Adaptive downlink and uplink channel split ratio determination for TCP-based best effort traffic in TDD-based WiMAX networks

In this paper, we study the determination of downlink (DL) and uplink (UL) channel split ratio for Time Division Duplex (TDD)-based IEEE 802.16 (WiMAX) wireless networks. In a TDD system, uplink and downlink transmissions share the same frequency at different time intervals. The TDD framing in WiMAX is adaptive in the sense that the downlink to uplink bandwidth ratio may vary with time. In this work, we focus on TCP based traffic and explore the impact of improper bandwidth allocation to DL and UL channels on the performance of TCP. We then propose an Adaptive Split Ratio (ASR) scheme which adjusts the bandwidth ratio of DL to UL adaptively according to the current traffic profile, wireless interference, and transport layer parameters, so as to maximize the aggregate throughput of TCP based traffic. Our scheme can also cooperate with the Base Station (BS) scheduler to throttle the TCP source when acknowledgements (ACKs) are transmitted infrequently. The performance of the proposed ASR scheme is validated via ns^-2 simulations. The results show that our scheme outperforms static allocation (such as the default value specified in the WiMAX standard and other possible settings in existing access networks) in terms of higher aggregate throughput and better adaptivity to network dynamics.     

TCP-Aware Uplink Scheduling for IEEE 802.16

In IEEE 802.16 networks, a bandwidth request-grant mechanism is used to accommodate various QoS requirements of heterogeneous traffic. However, it may not be effective for TCP flows since (a) there is no strict QoS requirement in TCP traffic; and (b) it is difficult to estimate the amount of required bandwidth due to dynamic changes of the sending rate. In this letter, we propose a new uplink scheduling scheme for best-effort TCP traffic in IEEE 802.16 networks. The proposed scheme does not need any bandwidth request process for allocation. Instead, it estimates the amount of bandwidth required for a flow based on its current sending rate. Through simulation, we show that the proposed scheme is effective to allocate bandwidth for TCP flows     

Bandwidth utilization efficiency enhancement for OFDM‐based WSN

Normally IEEE 802.16 (WiMAX) is used for mainly downlink traffic applications. However in the upper tier of 2‐tier (WiMAX‐WiFi) wireless sensor network, the uplink bandwidth faces bottlenecks for high throughput. In this paper, a solution has been proposed for this limitation of uplink bandwidth allocation through the use of queuing theoretic performance modeling. A Markov‐modulated Poisson process traffic model has been formed for orthogonal frequency division multiple access‐based transmission along with discrete time Markov chain system model for queuing. A downlink traffic pattern has been defined for wireless sensor network nodes. Analytical methods are used to estimate the performance parameters like throughput, delay, and probability of packet drop for resource allocation. An algorithm is formulated to find out minimum resource requirement for downlink and to transfer rest of the resources to uplink bandwidth allocation, for throughput enhancement. Uplink frame utilization is determined through another discrete time Markov chain model for adaptive triggering between the proposed maximum and the normal downlink to uplink ratio operations, for efficient distribution of bandwidth resources. Algorithm and simulation results prove outstanding improvement in the uplink throughput around 50%, without degrading the downlink throughput.     

A Cross-layer Dual Queue Approach for Improving TCP Fairness in Infrastructure WLANs

Fairness is one of the most important performance measures in IEEE 802.11 Wireless Local Area Networks (WLANs), where channel is accessed through competition. In this paper, we focus on the fairness problem between TCP uplink and downlink flows in infrastructure WLANs from the cross-layer perspective. First, we show that there exists a notable discrepancy between throughput of uplink flow and that of downlink flow, and discuss its root cause from the standpoint of different responses to TCP data packet drop and TCP ACK packet drop at the access point (AP) buffer. In order to mitigate this unfairness, we propose a dual queue scheme, which works in a cross-layer manner. It employs two separate queues at the AP, one for the data packets of downlink TCP flows and another for the ACK packets of uplink TCP flows, and selects these queues with appropriate probabilities so that TCP per-flow fairness is improved. Moreover, we analyze the behavior of the dual queue scheme and derive throughputs of uplink and downlink flows. Based on this analysis, we obtain the optimal queue selection probabilities for fairness. Extensive simulation results confirm that the proposed scheme is effective and useful in resolving the TCP unfairness problem without deteriorating overall utilization.     

Fair and efficient Transmission Control Protocol access in the IEEE 802.11 infrastructure basic service set

When the stations in an IEEE 802.11 infrastructure basic service set employ Transmission Control Protocol (TCP), this exacerbates per‐flow unfair access problem. We propose a novel analytical model to approximately calculate the maximum per‐flow TCP congestion window limit that prevents packet losses at the access point buffer and therefore provides fair TCP access both in the downlink and uplink. The proposed analysis is unique in considering the effects of varying number of uplink and downlink TCP flows, differing round trip times among TCP connections and the use of delayed TCP acknowledgment (ACK) mechanism. Motivated by the findings of this theoretical analysis and simulations, we design a link layer access control block to be employed only at the access point in order to resolve the unfair access problem. The proposed link layer access control block uses congestion control and ACK filtering approach by prioritizing the access of TCP data packets of downlink flows over TCP ACK packets of uplink flows. Via simulations, we show that the proposed algorithm can provide both short‐term and long‐term fair accesses while improving channel utilization and access delay. Copyright © 2013 John Wiley & Sons, Ltd.     

Resource Management and QoS Provisioning for Duplex Services in IEEE 802.16

Duplex services are multimedia services that requires good connectivity in both uplink and downlink such as VoIP, video conferencing and interactive gaming. A weak connection in either direction may cause degradation of performances and dissatisfaction of user experience. Most researchers do not consider this issue and treat resource allocations in uplink and downlink independently. For this reason, the conventional resource management schemes do not guarantee a good duplex connectivity. Generally, duplex schemes require some relation or information to be exchanged between uplink and downlink resource allocation processes. The existing duplex resource allocation schemes, however, have high complexity and do not adhere to the IEEE 802.16 standard. In this paper, we propose a duplex resource management scheme for IEEE 802.16 network to enhance the user experience and to improve the network performances. The proposed resource management scheme is a MAC layer function that co-relates the uplink and downlink allocation processes using a newly proposed duplex variable. Simulation studies show that the proposed scheme brings significant benefit to duplex services in the IEEE 802.16 networks and outperforms the conventional and existing schemes in terms of uplink and downlink transmission gap, QoS performances and fairness.     

A buffer management algorithm for improving up/down transmission congestion protocol fairness in IEEE 802.11 wireless local area networks

The fair allocation of the resources is an important issue in wireless local area network (WLAN) because all wireless nodes compete for the same wireless radio channel. When uplink and downlink transmission congestion protocol (TCP) flows coexist in WLAN, the network service is biased toward the uplink TCP flows, and the downlink TCP flows tend to starve. In this article, we investigate the special up/down TCP unfairness problem and point out that the direct cause is the uplink acknowledgement (ACK) packets occupy most buffer space of access point. We thus propose a buffer management algorithm to ensure the fairness among uplink and downlink TCP flows. In order to limit the greedy behavior of ACK packets, the proposed algorithm adjusts the maximum size of buffer allocated for the ACK packets. Analysis and simulation results show that the proposed solution not only provides the fairness but also achieves 10–20% lower queue delay and higher network goodput than the other solutions. Copyright © 2012 John Wiley & Sons, Ltd.     

Optimizing uplink TCP-ACK transmission in WiMAZ OFDMA systems

In WiMAX networks, a bandwidth request-grant process is required for uplink operation. However, the process is not optimized for TCP, since the uplink ACK stream is disrupted due to the following: (a) The process consists of several stages which in turn introduce big transmission delay; and (b) it requires additional uplink bandwidth which is significant compared to the ACK packet size. In this paper, the authors propose a new ACK transmission scheme, where ACK packets are combined with a bandwidth request (BR) header. Through simulation, it is demonstrated that the proposed scheme reduces the overheads of TCP-ACK transmissions effectively.     

移动WiMAX网络下行链路TCP吞吐量公平性的跨层优化

该文提出了一种移动WiMAX网络中的TCP公平性跨层优化模型,设计了基于此模型的cross-layer TCP改进协议。利用端节点链路层的速率信息和在基站BS(Base Station)处预分配ACK分组所需带宽的策略改善了下行终端的QoS (Quality of Service)指标,保证了下行终端和上行终端的吞吐量公平性。仿真结果表明cross- layer-TCP改进协议能够在保持原有系统吞吐量的前提下改善下行终端的公平性。     

A bandwidth allocation algorithm with channel quality and QoS aware for IEEE 802.16 base stations

Subscriber stations located in different places encounter various interferences in an IEEE 802.16 network, resulting in that their communication channels experience varying channel conditions. Thus, an excellent bandwidth allocation algorithm should not only satisfy various QoS required by heterogeneous traffic, but also consider the channel quality to maximize bandwidth utilization. In this paper, a bandwidth allocation algorithm with channel quality awareness and QoS guarantee, called CQQ, is proposed. CQQ not only satisfies each connection's QoS requirement, but also dynamically adjusts the downlink/uplink bandwidth to match current downlink/uplink traffic ratio. CQQ allocates more bandwidth to the connections having better channel quality by applying weighted fair queuing strategy to raise the bandwidth usage. CQQ provides lower delay violation ratio and higher goodput than the previous algorithms, as observed from the simulation results. Copyright © 2012 John Wiley & Sons, Ltd.     

一种用于IEEE 802.16无线城域网TDD模式中的带宽调度方案

该文提出了一种用于IEEE 802.16宽带无线接入系统TDD模式下的公平而有效的带宽分配调度体系。与该领域中传统的固定带宽分配方式相比,该文提出的调度体系结构综合考虑了上下行链路不同业务带宽需求并进行动态带宽分配。该文提出一种新的亏空公平优先级队列(DFPQ)算法来调度不同优先级的业务流,可以为系统提供更好的公平性。仿真结果显示该文提出的调度体系结构能够很好地满足所有类型业务的服务质量(QoS)需求,并提供较好的公平性。     

A Novel Bandwidth Allocation Algorithm for IEEE 802.16 TDD Mode Wireless Access Networks

In this paper, we propose a novel bandwidth allocation algorithm for a two-tier hierarchy in IEEE 802.16 time division duplex mode wireless access networks under symmetric and/or asymmetric uplink and downlink traffic input. We demonstrate the performance of the new bandwidth allocation algorithm in terms of accumulated throughput (cumulative bandwidth) and fairness in both infinite and finite buffer cases compared with others by simulations. The simulation results show that the proposed algorithm not only can provide much better fairness and maintain satisfactory QoS support and high cumulative bandwidth but also in the case of finite buffer depth is less buffer-consuming than the others, meaning that the hardware cost can be reduced by employing the proposed algorithm.     

Design of an enhanced access point to optimize TCP performance in Wi-Fi hotspot networks

In the last years, the number of Wi-Fi hotspots at public venues has undergone a substantial growth, promoting the WLAN technologies as the ubiquitous solution to provide high-speed wireless connectivity in public areas. However, the adoption of a random access CSMA-based paradigm for the 802.11 MAC protocol makes difficult to ensure high throughput and a fair allocation of radio resources in 802.11-based WLANs. In this paper we evaluate extensively via simulations the interaction between the flow control mechanisms implemented at the TCP layer and the contention avoidance techniques used at the 802.11 MAC layer. We conducted our study considering initially M wireless stations performing downloads from the Internet. From our results, we observed that the TCP downlink throughput is not limited by the collision events, but by the inability of the MAC protocol to assign a higher chance of accessing the channel to the base station. We propose a simple and easy to implement modification of the base station’s behavior with the purpose of increasing the TCP throughput reducing useless MAC protocol overheads. With our scheme, the base station is allowed to transmit periodically bursts of data frames towards the mobile hosts. We design a resource allocation protocol aimed at maximizing the success probability of the uplink transmissions by dynamically adapting the burst length to the collision probability estimated by the base station. By its design, our scheme is also beneficial to achieve a fairer allocation of the channel bandwidth among the downlink and uplink flows, and among TCP and UDP flows. Simulation results confirm both the improvement in the TCP downlink throughput and the reduction of system unfairness.     

Queuing Scheme for Improved Downlink Throughput on WLANs

A transmission queuing scheme is described that increases downlink throughput on wireless local area networks (WLANs) while also increasing the total throughput. When the amount of uplink traffic increases on a WLAN, the carrier sense multiple access with collision avoidance (CSMA/CA) protocol, which is the prescribed scheme for IEEE 802.11 WLAN channel access, may substantially reduce the rate of downlink data frame transmission. This results in severe throughput degradation for mobile stations with downlink traffic. The proposed scheme comprises a transmission control function based on consecutive transmission, as described in the IEEE 802.11e standard, and a dynamic queue prioritization algorithm. Simulation results demonstrate that the proposed scheme increases the maximum total throughput for uplink and downlink traffic by 17% compared with the conventional distributed coordination function (DCF) scheme and that it reduces the difference between uplink and downlink throughput. In an environment where transmission errors occur, the difference in throughput is reduced by about 50% compared with the conventional schemes.     

Efficient Uplink Bandwidth Request with Delay Regulation for Real-Time Service in Mobile WiMAX Networks

The emerging broadband wireless access technology based on IEEE 802.16 is one of the most promising solutions to provide ubiquitous wireless access to the broadband service at low cost. This paper proposes an efficient uplink bandwidth request-allocation algorithm for real-time services in Mobile WiMAX networks based on IEEE 802.16e. In order to minimize bandwidth wastage without degrading quality of service (QoS), we introduce a notion of target delay and propose dual feedback architecture. The proposed algorithm calculates the amount of bandwidth request such that the delay is regulated around the desired level to minimize delay violation and delay jitter for real-time services. Also, it can increase utilization of wireless channel by making use of dual feedback, where the bandwidth request is adjusted based on the information about the backlogged amount of traffic in the queue and the rate mismatch between packet arrival and service rates. Due to the target delay and dual feedback, the proposed scheme can control delay and allocate bandwidth efficiently while satisfying QoS requirement. The stability of the proposed algorithm is analyzed from a control-theoretic viewpoint, and a simple design guideline is derived based on this analysis. By implementing the algorithm in OPNET simulator, its performance is evaluated in terms of queue regulation, optimal bandwidth allocation, delay controllability, and robustness to traffic characteristics.     

QoS-aware Two-level Dynamic Uplink Bandwidth Allocation Algorithms in IEEE 802.16j Based Vehicular Networks

Wireless communications play an important role in improving transportation environment safety and providing Internet access for vehicles. This paper proposes a QoS-aware two-level uplink dynamic bandwidth allocation (DBA) algorithm for IEEE 802.16j-based vehicular networks. IEEE 802.16j is an extension of standard IEEE 802.16 to support relay mode operation where traffics from/to subscriber stations (SS) are relayed to/from a base station (BS) via a relay station (RS). In such a vehicular network, the IEEE 802.16j BSs are installed along a highway, RSs are installed in large vehicles such as coaches, and the 802.16j interface is equipped on SSs such as individual passengers’ mobile devices within a moving coach. In the proposed DBA algorithm, a utility function, which considers characteristics of different types of services, is designed. The objective of the proposed two-level DBA algorithm is to allocate bandwidth to different types of services from BS to RSs and then from a RS to SSs with given quality of service (QoS) requirements. It aims at maximizing the utility of the overall network and minimizing the average queuing delay of the overall network. The simulation results show the effectiveness and efficiency of the proposed DBA algorithm.     

Performance of packet voice transmission using IEEE 802.16 protocol

The IEEE 802.16 standard defines three types of scheduling services for supporting real-time traffic, unsolicited grant service (UGS), real-time polling service (rtPS), and extended real-time polling service (ertPS). In the UGS service, the base station (BS) offers a fixed amount of bandwidth to a subscriber station (SS) periodically, and the SS does not have to make any explicit bandwidth requests. The bandwidth allocation in the rtPS service is updated periodically in the way that the BS periodically polls the SS, which makes a bandwidth request at the specified uplink time slots and receives a bandwidth grant in the following downlink subframe. In the ertPS service, the BS keeps offering the same amount of bandwidth to the SS unless explicitly requested by the SS. The SS makes a bandwidth request only if its required transmission rate changes. In this article we study the performance of voice packet transmissions and BS resource utilization using the three types of scheduling services in IEEE 802.16-based backhaul networks, where each SS forwards packets for a number of voice connections. Our results demonstrate that while the UGS service achieves the best latency performance, the rtPS service can more efficiently utilize the BS resource and flexibly trade-off between packet transmission performance and BS resource allocation efficiency; and appropriately choosing the MAC frame size is important in both the rtPS and ertPS services to reduce packet transmission delay and loss rate     

IEEE802.16中竞争时隙的动态分配算法

文章通过对IEEE802.16中竞争方式的请求与分配关系进行分析,提出了一种竞争时隙的动态分配方法.与固定分配方式相比,该分配方法可有效提高上行带宽的使用效率,并减小竞争请求引入的时延.仿真结果表明,在各种负载条件下,该分配算法都能较高效地使用系统的上行带宽.     

Neural bandwidth allocation function (NBAF) control scheme at WiMAX MAC layer interface

The paper proposes a bandwidth allocation scheme to be applied at the interface between upper layers (IP, in this paper) and Medium Access Control (MAC) layer over IEEE 802.16 protocol stack. The aim is to optimally tune the resource allocation to match objective QoS (Quality of Service) requirements. Traffic flows characterized by different performance requirements at the IP layer are conveyed to the IEEE 802.16 MAC layer. This process leads to the need for providing the necessary bandwidth at the MAC layer so that the traffic flow can receive the requested QoS. The proposed control algorithm is based on real measures processed by a neural network and it is studied within the framework of optimal bandwidth allocation and Call Admission Control in the presence of statistically heterogeneous flows. Specific implementation details are provided to match the application of the control algorithm by using the existing features of 802.16 request–grant protocol acting at MAC layer. The performance evaluation reported in the paper shows the quick reaction of the bandwidth allocation scheme to traffic variations and the advantage provided in the number of accepted calls. Copyright © 2006 John Wiley & Sons, Ltd.     

iVoIP: an intelligent bandwidth management scheme for VoIP in WLANs

Voice over Internet Protocol (VoIP) has been widely used by many mobile consumer devices in IEEE 802.11 wireless local area networks (WLAN) due to its low cost and convenience. However, delays of all VoIP flows dramatically increase when network capacity is approached. Additionally, unfair traffic distribution between downlink and uplink flows in WLANs impacts the perceived VoIP quality. This paper proposes an intelligent bandwidth management scheme for VoIP services (iVoIP) that improves bandwidth utilization and provides fair downlink–uplink channel access. iVoIP is a cross-layer solution which includes two components: (1) iVoIP-Admission Control, which protects the quality of existing flows and increases the utilization of wireless network resources; (2) iVoIP-Fairness scheme, which balances the channel access opportunity between access point (AP) and wireless stations. iVoIP-Admission Control limits the number of VoIP flows based on an estimation of VoIP capacity. iVoIP-Fairness implements a contention window adaptation scheme at AP which uses stereotypes and considers several major quality of service parameters to balance the network access of downlink and uplink flows, respectively. Extensive simulations and real tests have been performed, demonstrating that iVoIP has both very good VoIP capacity estimation and admission control results. Additionally, iVoIP improves the downlink/uplink fairness level in terms of throughput, delay, loss, and VoIP quality.