On the Benefits of Network-Level Cooperation in Millimeter-Wave Communications

Relaying techniques for millimeter-wave wireless networks represent a powerful solution for improving the transmission performance. In this work, we quantify the benefits in terms of delay and throughput for a random-access multi-user millimeter-wave wireless network, assisted by a full-duplex network cooperative relay. The relay is equipped with a queue for which we analyze the performance characteristics (e.g., arrival rate, service rate, average size, and stability condition). Moreover, we study two possible transmission schemes: fully directional and broadcast. In the former, the source nodes transmit a packet either to the relay or to the destination by using narrow beams, whereas, in the latter, the nodes transmit to both the destination and the relay in the same timeslot by using a wider beam, but with lower beamforming gain. In our analysis, we also take into account the beam alignment phase that occurs every time a transmitter node changes the destination node. We show how the beam alignment duration, as well as position and number of transmitting nodes, significantly affect the network performance. Moreover, we illustrate the optimal transmission scheme (i.e., broadcast or fully directional) for several system parameters and show that a fully directional transmission is not always beneficial, but, in some scenarios, broadcasting and relaying can improve the performance in terms of throughput and delay.Comment: arXiv admin note: text overlap with arXiv:1804.0945

Link Selection Schemes For Cooperative Buffer-Aided Relay Networks

Recently, cooperative buffer-aided relaying technique has emerged. In which, the flexibility offered by the buffering capability is exploited to improve the performance in many aspects such as capacity, diversity gain and power consumption. However, the improvement comes at the price of higher transmission delay. In this thesis, the objectives are to develop the cooperative relaying systems with and without delay constraints as well as to determine an optimal link selection scheme that maximizes the throughput of cooperative relaying systems with simultaneous wireless information and power transfer (SWIPT). First, for cooperative relaying systems without delay constraints, a new link selection scheme that minimizes the outage probability is proposed. It exploits the channel state information (CSI) and buffer state information (BSI) to maintain the states of the buffers, thereby minimizing the outage probability. The outage probability performances in independent and identically distributed (i.i.d.) and independent and non-identically distributed (i.n.d.) Rayleigh fading channels are investigated. As compared to the buffer-state-based (BSB) scheme that offers the minimum outage probability among previous schemes, simulation results show that the proposed scheme offers lower outage probability and can achieve the BSB scheme’s performance using less transmission power. In the three-node network, the offered reduction in power has reached 2.5 dBW at some power values (e.g., using 17 dBW instead of 19.5 dBW). For real-time cooperative relaying systems with specific information rates and delay constraints, a new link selection scheme is proposed. The proposed scheme exploits the CSI, BSI and delay state information (DSI) to minimize the outage and packet dropping probabilities and achieve higher throughput. In order to achieve that, it uses these information to compromise between the selections of relays for reception and transmission. The proposed scheme is analysed in the i.i.d. and i.n.d. Rayleigh fading channels. For systems with high delay constraints, simulation results show that the proposed scheme offers lower packet dropping probability and higher throughput as compared to the renowned relay selection schemes. The proposed scheme offers reduction in power that exceeds 1 dBW in some simulations. Lastly, SWIPT in cooperative buffer-aided relaying systems is investigated. Power splitting (PS) technique is considered for SWIPT implementation. An optimal link selection scheme that maximizes the system throughput is proposed. In each time slot, an optimal PS ratio is employed if the source is chosen for transmission, while the relay transmits with optimal power if selected. As compared to the conventional schemes that use predefined transmission schedule, simulation results show that the proposed scheme offers higher throughput and signal-to-ratio (SNR) gain that exceeds 10 dB at some SNR regions

Secrecy Enhancement in Cooperative Relaying Systems

Cooperative communications is obviously an evolution in wireless networks due to its noticeable advantages such as increasing the coverage as well as combating fading and shadowing effects. However, the broadcast characteristic of a wireless medium which is exploited in cooperative communications leads to a variety of security vulnerabilities. As cooperative communication networks are globally expanded, they expose to security attacks and threats more than ever. Primarily, researchers have focused on upper layers of network architectures to meet the requirements for secure cooperative transmission while the upper-layer security solutions are incapable of combating a number of security threats, e.g., jamming attacks. To address this issue, physical-layer security has been recommended as a complementary solution in the literature. In this thesis, physical layer attacks of the cooperative communication systems are studied, and corresponding security techniques including cooperative jamming, beamforming and diversity approaches are investigated. In addition, a novel security solution for a two-hop decode-and-forward relaying system is presented where the transmitters insert a random phase shift to the modulated data of each hop. The random phase shift is created based on a shared secret among communicating entities. Thus, the injected phase shift confuses the eavesdropper and secrecy capacity improves. Furthermore, a cooperative jamming strategy for multi-hop decode-and-forward relaying systems is presented where multiple non-colluding illegitimate nodes can overhear the communication. The jamming signal is created by the transmitter of each hop while being sent with the primary signal. The jamming signal is known at the intended receiver as it is according to a secret common knowledge between the communicating entities. Hence, artificial noise misleads the eavesdroppers, and decreases their signal-to-noise-ratio. As a result, secrecy capacity of the system is improved. Finally, power allocation among friendly jamming and main signal is proposed to ensure that suggested scheme enhances secrecy

Learning to be energy-efficient in cooperative networks

Cooperative communication has great potential to improve the transmit diversity in multiple users environments. To achieve a high network-wide energy-efficient performance, this letter poses the relay selection problem of cooperative communication as a noncooperative automata game considering nodes’ selfishness, proving that it is an ordinal game (OPG), and presents a game-theoretic analysis to address the benefit equilibrium decision-making issue in relay selection. A stochastic learning-based relay selection algorithm is proposed for transmitters to learn a Nash-equilibrium strategy in a distributed manner. We prove through theoretical and numerical analysis that the proposed algorithm is guaranteed to converge to a Nash equilibrium state, where the resulting cooperative network is energy-efficient and reliable. The strength of the proposed algorithm is also confirmed through comparative simulations in terms of energy benefit and fairness performances