Hung-Huan Liu

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.

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.

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.

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.

The study of performance enhancement for integrated voice/data wireless networks by link adaptation

Link adaptation (LA) allows the selection of proper coding/modulation scheme in order to cope with the radio channel quality variation. The efficiency of LA is generally demonstrated with the link level performance in terms of spectral efficiency (b/s/Hz/Sector) from the transmitter-to-receiver pairs aspect. Few studies exist in literature that considers LA when the performance of a wireless network was assessed by means of a teletraffic analysis. In this paper, we estimate the data performance enhancement of having LA in an integrated voice/data wireless system from a cells point of view. The analytical system is GSM/GPRS where data service supports four coding schemes; the link level performance is simulated using the Rudimentary Network Emulator (RUNE) and the system level performance is obtained through queueing analysis. Analytical results show that both the data throughput and delay are improved. In our study, the percentage of four coding schemes used, from CS-1 to CS-4, are 5, 8, 29, and 58%, and the packet throughput shows an increase of 28.6% higher and the packet delay shows decrease of 26% less than those in a fixed CS-2 coding system.

Radio Resource Allocation in GSM/GPRS Networks

GPRS is a packet switched access mode for GSM system to improve wireless access to the Internet. In this paper, we study the design of radio resource allocation for GPRS and GSM services by allowing guard channels to be temporarily allocated to GPRS users to increase channel utilization. The call admission controller and channel allocation controller are employed to achieve good channel utilization and preserve the QoS of GSM services. Simulation results show that at low voice traffic load, there is no need to apply admission control to GPRS connections. While at high voice traffic load, applying call admission control to GPRS connections can guarantee the performance of voice service, but result in high GPRS connection blocking and low channel utilization. Furthermore, the QoS of voice service not being affected by the introduction of GPRS can be obtained by allowing voice arrivals to preempt the ongoing GPRS connections.

A multi-hop implicit routing protocol for sensor networks

The broadcast communication paradigm is in prevalent use to facilitate data acquisition in wireless sensor networks (WSNs). However, broadcasting simply by flooding results in serious redundancy. This paper proposes a location-information-free and flooding-like routing protocol for WSNs, called throw and drowned (T&D) flooding protocol. This protocol is a multi-hop implicit routing protocol. Packets are propagated without knowing the network topologies and without establishing prior routes. In addition, T&D is an energy saving protocol. It uses link-layer-relaying instead of network-layer-forwarding to propagate packets to the sink, which saves energy costs on next-hop selection and route establishment. It is also capable of switching the sensor node into sleep mode for the purpose of power saving. T&D is designed for applications with dynamic topology changes and scalable WSNs and can be used instead of pure flooding in existing WSNs. The performance of the proposed protocol is simulated and compared with the pure flooding and gossiping protocols, the well-known implicit routing protocols used in WSNs.

Performance evaluation for integrated voice/data wireless networks with link adaptation

Link adaptation (LA) allows the selection of a proper coding/modulation scheme based on the channel conditions in order to cope with the radio channel quality during the connection period of a call. The effectiveness of LA is generally demonstrated in terms of spectral efficiency (b/s/Hz/sector) at the link level. In this paper, the performance of integrated voice/data service is analyzed from the system point of view. Numerical results show that the improvement in data throughput is about 128%, and that in the mean data delay is about 26% if LA is used for data service. The system level performance is obtained through queueing analysis while the link level performance is simulated using RUNE.