WLAN Bandwidth Research Articles

WLAN Bandwidth-Based Handoff from WLAN to Cellular Network Assisted by Ad hoc Relaying

Loosely coupled interworking WLAN/cellular system has attracted a lot of attention recently, since the WLAN bandwidth is not restricted by the cellular network. In this kind of systems, a handoff from the WLAN to the cellular network is considered as a new call and therefore incurs a significant delay. Hence, the mobile station (MS) has to accomplish the handoff ahead of losing the WLAN coverage. In many cases the MS enters a region with a low bit rate before completing the handoff. This paper tries to aid the handoff by allocating the requested WLAN bandwidth to maintain the MS link with the serving access point as much as possible. In the case of WLAN bandwidth shortage, the handoff is assisted by using MS’s as ad hoc relay stations (RS’s) to extend the WLAN coverage. In a low-density WLAN, usually the handoff is accomplished by the aid of WLAN bandwidth. In contrast, in a high-density WLAN, the chance of finding a proper RS is high while the amount of available WLAN bandwidth is low. As a result, generally the handoff is accomplished by the assistance of potential RS’s. Both analytical and simulation results are provided to validate the effectiveness of the proposed method in terms of decreasing the call dropping probability.

WLAN bandwidth support for relay-based upward handover in WLAN/cellular systems

Handover from WLAN to a cellular network in loosely coupled WLAN/Cellular systems is considered as a new call and therefore is not given any priority in the cellular network. Hence, it induces a remarkable delay that makes loosely coupled WLAN/Cellular systems inappropriate for online services. Due to this fact, during a handover from a WLAN to a cellular network, a mobile station (MS) may be trapped in a low bit rate region before completing the handover. This paper suggests using relay stations (RS's) during a handover to extend WLAN coverage until the handover is completed. When RS’s are not available, especially in sparse hotspots, allocating a large amount of the WLAN bandwidth to the MS can assist the handover process. In contrast, in a dense hotspot, the probability of finding an appropriate RS is high. Thus, the handover could be completed by using the potential RS's inside the WLAN coverage. It is confirmed, by analytical modeling and simulation, that the proposed method can reduce the call dropping probability and improve the handover performance.

Channel width selection scheme for better utilisation of WLAN bandwidth

The channel access method, defined in the IEEE 802.11ac draft, forces stations (STAs) to transmit data over the widest currently available channel supported by the basic service set (BSS). Unfortunately, the transmission in a wide channel is very inefficient if data frames are short. A channel width selection scheme (CWSS) is proposed which reduces the bandwidth used by the STA, if the transmitted data frame is not sufficiently long. Simulation results show that the CWSS allows a better bandwidth utilisation in an environment of overlapping 802.11ac BSSs. The CWSS is compatible with the channel access procedure defined in the IEEE 802.11ac.

이중 대역 주파수 가변 1/8차 소형 기판집적형 도파관 안테나

새로운 주파수 가변 이중 대역 안테나를 제안한다. 기존의 기판집적형 도파관(SIW: Substrate-Integrated Waveguide)에 비하여 1/8 크기를 갖는, 전기적으로 작은 1/8차 기판집적형 도파관(EMSIW: Eighth-Mode Substrate-Integrated Waveguide) 공진기 구조를 이용하여 전기적으로 작은 크기의 안테나를 설계하였다. 설계한 EMSIW 안테나 표면에 상보적 분할 링 공진기(CSRR: Complementary Split Ring Resonator) 구조를 추가적으로 탑재하여 이중 대역에서 동작할 수 있게 하였다. EMSIW와 CSRR 구조는 각각 1.575 GHz(GPS), 2.4 GHz 대역(WLAN) 주파수 대역을 만족시킬 수 있어 이중 공진 특성을 만족하였다. 기본적으로 CSRR은 대역폭이 좁기 때문에 Varactor 다이오드를 탑재시켜 주파수를 2.4 GHz에서 2.5 GHz까지 연속적으로 가변할 수 있게 하였다. 그에 따라 WLAN 표준에서 사용하고 있는 채널 선택 기능 또한 구현할 수 있다. Varactor 다이오드에 따라 EMSIW의 공진은 독립적으로 고정되어 GPS 주파수 수신을 안정적으로 유지할 수 있도록 설계하였다. 결과적으로 DC 바이어스 전압을 11.4 V에서 30 V로 변경함에 따라 GPS 대역 주파수는 고정되어 있고, WLAN 대역의 공진 주파수가 2.38 GHz에서 2.5 GHz까지 연속적으로 변화한다. 시뮬레이션, 측정값 사이에 반사 손실, 방사 패턴 특성이 잘 일치함을 관찰할 수 있었다. In this paper, we propose a new frequency reconfigurable dual-band antenna. By using an electronically compact eighth-mode substrate-integrated-waveguide(EMSIW) resonator, we have designed a compact antenna, which performs dual-band movement by additionally loading a complementary split ring resonator(CSRR) structure. The EMSIW and CSRR structures are designed to satisfy the bandwidths of 1.575 GHz(GPS) and 2.4 GHz(WLAN), respectively. We load the CSRR with a varactor diode to allow a narrow bandwidth and to enable the resonance frequency to continuously vary from 2.4 GHz to 2.5 GHz. Thus, we realize a channel selection function that is used in the WLAN standards. Irrespective of how a varactor diode moves, the EMSIW independently resonates so that the antenna maintains a fixed frequency of the GPS bandwidth even at different voltages. Consequently, as the DC bias voltage changes from 11.4 V to 30 V, the resonance frequency of the WLAN bandwidth continuously changes between 2.38 GHz and 2.5 GHz, when the DC bias voltage changes from 11.4 V to 30 V. We observe that the simulated and the measured S-parameter values and radiation patterns are in good agreement with each other.

On the support of voice call continuity across UMTS and wireless LANs

AbstractIn this paper, we address the architecture and the procedures that can enable voice call handover from UMTS to WLAN and we also study how efficiently the WLAN can support the voice calls transferred from UMTS. Our study is based on a practical simulation model that lets us quantify the maximum number of voice calls that can be handed over from UMTS to WLAN, subject to maintaining the same level of UMTS QoS and respecting some WLAN policies. In addition, several other voice call performance metrics are derived. Our results indicate that an IEEE 802.11e access point can support a limited number of voice calls handed over from UMTS, which depends primarily on the applied WLAN bandwidth sharing policy (i.e., how the bandwidth is shared between WLAN voice and data users) and the QoS requirements. The performance of the WLAN scheduling algorithm is also of paramount importance and in our study we consider the so‐called ARROW scheduler. Although the simulation results are derived for a specific bandwidth sharing policy, they can readily be scaled and provide practical upper bounds for the number of UMTS voice calls that can be seamlessly admitted to a WLAN access point. Copyright © 2007 John Wiley & Sons, Ltd.

A broadband very‐high‐permittivity dielectric resonator antenna for WLAN application in the 5.2 GHz band

AbstractA novel broadband design of square‐disk dielectric resonator (DR) antennas with a very high relative permittivity of 90.5 is presented. Broadband operation is achieved by loading two narrow conducting strips of suitable lengths, which results in dual‐resonance excitation and leads to a wider operating bandwidth. A constructed prototype designed in the 5.2 GHz band (5150–5350 MHz) for WLAN application, having a cross section of 10×10 mm2 and a height of 1.9 mm only, shows an impedance bandwidth of 250 MHz covering the required WLAN bandwidth. Good broadside radiation characteristics with a peak antenna gain of about 4.1 dBi have also been obtained. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 32: 426–427, 2002.