On modelling network coded ARQ-based channels

Network coding (NC) has been an attractive research topic in recent years as a means of offering a throughput improvement, especially in multicast scenarios. The throughput gain is achieved by introducing an algebraic method for combining multiple input streams of packets which are addressing one output port at an intermediate node. We present a practical implementation of network coding in conjunction with error control schemes, namely the Stop-and-Wait (SW) and Selective Repeat (SR) protocols. We propose a modified NC scheme and apply it at an intermediate SW ARQ-based link to reduce ARQ control signals at each transmission. We further extend this work to investigate the usefulness of NC in the Butterfly multicast network which adopts the SR ARQ protocol as an error control scheme. We validate our throughput analysis using a relatively recent discrete-event simulator, SimEvents®. The results show that the proposed scheme offers a throughput advantage of at least 50% over traditional SW ARQ, and that this is particularly noticeable in the presence of high error rates. In the multicast network, however, simulation results show that when compared with the traditional scheme, NC-SR ARQ can achieve a throughput gain of between 2% and 96% in a low bandwidth channel and up to 19% in a high bandwidth channel with errors

Millimeter Wave Cellular Networks: A MAC Layer Perspective

The millimeter wave (mmWave) frequency band is seen as a key enabler of multi-gigabit wireless access in future cellular networks. In order to overcome the propagation challenges, mmWave systems use a large number of antenna elements both at the base station and at the user equipment, which lead to high directivity gains, fully-directional communications, and possible noise-limited operations. The fundamental differences between mmWave networks and traditional ones challenge the classical design constraints, objectives, and available degrees of freedom. This paper addresses the implications that highly directional communication has on the design of an efficient medium access control (MAC) layer. The paper discusses key MAC layer issues, such as synchronization, random access, handover, channelization, interference management, scheduling, and association. The paper provides an integrated view on MAC layer issues for cellular networks, identifies new challenges and tradeoffs, and provides novel insights and solution approaches.Comment: 21 pages, 9 figures, 2 tables, to appear in IEEE Transactions on Communication

The new enhancement of UMTS: HSDPA and HSUPA

During the last two decades, the world of the mobile communications grew a lot, as a consequence of the increasing necessity of people to communicate. Now, the mobile communications still need to improve for satisfies the user demands. The new enhancement of UMTS in concrete HSDPA and HSUPA is one of these improvements that the society needs. HSDPA and HSUPA which together are called HSPA, give to the users higher data rates in downlink and uplink. The higher data rates permit to the operators give more different types of services and at the same time with better quality. As a result, people can do several new applications with their mobile terminals like applications that before a computer and internet connection were required, now it is possible to do directly with the mobile terminal. This thesis consists in study these new technologies denominated HSDPA and HSUPA and thus know better the last tendencies in the mobile communications. Also it has a roughly idea about the future tendencies

Energy Optimization for Hybrid ARQ

Hybrid automatic repeat request (HARQ) \cite{costello1983error} plays an important role in providing reliable and efficient data transmission. In wireless communications, the wireless channel may vary fast, due to the mobility of the transmitter/receiver and the channel. Forward error correction (FEC) and automatic repeat request (ARQ) are two basic techniques to control errors. FEC employs error correction coding, by adding parity bits to the information bits, to combat channel errors. ARQ allows the receiver to request a retransmission of the packet when an error is detected in the received packet. HARQ gives protection to the wireless transmission by combining FEC and ARQ. In typical HARQ systems, redundancy is added to the information bits, and a retransmission is performed until either the packet is successfully decoded, or a maximum number of transmissions is reached.The motivation to optimize the energy consumption of HARQ is the high energy consumption of wireless communications on mobile devices. Wireless devices usually have a limited battery life, and wireless communications consume the majority of the battery energy of mobile devices. One example is that 3G and Wifi units consume more than 50\% of the energy for some smart phones \cite{tawalbeh2016studying}. Another example is that battery depletion has been identified as one of the primary factors that limit the lifetime of wireless sensor networks \cite{verdone2010wireless}.Previous works on HARQ mainly use information-theoretic approach, which assumes that the number of bits in each transmission round is sufficiently large. This assumption does not necessarily hold for actual codes with finite length. Therefore, in this dissertation, we consider HARQ with actual codes. We use turbo-coded HARQ, since turbo codes are well-known capacity-approaching codes \cite{berrou1993near} and widely used in standards such as 3GPP Long-Term Evolution (LTE) \cite{3gpp2007mulltiplexing}. We study the energy optimization for HARQ in two scenarios: the energy optimization for incremental redundancy (IR) HARQ, and the energy optimization for HARQ in wireless video transmission. For IR HARQ, each retransmission contains additional parity bits beyond those of the previous transmissions. For the first scenario, we consider different cases of channel state information (CSI) at the transmitter: the transmitter has no knowledge of any CSI, or knows the CSI in previous transmission rounds through a perfect feedback channel, or knows both current and previous CSI. The transmitter decides the forward error correction code rate based on the CSI it has. We minimize the energy consumption of turbo-coded HARQ, subject to a packet loss rate constraint. Numerical results show that the energy consumption of HARQ decreases when more CSI information is available at the transmitter. We also compare IR combining with both Chase combining and the system without combining, and IR combining yields the least energy consumption.For the second scenario, we formulate the problem as maximizing the video quality, subject to a constraint on the wireless transmission energy consumption. We consider multiple parameters in multiple layers in a wireless video transmission system: transmit power, alphabet size, FEC code rate, maximum number of transmissions and unequal video data importance. An analytical framework is proposed to include these parameters, which allows us to divide this problem into two sub-problems: data transmission and unequal error protection (UEP) for video content. The problem is tackled by solving the two sub-problems, which are done by exhaustive search and convex optimization, respectively. Simulations of different videos show that the proposed scheme outperforms methods using conventional data transmission and/or unequal error protection. For example, in the low SNR region, there is a total gain of 4.8 to 5.6dB on the peak signal-to-noise ratio of the received video compared to video transmission using conventional HARQ without any video UEP

Multicast MAC extensions for high rate real-time traffic in wireless LANs

Nowadays we are rapidly moving from a mainly textual-based to a multimedia-based Internet, for which the widely deployed IEEE 802.11 wireless LANs can be one of the promising candidates to make them available to users anywhere, anytime, on any device. However, it is still a challenge to support group-oriented real-time multimedia services, such as video-on-demand, video conferencing, distance educations, mobile entertainment services, interactive games, etc., in wireless LANs, as the current protocols do not support multicast, in particular they just send multicast packets in open-loop as broadcast packets, i.e., without any possible acknowledgements or retransmissions. In this thesis, we focus on MAC layer reliable multicast approaches which outperform upper layer ones with both shorter delays and higher efficiencies. Different from polling based approaches, which suffer from long delays, low scalabilities and low efficiencies, we explore a feedback jamming mechanism where negative acknowledgement (NACK) frames are allowed from the non-leader receivers to destroy the acknowledgement (ACK) frame from the single leader receiver and prompts retransmissions from the sender. Based on the feedback jamming scheme, we propose two MAC layer multicast error correction protocols, SEQ driven Leader Based Protocol (SEQ-LBP) and Hybrid Leader Based Protocol (HLBP), the former is an Automatic Repeat reQuest (ARQ) scheme while the later combines both ARQ and the packet level Forward Error Correction (FEC). We evaluate the feedback jamming probabilities and the performances of SEQ-LBP and HLBP based on theoretical analyses, NS-2 simulations and experiments on a real test-bed built with consumer wireless LAN cards. Test results confirm the feasibility of the feedback jamming scheme and the outstanding performances of the proposed protocols SEQ-LBP and HLBP, in particular SEQ-LBP is good for small multicast groups due to its short delay, effectiveness and simplicity while HLBP is better for large multicast groups because of its high efficiency and high scalability with respect to the number of receivers per group.Zurzeit vollzieht sich ein schneller Wechsel vom vorwiegend textbasierten zum multimediabasierten Internet. Die weitverbreiteten IEEE 802.11 Drahtlosnetzwerke sind vielversprechende Kandidaten, um das Internet für Nutzer überall, jederzeit und auf jedem Gerät verfügbar zu machen. Die Unterstützung gruppenorientierter Echtzeit-Dienste in drahtlosen lokalen Netzen ist jedoch immer noch eine Herausforderung. Das liegt daran, dass aktuelle Protokolle keinen Multicast unterstützen. Sie senden Multicast-Pakete vielmehr in einer "Open Loop"-Strategie als Broadcast-Pakete, d. h. ohne jegliche Rückmeldung (feedback) oder Paketwiederholungen. In der vorliegenden Arbeit, anders als in den auf Teilnehmereinzelabfragen (polling) basierenden Ansätzen, die unter langen Verzögerungen, geringer Skalierbarkeit und geringer Effizienz leiden, versuchen wir, Multicast-Feedback bestehend aus positiven (ACK) und negativen Bestätigungen (NACK) auf MAC-Layer im selben Zeitfenster zu bündeln. Die übrigen Empfänger können NACK-Frames senden, um das ACK des Leaders zu zerstören und Paketwiederholungen zu veranlassen. Basierend auf einem Feedback-Jamming Schema schlagen wir zwei MAC-Layer-Protokolle für den Fehlerschutz im Multicast vor: Das SEQ-getriebene Leader Based Protocol (SEQ-LBP) und das Hybrid Leader Based Protocol (HLBP). SEQ-LBP ist eines Automatic Repeat reQuest (ARQ) Schema. HLBP kombiniert ARQ und paketbasierte Forward Error Correction (FEC). Wir evaluieren die Leistungsfähigkeit von ACK/NACK jamming, SEQ-LBP und HLBP durch Analysis, Simulationen in NS-2, sowie Experimenten in einer realen Testumgebung mit handelsüblichen WLAN-Karten. Die Testergebnisse bestätigen die Anwendbarkeit der Feedback-Jamming Schemata und die herausragende Leistungsfähigkeit der vorgestellten Protokolle SEQ-LBP und HLBP. SEQ-LBP ist durch seine kurze Verzögerung, seine Effektivität und seine Einfachheit für kleine Multicast-Gruppen nützlich, während HLBP auf Grund seiner hohen Effizienz und Skalierbarkeit im Bezug auf die Größe der Empfänger eher in großen Multicast-Gruppen anzuwenden ist

WIMAX Basics from PHY Layer to Scheduling and Multicasting Approaches

WiMAX (Worldwide Interoperability for Microwave Access) is an emerging broadband wireless technology for providing Last mile solutions for supporting higher bandwidth and multiple service classes with various quality of service requirement. The unique architecture of the WiMAX MAC and PHY layers that uses OFDMA to allocate multiple channels with different modulation schema and multiple time slots for each channel allows better adaptation of heterogeneous user’s requirements. The main architecture in WiMAX uses PMP (Point to Multipoint), Mesh mode or the new MMR (Mobile Multi hop Mode) deployments where scheduling and multicasting have different approaches. In PMP SS (Subscriber Station) connects directly to BS (Base Station) in a single hop route so channel conditions adaptations and supporting QoS for classes of services is the key points in scheduling, admission control or multicasting, while in Mesh networks SS connects to other SS Stations or to the BS in a multi hop routes, the MMR mode extends the PMP mode in which the SS connects to either a relay station (RS) or to Bs. Both MMR and Mesh uses centralized or distributed scheduling with multicasting schemas based on scheduling trees for routing. In this paper a broad study is conducted About WiMAX technology PMP and Mesh deployments from main physical layers features with differentiation of MAC layer features to scheduling and multicasting approaches in both modes of operations

A Scheduling and Resource Allocation Algorithm for LTE Networks Using Tree Structures

Το σύστημα LTE σχεδιάστηκε από τη 3GPP με στόχο την ικανοποίηση των ολοένααυξανόμενων αναγκών για ασύρματη ευρυζωνική πρόσβαση. Τεχνικές όπως το σχήμα πολλαπλής πρόσβασης OFDMA, το MIMOκαι η Προσαρμοστική Διαμόρφωση και Κωδικοποίηση υιοθετήθηκαν προκειμένου να αυξήσουν τους επιτεύξιμους ρυθμούςμετάδοσης και να βελτιώσουν τη φασματική απόδοση. Ωστόσο, απαιτείται η ανάπτυξη εξελιγμένων αλγορίθμωνχρονοπρογραμματισμού προκειμένου να αξιοποιηθεί η πλήρης δυναμική αυτών των τεχνικών. Παρά το γεγονός ότι η 3GPPέχειπροτυποποιήσει πλήρως τη σηματοδοσία ελέγχου που απαιτείται για την εκτέλεση του χρονοπρογραμματισμού, οι αλγόριθμοι πουχρειάζεται να εκτελεστούν προκειμένου να ληφθούν αποδοτικές αποφάσεις έχουν αφεθεί στους κατασκευαστές για υλοποίηση.Ωςεκ τούτου, σημαντική ερευνητική προσπάθεια έχει καταβληθεί προς αυτή την κατεύθυνση και έχουν προταθεί αρκετοίαλγόριθμοιχρονοπρογραμματισμού. Το κύριο συμπέρασμα που εξάγεται από τη μελέτη της βιβλιογραφίας είναι ότι οχρονοπρογραμματισμόςσε ένα σύστημα πολλών φερουσών με τους περιορισμούς του LTE αποτελεί ένα πολυδιάστατο πρόβλημα.Ανάμεσα στις πολλέςδιαστάσεις του, αυτές που κυρίως λαμβάνονται υπόψη στους προτεινόμενους αλγορίθμους είναι ηρυθμαπόδοση, η δικαιοσύνη και η εξασφάλιση εγγυημένης ποιότητας υπηρεσίας.Η κύρια συμβολή της παρούσας διατριβής είναι η πρόταση ενός νέου αλγόριθμου χρονοπρογραμματισμού και διαχείρισης πόρων ο οποίος αντιμετωπίζει τα περισσότερα από τα θέματα που καθορίζουν τησυνολική απόδοση μίας οντότητας χρονοπρογραμματισμού του LTE. Η πρόταση εστιάζει κυρίως στην πολυπλοκότητα πουεισάγεται κατά τη λήψη μίας απόφασης χρονοπρογραμματισμού. Επιχειρεί δε να επιλύσει αυτό το πρόβλημα με την εισαγωγή μίαςεξελιγμένης δενδρικής δομής η οποία επιτρέπει την αποδοτική αποθήκευση όλων των παραμέτρων που θεωρούνται ουσιώδεις στηδιαδικασία λήψης μίας απόφασης χρονοπρογραμματισμού. Με αυτό τον τρόπο η οντότητα χρονοπρογραμματισμού έχει άμεσηπρόσβαση σε αυτές τις πληροφορίες. Στην εργασία περιγράφεται ένας πλήρης αλγόριθμος προγραμματισμού στο πεδίο τουχρόνου που αξιοποιεί αυτή τη δενδρική δομή και επιπλέον προτείνονται δύο νέοι αλγόριθμοι κατανομής πόρων. Οι αλγόριθμοιαυτοί επίσης αξιοποιούν κάποιες επιπρόσθετες δενδρικές δομές οι οποίες παράγονται ύστερα από κατάλληλη προ-επεξεργασίαπου λαμβάνει χώρα πριν τη λήψη της απόφασης χρονοπρογραμματισμού. Ο πρώτος αλγόριθμος παρουσιάζει χαμηλήπολυπλοκότητα και ικανοποιητική απόδοση ενώ ο δεύτερος βελτιωμένη απόδοση με το κόστος κάποιας επιπρόσθετηςπολυπλοκότητας. Αποτελέσματα εκτεταμένων προσομοιώσεων επιβεβαιώνουν την ικανότητα του προτεινόμενου σχήματος στηνικανοποίηση των αυστηρών απαιτήσεων του LTE σε ότι αφορά την ποιότητα υπηρεσίας, ενώ ταυτόχρονα η απόδοση τωνπροτεινόμενων αλγορίθμων συγκρίνεται με γνωστές τεχνικές χρονοπρογραμματισμού. Οι προτεινόμενες λύσεις είναι εφαρμόσιμες μόνο στην περίπτωση της κατωφερούς ζεύξης, ωστόσο η ίδια ιδέα μπορεί να προσαρμοστεί κατάλληλα για να παρέχει μία αποδοτική λύση και στην περίπτωση της ανωφερούς ζεύξηςLong Term Evolution (LTE) has been designed by 3GPP with the target to meet the ever increasing demands in broadband wireless access. Techniques such as OFDMA multiple access scheme, MIMO and Adaptive Modulation and Coding (AMC) have been adopted in order to boost the achieved data rates and improve spectral efficiency. However, the development of sophisticated scheduling algorithms is required so that the full potential of those techniques is exploited. Even though 3GPP has fully standardized the control signaling required to perform scheduling, the algorithms that need to be executed to make efficient decisions are left to vendor implementation. Therefore significant research effort has been dedicated to this direction and several scheduling algorithms have been proposed. The main conclusion drawn from the study of the literature is that scheduling in a multicarrier system with the restrictions of LTE constitutes a multidimensional problem. Among the multiple dimensions, those that are mostly considered in the proposed algorithms are throughput, fairness and QoS guarantee. The main contribution of this thesis is to propose a new scheduling algorithm that addresses most of the issues that define the overall performance of an LTE scheduler. The proposal focuses mainly on the complexity involved in making a scheduling decision. It attempts to resolve this issue by the introduction of a sophisticated tree structure that enables the efficient storage of all the parameters that are considered essential in the scheduling decision process. Thus the scheduler can have immediate access to this information. A full time domain scheduling algorithm that utilizes this tree structure is described and two new resource allocation algorithms are proposed. These algorithms also utilize some additional tree structures derived from appropriate preprocessing actions that take place before the actual scheduling decision. The first algorithm has low complexity and satisfactory performance while the second has improved performance with the cost of some additional complexity. Extensive simulation results confirm the capability of the proposed scheme in satisfying the strict QoS requirements of LTE, while the performance of the newly proposed algorithms is compared with well-known scheduling techniques. The proposed solutions are applicable to the downlink case, while the same concept may be adapted properly to provide an efficient solution for the uplink case