Ultra-wideband (UWB) technology offers a promising solution to the RF spectrum drought by allowing new services to coexist with current radio systems with minimal or no interference. This coexistence brings the advantage of avoiding the expensive spectrum licensing fees that providers of all other radio services must pay.
Ultra-wideband communications is not a new technology; in fact, it was first employed by Guglielmo Marconi in 1901 to transmit Morse code sequences across the Atlantic Ocean using spark gap radio transmitters. However, the benefit of a large bandwidth and the capability of implementing multiuser systems provided by electromagnetic pulses were never considered at that time.
Ultra-wideband communications is fundamentally different from all other communication techniques because it employs extremely narrow RF pulses to communicate between transmitters and receivers. Utilizing short-duration pulses as the building blocks for communications directly generates a very wide bandwidth and offers several advantages, such as large throughput, covertness, robustness to jamming, and coexistence with current radio services.
The FCC UWB rulings allocated 1500-times the spectrum allocation of a single UMTS (universal mobile telecommunication system) license, and, worse, the band is free to use. It was no wonder, therefore, that efforts to bring UWB into the mainstream were greeted with great hostility. First, the enormous bandwidth of the system meant that UWB could potentially offer data rates of the order of Gbps. Second, the bandwidth sat on top of many existing allocations causing concern from those groups with the primary allocations.
When the FCC proposed the UWB rulings, they received almost 1000 submissions opposing the proposed UWB rulings. Fortunately, the FCC UWB rulings went ahead. The concession was, however, that available power levels would be very low. If the entire 7.5GHz band is optimally utilized, the maximum power available to a transmitter is approximately 0.5mW. This is a tiny fraction of what is available to users of the 2.45 GHz ISM (Industrial, Scientific and Medical) bands such as the IEEE 802.11 a/b/g standards (the Institute of Electrical and Electronics Engineers). This effectively relegates UWB to indoor, short-range, communications for high data rates, or very low data rates for substantial link distances.
Applications such as wireless UWB and personal area networks have been proposed, with hundreds of Mbps to several Gbps and distances of 1 to 10 metres. For ranges of 20 metres or more, the achievable data rates are very low compared with existing wireless local area network (WLAN) systems.