Power control optimization for uplink grant-free URLLC

Abstract

Abstract-Ultra-reliable and low latency communication (URLLC) presents the most challenging use cases for fifth generation (5G) mobile networks. Traditionally the focus for mobile broadband has been to optimize the system throughput for high speed data traffic. However the optimization criteria for URLLC should focus on achieving small packets transmissions under strict targets such as 99.999% reliability within 1 ms. Power control is one candidate technology component for improving reliability and latency. In this work we investigate the power control for grant-free URLLC transmissions through extensive system level simulations in a urban outdoor scenario. We initially compare different settings for open loop power control (OLPC) with full and with fractional path loss compensation. Then we evaluate whether power boosting the retransmission can reduce the probability of packets delays under the 1 ms constraint. We also discuss the practical implication of applying power boosting. With full path loss compensation and boosting retransmissions, we show that a URLLC load such as 1200 small packets per second per cell can be achieved in the considered scenario.

Joint Resource Configuration and MCS Selection Scheme for Uplink Grant-Free URLLC

“…This section evaluates a two MCS resource allocation configuration M = {M CS 1 (1) , M CS 2 (4)} = {QPSK1/8, QPSK1/2}. QPSK1/8 is used as the conservative MCS option (as in [13], [17]) and QPSK1/2 as the higher MCS option. We set the initial power spectral density offset ∆ MCS2 = 6 dB by following (2).…”

“…The simulator models the 5G NR design, adopting the commonly agreed mathematical models in 3GPP for radio propagation, traffic models, key performance indicators, etc [10]. The same simulator was also used in the earlier URLLC studies published in [4], [13], [17]. The network layout is a single layer urban macro network consisting of 7 sites, each having 3 sectors composing a regular hexagonal grid topology with 500 meters of inter-site distance (ISD), using wrap-around [21].…”

“…The ∆ MCS setting will be further discussed in this paper. As discussed in [13], we apply full pathloss compensation (α = 1).…”

“…The prior-art solutions use a conservative single-MCS, to meet the performance target [11], [13], [17]. In the baseline case, all UEs transmit using the full band in an entire TTI, using QPSK1/8 as the conservative single-MCS.…”

“…This is communicated to the user equipment (UE) by radio resource control (RRC) with possible activation via downlink control channel [9]. For GF transmissions, it is further assumed; that a configuration can be shared by multiple UEs [10], the MCS and transmission bandwidth is fixed [11], [12] and open loop power control is used [13].…”