Xuelian Cai

Performance analysis of IEEE 802.11 WLAN to support voice services

This paper studies the performance of the IEEE 802.11 standard MAC protocol for integrated data and voice transmission with the DCF (distributed coordination function) and the PCF (point coordination function). By simulation, we evaluate the network performance for various protocol parameters, especially, the delay jitter for voice traffic. The main factor to influence delay jitter is given. Numerical results show that it is important to choose appropriate parameters and compromise the number of voice stations and the data traffic throughput to get the enhanced performance of IEEE 802.11. The performance of protocol in theory is derived and is verified by the simulation results.

Cross-layer design of AODV-based routing in ad hoc networks with MIMO links

Multiple input multiple output (MIMO) transceivers can potentially increase overall network throughput via spatial reuse of spectrum by allowing multiple simultaneous communications. Efficient use of MIMO technique in wireless ad hoc networks still meets challenges especially for upper layer protocols. In this paper we propose a cross-layer strategy of allowing the data stream and routing control stream transmitting concurrently with different antennas of the MIMO system. Implementing on the ad hoc on-demand distance vector (AODV) protocol, simulation results show that the strategy of queuing different type of packets obviously decreases the duration of route establishment, especially when the network is suffering heavy traffic load.

A novel self-adaptive transmission scheme over an IEEE 802.11 WLAN for supporting multi-service

The IEEE 802.11 wireless local area network (WLAN) media access control (MAC) specification is a hybrid protocol of random access and polling when both distributed coordination function (DCF) and point coordination function (PCF) are used. Data traffic is transmitted with the DCF, while voice transmission is carried out with the PCF. Based on the performance analysis of the MAC protocol for integrated data and voice transmission by simulation, this paper puts forward a self-adaptive transmission scheme to support multi-service over the IEEE 802.11 WLAN. The simulation results show that, on the premise of satisfying the maximum allowable delay of packet voice, the self-adaptive transmission scheme can improve the data traffic performance and increase the WLAN capacity through dynamic and appropriate adjustment of the protocol parameters. Especially, voice traffic is sensitive to delay jitter, and the self-adaptive scheme can effectively decrease it. Finally, it is worth noting that the adaptive scheme is easy to be realized, whereas no change in the MAC protocol is needed. Copyright

Performance evaluation of IEEE 802.11 WLAN - high speed packet wireless data network for supporting voice service

The IEEE 802.11 standard MAC is a hybrid protocol of random access and polling when both DCF (distributed coordination function) and PCF (point coordination function) are used. This paper evaluates the performance of the MAC protocol for integrated data and voice transmission with the two access mechanisms. By simulation, we evaluate the network performance for various values of the protocol parameters. Especially, voice traffic is sensitive to delay jitter and here we point out the main factors to influence it. Numerical results show that it is important to choose appropriate parameters and we should compromise the number of the voice stations and the data traffic throughput to get the enhanced performance of IEEE 802.11. Finally, the performance of protocol in theory is derived and is verified by the simulation results.

A study of self-adaptive transmission for integrated voice and data services over an IEEE 802.11 WLAN

The IEEE 802.11 standard MAC is a hybrid protocol of random access and polling when both DCF (distributed coordination function) and PCF (point coordination function) are used. On the base of the performance analysis of the MAC protocol for integrated data and voice transmission by simulation, this paper puts forward a self-adaptive transmission scheme to support multi-service over the IEEE 802.11 WLAN. The simulation results show that, on the premise of satisfying the maximum allowable delay of packet voice, the self-adaptive transmission scheme can improve the data traffic performance and increase the WLAN capacity through dynamic and appropriate adjustment of the protocol parameters. Especially, the scheme is easy to be realized for no change in the MAC protocol is needed.

A novel internal collision managing mechanism of IEEE 802.11e EDCA

The internal collision managing mechanism in Enhanced Distributed Channel Access (EDCA) makes it more difficult to successfully access the channel for the data with low priority. To address this issue, a novel Mechanism to solve the Internal Collision problem (MIC) is proposed to improve the performance of EDCA. The main concept of MIC is to decrease the backoff time of the Access categories (ACs) with low priority. In this way, MIC can improve the performance of the low priorities without compromising that of the high priorities. A Markov chain model is used to analyze the performance of MIC under saturated conditions. The correctness of the analysis results are verified by simulating MIC with NS-2. Both the analysis results and simulation results confirm that MIC outperforms EDCA in terms of the average access delay.

On Resource Management in Vehicular Ad Hoc Networks: A Fuzzy Optimization Scheme

Resource management is a crucial task in vehicular ad hoc networks (VANETs) due to the existence of various resources, such as text, audio and video. However, the highly dynamic network feature and the limited memory of the local server pose challenges to resource management, which not only lead to the failure of resource presentations to users, but the transmission of the invalid fragment data would also result in the significant waste of precious bandwidth and memory. To address the issue, our paper proposes a Fuzzy Logic based Resource Management scheme (FLRM) under fog computing platform in VANETs. In the scheme, we first gather and record the request time and download time for each resource by the designed Vehicle to Infrastructure (V2I) communication mode. Depending on the above information, we define a survival time for each stored resource by the proposed fuzzy logic based popularity evaluation algorithm. Motivated by the defined survival time, the local server can update the resource list in real time. In the end, we conduct simulations to verify the performance of FLRM. Results demonstrate that the proposed scheme performs well in terms of throughput, which increases the user experience with fresh resources.

Performance evaluation of access delay of efficient media access schemes for WLAN with smart antenna

The use of smart antennas in extending coverage range and capacity of wireless LANs dictates the employment of novel media access control (MAC) schemes, with which the access point (AP) provides access to users by learning their spatial signatures. This paper puts forward an exact approach to analyze the performance of the schemes in terms of required time so that the AP becomes aware of user locations and grants access to the system. The numerical results show that the scheme which distinguishes the users residing in or out of broadcasting coverage range of the AP can provide rapider media access. In addition, the simulation results verify the theoretical approach.

A FLRBF scheme for optimization of forwarding broadcast packets in vehicular ad hoc networks

Due to the highly dynamic network feature, Vehicular Ad Hoc Networks (VANETs) suffer from the frequent link breakage and low packet delivery rate, which pose challenges to design routing protocols. To address this issue, we propose a Fuzzy Logic Routing Based on Forwarding (FLRBF) optimization scheme depending on receiving nodes for optimizing forwarding broadcast packets. We first calculate and record the distance factor and time delay from one source node to the destination node. Via the above information, we define a forwarding probability value for each node by the proposed fuzzy logic system based on high priority routing algorithm. Motivated by the defined forwarding probability values, nodes set timers and forward packets to achieve balancing broadcast efficiency, network throughput and average end-to-end delay. In the end, we conduct simulations to verify the performance of FLRBF. Results demonstrate that the proposed protocol performs well in terms of packet delivery ratio, end-to-end delay and overhead.

Performance of Vector Perturbation MU-MIMO Systems in a Composite Fading Channel

In this paper, we analyze the performance of vector perturbation (VP) precoded multiuser multiple-input multiple-output (MU-MIMO) systems in a composite fading channel including not only small-scale Rayleigh fading but also large-scale fading for getting useful conclusion in a more realistic scenario. Through the derivation of average power of sphere-encoded vectors, we obtained the closed-form expression of the sum rate tight lower bound of VP precoded MU-MIMO systems, which is a function of the number of transmit/receive antennas, transmit power and large-scale fading parameters. From the analytical expression of sum rate and error probability bounds, it is concluded that the performance of VP precoded MU-MIMO systems deteriorates severely when intended users experience very different large-scale fadings. Simulation results validate our analysis.