Jenhui Chen

The design and implementation of WiMAX module for ns-2 simulator

The network simulator 2 (ns-2) is a popular and powerful simulation tool for the simulation of packet-switched networks, which provides substantial support for simulation of TCP, routing, and MAC protocols over wired and wireless networks, such as wireless LANs, mobile ad hoc networks (MANETs), and satellite communications, etc, and is widely used in both academia and industry. Although many protocol modules have been implemented in the ns-2, the IEEE 802.16 broadband wireless access networks (BWANs) or WiMAX module has not been contributed yet. Thus, in this paper, we present our detailed design and implementation of the WiMAX module based on the IEEE 802.16 standard with the point-to-multipoint (PMP) mode for the ns-2. The implemented module comprises fundamental functions of the service-specific convergence sublayer (CS), the MAC common part sublayer (CPS), and the PHY layer. A simple call admission control (CAC) mechanism and the scheduler are also included in this module.

A new multichannel access protocol for IEEE 802.11 ad hoc wireless LANs

The IEEE 802.11 wireless local area networks (WLANs) standard supports several equal-capacity communication channels which can be simultaneously shared and accessed by mobile stations. In such multichannel communication system, a mobile station basically can transmit on any of these channels based on a suitable access control protocol. However, with the feature of one transceiver per mobile station, the standard restricts mobile stations to operate in one selected channel and the other channel capacities are wasted inevitably. In this paper, we propose a new carrier sense multiple access (CSMA) based protocol, called multichannel access protocol (MAP), to support parallel transmissions in IEEE 802.11 ad hoc WLANs. To realize the proposed MAP protocol over contemporary ad hoc WLANs, the MAP protocol is not only compliant with the IEEE 802.11 standard but also taking one transceiver constrain into consideration. All mobile stations with MAP will contend for channel access right in a dedicated channel during a periodical contention reservation interval (CRI) and then transmit data frames over different channels by a channel scheduling algorithm (CSA). Given a number of requests, the problem of finding a proper schedule for these requests to be served on a multichannel system so that the longest channel busy period is minimal is known to be NP-hard (Hou, et al. 1994). The time complexity of proposed heuristic CSA is O(|X| log |X| + |X|M/sup 2/) where |X| and M denote the number of successful requests in the CRI and the number of available channels respectively. Simulation results show that the proposed MAP protocol with CSA achieves an obviously higher throughput than conventional IEEE 802.11 WLAN with single channel.

A highly reliable broadcast scheme for IEEE 802.11 multi-hop ad hoc networks

In wired networks, the broadcast data packets can be easily and safely delivered to destinations. Nevertheless, it is a big challenge to transfer the broadcast frames over the IEEE 802.11 based multi-hop ad hoc wireless networks due to the high bit error rate, the high collision probability, and the lake of acknowledgement (ACK). Unfortunately, most of routing protocols need the broadcast function to exchange important information between nodes. From our observations, the efficiency of the routing protocol, such as dynamic source routing (DSR) and ad-hoc on-demand distance vector (AODV), finding the path from source to destination is strongly depending on the supported broadcast scheme in the underlying media access control (MAC) protocol. In this paper, we first investigate the uncertain broadcast problem in the IEEE 802.11 MAC protocol while delivering the necessary broadcast frames. Since no acknowledgement will be sent by any recipient of the broadcast frame in IEEE 802.11 MAC protocol, we propose a highly reliable broadcast scheme to solve such uncertain problem. The proposed scheme, which is still compatible with standard, can efficiently minimize bandwidth consumption as well as propagation delay.

A novel delay-oriented shortest path routing protocol for mobile ad hoc networks

In wireless ad hoc mobile network, a host which desires to communicate with another host may need some intermediate nodes to relay data packets. To maximize the channel resource utilization and minimize the network transfer delay along the path, the shortest path with minimum hops approach is often adapted. However, by considering employing the medium access control (MAC) protocol, the minimum transfer delay from source to destination may be achieved by choosing a longer path but with less contention delay. We propose an efficient delay-oriented routing protocol for mobile ad hoc wireless networks. The expected access contention delay of the IEEE 802.11 protocol is analyzed to support the routing decision. Simulation results show that the derived path length in the proposed delay-oriented routing protocol is slightly higher than that of the conventional shortest path with minimum hops approach but it can significantly reduce both the average transfer delay and packet loss rate.

MR 2 RP: the multi-rate and multi-range routing protocol for IEEE 802.11 ad hoc wireless networks

This paper discusses the issue of routing packets over an IEEE 802.11 ad hoc wireless network with multiple data rates (1/2/5.5/11 Mb/s). With the characteristics of modulation schemes, the data rate of wireless network is inversely proportional with the transmission distance. The conventional shortest path of minimum-hops approach will be no longer suitable for the contemporary multi-rate/multi-range wireless networks (MR2WN). In this paper, we will propose an efficient delay-oriented multi-rate/multi-range routing protocol (MR2RP) for MR2WN to maximize the channel utilization as well as to minimize the network transfer delay from source to destination. By analyzing the medium access delay of the IEEE 802.11 medium access control (MAC) protocol, the proposed MR2RP is capable of predicting the transfer delay of a routing path and finding the best one, which has the minimum transfer delay from source to destination. The proposed MR2RP may choose a longer path but with less contention competitors and buffer queuing delay. Simulation results show that MR2RP performs the load balancing and fast routing very well, and its call blocking probability is obviously lower than that of conventional minimum-hops approach with fixed transmission rate.

AMNP: ad hoc multichannel negotiation protocol for multihop mobile wireless networks

Increasing the capacity of wireless communication is an open and interesting research area which has attracted much attention. The familiar solution is dividing the radio spectrum into several independent radio channels, which can be operated and accessed simultaneously by all nodes within its radio transmitting power. All solutions of researches adopt multiple transceivers to fulfil this goal. Nevertheless, these schemes will be short of implementation and may increase the prime cost since most wireless devices only equip one transceiver. Moreover, with a few exceptions, most researchers have emphasized centralized resource allocation algorithms for cellular systems where the base station keeps track of the requirements of the various users and is thus responsible for the management of network resources. However, on the other hand, multihop mobile ad hoc networks (MANETs) are generally configured as peer-to-peer networks with no centralized hubs or controllers. Therefore, in this paper, we proposed a multichannel medium access control (MAC) protocol, named ad hoc multichannel negotiation protocol (AMNP), for multichannel transmission in distribution fashion. We address the issue of distributed resource allocation for multihop MANETs by presenting an AMNP that builds on the multichannel request-to-send/clear-to-send (MRTS/MCTS) bandwidth reservation mechanism under the constraint of single transceiver. We show via simulations that AMNP provides a higher throughput compared to its single channel counterpart by promoting simultaneous transmissions in different channels. Simulation results also show that the performance of proposed AMNP derives well than other multichannel approaches with multiple transceivers.

Modeling and Analysis of an Extended Access Barring Algorithm for Machine-Type Communications in LTE-A Networks

Simultaneous channel accesses from mass machine-type communications (MTC) devices may congest the random-access channels (RACHs) of LTE-A networks. Currently, 3GPP selects extended access barring (EAB) mechanism as the baseline solution to relieve the congestion of RACHs by barring low-priority devices. Different settings of EAB parameters may re-shape the arrival process of MTC traffic and thus, lead to unpredictable performance. This paper presents an analytical model to investigate the performance of the EAB algorithm on the RACHs in LTE-A networks. Computer simulations were conducted to verify the accuracy of the analysis. The optimal values of paging cycle and repetition period of system information block type 14 (SIB14) can then be obtained from the analytical model subject to a target quality-of-service (QoS) constraint.

The impact of RTS threshold on IEEE 802.11 MAC protocol

Wireless technologies and applications received great attention in recent years. The medium access control (MAC) protocol is the main element that determines the efficiency in sharing the limited communication bandwidth of the wireless channel in wireless local area networks (WLANs). The request-to-send/clear-to-send (RTSICTS) mechanism is an optional handshaking procedure used by the IEEE 802.11 wireless network to reduce the possibility of collision. The RTS-Threshold (RT) value which determines when the RTS/CTS handshaking mechanism should be used is an important parameter to investigate; since different RT values will produce different performance characteristics in data transmission. This paper presents an analysis of the influence of the RT parameter on the IEEE 802.11 wireless network, and gives a guideline to dynamically adjust the RT value. Simulation results of this paper show that the RTSICTS mechanism should be always turned on (RT = 0) to achieve an excellent performance while saving complex work designing a dynamic RT mechanism which will not have notable effect.

An improved data flushing MAC protocol for IEEE 802.11 wireless ad hoc network

We propose a data flushing data transfer (DFDT) protocol. The distributed coordinate function (DCF) of IEEE 802.11 supports data transmissions using the data-ACK method and the request-to-send/clear-to-send (RTS/CTS) method. The data-ACK method has a low protocol overhead, however, the transmissions are prone to collision. Although the RTS/CTS mechanism reduces the probability of collisions of data packets, the handshaking generates extensive overhead. Another issue with the IEEE 802.11 DCF is the contention for channel access; much bandwidth is wasted with the contention, especially when the mean data length is short. DFDT is capable of sending out multiple data packets from the upper layer, after acquiring channel access by a successful contention, within one frame which we call compiled MPDU (cMPDU). Right after the transmission of the data frame, the destination nodes will reply an positive/negative acknowledgement in a consecutive manner. By using this method, the protocol overhead is relatively lowered while retaining service quality and the waste of bandwidth for contention is also reduced. Simulation results show that DFDT can handle higher traffic load and has better throughput then the IEEE 802.11 MAC protocol.

Pre-Coordination Mechanism for Fast Handover in WiMAX Networks

The most challenging research issue of investigating broadband wireless access (BWA) technologies is how to support mobility in WiMAX networks smoothly and seamlessly. It is essential that providing continuous services of multimedia streaming data when a mobile subscriber station (MSS) is across a boundary of a serving area to another one. Although the IEEE 802.16e standard is proposed to tackle this difficult problem, the disruption time (DT) of handover is still too long to overcome the maximum delay time of real-time services. To deal with this problem, this paper proposes a pre-coordination mechanism (PCM) for supporting fast handover in WiMAX networks. This goal is achieved by measuring the distance between the BS and the MSS and predicting the time of handover occurs, and thus pre-allocating available resources for handover usages. Simulation results show that the enhanced DT of handover can achieve approximately to 11 milliseconds. The proposed mechanism is fully compatible with the IEEE 802.16e standard.