency bands and the high spatial resolution enabled by both short wavelengths and bandwidths. Different from earlier surveys, this paper presents a comprehensive treatment and technology survey on THz communications and sensing in terms of the advantages, applications, propagation characterization, channel modeling, measurement campaigns, antennas, transceiver devices, beamforming, networking, the integration of communications and sensing, and experimental testbeds. Starting from the motivation and use cases, we survey the development and historical perspective of THz communications and sensing with the anticipated 6G requirements. We explore the radio propagation, channel modeling, and measurements for THz band. The transceiver requirements, architectures, technological challenges, and approaches together with means to compensate for the high propagation losses by appropriate antenna and beamforming solutions. We survey also several system technologies required by or beneficial for THz systems. The synergistic design of sensing and communications is explored with depth. Practical trials, demonstrations, and experiments are also summarized. The paper gives a holistic view of the current state of the art and highlights the issues and challenges that are open for further research towards 6G.Comment: 55 pages, 10 figures, 8 tables, submitted to IEEE Communications Surveys & Tutorial