WIRELESS NETWORK COCAST: COOPERATIVE COMMUNICATIONS WITH SPACE-TIME NETWORK CODING

Traditional cooperative communications can greatly improve communication performance. However, transmissions from multiple relay nodes are challenging in practice. Single transmissions using time-division multiple access cause large transmission delay, but simultaneous transmissions from two or more nodes using frequency-division multiple access (FDMA), code-division multiple access (CDMA), or distributed space-time codes are associated with the issues of imperfect frequency and timing synchronization due to the asynchronous nature of cooperation. In this dissertation, we propose a novel concept of wireless network cocast (WNC) and develop its associated space-time network codes (STNCs) to overcome the foretold issues. In WNC networks, each node is allocated a time slot for its transmission and thus the issues of imperfect synchronization are eliminated. To reduce the large transmission delay, each relay node forms a unique signal, a combination of the overheard information, and transmits it to the intended destination. The combining functions at relay nodes form a STNC that ensures full spatial diversity for the transmitted information as in traditional cooperative communications. Various traditional combining techniques are utilized to design the STNCs, including FDMA-like and CDMA-like techniques and transform-based techniques with the use of Hadamard and Vandermonde matrices. However, a major distinction is that the combination of information from different sources happens within a relay node instead of through the air as in traditional cooperative communications. We consider a general case of multiuser relay wireless networks, where user nodes transmit and receive their information to and from a common base node with the assistance from relay nodes. We then apply the STNCs to multiuser cooperative networks, in which the user nodes are also relay nodes helping each other in their transmission. Since the cooperative nodes are distributed around the network, the node locations can be an important aspect of designing a STNC. Therefore, we propose a location-aware WNC scheme to reduce the aggregate transmit power and achieve even power distribution among the user nodes in the network. WNC networks and its associated STNCs provide spatial diversity to dramatically reduce the required transmit power. However, due to the additional processing power in receiving and retransmitting each other's information, not all nodes and WNC networks result in energy efficiency. Therefore, we first examine the power consumption in WNC networks. We then offer a TDMA-based merge process based on coalitional formation games to orderly and efficiently form cooperative groups in WNC networks. The proposed merge process substantially reduces the network power consumption and improves the network lifetime

Baseband Implementation and Performance Analysis of the Multiband OFDM UWB System

In this thesis, we follow the standard proposal IEEE 802.12.3a to implement the MB-OFDM UWB system in C programming language. We also analyze the system performance in the multipath fading channel, the IEEE 802.15.3a channel standard. Four different conditions of frequency and timing synchronization are considered. Since the entire system consists of two subsystems: (a) the channel coding with the bit-interleaving and (b) OFDM modulation, the analysis is proceeded in two stages. First, we consider the performance of the only OFDM subsystem. Degradation ratio and average bit error probability are the two metrics used to evaluate the performance. Secondly, we provide the performance bound of the entire UWB system. The performance analysis provides a good understanding of the system behavior in the IEEE 802.15.3a channel standard under various synchronization conditions. The knowledge about the performance of the MB-OFDM UWB system defines our main contribution to the area of wireless communications

Hybrid Surface-Enhanced Raman Scattering Substrate from Gold Nanoparticle and Photonic Crystal: Maneuverability and Uniformity of Raman Spectra

[[abstract]]A novel hybrid surface-enhanced Raman scattering (SERS) substrate based on Au nanoparticles decorated inverse opal (IO) photonic crystal (PhC) is presented. In addition to the enhancement contributed from Au nanoparticles, a desired Raman signal can be selectively further enhanced by appropriately overlapping the center of photonic bandgap of the IO PhC with the wavelength of the Raman signal. Furthermore, the lattice structure of the IO PhC provides excellent control of the distribution of Au nanoparticles to produce SERS spectra with high uniformity. The new design of SERS substrate provides extra maneuverability for ultra-high sensitivity sensor applications.[[notice]]補正完

Multipoint-to-point and point-to-multipoint space-time network coding

Traditional cooperative communications can improve communication reliability. However, the simultaneous transmissions from multiple relays are challenging in practice due to the issue of imperfect frequency and timing synchronization. In this work, we propose space-time network codes (STNCs) that overcome the issue of imperfect synchronization, reduce the large transmission delay, and still provide full spatial diversity in multipoint-to-point (M2P) and point-to-multipoint (P2M) transmissions. Relays form single linearly-coded signals from the overheard symbols and transmit them to the destination, where multiuser detection is utilized to detect the desired symbol. For a network of N client nodes, M2P and P2M STNCs result in a diversity order of N with only 2N time slots, a significant reduction from N 2 time slots in traditional cooperative communications using TDMA. Index Terms — Space-time network coding, cooperative communications, frequency synchronization, timing synchronization 1