Dong Ku Kim

Packet Scheduling Algorithms for Throughput Fairness and Coverage Enhancement in TDD-OFDMA Downlink Network

The present paper proposes two different packet scheduling algorithms in the IEEE 802.16e type TDD-OFDMA downlink, which are the weighted fair scheduling(WFS) and the throughput guarantee scheduling(TGS). The performance of proposed scheduling algorithms are compared to some of conventional schedulers such as round robin(RR), proportional fair(PF), fast fair throughput(FFTH), and fair throughput(FH) in terms of service coverage, effective throughput and fairness at 64 kbps and 128 kbps minimum user throughput requirements. For a relatively smaller throughput(64 kbps) requirement, the proposed algorithms provide higher improvement in the number of users per sector within 95 service coverage while satisfying the lxEV-DV fairness criterion. For a relatively larger throughput(128 kbps) requirement, the proposed algorithms provide higher coverage enhancement while maintaining the same effective aggregate throughput over PF scheduler.

Downlink Scheduling and Resource Management for Best Effort Service in TDD-OFDMA Cellular Networks

Throughput performance and geographical service fairness of best effort service used for downlink of a 802.16e based TDD-OFDMA sectored cellular networks are evaluated in conjunction with different scheduling schemes and frequency reuse plans. The OFDM systems are based on two multiple access schemes, which are the OFDM-TDM and OFDMA, and considered scheduling schemes are round robin, max C/I, PF and G-fair schedulers with adaptive rate control. The 3-sectored 1 FA, 3-sectored 3 FA, and 6-sectored 3 FA plans are compared in terms of throughput, capacity, and geographical service fairness, which assist in determining the choice of a scheduling and frequency reuse plan.

Downlink packet scheduling with minimum throughput guarantee in TDD-OFDMA cellular network

This paper proposes a channel scheduler in downlink of IEEE 802.16e TDD-OFDMA cellular network which provides users the minimum throughput for best effort traffic. The proposed scheduler is further developed in the consideration of the case that network might become unfeasible, where extra weight functions are introduced into the proportional fair (PF) scheduler so that the proposed extra weight function provides more resources to users who are easier to achieve the target throughput than those who cannot. It does not guarantee target throughput for all users but eventually increases the number of users being served with the guaranteed minimum throughput. It is investigated for the proposed schedulers and other conventional ones how large the throughput is and how many users are guaranteed the target throughput. Simulation results show that the proposed algorithms have 10 to 20 % more users being served with the minimum guaranteed throughput. The trade-off between the throughput guarantee level and sector throughput is shown in the proposed schedulers.

Coverage Enhancement in TDD-OFDMA Downlink by Using Simple-Relays with Resource Allocation and Throughput Guarantee Scheduler

Simple-relay aided resource allocation (SRARA) schemes are incorporated with throughput guarantee scheduling (TGS) in IEEE 802.16 type time division duplex-orthogonal frequency division multiple access (TDD-OFDMA) downlink in order to enhance service coverage, where the amount of resources at each relay is limited due to either its available power which is much smaller than base station (BS) power or the required overhead. The performance of SRARA schemes is evaluated with both proportional fair (PF) and TGS schedulers at 64kbps and 128kbps user throughput requirements when total RS power is set to 500 mW or 1 W. For SRARA with RSs of relatively lower power (500mW), schemes that put total power into only one subchannel offer larger coverage than when both subchnnels are used with equal power allocation, while the RS with evenly power-allocated two subchannels could provide larger coverage gain for a relatively higher power (1 W). Depending upon the target throughputs it is shown which of the relay scheme or scheduler design would play more important role in improving coverage. In a lower target (64 kbps), more improvement comes from relay scheme rather than scheduler design. For a relatively higher level (128 kbps), it comes from scheduler design rather than relay due to the fact that simple relay cant help using strictly limited amount of resources.

Modified RWGH and positive noise mitigation schemes for TOA geolocation in indoor multi-hop wireless networks

Time of arrival (TOA) based geolocation schemes for indoor multi-hop environment are investigated and compared to some of conventional geolocation schemes such as least squares (LS) or residual weighting (RWGH). The multi-hop ranging involves positive multi-hop noise as well as non-line of sight (NLOS) and Gaussian measurement noise, so that it is more prone to ranging error than one-hop range. In this paper, RWGH algorithm is modified by adapting weighted residual normalization considering the number of hops taken to measure each ranging. The iterative positive noise mitigation schemes are further developed by using distance enlargement test (DET) to mitigate the multi-hop ranging noise. Simulation results show that the proposed modified RWGH algorithms show 5 to 25% smaller average estimation error compared to LS and RWGH for both positive noise mitigation and no mitigation cases, and the positive noise mitigation schemes provide 28 to 42% error mitigation compared to no mitigation schemes.

Channel state-aware joint dynamic cell coordination scheme using adaptive modulation and variable reuse factor in OFDMA downlink

In this paper, two different dynamic cell coordination stratagies for frequency selective and flat fading are proposed for efficient subcarrier allocation in the joint consideration of adaptive modulation and variable frequency reuse in the channel-aware OFDMA downlink multicellular environment. Compared to a conventional OFDMA system without cell coordination, where system throughput may become degraded due to the persistent interference from other cells, the proposed system dynamically allows RNC to apply different reuse factors on each subchannel and scheduling in consideration of channel and interference conditions of individual users so as to increase the system throughput and guarantee QoS of each user. In a selective fading channel, the proposed schemes showed 2.6 times as large throughput as that of a single reuse factor of one for all subcarriers. In a frequency flat fading, the dynamic scheme with the proposed scheduling achieves on average three times larger throughput than the conventional dynamic scheme [8].

Analysis on Call Blocking Probability of Streaming Data Service in CDMA System Interworking with WLAN for Different Cell Geometry

Call blocking probability of streaming data service in CDMA system interworking with access point(AP) of WLAN is analyzed for different cell geometry of base station(BS) and AP. Queuing is modeled. The considered system leads to successful handoff between APs of WLAN. Blocking probability is calculated as a function for the ratio of BS and AP size, their location and the number of buffers. Results show that blocking probability is not influenced by BS and AP location but mainly by the ratio of their size. For CDMA system of radius 100m, 5 buffers and 7dB noise rise(NR), in order to obtain 1% call blocking probability, CDMA system interworking with WLAN of radius 20m has more 0.4Erlang than that of radius 60m.

Scheduling of QoS Guaranteed Services in DS-CDMA Uplink Networks: Modified Weighted G-Fair Algorithm

In this paper, the modified weighted g-fair (MWGF) scheduling scheme with rise over thermal (RoT) filling is proposed for QoS guaranteed services in DS-CDMA uplink networks, in which RoT is directly related to the loading factor of a wireless network. The proposed scheme computes priorities of QoS guaranteed traffic for each slot based upon the weighted values of the QoS factor, channel factor, and fairness factor. Once priorities are assigned, power and rate used for each user are computed within a limited RoT by using RoT filling, which adjusts the transmit rate of the traffic assigned least priority. The proposed algorithm increases more throughput by 6 to 10 % compared to that of the current autonomous rate control (ARC) scheme. It also lowers transmission delays and ensures more fairness in delay outages than the round robin scheduler and ARC scheme.