SAN JOSE, Calif. — As ultrawideband communications gathers steam, Pegasus Data Systems Inc. is pushing an alternative wireless technology called ultranarrowband (UNB) that can increase the data rate performance of mobile networks, the company said. UNB will allow GPRS and other carriers to deliver 3-Mbit/second channels over existing infrastructure designs, Pegasus said.
The UNB approach is the opposite of ultrawideband, which generates a narrow pulse of electromagnetic radiation to provide 2 GHz of bandwidth. Rather than spreading a signal across a 2-GHz bandwidth, UNB creates a single narrowband spike that can be used to transmit high-speed data traffic, said Harold Walker, chief executive officer of Pegasus (Edison, N.J.). To create this spike, a very minimum shift-keying (VMSK) modulation scheme is applied to a coded binary phase-shift keying (BPSK) modulated stream.
VMSK is one of a class of modulation methods intended to remove dc components from a coded BPSK pattern. The produces two separate sidebands, as required by Nyquist's theorem, each 1 Hz wide. One 1-Hz signal is transmitted and the other is filtered down to a 60 dB rms level. The generated signal features a small signal spread of 4 MHz, worst case, Walker said.
Designer benefits
Filtering sideband signals below 60 dB rms provides several benefits to designers, Walker said. First, the UNB system operates within the requirements of the Federal Communications Commission's part 22 requirements, so the technology can be rolled out commercially today. Second, UNB can achieve bandwidth efficiency on the order of 90 bits/second per Hz, which compares favorably to the 8-to-10 bits/second per Hz efficiency of traditional architectures, Walker said.
VMSK modulation can be implemented in existing wireless equipment architectures and increase their performance, Walker said. It operates within the 30-kHz bands used in existing cellular structures and deliver six channels in each, achieving data rates up to 3 Mbits/s per channel, he said. Thus, by adding UNB to an existing design, engineers can enhance data services without making the leap to GPRS, which requires wider channel structures. In addition, companies can add between 20 to 40 more channels to an equipment design with UNB, Walker said.
A major test of UNB will be in its acceptance. Pegasus first produced the VMSK-based UNB technology in 1996. Walker said the company was delayed when one of its financial backers went out of business in late 2000. Now armed with new backers, the company is again moving forward, he said.
At least three big wireless players are looking at the technology. Verizon is providing UNB with some airtime to test it out, and BellSouth is providing Pegasus with access to a cell site in the Atlanta market to test UNB's performance. On the equipment side, Siemens is evaluating the technology, Walker said.
Robert Keenan is editor-in-chief of CommsDesign.com, an online sister publication of EE Times.
