Yun Han Bae

Performance Analysis of Modified IEEE 802.11-Based Cognitive Radio Networks

This letter considers a modified IEEE 802.11-based cognitive radio network where primary users (PUs) operate on a slot-by-slot basis and secondary users (SUs) try to exploit the time unused by primary users (PUs). To improve the throughput for SUs, our IEEE 802.11-based opportunistic spectrum access (OSA) allows SUs to transmit packets with variable length depending on the remaining time of the current slot. To investigate the throughput for SUs, a novel analytical model is developed. Also, analytical results are validated by extensive simulation.

Analysis of IEEE 802.11 non-saturated DCF by matrix analytic methods

In the IEEE 802.11 MAC layer protocol, the basic access method is the Distributed Coordination Function based on the CSMA/CA. In this paper, we investigate the analytic performance of IEEE 802.11 DCF in the non-saturation mode. We assume that there is a fixed number n of competing stations and the packet arrival process to each station is a Poisson process. We model IEEE 802.11 DCF in non-saturation mode by a 3-dimensional Markov chain and derive the steady state probability of the Markov chain by applying the matrix analytic method. We obtain the probability generating function of Head-of-Line delay (HoL-delay), non-saturation throughput and packet loss probability. Our results can be used for finding the optimal number of stations that can be accommodated while satisfying a given QoS requirement.

Performance analysis of a slotted multi-channel MAC protocols for cognitive radio networks

Cognitive radio has emerged as one of effective methods to enhance utilization of radio spectrum. Main principle of cognitive radio is that the secondary users (SUs) are allowed to use the spectrum not used by primary users (PUs) without interfering PUs transmission. In this paper, we consider network system where PUs use channels under super-slot time structure and SUs content to access channels during unused super-slot so as not to interfere PUs transmission. For contention resolution, super-slot is divided into slots of fixed size which are used as backoff unit for backoff algorithm. For contending SUs, our proposed MAC protocol operates by the following modified CSMA/CA with binary backoff algorithm: Each SU uniformly chooses a backoff counter from the current backoff window. The backoff counter indicates the number of slots that the station has to wait before the transmission. At the beginning of super-slot, SU senses pre-determined number of channels. If there are no idle channels, then the backoff counter of the SU is frozen during a current super-slot duration. If there are idle channels, then the SU decrements its backoff counter by one per each time slot as long as time slot is idle. When the backoff counter of the SU reaches zero, the SU transmits the packets as many of fixed size as idle channels accommodate in the current super-slot. During backoff procedure of the SU, if other SUs occupy the remaining idle channels, backoff counter of the SU is frozen during the remaining part of super-slot and is reactivated when at least one channel is sensed idle at the beginning of the super-slot. We construct the three-dimensional discrete time Markov chain (DTMC) to investigate the performance of the proposed multi-channel MAC protocol and we obtain stationary probability vector of DTMC by censored Markov chains method. Then, using the stationary probability vector of DTMC, we obtain the head of line (HoL) packet delay distribution and the normalized throughput of SUs.

Tail asymptotic behaviour of resequencing buffer content for selective repeat ARQ

We consider resequencing buffer content at receivers side where the selective repeat automatic repeat request scheme is implemented for retransmission of erroneous packets in wireless networks. The error process of the wireless channel due to the fading is described by a discrete-time Markov chain. The study is carried out assuming that the round-trip time of packet over the channel is constant. The main concern in this paper is to characterize the tail asymptotics of the probability mass function of the resequencing buffer content at receivers side. Numerical results show that this approximation matches well with simulation.

Packet management scheme for location-independent end-to-end delay in IEEE 802.11s multi-hop wireless mesh networks

We consider IEEE 802.11s multi-hop wireless mesh network under multi-channel and multi-radio environments. We decompose the mesh network into disjoint zones by using multiple channels and multiple radios such a way that (i)mesh nodes in a zone are within one-hop distance and compete with other nodes to access the channel using IEEE 802.11e EDCA, (ii) neighbor zones use different channels, (iii) each node can send and receive the packets simultaneously. Thus we may focus on a single zone in order to derive the performance measure such as end-to-end delay. We propose packet management scheme at relay node where relay packets passing by more hops are buffered in higher priority AC of EDCA. Firstly, we model one zone as one-hop 802.11e EDCA network and find the HoL-delay of packet of each AC at relay node in a zone. Secondly, by modeling each AC as M/G/1 queue with HoL-delay as service time, we obtain packet delay (sum of queueing delay and HoL-delay) in a zone. The average end-to-end delay is calculated by summing up of packet delays in zones along the designated route. The goal of the packet management scheme in this paper is to provide location-independent end-to-end packet delays in the sense that all end-to-end packet delays regardless of nodespsila location are almost same. To do this, we propose a method to determine the minimum contention window size of ACs so as to have shorter delay for AC with relay packets passing by more hops. Finally, we suggest a heuristic algorithm to reduce the difference of delays due to packetspsila originated location and eventually to achieve the fair end-to-end delay of packets regardless of nodespsila location. Numerical results show that our proposed algorithm guarantees the location-independent end-to-end delay of packets in all the zones, regardless of locations.

Matrix method to study IEEE 802.11 network

In this paper, we estimate characteristics of the IEEE 802.11 DCF (Distributed Coordination Function) in non-saturation mode. We take into account two significant features inherent to the non-saturated 802.11 DCF: (i) the possibility of asynchronous transmission performed without preceding backoff for the first packet arriving at the idle staion; and (ii) so-called post backoff meaning that a station must perform a backoff once after any of its transmissions even if its queue becomes empty. We derive the probability generating function (PGF) of Head-of-Line delay (HoL-delay). Our method to find PGF of HoL-delay is quite intuitive and straightforward. Also, we obtain the packet loss probability and non-saturation throughput. Numerical results show that these two features inherent to the non-saturated 802.11 DCF influence on the performance measures of DCF such as delay considerably and it should be taken into account for accurate modeling of DCF.

Admission Control Scheme for Voice Calls Guaranteeing Both Packet-Level QoS and Call-Level QoS in IEEE 802.16e

In this paper, we propose an new admission control scheme jointly taking into account call-level QoS based on the dropping probability of handoff call and packet-level QoS based on the outage probability over threshold in IEEE 802.16e where user mobility is allowed and adaptive modulation and coding (AMC) is employed. The proposed admission control scheme is characterized by both a threshold for handoff calls at call-level and the outage probability over threshold at packet-level. First, we investigate the outage probability over threshold at packet-level. In order to determine the threshold, we derive the dropping probability of handoff call by using Markov chain model at call-level. Numerical results show that our proposed admission control scheme protects well the quality of service (QoS) of ongoing calls including handoff calls.

Performance Analysis of MAC Protocols for Location-Independent End-to-End Delay in Multi-Hop Wireless Mesh Networks

Backbone wireless mesh networks (WMNs) are emerging alternatives to conventional wired backbones for metropolitan and have attracted much attention from both academic and industrial world as an infrastructure network for realizing the ubiquitous computing environment. WMN is a generalization of Wireless Ad-Hoc Networks that considers the use of heterogeneous nodes (e.g., clients and routers) and both wired and wireless connections to exchange data between these devices. The basic architecture of a WMN consists of a backbone of mesh routers (MR) and the clients that access communication services through the use of this backbone. Therefore, this backbone serves as a last mile solution that is interconnected to provide direct communication between clients (i.e., without routing the interclient traffic through any other intermediate network). This characteristic of a WMN enables it to function as an isolated autonomous network or as a last mile solution depending on the telecommunication facilities available at the place where the WMN is deployed. In a multi-hop WMN, communication between two nodes is basically carried out by forwarding packets through a number of intermediate nodes. In WMNs, nodes are comprised of mesh routers in fixed sites and mobile clients as shown in Fig.1. We call a mesh router (also called mesh node) with gateway functions a gateway node, which is equipped with wireline network interfaces to connect the internet backbone. In this chapter each mesh node operates not only as an access point (AP) for mobile clients in its own basic service set (BSS) but also as a router, forwarding packets on behalf of other nodes that may not be within direct wireless transmission range of their destinations (see Fig. 1). Mobile clients are attached to a node in their BSS. Data originating from mobile clients are relayed by intermediate relay nodes hop by hop and delivered to the gateway. One of the important problems to be solved in WMNs is the unfair bandwidth sharing problem depending on the nodes’ location. More specifically, the per node throughput may decrease and the end-to-end delay may dramatically increase with an increasing hop-count distance from the gateway. In particular, WMNs based on single radio, irrespective of its simplicity and high fault tolerance, face a significant limitation of limited network capacity. It has been shown (2) that the theoretical upper limit of the per node throughput 3