Wireless Local Area Network Cell Research Articles

A novel model for minimizing unnecessary handover in heterogeneous networks

Over the years, vertical handover necessity estimation has attracted the interest of numerous researchers. Despite the attractive benefits of integrating different wireless platforms, mobile users are confronted with the issue of detrimental handover. This paper uses extensive geometric and probabilistic techniques to develop a realistic and novel model for the coverage area of a wireless local area network (WLAN) cell with an aim to minimize unnecessary handover and handover failure of a mobile node (MN) traversing the WLAN cell from a third-generation network. The dwell time is estimated along with the threshold values to ensure an optimal handover decision by the MN, while the probability of unnecessary handover and probability of handover failure are kept within tolerable bounds. Monte Carlo simulations were carried out to assess the behavior of the proposed and existing models. Simulation results showed that our proposed model is more robust and capable of keeping unnecessary handover probability and handover failure probability closest to a predefined probability benchmark. For model validation, the Nash--Sutcliffe coefficient was used to compute the efficiency of the proposed model, which achieved a value of 98.82{\%} indicating the accuracy of the model.\vs{2mm

New Vertical Handover Method to Optimize Utilization of Wireless Local Area Network in High-Speed Environment.

In heterogeneous wireless networks, wireless local area network (WLAN) is highly preferred by mobile terminals (MTs) owing to its high transmission bandwidth and low access cost. However, in high-speed environment, handover from a cellular network to a WLAN cell will lead to a high number of handover failures and unnecessary handovers due to the WLAN coverage limitation and will become worse at high speed. A new vertical handover method is proposed to minimize the probability of handover failure and unnecessary handover while maximizing the usage of WLAN in high-speed environment. The simulation results show that the proposed method kept the probability of handover failure and unnecessary handover below 0.5% and 1%, respectively. Compared with previous studies, the proposed method reduced the number of handover failures and unnecessary handovers up to 80.0% and 97.7%, respectively, while the MT is highly mobile. Using the proposed prediction method, the MT can benefit high bandwidth and low network access cost from the WLAN with minimum interruption regardless of speed.

The Study of WLAN Cell Radius for Outdoor Coverage in Wireless Digital City Deployment

Firstly, the technical features and frequency characteristics of IEEE802.11x protocol in wireless local area network (WLAN) are introduced. The functional relationship of path loss and coverage distance in dense urban and suburb is shown in figures. The uplink and downlink radio power budget of current WLAN outdoor coverage is calculated. Secondly, calculation and comparison of WLAN pass loss, link budget and cell coverage radius is done for dense urban and suburb. Thirdly, hot spot area WLAN outdoor coverage signal strength is simulated in dense urban for several situations by using simulation software. The results of simulation validate the accuracy of the calculation for uplink/downlink power budget, path loss in WLAN 2.4GHz band and WLAN cell coverage radius. The cell coverage radius for dense urban and suburb is 300∼500m and 1000∼1200m respectively. Finally, a valuable hot spot area WLAN outdoor coverage deployment suggestion is given: high power WLAN BTS/AP and high gain antenna with 4 sectors deployment will improve the uplink/downlink power budget; enlarge radio coverage in hot spot area. The analysis in this paper is significant for the deployment of wireless digital city.

A Traveling Distance Prediction Based Method to Minimize Unnecessary Handovers from Cellular Networks to WLANs

We propose a handover decision method based on the prediction of traveling distance within an IEEE 802.11 wireless local area network (WLAN) cell. The method uses two thresholds which are calculated by the mobile terminal (MT) as it enters the WLAN cell. The predicted traveling distance is compared against these thresholds to make a handover decision in order to minimize the probability of handover failures or unnecessary handovers from a cellular network to a WLAN. Our analysis shows that the proposed method successfully keeps the number of failed or unnecessary handovers low.

Directional distributed co-ordination function – a medium access control protocol to simultaneously support both omni-directional and smart antennas in a same WLAN cell

Directional distributed co-ordination function (D-DCF), a modified medium access control protocol of IEEE 802.11, is proposed to support hybrid antennas such as smart adaptive array antennas and normal omni-directional antennas, in one wireless local area network cell. Nodes equipped with smart antennas follow D-DCF and nodes equipped with normal antennas follow DCF. D-DCF based on a hybrid virtual carrier sense mechanism maintains compatibility with DCF. In D-DCF, before sending any data-frames, the sender and receiver node transmit a pilot sequence by means of an omni-directional request-to-send/clear-to-send handshake mechanism. Based on the pilot, the directional beam can be formed by the smart antenna. Then the node can transmit its data-frame in the directional mode. The other nodes save the transmission time between the sender and receiver in the omni-directional mode in their network allocation vectors. When the sender and receiver communicate in the directional mode, the other nodes can access the channel to send their data-frames. Hence, D-DCF supports space division multiplexing. Moreover, D-DCF fully supports time division duplex, namely both the forward and backward transmission in one access period. Simulation results show that D-DCF can support the hybrid antenna system effectively and provide much higher network throughput, lower delay, jitter and packet-loss-rate than DCF does.

Maximizing signal strength for OFDM inside buildings

Propagation inside buildings suffer from large shadowing and high multipath effects. This is a serious problem for wireless local area network (WLAN) systems. This paper shows that shadowing and path loss can be minimized by exploiting the multipath tolerance of orthogonal frequency-division multiplexing (OFDM). This can be achieved by using multiple transmission antennas spread over the area of a WLAN cell. These antennas act as repeaters, transmitting and receiving the same signal at the same time. This decreases the average path loss, but increases the multipath delay spread. Using OFDM allows the advantage of reduced path loss to be utilized without detrimental effects of inter-symbol interference caused by the increased delay spread. The reduced path loss allows an increased system capacity, quality of service, or a decrease in intercellular interference in a cellular WLAN.