ADVANTAGES OF ULTRA WIDEBAND COMMUNICATIONS

The nature of the short-duration pulses used in UWB technology offers several advantages over narrowband communications systems. In this
section, we discuss some of the key benefits that UWB brings to wireless communications.

5.1 Ability to share the frequency spectrum.

The FCC’s (Federal Communications Commission) power requirement of –41.3dBm/MHz, 5 equal to 75 nano watts/MHz for UWB systems, puts them in the category of unintentional radiators, such as TVs and computer monitors. Such power restriction
allows UWB systems to reside below the noise floor of a typical narrow band receiver and enables UWB signals to coexist with current radio services with minimal or no interference. However, this all depends on the type of modulation used for data transfer in a UWB system.
Some modulation schemes generate undesirable discrete spectral lines in their PSD, which can both increase the chance of interference to other systems and increase the vulnerability of the UWB system to interference from other radio services. Figure 1–6 illustrates the general idea of UWB’s coexistence with narrow band and wide band technologies.

5.2. Large channel capacity

One of the major advantages of the large bandwidth for UWB pulses is improved channel capacity. Channel capacity, or data rate, is defined as the maximum amount of data that can be transmitted per second over a communication channel. The large channel capacity of UWB communication systems is evident from Hartley-Shannon’s capacity formula:
where C represents the maximum channel capacity, B is the bandwidth, and SNR is the signal-to-noise power ratio. As shown in Equation 1–5, channel capacity C linearly increases with bandwidth B. Therefore, having
several gigahertz of bandwidth available for UWB signals, a data rate of gigabits per second (Gbps) can be expected. However, due to the FCC’s current power limitation on UWB transmissions, such a high data rate is
available only for short ranges, up to 10 meters. This makes UWB systems perfect candidates for short-range, high-data-rate wireless applications
such as wireless personal area networks (WPANs). The trade-off between the range and the data rate makes UWB technology ideal for a wide array of applications in military, civil, and commercial sectors.

5.3. Ability to work with low signal to noise ratios

The Hartley-Shannon formula for maximum capacity (Equation 1–5) also indicates that the channel capacity is only logarithmically dependent on signal-to-noise ratio (SNR). Therefore, UWB communications systems
are capable of working in harsh communication channels with low SNRs and still offer a large channel capacity as a result of their large BW.

5.4 Low probability of intercept and detection.
Because of their low average transmission power, as discussed in previous sections, UWB communications systems have an inherent immunity to detection and intercept. With such low transmission power, the eavesdropper has to be very close to the transmitter (about 1 meter) to be able to detect the transmitted information. In addition, UWB pulses are time modulated with codes unique to each transmitter/receiver pair. The time modulation of extremely narrow pulses adds more security to UWB transmission, because detecting picoseconds pulses without knowing when they will arrive is next to impossible. Therefore, UWB systems hold
significant promise of achieving highly secure, low probability of intercept and detection (LPI/D) communications that is a critical need for military operations.

5.5 Resistance to jamming

Unlike the well-defined narrow band frequency spectrum, the UWB spectrum covers a vast range of frequencies from near DC to several gigahertz and offers high processing gain for the UWB signals. Processing gain (PG) is a measure of a radio system’s resistance to jamming and is defined as the ratio of the RF bandwidth to the information bandwidth of a signal

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