Investigations on heuristic bandwidth request mechanism with signaling analysis for BWA networks

Best effort services in next generation broadband wireless access (BWA) networks would be more interactive and bandwidth demanding. This attracted a substantial amount of researches to focus on contention bandwidth request mechanisms for best effort services. The contention resolution with code division multiple access (CDMA) based mobile assisted truncated binary exponential backoff (C-MAB) suffers low contention efficiency and high access delay due to the nature of accessing mechanism in worldwide interoperability for microwave access (WiMAX) network that confines the mobile station in estimating the optimum contention window. Further, these performances decrease when transmission failure is modeled with unavailability of bandwidth, collision due to contention, transmission code failure, and channel error. To improve the performances, in this paper, we suggest a contention resolution with CDMA based base station assisted backoff (C-BAB) for orthogonal frequency division multiple access (OFDMA) based WiMAX networks. With C-BAB, the base station computes an optimum contention window by accounting average contention window and probability of failure. With a 2.69% additional overhead at the BS, the proposed C-BAB shows a 32.82% increase in contention efficiency and 24.21% decrease in access delay (25% error rate, q = 0.60 and ranging slot = 64) compared to C-MAB.     

Contention resolution with EIED backoff for bandwidth request in IEEE 802.16 networks

In this letter, we suggest contention resolution with exponential increase and exponential decrease (EIED) backoff for bandwidth request in worldwide interoperability for microwave access (WiMAX) networks. In EIED, setting of backoff factor to overcome collision due to contention is very challenging and hence we suggest a method to compute backoff factor with average contention window. Further, to reduce access delay, we estimate the response time based on probability of failure and average contention window. Simulations validate the proposed EIED backoff in terms of contention efficiency, capacity and access delay. The contention efficiency and capacity is improved by 47.50% (for q value of 0.25) and 28.57% (for 25 numbers of transmission opportunity), respectively, when bandwidth request is made with the proposed EIED backoff mechanism.     

Free access stack algorithms for microcellular radio systems

We evaluate the data traffic performance of a centralized packet access protocol for microcellular radio systems supporting both speech and data users. A time-slotted radio channel is assumed. Speech contention is decoupled from data contention to give speech priority over data. A free access stack algorithm is used for handling data contention. An out-slot access scheme is used in which the slots are divided into user-information transmission slots and contention slots for sending transmission requests. The contention slots are subdivided in minislots to improve the access capacity. The out-slot algorithm performances are compared with the performances of a previously proposed in-slot one in which all slots can be used for sending user information. A memoryless channel, with capture and errors, is considered. The effects of speech traffic on data performance are evaluated. Moreover, the paper presents a method for evaluating the packet error probability of a packet cellular system. This method is used for evaluating the proposed algorithm in a microcellular system. An access technique with coordinated operation among cochannel cells is studied. The effects of sectorization on data performances and protocol unfairness are investigated. Different frequency reuse factors are taken into consideration     

A dynamic ID management protocol for CSMA/IC in ad hoc networks

Contention based MAC protocols are widely used in ad hoc networks because they are suitable, where no central control node exists. However, contention based MAC protocols waste much time because of frequent collisions and long contention times. Moreover, it is hard for them to fairly distribute medium access opportunities. As a result, the problem of unfair medium access may arise under normal network conditions. Recently, another contention based MAC protocol, named the Carrier Sense Multiple Access/ID Countdown (CSMA/IC) was proposed. CSMA/IC resolves medium access contention by comparing the IDs of contending nodes with a simple signaling process. Therefore, medium access collisions never happen as long as each node possesses a unique ID, and the time cost for contention may be smaller than any other contention based MAC protocols if the number of IDs is managed so as to be as small as possible. Furthermore, CSMA/IC may support fair medium access by manipulating the ID of each node properly. In this paper, we propose a novel dynamic ID management protocol which enables a node to acquire a unique ID without any message exchanges and fairly distributed the number of medium access opportunities to all contending nodes. The proposed protocol also makes the contention process of CSMA/IC efficient by dynamically managing the length of the ID field according to the network traffic. The simulation results show that the proposed ID management protocol significantly improves the aforementioned aspects of CSMA/IC MAC protocol compared to previous ID management schemes.     

Performance Analysis of a Bandwidth Guaranteed Medium Access Control Protocol for WDM Local Networks

In this paper, we propose and analyze a bandwidth guaranteed medium access control protocol for broadcast-and-select WDM local networks with a star topology. The proposed protocol is based on a combination of contention and dedicated reservation mechanisms for time slotted WDM networks. Every node accesses the data channel by transmitting request packets in minislots on a separate control channel. There are two types of minislots; dedicated minislots and contention minislots. Nodes requiring bandwidth guarantees, called guaranteed nodes, use dedicated minislots that are assigned by the centralized control node. The remaining nodes, called random-access nodes, share contention minislots using a distributed random access mechanism. The dedicated minislots can guarantee a minimum bandwidth for the guaranteed nodes. The contention minislots enable on-demand services at the optical layer and achieve good fairness for the remaining bandwidth. Here, the data channels are dynamically assigned to the minislots successfully returned on a first-come-first-served (FCFS) basis. This protocol can combine the best of centralized and distributed access protocols such as simplicity, efficiency, and flexibility. We analyze the maximum throughput and verify the results by simulation.     

Minimizing contention through cooperation between densely deployed wireless LANs

Contention at shared medium access may seriously degrade the performance of a CSMA/CA-based wireless LAN. Where wireless LANs from different operators are densely deployed, controlling contention merely by intelligent selection of installation sites and assignment of operating channels becomes challenging at least. We show that cooperation between these networks may lead to a significant reduction in overall contention. To this end, we present a mathematical programming formulation of the minimal inter-domain contention problem and derive theoretical lower bounds for it. We show how to practically determine exact solutions for small problem instances and near-optimal solutions for larger scenarios. Most importantly, we introduce a distributed algorithm and protocol that allows access points to self-coordinate in order to minimize contention and relies solely on information about each access point’s immediate neighborhood. In experiments, we show that cooperation between domains may more than halve contention even in only moderately dense deployments. Furthermore, we demonstrate that our distributed algorithm may reduce contention by 19% compared to cooperation using standard WLAN mechanisms. Contrary to common belief, our findings suggest that in dense deployments switching off selected access points may be more effective in decreasing contention than using them for load balancing.

Performance modeling and analysis of IEEE 802.11 DCF based fair channel access for vehicle-to-roadside communication in a non-saturated state

This paper considers the fair access problem in vehicular ad hoc networks and develops analytical models for analyzing the performance of an IEEE 802.11 distributed coordination function based fair channel access protocol in a non-saturated state. We first derive the relationship between the transmission probability and the minimum contention window size of a vehicle, and the relationship between the velocity and the minimum contention window size of a vehicle in a non-saturated state. Based on the analytical model, the minimum contention window size of a vehicle for a given velocity can be determined in order to achieve fair access among different vehicles. Moreover, an analytical model is also developed for analyzing the throughput performance of the fair channel access protocol in a non-saturated state. The effectiveness of the analytical models is justified through simulation results.

     

Carrier sense multiple access with improvised collision avoidance and short-term fairness

In this paper, we present a simple method to simultaneously enhance collision avoidance efficiency and short-term fairness of a most popular contention based medium access control protocol, carrier sense multiple access with collision avoidance. The key idea here is to adaptively tune the shape of contention slot selection distribution over the temporal contention window during ongoing collision resolution process which, in the legacy scheme, used to be flat throughout. The tuning mechanism is such designed that it not only maximizes the selection likelihood of relatively less collision prone contention slots over the contention window but also compensates the idle delay that the contending stations have suffered in their recent access attempt. Through rigorous numerical and simulation based analysis, the proposed scheme is shown to enhance the performance of a IEEE 802.11 based distributed wireless network in terms of network throughput efficiency and packet transmission delay while allowing individual stations to share the channel fairly even in short time scale.     

The Contention Behavior of DOCSIS in CATV Networks

In this paper, we study the contention behavior of DOCSIS in cable TV networks. Specifically, we focus on the behavior of TCP over DOCSIS. We determine the expected access delay for TCP transmissions in CATV networks. The access delay here is defined as the interval between the time when a data packet arrives at a cable modem (CM) and the time when that packet is successfully sent by the CM. The analytical model is comprised of two parts. The first part is to calculate the probability that a CM sends a request in a randomly selected minislot, and the second part is to derive the expected access delay based on the probability derived in the first part. The accuracy of the analytical model is validated by simulations. The results show that our analytical model can accurately model the contention behavior of DOCSIS in CATV networks.     

基于S-CDMA的HFC网上行信道接入协议

本文着重讨论了一个基于S-CDMA的HFC网上行信道的高效的接入协议--SAMA接入协议，其中包括了请求冲突解决协议和初始化协议两部分，并对这个接入协议的冲突率和吞吐量性能进行了详细分析，最后提出了该接入技术中尚待解决的问题。     

Effectiveness of Explicit Stations Grouping in Crowded Wireless LANs

In this letter, we evaluate the effectiveness of a multi-stage contention scheme for wireless local area networks (WLANs) medium access control (MAC). Multi-stage contention schemes basically divide the stations into smaller groups to resolve the contention more efficiently. Previous researchers have proposed virtual grouping schemes for WLANs MAC. Here we quantitatively analyze what can be achieved with a simple grouping scheme, i.e. through multi-stage contention. Our analysis shows that the multi-stage scheme is efficient in resolving contention, making it a good alternative to the commonly used exponential backoff mechanism.     

WiMAX中的多业务接入性能分析

针对IEEE802.16媒体接入机制,研究了WiMAX(微波存取全球互通)系统中多业务场景下的吞吐量、接入延时和丢包率性能,考察了帧结构、最小竞争窗和延时约束对不同优先级业务性能的影响。仿真结果表明,选择最优的帧结构并为有不同QoS(服务质量)需求的业务选择接入参数,能够增加系统吞吐量,减小业务接入延时和丢包率。     

Analysis of contention tree algorithms

The Capetanakis-Tsybakov-Mikhailov (1978, 1979) contention tree algorithm provides an efficient scheme for multiaccessing a broadcast-communication channel. This paper studies the statistical properties of multiple-access contention tree algorithms with ternary feedback for an arbitrary degree of node. The particular quantities under investigation are the number of levels required for a random contender to have successful access, as well as the number of levels and the number of contention frames required to provide access for all contenders. Through classical Fourier analysis approximations to both the average and the variance are calculated as a function of the number of contenders n. It is demonstrated that in the limit of large n these quantities do not converge to a fixed mode, but contain an oscillating term as well     

Polling- and contention-based schemes for TDMA-TDD access towireless ATM networks

The design of an efficient MAC protocol is of paramount interest for the definition of a wireless ATM (WATM) access. In the case of TDMA-TDD WATM access, the current trend in the standardization bodies is to adopt frames of fixed duration, whose slots are shared among uplink and downlink connections under the control of a MAC scheduler located in the base station. In this paper, we first compare polling and contention techniques, in order to identify the best access scheme to serve ATM connections. Then, since the knowledge of the queue status of the portable terminals can be used by the centralized scheduler to increase the efficiency of the slot assignment procedure, we propose different algorithms to code the buffer occupancy status. Moreover, we compare their performance by considering two different scenarios; the first loaded with ON-OFF sources served by nrt-VBR ATM connections, and the second with TCP/IP sources served by UBR ATM connections. The results show the superiority of the contention access and the advantages of the buffer status notification for the scheduler at the base station     

A successive transmission medium access scheme with dynamic contention window for VLC system with saturated traffic

The visible light communication (VLC) network is usually relatively small scale and can provide high-data-rate information transmission, where multiple users get access to the network according to the carrier sense multiple access with collision avoidance (CSMA/CA) mechanism specified by IEEE 802.15.7 standard. In this paper, we propose a novel dynamic contention window with successive transmission (DCW-ST) scheme to improve the performance of this channel access mechanism and to achieve better network throughput without delay performance degradation. Specifically, we propose to adjust the contention window dynamically to adapt to the time-changing network size. Further, we derive the contention window size to achieve trade-off of throughput and delay, and the minimum contention window size required for the throughput enhancement. In addition, in order to further improve the delay performance, we present a successive transmission scheme that allows the nodes which have completed one transmission successfully to get the chance of transmitting information successively according to the network condition. Simulations are performed for the VLC system in saturated traffic and compared with the theoretical performances, which demonstrate that our proposed scheme outperforms the legacy CSMA/CA of IEEE 802.15.7.     

A review of contention resolution algorithms for IEEE 802.14 networks

Bidirectional Cable TV networks using hybrid fiber coaxial (HFC) systems are good examples of broadcast environments where a contention resolution algorithm is needed in order to allocate the multiaccess medium (in this case the upstream link) among the various nodes. Recent activities of the IEEE 802.14 Working Group aimed at defining the physical and medium access control (MAC) layer protocols for HFC cable networks have focused on the study and evaluation of several contention resolution solutions for inclusion in the MAC protocol specifications. In this article several contention resolution algorithms considered by the IEEE 802.14 group are reviewed. Different implementations for several well known contention resolution algorithms such as tree-based and p-persistence are presented. Their performance is evaluated in the HFC context with respect to upstream channel allocation, roundtrip delay, various traffic types, and number of stations in the network. Simulation results for configurations and scenarios of interest are also presented.     

Quality-of-service in ad hoc carrier sense multiple access wirelessnetworks

Carrier sense multiple access (CSMA) is one of the most pervasive medium access control (MAC) schemes in ad hoc, wireless networks. However, CSMA and its current variants do not provide quality-of-service (QoS) guarantees for real-time traffic support. This paper presents and studies black-burst (BB) contention, which is a distributed MAC scheme that provides QoS real-time access to ad hoc CSMA wireless networks. With this scheme, real-time nodes contend for access to the channel with pulses of energy-so called BBs-the durations of which are a function of the delay incurred by the nodes until the channel became idle. It is shown that real-time packets are not subject to collisions and that they have access priority over data packets. When operated in an ad hoc wireless LAN, BB contention further guarantees bounded and typically very small real-time delays. The performance of the network can approach that attained under ideal time division multiplexing (TDM) via a distributed algorithm that groups real-time packet transmissions into chains. A general analysis of BB contention is given, contemplating several modes of operation. The analysis provides conditions for the scheme to be stable. Its results are complemented with simulations that evaluate the performance of an ad hoc wireless LAN with a mixed population of data and real-time nodes     

Fast neighbor positioning and medium access in wireless networks with directional antennas

We study the problem of fast neighbor positioning and medium access in wireless networks with directional antennas. In this problem, the cross-layer dimension inherently comes into stage through the impact of PHY-layer antenna directionality on medium access. Fast neighbor positioning reduces the network initialization overhead and leaves more time for executing other protocols. Fast medium access leads to larger volume of transmitted data per unit of time. The two problems are studied in a unified manner in a system with one Access Point (AP) and multiple users around it. The AP sequentially scans the space by forming directional beams and applies contention-free or contention-based user polling within each beam. In the former method, polling messages are addressed to a specific user. In the latter, users in a beam contend to have their message received by the AP.We explore the impact of the contention resolution protocol and the directional beam width on user positioning and medium access delay. A large beam width incurs large expected delay for contention resolution due to the larger expected amount of contention in the beam, but on the other hand, it implies that fewer beams, and hence smaller delay is needed to scan the entire space. We obtain analytic expressions for the total average user positioning and the medium access delay, and we present an optimization method for minimizing it by appropriately selecting the beam width and the persistence probability of the collision resolution protocol. Our method uses accumulated knowledge from previous scans to estimate the anticipated amount of contention in upcoming scans and to adjust the beam width and persistence probability accordingly. Our numerical results demonstrate the efficiency of our techniques in terms of fast neighbor positioning.     

有效提高吞吐量的UPMA+ +协议

本文提出了基于有效竞争接入、高效无冲突传输的多址接入协议—UPMA+ +.该协议采用了有效的冲突分解策略和及时重获信道资源的方法,克服了UPMA(根据用户数目妥善安排传输的多址接入)协议中的开销;通过自适应调整竞争接入周期长度和限制无冲突服务周期长度的方法,很好地解决了激活节点快速接入信道和传输节点尽快传输分组之间的矛盾,从而提高了协议的吞吐量.本文还应用排队论的方法对UPMA+ +协议的性能进行了理论分析,计算结果与仿真结果基本一致.     

A load awareness medium access control protocol for single‐hop wireless ad hoc networks

A contention‐based wireless ad hoc medium access control (MAC) protocol, such as carrier sense multiple access with collision avoidance (CSMA/CA), has excellent efficiency when the system is light loaded. The main drawback of such protocols is their inefficiency and unbounded delay when the system load is heavy. On the other hand, a contention‐free MAC protocol, such as token passing, has a better and fair throughput when the system is heavy loaded. The main drawback of such protocols is their inefficiency when only a small amount of users want to transmit. In this paper, we propose a new load awareness single‐hop wireless ad hoc MAC protocol (which is called the LA protocol) that exploits the benefits of both contention‐based and contention‐free protocols. A contention‐based MAC protocol is used when the system is light loaded and a contention‐free one is used otherwise. Our LA protocol, which operates in a distributed fashion and is fully compatible with the IEEE 802.11 wireless local area network (WLAN) standard, can switch smoothly between the contention‐based protocol and the contention‐free one. Simulation results show that our protocol indeed extracts the better part of two kinds of protocols. Copyright © 2006 John Wiley & Sons, Ltd.