Space-Time Super-Modulation and its Application to the Joint Medium Access and Data Transmissions
Creators: name: MEHRAN, FARHAD
Publisher: name: University of Surrey
Year: 2021

description: Machine-Type Communications (MTCs) are now deemed to be a major source of traffic in future wireless networks. To foster the development of future wireless ecosystem with MTCs, the design of existing technologies that are primarily developed for human-centric communications need to be revisited. In this context, to allow MTC devices gaining access to the shared medium while also fulfilling their transmission characteristics, joint medium access and data transmission approaches have emerged as potential key enablers. The objective of this thesis is to introduce the cutting-edge information transmission schemes that form a basis for development of practical and efficient joint medium access and data transmission for the future MTCs. The introduced concepts can be also employed in a generic wireless system to attain significant throughput gains.
description: We first propose the concept of Space-Time Super-Modulation (STSM) according to which additional highly-reliable information stream with flexible-rate can be transmitted concurrently with conventional information stream. This is achieved without the need to increase the corresponding packet length. We will show that in short block-length regime, STSM yields up to 20% throughput gain without practically affecting the performance of the conventional information stream. Then, we will show that in the context of joint medium access and data transmission, STSM reduces (or even eliminates) the need for using preambles to convey packet's signature information; hence, resulting in throughput gains of up to 35% compared to the best-examined preamble-based approach.
description: It is also shown that even in challenging scenarios where the user's packets are colliding (similarly to MTCs), STSM-enabled approaches have the closet performance to the ideal case. For the same transmission scenario and in short block-length regime, it is shown that while using long orthogonal preambles results in a more reliable transmission of signature information compared with STSM-based approach, the latter still yields higher achievable throughput due to elimination of packet headers. In addition, in contrast to the schemes that require centralized coordination such as Time-Division Multiple Access (TDMA), STSM-enabled uncoordinated transmissions yield up to 26% throughput gains by exploiting collided packets rather than avoiding them. We will show that in collision scenarios, successive interference cancellation allows to further enhance the achievable throughput by up to 25%.
description: Moreover, we introduce Generalized Space-Time Super-Modulation (GSTSM) that is the generalization of STSM concept for the state-of-the-art systems that are not relying on Space-Time Block Codes (STBCs), and might adopt several antennae at the transmitter side (even with one RF chain) and a large number of antennae at the access point. It is presented that GSTSM yields additional throughput gain of up to 10% without any error-performance degradation on conventional information bit stream; and the reliability of detection for both information bit sequences can be substantially enhanced by exploiting the receiver diversity of large Multiple-Input Multiple-Output (MIMO) systems. Unlike conventional spatial modulation, GSTSM is not solely relying on the distinction between the propagation characteristics of available transmitter-receiver links; hence, it is presented that additional flexible-rate information stream of GSTSM can efficiently operate in correlated channels and even AWGN channels.
description: In addition, it is shown that by leveraging state-of-the-art channel codes, GSTSM yields throughput increase of up to 85% compared to STSM that relies on STBCs for attaining transmit diversity gain. Furthermore, it is shown that GSTSM enables efficient headerless joint medium access and data transmission; which even in the case that information packets of two devices are continuously colliding, results in up to 33% throughput increase compared with the best candidate of header-based cases. For the same transmission scenario, it is shown that the GSTSM-enabled approach based on joint multi-user detection can attain up to 2.5x additional throughput gains compared with the schemes that realize independent detection for the users by accounting the inter-user-interference as noise. Subsequently, we present that for multi-user scenarios with packet collisions, Iterative Detection and Decoding (IDD) can be used to cancel the inter-user-interference components upon successful decoding of one user; the resultant signal is then re-processed for decoding the information message of the other user. Hence, it is shown that by adopting IDD, throughput increase of up to 15% and 55% can be achieved for the schemes that are implemented based on joint and independent multi-user detection, respectively. Moreover, it is shown that GSTSM-enabled systems can operate based on dense symbol constellations; and by taking advantage of the receiver diversity of massive MIMO systems, they yield up to 6x throughput increase compared with their counterparts based on BPSK.