Abstract
Although grant-based mechanisms have been a predominant approach for wireless access for years, the additional latency required for initial handshake message exchange and the extra control overhead for packet transmissions have stimulated the emergence of grant-free (GF) transmission. GF access provides a promising mechanism for carrying low and moderate traffic with small data and fits especially well for massive machine type communications (mMTC) applications. Despite a surge of interest in GF access, how to handle heterogeneous mMTC traffic based on GF mechanisms has not been investigated in depth. In this paper, we propose a priority enabled GF access scheme which performs dynamic slot allocation in each 5G new radio subframe to devices with different priority levels on a subframe-by-subframe basis. While high priority traffic has access privilege for slot occupancy, the remaining slots in the same subframe will be allocated to low priority traffic. To evaluate the performance of the proposed scheme, we develop a two-dimensional Markov chain model which integrates these two types of traffic via a pseudo-aggregated process. Furthermore, the model is validated through simulations and the performance of the scheme is evaluated both analytically and by simulations and compared with two other GF access schemes.
Highlights
S IMULTANEOUS packet transmissions over the same radio resource cause performance deterioration for wireless access due to potential collisions among transmissions from competing devices
The uniqueness and novelty of our paper are reflected by the fact that this work is anchored at a niche with an intersection among 5G new radio (NR) numerology, traffic estimation based dynamic slot allocation, proper handling of heterogeneous traffic considering the performance of both high priority traffic (HPT) and low priority traffic (LPT), and pseudo-aggregated 2D Markov chain modeling for heterogeneous traffic
To the best of our knowledge, this is the first attempt which is dedicated for 5G NR numerology based GF transmission with dynamic slot allocation at the subframe level for heterogeneous traffic, combined with a Markov model with a significantly reduced state space bridging both types of traffic together for performance evaluation
Summary
S IMULTANEOUS packet transmissions over the same radio resource cause performance deterioration for wireless access due to potential collisions among transmissions from competing devices. For GB channel access, a device follows a four-step handshake procedure for initial access with an evolved nodeB (eNB) by first transmitting a preamble before it obtains a grant for its data packet transmission. Different from the GB principle, devices in GF communications transmit their data packets together with (or without using specific) control messages directly to a 5G NR nodeB (gNB) in available GF slots without requiring the initial access procedure. No dedicated preamble transmission for granting access and allocating radio resources is required for GF communications before starting a data packet transmission [3]. For periodic or deterministic traffic, a gNB can allocate dedicated slots to devices for their data transmissions Such a mechanism will lead to resource underutilization and. GF transmissions are generally recommended for small data transmission with a low or moderate level of traffic arrivals [7], [8]
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