Wi-Fi Performance Research Articles

Impact of Packet Arrivals on Wi-Fi and Cellular System Sharing Unlicensed Spectrum

We investigate the coexistence performance of Wi-Fi and cellular systems under an unlicensed spectrum sharing environment. For this, we provide a mathematical framework based on queuing theory depicting the time-domain behaviors of a Wi-Fi access point (AP) and a cellular small-cell base station (SCBS) under unlicensed spectrum sharing. Based on the proposed framework, we make an analysis of the delay performance of both systems with respect to the changes in their packet arrival rates. Through the analysis, we identify the maximum allowable packet arrival rates of both systems, under which the required Wi-Fi delay performance is achieved without spectrum etiquette for coexistence at the cellular SCBS, such as carrier-sensing adaptive transmission. This will serve as a guideline for the cellular SCBS on when it needs to employ the spectrum etiquette.

Modeling and Analyzing the Coexistence of Wi-Fi and LTE in Unlicensed Spectrum

We leverage stochastic geometry to characterize key performance metrics for neighboring Wi-Fi and LTE networks in unlicensed spectrum. Our analysis focuses on a single unlicensed frequency band, where the locations for the Wi-Fi access points and LTE eNodeBs are modeled as two independent homogeneous Poisson point processes. Three LTE coexistence mechanisms are investigated: 1) LTE with continuous transmission and no protocol modifications; 2) LTE with discontinuous transmission; and 3) LTE with listen-before-talk and random back-off. For each scenario, we derive the medium access probability, the signal-to-interference-plus-noise ratio coverage probability, the density of successful transmissions (DST), and the rate coverage probability for both Wi-Fi and LTE. Compared with the baseline scenario where one Wi-Fi network coexists with an additional Wi-Fi network, our results show that Wi-Fi performance is severely degraded when LTE transmits continuously. However, LTE is able to improve the DST and rate coverage probability of Wi-Fi while maintaining acceptable data rate performance when it adopts one or more of the following coexistence features: a shorter transmission duty cycle, lower channel access priority, or more sensitive clear channel assessment thresholds.

Novel learning-based spatial reuse optimization in dense WLAN deployments

To satisfy the increasing demand for wireless systems capacity, the industry is dramatically increasing the density of the deployed networks. Like other wireless technologies, Wi-Fi is following this trend, particularly because of its increasing popularity. In parallel, Wi-Fi is being deployed for new use cases that are atypically far from the context of its first introduction as an Ethernet network replacement. In fact, the conventional operation of Wi-Fi networks is not likely to be ready for these super dense environments and new challenging scenarios. For that reason, the high efficiency wireless local area network (HEW) study group (SG) was formed in May 2013 within the IEEE 802.11 working group (WG). The intents are to improve the “real world” Wi-Fi performance especially in dense deployments. In this context, this work proposes a new centralized solution to jointly adapt the transmission power and the physical carrier sensing based on artificial neural networks. The major intent of the proposed solution is to resolve the fairness issues while enhancing the spatial reuse in dense Wi-Fi environments. This work is the first to use artificial neural networks to improve spatial reuse in dense WLAN environments. For the evaluation of this proposal, the new designed algorithm is implemented in OPNET modeler. Relevant scenarios are simulated to assess the efficiency of the proposal in terms of addressing starvation issues caused by hidden and exposed node problems. The extensive simulations show that our learning-based solution is able to resolve the hidden and exposed node problems and improve the performance of high-density Wi-Fi deployments in terms of achieved throughput and fairness among contending nodes.

Efficient Coexistence of LTE With WiFi in the Licensed and Unlicensed Spectrum Aggregation

The exploitation of unlicensed bands by the LTE-advanced (LTE-A) system has become a reality through the proposal of licensed assisted access (LAA) that relies on the carrier aggregation concept within the 3GPP framework. The efficient coexistence of LTE-A and WiFi in the unlicensed spectrum bands requires advanced intelligent techniques. This paper first investigates the concept of LAA, which consists of four main functionalities: 1) carrier selection (CS); 2) listen-before-talk; 3) discontinuous transmission (DTX); and 4) transmit power control (TPC). Second, the LAA functionality implementation is provided using an open source LTE-A downlink link level simulator. Third, we devise an enhanced learning technique for CS and DTX for efficient coexistence among LTE-A and WiFi users. In particular, we provide a Q-learning mechanism for the advanced learning of the unlicensed band activity resulting in the efficient coexistence. Finally, we enhance the coexistence further through a double Q-learning method as a proposal for CS that takes into account both DTX and TPC improving both LTE and WiFi performance. Simulation results are provided for all the use cases that reveal the benefit of exploiting unlicensed bands in next generation mobile cellular networks.

Exciting Projects for PHY and MAC Layers of IEEE 802.11 [Standards

The first few widely accepted amendments to IEEE 802.11 wireless networking specifications, namely IEEE 802.11a, IEEE 802.11b, and IEEE 802.11g, featured relatively low spectral efficiencies and data rates. Driven by technological advances in signal processing and communications theory, sustained improvement in spectral efficiency, coverage, and quality of service has been achieved in IEEE 802.11n and IEEE 802.11ac. Particularly, progressive system improvement is achieved by the successive introduction of novel techniques, including orthogonal frequency division multiplexing (OFDM) and multiple-input, multiple-output (MIMO) antenna techniques. Some advanced transmission techniques, especially multiuser (MU)-MIMO and transmit beamforming, have also helped to boost the performance of Wi-Fi to gigabit-persecond speed, and they have led to the current state of the art, namely IEEE 802.11ac in 2.4- and 5-GHz bands, and IEEE 802.11ad in the 60-GHz frequency band.

Licensed-Assisted Access LTE: coexistence with IEEE 802.11 and the evolution toward 5G

LAA is a new operation mode of LTE in the unlicensed spectrum, which will be featured in LTE Release 13. Under LAA, licensed carriers will be aggregated with unlicensed carriers in order to opportunistically enhance downlink user throughput while still offering seamless mobility support. In order to coexist with WiFi, some of the new functionalities required of LAA LTE include a mechanism for channel sensing based on listen-before-talk, discontinuous transmission on a carrier with limited maximum transmission duration, and multicarrier transmission across multiple unlicensed channels. This article presents a detailed overview of the design agreements for LAA, the impact of unlicensed spectrum operation on the LTE physical layer architecture, and the scope of additional enhancements beyond LTE Release 13. A range of simulations for indoor and multicarrier scenarios show that fair coexistence between LAA and WiFi can be achieved, and that deployment of LAA can provide a boost in WiFi performance.

Coexistence of Wi-Fi and Cellular With Listen-Before-Talk in Unlicensed Spectrum

In this letter, we analyze the coexistence performance of Wi-Fi and cellular networks with different listen-before-talk (LBT) procedures in the unlicensed spectrum. For this analysis, the behavior of a cellular base station is modeled as a Markov chain that is combined with Bianchi's Markov model depicting the behavior of a Wi-Fi access point. The proposed mathematical framework finds the optimal contention window size of cellular base stations, which maximizes the total throughput of both networks while satisfying the required throughput of each network. Numerical results show the validity of adjustment in the parameter of LBT.

Compensating for Orientation Mismatch in Robust Wi-Fi Localization Using Histogram Equalization

The performance of Wi-Fi positioning systems degrades severely when the user orientation differs between locating and training phases. This paper proposes a novel approach based on histogram equalization (HEQ) to compensate for an orientation mismatch in robust Wi-Fi localization. The proposed method involves converting the temporal–spatial radio signal strength into a reference function (i.e., equalizing the histogram). By using equalized signals, the proposed algorithm improves the robustness of location estimation, even in the presence of mismatch orientation. The advantages of the proposed algorithm over traditional methods are that the assumption of user behavior is not required, and a digital compass does not need to be embedded on a mobile device. Experiments conducted in Wi-Fi networks demonstrated the effectiveness of the proposed algorithm. The results show that the proposed algorithm outperforms the orientation classifier method and provides comparable positioning accuracy to the compass-assisted approach.

On the Impact of LTE-U on Wi-Fi Performance

With the exponential growth in mobile data traffic taking place currently and projected into the future, mobile operators need cost effective ways to manage the load of their networks. Traditionally, this has been achieved by offloading mobile traffic onto Wi-Fi networks due to their low cost and increasingly ubiquitous deployment. Recently, LTE operating in the unlicensed spectrum has drawn significant interests from mobile operators due to the availability of the unlicensed spectrum. Using this technology, the unlicensed spectrum is directly utilized by LTE without the need to offload traffic to an alternative radio access technology such as Wi-Fi. However, the deployment of LTE networks in the unlicensed band poses significant challenges to the performance of current and future Wi-Fi networks. We discuss the LTE and Wi-Fi coexistence challenges and present analysis on performance degradation of the Wi-Fi networks at the presence of LTE.

와이파이 수신신호세기를 사용하는 실내위치추정의 성능 향상을 위한 수정된 잔차 기반 확장 칼만 필터

와이파이 수신신호세기를 사용하는 실내위치추정의 성능 향상을 위한 수정된 잔차 기반 확장 칼만 필터

The future of Wi-Fi [Guest Editorial

Driven by the rapidly increasing demand for high data rate services and usage in a spectrum of application areas, wireless systems are compelled to evolve in order to meet the extraordinary performance requirements, especially in terms of spectral efficiency, coverage, latency, and energy efficiency. Regarding wireless local area networks, the first few widely accepted amendments to IEEE 802.11 wireless networking specifications, IEEE 802.11b/a/g, featured low spectral efficiencies, which are becoming insufficient to satisfy explosive traffic growth and the ever increasing consumer connectivity demand. With the soaring cost of the limited bandwidth at the 2.4 GHz frequency band, sustained improvement in spectral efficiency and quality of service has been achieved in IEEE 802.11n, which is mainly driven by advances in communication theory and the use of the 5 GHz frequency band. Specifically, the successive introduction of novel techniques such as multiple-input multiple-output (MIMO) antenna techniques and space-time coding, and the massive improvement in hardware and processing power, have enabled progressive system improvement. The introduction of advanced transmission techniques in recent years, notably multiuser MIMO and transmit beamforming, has provided additional powerful means for boosting the performance of Wi-Fi to gigabit per second speed and leading to the emerging IEEE 802.11ac. This is followed by the future introduction of IEEE 802.11ad products utilizing the 60 GHz frequency band, which are expected to take Wi-Fi speeds to multiple gigabits per second, and IEEE 802.1lax products, which are expected to improve the spectrum efficiency of Wi-Fi, thus enhancing system throughput per area in high-density scenarios of access points and client stations.

Coexistence Wi-Fi MAC Design for Mitigating Interference Caused by Collocated Bluetooth

A non-collaborative coexistence mechanism for wireless-fidelity (Wi-Fi) and bluetooth (BT) systems based on dynamic packet fragmentation is proposed in this work. The basic idea is to adapt the packet length of Wi-Fi in the MAC layer such that the fragmented packet has a better chance to survive the interference from the nearby BT devices. We first develop an analytical model that specifies the information required by the Wi-Fi MAC layer to decide the best fragmentation strategy. Then, this model is extended to analyze the throughput and transmission delay of the Wi-Fi device. The analytical model is validated by computer simulation. Furthermore, it is demonstrated by simulation results that the proposed coexistence mechanism improves the performance of Wi-Fi in throughput and transmission delay significantly while relatively smaller performance improvement is observed for BT.

SIRA: SNR-Aware Intra-Frame Rate Adaptation

An intra-frame rate control algorithm (Intra-RCA), called SNR-aware Intra-frame Rate Adaption (SIRA), is proposed to enhance the system performance of WiFi in fast time-varying environments. Widely used inter-frame rate control algorithms (Inter-RCA), which select the physical layer (PHY) rate of each frame based on the time averaged frame loss rate and the signal strength statistics, perform poorly for a long aggregate MAC protocol data unit (A-MPDU) due to the channel variation in mobile environments. Unlike the previous approaches, SIRA adapts the PHY rate on intra-frame basis, i.e., the PHY rate is updated in the middle of a frame according to user mobility. The performance of the proposed scheme is also evaluated by a trace-driven link level simulator employing the collected channel traces from real measurements. The simulation results show that SIRA outperforms the standalone Inter-RCA in all tested traces.

Exploiting programmable architectures for WiFi/ZigBee inter-technology cooperation

The increasing complexity of wireless standards has shown that protocols cannot be designed once for all possible deployments, especially when unpredictable and mutating interference situations are present due to the coexistence of heterogeneous technologies. As such, flexibility and (re)programmability of wireless devices is crucial in the emerging scenarios of technology proliferation and unpredictable interference conditions. In this paper, we focus on the possibility to improve coexistence performance of WiFi and ZigBee networks by exploiting novel programmable architectures of wireless devices able to support run-time modifications of medium access operations. Differently from software-defined radio (SDR) platforms, in which every function is programmed from scratch, our programmable architectures are based on a clear decoupling between elementary commands (hard-coded into the devices) and programmable protocol logic (injected into the devices) according to which the commands execution is scheduled. Our contribution is two-fold: first, we designed and implemented a cross-technology time division multiple access (TDMA) scheme devised to provide a global synchronization signal and allocate alternating channel intervals to WiFi and ZigBee programmable nodes; second, we used the OMF control framework to define an interference detection and adaptation strategy that in principle could work in independent and autonomous networks. Experimental results prove the benefits of the envisioned solution.

MCNet: Crowdsourcing wireless performance measurements through the eyes of mobile devices

Measurement of network performance in complex WiFi networks, such as in corporations and universities, is an important but challenging task, as wireless performance in networks with many access points is hard to measure and model. We demonstrate that crowdsourcing the task of measuring WiFi performance is an effective solution to this problem. By measuring performance directly with unmodified consumer mobile devices such as smartphones, it is possible to cheaply and easily detect problems that matter to users. Aggregated performance data across clients can then provide a global view of performance trends in an enterprise network. We demonstrate that periodic sampling allows the collection of representative data while keeping battery consumption low, and we leverage mobile sensor information to intelligently schedule these measurements. This system was deployed in two different large WLANs, where we discovered numerous previously undetected performance problems.

HMM Driven White Space for IEEE 802.11

Wi-Fi has been adopted more and more extensively in various applications such as wireless patient monitoring in hospitals, herds monitoring in pastures, smart control in home networking and game remote controllers. Most of these applications are performancesensitive so the throughput and packet delivery ratio should be guaranteed for Wi-Fi system to work properly. However, since Wi-Fi operates in unlicensed ISM spectrum. White spaces between frame clusters in time domain observed in Wi-Fi its advantage should be taken to improve the performance of the system. In this paper, we propose a novel approach that ensures high performance of Wi-Fi data trace to time keep the Wi-Fi performance almost unaffected. First we learn an HMM (Hidden Markov Model) based on the data traces of the network. With HMM model we can accurately characterize the dynamic distribution of the durations of white spaces in different times. Second, we estimate the data trace of the Wi-Fi in time domain. Thus based on the HMM model of the white space and the performance estimation we develop a novel frame control protocol called HMM-driven White Space for Wi-Fi.

On the Performance of Wi-Fi, Ad Hoc and WiMAX Handovers with MIPv4 versus MIPv6

the most of the available data rates, coverage areas and different networks; wireless communication must be used .Vertical and Horizontal handover were explored in Wi-Fi, WiMAX and Ad-Hoc environments. The vertical handover between Wi-Fi and other wireless technologies could be achieved using Mobile IP and (ABC) CONCEPT. This paper is a comparative study between Mobile IPv4 and Mobile IPv6 to find out which of them performs better when it comes to send datagram from the correspondent node to the mobile node. The tests were carried out to measure delay and throughput metrics and maintain session continuity of mobile node while roaming .The tests were done using OPNET Modeler and NS2 (Network Simulator 2). The results showed that Mobile IPv6 performed better than the other systems in all the tests done. KeywordsMIPv6, Handover, ABC, MANEMO.

서비스 연속성 지원을 위한 WiBro-WiFi 상호연동 아키텍쳐 설계 및 성능 분석에 관한 연구

서비스 연속성 지원을 위한 WiBro-WiFi 상호연동 아키텍쳐 설계 및 성능 분석에 관한 연구

Use of negative information in positioning and tracking algorithms

To avoid additional hardware deployment, indoor localization systems have to be designed in such a way that they rely on existing infrastructure only. Besides the processing of measurements between nodes, localization procedure can include the information of all available environment information. In order to enhance the performance of Wi-Fi based localization systems, the innovative solution presented in this paper considers also the negative information. An indoor tracking method inspired by Kalman filtering is also proposed.

Cooperative Carrier Signaling: Harmonizing Coexisting WPAN and WLAN Devices

The unlicensed ISM spectrum is getting crowded by wireless local area network (WLAN) and wireless personal area network (WPAN) users and devices. Spectrum sharing within the same network of devices can be arbitrated by existing MAC protocols, but the coexistence between WPAN and WLAN (e.g., ZigBee and WiFi) remains a challenging problem. The traditional MAC protocols are ineffective in dealing with the disparate transmit-power levels, asynchronous time-slots, and incompatible PHY layers of such heterogeneous networks. Recent measurement studies have shown moderate-to-high WiFi traffic to severely impair the performance of coexisting ZigBee. We propose a novel mechanism, called cooperative carrier signaling (CCS), that exploits the inherent cooperation among ZigBee nodes to harmonize their coexistence with WiFi WLANs. CCS employs a separate ZigBee node to emit a carrier signal (busy tone) concurrently with the desired ZigBee's data transmission, thereby enhancing the ZigBee's visibility to WiFi. It employs an innovative way to concurrently schedule a busy tone and a data transmission without causing interference between them. We have implemented and evaluated CCS on the TinyOS/MICAz and GNURadio/USRP platforms. Our extensive experimental evaluation has shown that CCS reduces collision between ZigBee and WiFi by 50% for most cases, and by up to 90% in the presence of a high-level interference, all at negligible WiFi performance loss.