J. Wigard

Aalborg University, Ålborg, North Denmark, Denmark

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Publications (51)0.43 Total impact

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    ABSTRACT: Small cells are popular deployment options for coverage holes and capacity hotspot areas. Due to the poor outdoor-to-indoor propagation property of in-building environment, a dedicated wireless system installed inside the building is often preferred for providing indoor users high- data-rate services. Distributed antenna systems and Femto cells are cost-efficient techniques for this application. In this paper, their performance is evaluated in an LTE downlink context along with a proposed joint scheduling system, which maximizes the supported number of users under a QoS constraint. The selection of the enterprise building model includes a general office building model described in the WINNER II project and a site-specific office building with large scale path-loss values retrieved from measurements. Results show superior performance of the Femto system compared to DAS in providing high-data-rate services in most cases with a quality-guaranteed scheduler, while the centralized joint scheduling system gives the best performance. The centralized scheme can also help improve the system robustness in obtaining high performance even in the situation where access points are placed non-optimally.
    Proceedings of the 73rd IEEE Vehicular Technology Conference, VTC Spring 2011, 15-18 May 2011, Budapest, Hungary; 01/2011
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    ABSTRACT: In this paper traffic steering between a High- Speed Downlink Packet Access (HSDPA) network and a 3GPP Long Term Evolution (LTE) network with different carrier frequencies is investigated. First, two traffic steering algorithms, relying on static network information, are assessed from a traffic theoretical point of view and numerically. Furthermore, numerical analysis of two traffic steering algorithms, relying on dynamic information such as user SINR and cell load, is also performed. It is shown that the dynamic traffic steering algorithms outperform the static methods in terms of end user performance. Finally, it is investigated how the LTE terminal penetration affects the performance of the proposed traffic steering algorithms. For low LTE terminal penetration all LTE capable terminals should be pushed to the LTE network, and for high LTE terminal penetration a more dynamic traffic steering scheme should be used. I. INTRODUCTION
    Proceedings of the 73rd IEEE Vehicular Technology Conference, VTC Spring 2011, 15-18 May 2011, Budapest, Hungary; 01/2011
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    ABSTRACT: In the Long Term Evolution system Discontinuous Transmission and Reception (DRX/DTX) has been introduced to extend the terminal battery lifetime. In this paper, we study the energy-saving provided by this mechanism and the impact on the QoS performance of Voice over IP (VoIP) traffic under dynamic and semi persistent packet scheduling strategies. Simulations and analytical results show that the DRX/DTX scheme can reduce the terminal power consumption without compromising the required VoIP QoS in terms of maximum air-interface delay. However, it does not provide any further power savings if the terminal is asleep for a period longer than 20 ms. It is shown that the power savings are larger for semi persistent scheduling than for dynamic packet scheduling at the cost of a lower spectral efficiency. I. INTRODUCTION HE development of new mobile communication systems, such as Long Term Evolution (LTE), aim to promote an improved perceived experience for the end user, providing higher data rates and lower latencies. This makes wireless devices a great platform to run a whole new set of services and applications. However, the improvement of data transmission and computation technologies in mobile devices stands significantly above the slower growth of battery performance. This makes the power consumption one of the critical issues to solve when developing new mobile systems. For this reason, one of the key objectives in supporting the LTE system is an improved efficient utilization of battery power. LTE exploits the mechanism of Discontinuous Reception (DRX) and Discontinuous Transmission (DTX) as a practical solution to this issue (1). Normally, the terminal is required to monitor the control channels to receive e.g. scheduling information, and therefore needs to activate its RF modem at regular intervals. With DRX/DTX the terminal can limit the monitoring intervals and thereby avoid the high power consumption of the modem. Due to the lower terminal activity, and thus eligibility for scheduling, the network is however somewhat constrained in fulfilling Quality of Service (QoS) and spectral efficiency targets. Discontinuous reception was studied previously for web browsing traffic in (2,3). It was found that with DRX more than 80% of the power consumption could be saved, while having a marginal impact on the end user performance. In this article, instead, we want to focus on DRX/DTX performance for VoIP application where different QoS requirements are evident and hence necessitates a dedicated study. Since LTE completely relies on packet switched networks and voice data will be routed with the VoIP technology. the LTE scheduler has to provide tight packet delivery in order to meet QoS requirements in terms of maximum air-interface delay. Clearly, the use of DRX/DTX, and its configuration, has an impact on the scheduling delays and this puts a limitation on how much power saving can be achieved for VoIP traffic. The outline of this article is as follows. In section II and III the DRX concept for LTE and different scheduling strategies are explained. Section IV contains the simulation setup, while an analytical model estimating the power savings of DRX for VoIP is introduced in section V. Section VI contains the simulations results and analysis. Finally, the conclusions can be found in section VII.
    Proceedings of the 73rd IEEE Vehicular Technology Conference, VTC Spring 2011, 15-18 May 2011, Budapest, Hungary; 01/2011
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    ABSTRACT: For the future LTE-Advanced network, one of the requirements in the uplink (UL) direction is to enhance the celledge user performances. Coordinated multi-point reception in the UL is one of the techniques being investigated to further improve the performance of LTE networks. With the help of the information coordination through the links between the sites and advanced receivers the UL performance can be improved. The simulation results show that, with the ideal interference cancellation, inter-Site maximum ratio combining, and optimized closed-loop and open-loop fractional power control, there are about 27% gains for the 5% outage user throughput and 12% gains for the average user throughput. As shown in this paper, these gains from UL macro-scopic multi-cell combining between sites are achieved for optimized power control, ideal interference cancellation receivers, and X2 with no delay and high bandwidth.
    Vehicular Technology Conference (VTC 2010-Spring), 2010 IEEE 71st; 06/2010
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    ABSTRACT: This paper deals with packet scheduling for Voiceover-IP (VoIP) traffic in the Long Term Evolution (LTE) EUTRAN Downlink. The more specific target is to optimize the performance of dynamic scheduling for traffic mixes of VoIP and best effort users. To this end, we introduce the Required Activity Detection (RAD) packet scheduling algorithm with Delay Sensitivity (RAD-DS).With an appropriate delay sensitivity function, it is shown that a MACRO 1 cell with 5MHz transmission bandwidth can support up to 346 VoIP users. Furthermore, a novel delay sensitivity based soft prioritizing strategy is proposed for handling traffic mixes. It is shown that when 200 VoIP users are present in a cell along with best effort users, the proposed strategy can provide a cell throughput of up to 82% of the cell throughput with only best effort users.
    Vehicular Technology Conference (VTC 2010-Spring), 2010 IEEE 71st; 06/2010
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    ABSTRACT: This paper studies the different ways of extending wireless coverage for high data rates and improving the data capacity in a building. The solutions considered include deployments of single or multiple small base stations, i.e. Picocell or Femtocell, and distributed antenna system, operated on the same frequency as the macro cellular network. We look at the radio performance of each solution in a LTE downlink context with in-building path loss values retrieved from real-life measurements. The performance is compared by means of maximum supportable user numbers and average system throughput. Potential gains by hard frequency reuse in the building and QoS based packet scheduling are examined. Simulation results show the robustness of the proposed distributed antenna system and the conditions for multi-Femtocell deployment.
    Vehicular Technology Conference (VTC 2010-Spring), 2010 IEEE 71st; 06/2010
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    ABSTRACT: In LTE Uplink, the slow varying pathgain and shadowing are compensated by the standardized open loop power control (OLPC) which is based on a power density offset and a compensating factor for the pathloss experienced by the users. The optimization of those parameters reveals a dependency on the allocated bandwidth. A Load Adaptive Power Control (LAPC) algorithm is proposed to handle the bandwidth variations and ensure optimal system performance. In this contribution it is shown that using closed loop power control commands to adapt the transmission power density to the used bandwidth, it is possible to achieve coverage gains up to 60% while maintaining a cell throughput comparable to the reference case.
    Wireless Conference (EW), 2010 European; 05/2010
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    ABSTRACT: This paper focuses on the Physical Downlink Control Channel (PDCCH) and describes the impact of its realistic constraints on the performance in E-UTRAN LTE TDD system, particularly considering the asymmetric slot resources between downlink and uplink. It is described, when adopting the same PDCCH manager framework in LTE FDD system as in LTE FDD system, the uplink users are not prioritized sufficiently regarding less uplink subframe under most of TDD UL/DL configurations. Therefore, it is proposed, the joint list in the PDCCH manager framework can be adjusted semi-statically to perfectly match TDD UL/DL configurations, and assuming ideal traffic monitoring this can furthermore provide more freedom and flexibility for wider range of UL/DL service requirement, without changing the overall TDD UL/DL configurations. The simulation results proved that the TDD-oriented PDCCH framework can satisfy UL/DL traffic requirement via exploiting the flexibility of joint list based on semi-statistically monitoring and adjustment.
    01/2010;
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    ABSTRACT: In the UTRAN long term evolution (LTE), the downlink data channel is shared among the active users through the orthogonal frequency division multiple access (OFDMA) technique, and high gains can be achieved by using dynamic packet scheduling. Control channels introduce an additional overhead, but also play a key role in exploiting such gains. This paper focuses on the physical downlink control channel (PDCCH) and introduces the main PDCCH related features which need to be analyzed in order to minimize its impact on the system performance.
    Vehicular Technology Conference Fall (VTC 2009-Fall), 2009 IEEE 70th; 10/2009
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    ABSTRACT: This paper focuses on the Physical Downlink Control Channel (PDCCH) and describes the impact of its realistic constraints. Specifically, the impact on the performance of the UTRAN LTE FDD downlink and on the QoS provisioning is studied. It is described, when adopting a QoS-aware packet scheduling policy, how scheduling limitations due to control channel may affect the scheduler behavior. It is shown that the system level performance degradation could be kept negligible utilizing the dynamic link-adaptation mechanisms available on the control channel and adopting careful control channel-related design solutions. Therefore, assuming a proper dimensioning in terms of OFDM symbols reserved for control, the PDCCH could simply be modeled for LTE FDD system level simulation purposes by limiting the number of PDCCH allocations. Such a number primarily depends on the system bandwidth.
    Vehicular Technology Conference Fall (VTC 2009-Fall), 2009 IEEE 70th; 10/2009
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    ABSTRACT: The UTRAN long-term evolution (LTE) specifications provide flexible means to achieve micro-sleep operation for user equipment (UE) even though it is in active mode and running a service. By means of a discontinuous reception (DRX) framework, pauses in the transmission due to natural traffic characteristics or network prioritization can be utilized. The specifications give a number of options to optimize the performance. In this paper two of those possibilities are compared. Long DRX with the use of an inactivity timer is compared to the usage of short DRX on top of long DRX. The performance is evaluated in terms of user throughput, power consumption, and network performance, while using a realistic RF modem power consumption model for the UE. For bursty traffic, short DRX shows a gain of up to 100% over DRX with just an inactivity timer, when measuring throughput per power unit consumed in case of one or multiple users being present in the cell.
    Communications Workshops, 2009. ICC Workshops 2009. IEEE International Conference on; 07/2009
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    ABSTRACT: Antenna tilt is an effective inter-cell interference reduction technique which has been studied a lot previously in the CDMA-based systems. In this paper, we concentrate on the evaluations of the mechanical antenna downtilt in the uplink LTE networks. The SINR performance and the trade-off between the cell coverage and capacity are studied in a homogeneous scenario. Simulation results in Macro 1 show, downtilt angle at 12° to 16° has the optimal performance in terms of SINR and the cell coverage is maximized at downtilt angle 16°. The interaction of the antenna tilt with the open loop power control scheme defined in the 3GPP standard is also studied. Results show that, with certain ¿ value, there is no impact to the choice of optimal P<sub>0</sub> value with different antenna downtilt angles. For the ¿ value equal to 0.6 and 1.0 respectively, there are about 75% and 37.5% increases in terms of cell coverage and about 47% and 39% increases in terms of cell capacity.
    Wireless Communication Systems. 2008. ISWCS '08. IEEE International Symposium on; 11/2008
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    ABSTRACT: In LTE uplink, the slow varying path gain and shadowing are compensated by the standardized open loop power control (OLPC). Further optimization of the system performance can be done via closed loop power control commands. In this contribution, it is shown that using such commands to control the interference caused by users to the system, it is possible to achieve a gain in the order of 20% on the average cell throughput while maintaining the same outage cell throughput compared to the performance of the OLPC. Furthermore, gain on both average and outage cell throughput can be achieved by tuning the parameters of the proposed scheme.
    Wireless Communication Systems. 2008. ISWCS '08. IEEE International Symposium on; 11/2008
  • T. Kolding, J. Wigard, L. Dalsgaard
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    ABSTRACT: The UTRAN long-term evolution (LTE) provides flexible means to achieve micro-sleep operation for user equipment (UE) even though it is in active mode and running a service. By means of a discontinuous reception (DRX) framework pauses in transmission due to natural traffic characteristics or network prioritization can be utilized. However, the optimum setting of parameters must be provided as a compromise among reaction latency, user throughput, power consumption, and network performance. Using a realistic RF modem power consumption model for the UE, we investigate different algorithms for optimizing the balance among user throughput and power saving using a Web-browsing session as the reference. We show that with proper configuration of the DRX parameters we can optimally achieve a 95% reduction of the UE power consumption with only a moderate and acceptable 10-20% loss of experienced throughput.
    Wireless Communication Systems. 2008. ISWCS '08. IEEE International Symposium on; 11/2008
  • Naizheng Zheng, J. Wigard
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    ABSTRACT: The 3GPP UTRAN Long Term Evolution (LTE) system utilizes packet based architecture with distributed mobility management, where the E-UTRANNode-B (eNB) takes the responsibility of making the hard handover/handoff (HO) decisions based on the user equipment (UE) measurements. To cope with the corner effect due to the loss of the line of sight (LOS), a fast HO decision algorithm is required which can guarantee the LTE seamless HO requirement and keep the quality of service (QoS) criteria. In this paper, a HO decision algorithm, the integrator algorithm, has been evaluated in the Manhattan scenario, and is compared with the traditional power budget (PBGT) handover. The study focuses on the LTE intra-frequency HO scenario and uses the reference symbol received power (RSRP) measurement as input. The results show that the integrator algorithm has the same performance as the PBGT algorithm based on the number of HOs per UE and signal to interference plus noise ratio (SINR) evaluations for different UE speeds.
    Vehicular Technology Conference, 2008. VTC 2008-Fall. IEEE 68th; 10/2008
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    ABSTRACT: This paper illustrates the optimization of design parameters for quality-of-service (QoS) aware packet schedulers in multi-service environments with WCDMA/HSDPA. The optimization sets the objective of maximizing the cell throughput while meeting certain minimum QoS criteria and focuses on two variants of the proportional fair with barrier function (PF-B) family of schedulers and on the proportional fair with required activity detection. The assessment on the sensitivity of the scheduler parameters to the traffic load and mixture is evaluated in scenarios with both real-time (streaming) and non real-time type of users (web browsing). This study shows that the PF-B schedulers require a per scenario dedicated optimization, while PF-RAD is quite insensitive and robust to support a general traffic mix. Overall, PF-RAD significantly outperforms PF-barrier schedulers in the investigated scenarios, providing up to 100% streaming cell throughput gain.
    Wireless Communication Systems, 2007. ISWCS 2007. 4th International Symposium on; 11/2007
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    ABSTRACT: To minimize the terminal's transmission power in bursty uplink traffic conditions, the evolved high-speed uplink packet access (HSUPA) concept in 3GPP WCDMA includes a feature known as dedicated physical control channel (DPCCH) gating. We present here a detailed link level study of gating from a link efficiency (LE) perspective; LE being expressed in bits per second per Watt. While the overall gain mechanisms of gating are well known, we show how special challenges related to discontinuous enhanced dedicated channel (E-DCH) transmission can be addressed for high link and system performance. We consider the E-DCH performance degradation caused by gating on other radio procedures relying on the DPCCH, such as inner and outer loop power control. Our studies show that gating is beneficial for both for 2 and 10 ms transmission time intervals. The gains in terms of LE with a vehicular A 30 kmph channel are in the range of 4-5 dB for a bit rate of 32 kbps and an E-DCH activity factor of 0.1. For bit rates higher than 1 Mbps and an activity factor of 0.25, the gains are close to zero or even negative.
    Personal, Indoor and Mobile Radio Communications, 2007. PIMRC 2007. IEEE 18th International Symposium on; 10/2007
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    ABSTRACT: The E-HICH is a downlink control channel associated to the HARQ procedure in HSUPA. It allows the MAC-e entity in the NodeB to signal the correct or incorrect reception of a given MAC-e PDU by transmitting ACKs or NACKs. Errors on this channel can cause misinterpretations and impact the overall system performance. This paper looks at the performance impact caused by two types of errors: ACK misinterpreted as NACK and vice versa. Detailed user and system performance results versus the error levels on the E-HICH are provided for both cases. A2N errors cause a direct degradation of the user throughput that increases with the probability. N2A errors have a more intricate impact that leads to opposite effects. On the one hand, it causes the level of RLC retransmissions to increase. On the other hand, the missing PDUs change the HARQ operating point which will then decrease the RLC retransmission level. The overall consequence is a lowered cell and user throughput for lowly loaded networks, whereas it is almost imperceptible in fully loaded networks.
    Proceedings of the 65th IEEE Vehicular Technology Conference, VTC Spring 2007, 22-25 April 2007, Dublin, Ireland; 01/2007
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    ABSTRACT: The relative contribution of the transport network towards the per-user capacity in mobile telecommunication systems is becoming very important due to the ever increasing air-interface data rates. Thus, resource management procedures such as admission, load and handover control can make use of information regarding the available bandwidth in the transport network, as it could end up being the bottleneck rather than the air interface. This paper provides a comparative study of three well known available bandwidth estimation techniques, i.e. TOPP, SLoPS and pathChirp, taking into account the statistical conditions of the available bandwidth and assessing the variability of their estimations. Simulation-based studies on a mobile transport network show that pathChirp outperforms TOPP and SLoPS, both in terms of accuracy and efficiency
    Personal, Indoor and Mobile Radio Communications, 2006 IEEE 17th International Symposium on; 10/2006
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    ABSTRACT: This paper presents HSDPA performance evaluation in an urban micro cell environment with outdoor base station antenna heights below roof-top level (10 m) and both outdoor and indoor pedestrian mobiles (3 km/h). A path loss model which accounts for the 3D geometry of the radio environment is used, thus allowing the simulation of indoor user locations at different building floor levels. The single user throughput evaluation is carried out using realistic HSDPA link-level simulations combined with the newly obtained statistics of the geometry factor in the considered micro cell environment. The results with 80% HSDPA power and 15 HS-PDSCH multi-codes showed median single-user throughput in the range of 4.8 Mbps/cell. It was also found that ground floor areas can be served with up to 5% better median throughputs compared to the outdoor and high (top) floor areas
    Personal, Indoor and Mobile Radio Communications, 2006 IEEE 17th International Symposium on; 10/2006

Publication Stats

331 Citations
0.43 Total Impact Points

Institutions

  • 1995–2010
    • Aalborg University
      • Department of Electronic Systems
      Ålborg, North Denmark, Denmark
  • 2006–2009
    • Nokia Siemens Networks
      Esbo, Southern Finland Province, Finland
  • 2005
    • Nokia
      Esbo, Southern Finland Province, Finland