Fang-Chang Kuo

Energy-Efficient DRX Scheduling for QoS Traffic in LTE Networks

LTE has been touted as a leading-edge mobile communication technology offering high data rate and low latency. However, with a sophisticated physical layer to boost performance, the processing demand on user equipment (UE) is tremendous, which implies that the energy consumption is heavy. To curb undesirable energy waste and extend battery life, a variety of energy-conserving measures have been developed, among which discontinuous reception (DRX) is shown to be useful. This paper introduces the light sleeping mode in order to further improve the performance of DRX for traffic with QoS requirements in LTE networks. The key idea of light sleeping is to turn off the power amplifier but leave the other components in the transceiver on to cut down energy consumption while allowing fast wakeup. Quantitative analysis shows that the proposed method can substantially reduce energy consumption and satisfy the delay requirement of QoS traffic.

An accurate power analysis model based on MAC layer for the DCF of 802.11n

The 802.11 wireless local area network technology is popular in power-sensitive devices such as smart phones and personal digital assistants. In this article, we present an accurate power consumption model based on the Bianchi model and power measurement in the physical layer to predict the power consumption of 802.11n and multiple-input–multiple-output mode of 802.11n. In this model, we calculate the total energy consumption by summing up several components: the idle listening energy consumed in the distributed inter-frame space period and backoff stages, the energy consumed in transmitting a frame, the idle listening energy consumed in the short inter-frame space turnaround time, the energy consumed in receiving an acknowledgment frame from the access point, and the energy consumed in collisions for one frame transmission. The probability of successful frame transmission and medium access control (MAC) efficiency of 802.11n are also analyzed as a function of the number of active stations and different choices of frame transmission probability by each active station. Finally, the impact of imperfect channels on energy consumption and MAC efficiency is explored.

A Power-Saving and Robust Point Coordination Function for the Transmission of VoIP over 802.11

Group-polling based schemes for the enhancement of the Point Coordination Function (PCF) in the 802.11 have been supposed to be the most efficient scheme for the transmission of VoIP frame. However, most of the group-polling schemes are not energy-efficient at all due to the fact that all the stations in this list must listen to the channel during all the transmissions belonging to this polling list. Furthermore, if some stations loss this group-polling frame, it will result in many empty group slots leading to unstable system states. In this article, we propose a Power-Saving and Robust Point Coordination function (PSR-PCF) for the transmission of VoIP over 802.11. Any stations can set its wakeup timer and fall asleep according to the schedule information of the received group polling frame. In order to make this system more robust, we propose a chained-scheme, that is, the MAC address of next active station is piggybacked in the frame header of the uplink data frame to the AP with no additional overheads. Analysis shows that the energy consumption can be reduced by over 93.2% compared with that of ICF [20]. The number of active VoIP stations sustained can be up to about 260 without any data loss under the 802.11a with 54Mbps data rate. Whereas, in the same parameters of 802.11a, the PCF with the Round-Robin (RR) scheduler will have more than 10% data losses if the number of active VoIP stations is larger than 60.

Robust LTE uplink scheduling based on call admission control

In LTE system, it is difficult for an eNB to properly allocate uplink resource blocks (RBs) to UEs as many factors complicate the issue. So far, most research has focused on maximizing system throughput. However, this is often achieved by downgrading other performance metrics and may result in the waste of resources. In this paper, a resource allocation scheme for LTE uplink is proposed which takes into account the data rate granted by call admission control (CAC). Data rate is defined based on exponentially weighted moving average (EWMA). The scheme leads to a close match between user demand and resources actually allocated, thereby making better use of the resources. In addition, robust modulation-coding is considered in resource allocation. Results obtained via simulation show that the proposed scheme demonstrates good performance in important aspects compared to other resource allocation methods.

An Accurate Power Analysis Model Based on MAC Layer for the DCF of 802.11n

802.11 Wireless Local Area Network (WLAN) technology is now common in power sensitive devices like smart phones and personal digital assistants (PDAs). In this article, we present an accurate power consumption model based on the Bianchi model [13] and the power measurement in PHY layer [9] to predict the power consumption of 802.11n and Multiple-Inputs-Multiple-Outputs (MIMO) mode of 802.11n. In this model, we calculate the total power consumption by summing six consumed powers: the idle listening power consumed in the DIFS period, the back-off stage, the power consumed in transmitting a frame, the idle listening power consumed in the SIFS turn-around time, the power consumed in receiving an ACK frame from AP and the power consumed in the collision for one frame transmission. Our analyses and simulations show that the power consumed in idle listing will dominate the total power consumption when the number of the active stations is large. The successful possibility and MAC efficiency of 802.11n are also analyzed and simulated in this article. The imperfect channel scenario will be evaluated, too. This power analysis model to our knowledge has not been presented in the previous works so far.

Differentiating and Scheduling LTE Uplink Traffic Based on Exponentially Weighted Moving Average of Data Rate

The importance of uplink resource allocation in ensuring the Quality of Service (QoS) of guaranteed bit rate (GBR) bearers has led to the development of numerous resource allocation schemes. The criteria used in the development of such schemes include maximizing system throughput or fairness and the ability to take transmission power or user priority into account. After accepting a GBR bearer, the eNodeB (eNB) must allocate sufficient resource blocks (RBs) to guarantee the requested QoS. In order to achieve high utilization of radio resource, eNB also must allocate remaining RBs to non-GBR bearers. The QoS is generally specified by the data rate (throughput) or packet delay; however, the 3rd Generation Partnership Project (3GPP) has not specified the means by which data rates for a GBR bearer are to be measured. In this paper, we define the measurement of data rates based on the exponentially weighted moving average (EWMA), thereby enabling the eNB to perform scheduling tasks with greater accuracy. We also present an AAG-2 (Allocate As Granted-version 2) scheme capable of supporting the QoS for GBR bearers, while enabling the efficient allocation of RBs to non-GBR bearers. The existence of parties seeking superior levels of service makes it necessary for telecommunications operators to provide options with regard to QoS. This study proposes a revision of the AAG-2 scheme referred to as AAG-D to accommodate such demands. Simulation results demonstrate the efficacy of the new scheme in achieving goals related to throughput and average packet delay.

Power saving by LTE DRX mechanism using a mixture of short and long cycles

As mobile devices proliferate and their applications become diversified, energy consumption has become an important issue. Long-term evolution (LTE) and its advanced version have been standardized for the future mobile communication to meet the demand for high-speed transmission. But the heavy processing demand on the user equipment (UE) leads to excessive power consumption. Discontinuous reception (DRX) was proposed to tackle the issue. This paper focuses on the effectiveness of the mechanism in power saving. Quantitative analysis of the power saving achieved by DRX using a mixture of short and long DRX cycles is conducted. To this end two metrics, power saving factor and relative power saving, are introduced. The analysis is further corroborated by simulations using parameter values in compliance with LTE specifications. Furthermore, DRX parameters have significant influence on power saving. Therefore, values of the key parameters are varied to investigate their impacts. The findings provide insights into the operation of the DRX mechanism and form the basis for its improvement.

Co-tier uplink power control in femtocell networks by Stackelberg game with pricing

A two-way pricing mechanism is incorporated into the Stackelberg game to mitigate the co-tier interference by controlling the uplink transmit power. Specifically, by employing the pricing mechanism, leader femto base station (FBS) can get reward from follower femtocell user equipments (FUEs) and vice versa. All FBSs are assumed to operate under the co-channel mode, i.e., all FBSs use the same frequency band and every FBS is operated in the closed subscriber group (CSG) access mode. By assigning the maximum tolerable co-tier interference, the leader FBS protects itself by pricing the interference from follower FUEs. On the contrary, follower FUEs control the transmit power based on the pricing strategy of the leader. For different interference constraints, simulation results obtained by Matlab show that leader and followers can always compromise on a Stackel-berg equilibrium (SE) point where both leader and followers achieve the maximal utility. Hence, the proposed Stackelberg game with two-way pricing mechanism power control scheme provides a viable solution to mitigate co-tier interference in femtocell networks.

Fast game-based handoff mechanism with load balancing for LTE/LTE-A heterogeneous networks

Due to the development of femtocell technologies, indoor LTE/LTE-A signal quality can be significantly improved. However, since femtocells and macrocell are deployed into a coexisted heterogeneous network, handoff from macrocell to femtocell turns out to be one of the major design issues to achieve better user experience provided by femtocells. In general, the macrocell user equipment (MUE) selects a handoff target femtocell base station (FBS) in the handoff procedure solely based on the received signal strength indicator (RSSI), signal to interference plus noise ratio (SINR), or signal to noise ratio (SNR). Although this approach is very simple and easy to implement, it can result in load imbalance among FBSs. Hence, this paper proposes a novel game-based handoff mechanism that combines the modified Dutch Auction (MDA) and stochastic election process (SEP) to jointly take the uplink and downlink signal qualities and load balance of the handoff candidate FBSs into consideration when selecting handoff target FBS. Besides, in order to speed up the execution of the handoff mechanism and reduce the percentage of handoff failures, the Fast SEP and Go Back B are further developed, respectively. Simulation results confirm that the proposed MDA+Fast SEP+Go Back B handoff mechanism provides better load balance, faster handoff and higher percentage of successful handoffs.

A load-balancing handoff mechanism for two-tier femtocell networks: A game approach

In the two-tier femtocell networks, a macrocell user equipment (MUE) initiates a handoff procedure when the received signal strength from its serving macrocell base station (MBS) is below a predefined threshold. By introducing the concept of game theory, this paper proposes a handoff mechanism that comprises two phases. In the first phase, a modified Dutch auction (MDA) is used to sift the candidate femtocell base stations (FBSs) from the neighboring FBSs of the MUE. If the number of candidate FBSs is greater than one, the second phase is initiated. In the second phase, each candidate FBS determines if it wants to accept the handoff request of the MUE by executing a stochastic election process (SEP). In SEP, in order to balance the load of FBSs, an FBS with light load is with higher probability to accept the handoff request. Simulation results show that the loads of FBSs are balanced by employing the proposed game based handoff mechanism in the two-tier femtocell networks.