Truncated Channel Inversion Power Control to Enable One-Way URLLC with Imperfect Channel Reciprocity
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We propose to use channel inversion power control (CIPC) to achieve one-way ultra-reliable and low-latency communications (URLLC), where only the transmission in one direction requires ultra reliability and low latency. Based on channel reciprocity, our proposed CIPC schemes guarantee the power of received signals to be a constant value Q, by varying the transmit signals and power, which relaxes the assumption of knowing channel state information (CSI) at the receiver. Thus, the CIPC schemes eliminate the overhead of CSI feedback, reduce communication latency, and explore the benefits of multiple antennas to significantly improve transmission reliability. We derive analytical expressions for the packet loss probability of the proposed CIPC schemes, based on which we determine a closed interval and a convex set for optimizing Q in CIPC with imperfect and perfect channel reciprocities. Our results show that CIPC is an effective means to achieve one-way URLLC. For example, increasing the number of transmit antennas continuously improves reliability and reduces latency, which is a different conclusion from the system using traditional channel estimation and feedback mechanisms. The tradeoff among reliability, latency, and required resources (e.g., transmit antennas) is further revealed, which provides novel principles for designing one-way URLLC systems.
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