ABSTRACT
The 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. 

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 
correlation coefficient between the powers of a pair of sub-carriers in terms of the 
parameters defined in proposed models by the IEEE. This estimation method is 
called PSAM (Pilot Symbol Assisted Modulation).

Once knowed the channel state information and defined the metric that allows 
its evaluation, we calculate and validate through simulation the performance of 
adaptive multilevel modulation with constant envelope M-PSK and MB-OFDM 
transmission. We propose closed-form expressions for the average capacity in bits per 
symbol, the bit error probability average and the outage probability. We also find 
expressions for the distribution and the statistical parameters of the estimation error 
in the case of imperfect channel estimation. 

On the other hand, from the result obtained for statistical distribution of 
the amplitude of each sub-carrier in the frequency domain, in this thesis are 
studied the variation of the received power as a function of the bandwidth channel 
due to the fading small-scale. Analytical expressions for the fade depth and the 
fade margin validated through simulations are of special interest in the link budget 
evaluation in wireless mobil communication systems