A Novel Uplink Data Transmission Scheme For Small Packets In Massive MIMO System

Intelligent terminals often produce a large number of data packets of small lengths. For these packets, it is inefficient to follow the conventional medium access control (MAC) protocols because they lead to poor utilization of service resources. We propose a novel multiple access scheme that targets massive multiple-input multiple-output (MIMO) systems based on compressive sensing (CS). We employ block precoding in the time domain to enable the simultaneous transmissions of many users, which could be even more than the number of receive antennas at the base station. We develop a block-sparse system model and adopt the block orthogonal matching pursuit (BOMP) algorithm to recover the transmitted signals. Conditions for data recovery guarantees are identified and numerical results demonstrate that our scheme is efficient for uplink small packet transmission.Comment: IEEE/CIC ICCC 2014 Symposium on Signal Processing for Communication

Multiple Access for Small Packets Based on Precoding and Sparsity-Aware Detection

Modern mobile terminals often produce a large number of small data packets. For these packets, it is inefficient to follow the conventional medium access control protocols because of poor utilization of service resources. We propose a novel multiple access scheme that employs block-spreading based precoding at the transmitters and sparsity-aware detection schemes at the base station. The proposed scheme is well suited for the emerging massive multiple-input multiple-output (MIMO) systems, as well as conventional cellular systems with a small number of base-station antennas. The transmitters employ precoding in time domain to enable the simultaneous transmissions of many users, which could be even more than the number of receive antennas at the base station. The system is modeled as a linear system of equations with block-sparse unknowns. We first adopt the block orthogonal matching pursuit (BOMP) algorithm to recover the transmitted signals. We then develop an improved algorithm, named interference cancellation BOMP (ICBOMP), which takes advantage of error correction and detection coding to perform perfect interference cancellation during each iteration of BOMP algorithm. Conditions for guaranteed data recovery are identified. The simulation results demonstrate that the proposed scheme can accommodate more simultaneous transmissions than conventional schemes in typical small-packet transmission scenarios.Comment: submitted to IEEE Transactions on Wireless Communication

Performance optimisation of the MAC protocol with multiple contention slots in MIMO ad hoc networks

The multiple-input multiple-output (MIMO) technique can be used to improve the performance of ad hoc networks. Various medium access control (MAC) protocols with multiple contention slots have been proposed to exploit spatial multiplexing for increasing the transport throughput of MIMO ad hoc networks. However, the existence of multiple request-to-send/clear-to-send (RTS/CTS) contention slots represents a severe overhead that limits the improvement on transport throughput achieved by spatial multiplexing. In addition, when the number of contention slots is fixed, the efficiency of RTS/CTS contention is affected by the transmitting power of network nodes. In this study, a joint optimisation scheme on both transmitting power and contention slots number for maximising the transport throughput is presented. This includes the establishment of an analytical model of a simplified MAC protocol with multiple contention slots, the derivation of transport throughput as a function of both transmitting power and the number of contention slots, and the optimisation process based on the transport throughput formula derived. The analytical results obtained, verified by simulation, show that much higher transport throughput can be achieved using the joint optimisation scheme proposed, compared with the non-optimised cases and the results previously reported

An Adaptive Mac Protocol for Wireless Multi-Hop Networks with Multiple Antennas

Radio links that use multiple antennas at both transmitter and receiver sides are referred to as Multiple-Input Multiple-Output (MIMO) links. MIMO links are known to provide multiplicative increase in capacity and spectral efficiency by simultaneously transmitting multiple independent data streams in the same channel. However, current medium access control (MAC) protocols can't fully exploit the bandwidth and capacity of the MIMO links. In this thesis, we present a new MAC protocol, Achieving Maximum Transmit Antenna MAC (AMTA-MAC), which can fully utilize the feature of MIMO links to achieve better performance in terms of fairness and throughput. We implement the AMTA-MAC protocol in the network simulator ns-2 for a system with two antennas. Simulation results show that the AMTA-MAC outperforms the throughput of IEEE 802.11 and MIMA-MAC and mitigates the unfairness problem of IEEE 802.11

Optimisation inter-couches du protocole SCTP en réseaux ad hoc

Les protocoles de transport fiables ont été conçus pour s'adapter aux problèmes de congestion dans les réseaux filaires. Dans les réseaux ad hoc, leur fonctionnement conduit à une dégradation de performances que nous nous proposons de traiter par une adaptation à la mobilité en utilisant une méthode de communication inter-couches. Plus précisément, nous étudions l’amélioration des performances du protocole SCTP; très semblable au protocole TCP il définit un fonctionnement multihoming qui en environnement filaire améliore les performances du transfert. Nous montrons que cette option est également intéressante en réseaux ad hoc. Dans ce travail nous définissons deux modes d'adaptation: un mode local et un mode réparti. Dans un premier temps nous proposons une adaptation locale du transport selon l'état du réseau perçu par le protocole de routage. Dans un second temps, nous proposons une optimisation inverse, répartie sur les nœuds, où il s'agit d'adapter le routage au fonctionnement du protocole transport, de façon à pouvoir bénéficier du traitement multihoming de SCTP. Nous évaluons nos propositions par simulation et déterminons leur domaine de validité. Ce travail se conclut par la proposition d'une architecture d'adaptation permettant d'utiliser selon leurs domaines de validité les optimisations proposées. ABSTRACT : The utilization of reliable transport protocol over ad hoc networks leads to degraded performances due to the incapacity to react to non congestion errors. We propose to treat this problem by introducing mobility adaptation with a cross layer design. More precisely, we study the performance improvement of the SCTP transport protocol. Very similar to TCP, SCTP includes a multihoming option that improves its performance in the wired networks; we show that this option is also interesting in ad hoc networks. In this thesis, two methods of adaptation are proposed: a local method and a distributed one. First, we propose a local adaptation of the transport according to the network state obtained from the routing protocol. Second, we propose a reverse optimisation, distributed on the nodes, where the routing is adapted from the transport process in such a way that it can take benefit from SCTP multihoming process. We evaluate our propositions through simulations and precise their limitations. Finally, an adaptation architecture using our propositions in function of their limitation domain is proposed to conclude our work

Reconfigurable antennas for adaptive MIMO communication systems

The requirements for the next generation wireless systems seek to provide reliable high data rate at low cost. Unfortunately the current wireless communication infrastructure is notfully equipped to over this unprecedented quality of service. Major obstacles include: limited bandwidth availability, limited transmit power, and signal strength uctuations which are intrinsic to the multivariate wireless channel. Multiple Input Multiple Output (MIMO) antenna systems have emerged as one of the most significant technical breakthrough in modern wireless communications able to satisfy these stringent requirements. However the necessity of assuring a high data rate in a large variety of environments while reducing the antenna array space occupation on portable devices requires an improvement in current MIMO technology. To overcome these limitations, we propose in this thesis, the use of reconfigurable antennas that adaptively change, through RF switches, their radiation properties and frequency of operation according to wireless channel characteristics.The key idea of this work is to show that reconfigurable antennas, through their capability to dynamically change their electrical and radiation properties, can be used to change the propagation characteristics of the wireless channel existing between the transmitting and receiving antennas. The proposed MIMO system breaks from the conventional wisdom that the wireless propagation channel cannot be changed intentionally by the transceivers in the link.Three different novel classes of electrically multi element reconfigurable antennas are proposed as suitable candidates for reconfigurable MIMO systems: i ) a reconfigurable printeddipole antenna array that exploits inter element mutual coupling to achieve pattern reconfigurability, ii ) circular patches capable of exciting higher order modes to achieve pattern and polarization diversity, and iii ) a metamaterial leaky wave array that can be reconfigured in pattern to achieve unprecedented degrees of pattern reconfigurability.To effectively use such antennas with actual communication systems, a low power consumption method for selecting the array configuration is proposed. This technique exploits the close relationship between the environment that surrounds the antenna array and the antenna radiation characteristics in order to select optimal array radiation patterns without the need for intense channel sensing or excessive training. A complete reconfigurable antenna system composed of mutli-element reconfigurable antennas and a control unit capable of efficently driving the antennas is proposed to deliver unprecedented system performance.Analytical models of the proposed system are used to fully characterize the functionality and performance of the technology. A complete evaluation of the proposed system is conducted through electromagnetic simulations and eld measurements collected with a channel sounder speciiically designed to measure the performance of multi element antennasystems. It is demonstrated that the novel multi element reconfigurable antenna system is capable of providing i ) increased data rate compared to common non reconfigurable antennas in single link communications as well as in multi-link ad hoc networks, ii ) reduced space occupation by the antenna on the communication device exploiting the principles of pattern and polarization diversity, iii ) reduced number of radio-frequency chains needed at the receiver/transmitter and iv ) reduced amount of transmit power for achieving performancecomparable to that of standard non reconfigurable antenna systems.Ph.D., Electrical Engineering -- Drexel University, 200