Wireless Innovation Forum Top Ten Most Wanted Innovations

Innovation #5: Efficient Techniques to Minimize Power Amplifier Spectral Regrowth in Non-contiguous Spectral Environment

5.1 Executive Summary

Techniques (algorithms, software, hardware, or mixed technique) that significantly reduce spectral regrowth (target of -70 dBc) when a wideband (>= 20 MHz), but non-contiguous, signal is passed through a nonlinear transmitter.

5.2 Application

In many secondary spectrum deployment scenarios, it will be difficult to find contiguous wideband spectrum due to primary users. Thus to achieve sufficient communications bandwidth for high data rate applications, it will be necessary to combine together multiple smaller pieces of contiguous spectrum which would ideally be transmitted from a single transmitter. In such a scenario, it is vital that the primary user signals are protected from interference.

5.3 Description

Simply filtering or nulling the transmitted signal energy in the intermediate subbands at baseband will not provide sufficient protection to the primary users due to transmitter nonlinearities leading to spectral regrowth in the primary users’ bands. Likewise, while narrower bandwidth signals can be used that eliminate the possibility of spectral overlap, this narrow bandwidth is often insufficient. Similarly, significantly increasing guardbands can improve primary user protection, but this is highly inefficient use of spectrum. Ideally techniques should mitigate this spectral regrowth in unused bands in transmissions over non-contiguous spectrum without increasing guardbands to achieve suppression that yields -70 dBc signal level in protected bands.

5.4 Qualifiers

Single band (e.g., TV bands) is acceptable. Multiple transceiver chains to multiple antennas are not desirable for this topic. Technology of interest can be a software, hardware, or mixed signal solution. Many different techniques have been proposed, including predistortion and subcarrier manipulation techniques, but these techniques individually normally achieve suppression at least 30 dB. This is significantly less than the 70 dB required in most bands.