Kuo-Chang Ting

An idle listening-aware energy efficient scheme 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). However, the energy efficiency of such devices will be very low, especially for next generation WLAN technology. The reasons for this include the existence of a large number of active stations, short data time and ultra high physical layer (PHY) data rate, which are the characteristics of next generation WLAN technology. This poor energy efficiency will be due to the fact that the device will consume a lot of idle-listening energy during the Distributed InterFrame Space (DIFS) and back-off time, and that the energy consumed for idle listening is similar to the energy consumed while receiving data. In this article, we propose an intelligent scheme for reducing the energy consumed in idle listening. Our analysis and simulation programs show that our scheme can lengthen the battery endurance due to the shortening in idle-listening time effectively especially when the number of active stations is large. An important characteristic of our scheme is that it is fully compatible with legacy Distributed Coordinated Function (DCF), and there will be no throughput reduction if this power saving scheme is applied to the DCF of 802.11. We also propose an accurate power consumption model in the MAC layer which to the best of our knowledge has not been presented in any earlier research.

Delay and Power Consumption in LTE/LTE-A DRX Mechanism With Mixed Short and Long Cycles

Energy consumption is a major concern in todays wireless communications due to the consensus for a greener world. LTE-Advanced (LTE-A) has been standardized for the fourth-generation mobile communications to meet the growing demands for high-speed wireless communications. However, high-speed signal processing on LTE/LTE-A user equipment (UE) causes excessive power consumption. The discontinuous reception (DRX) mechanism is a critical technique for tackling this issue. Delay constraint and power savings are two contradictory performance metrics associated with the DRX mechanism. Using recursive deduction and Markov model, this paper provides an in-depth analysis on the average delay and average power consumption of the DRX mechanism. Two performance metrics, namely, power-saving factor and relative power saving, are devised to assess the power-saving performance of the DRX mechanism. The accuracy of theoretical analysis is validated by computer simulations using the parameters in compliance with LTE specifications. The performance of the DRX mechanism is governed by a set of parameters that interact with one another in an intricate manner. Therefore, the values of key parameters are tested to assess their impacts on the performance of the DRX mechanism. The results shown in this paper give an insight into the operation and further improvement of the DRX mechanism.

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.

Design and Analysis of Enhanced Grouping DCF Scheme for the MAC Layer Enhancement of 802.11n with Ultra-high Data Rate

The 802.11 has emerged as the prominent wireless LAN technology as the mobile computing devices such as notebooks and PDA have replaced the desktop computers to be the main trend products. However, if the number of active stations is large, that is high-loading condition for the legacy DCF of 802.11, the capacity will be very low due to high collision costs. In this paper, <i>we</i> <i>introduce</i> <i>the</i> <i>TDMA</i> <i>concept</i> <i>to</i> <i>partition</i> <i>all</i> <i>numerous</i> <i>active</i> <i>stations</i> <i>into</i> <i>several</i> <i>groups</i> <i>to</i> <i>avoid</i> <i>all</i> <i>stations</i> <i>transmitting</i> <i>the</i> <i>frames</i> <i>simultaneously</i>. When Point Coordinator (PC, generally referring to AP) finds that the number of active stations (<i>M</i>) is large i.e. bigger than 8, it broadcasts number of groups (<i>N</i>), group head (<i>Nh</i>) bits and start grouping bit sequence (<i>k</i>) (such as 00000100 00000000 00000000) information in the TIM field of the beacon frame. Once all stations receive this instruction, the stations which last two LSB bits (because <i>k</i>=0, <i>N</i>=4) of the MAC address (IEEE EUI-48 or EUI-64) are 00 belonging to group 0 will transfer their frame first. On the contrary, all stations belonging to other groups will set their waiting time, that is, Network Allocation Vector (NAV) much more precisely. In this article, we also proposed a fast selection scheme to get the optimal start grouping bit sequence which aims to partition all the active stations into a few groups more uniformly to reduce the number of members in each group so that we can reduce the Contention window Minimum (<i>CWMiri</i>), that is, backoffs idle overhead.

WLC34-5: GDCF: Grouping DCF for the MAC layer enhancement of 802.11

The 802.11 has emerged as the prominent wireless LAN technology as the mobile computing devices such as notebooks and PDA have replaced the desktop computers to be the main trend products. However, if the number of active stations is large for the legacy backoff algorithm (DCF) of the 802.11, the capacity will be very low due to high collision cost. In this paper, we introduce the TDMA concept to partition all numerous active stations into several groups to avoid all stations transmitting the frames simultaneously. When Point Coordinator (PC, generally referring to AP) finds that the number of active stations (M) is large i.e. bigger than 16, it broadcasts grouping number and grouping head bits (such as 00000100 00000000) information in the TIM field of the beacon frame. Once all stations receive this instruction, the stations which last two LSB bits of the MAC address are 00 belonging to group 0 will transfer their frame first. On the contrary, all stations belonging to other groups will set their waiting time, that is, Network Allocation Vector (NAV) much more precisely. Analysis shows that the capacity of our GDCF will be near to the theoretical capacity of 802.11 WLAN even if the distributions of all active stations among all groups are not so uniform. This capacity could be independent of the number of active stations and CWmax (contention window maximum).

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.