Jean-Lien C. Wu

An adaptive multirate IEEE 802.11 wireless LAN

In order to enhance the system capacity of wireless LANs, we propose in this paper using the frame-based adaptive multirate transmission scheme in the IEEE 802.11 and evaluate its performance. Typically, high-speed modulation schemes would require higher SNR to maintain the transmission quality and BER. The transmission rate is selected dynamically based on the detected SNR, each frame shall be transmitted at the highest available rate. The original virtual carrier sense mechanism in IEEE 802.11 is no longer suitable because the multirate hidden terminal problem. We redefine the MAC header and modify the reservation scheme of the network allocation vector (NAV) to resolve these problems. The throughput and delay are evaluated using simulations and the results show that they can be significantly improved compared with those of the single-rate WLAN.

Performance comparisons of dynamic resource allocation with/without channel de-allocationin GSM/GPRS networks

In this letter, we analyzed and compared the performance of dynamic resource allocation with/without channel de-allocation in GSM/GPRS networks. It is quite known that dynamic resource allocation allows communication systems to utilize their resources more efficiently than the traditional fixed allocation schemes. In GPRS, multiple channels may be allocated to a user to increase the transmission rate. In the case when there are no free channels in the system, some of these channels may be de-allocated to serve higher priority calls. The results show that with channel de-allocation mechanism, the voice blocking probability can be greatly reduced, especially at high GPRS traffic load. Besides, the scheme with channel de-allocation mechanism can achieve higher channel utilization.

Delay analysis of integrated voice and data service for GPRS

The quality-of-service (QoS) requirements of typical mobile packet data applications are very diverse. QoS profiles of the General Packet Radio Service (GPRS) are defined using the parameters service precedence, reliability, delay, and throughput. A one-dimensional decomposing Markov chain is used as the queueing model to analyze the GPRS performance in terms of the mean delay and 95% delay. In addition, the impact of buffer assignment and guard channels on the GPRS traffic is also investigated. The analytical results are verified by simulation and the comparison shows that they are very close.

Packet telephony support for the IEEE 802.11 wireless LAN

Packet telephony is one of the most promising applications in the Internet. In this paper, we propose a modified MAC protocol supporting voice traffic over the IEEE 802.11 WLAN. The proposed scheme adapts the power-saved mode of the IEEE 802.11 specifications in such a way that it approaches the TDM access mode carrying voice traffic, and is compatible with the IEEE 802.11 standard. Simulation results show that the proposed scheme does not degrade the performance of the IEEE 802.11 WLAN using the DCF and also provides good voice quality.

Performance analysis of radio resource allocation in GSM/GPRS networks

General packet radio service (GPRS) is a packet switched access mode for GSM system to efficiently utilize the radio resources. In this paper, we analyzed the performance of radio resource allocation in GSM/GPRS networks. To guarantee the QoS of voice service not being affected by the introduction of GPRS, preemptive priority is applied for voice calls to preempt GPRS data packets. Three cases of radio resource allocation are considered: no-buffer; buffer-only-for-preempted-GPRS-packets; and buffer-for-GPRS-packets. The results show that employing a buffer for GPRS packets can greatly reduce its blocking probability even under the condition of voice preemption. For real-time data applications, the mechanism of buffer-only-for-preempted-GPRS-packets is suitable since the queueing delay is relatively small.

Survivable and delay-guaranteed backbone wireless mesh network design

Backbone wireless mesh networks (BWMNs) consisting of wireless mesh routers are emerging alternatives to implementations of metropolitan area networks (MANs). In a BWMN, gateways connect to the Internet via wireline links and provide Internet access services for users. Due to the limited wireless channel bit rate, multiple gateways are usually required in a BWMN, which costs budget and takes time to set up. In this paper, we study the network topology design and the gateway arrangement so that the construction cost of a BWMN is minimal. Two algorithms, namely, the Predefined Gateway Set Algorithm (PGSA) and the Self-Constituted Gateway Algorithm (SCGA), are proposed for the BWMN design. A genetic algorithm and a proposed enhanced Djikstras algorithm are employed to search for the low-cost network configuration with constraints such as survivability, link capacity, degree limitation and maximum tolerable delay. Computational results show that the PGSA can give an acceptable network configuration rapidly. In case the gateway cost is high, using the SCGA can lower the network construction cost at the expense of more computational time.

Handoff prediction by mobility characteristics in wireless broadband networks

The paper proposes mobility-aided resource reservation (MARR) with admission control (AC) to provide better usage of scarce resources in wireless broadband networks. The area of a cell is divided into an outer ring and an inner ring. A target cell is predicted by extrapolating the trajectory of each MS. In order to reduce signaling overhead, bandwidth is reserved only in the target cell as MSs move into the outer ring and leave the serving base station (BS). The amount of bandwidth to be reserved is dynamically adjusted according to the instantaneous variation of mobility ratio, location, and direction of an MS. Two scenarios of the MARR scheme are investigated by OPNET simulation and compared by considering the mobility ratio threshold in the calculation of the direction weighting. Simulation results show that employing the MARR scheme can indeed reduce connection dropping probability, and make better bandwidth utilization when appropriate parameters are chosen.

A cluster-based algorithm for redundant nodes discovery in dense sensor networks

In dense sensor networks, there are a large number of low-power, short-lived, low-cost and unreliable sensors. A major challenge in constructing dense sensor networks is to prolong network lifetime as well as to keep sensing coverage loss ratio low. To prolong network lifetime, it is necessary to turn off redundant nodes to save energy. Moreover, obtaining low sensing coverage loss ratio is an important issue in dense sensor networks. We propose a cluster-based algorithm that can present a flexible, adjustable and energy-efficient scheme to identify redundant nodes for different requirements of network lifetime and low sensing coverage loss ratio. This algorithm needs additional GPS and directional antennas support to identify redundant nodes. Our simulation results show that the cluster-based algorithm could save energy consumption in the process of determining redundant nodes for prolonging network lifetime and could achieve low sensing coverage loss ratio.

Mobility-aided adaptive resource reservation schemes in wireless multimedia networks

This paper proposes the mobility-aided adaptive resource reservation (MARR) with admission control (AC) to provide better usage of scarce resource in wireless multimedia networks. The area of a cell is divided into: the reservation zone and the non-reservation zone. A target cell is predicted by extrapolating the trajectory of mobile stations (MSs). In order to reduce signaling overhead, bandwidth is reserved only in the target cell as MSs move into the reservation zone and leave the serving base station (BS). The amount of bandwidth to be reserved is dynamically adjusted according to the instantaneous variation of mobility ratio, location, and direction of MSs. Two scenarios of the MARR scheme are investigated by OPNET simulation and compared by considering the mobility ratio threshold in the calculation of the direction weighting. The simulation results show that employing the MARR scheme can indeed reduce connection dropping and blocking probability, and make better bandwidth utilization when appropriate parameters are chosen.

Finding stable routes in mobile ad hoc networks

A mobile ad hoc network (MANET) is an infrastructureless and highly dynamic network. Routes in such a network may fail frequently because of node mobility or other issues. Stability therefore can be an important element in the design of routing protocols. Stable routes, also called long-lived routes, can be discovered and used to reduce the overhead resulted from route maintenance in ad hoc networks. We propose the long-lived route prediction (LRP) scheme to discover stable routes. The LRP scheme is distributed and predicts long-lived routes based on the history of link lifetime. Furthermore, we apply the LRP scheme to both the open area and urban area using simulation. Simulation results show that the LRP scheme can indeed discover stable routes to reduce route rediscovery, and can be much more efficient and scalable.