Section 1.4. The MC-UWB System Model

1.4. The MC-UWB System Model

1.4.1. Overview of the MC-UWB System

In the past several years, MC-UWB (also called frequency domain UWB) has received a significant amount of attention. The transmit MC-UWB signal s(t) has the following complex baseband form

Equation 1.18

where N is the number of subcarriers, is the symbol that is transmitted in the r^th transmission interval over the n^th subcarrier, and A is a constant that controls the transmitted power spectral density and determines the energy per bit. The fundamental frequency is .

1.4.2. OFDM UWB

OFDM is a special case of multicarrier transmission that permits subcarriers to overlap in frequency without mutual interference and hence spectral efficiency is increased. Multiple users can be supported by allocating each user a group of sub-carriers. OFDM-UWB is a novel system that has been proposed as a physical layer for high bit rate, short-range communication networks. Reliable communication systems achieve high throughput by transmitting multiple data streams in parallel on separate carrier frequencies. Unlike narrowband OFDM, the OFDM-UWB spectrum can have gaps between subcarriers. OFDM-UWB is one proposed physical layer standard for 802.15.3a Wireless Personal Area Networks.

OFDM-UWB uses a frequency coded pulse train as a shaping signal. The frequency coded pulse train is defined by

Equation 1.19

where s (t) is an elementary pulse with unit energy and duration T_s < T, and p (t) has duration T_p = NT. Each pulse is modulated with a frequency where c (n) is a permutation of the integers {1, 2,...,N}. As shown in Chapter 6, the set is orthogonal for k = 1, 2,...,N.