Cooperative Communication with Systematic Raptor Codes in 3GPP

In this thesis, considering a one-relay cooperative system, we propose a new cooperative transmission scheme which implements the systematic Raptor code standardized in 3GPP. Within the framework of this scheme, we compare the bandwidth efficiency perfomance of different relaying protocols. To improve the performance of this cooperative system, we use Reed-Solomon(RS) code as inner code which is concatenated with the systematic Raptor code. We first study the scenario when Channel State Information(CSI) is available at the receiver but not available at the transmitter. In this case, only fixed-rate RS code can be implemented. Then we study the scenario when CSI is available at both the transmitter and receiver, and develop an adaptive scheme applied to our model. Last, a straight forward channel estimation method is studied to make the estimation of CSI available at the transmitter. The performance of all the proposed models and protocols are obtained with Monte Carlo simulation

FPGA Implementation of encoders for CCSDS Low-Density Parity-Check (LDPC) codes.

Η παρούσα διπλωματική εργασία παρουσιάζει την υλοποίηση με τεχνολογία FPGA αλγορίθμων κωδικοποίησης καναλιού που έχουν προτυποποιηθεί από τον οργανισμό CCSDS για χρήση σε διαστημικές επικοινωνίες. Ο CCSDS προτείνει δύο κατηγορίες κωδίκων για εφαρμογές τηλεμετρίας: μία για επικοινωνίες στο εγγύς (near-earth) διάστημα (π.χ. δορυφορικές επικοινωνίες) και άλλη μια για επικοινωνίες βαθέος διαστήματος (deep-space), με χαρακτηριστικά η κάθε μία βελτιστοποιημένα ως προς το πεδίο εφαρμογής τους. Και στις δύο περιπτώσεις, οι κώδικες είναι γραμμικοί μπλοκ κώδικες με μεγάλο μέγεθος μπλοκ και πίνακα ισοτιμίας με χαμηλή πυκνότητα (LDPC). Στην παρούσα εργασία, γίνεται εκμετάλλευση της δομής των πινάκων-γεννητόρων των κωδίκων deep-space προκειμένου να μεγιστοποιηθεί η απόδοση. Προκύπτουν δύο ειδών παραλληλίες στη δομή των εν λόγω πινάκων, η ταυτόχρονη αξιοποίηση των οποίων οδηγεί σε βελτίωση των επιδόσεων με ελαχιστοποίηση των καταναλισκόμενων πόρων. Αντίστοιχα στην περίπτωση του κώδικα near-earth, περιγράφεται μια αποδοτική μέθοδος στη σχεδίαση των επί μέρους οντοτήτων του κυκλώματος που βελτιστοποιεί την αξιοποίηση των πόρων, σε σχέση με γνωστές λύσεις. Η περιγραφή των κωδικοποιητών σε VHDL επαληθεύεται ως προς την ορθή της σχεδίαση με προσομοιώσεις για όλες τις υποστηριζόμενες περιπτώσεις, όπου απαιτείται η μέγιστη κάλυψη κώδικα (code coverage). Τέλος, το σχέδιο επαλήθευσης περιλαμβάνει την επίδειξη λειτουργίας σε ένα ενσωματωμένο σύστημα υλοποιημένο στην κάρτα XUPV505-LX110T, όπου καταγράφονται και οι πραγματικές επιδόσεις του συστήματος, όπου βρίσκονται στην περιοχή των μερικών Gbps. Η παρούσα υλοποίηση προκύπτει ότι είναι η ταχύτερη για την συγκεκριμένη οικογένεια LDPC κωδικών, που έχει επιτευχθεί μέχρι σήμερα.The FPGA implementation of LDPC encoders for channel codes standardized by CCSDS for space communication applications is described in this work. CCSDS suggests two classes of channel codes for telemetry applications: one for near-earth and another for deep-space communications, each one optimized for the demands of the specific field. In both cases, the specification concerns linear block codes with large block size and sparse generator matrices. Regarding near-earth codes, the specification describes a Euclidean geometry based (8160,7136) LDPC code at rate 7/8, while in the deep-space case, 9 codes are defined which are the combination of thee block lengths (1024,4096,16384 bits) with three rates (½, 2/3, 4/5), sharing a common mathematical description. This fact enables the VHDL description of a common encoder for all of them. The generator matrices of these codes possess considerable structure which facilitates implementation. Concerning deep-space codes generator matrices, parallelism extends over two dimensions, which can be exploited concurrently to optimize timing performance and at the same time minimize resource utilization. The price to be paid however is increased latency, which can be mitigated by the pipelined operation of the output interface. VHDL description of the encoder is generic, allowing the easy modification of the code parameters (block size, rate), the amount of parallelism in each dimension and the input-output bus width, leading to different performance-latency balances. Also in the case of the near-earth code, an efficient design of the encoder's sub-entities is described, leading to resources utilization optimizations, compared to existing implementations. The encoder in this case is designed for 16-bit input-output bus. All described encoders input-output is performed on AMBA AXI-4 Stream compliant interfaces, facilitating their integration in an embedded system's design and communication with standard FIFO interfaces. The encoders' operation is optimal in that an uninterrupted flow of data is provided on the output interface, without idle cycles. The only exception is the near-earth encoder for which just one idle cycle every 513 is inserted. The correctness of the VHDL description's is validated by functional simulation for all supported cases, where 100% code coverage is demanded. The verification plan includes also the demonstration of real-time operation of the encoders in an integrated system implemented on a XUPV505-LX110T development board, where the actual performance of the encoders is recorded and lies in the multi-Gbps range. Finally, the proposed encoders are shown to be the fastest stream-oriented implementations for the specified family of LDPC codes, with minimal resource utilization

逐次干渉除去を用いた多元接続システムのパワー割り当てに関する研究

In future wireless communication networks, the number of devices is likely to increase dramatically due to potential development of new applications such as the Internet of Things (IoT). Consequently, radio access network is required to support multiple access of massive users and achieve high spectral efficiency. From the information theoretic perspective, orthogonal multiple access protocols are suboptimal. To achieve the multiple access capacity, non-orthogonal multiple access protocols and multiuser detection (MUD) are required. For the non-orthogonal code-division multiple access (CDMA), several MUD techniques have been proposed to improve the spectrum efficiency. Successive interference cancellation (SIC) is a promising MUD techniques due to its low complexity and good decoding performance. Random access protocols are designed for the system with bursty traffic to reduce the delay, compared to the channelized multiple access. Since the users contend for the channel instead of being assigned by the base station (BS), collisions happen with a certain probability. If the traffic load becomes relatively high, the throughput of these schemes steeply falls down because of collisions. However, it has been well-recognized that more complex procedures can permit decoding of interfering signals, which is referred to as multi-packet reception (MPR). Also, an SIC decoder might decode more packets by successively subtracting the correctly decoded packets from the collision. Cognitive radio (CR) is an emerging technology to solve the problem of spectrum scarcity by dynamically sharing the spectrum. In the CR networks, the secondary users (SUs) are allowed to dynamically share the frequency bands with primary users (PUs) under primary quality-of-service (QoS) protection such as the constraint of interference temperature at the primary base station (PBS). For the uplink multiple access to the secondary base station (SBS), transmit power allocation for the SUs is critical to control the interference temperature at the PBS. Transmit power allocation has been extensively studied in various multiple access scenarios. The power allocation algorithms can be classified into two types, depending on whether the process is controlled by the base station (BS). For the centralized power allocation (CPA) algorithms, the BS allocates the transmit powers to the users through the downlink channels. For the random access protocols, there are also efforts on decentralized power allocation (DPA) that the users select transmit powers according to given distributions of power and probability, instead of being assigned the transmit power at each time slot by the BS. In this dissertation, the DPA algorithms for the random access protocols with SIC are investigated and new methods are proposed. First a decentralized multilevel power allocation algorithm to improve the MAC throughput performance is proposed, for the general SIC receiver that can decode multiple packets from one collision. Then an improved DPA algorithm to maximize the overall system sum rate is proposed, taking into account of both the MAC layer and PHY layer. Finally, a DPA algorithm for the CR secondary random access is proposed, considering the constraint of interference temperature and the practical assumption of imperfect cancellation. An opportunistic transmission protocol for the fading environment to further reduce the interference temperature is also proposed. For the future work, the optimal DPA for the random access with the SIC receiver is still an open problem. Besides, advanced multiple access schemes that aim to approach the multiple access capacity by combining the advantages of the network coded cooperation, the repetition slotted ALOHA, and the SIC receiver are also interesting.電気通信大学201