Majlinda Mjeku

Effects on IEEE 802.11 MAC Throughput in Wireless LAN Over Fiber Systems

An experimental investigation of the influence of the fiber distribution of wireless LAN (WLAN) signals on throughput performance is presented. Transmission using different medium-access-control mechanisms and IEEE 802.11b and 802.11g physical layers is considered, and results are compared with those from the corresponding simulations in a commercial event-driven network simulator (OPNET). Performance of the WLAN-over-fiber network in the presence of multiple clients is also analyzed. This paper confirms that a fiber delay does not significantly affect the performance obtained by fragmentation mechanism. Furthermore, when multiple antenna units are fed by a single access point, it is demonstrated that the presence of hidden nodes can cause the performance of WLAN-over-fiber networks to deteriorate. Finally, it is shown that the request-to-send/clear-to-send mechanism can be utilized to mitigate the negative effects associated with the hidden node problem.

Analysis of the Request to Send/Clear to Send Exchange in WLAN Over Fiber Networks

A study of the effect of the optical path delay on the effectiveness of the request to send/clear to send (RTS/CTS) exchange in high-speed IEEE 802.11 wireless LAN (WLAN) over fiber networks has been carried out. It is shown that although the fiber delay might violate some of the timing boundaries of the medium access control (MAC) protocol, with a careful choice of the RTS threshold parameter, which determines when the RTS/CTS is used, these networks can benefit significantly from the four-way handshake even without the need for modifying the existing protocol.

Performance Impairments in Single-Mode Radio-Over-Fiber Systems Due to MAC Constraints

This paper investigates performance impairments due to constraints imposed by the MAC layer when single-mode fiber (SMF) is used to extend the reach of an IEEE 802.11 network. It is shown that data throughput decreases as fiber length increases. It is also noted that the network fails long before physical layer limitations set in due to the timeout values defined within the MAC protocol. This study is based on both variants of the IEEE 802.11 Distributed Coordination Function. Moreover, both UDP and TCP packet transmissions are taken into account. An experimental enquiry is initially developed to provide a set of validation points before extending these results by simulations using the OPNET platform. Finally, an analytical approximation is presented to these results that allows designers of Radio-over-fiber (RoF) systems to quickly and accurately predict the data throughput given the specific parameters of their network. To our knowledge, this is the first analysis of this kind for a long reach fiber system.

Use of Different Acknowledgement Policies for Burst Transmission in Fiber-fed Wireless LANs

The IEEE 802.11 e medium access control (MAC) for quality-of-service (QoS) support in 802.11 networks defines burst transmission and new acknowledgment (ACK) operations as optional mechanisms for increasing channel utilization. In this paper, we investigate how the performance of these new features is affected by the presence of fiber delay in high speed Wireless LAN (WLAN) over fiber networks. It is shown that the negative effect of the fiber delay on the throughput performance of the 802.11 MAC protocol can be significantly reduced when burst transmission is used with the block or the no ACK policies.

Multimode Fiber-fed Indoor Wireless Networks

A summary of results obtained for radio over multimode fiber links and system demonstrations is presented. It is stated that when using low-cost technologies such as pre-installed MMF and VCSELs, although adequate link performance is achievable, with careful design when taking into account the wireless path, MAC protocol effects may need to be considered for WLAN operation. For the simultaneous transmission of multiple signals, practical considerations of crosstalk and interference may cause an increase in the necessary complexity of remote antenna units

MAC layer performance evaluation of IEEE 802.16e Radio-over-Fiber networks

This paper investigates the performance of the IEEE 802.16e Medium Access Control (MAC) in 802.16e Radio-over-Fiber (RoF) networks, in terms of MAC Data Rate (MDR). It is shown that the accommodation of the extra propagation delay induced by the optical fiber links increases the protocol overheads and reduces the protocols efficiency.

Performance analysis of 802.11e transmission bursting in fiberfed networks

A burst transmission mechanism has been defined in the IEEE 802.11e medium access control extension in order to reduce the overheads in protocol operation and improve efficiency. In this paper, we analyze the throughput and delay performance when this mechanism is used with the immediate acknowledgment policy in a fiber-fed wireless LAN (WLAN). It is shown that the extra propagation delay caused by the optical distribution network in the system affects the burst transmission operation in the presence or otherwise of channel errors and affects the optimum thresholds for switching between the basic access and the request-to-send/clear-to-send (RTS/CTS) modes. It is also shown that significant throughput and media access delay improvements can be gained by the use of burst transmission in contention based 802.11e fiber-fed WLANs, regardless of the load in the network.

Performance evaluation of IEEE 802.11e medium access control in fiber-fed networks

An evaluation of the performance of the IEEE 802.11e medium access control (MAC) for quality-of-service (QoS) support in 802.11 networks has been carried out in a fiber-fed wireless local area network (WLAN) scenario. The effect of the additional optical path delay on the effectiveness of the new mechanisms of the 802.11e extension for efficiency increase, i.e., the burst transmission, and new ACK policies have been investigated. It is shown by means of analysis and simulations that although the fiber delay degrades the performance of the new mechanisms, compared with the original 802.11 MAC, significant throughput improvement can be gained when burst transmission is used with the Immediate, Block, or No ACK policies in fiber-fed networks. An experimental evaluation of the throughput improvement with the 802.11e extension is also reported. Our measurements, supported by simulations, show that higher layer operation can have a significant effect on the performance of the new MAC mechanisms, especially when transmission errors are present.

Protocol parameter selection for fiber-supported IEEE 802.16m networks

In this paper we investigate protocol issues that might arise due to the extra fiber propagation delay in fiber-fed IEEE 802.16m networks. Our study indicates that although the fiber delay might affect network performance, an informed choice of protocol parameters, such as the guard times and the ranging channel structure, can minimize the reduction in efficiency and allow for relaxation of some of the constraints imposed on the optical distribution network architecture.