Delay QoS Provisioning and Optimal Resource Allocation for Wireless Networks

Recent years have witnessed a significant growth in wireless communication and networking due to the exponential growth in mobile applications and smart devices, fueling unprecedented increase in both mobile data traffic and energy demand. Among such data traffic, real-time data transmissions in wireless systems require certain quality of service (QoS) constraints e.g., in terms of delay, buffer overflow or packet drop/loss probabilities, so that acceptable performance levels can be guaranteed for the end-users, especially in delay sensitive scenarios, such as live video transmission, interactive video (e.g., teleconferencing), and mobile online gaming. With this motivation, statistical queuing constraints are considered in this thesis, imposed as limitations on the decay rate of buffer overflow probabilities. In particular, the throughput and energy efficiency of different types of wireless network models are analyzed under QoS constraints, and optimal resource allocation algorithms are proposed to maximize the throughput or minimize the delay. In the first part of the thesis, the throughput and energy efficiency analysis for hybrid automatic repeat request (HARQ) protocols are conducted under QoS constraints. Approximations are employed for small QoS exponent values in order to obtain closed-form expressions for the throughput and energy efficiency metrics. Also, the impact of random arrivals, deadline constraints, outage probability and QoS constraints are studied. For the same system setting, the throughput of HARQ system is also analyzed using a recurrence approach, which provides more accurate results for any value of the QoS exponent. Similarly, random arrival models and deadline constraints are considered, and these results are further extended to the finite-blocklength coding regime. Next, cooperative relay networks are considered under QoS constraints. Specifically, the throughput performance in the two-hop relay channel, two-way relay channel, and multi-source multi-destination relay networks is analyzed. Finite-blocklength codes are considered for the two-hop relay channel, and optimization over the error probabilities is investigated. For the multi-source multi-destination relay network model, the throughput for both cases of with and without CSI at the transmitter sides is studied. When there is perfect CSI at the transmitter, transmission rates can be varied according to instantaneous channel conditions. When CSI is not available at the transmitter side, transmissions are performed at fixed rates, and decoding failures lead to retransmission requests via an ARQ protocol. Following the analysis of cooperative networks, the performance of both half-duplex and full-duplex operations is studied for the two-way multiple input multiple output (MIMO) system under QoS constraints. In full-duplex mode, the self-interference inflicted on the reception of a user due to simultaneous transmissions from the same user is taken into account. In this setting, the system throughput is formulated by considering the sum of the effective capacities of the users in both half-duplex and full-duplex modes. The low signal to noise ratio (SNR) regime is considered and the optimal transmission/power-allocation strategies are characterized by identifying the optimal input covariance matrices. Next, mode selection and resource allocation for device-to-device (D2D) cellular networks are studied. As the starting point, ransmission mode selection and resource allocation are analyzed for a time-division multiplexed (TDM) cellular network with one cellular user, one base station, and a pair of D2D users under rate and QoS constraints. For a more complicated setting with multiple cellular and D2D users, two joint mode selection and resource allocation algorithms are proposed. In the first algorithm, the channel allocation problem is formulated as a maximum-weight matching problem, which can be solved by employing the Hungarian algorithm. In the second algorithm, the problem is divided into three subproblems, namely user partition, power allocation and channel assignment, and a novel three-step method is proposed by combining the algorithms designed for the three subproblems. In the final part of the thesis, resource allocation algorithms are investigated for content delivery over wireless networks. Three different systems are considered. Initially, a caching algorithm is designed, which minimizes the average delay of a single-cell network. The proposed algorithm is applicable in settings with very general popularity models, with no assumptions on how file popularity varies among different users, and this algorithm is further extended to a more general setting, in which the system parameters and the distributions of channel fading change over time. Next, for D2D cellular networks operating under deadline constraints, a scheduling algorithm is designed, which manages mode selection, channel allocation and power maximization with acceptable complexity. This proposed scheduling algorithm is designed based on the convex delay cost method for a D2D cellular network with deadline constraints in an OFDMA setting. Power optimization algorithms are proposed for all possible modes, based on our utility definition. Finally, a two-step intercell interference (ICI)-aware scheduling algorithm is proposed for cloud radio access networks (C-RANs), which performs user grouping and resource allocation with the goal of minimizing delay violation probability. A novel user grouping algorithm is developed for the user grouping step, which controls the interference among the users in the same group, and the channel assignment problem is formulated as a maximum-weight matching problem in the second step, which can be solved using standard algorithms in graph theory

Energy-efficient wireless communication

In this chapter we present an energy-efficient highly adaptive network interface architecture and a novel data link layer protocol for wireless networks that provides Quality of Service (QoS) support for diverse traffic types. Due to the dynamic nature of wireless networks, adaptations in bandwidth scheduling and error control are necessary to achieve energy efficiency and an acceptable quality of service. In our approach we apply adaptability through all layers of the protocol stack, and provide feedback to the applications. In this way the applications can adapt the data streams, and the network protocols can adapt the communication parameters

Effective capacity based resource allocation for Rayleigh-fading parallel channels

International audienceWe address the problem of allocating different powers amongst parallel channels when effective capacity is the performance metric and sum-power is constrained. We assume that Chase-Combining-HARQ mechanism is applied. Closed-form expressions for the powers are exhibited. Numerical comparisons with other power allocations obtained through either ergodic capacity or throughput optimizations are done

How URLLC can Benefit from NOMA-based Retransmissions

Among the new types of connectivity unleashed by the emerging 5G wireless systems, Ultra-Reliable Low Latency Communication (URLLC) is perhaps the most innovative, yet challenging one. Ultra-reliability requires high levels of diversity, however, the reactive approach based on packet retransmission in HARQ protocols should be applied carefully to conform to the stringent latency constraints. The main premise of this paper is that the NOMA principle can be used to achieve highly efficient retransmissions by allowing concurrent use of wireless resources in the uplink. We introduce a comprehensive solution that accommodates multiple intermittently active users, each with its own HARQ process. The performance is investigated under two different assumptions about the Channel State Information (CSI) availability: statistical and instantaneous. The results show that NOMA can indeed lead to highly efficient system operation compared to the case in which all HARQ processes are run orthogonally

Performance of delay constrained multi-user networks under block fading channels

Abstract. Effective Capacity (EC) indicates the maximum communication rate subject to a certain delay constraint while the effective energy efficiency (EEE) is the ratio between this EC and power consumption. In this thesis, we analyze the EC and EEE of multi-user networks operating in the finite blocklength (FB) regime. We consider a layout in which a number of users communicate through a common controller. A closed form approximation for the per-user EC is obtained in Nakagami-$m$ fading collision channels. The interference between transmitted data packets degrades the EC of each user. We analyze this decrease proposing three methods to alleviate the interference effect for one of the users namely power control, delay relaxation and joint compensation. Our results show that systems with stringent delay constraints favor power controlled compensation while for shorter packets, the amount of compensation needed by both $\theta$ relaxation and power increases is higher. Thus, it is more costly to compensate networks transmitting shorter packets. For the hybrid method, we maximize an objective function whose parameters are determined according to the design priorities (e.g. rate and latency requirements). Results reveal that there is a unique throughput maximizer which is obtained at an intermediate operational point applying both power control and delay relaxation in the joint compensation process. Furthermore, we characterize the per-user EEE for different power consumption models. The results show that accounting for empty buffer probability enhances the per-user EEE. Considering flexible transmission power and extending the maximum delay tolerance boosts the per-use EEE which is depicted in the thesis as well.Suorituskyvyn analysointi viiverajoitetussa usean käyttäjän verkossa lohkohäipyvissä kanavissa. Tiivistelmä. Efektiivinen kapasiteetti kertoo suurimman tietoliikenteen datanopeuden määritetyillä viiverajoituksilla, kun taas efektiivinen energiatehokkuus on efektiivisen kapasiteetin ja tehonkulutuksen suhde. Tässä diplomityössä analysoidaan efektiivistä kapasiteettia ja efektiivistä energiatehokkuutta monisolmuverkoissa, kun käytetään äärellistä lohkon pituutta. Työssä käytetään mallia, jossa tietty määrä käyttäjiä kommunikoi yhteisen kontrolliyksikön ohjaamana. Käyttäjäkohtaisen efektiivisen kapasiteetin approksimaatio datapakettien törmäyksiä mallintavassa Nakagami-m -häipyvässä kanavassa esitetään suljetussa muodossa. Lähetettyjen pakettien välinen häiriö pienentää kunkin käyttäjän efektiivistä kapasiteettia. Tätä ilmiötä pyritään lieventämään kolmella ehdotetulla menetelmällä eli tehonsäädöllä, viiveen relaksoinnilla ja näiden yhdistelmällä. Tutkimustulokset osoittavat, että tiukkojen viiverajoitusten voimassa ollessa tehopohjainen kompensointi toimii parhaiten kun taas lyhyille paketeille vaaditaan molempia menetelmiä. Niinpä lyhyitä paketteja lähettävien verkkojen kompensointimenetelmät ovat kalliita. Hybridimenetelmässä maksimoidaan kohdefunktio, jonka parametrit määritellään suunnittelukriteerien mukaan (esim. datanopeus- ja viivevaatimukset). Tulokset paljastavat, että löytyy yksittäinen verkon läpäisykyvyn maksimoiva keskialueen toimintapisteen kohta teho- ja viivepohjaista kompensointia yhdessä käytettäessä. Lisäksi työssä mallinnetaan solmukohtaista efektiivistä energiatehokkuutta eri tehonkulutusmalleilla. Tulokset osoittavat, että ei-tyhjän puskurin todennäköisyyden huomioon ottaminen parantaa käyttäjäkohtaista efektiivistä energiatehokkuutta. Työssä kuvataan myös, että joustavan lähetystehon käyttö yhdessä väljennetyn maksimiviivetoleranssin kanssa parantaa efektiivistä energiatehokkuutta