Packet data communications over coded CDMA with hybrid type-II ARQ

This dissertation presents in-depth investigation of turbo-coded CDNIA systems in packet data communication terminology. It is divided into three parts; (1) CDMA with hybrid FEC/ARQ in deterministic environment, (2) CDMA with hybrid FEC/ARQ in random access environment and (3) an implementation issue on turbo decoding. As a preliminary, the performance of CDMA with hybrid FEC/ARQ is investigated in deterministic environment. It highlights the practically achievable spectral efficiency of CDMA system with turbo codes and the effect of code rates on the performance of systems with MF and LMMSE receivers, respectively. For given ensemble distance spectra of punctured turbo codes, an improved union bound is used to evaluate the error probability of ML turbo decoder with MF receiver and with LMMSE receiver front-end and, then, the corresponding spectral efficiency is computed as a function of system load. In the second part, a generalized analytical framework is first provided to analyze hybrid type-11 ARQ in random access environment. When applying hybrid type-11 ARQ, probability of packet success and packet length is generally different from attempt to attempt. Since the conventional analytical model, customarily employed for ALOHA system with pure or hybrid type-I ARQ, cannot be applied for this case, an expanded analytical model is introduced. It can be regarded as a network of queues and Jackson and Burke\u27s theorems can be applied to simplify the analysis. The second part is further divided into two sub topics, i.e. CDMA slotted ALOHA with hybrid type-11 ARQ using packet combining and CDMA unslotted ALOHA with hybrid type-11 ARQ using code combining. For code combining, the rate compatible punctured turbo (RCPT) codes are examined. In the third part, noticing that the decoding delay is crucial to the fast ARQ, a parallel MAP algorithm is proposed to reduce the computational decoding delay of turbo codes. It utilizes the forward and backward variables computed in the previous iteration to provide boundary distributions for each sub-block MAP decoder. It has at least two advantages over the existing parallel scheme; No performance degradation and No additional computation

大規模多元接続ネットワークのためのグラフ構造に基づくランダムアクセス方式

電気通信大学201

Arrival Rate Estimation Algorithm for Single Group Slotted ALOHA Systems

Abstract-In this letter, a new recursive tracking algorithm is presented that is capable of estimating the real arrival rate, real , to the system. The estimated value of the arrival rate, estimated , is used to dynamically adjust the control parameters of the system, hence ensuring that the operating point of the system is pushed toward the required settling point, whatever the real arrival rate to the system. This algorithm utilizes system information through the feedback channel in order to dynamically adjust the estimated value of the arrival rate and hence update the values of the control parameters

Performance evaluation of packet radio networks

The first ground wireless packet switching radio network, named the ALOHA network, was implemented in the early 1970s at University of Hawaii. The most distinct features of a packet radio network are: (1) the absence of physical connections between users, (2) the sharing of a common transmission medium, and (3) the broadcasting capability of each user. Today, the packet radio network technology is widely used in a variety of civilian as well as military applications;The throughput of a packet radio network is defined as the percentage of time the channel carries good packets. It is largely determined by the channel access method, the signal propagation characteristics, and the capture effect at a receiver. In this dissertation, we present two packet radio network models under the Slotted ALOHA channel access method and a capture model which is based on the relative strength of signal powers of the desired packet and the interfering packets;The first model is a single-hop network with a central station and finite number of users randomly distributed in a limited area. All the users communicate with each other through the central station, which is within one hop distance of all users. Given a density distribution function for the distance of a user, we show that there is an optimal transmission probability which maximizes the throughput of the network. Also, under a light traffic load, the throughput of a remote user is relatively insensitive to its distance from the station;The second model is a multi-hop network where a user is equipped with a directional antenna and not every user can directly communicate with every other else. As a result, a user communicates with another user either directly in a single hop or through some intermediate users in multiple hops. The location of all users is modeled by a two-dimensional Poisson process with an average of [lambda] users per unit area. By balancing the transmission probability and the antenna beam width, we show that the maximum hop-by-hop progress of a packet can be achieved when the transmitter and the receiver are separated by an optimal distance

Tree LANS with collision avoidance : protocol, switch architecture, and performance

Packet collisions and their resolution create a performance bottleneck in random access LANs. A hardware solution to this problem is to use collision avoidance switches. These switches allow the implementation of random access protocols without the penalty of collisions among packets. We review and compare the designs of some tree LANs that use collision avoidance switches. They have the potential of combining the benefits of random access (low delay when traffic is light, simple and distributed, and therefore robust, protocols) with excellent network utilization and concurrency of transmission. The collision avoidance LANs we review are broadcast star, Hubnet-like tree, Tinker-Tree, and a treenet that allows concurrent broadcasts within non-intersecting subtrees. After this review, we present a slotted-time, infinite user analysis of the broadcast star network

Energy-efficient diversity combining for different access schemes in a multi-path dispersive channel

Dissertação para obtenção do Grau de Doutor em Engenharia Electrotécnica e ComputadoresThe forthcoming generation of mobile communications, 5G, will settle a new standard for a larger bandwidth and better Quality of Service (QoS). With the exploding growth rate of user generated data, wireless standards must cope with this growth and at the same time be energy efficient to avoid depleting the batteries of wireless devices. Besides these issues, in a broadband wireless setting QoS can be severely affected from a multipath dispersive channel and therefore be energy demanding. Cross-layered architectures are a good choice to enhance the overall performance of a wireless system. Examples of cross-layered Physical (PHY) - Medium Access Control (MAC) architectures are type-II Diversity Combining (DC) Hybrid-ARQ (H-ARQ) and Multi-user Detection (MUD) schemes. Cross-layered type-II DC H-ARQ schemes reuse failed packet transmissions to enhance data reception on posterior retransmissions; MUD schemes reuse data information from previously collided packets on posterior retransmissions to enhance data reception. For a multipath dispersive channel, a PHY layer analytical model is proposed for Single-Carrier with Frequency Domain Equalization (SC-FDE) that supports DC H-ARQ and MUD. Based on this analytical model, three PHY-MAC protocols are proposed. A crosslayered Time Division Multiple Access (TDMA) scheme that uses DC H-ARQ is modeled and its performance is studied in this document; the performance analysis shows that the scheme performs better with DC and achieves a better energy efficiency at the cost of a higher delay. A novel cross-layered prefix-assisted Direct-Sequence Code Division Multiple Access (DS-CDMA) scheme is proposed and modeled in this document, it uses principles of DC and MUD. This protocol performs better by means of additional retransmissions, achieving better energy efficiency, at the cost of higher redundancy from a code spreading gain. Finally, a novel cross-layered protocol H-ARQ Network Division Multiple Access (H-NDMA) is proposed and modeled, where the combination of DC H-ARQ and MUD is used with the intent of maximizing the system capacity with a lower delay; system results show that the proposed scheme achieves better energy efficiency and a better performance at the cost of a higher number of retransmissions. A comparison of the three cross-layered protocols is made, using the PHY analytical model, under normalized conditions using the same amount of maximum redundancy. Results show that the H-NDMA protocol, in general, obtains the best results, achieving a good performance and a good energy efficiency for a high channel load and low Signal-to-Noise Ratio (SNR). TDMA with DC H-ARQ achieves the best energy efficiency, although presenting the worst delay. Prefix-assisted DS-CDMA in the other hand shows good delay results but presents the worst throughput and energy efficiency