Frame‐Size Adaptive MAC Protocol in High‐Rate Wireless Personal Area Networks

In this letter, we propose a frame‐size adaptive MAC protocol for high rate wireless personal area networks (WPANs). In the proposed scheme, during communication, frame error rate is periodically reported to a transmitting device and the frame size is changed according to the measured results. Thus, the channel can be more effectively utilized by adapting to variable radio conditions. Analytical results show that this scheme achieves a much higher throughput than a non‐frame‐size adaptive media access control protocol in high‐rate WPANs.     

Study of an adaptive frame size predictor to enhance energy conservation in wireless sensor networks

Technological advances in low-power digital signal processors, radio frequency (RF) circuits, and micromechanical systems (MEMS) have led to the emergence of wirelessly interconnected sensor nodes. The new technological possibilities emerge when a large number of tiny intelligent wireless sensor nodes are combined. The sensor nodes are typically battery operated and, therefore, energy constrained. Hence, energy conservation is one of the foremost priorities in design of wireless sensor networks (WSNs) protocols. Limited power resources and bursty nature of the wireless channel are the biggest challenges in WSNs. Link adaptation techniques improve the link quality by adjusting medium access control (MAC) parameters such as frame size, data rate, and sleep time, thereby improving energy efficiency. In This work, our study emphasizes optimizing WSNs by building a reliable and adaptive MAC without compromising fairness and performance. Here, we present link adaptation techniques at MAC layer to enhance energy efficiency of the sensor nodes. The proposed MAC uses a variable frame size instead of a fixed frame size for transmitting data. In order to get accurate estimations, as well as reducing the computation complexity, we utilize the extended Kalman filter to predict the optimal frame size for improving energy efficiency and goodput, while minimizing the sensor memory requirement. Next, we designed and verified different network models to evaluate and analyze the proposed link adaptation schemes. The correctness of the proposed theoretical models have been verified by conducting extensive simulations. We also prototype the proposed scheme with the MAC protocol on Berkeley Motes. Both prototype and simulation results show that the proposed algorithms improve the energy efficiency by up to 15%.     

iFrag: interference-aware frame fragmentation scheme for wireless sensor networks

Reliable data transmission is a fundamental challenge in resource-constrained wireless sensor networks. In current implementations, a single bit error requires retransmitting the entire frame. This incurs extra processing overhead and power consumption, especially for large frames. Frame fragmentation into small blocks with individual error detection codes can reduce the unnecessary retransmission of the correctly received blocks. The optimal block size, however, varies based on the wireless channel conditions. In this paper, we propose an interference-aware frame fragmentation scheme called iFrag. iFrag dynamically adjusts the number of blocks inside a frame based on current channel conditions, and effectively addresses all challenges associated with such dynamic partitioning. Through analytical and experimental results, we show that iFrag achieves up to \(3\times\) improvement in goodput when the channel is noisy, while reducing the delay by 12 % compared to other static fragmentation approaches. On average, it shows a 13 % gain in goodput across all channel conditions used in our experiments. Our testbed results also show that iFrag lowers the energy consumed per useful bit by 60 %, as improved data transmission reliability reduces the number of frame retransmissions which increases the motes energy efficiency.     

Optimal frame aggregation level for IEEE 802.11 PCF protocol

In this paper, we analyze the effect of the frame aggregation level on the PCF (Point Coordination Function) MAC performance in IEEE 802.11 wireless LANs and analytically derive the optimal frame aggregation level for maximizing the PCF MAC performance. For various values of unit data frame size and transmission error probability, we propose the optimal frame aggregation levels. By computer simulations, we show that the derived optimal frame aggregation level significantly enhances the PCF MAC performance in IEEE 802.11 wireless LANs.     

基于IEEE 802.11高速无线局域网的速率自适应MAC协议研究

目前的IEEE 802.11标准在物理层提供了对多种发送速率的支持,然而在MAC层却没有规定速率自适应的方法。该文研究了高速IEEE 802.11 无线局域网中的速率自适应方案。首先,提出了EACK协议,EACK使用基本速率发送MAC头,并在ACK帧中携带信道信息,因而能够较快速地响应信道的变化,同时具有少的开销;其次,在EACK基础上,提出了一种恒定发送时间(CEACK)的策略,CEACK能够克服传统IEEE 802.11 DCF MAC协议的理论吞吐量上限,并且具有更好的时间公平性能,能够应用于高速的无线局域网。     

Goodput analysis and link adaptation for IEEE 802.11a wireless LANs

Link adaptation to dynamically select the data transmission rate at a given time has been recognized as an effective way to improve the goodput performance of the IEEE 802.11 wireless local-area networks (WLANs). Recently, with the introduction of the new high-speed 802.11a physical layer (PHY), it is even more important to have a well-designed link adaptation scheme work with the 802.11a PHY such that its multiple transmission rates can be exploited. In this paper, we first present a generic method to analyze the goodput performance of an 802.11a system under the distributed coordination function (DCF) and express the expected effective goodput as a closed-form function of the data payload length, the frame retry count, the wireless channel condition, and the selected data transmission rate. Then, based on the theoretical analysis, we propose a novel MPDU (MAC protocol data unit)-based link adaptation scheme for the 802.11a systems. It is a simple table-driven approach and the basic idea is to preestablish a best PHY mode table by applying the dynamic programming technique. The best PHY mode table is indexed by the system status triplet that consists of the data payload length, the wireless channel condition, and the frame retry count. At runtime, a wireless station determines the most appropriate PHY mode for the next transmission attempt by a simple table lookup, using the most up-to-date system status as the index. Our in-depth simulation shows that the proposed MPDU-based link adaptation scheme outperforms the single-mode schemes and the autorate fallback (ARF) scheme-which is used in Lucent Technologies' WaveLAN-II networking devices-significantly in terms of the average goodput, the frame drop rate, and the average number of transmission attempts per data frame delivery.     

Low-latency mobile IP handoff for infrastructure-mode wireless LANs

The increasing popularity of IEEE 802.11-based wireless local area networks (LANs) lends them credibility as a viable alternative to third-generation (3G) wireless technologies. Even though wireless LANs support much higher channel bandwidth than 3G networks, their network-layer handoff latency is still too high to be usable for interactive multimedia applications such as voice over IP or video streaming. Specifically, the peculiarities of commercially available IEEE 802.11b wireless LAN hardware prevent existing mobile Internet protocol (IP) implementations from achieving subsecond Mobile IP handoff latency when the wireless LANs are operating in the infrastructure mode, which is also the prevailing operating mode used in most deployed IEEE 802.11b LANs. In this paper, we propose a low-latency mobile IP handoff scheme that can reduce the handoff latency of infrastructure-mode wireless LANs to less than 100 ms, the fastest known handoff performance for such networks. The proposed scheme overcomes the inability of mobility software to sense the signal strengths of multiple-access points when operating in an infrastructure-mode wireless LAN. It expedites link-layer handoff detection and speeds up network-layer handoff by replaying cached foreign agent advertisements. The proposed scheme strictly adheres to the mobile IP standard specification, and does not require any modifications to existing mobile IP implementations. That is, the proposed mechanism is completely transparent to the existing mobile IP software installed on mobile nodes and wired nodes. As a demonstration of this technology, we show how this low-latency handoff scheme together with a wireless LAN bandwidth guarantee mechanism supports undisrupted playback of remote video streams on mobile stations that are traveling across wireless LAN segments.     

Cross-Layer Analysis of Joint Rate and Power Adaptation in Nakagami Fading Channels with Multiple-User Contention

Adaptively adjusting transmit rate and power concurrently to enhance goodput and save energy is a challenging issue in a wireless local area network (WLAN) because goodput enhancement and energy saving are usually two contradictory goals. In this paper, we propose channel-driven rate and power adaptation (CDRPA) schemes and develop a physical (PHY)/medium access control (MAC) cross-layer analytical method incorporating the impacts of Nakagami fading channel and the carrier sense multiple access (CSMA) MAC protocol. The CDRPA scheme has much lower computation complexity than the energy-optimal complete-search scheme. In a multiuser contention scenario, we analyze the energy efficiency and the goodput of the power-first and rate-first CDRPA schemes as well as the energy-optimal complete-search adaptation scheme. At the cost of lower goodput, the power-first scheme has better energy efficiency than the rate-first CDRPA scheme, whereas if the goodput is the main concern, the rate-first CDRPA scheme shall be chosen due to better goodput performance. More interestingly, we find that the power-first CDRPA scheme can achieve about the same goodput and energy efficiency as the energy-optimal complete-search link adaptation scheme.     

A short-term fair MAC protocol for WLANs

Designing a medium access control (MAC) protocol that simultaneously provides high throughput and allows individual users to share limited spectrum resources fairly, especially in the short-term time horizon, is a challenging problem for wireless LANs. In this paper, we propose an efficient cooperative MAC protocol with very simple state information that considers only collisions, like the standard IEEE 802.11 MAC protocol. However, contrary to the IEEE 802.11 MAC, the cooperative MAC gives collided users priority to access the channel by assigning them shorter backoff counters and interframe-spaces than users who did not participate in the collision event. In other words, collided users are the only ones allowed to transmit in the following contention period. For the cooperative MAC protocol, we utilize an analytical throughput model to obtain the optimal parameter settings. Simulation results show that the cooperative MAC provides significant improvement in short-term fairness and access delay, while still providing high network throughput.     

Performance analysis of variable rate: symbol-by-symbol adaptivebit interleaved coded modulation for Rayleigh fading channels

A challenging problem for a high-speed data service over wireless is to protect data over the error-prone fading channel in an effective way (high-bandwidth efficiency). We propose a bandwidth-efficient error correction scheme, namely variable rate adaptive bit interleaved coded modulation (ABICM), for the wireless mobile channel. The code rate and modulation level are varied according to the current channel state to exploit the time-varying nature of the wireless channel. Design challenges to achieve symbol-by-symbol adaptation are addressed. In particular, we address the criteria for choosing the family of component codes for the ABICM system. We propose a multilevel puncturing scheme that solves the problem of symbol-by-symbol adaptive puncturing and interleaving. The equivalent distance spectrum for variable rate symbol-by-symbol adaptive codes is introduced and analytical bounds on adaptive codes are derived that enable us to determine the optimal adaptation thresholds. Two operation modes, namely constant throughput and constant bit error rate (BER) controls, are proposed. It is found that there are significant gains relative to fixed-rate coding in terms of signal-to-noise ratio (SNR) and throughput. It is also found that the ABICM scheme is essentially not degraded when used with small interleaving depths. This makes the ABICM very suitable for real-time applications     

Packet level acknowledgement and Go‐Back‐N protocol performance in infrared wireless LANs

Infrared wireless LANs may employ repetition rate (RR) coding to increase the symbol capture probability at the receiver. This paper examines the effectiveness of RR coding to utilization for infrared LANs using the physical and link layer parameter values proposed in the Advanced Infrared (AIr) protocol standard, which is developed by the Infrared Data Association (IrDA). Infrared LANs employ a Go‐Back‐N (GBN) automatic repeat request (ARQ) retransmission scheme at the Link Control (LC) layer to ensure reliable information transfer. To efficiently implement RR coding, the receiver may return after every DATA packet a suggestion for the suitable RR value to be used by the transmitter and implement a Stop‐and‐Wait (SW) ARQ scheme at the medium access control (MAC) layer. The effectiveness of employing this optional SW ARQ scheme at the MAC layer is discussed. Analytical models for the ARQ retransmission schemes are developed and employed to compare protocol utilization for different link parameter values such as window size, packet length and LC time out periods. This analysis identifies the ARQ protocol that maximizes performance for the specific link quality and the implemented link layer parameters. The effectiveness of the proposed RR coding to LAN utilization for different ARQ scheme implementation is finally explored. This analysis identifies the link quality level at which RR should be adjusted for maximum performance. It is concluded that if the packet error rate is higher than 0.1–0.4 (depending on the implemented ARQ protocol), the receiver should advise the transmitter to double the implemented RR for maximum performance. These error rate values are high and can be effectively estimated by the transmitter based on packet retransmissions. Thus, the usefulness of the receiver indicating to the transmitter to adjust RR is questionable, as the transmitter can effectively implement the suitable RR value based on packet retransmissions. Copyright © 2003 John Wiley & Sons, Ltd.     

Design of an access mechanism for a high speed distributed wirelessLAN

The medium used by indoor wireless LANs is a shared, scarce resource. Hence, efficient use of this medium is important, which in turn requires an efficient MAC protocol. Moreover, next generation wireless LANs will have to support data rates from 10 to 100 Mbits/s. At these data rates, turnaround times in half-duplex radios are a large overhead. This makes the current wireless standards inefficient. However, busy-tone solutions can get around this problem. In spite of their better performance, the busy-tone protocols are not widely used because of the hardware cost, i.e., the requirement of two transceivers-one each for the data and feedback channel. A novel wireless transceiver architecture which mitigates this hardware cost by overlaying the data channel and the feedback channel in the same frequency band is designed. It is shown that this transceiver can be built with current technology. Based on this wireless transceiver, a new MAC protocol called wireless collision detect (WCD) is proposed. This protocol uses a carrier detect signal to decrease the collision probability and receiver initiated feedback to handle hidden nodes. We derive a mathematical expression for the throughput of the protocol. The simulation results match the analysis. At 100 Mbits/s, WCD achieves 77% efficiency with 192 byte packets. For this scenario, the throughput of the IEEE 802.11 MAC protocol and RI-BTMA is 3% and 52%, respectively     

A novel learning based solution for efficient data transport in heterogeneous wireless networks

There has been a spectacular growth in the use of wireless networks in recent times and consequently, adapting TCP to the wireless networks is a hot topic of current research. However, most of the existing works proposed for this problem have been designed for specific wireless networks, or they necessitate changes at either the receiver or the intermediate nodes, or at both, because of which their deployment becomes difficult. In this work, we propose a TCP variant which works over both multi-hop ad hoc wireless networks as well as single-hop (last-hop) wireless networks, like Wireless LANs, cellular, and satellite networks. We use a learning based method to dynamically change the congestion window size according to the network conditions. Our protocol does not rely on any explicit feedback from the network and requires only sender-side modifications. Through extensive simulations we show that our protocol achieves the desired goals of performance improvement in goodput, reduction in packet loss, and fairness to the competing flows. To the best of our knowledge, this is the first unified solution for both single-hop and multi-hop wireless networks.     

Optimal designs for IEEE 802.15.4 wireless sensor networks

This paper investigates the maximum achievable channel throughput in a single‐channel and single‐hop wireless sensor network using IEEE 802.15.4 Medium Access Control (MAC) protocol. We introduce a simple mean‐field approach to model the Carrier Sense Multiple Access with Collision Avoidance mechanism of the 802.15.4 MAC protocol under unsaturated conditions. We derive a set of expressions such as optimal sensing rate of a sensor node, its corresponding failure probability, and the channel throughput for both saturated and unsaturated networks. With those expressions, we propose several network designs to achieve the optimal throughput by choosing the appropriate MAC parameters. We validate the proposed optimal designs using ns‐2 simulations. Furthermore, we evaluate the network lifetime expectancy of the optimal designs and compare it with the lifetime of network settings under saturated conditions that use the default MAC parameters of IEEE 802.15.4. Copyright © 2011 John Wiley & Sons, Ltd.     

ATM infrared wireless LANs: a proposed architecture

As infrared wireless LANs for in-building applications become more popular because of their many advantages, it is of interest to design such LANs to support the ATM protocol and therefore provide wireless access to fixed ATM networks. The architecture of such a LAN is presented in this article. Emphasis is placed on the protocol stacks of the model to provide seamless operation with the wired network, on the cellular topology, and on the MAC protocol. Under the proposed topology the system performance is revealed in terms of packet dropping probability, average access delay, channel throughput, and statistical multiplexing gain for a range of system parameters     

Carrier‐sense‐assisted adaptive learning MAC protocols for distributed wireless LANs

A Carrier‐sense‐assisted adaptive learning MAC protocol for wireless LANs, capable of operating efficiently in bursty traffic wireless networks with unreliable channel feedback, is introduced. According to the proposed protocol, the mobile station that is granted permission to transmit is selected by means of learning automata. At each station, the learning automaton takes into account the network feedback information in order to update the choice probability of each mobile station. The proposed protocol utilizes carrier sensing in order to reduce the collisions that are caused by different decisions at the various mobile stations due to the unreliable channel feedback. Simulation results show satisfactory performance of the proposed protocol compared to similar MAC protocols. Copyright © 2005 John Wiley & Sons, Ltd.     

Dynamic bandwidth partition schemes for integrated voice,video, and data traffic in the IEEE 802.11e distributed wireless LANs

In mobile cellular networks, bandwidth is deterministic in terms of the number of channels by frequency division, time division, or code division. On the other hand, bandwidth partition schemes in the contention‐based medium access control (MAC) in distributed wireless LANs are extremely challenging due to the contention‐based nature, packet‐based network, and the most important aspect: only one channel available, competed by an unknown number of stations. In this paper, we study this challenging issue. We propose and study four different bandwidth partition schemes for integrated voice/video/data traffic in the IEEE 802.11e wireless LANs: a Static bandwidth Partition (SP) scheme, a Dynamic budget Partition (DP) scheme, a Dynamic bandwidth Partition with Finer‐Tune (DP‐FT) scheme, and a Dynamic bandwidth Partition with Reserved Region (DP‐RR). The proposed schemes are compared and evaluated via extensive simulations. Results show that the DP‐FT scheme is the best scheme. Copyright © 2009 John Wiley & Sons, Ltd.     

Throughput and QoS optimization for EDCA-based IEEE 802.11 WLANs

The enhanced distributed channel access (EDCA) mechanism has been adopted by both the IEEE 802.11e standard and the Multiband OFDM Alliance (MBOA) for quality of service (QoS) provisioning in high speed wireless LANs and UWB-based wireless PANs. Based on an analytical model of EDCA, this paper presents an optimal solution to providing maximum system throughput while maintaining the service differentiation among traffic classes. Contention window sizes are adapted to achieve throughput optimization according to the throughput ratio and number of active stations of each traffic class. To overcome the difficulty of accurate estimation of the number of competing stations we propose to use the method of subrange partitioning. An admission control scheme is also discussed. Simulation results demonstrate the effectiveness of the proposed MAC optimization framework.     

Improving Spatial Reuse in Multihop Wireless Networks - A Survey

In multihop wireless ad-hoc networks, the medium access control (MAC) protocol plays a key role in coordinating the access to the shared medium among wireless nodes. Currently, the distributed coordination function (DCF) of the IEEE 802.11 is the dominant MAC protocol for both wireless LANs and wireless multihop ad hoc environment due to its simple implementation and distributed nature. The current access method of the IEEE 802.11 does not make efficient use of the shared channel due to its conservative approach in assessing the level of interference; this in turn affects the spatial reuse of the limited radio resources and highly affect the achieved throughput of a multihop wireless network. This paper surveys various methods that have been proposed in order to enhance the channel utilization by improving the spatial reuse.     

An opportunistic cross‐layer architecture for voice in multi‐hop wireless LANs

We propose an opportunistic cross‐layer architecture for adaptive support of Voice over IP in multi‐hop wireless LANs. As opposed to providing high call quality, we target emergencies where it is important to communicate, even if at low quality, no matter the harshness of the network conditions. With the importance of delay on voice quality in mind, we select adaptation parameters that control the ratio of real‐time traffic load to available bandwidth. This is achieved in two ways: minimizing the load and maximizing the bandwidth. The PHY/MAC interaction improves the use of the spectral resources by opportunistically exploiting rate‐control and packet bursts, while the MAC/application interaction controls the demand per source through voice compression. The objective is to maximize the number of calls admitted that satisfy the end‐to‐end delay budget. The performance of the protocol is studied extensively in the ns‐2 network simulator. Results indicate that call quality degrades as load increases and overlonger paths, and a larger packet size improves performance. For long paths having low‐quality channels, forward error correction, header compression, and relaxing the delay budget of the system are required to maintain call admission and quality. The proposed adaptive protocol achieves high performance improvements over the traditional, non‐adaptive approach. Copyright © 2008 John Wiley & Sons, Ltd.