Hyong-Woo Lee

Performance analysis of sleep mode operation in IEEE 802.16e

The paper investigates the queueing behavior of the sleep mode operation in IEEE 802.16e for conserving the power of an mobile station (MS) in terms of the dropping probability and the mean waiting times of packets in the base station (BS) queue. In the sleep mode, when an MS wakes up at the end of each sleep interval and there is traffic addressed to it, this is notified in the listening interval immediately following the sleep interval. Otherwise, an MS again enters the sleep mode with a sleep interval which is double the length of the previous one. We modeled this sleep mode operation as M/GI/1/N with multiple vacations whose periods depend on the previous one. Our work may be a rough guide to understanding the BS queueing behavior according to parameters such as the minimum and maximum sleep interval, the BS queue size and the arrival rate of packets at a BS.

Multi-Hop Relay Based Coverage Extension in the IEEE802.16j Based Mobile WiMAX Systems

In this paper, we investigate various issues of cost- effective coverage extension in a multi-hop relay based WiBro/WiMAX systems. Since the coverage extension problem may occur in metropolitan areas as well as suburban or rural areas where user density is relatively low or moderate, we first introduce several topologies and the resulting cost-effective coverage extension methods for each case. Secondly, we propose two cost-effective coverage extension methods using two sectorized cellular approaches, one using the wide-beam tri-sector cell (WBTC) and the other using the narrow-beam tri-sector cell (NBTC). Finally, we present a practical deployment scenario consisting of three phases depending on user traffic density.

An adaptive QoS provisioning distributed call admission control using fuzzy logic control

Faced with limited radio spectrum and increased demand for broadband multimedia services in an advanced wireless network, it is becoming important to carefully manipulate handoff calls as well as new calls. In particular, there is a need for well designed call admission control (CAC) schemes that enable one to provide guaranteed QoS while efficiently utilizing the scarce radio spectrum. There have been CAC methods called distributed call admission control (DCAC) which take into consideration the traffic pattern in its adjacent cells, in addition to that in the cell where a new call request is made. However, DCAC tends to be conservative in QoS provisioning to the point that it excessively restricts access of new calls. We propose an adaptive algorithm named fuzzy logic controller for DCAC (FDCAC) which is an adaptive version of DCAC. We show by the simulation that it is possible to manage radio spectrum more flexibly than DCAC while guaranteeing the required QoS. The performance of the proposed algorithm in terms of new call blocking probability, handoff dropping probability, and channel utilization is analyzed and compared with that of previously known algorithm.

Performance analysis of a cellular network using frequency reuse partitioning

In this paper, we propose an analytical model to evaluate the performance of Frequency Reuse Partitioning (FRP) based cellular systems. In an FRP scheme, a channel with a smaller reuse factor is assigned to Mobile Stations (MSs) located near the serving Base Station (BS), whereas a channel with a larger reuse factor is assigned to MSs located near the edge of a cell. In this manner, FRP can reduce the effect of Co-Channel Interference (CCI) and improve system throughput. In order to establish an analytical model for FRP based cellular systems, we introduce a model for traffic analysis using a two dimensional Markov chain and approximate CCI levels with the power sum of multiple log-normal random components in a multi-cell environment. The performance of the FRP based system is presented in terms of channel utilization, call blocking probability, outage probability and effective throughput. The analytical results are compared with computer simulations.

Queueing Performance of IEEE 802.16 Random Access Protocol with Bulk Transmissions

In this paper, we consider the queueing performance of a subscriber station for IEEE802.16e random access protocol with bulk transmissions which is allowed with an ARQ protocol according to resource allocation scheme of a base station or adaptive modulation scheme. The queueing model of this system is modelled by using an M/G/1 type queue with set-up times and exhaustive batch service, which is solved by a generating function approach. Additionally, a piggyback probability in accordance with batch size is also obtained by analyzing a busy period.

Performance Analysis of IEEE802.16d Random Access Protocol

In this paper, we investigate the performance of IEEE802.16d random access protocol based on orthogonal code-division-multiple-access and frequency-division-multiple-access in time division duplexing mode using equilibrium point analysis. The random access protocol of IEEE802.16d is similar to demand-assigned multiple access with piggyback, in which bandwidth request is allowed at the end of data transmission. In the analysis, we consider the retransmission probability derived from a binary exponential backoff algorithm. The performance is presented in terms of initial access delay, its throughput, message transmission delay and the system throughput with piggyback by varying number of subscriber stations, number of PN codes for bandwidth request ranging, number of slot-subchannel and the parameters of the binary exponential backoff algorithm.

WLC17-2: Performance of IEEE802.16 Random Access Protocol - Steady State Queuing Analysis

In this paper, we consider the queueing performance of a subscriber station for IEEE802.16e random access protocol with piggyback operation and an ARQ. The random access protocol of IEEE802.16 is based on orthogonal frequency-division-multiple-access and code-division-multiple-access with time division duplexing mode. It is a type of demand-assigned multiple access with piggyback, in which a bandwidth request can be allowed either before transmitting data or at the end of data transmission. The queueing model of our interest is an M/G/l type queue with set-up times and exhaustive service, which is solved by a generating function approach. From the queueing analysis, we obtain the piggyback probability and the output process from the queue. The performance is presented in terms of the first and second moments of queue-size by varying number of subscriber stations in a cell, number of PN codes for bandwidth request ranging and number of slot-subchannels.

Traffic characteristics based performance analysis model for efficient random access in OFDMA-PHY system

Currently, IEEE 802.16a wireless MAN supports the contention based OFDMA-CDMA ranging subsystem for ranging operation (Initial Ranging, Periodic Ranging, Bandwidth Request)[1]. This system uses essentially the slotted ALOHA protocol. However, the number of code-slots/frame for random access transmission tends to be much greater than one and a simple Markov chain analysis may not be numerically feasible. At the same time, the frame size in number of code-slots may be dynamically adjusted based on the traffic load. In order to evaluate delay-throughput performance and stability measure of the random access protocol, we first examine the possible traffic load to be carried throughput the ranging subchannel. We the present performance analysis and numerical examples.

Performance Analysis of a Type-II Hybrid-ARQ in a TDMA System with Correlated Arrival over a Non-Stationary Channel

In this work, queueing performance of a type-II hybrid ARQ (automatic repeat request) scheme in a TDMA/TDD system with Markovian source over a non-stationary channel is analyzed by assuming infinite queue size. The system of interest can be described by an embedded Markov chain of M/G/1 type which can be solved by matrix analytic method of M/G/1 type. In the numerical examples, power and coding gains are expressed in terms of mean packet delay and dropping probability with various source and channel correlation

Stabilization of contention-based CDMA ranging channel in wireless metropolitan area networks

The current IEEE 802.16a and 802.16d standards of wireless metropolitan area networks specify a ranging channel in the OFDMA physical layer that employs a set of CDMA codes for ranging and bandwidth requests. The ranging channel is contention-based and inherently unstable. In this paper, we propose two stabilization algorithms to enable efficient utilization of the ranging channel at close to the theoretical throughput limit, and analyze their performance using a continuous time Markov chain M/M/1 model. We show how to estimate system parameters such as the number of backlogged users, arrival rate and the first exit time for the critical. Based on these parameters, we present two methods for channel stabilization, for the cases that the number of ranging codes per frame is fixed and adjusted dynamically, respectively. We then present simulation results to show that, by restricting the actual arrival rate or dynamically adjusting the number of ranging codes, the ranging channel can be stabilized under all traffic conditions.