Saewoong Bahk

Cell-Throughput Analysis of the Proportional Fair Scheduler in the Single-Cell Environment

The fairness concept has been widely studied in the area of data networks. The most well-known fairness criterion (max-min fairness) gives priority to the minimum-rate session. Kelly questioned its appropriateness in his works on the bandwidth sharing among the end-to-end flows and proposed another fairness criterion preferring short-distance flows to enhance the overall throughput, which is called the proportional fairness (PF). A simple scheduler achieving this objective was introduced in wireless access networks and revealed that it can achieve a good compromise between cell throughput and user fairness. Although it has received much attention for some time, research on its performance mainly depended on computer simulations. In this paper, we analyze the PF scheduler to obtain the cell throughput, which is a primary-performance metric, and extend the result to analyze the capacity of multiple-input-multiple-output systems. We evaluate the effect of various parameters on the throughput of the PF scheduler through the numerical analysis

Dynamic multi-path routing and how it compares with other dynamic routing algorithms for high speed wide area network

In this paper we describe briefly a dynamic multi-path routing scheme that has been considered for connection oriented homogeneous high speed networks. The fundamental objective of the scheme is to bridge the gap between routing and congestion control as the network becomes congested. Because propagation delay far out shadows queueing and transmission delay in high speed networks, the proposed routing scheme works as a shortest path (minimum hop) first algorithm under light traffic conditions. However as the shortest path becomes congested, the source node uses multiple paths when and if available in order to distribute the load and reduce packet loss. The scheme is a cross between Alternate Path routing and Trunk Reservation. We compare the performance of the proposed scheme with the Shortest Path Only algorithm, the Alternate Path routing algorithm, the Random Routing algorithm, and the Trunk Reservation scheme. The throughput and packet loss performance are compared via simulations. These have been carried out concentrating on a 5 node network with varying traffic patterns, the intention being to gain insight into the strengths and weaknesses of the various schemes.

Resource management policies for fixed relays in cellular networks

Mobile stations in the cell boundary have poor spectral efficiency due to the path loss and the interference from adjacent cells. Therefore it becomes an important issue to satisfy QoS requirements of each MS at the cell boundary. The deployment of fixed relay stations has been actively considered to solve this spectral efficiency problem at the cell boundary. In this paper, we consider some radio resource management policies that are path selection rule, frequency reuse pattern matching, and frame transmission pattern matching among cells. We evaluate performances of using relays under these policies by varying parameter values such as the relay stations position and frequency reuse factor. Through Monte Carlo simulations and mathematical analysis, we also suggest some optimal values of parameters and policies.

Flexible Design of Frequency Reuse Factor in OFDMA Cellular Networks

The OFDMA systems are emerging for future cellular networks. Creating multiple data channels, they can support the flexible frequency reuse factor (FRF). Although FRF 1 is the best choice in terms of cell throughput, it causes intercell interference at the cell boundary, thereby being unable to serve the whole cell area. Therefore it was proposed to use the FRF of greater than 3. In this paper, we develop a flexible FRF design mechanism that provides an intermediate value between 1 and 3 while the conventional schemes are dedicated to use some integer numbers only such as 3, 4, or 7. In our design, if the number of shared channels between any neighboring cells is given, we implement it simply according to a difference set. Simulation results show that a FRF of 7/4 achieves better throughput than FRF 3 and overcomes the intercell interference problem of FRF 1, so it can replace the conventional FRF such as 3. We expect that our new FRFs have the advantage in supporting smooth handoff because there are always some common channels between two neighboring cells.

A novel multiple access scheme for uplink cellular systems

A novel multiple access scheme for the uplink cellular systems, referred to as FH/SS-OFDMA, is proposed. The proposed scheme employs both frequency hopping and code multiplexing on the frequency domain to acquire frequency diversity and suppress intercell interference. The performance of the proposed scheme is investigated and evaluated in cellular environments and compared with that of other multiple access schemes. It has been found that the proposed one outperforms other multiple access schemes. Simulation results for various parameters, such as system load, modulation scheme, spreading factor, and interference level are also presented.

Realistic cell-oriented adaptive admission control for QoS support in wireless multimedia networks

An important quality-of-service (QoS) issue in wireless multimedia networks is how to control handoff drops. We propose admission-control algorithms that adaptively control the admission threshold in each cell in order to keep the handoff-dropping probability below a predefined level. The admission threshold is dynamically adjusted based on handoff-dropping events. We first present a simple admission-control scheme that brings out an important performance evaluation criterion - intercell fairness - and serves as a reference point. We then investigate the intercell unfairness problem and develop two enhanced schemes to overcome this problem. The performance of these protocols is benchmarked and compared with other competitive schemes. The results indicate that our schemes perform very well while, in addition, achieving significantly reduced complexity and signaling load.

Joint Subcarrier Assignment and Power Allocation in Full-Duplex OFDMA Networks

Recent advances in the physical layer have demonstrated the feasibility of in-band wireless full-duplex which enables a node to transmit and receive simultaneously on the same frequency band. While the full-duplex operation can ideally double the spectral efficiency, the network-level gain of full-duplex in large-scale networks remains unclear due to the complicated resource allocation in multi-carrier and multi-user environments. In this paper, we consider a single-cell full-duplex OFDMA network which consists of one full-duplex base station (BS) and multiple full-duplex mobile nodes. Our goal is to maximize the sum-rate performance by jointly optimizing subcarrier assignment and power allocation considering the characteristics of full-duplex transmissions. We develop an iterative solution that achieves local Pareto optimality in typical scenarios. Through extensive simulations, we demonstrate that our solution empirically achieves near-optimal performance and outperforms other resource allocation schemes designed for half-duplex networks. Also, we reveal the impact of various factors such as the channel correlation, the residual self-interference, and the distance between the BS and nodes on the full-duplex gain.

MAC sleep mode control considering downlink traffic pattern and mobility

Energy of a mobile terminal (MT) is an important resource, so recent wireless network protocols like IEEE 802.11 and IEEE 802.16 include energy saving techniques. These protocols, however, have a problem in minimizing energy loss under varying traffic pattern and mobile environment. In this paper, we propose a sleep mode interval control algorithm that considers downlink traffic pattern and terminal mobility to maximize energy-efficiency. Through simulations, we show that our proposed algorithm improves energy saving and delay performance. There is no energy loss because it does not incur unnecessary cell searching in multi-cell environments.

Scheduler Design for Multiple Traffic Classes in OFDMA Networks

This paper considers some scheduler structures that are executable in environments of multiple traffic classes and multiple frequency channels. In designing a scheduler structure for multiple traffic classes, we first propose a scheduler selection rule that uses the priority of traffic class and the urgency level of each packet. Then we relax the barrier of traffic class priority if a packet of higher priority has some room in waiting time. This gives us a chance to exploit multi user diversity, thereby giving more flexibility in scheduling. Our considered scheduler can achieve higher throughput compared to the simple extension of conventional modified largest weighted delay first (MLWDF) scheduler while maintaining the delay performance of QoS class traffic. We also design a scheduler structure for multiple frequency channels that chooses a good channel for each user as much as possible to exploit frequency diversity. The simulation results show that our proposed scheduler increases the total system throughput up to 50% without degrading the QoS performance of delay. Our schedulers are suited to be deployed for OFDMA systems like IEEE 802.16 systems that have plenty of frequency channels and use the adaptive modulation and coding (AMC) scheme.

Opportunistic Routing for Smart Grid With Power Line Communication Access Networks

Power line communications (PLCs) have recently absorbed interest in the smart grid since they offer communication capability in an easy and simple deployment. The main role of PLC access network (PLC-AN), which is constructed with medium and low voltage distribution networks, is to exchange control signals between substations and end users or to provide the Internet access to homes. Since a transmission signal of narrowband PLC penetrates electronic devices, a use of opportunistic routing (OR) can be a viable option in PLC-AN design. In this paper, we investigate the feasibility of OR use in PLC-AN and propose a customized OR for it, named PLC-OR, which uses static geographical information. For doing this, we formulate a bit-meter per second maximization problem and solves it in a distributed manner. Through simulations, we confirm that our proposed PLC-OR successfully reduces packet transmission time compared to the traditional sequential routing while achieving the same level of reliability in packet delivery.