**6. Multiband OFDM (MB-OFDM) scheme and transceiver architecture**

According to (Batra et al., 2003, 2004a, 2004b), Multiband OFDM (MB-OFDM) scheme divides the available band into 14 sub-bands of 528 MHz each, as illustrated in Fig. 5. Each subband contains 128 subcarriers of which 10 are used for guard tones and can be used for various purposes, 12 are dedicated to the pilot signals and 100 are for information. It can be seen from the figure, each band group being made from three consecutive sub-bands, except for the fifth one which encompasses only the last two sub-bands. A WiMedia compatible device uses only one out of these six defined channels. Initially, most of the studies done in the literature have been performed on the first band group from 3.1 to 4.8 GHz.

The MB-OFDM system can transmit information at different data rates varying from 53.3 to 480 Mbps, listed in Table 1. These data rates are obtained through the use of different convolutional coding rates, frequency-domain spreading (FDS) and time-domain spreading (TDS) techniques. FDS consists in transmitting each complex symbol and its conjugate symmetric within the same OFDM symbol. It is used for the modes with data rates of 53.3 and 80 Mbps. With the TDS, the same information is transmitted during two consecutive OFDM symbols using a time-spreading factor of 2. It is applied to the modes with data rates between 53.3 and 200 Mbps.

In MB-OFDM, quadrature phase-shift keying (QPSK) and dual carrier modulation (DCM) are used for data modulation. For data rates lower than 320 Mbps, the constellation applied to the different subcarriers using quadrature phase-shift keying (QPSK) and for data rates of 320 Mbps and higher, the binary data is mapped onto two different 16-point constellations using a dual-carrier modulation (DCM) technique.

As illustrated the MB-OFDM transmitter in Fig. 6, the first LO1 signal down-converts RF signals to a fixed IF which is further down converted to another IF by LO2. As a unique feature of MB-OFDM transceiver, a single RF mixer is proposed for both RF to IF down conversion in the receiver and IF to RF up conversion in the transmitter.

**Figure 5.** MB-OFDM system

**Figure 5.** MB-OFDM system

**5.4. Variable Gain Amplifier** 

between 53.3 and 200 Mbps.

using a dual-carrier modulation (DCM) technique.

5–6 GHz for IEEE 802.11a wireless local area networks (WLANs). To avoid the frequency use of WLAN radio signals, the direct sequence ultra-wideband (DS–UWB) specifications for wireless personal area networks (WPANs) need further to divide into a low band of 3.1–

Variable gain amplifier (VGA) is an essential block at the front end of ultra-wideband transceiver to maximize the dynamic range of the receivers. VGAs are also used in the transmitter part of ultra-wideband transceivers to control the transmission signal power. The VGA is typically implanted in an automatic gain control amplifier (AGC) loops to provide constant output signal regardless the variations in the input signal. The variable gain amplifier suppresses even harmonics, rejects common-mode noises and provides good

**6. Multiband OFDM (MB-OFDM) scheme and transceiver architecture** 

the literature have been performed on the first band group from 3.1 to 4.8 GHz.

According to (Batra et al., 2003, 2004a, 2004b), Multiband OFDM (MB-OFDM) scheme divides the available band into 14 sub-bands of 528 MHz each, as illustrated in Fig. 5. Each subband contains 128 subcarriers of which 10 are used for guard tones and can be used for various purposes, 12 are dedicated to the pilot signals and 100 are for information. It can be seen from the figure, each band group being made from three consecutive sub-bands, except for the fifth one which encompasses only the last two sub-bands. A WiMedia compatible device uses only one out of these six defined channels. Initially, most of the studies done in

The MB-OFDM system can transmit information at different data rates varying from 53.3 to 480 Mbps, listed in Table 1. These data rates are obtained through the use of different convolutional coding rates, frequency-domain spreading (FDS) and time-domain spreading (TDS) techniques. FDS consists in transmitting each complex symbol and its conjugate symmetric within the same OFDM symbol. It is used for the modes with data rates of 53.3 and 80 Mbps. With the TDS, the same information is transmitted during two consecutive OFDM symbols using a time-spreading factor of 2. It is applied to the modes with data rates

In MB-OFDM, quadrature phase-shift keying (QPSK) and dual carrier modulation (DCM) are used for data modulation. For data rates lower than 320 Mbps, the constellation applied to the different subcarriers using quadrature phase-shift keying (QPSK) and for data rates of 320 Mbps and higher, the binary data is mapped onto two different 16-point constellations

As illustrated the MB-OFDM transmitter in Fig. 6, the first LO1 signal down-converts RF signals to a fixed IF which is further down converted to another IF by LO2. As a unique feature of MB-OFDM transceiver, a single RF mixer is proposed for both RF to IF down

conversion in the receiver and IF to RF up conversion in the transmitter.

4.9 GHz and a high band of 6.2–9.7 GHz [IEEE.15 Working Group].

linearity and wideband performance regardless of the control voltage.


Ultra-Wideband RF Transceiver 11

**7. UWB antennas** 

goal to reach.

An UWB communication system requires transmitter and receiver with a wideband antenna. Antennas are the fundamental component of a communication system, both at the receiver and at the transmitter, subject to performance requirements while at the same time supporting demand constraints to incorporate it in terminals or network access points. The contradiction between requirements and constraints make the selection or the design of an antenna something difficult in the ultra-wideband (UWB) case as the large bandwidth places additional needs in comparison to narrowband radio. The second problem for the antenna designer is the lack of tools to evaluate the performance of an antenna embedded in a radio system, apart from tools intended to determine the antenna input impedance, gain, efficiency, and its radiation patterns. These tools are obviously quite important in order to describe where the direction of the radiation would go or would be received, and what signal power can be lost due to antenna losses, but nothing about the "matching" between the antenna and the channel. It is well known that matched filtering is a necessary requirement for optimal signal reception, therefore since both antennas and channels are filters that are involved in the transfer function between the signal to be transmitted and the signal at the receiver output. This means, we should analyze antenna performance and channel properties in a correlated manner, if optimization of the radio link performance is a

As Antennas are considered to be the largest components of integrated wireless systems; antenna miniaturization is necessary to achieve an optimal design. The printed antennas present good solution because of providing several advantages compared to the conventional microwave antennas. The main advantages are: lightweight, small volume, low-profile, planar configuration, compact, can be made conformal to the host surface, easy integrated with printed-circuit technology and with other MICs on the same substrate, low cost, allow both linear polarization and circular polarisation. Monopole disc antennas, with circular, elliptical and trapezoidal shapes, have simpler two-dimensional geometries and are easier to fabricate compared to the traditional UWB monopole antennas with threedimensional geometries such as spheroidal, conical and teardrop antennas. These disc monopole antennas can be designed to cover existing and upcoming UWB communication

In the last few years, circular monopole antennas have been studied extensively for UWB communications systems because of some appealing features (easy fabrication, feedgap optimization alone gives wide impedance matching and omnidirectional radiation patterns). One of the strongest competitors in terms of good impedance bandwidth, radiation efficiencies, and omnidirectional radiation patterns are the circular disc monopole (CDM) and elliptical antennas (Abbosh & Bialkowski, 2008; Allen et al., 2007; Antonino et al., 2003, Liang et al., 2004; Powell, 2004; schartz, 2005; Srifi et al., 2009). There is great demand for UWB antennas that offer miniaturized planar structure, so the vertical disc monopole is still not suitable for integration with a PCB. This drawback limits its practical application. For this reason, a printed structure of the UWB disc monopole is well desired, which consist on

applications, (Honda et al., 1992) & (Hammoud & Colomel, 1993).

Data Rate =640Mbps\*Coding Rate/Spreading

**Table 1.** Data rate dependent parameters [26]

**Figure 6.** MB-OFDM Transceiver

#### **7. UWB antennas**

10 Ultra Wideband – Current Status and Future Trends

Data Rate =640Mbps\*Coding Rate/Spreading **Table 1.** Data rate dependent parameters [26]

**Figure 6.** MB-OFDM Transceiver

Modulation/ Constellation FFT Size

53.3 OFDM/QPSK 128 1/3 4 55 OFDM/QPSK 128 11/32 4 80 OFDM/QPSK 128 1/2 4 106.7 OFDM/QPSK 128 1/3 2 110 OFDM/QPSK 128 11/32 2 160 OFDM/QPSK 128 1/2 2 200 OFDM/QPSK 128 5/8 2 320 OFDM/QPSK 128 1/2 1 400 OFDM/QPSK 128 5/8 1 480 OFDM/QPSK 128 3/4 1

Coding Rate

(K=7) Spreading rate

Info. Data Rate (Mbps)

An UWB communication system requires transmitter and receiver with a wideband antenna. Antennas are the fundamental component of a communication system, both at the receiver and at the transmitter, subject to performance requirements while at the same time supporting demand constraints to incorporate it in terminals or network access points. The contradiction between requirements and constraints make the selection or the design of an antenna something difficult in the ultra-wideband (UWB) case as the large bandwidth places additional needs in comparison to narrowband radio. The second problem for the antenna designer is the lack of tools to evaluate the performance of an antenna embedded in a radio system, apart from tools intended to determine the antenna input impedance, gain, efficiency, and its radiation patterns. These tools are obviously quite important in order to describe where the direction of the radiation would go or would be received, and what signal power can be lost due to antenna losses, but nothing about the "matching" between the antenna and the channel. It is well known that matched filtering is a necessary requirement for optimal signal reception, therefore since both antennas and channels are filters that are involved in the transfer function between the signal to be transmitted and the signal at the receiver output. This means, we should analyze antenna performance and channel properties in a correlated manner, if optimization of the radio link performance is a goal to reach.

As Antennas are considered to be the largest components of integrated wireless systems; antenna miniaturization is necessary to achieve an optimal design. The printed antennas present good solution because of providing several advantages compared to the conventional microwave antennas. The main advantages are: lightweight, small volume, low-profile, planar configuration, compact, can be made conformal to the host surface, easy integrated with printed-circuit technology and with other MICs on the same substrate, low cost, allow both linear polarization and circular polarisation. Monopole disc antennas, with circular, elliptical and trapezoidal shapes, have simpler two-dimensional geometries and are easier to fabricate compared to the traditional UWB monopole antennas with threedimensional geometries such as spheroidal, conical and teardrop antennas. These disc monopole antennas can be designed to cover existing and upcoming UWB communication applications, (Honda et al., 1992) & (Hammoud & Colomel, 1993).

In the last few years, circular monopole antennas have been studied extensively for UWB communications systems because of some appealing features (easy fabrication, feedgap optimization alone gives wide impedance matching and omnidirectional radiation patterns). One of the strongest competitors in terms of good impedance bandwidth, radiation efficiencies, and omnidirectional radiation patterns are the circular disc monopole (CDM) and elliptical antennas (Abbosh & Bialkowski, 2008; Allen et al., 2007; Antonino et al., 2003, Liang et al., 2004; Powell, 2004; schartz, 2005; Srifi et al., 2009). There is great demand for UWB antennas that offer miniaturized planar structure, so the vertical disc monopole is still not suitable for integration with a PCB. This drawback limits its practical application. For this reason, a printed structure of the UWB disc monopole is well desired, which consist on

printed radiator disc on substrate. Printed CDM antennas can be fed simple microstrip line, coplanar waveguide (CPW), or slotted structures.

Ultra-Wideband RF Transceiver 13

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**Figure 7.** The prototype of simple fed CDM antenna
