The Wideband Slope of Interference Channels: The Large Bandwidth Case

It is well known that minimum received energy per bit <i>Eb</i>/<i>N</i><sub>0</sub>|<sub>min</sub> in the interference channel is -1.59 dB as if there were no interference. Thus, the best way to mitigate interference is to operate the interference channel in the low-signal-to-noise-ratio ( SNR) regime. However, when the SNR is small but nonzero, <i>Eb</i>/<i>N</i><sub>0</sub>|<sub>min</sub> alone does not characterize performance. Verdu introduced the wideband slope <i>S</i><sub>0</sub> to characterize the performance in this regime. We show that a wideband slope of <i>S</i><sub>0</sub>/<i>S</i><sub>0, no interference</sub> = 1/2 is achievable. This result is similar to recent results on degrees of freedom in the high-SNR regime, and we use a type of interference alignment using delays to obtain the result. We also show that in many cases, the wideband slope is upper bounded by <i>S</i><sub>0</sub>/<i>S</i><sub>0, no interference</sub> ≤ 1/2 for large number of users <i>K</i>.

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