Channel Quality Indicator Preamble for Discontinuous Reception

Abstract

This paper proposes a potential enhancement for Discontinuous Reception (DRX) operation in Long Term Evolution (LTE) networks. In Third Generation Partnership Project's (3GPP's) Release 8 it is specified that User Equipment (UE) may be configured with DRX which controls the UE's Physical Downlink Control Channel (PDCCH) monitoring activity. By allowing discontinuous monitoring of PDCCH the UE can switch its receiver circuitry on and off for battery saving purposes. However, if UE turns its receiver circuitry off it is not capable to neither perform nor send any Channel Quality Indicator (CQI) measurements to the network prior to 'on-duration' (i.e., activity) period. This means that the Evolved Node B (e- Node B) might not have accurate CQI information and the scheduling and resource allocation could be based on outdated CQI information. To avoid reduced performance caused by the out-of-date information, this paper evaluates a scheme where a CQI preamble period is introduced prior to the actual 'on duration' time. During the preamble period UE measures the CQI and sends the measurement result to the e-Node B. The performance of the scheme is evaluated together with Voice over IP (VoIP) service. Used tool is a dynamic system level simulator which enables detailed simulation of users in multiple cells with realistic call generation, propagation, fading and mobility models. In addition to VoIP performance the UE power consumption is also evaluated with a simple model. This paper concludes that the preamble scheme can lead to improved performance in terms of VoIP capacity, and that the improvements can be achieved with acceptable trade-off in terms of battery saving opportunities