Wireless Innovation Forum Top Ten Most Wanted Innovations

Innovation #5: Advanced Interference Mitigation Techniques

5.1 Executive Summary

Improved mechanisms are required to reduce intrusive and 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. Interference reduction and mitigation techniques continue to mature for a subset of communications systems including military and some commercial applications.  Development of interference rejection systems that are realizable in consumer communications devices including broadband consumer handsets and base sites, land mobile narrowband and broadband systems including public safety and mission critical applications, and other cost and size-conscious systems are needed.

5.2 Application

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 including operation outside of authorized bands, exceeding necessary or licensed power levels, etc.), equipment failure / degradation, or emission spillover from 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, unlicensed, and lightly licensed 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 degrade quality of service or deny service entirely.  This can range from impaired or obliterated voice quality degraded data fidelity, or complete denial of data throughput.

5.3 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 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 of design tradeoffs such as the implementation cost of such techniques would be prohibitive for many applications or other factors necessary for their deployment. It is recognized that CR techniques, whereby the frequency plans could be modified to operate in non-interfering bands, might be a solution but spectrum availability or operating frequency range of the radio may be cost prohibitive.  Significant cost/implement size of current techniques as well as new techniques are being sought.  Examples of potential research categories applicable to interference mitigation are given below.

• Development and 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.  Cost-effective, solutions that can be integrated for incorporation into consumer and professional narrow and broadband equipment is required.
• Enhanced Uplink and Downlink power control throughout the communications system, using only enough power to maintain communications at prescribed levels of acceptability. In particular, development of enhanced open-loop control systems that sense the radio environment, requests for re-transmission, and predictive path analysis to minimise power on channel, necessary bandwidth, and other scalable features of the transmission system based on local environmental observations.  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. Closed-loop, scheduled systems such as LTE take advantage of power control today.  Unlicensed, opportunistic systems, in general, do not.  Development of incorporated open-loop control systems into non-homogeneous systems will substantially mitigate interference and allow more efficient use of available spectrum.
• Advanced, adaptive beam-forming techniques to maximize antenna gain in the direction of the communications path and minimize gain in the interference direction. Null-steering techniques should also be utilized to actively protect critical link paths.  The latter technique could be extremely valuable in the 6-7GHz band to protect critical PtP links.  Additional spectrum allocations are also anticipated to exhibit similar limitations.
• 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.  In example, 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.   Scheduled systems take advantage of spectral, temporal, and modified waveform techniques today.  Further development of algorithms for implementation of these techniques using learned knowledge of the channel for independent, autonomous users of spectrum is required to improve spectrum efficiency and quality of service among the various users of opportunistic, unlicensed, and shared spectrum.
• 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.  Adaptive truncation of bandwidth, coupled with shared or learned intelligence of factors affecting the current channel and surrounding spectrum, further augmented by modified waveforms including modulation constellation depth and signalling cadence can substantially improve integrity of communications for channels that experience interference.
• Adapting the communications system to survive using learned knowledge of the temporal and/or spectral cadence of interfering signals.  Interference often exhibits characteristics that can be learned. This learned knowledge of the interfering signal can then be utilized to improve the overall resiliency of communications.  Examples of unintentional sources are 1) Interference from sources such as power conversion, 2) Efficient lighting, and 3) Wired data signalling systems. Techniques of this nature are particularly important for avoidance of chirped interference signalling.