Enhanced DRX Quick Sleeping Mechanism For Power Aware LTE System

Transcription

1 Enhanced DRX Quick Sleeping Mechanism For Power Aware LTE System M.Leeban Moses 1, R.Alwin 2, J.Prabakaran 3 1,2,3 ECE, Coimbatore Institute of Engineering and Technology Abstract - Discontinuous Reception (DRX) is one of the mechanisms to reduce User Equipment (UE) power consumption in Long Term Evolution (LTE) systems. The Discontinuous Reception (DRX) mechanism which is widely adopted in LTE to conserve the user equipment (UE) s battery resources, not only introduces high handover latency but also reduces the downlink scheduler efficiency. A key objective of this work is to design battery power aware scheduling by incorporating the per-ue DRX parameters in downlink scheduling. In this paper, we propose a modified DRX mechanism incorporating the Quick Sleeping Indication (QSI) as a novel, simple and energy efficient solution for low-complexity, low-mobility MTC UEs. The UE power consumption is minimized by reducing the time that a UE spends receiving data. This is achieved by predominantly scheduling a single UE at a time. This allows maximizing the UEs battery lifetime while satisfying the application quality of service (QoS) requirement. In this paper, we propose an enhanced DRX-Aware scheduling Quick sleeping mechanism that can balance the trade-off between application QoS requirements and UE s power consumption. Based on LTE system level simulation results, the UE power consumption could be significantly reduced while improving the mean delay using the scheduler, comparing to conventional proportional fair scheduler. Keywords Long Term Evolution (LTE), Discontinuous Reception (DRX), Paging, Quick Sleeping Indication (QSI), quality of service (QoS), user equipment (UE) I. INTRODUCTION The introduction of smart phones and tablets along with the increasing number of mobile applications is making user equipment s (UEs) more active than ever. While data rate in Long Term Evaluation (LTE) network has increased by a factor of 50 over 3G network, wireless device batteries are still the same size. Long Term Evolution (LTE), a new-generation technology for mobile communication was specially created to fulfill the need of bandwidth ravenous users. With aims to entitle users with a new smartphone experience, providing higher data-rates and lower latencies that could transform the overall industry into a new wireless ecosystem of smartphone devices and applications. LTE render remarkable improvements over older cellular communication standards like GPRS, EDGE and WCDMA, and because of this outstanding improvement it is called as 4G (fourth generation) technology. LTE architecture is based on Internet Protocol (IP) distinct from other cellular Internet protocols, the 4G-LTE supports browsing Web sites, VoIP and other IP-based services as well. LTE was proposed to achieve theoretically download rate of 300Mbps or more based on experimental trials. In practical the rates vary on actual network bandwidth accessible to an individual LTE subscriber sharing the service provider's network (ISP) with other customers is significantly less. Most of the commercially established LTE networks are optimized for USB data dongles where the power consumption is not a crucial concern. With the inception of LTE, power consumption has become a major problem to the end user using smartphones and tablets and other handheld LTE device. So power efficiency can be increased at Network architecture and protocol level, OFDM access, SC-FDMA and MIMO All Rights Reserved 89

2 Figure 1: LTE Utran Architecture Figure 1 depicts the essential design of LTE. The radio network architecture projected by the 3GPP LTE consists of evolved NodeB (enodeb). The enodeb provides a link between the user instrumentality and core network. As shown in Figure 1, enodeb is connected to the core network via the S1 interface, and every enodeb is interconnected via the X2 interface. The enodeb is responsible for the bulk of the radio resource management (RRM) functions like packet programing. Both mobility management entity (MME) and serving gateway (S-GW) are a part of the core networks. The MME is responsible for paging and user instrumentality (UE/UI) quality in idle mode inside the network, whereas the S-GW node is responsible for routing user information packets and handling alternative user requests, as an example handover. LTE uses orthogonal frequency division multiple access (OFDMA) as a radio interface. OFDMA divides the bandwidth into subcarriers and assigns them to the users depending on the present demand of service. Every subcarrier carries information at low rate, however exploitation of multiple subcarriers at once to produce high information rates. II. DRX MECHANISM The DRX mechanism has been implemented on 2G (GSM) and 3G (UMTS) cellular networks. LTE specification has adopted DRX at the link level to save power and extend the battery life of the UE. In LTE networks, the DRX mechanism can observe the Radio Resource Control (RRC) states between the UEs and the enodeb. The RRC has two different states where DRX mechanism can be worked, i.e., RRC_Idle and RRC_Connected. In the RRC_Idle state, the UE is registered in the LTE network with a specific unique identifier, but it does not have an active session with the enodeb. In this state, the enodeb can page the UE at any time for a different purpose (e.g., get location information), while the UE can request an uplink channel by establishing All Rights Reserved 90

3 RRC_Connected state, so that it can receive and transmit data. In the RRC_Connected state, the DRX mode can be enabled during idle periods between successive packet arrivals. In case there is no data packet, theuecan go intodrxmode. The LTE s DRX mechanism, i.e., the sleep/wakeup scheduling of each UE receiver, could be described in terms of three periods (ON-duration, inactivity, and sleep interval), as shown in Fig. 1. The values of LTE s DRX parameter are defined in [1]. In this paper, we are considering the following parameters: 1) DRX cycle: It is a time interval between the start of two consecutive ON-duration periods, in which the UE remains active. One DRX cycle consists of an ON-duration and a sleep interval. 2) ON-Duration (t): It is the time when the UE is in active state and listening to the Physical Downlink Control Channel (PDCCH). If any data packet is scheduled, the UE starts its inactivity timer (ti ); otherwise, it continues its DRX Sleep cycle. We set the value of ON-duration to 1 ms because this timer only checks the availability of scheduled data. 3) Inactivity timer (ti ): When a packet is found during ONduration, the UE starts its ti and receives data packets. During ti, if another PDCCH packet arrives, the inactivity time restarts itself. When ti expires, the DRX cycle starts with a sleep interval. The value of ti is set to 5 ms. 4) Sleep interval: It is a time interval during which the UE is either in DRX Light Sleep tds mode (consumes low power) or in DRX Deep Sleep tdl (consumes no power) mode. In Deep Sleep mode, the sleep interval is longer than in the Light Sleep mode. This paper considers that the values of Light Sleep duration are 2, 5, 10, 16, and 20 ms and for Deep Sleep duration 10, 20, 42, 64, and 80 ms [31], as longer duration not only saved more power but also increased the packet delay. LTE has two Radio Resource Control (RRC) states, RRC CONNECTED and RRC IDLE [10,17], as shown in Figure 3. At RRC CONNECTED state, User Equipment (UE) can be in one of the three modes: Continuous Reception, Short DRX, and Long DRX. The transition from one state to another depends on the traffic activity. Network runs an inactivity timer referred as RRC Inactivity timer to push the device to Idle mode. When there is no packet activity for a long duration (equal to RRC Inactivity Timer), UE is moved to Idle state from Connected state. RRC Inactivity timer is reset with any uplink or downlink data activity. In LTE, UE may be configured with a DRX mechanism by radio resource control (RRC) in both Connected and Idle states [14]. However, the functionality and configuration parameters of DRX are different in these LTE states. Since data traffic mainly take place in connected state. DRX can be configured by RRC on per UE basis to control UE s Physical DL Control Channel (PDCCH) monitoring activity in order to save UE s battery power. Network runs an inactivity timer called DRX Inactivity timer for the connected UEs to push them to DRX mode. When there is no packet activity for duration of DRX Inactivity timer, UE stays in connected state but moves to DRX mode. DRX inactivity timer is also reset with any uplink or downlink data activity. RRC Inactivity timer is used to move the UEs to Idle and DRX Inactivity timer is used to move the UEs into DRX mode while still staying in Connected. In current LTE deployments, RRC Inactivity timer is larger than DRX Inactivity All Rights Reserved 91

4 III. ENHANCED DRX QUICK SLEEPING MECHANISM The flowchart of proposed function is illustrated in Figure. There are three incoming information to the proposed function: a) queue information, b) DRX status information, and c) channel quality information (CQI) report. Figure 2: The flowchart describing the main steps in the edas scheme to implement the Proposed Function The queue information contains the packet head-of-line delay for each queue at enodeb. This is denoted as wi(t), where i is UE number and t is the current time slot (TTI). The CQI report contains data rate information for each UE, such as instantaneous data rate ri(t) and the average achieved data rate Ri(t) computed using an exponentially weighted moving average technique. DRX status information includes the DRX parameters for each UE. After receiving incoming information, the ratio of number of UEs with handover to the total number of UEs that connects to the enodeb is calculated. This is denoted as HOrate. If HOrate is greater than a pre-defined threshold ω, the method which is named DRX-Aware Scheduling with High Mobility (edas-hm) is chosen. Otherwise, the method which is named DRX-Aware Scheduling with Low Mobility (edas-lm) is chosen. The output of the proposed function is a priority matrix containing the priority information for each UE which is used by the scheduler to allocate the available transmission opportunity. Each UE s data packets are sent to the corresponding queue at enodeb. The edas scheme will first check for current buffer status after receives information from each buffer. Only those UEs with non-empty queue will be considered for scheduling. For each of non-empty queue, the DRX status for the corresponding UE is checked. This UE specific information is obtained from the data continuously aggregated by the DRX Manager at Layer 3. Let tron and fi be the remaining awake time and a function of tron, respectively. For those UEs that are not on DRX sleep mode, the remaining DRX awake time will be estimated. The UEs that are All Rights Reserved 92

5 Continuous Reception State (S1), the remaining awake time equals to the remaining time of Inactivity Timer. While for the UEs that are on DRX awake state, the remaining awake time is the remaining time of the On Duration Timer. The function fi(tron) is such that it is a should be a non-increasing function for edas-lm, for delay sensitive application. This will imply that static UE with a shorter tron will have a higher priority. In case the static UE enters DRX sleep state, higher priority for shorter remaining awake time will help decrease packet delay as well as packet drops at enodeb. On the other hand, the fi(tron) should be an increasing function for edas-hm so that a mobile UE with a longer tron will have a higher priority. Thus is because longer remaining awake time for mobile UEs which are performing handover will help decrease HO latency which is caused by the DRX sleep state. IV. PERFORMANCE ANALYSIS We evaluate performance of the proposed edas scheme by using simulation. Figure 3 shows the comparisons of of the various schemes with respect to the average PD. The results show that using edas scheme decreases the average PD. For low mobility conditions (i.e., % of UEs on HO < ω), the UEs that contain shorter remaining awake time can get higher scheduling priority.this will minimize the packet delays that are generated by the DRX sleep mode. For high mobility conditions (i.e., % of UEs on HO > ω), since most UEs handover from the serving enodeb to other target enodebs, the UEs that have longer remaining awake time get higher priority benefit for HO preparation latency. This also results in decreasing the average PD. Figure 4 shows the percentage of time that UEs stay in DRX sleep mode for different scheduling schemes. It is clear that the PSR for edas scheme is quite close to M-LWDF with DRX, while at the same time for edas the PDR in Figure 4 as well as average PD in Figure 3 are also much lower. From this figure, we can see that edas scheme achieved good QoS performance without sacrificing UE s power saving. By using edas, the PDR and PD achieve significant improvement, however, the power conservation decreases very slightly. Figure 3-Comparison of edas with traditional scheduling schemes with respect to average packet delay All Rights Reserved 93

6 Figure 4-Comparison of edas with traditional scheduling schemes with respect to Power Saving Rate (PSR). REFERENCES 1. F. Semiconductor, Long Term Evolution Protocol Overview, Document Number: LTEPTCLOVWWP, Enhanced DRX-Aware Scheduling for Mobile Users in LTE Networks, 2016 International Conference on Computing, Networking and Communications (ICNC), Workshop on Computing, Networking and Communications (CNC). 3. DRX-Aware Power and Delay Optimized Scheduler for Bursty Traffic Transmission Sofonias Hailu, Petteri Lunde n Elena Virtej, Niko Kolehmainen, Olav Tirkkonen, and Carl Wijting 4. Overview of Power Optimization in LTE Network, International Journal of Computer Applications ( ) National Conference on Emerging Trends in Advanced Communication Technologies (NCETACT-2015) 5. S. Arul Jothi, N. Santhiya Kumari, and M. Ram Kumar Raja. "An Efficient Denoising Architecture for Impulse Noise Removal in Colour Image Using Combined Filter." Jsoftware,vol11, , 6. M. Ramkumar Raja, and Amitha AP Pankaj. "Design of Modified Variable-Latency Speculating Booth Multiplier with Carry Skip Adder." Asian Journal of Research in Social Sciences and Humanities 6.9(2016): Arthi, V., Praveen S. Chakkravarthy, and R. Ramya. "Improved Two Stage Detection in Cooperative Spectrum Sensing In Cognitive Radio Networks."Asian Journal of Research in Social Sciences and Humanities 6.9 (2016): S. Praveen Chakkravarthy, N. Nagarajan, and V. Arthi. "Selection based successive interference cancellation for multicode multicarrier CDMA transceiver." WSEAS TRANSACTIONS on COMMUNICATIONS 9.8 (2010): All Rights Reserved 94