Abstract
3GPP cellular communications in unlicensed spectrum allow transmission only after completing listen-before-talk (LBT) operation. For downlink, the LBT operation helps cellular traffic to coexist well with Wi-Fi traffic. However, cellular uplink transmission is attempted only at the time specifically determined by the base station after having a successful LBT and the user equipment (UE) may suffer transmission failure and delayed transmission due to Wi-Fi interference. As a result, cellular uplink traffic does not coexist well with Wi-Fi traffic. This article mathematically analyzes the problem of unfairness between cellular and Wi-Fi for uplink channel access. To address the coexistence problem in unlicensed spectrum, we propose a standard-compliant approach, termed UpChance, which allows the UE to use a minimum length of uplink reservation signal and the base station to determine the optimal timing for the UE’s uplink transmission. Through ns-3 simulation, we verify that UpChance improves the performance of fairness and random access completion time by up to 88% and 99%, respectively.
Highlights
Due to the high price and scarce bandwidth of licensed spectrum, cellular communication technologies have been developed to operate in unlicensed and licensed spectrum
We consider three competitive schemes: 1) The baseline scheme is the legacy enhanced LAA (eLAA), which starts UL transmission only when 25 μs LBT succeeds without using RS, 2) user equipment (UE) only scheme applies only the UE operation of UpChance, and 3) DL reservation signal (DL-RS) scheme allows the evolved Node B (eNB) to continuously transmit DL-RS after transmitting a UL grant or random access response (RAR), which helps the UE to occupy the channel until 25 μs before UL transmission
We investigated the uplink channel access problem of cellular communication in the unlicensed spectrum through mathematical analysis, and proposed a standardcompliant solution named UpChance
Summary
Due to the high price and scarce bandwidth of licensed spectrum, cellular communication technologies have been developed to operate in unlicensed and licensed spectrum. Cellular communications in unlicensed spectrum developed based on LTE-LAA technology use listen-before-talk (LBT) for channel access. J. Kim et al.: Uplink Channel Access Enhancement for Cellular Communication in Unlicensed Spectrum user equipment (UE) transmits a scheduling request (SR) to the eNB at a predetermined time. Our work highlights that cellular uplink transmission in unlicensed spectrum has a problem of not properly occupying the channel, especially when the channel is overloaded To address this problem, we suggest that the UE uses additional Category 4 LBT (Cat. 4 LBT) and UL-RS, and the eNB uses appropriate scheduling considering network traffic. MATHEMATICAL ANALYSIS FOR UNFAIRNESS BETWEEN UPLINK CELLULAR AND WI-FI we mathematically analyze the success probability of 25 μs LBT performed by the UE for uplink transmission.. This means that the UE transmits a PRACH preamble with a very low probability under the saturated Wi-Fi traffic condition
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