Modelado en frecuencia del canal UWB y su aplicación en el análisis de técnicas de modulación adaptativa en sistemas MB-OFDM UWB para redes WPAN

Abstract

Modelado en frecuencia del canal UWB y su aplicación en el análisis de técnicas de modulación adaptativa en sistemas MB-OFDM UWB para redes WPAN ABSTRACTThe current trend to integrate the different services and applications on a single network infrastructure has generated a growing deployment of wireless wide area network (WWAN), local area network (WLAN) and personal area network (WPAN) with differentiated traffic requirements (QoS), security and high bit rate transmission, requires the development of protocols and new transmission techniques that allow better integration of applications and communications services in a environment hostile, as the mobile wireless channel with multipath propagation.One of the greatest challenges for carrying out this integration is to achieve a communication link with certain quality and high transmission capacity.The combination of adaptive modulation and coding techniques in conjunction with multicarrier transmission such as OFDM (Orthogonal Frequency Division Multiplexing) and other advanced technologies such as MIMO-UWB (transmission and reception with multiple antennas in ultra wideband systems) represents a powerful tool to improve the performance and allow compliance with the goals and challenges defined by these networks.This thesis deals with the improvement the quality and capacity of transmission in a WPAN networks, using the standard MB-OFDM (OFDM over multiple bands) in UWB channels with adaptive modulation performing a discrete rate adaptation of bits transmitted per sub-carrier.The basic principle of a modulation scheme and/or adaptive coding is to obtain information on the characteristics, structure and variability of the wireless mobile channel. With the information obtained from the receiver the transmitter adapts the symbol transmission rate, constellation size, coding rate or any combination of these parameters based on the channel state information. This Ph.D dissertation begins with an analysis in time and frequency domain of the two UWB channel proposed models by the IEEE 802.15.3a and IEEE 802.15.4a working groups. The objective is to determine the statistical distribution that best approximates the amplitude of each sub-carriers in frequency domain, and later to define the metric to use in the assessing the UWB channel state and dynamics. v The adaptive modulation requires the transmitter to adapt to the variability of the channel. The analysis can be done in two ways• Assuming perfect adaptation (ideal estimation) which implies that the transmitter always knows the dynamics and structure of the channel.• Assuming an error (imperfect channel estimation) in the adaptation due to uncertainty in the knowledge of the channel.The estimation method of the UWB channel used in this thesis is based on the knowledge of the power correlation coefficient between data sub-carriers and pilot sub-carrier, given that the position of each in the spectrum is well defined according to the MB-OFDM standard. We propose a closed-form expression to calculate the correla...