Contention Based Bandwidth Request Research Articles

Improved random access for contention bandwidth request in LTE networks under extended typical urban 70 channel

In this paper, a group-based random access configuration is proposed for long term evolution (LTE) networks to improve the probability of detection under the multipath fading channel of extended typical urban 70 (ETU70) with high delay spread. By suggesting a scheme to account the possible failure events, we develop an analytical model for contention-based bandwidth request in LTE networks. In addition, two backoff mechanisms are proposed to resolve contention among user equipments effectively. The developed model is verified by means of simulation result.

Investigation on group based contention bandwidth request in LTE-A networks under high delay spread environment

In this paper, contention bandwidth request has been investigated for long term evolution-advanced (LTE-A) networks under extended typical urban based multipath fading channel that displays high delay spread environment. As the choice of preambles has to provide high detection probability under such environments, at the outset, this paper examines various group based preamble selection mechanisms, namely, Type I, Type II and Type III preamble sets. With suitable type of group based preamble, the challenge during contention bandwidth request is the appropriate choice of contention window during contention resolution. The contention window in this paper is chosen based on the indicators of various failure events, namely, probability of collision due to contention, probability of unavailability of bandwidth, probability of channel error and probability of improper detection of Zadoff---Chu sequences. After suggesting a scheme to account the possible failure events, an analytical model for contention-based bandwidth request has been developed for LTE-A networks. In addition, two backoff mechanisms are proposed to resolve contention among user equipment's effectively and these mechanisms are compared to the existing techniques, namely, binary exponential backoff and uniform backoff. Further, the contention mechanism has been substantiated for varying depth of channel errors. With Type I grouping, the backoff with optimized contention window improves the efficiency by 13.95 %, reduces the access delay by 18.71 % and decreases the dropping probability by 59.33 % than the existing uniform backoff mechanism.

Investigation on cooperative contention-based bandwidth request mechanism for heterogeneous networks

In this paper, the suitability of contention parameters that influence the heterogeneous network performance is investigated using cooperative contention-based bandwidth request BR scheme. The proposed scheme is unique since contention BR is carried out by wireless local area network WLAN/worldwide interoperability for microwave access WiMAX gateways WWG besides other mobile stations. To improve the contention efficiency with reduced access delay in contention mechanism, we propose failure models by including collision due to contention, channel error, improper detection of code and unavailability of bandwidth. In addition, for effective transmission of BR under these conditions, the stations at various hops update their contention window by appropriate consideration of transmission failure. Upon robust update of contention window, we investigate the cooperative BR by deriving the overall contention efficiency and access delay in heterogeneous networks. Simulation results validate the effectiveness of the derived model.

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.

Investigation on uplink collaborative contention-based bandwidth request for WiMAX three hop relay networks

This paper suggests a collaborative contention bandwidth request (BR) mechanism for worldwide interoperability for microwave access (WiMAX) three-hop relay networks. By complimenting message and code BR in three hops of a link, the proposed framework enables low block error rate (BLER), packet dropping and signaling overhead while preserving the connection throughput and access delay requirements of best effort (BE) services. With three hops between base station (BS) and mobile station (MS) via relay station 1 (RS1) and relay station 2 (RS2), there take place eight possible BR mechanisms with message and code BR. Among eight BR mechanisms, message-message-code (MMC) BR performs better with message dominant BR and code-message-code (CMC) BR performs better with code dominant BR. Further, with CMC BR, the BLER is reduced by 5.88%, packet dropping is reduced by 8.68%, medium access control (MAC) overhead is reduced by 7.6%, MAC wastage is reduced by 4.47%, connection delay is reduced by 28.30%, queuing delay is reduced by 8.65%, queue size is reduced by 15.25% and throughput is improved by 11.51% than MMC BR mechanism.

Failure aware contention based bandwidth request for multihop relay networks

Failure aware contention based bandwidth request for multihop relay networks

Contention based bandwidth request with signaling analysis in IEEE 802.16 two hop relay networks

In this paper, we propose a joint contention-based bandwidth request mechanism for WiMAX two-hop relay networks. For this purpose, we considered contention by message and code mechanisms. These are normally deployed in single-hop networks. This message scheme suffers from low contention efficiency and higher access delay when the number of mobile stations (MSs) in the network increases. Conversely, this code technique undergoes transmission failure due to the inappropriate setting of the detection threshold at relay stations (RSs). However, these message and code mechanisms are advantageous when they are carried out at appropriate hops. Among the four possible options created by combining the message and code methods, the message requests from MS to RS and code requests from RS to base stations (BSs) performed better than other possible combinations. Using a comprehensive case study and simulation results, we generated signaling examples that confirmed the significance of the proposed method in terms of signaling overhead, network throughput, connection delay and queuing size.

An Effective Approach to Contention Based Bandwidth Request Mechanism in WiMAX Networks

In this paper the IEEE 802.16 standard based Mobile WiMAX (Worldwide Interoperability for Microwave Access) system is investigated for the purpose of Quality of Service provisioning. As a potential solution, scheduling algorithms have been taken into major concern. Within the pool of scheduling algorithms and for the purpose Contention based bandwidth request resolution, the Modified Contention Based BW Resolution algorithm (MCB-BWR-Scheme) is proposed. Supported by the fact that the standard does not emphasize a specific scheduling algorithm for contention period based services, therefore, the choice of the scheduling algorithm for the WiMAX systems is very important. There are several scheduling algorithms for WiMAX in the literature, however, studies show that an efficient, fair and robust scheduling algorithm for WiMAX systems is still an open research area and hence a well thought out algorithm will be of great contribution to the area under investigation. Results from the OPNET Modeler simulation program show that the adjusted algorithm works well with delay and throughput constraints. It is also in consistent with the quality of service demands of the video and voice traffic.

MSCR based bandwidth request mechanism for heterogeneous WiMAX networks

The next generation wireless networks aim to provide users with always-best connectivity through available different access networks. In this paper, we consider heterogeneous of worldwide interoperability for microwave access (WiMAX) and wireless local area network (WLAN). These heterogeneous networks suffer from low bandwidth utilization and access delay with contention based bandwidth request through single stage truncated binary exponential backoff (TBEB) algorithm. To resolve contention effectively, we propose exponential increase exponential decrease (EIED) backoff with multistage contention resolution (MSCR). The results show that the proposed backoff scheme outperforms the conventional TBEB scheme with an improvement of 35.29% in access delay, 26.67% in queuing delay and 67.65% in throughput.

Performance Analysis of Contention Based Bandwidth Request Mechanisms in WiMAX Networks

WiMAX networks have received wide attention as they support high data rate access and amazing ubiquitous connectivity with great quality-of-service (QoS) capabilities. In order to support QoS, bandwidth request (BW-REQ) mechanisms are suggested in the WiMAX standard for resource reservation, in which subscriber stations send BW-REQs to a base station which can grant or reject the requests according to the available radio resources. In this paper we propose a new analytical model for the performance analysis of various contention based bandwidth request mechanisms, including grouping and no-grouping schemes, as suggested in the WiMAX standard. Our analytical model covers both unsaturated and saturated traffic load conditions in both error-free and error-prone wireless channels. The accuracy of this model is verified by various simulation results. Our results show that the grouping mechanism outperforms the no-grouping mechanism when the system load is high, but it is not preferable when the system load is light. The channel noise degrades the performance of both throughput and delay.

An unsaturated model for request mechanisms in WiMAX

Worldwide interoperability for microwave access (WiMAX) based wireless metropolitan area networks have recently received wide attention as they support high data rates with great quality of service (QoS) capabilities. In order to support QoS, bandwidth request (BW-REQ) mechanisms are suggested in the WiMAX standard for resource reservation. In this letter we propose a simple and accurate analytical model for the performance analysis of contention-based bandwidth request mechanisms. The accuracy of this model is verified with simulation results.

Performance Analysis of Best-Effort Service in Saturated IEEE 802.16 Networks

The IEEE 802.16 standard is a promising technology for the fourth-generation mobile networks and is being actively promoted by the Worldwide Interoperability for Microwave Access (WiMAX) Forum: an industry-led consortium. Among the various service classes supported in the standard, best-effort service is expected to be the major service class subscribed to by users due to its operational simplicity and lower charging rate compared with other service classes. In this paper, we investigate the throughput and packet-access-delay performance of best-effort service using the contention-based bandwidth request mechanism in a saturated IEEE 802.16 network. In particular, we develop a simple fixed-point analysis to approximate the failure probability of a bandwidth request and derive analytical expressions for network throughput and packet access delay. Furthermore, the uniqueness of the fixed point is established. The accuracy of the analytical model is validated by comparison with simulation over a wide range of operating conditions. The implications of various different parameter configurations on the system performance are investigated using the analytical model. The utility of the model is further demonstrated by finding the maximum achievable throughput and obtaining its corresponding optimal initial contention window.

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.

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.