Abstract
NarrowBand-Internet of Things (NB-IoT) is a new 3GPP radio access technology designed to provide better coverage for Low Power Wide Area (LPWA) networks. To provide reliable connections with extended coverage, a repetition transmission scheme and up to three Coverage Enhancement (CE) groups are introduced into NB-IoT during both Random Access CHannel (RACH) procedure and data transmission procedure, where each CE group is configured with different repetition values and transmission resources. To characterize the RACH performance of the NB-IoT network with three CE groups, this paper develops a novel traffic-aware spatio-temporal model to analyze the RACH success probability, where both the preamble transmission outage and the collision events of each CE group jointly determine the traffic evolution and the RACH success probability. Based on this analytical model, we derive the analytical expression for the RACH success probability of a randomly chosen IoT device in each CE group over multiple time slots with different RACH schemes, including baseline, back-off (BO), access class barring (ACB), and hybrid ACB and BO schemes (ACB&BO). Our results have shown that the RACH success probabilities of the devices in three CE groups outperform that of a single CE group network but not for all the groups, which is affected by the choice of the categorizing parameters.This mathematical model and analytical framework can be applied to evaluate the performance of multiple group users of other networks with spatial separations.
Highlights
T HE Internet of Things (IoT) offers a wide spectrum of opportunities for innovative applications designed to improve our life quality
We evaluate the efficiency of several Random Access CHannel (RACH) schemes based on the presented analytical model, including baseline, back-off (BO), access class barring (ACB), and hybrid ACB and BO schemes (ACB&BO), in the NarrowBand-Internet of Things (NB-IoT) network to alleviate uplink congestion by reducing the high interference and high collision probability when massive IoT devices contend for the uplink channel resource at the same time [25], [26]
The contention-based RACH procedure consists of four steps, where a randomly selected preamble is transmitted to the associated Base Station (BS) on NB-IoT Physical Random Access CHannel (NPRACH), for a given number of times in step 1, and control information with the BS is exchanged in step 2,3,4 [13], [23]
Summary
T HE Internet of Things (IoT) offers a wide spectrum of opportunities for innovative applications designed to improve our life quality. The new challenges of this work are listed as: 1) both the intra- and inter- group interference for the same group is considered, due to that the IoT devices in the same group in a cell may randomly choose and transmit the same preamble using the same sub-channel; 2) the interference field of each CE group needs to be modeled separately based on their different received power region; 3) the transmit powers of CE group 1 and 2 are generally a fixed power, and the interference from interfering IoT devices depends on the different and random transmission distances in each CE group; 4) the configured parameters of three CE groups are different and related, which determines the definition equation of RACH success probability; 5) our analysis considering multiple time slots need capture the traffic change over time due to new arrival packets, and previous unsuccessful packets.
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