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

Beyond the Bits: Cooperative Packet Recovery Using Physical Layer Information

PhD thesisWireless networks can suffer from high packet loss rates. This paper shows that the loss rate can be significantly reduced by exposing information readily available at the physical layer. We make the physical layer convey an estimate of its confidence that a particular bit is ``0'' or ``1'' to the higher layers. When used with cooperative design, this information dramatically improves the throughput of the wireless network. Access points that hear the same transmission combine their information to correct bits in a packet with minimal overhead. Similarly, a receiver may combine multiple erroneous transmissions to recover a correct packet. We analytically prove that our approach minimizes the errors in packet recovery. We also experimentally demonstrate its benefits using a testbed of GNU software radios. The results show that our approach can reduce loss rate by up to 10x in comparison with the current approach, and significantly outperforms prior cooperation proposals

The Poisson multiple access channel

Cover title. "Presented in part at IEEE Info Theory Workshop, June 9-13, Haifa, Israel."Includes bibliographical references (p. 29-32).Research supported by the Laboratory for Information and Decision Systems, Massachusetts Institute of Technology. DAAH04-95-1-0103Lapidoth, A., Shamai, Shlomo (Shitz)

OFDM-based schemes for next generation wireless systems

The purpose of this study is to investigate two candidate waveforms for next generation wireless systems, filtered Orthogonal Frequency Division Multiplexing (f-OFDM) and Unified Filtered Multi-Carrier (UFMC). The evaluation is done based on the power spectral density analysis of the signal and performance measurements in synchronous and asynchronous transmission. In f-OFDM we implement a soft truncated filter with length 1/3 of OFDM symbol. In UFMC we use the Dolph-Chebyshev filter, limited to the length of zero padding (ZP). The simulation results demonstrates that both waveforms have a better spectral behaviour compared with conventional OFDM. However, the induced inter-symbol interference (ISI) caused by the filter in f-OFDM, and the inter-carrier interference (ICI) induced in UFMC due to cyclic prefix (CP) reduction , should be kept under control. In addition, in a synchronous transmission case with ideal parameters, f-OFDM and UFMC appear to have similar performance with OFDM. When carrier frequency offset (CFO) is imposed in the transmission, UFMC outperforms OFDM and f-OFDM

Networking Aspects based on the Talkative Power Concept for DC Microgrid Systems

The talkative power concept is a simultaneous power-line communication and energy transfer technique which integrates data modulation into a power converter. The information sequence is deterministically represented by the ripple, which superimposes the output voltage. With a few exceptions, so far emphasis has been on scenarios where only a single node is actively transmitting data in a certain time slot in simplex mode. In microgrid applications, however, multiple active power sources are of interest as well. Examples include battery management systems, smart metering, electricity trading systems, and smart grids with several power sources, energy storage devices, loads, and data receivers. In this contribution, bus networking aspects based on the talkative power concept are presented for scenarios with several active nodes and for full-duplex communication. The paper addresses potential multiple access techniques as well as duplexing schemes for connected power converters supporting bidirectional power and information flow. In numerical results, a spread spectrum scheme based on orthogonal variable spreading factor codes in conjunction with frequency shift keying (FSK) is presented for four simultaneously active buck converters with a sum data rate of 500 kbps at a switching frequency of 1 MHz. In general, with 2-ary FSK, the maximum achievable sum data rate is half of the switching frequency in a synchronous setup

Ultra Wide Band Multiple Access Performance Using TH-PPM and DS-BPSK Modulations

The increasing demand for portable, high data rate communications has focused much attention on wireless technology. Ultra Wide Band (UWB) waveforms have the ability to deliver megabits of information while maintaining low average power consumption. In accordance with recent FCC ruling, UWB systems are now allowed to operate in the unlicensed spectrum of 3.1 to 10.6 GHz, motivating renewed interest in the forty year old concept of impulse radio. Gaussian monocycles produce UWB waveforms occupying large bandwidths with multiple access (MA) capability enabled by spread spectrum techniques. Time Hopping (TH) and Direct Sequence (DS) modulations are considered here for UWB MA applications. This work extends Gold coding results and characterizes UWB performance using Simulated Annealing (SA) and Random Integer (RI) codes for TH and DS UWB applications. TH-PPM and DS-BPSK performance is evaluated using simulated probability of bit error P(sub b) under MA interference (MAI), multipath interference (MPI), and narrow band interference (NBI) conditions for synchronous and asynchronous networks

Techniques for improving the performance of frequency-hopped multiple-access communication systems

Imperial Users onl

TDRSS telecommunications study. Phase 1: Final report

A parametric analysis of the telecommunications support capability of the Tracking and Data Relay Satellite System (TDRSS) was performed. Emphasis was placed on maximizing support capability provided to the user while minimizing impact on the user spacecraft. This study evaluates the present TDRSS configuration as presented in the TDRSS Definition Phase Study Report, December 1973 to determine potential changes for improving the overall performance. In addition, it provides specifications of the user transponder equipment to be used in the TDRSS