Improvement in Interference Rejection and Suppression Technology

By | May 21, 2014
  • Rel. 11 LTE has introduced MMSE-Interference Rejection Combining (MMSE-IRC) receivers as a mobile terminal interference rejection and suppression technology to mitigate the effects of these interference signals and increase user throughput even in areas that are recently experiencing high interference. Rel. 8 LTE receivers support MIMO transmission technology, so receivers were equipped with at least two antennas since it was first introduced. The MMSE-IRC receivers in Rel. 11 LTE, are able to use the multiple receiver antennas to create points, in the arrival direction of the interference signal, where the antenna gain drops (“nulls”) and use them to suppress the interference signal (Figure 1). The terminal orients a null toward the main interference signal, which is the signal that particularly affects the degradation of throughput, thereby improving the Signal-to-Interferenceplus-Noise power Ratio (SINR) and improving throughput performance.
  • On the other hand, the 3GPP has already included interference rejection and suppression technology in performance specifications for mobile terminals equipped with W-CDMA/High-Speed Downlink Packet Access (HSDPA) in Rel. 7 of the Universal Mobile Telecommunications System (UMTS). With W-CDMA, receivers normally use one receiver antenna and perform Rake reception, but the effects of multipath interference degrading reception performance was an issue.
  • Thus, the following three receiver extensions were studied and introduced.
    • Type 1/1i extends the Rake receiver to use two antennas.
    • Type 2/2i extends the Rake receiver to an MMSE receiver that suppresses multipath and adjacent-cell interference.
    • Type 3/3i extends the MMSE interference-suppressing receiver defined in Type 2/2i to use two receiver antennas.
  • Interference Rejection and Supression technology being standardized in Rel 11 LTE at 3GPP.
  • It is a promising technology for improvement user throughput in high interference environments where cells are densely installed to handle recent high traffic.
  • This functionality can also be used in ordinary LTE such as Rel 8 LTE.

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