**2. UWB modulation**

As UWB pulse itself does not contain information, we must add digital information to the analog pulse through modulation. The MB-OFDM systems are dealing with

© 2012 Matin, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Matin, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

continuous ultra-wideband modulated signals while DS-UWB systems are transmitting discrete short pulses which cover ultra-wide bandwidth. On the other hand, IR-UWB is a carrier-less pulse-based system which means IR-UWB and DS-UWB are the two different categorizes of pulse based UWB. Pulse modulation scheme includes OOK (On Off Keying), BPSK (Binary Phase Shift Keying) and PPM (Pulse Position Modulation). OOK modulation is performed by generating transmitted pulses only while transmitting '1' symbols. BPSK modulation generates 180° phase-shifted pulses while transmitting baseband symbols '1' and '0'. PPM modulation is performed by generating pulses where each pulse is delayed or sent in advance of a regular time scale. Thus a binary communication system can be established with a forward and backward shift in time. By specifying specific time delays for each pulse, an M-ary system can be created. BPSK has an advantage over other modulation types due to an inherent 3 dB increase in separation between constellation points (Wentzloff & Chandrakasan, 2006); however, BPSK modulation is not suitable for some receiver architectures, e.g., noncoherent receivers.

Ultra-Wideband RF Transceiver 3

**3.1. UWB transmitter/Pulse generator** 

other radio systems.

of the generator.

**3.2. UWB receiver** 

used in what application.

is the signal to noise ratio.

In principle, all the pulses with the spectra (≥ 500 MHz) falling into the UWB band can be used as signals. However, for practical purposes, the pulses which are simple to generate, controlled, and have low power-consumption (no direct component), are selected to generate UWB signals. The proper selection of the source pulse can maximize the radiated power within the UWB band and meet the required emission limits without filters before the transmitting antennas while minimizing anticipated inter-symbol (and in the case of DS-UWB, inter-chip) interference and providing spectral flexibility as a method to coexist with

In the transmitter, the binary information stream from devices such as PC, PDA or DVD player is passed to the front end of the transmitter and mapped from bits to symbols if higher order modulation schemes are to be used. Each symbol representing multiple bits is then mapped to analog pulse shape which is generated by pulse generator. The mapping of information into waveforms is referred to data mapping or modulation. The generated pulse then can be optionally amplified before being passed to transmitting antenna. Typical IR-UWB use transition generators with edge rates designed to occupy 3 GHz of bandwidth or more while other systems use various forms of gated frequency generators, where the edge rates are selected to spread the energy around the fundamental frequency

It is necessary to have an optimal receiving system same as generating signal with the desired spectral characteristics. The optimal receiving technique often used in UWB is a correlation receiver. The correlator in the receiver multiplies the received signal with the template waveform. It is critical to note that the mean value of the correlator is zero. Thus, for in-band noise signals received by a UWB radio, the correlator's output has an average value of zero. Moreover, the standard deviation or rms of the correlator output is related to the power of those in-band noise signals. The level of hardware implementation and computational complexity plays an important role in determining which modulation to be

The receiver sensitivity is generally defined by the signal level required to gain the given signal-to-noise (S/N) ratio. This means sensitivity is increased when there is less noise. The

Where, S (dBm) is the receiver sensitivity, NF is the noise figure, B is the bandwidth and S/N

If communication is established by QPSK with 8 dB of S/N ratio and 6 dB of total circuit NF, receiver sensitivity with MBOFDM receiver will become –73dBm, when the bandwidth, B= 528 MHz for the data rate 480 Mb/s, To raise the data rate from 54 to 480 Mb/s, the channel

S (dBm) = -174+NF+10logB+10log(S/N) (2)

following formula shows the factors used to define receiver sensitivity.
