DRX over LAA-LTE-A New Design and Analysis Based on Semi-Markov Model

Ever-increasing demand of data rate and subscriber penetration are resulting in continuous growth of mobile data traffic. In order to meet this exponential data traffic growth 3GPP Release 13, we have decided to enable the operation of Long Term Evolution (LTE) in the unlicensed band, termed as Licensed-Assisted Access (LAA). As the unlicensed spectrum is mainly used by WiFi, LTE evolved NodeB (eNB) has to perform Listen Before Talk (LBT) procedure to access the unlicensed channel. If the unlicensed spectrum is occupied by other services, User Equipment (UE) should remain active and wait for unlicensed channel to become idle. UE consumes a high power by remaining active, when unlicensed channel is not available. The UE's energy consumption could be saved by configuring Discontinuous Reception (DRX) in the unlicensed band, similar to DRX in LTE. In this article, we introduce and analyze a new Licensed-Assisted Access DRX mechanism (LAA-DRX) over LTE networks. Using our novel four state semi-Markov model, we show the probabilistic estimation of power saving and wake up latency associated with our proposed LAA-DRX process. Mathematical analysis and simulation results, using real wireless trace, point out that comparing to existing LTE DRX process, our LAA-DRX can achieve almost 4 percent higher power savings and up to 58 percent reduction in resource usage.

1 Introduction

The number of the mobile broadband subscribers are increasing exponentially. By 2,022 there would be 8.9 billion mobile subscribers, of which 90 percent are expected to be using mobile broadband [1]. This increase requires not only high capacity in the system, but also high data rate to meet the customer's expectation. In Long Term Evolution (LTE) wireless systems, spectrum efficiency is improved by using Multiple-Input Multiple-Output (MIMO) transmission, frequency reuse, by deploying small cells and higher multiple access techniques [2]. Unfortunately, dense small cell deployment is gradually creating congestion in the licensed LTE spectrum. Thus, cellular network operators are now in need of more spectrum to meet the increasing demands. As the limited licensed spectrum is an expensive resource for the operator, a cost-effective approach to meet the rapid mobile data growth is to deploy LTE in the unlicensed band [3]. The vast availability of unlicensed spectrum promises to fill the gap of licensed spectrum bandwidth limitation. Dual connectivity between the licensed band and unlicensed band is identified as one of the key technologies for future cellular systems.