Wireless Innovation Forum Top Ten Most Wanted Innovations

 

Innovation #8: Interference Mitigation Techniques

 

8.1 Executive Summary

 

Improved mechanisms are required to reduce destructive interference to communications signals and circuits.  Improved and applied interference mitigation and cancellation techniques may be utilized to improve quality of service, range, spectrum efficiency and spectrum re-use if properly implemented.

 

8.2 Applications

 

Interference can take multiple forms.  Some common forms are  1) intentional jamming, as often occurs in military communications or as a denial of service attack to existing systems, 2) unintentional or non-intentional interference, often resulting from misuse of equipment (wrong frequency settings, misplaced of towers, exceeding necessary power levels, etc.) or emission spillover from Out of Band Emissions (OOBE) in other bands, or 3) collisions of like waveforms such as those that occur in unscheduled or collision-sensed environments (ex: Wi-Fi), and 4) dissimilar or disparate  waveforms vying for use of identical spectrum allocations such as in ISM and unlicensed bands.  In all cases, the resulting interference acts to decrease the signal to interference plus noise ratio at the receiving end of the communications path and, if of sufficient level, will act to substantially degrade quality of service  or deny service entirely.  This can range from impaired or obliterated voice quality in a voice system and data degraded or denied throughput in a data system.

 

8.3 Description

 

Innovations are sought that deal with how Software Defined Radio (SDR) and/or Cognitive Radio (CR) might alter the system design tradeoffs  either to enable better rejection of interference without the exponential cost growth associated with more traditional solutions. Such innovations might include, but are certainly not limited to, the ones listed below. It is realized that many of these techniques are already used in some advanced communications systems, but not used in others because design tradeoffs or other factors may not have their deployment. It is recognized that cognitive radio techniques, whereby the frequency plans could be modified to operate in non-interfering bands, might be a solution, but the implementation cost of such techniques would be prohibitive for many applications. In the present cases, other techniques are sought.  Examples are given below.

 

  • Use of active cancellation techniques where a-priori knowledge of the interfering system can be utilized to an advantage to partially cancel the undesired, interfering signal, thus improving the figure of merit of the desired communications channel for a given communications path.
  • Uplink and downlink power control throughout the communications system, using only enough power to maintain communications at prescribed levels of acceptability. Furthermore, and in example, for low priority communications paths, the power could even be set for degraded voice quality relative to the paths with the highest priority to reduce interference to critical systems.
  • Adaptive beamforming to maximize antenna gain in the direction of the communications path and minimize gain in the interference direction.
  •  Adaptive polarization, including linear and circular, to optimize desired communications while reducing or nulling interfering signals.  This could include minimizing co-channel interference first, followed by transmission of desired signals using conjugate polarizations.
  • Adaptable data rate to the minimum throughput rate needed for the communication and/or according to priority of the operator. This may be implemented in several forms including the use of slower data rates spread over a wider channel or running bursts of larger constellations on a given channel if the channel will support it.
  • Adaptive frequency control to increase frequency separation of the interference sources from the desired radio path.  This implies the use of dynamic spectrum assignment wherein interference avoidance is a key decision factor in choice of channel.
  • Adaptive receive filtering to provide better rejection of the interference balanced against possible sensitivity degradation and / or signal quality factors such as BER, etc.  This would include greater reliance upon error correction within the receiver to offset degraded performance due to information truncation and the resulting effect upon demodulation such as constellation decision points.
  • Improved roaming algorithms (Change sites or systems to one that has a better Signal to Noise plus Interference ratio).
  • Change channel coding algorithms to relax the required signal to interference plus noise ratio at the expense of more data overhead.
  • Adapting to the temporal or spectral cadence of interfering signals.