Bandwidth Request Scheme Research Articles

Investigation on Mutual Contention Bandwidth Request Mechanisms in Two-Hop Relay Network with ITU-R Path Loss Models

The performance of two-hop contention based bandwidth request (BR) mechanism for WiMAX relay networks is investigated under ITU-R path loss models. In conventional WiMAX systems, the mobile stations (MS) update their contention window irrespective of their transmission failures. Those systems update their contention window on collision and due to channel error or unavailability of bandwidth. Further, these failure models have been suggested for single hop networks. The failure model in two-hop systems becomes complex since it may include additional failure events such as improper detection of codes and channel error due to varying path loss. Interestingly, these failure events (collision, channel error, unavailability of bandwidth, and improper detection of codes) do not occur evenly for both hops of a link. Hence, to set the contention window effectively, unique failure models are developed by considering the characteristics of BR mechanism and hop at which the BR is performed. In the proposed system, the two-hop BR is carried out with all combinations of message and code bandwidth request schemes. Among them, the message-code BR mechanism performs better under suburban fixed and outdoor to indoor or pedestrian environment, and code-code BR scheme performs better for vehicular environment.

Modelling of Differentiated Bandwidth Requests in IEEE 802.16m Systems

In order to support a large number of mobile stations (MSs) with statistical multiplexing in cellular networks, a random access scheme is widely used for uplink (UL) bandwidth request (BR). In the design of a random access based BR scheme, there are two important requirements: short connection delay and diverse Quality of Services (QoSs) support. Such requirements are crucial for IMT-Advanced systems like IEEE 802.16m to provide various types of fourth generation (4G) data services. IEEE 802.16m provides advanced UL BR schemes for non-real time polling service (nrtPS) and best-effort (BE) service to meet the requirements of short connection time and multiple QoS level support. In order to provide short connection time and multiple QoS support, three-step and differentiated BR procedures are adopted. In this paper, a novel modelling of IEEE 802.16m contention based BR scheme is proposed that uses a 2-dimensional discrete time Markov chain. Both the short access delay three-step BR procedures and normal five-step BR procedure are considered in the model. Our proposed model also incorporates the IEEE 802.16m differentiated BR procedure. With the proposed model, we extensively evaluate the performance of IEEE 802.16m BR for two different service classes by changing QoS parameters, such as backoff window size and BR timer. Computer simulations are performed to corroborate the accuracy of the proposed model for various operation scenarios. With the proposed model, accurate QoS parameter values can be derived for the IEEE 802.16m contention-based BR scheme.

Adaptive QoS provision for IEEE 802.16e BWA networks based on cross-layer design

This article proposes an integrated framework for adaptive QoS provision in IEEE 802.16e broadband wireless access networks based on cross-layer design. On one hand, an efficient admission control (AC) algorithm is proposed along with a semi-reservation scheme to guarantee the connection-level QoS. First, to guarantee the service continuity for handoff connections and resource efficiency, our semi-reservation scheme considers both users' handoff probability and average resource consumption together, which effectively avoids resource over-reservation and insufficient reservation. For AC, a new/handoff connection is accepted only when the target cell has enough resource to afford both instantaneous and average resource consumption to meet the average source rate request. On the other hand, a joint resource allocation and packet scheduling scheme is designed to provide packet-level QoS guarantee in term of "QoS rate", which can ensure fairness for the services with identical priority level in case of bandwidth shortage. Particularly, an enhanced bandwidth request scheme is designed to reduce unnecessary BR delay and redundant signaling overhead caused by the existing one in IEEE 802.16e, which further improves the packet-level QoS performance and resource efficiency for uplink transmission. Simulation results show that the proposed approach not only balances the tradeoff among connection blocking rate, connection dropping rate, and connection failure rate, but also achieves low mean packet dropping rate (PDR), small deviation of PDR, and low QoS outage rate. Moreover, high resource efficiency is ensured.

A simulation study of service differentiation for the bandwidth request scheme in fixed IEEE 802.16 network

Various flexible mechanisms related to quality of service (QoS) provisioning have been specified for uplink traffic at the medium access control (MAC) layer in the IEEE 802.16 standards. Among the mechanisms, contention based bandwidth request scheme can be used to indicate bandwidth demands to the base station for the non-real-time polling and best-effort services. These two services are used for most applications with unknown traffic characteristics. Due to the diverse QoS requirements of those applications, service differentiation (SD) is anticipated over the contention based bandwidth request scheme. In this paper we investigate the SD with the bandwidth request scheme by means of assigning different channel access parameters and bandwidth allocation priorities at different packets arrival probability. The effectiveness of the differentiation schemes is evaluated by simulations. It is observed that the initial backoff window can be efficient in SD, and if combined with the bandwidth allocation priority, the SD performances will be better.

Service Differentiation in OFDM-Based IEEE 802.16 Networks

IEEE 802.16 network is widely viewed as a strong candidate solution for broadband wireless access systems. Various flexible mechanisms related to QoS provisioning have been specified for uplink traffic at the medium access control (MAC) layer in the standards. Among the mechanisms, bandwidth request scheme can be used to indicate and request bandwidth demands to the base station for different services. Due to the diverse QoS requirements of the applications, service differentiation (SD) is desirable for the bandwidth request scheme. In this paper, we propose several SD approaches. The approaches are based on the contention-based bandwidth request scheme and achieved by the means of assigning different channel access parameters and/or bandwidth allocation priorities to different services. Additionally, we propose effective analytical model to study the impacts of the SD approaches, which can be used for the configuration and optimization of the SD services. It is observed from simulations that the analytical model has high accuracy. Service can be efficiently differentiated with initial backoff window in terms of throughput and channel access delay. Moreover, the service differentiation can be improved if combined with the bandwidth allocation priority approach without adverse impacts on the overall system throughput.

Impact of bandwidth request schemes for Best-Effort traffic in IEEE 802.16 networks

In IEEE 802.16 networks, bandwidth request–grant schemes are employed for reducing data collision and supporting various QoS requirements. In this paper, we investigate the impact of such schemes on Best-Effort (BE) traffic. We examine three candidate schemes. In the first scheme, each Subscribe Station (SS) attempts to request bandwidth in every frame to reduce delay. In the second scheme, the number of bandwidth request is limited to avoid collisions in bandwidth request. In the third scheme, a base station allocates bandwidth to each SS based on the measured sending rate without explicit bandwidth request. We quantitatively analyze the performance of these schemes in terms of the collision rate and buffer length. We also present a simulation study to validate our analysis and to observe the impact of these schemes on BE traffic. This paper shows that IEEE 802.16 networks can be effectively managed through appropriate bandwidth request schemes. It is also shown that bandwidth allocation without request can be an alternative for increasing utilization.

Analytical Modeling of Contention-Based Bandwidth Request Mechanism in IEEE 802.16 Wireless Networks

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The IEEE 802.16 wireless metropolitan area network (WMAN) standard is a promising and cost-effective, last-mile wireless technology for the provision of broadband Internet access to end users. In this paper, we present an accurate analytical model that describes the contention-based bandwidth (BW) request scheme of the 802.16 standard, which is also known as WiMAX, for the persistent and nonpersistent request generation cases. We first model the contention procedure with a Markov chain, taking into account the exponential back-off procedure as well as the waiting time for a BW assignment and the possible timeout for lost messages. The accuracy of the model is then evaluated by comparing it with simulation results for a wide range of values of the parameters involved. We use this model to accurately calculate the capacity of the contention slots in delivering BW requests, from which the average access delay is also found. These measures are used to determine a proper configuration for the efficient operation of the contention-based BW request scheme. The proposed model provides a useful analytical tool for devising adaptive configuration mechanisms for the contention access mode of the 802.16 medium access control (MAC) layer. </para>

Performance comparison of OFDM bandwidth request schemes in fixed IEEE 802.16 networks

IEEE 802.16 standard specifies two contention based bandwidth request schemes working with OFDM physical layer specification in point-to-multipoint (PMP) architecture, the mandatory one used in region-full and the optional one used in region-focused. This letter presents a unified analytical model to study the bandwidth efficiency and channel access delay performance of the two schemes. The impacts of access parameters, available bandwidth and subchannelization have been taken into account. The model is validated by simulations. The mandatory scheme is observed to perform closely to the optional one when subchannelization is active for both schemes.

Modeling Contention Based Bandwidth Request Scheme for IEEE 802.16 Networks

IEEE 802.16 standard specifies a contention based bandwidth request scheme for best-effort and non-real time polling services in point-to-multipoint (PMP) architecture. In this letter we propose an analytical model for the scheme and study how the performances of bandwidth efficiency and channel access delay change with the contention window size, the number of contending subscriber stations, the number of slots allocated for bandwidth request and data transmission. Simulations validate its high accuracy.