Jun-Bae Seo

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.

Design and Analysis of Backoff Algorithms for Random Access Channels in UMTS-LTE and IEEE 802.16 Systems

In this paper, we examine the performance of uniform backoff (UB) and binary exponential backoff (BEB) algorithms with retry limit, which can be used in the random-access channels of Universal Mobile Telecommunication System (UMTS)-Long Term Evolution (LTE) and IEEE 802.16 systems under the assumption of finite population under unsaturated traffic conditions. Additionally, we consider access prioritization schemes to provide differential performance by controlling various system parameters. We show that controlling the persistence value as specified in UMTS is effective in both backoff algorithms. The performances with and without access prioritization schemes are presented in terms of throughput, mean, and variance of packet retransmission delay, packet-dropping probability, and system stability. Finally, we consider a dynamic window assignment algorithm that is based on Bayesian broadcasting, in which the base station adaptively controls the window size of the UB algorithm under unsaturated traffic conditions. Results show that the proposed window assignment algorithm outperforms fixed window assignment in static and dynamic traffic conditions under the assumption of perfect orthogonality between random-access codes.

Social Groupcasting Algorithm for Wireless Cellular Multicast Services

In this letter, we propose a cooperative multicasting algorithm called a social groupcasting algorithm (SGA), in which the members of a social network group download the content over a wireless cellular link and disseminate it among them over a short-range ad-hoc wireless network. While only one member downloads the content, our proposed SGA dynamically changes the downloading member according to channel quality, remaining energy to distribute the content downloaded and social fairness. We characterize the SGA in terms of the social groupcasting gain relative to the social network group size and social fairness in comparison with conventional multicasting algorithm and also discuss the energy consumed for disseminating the content over a short-range ad-hoc network.

Performance Modeling and Stability of Semi-Persistent Scheduling with Initial Random Access in LTE

In this paper we examine the feasibility of semi-persistent scheduling (SPS) for voice over IP (VoIP) by random access and evaluate its performance in terms of throughput of random access and traffic channels, and random access delay. We further investigate system stability issues and present methods to stabilize the system. To see the VoIP capacity gain, we show the maximum number of acceptable VoIP terminals without exceeding some front-end packet dropping (i.e., voice clipping) probability. In addition, we examine the effect of the parameter called implicit release after in the LTE standard on the system performance, which is used for silence period detection. Our performance evaluation model based on Equilibrium Point Analysis is compared to simulations.

An Energy Efficient Implementation of C-RAN in HetNet

This paper introduces the Cloud-based Radio Access Network (C-RAN) architecture into heterogeneous network (HetNet), in which distributed antennas are connected to a cloud-based baseband processing unit through optical fibers. Among various opportunities realized by this architecture, our focus in this paper is on the spectral efficiency (SE) advantages achieved by cooperative transmission and its associated power consumption that may affect the energy efficiency (EE) of the system. A simple but efficient pre-coding scheme is proposed to reduce the computation complexity of cooperative transmission, thus lowering the associated power consumption, and a detailed power model is then developed to benchmark the various sources of energy consumption in C-RAN. Through detailed simulation, an early performance evaluation of the potentially energy efficient C-RAN implementation was demonstrated.

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.

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

Cooperative Pseudo-Bayesian Backoff Algorithms for Unsaturated CSMA Systems with Multi-Packet Reception

This paper proposes efficient backoff algorithms for uplink multi-packet reception (MPR) capable IEEE 802.11 systems in order to maximize the system throughput. According to the proposed algorithms, each station (STN) estimates, in a Bayesian manner under an unsaturated channel traffic condition, the number of backlogged STNs sharing the multiple access channel to obtain an optimal (re)transmission probability. Additionally, an access point and associated STNs cooperate by exchanging information piggybacked in transmitted data packets and the corresponding acknowledgment packets. The mean and variance of the queuing delays of the proposed algorithms are extensively evaluated via simulations under various environments such as time-varying populations and various asymmetric traffic conditions and compared to those of the conventional binary exponential backoff (BEB) algorithm. Furthermore, the queuing performance of the proposed algorithms is compared to the queuing delay lower bound obtained from a system that has perfect knowledge of the backlog size. Numerical results demonstrate the robustness of the proposed algorithms in various environments, and that they outperform the BEB algorithm.

Optimizing a Playout Buffer with Queueing Performance Metrics for One-Way Streaming Video

In this paper we consider a playout buffer with two thresholds based on its occupancy. Playout begins when the occupancy exceeds one threshold, say L o, while it slows down the playout rate in order to prevent buffer starvation whenever the occupancy drops below the other threshold, say L u(les L o). The design parameters here are two thresholds and the reduction factor of the playout rate whose optimal values are sought by minimizing a cost function with constraints. The cost function consists of queueing performance metrics, such as starvation probability, frame loss probability and the quality degradation probability by slowing down playout rate, while the constraints are given as excess preroll delay distribution, excess slow-down playout time distribution and the coefficient of variation of the departure process from the playout buffer. In numerical studies, we present optimal values of those parameters.

Queueing for handover calls in a hierarchical cellular network

In this work, the performance of queues for handover calls in both a micro- and a macrocell is analysed by varying the number of microcells under a macrocell, arrival rates of new calls in micro- and macrocells, cell dwell times, signal degradation interval, and queue size of both micro- and macrocells. In the model, the role of a macrocell is as a secondary server for handover calls overflowed from microcells and the overflow process of handover calls from microcells is modelled by Poisson and Markov modulated Poisson process (MMPP) approximations. In the numerical examples, it is found that Poisson approximation optimistically estimates call performance compared to MMPP, and that queues in a macrocell are more effective than those in microcells.