The Industrial Internet of Things (IIoT) involves deploying heterogeneous networks consisting of a large number of low-powered sensors that quickly report critical events and other devices serving saturated traffic. To combine power saving with fast and reliable transmissions, Wi-Fi 7 introduces the Restricted Target Wake Time (R-TWT) mechanism that aims to provide a strict quality of service (QoS) for real-time applications and thus can be used by IIoT sensors. To investigate the usability of R-TWT in IIoT networks, we develop an analytical model for a scenario of low-intensity critical events using worst-case analysis. This model allows finding settings of TWT-like mechanisms and channel access parameters that maximize the network throughput under QoS provision for sensors. Comparing throughputs for each mechanism, we find that under strict energy consumption requirements, R-TWT can be effectively used only with additional protection. For this protection, we propose the PR-TWT mechanism and prove that it significantly increases the throughput.

Industrial Internet of Things applications require low and deterministic delays, which is a challenging target for emerging wireless communication technologies. While the upcoming Wi-Fi 7 and Wi-Fi 8, tailored for real-time and reliable communications, are under development, this article focuses on Wi-Fi 6 and explores its capabilities to support industrial applications. This article summarizes key lessons learned during an industrial project on factory automation with Wi-Fi 6, describes and advocates a solution that satisfies quality of service requirements in industrial scenarios. To generalize the designed scheme, this article proposes a framework that maximizes the capacity of the system under reliability and latency constraints. Through extensive simulations, this article shows that the proposed scheme more than doubles the network capacity compared with the default Wi-Fi 6 implementation in terms of the number of stations served with low and deterministic packet delivery delays.

NB-Fi is a new low-power wide-area network technology, which has become widely used for smart cities, smart grids, the Industrial Internet of Things, and telemetry applications. Although many countries use NB-Fi, almost no papers study NB-Fi, and its peak performance is unknown. This article aims to fill this gap by analyzing this technology and studying the problem of rate assignment in NB-Fi networks. For that, this article develops a mathematical model used to find the packet loss ratio, packet error rate, and the average delay for various rate assignment approaches. The performance evaluation results are used to develop the guidelines for NB-Fi configuration to optimize the network performance.

To achieve higher throughputs in cellular networks, 3GPP proposes to use unlicensed frequency bands and develops technologies — the latest one is NR-U — allowing a cellular base station to transmit in unlicensed bands, which are already occupied by Wi-Fi networks. To enable fair channel sharing between two technologies, the base station uses a sort of CSMA/CA with binary exponential backoff similar to Wi-Fi. However, the base station can start data transmission only at strictly periodic time moments. Many papers propose sending a reservation signal between the end of the backoff procedure and such a moment to prevent nearby devices from accessing the channel. However, this approach significantly reduces Wi-Fi performance. The paper proposes a novel method CR-LBT of transmitting a reservation signal that greatly decreases channel resource waste caused by collisions and improves channel resource sharing fairness. With developed analytical models and simulations, it is shown that CR-LBT may simultaneously increase the throughput of both NR-U and Wi-Fi networks. The effect is more noticeable for the Wi-Fi network, the throughput of which may rise three times compared with the traditional method of sending the reservation signal. Finally, the influence of various factors on CR-LBT performance is studied.

LoRaWAN is a popular low power wide area network technology widely used in many scenarios, such as environmental monitoring and smart cities. Different applications demand various quality of service (QoS), and their service within a single network requires special solutions for QoS provision. We consider the problem of QoS provision in heterogeneous LoRaWAN networks that consist of several groups of devices that require different packet loss rate (PLR). To solve this problem, we develop a mathematical model that can find the PLR distribution in a LoRaWAN network. With the model, we show that the PLR can vary significantly, and it is wrong to consider only the average PLR for the QoS provision. Finally, we develop an algorithm for assigning modulation and coding schemes to end-devices that provides PLRs below the required thresholds.

Rapidly evolving, the Internet of Things poses new challenges for the developers of wireless networks. Various industrial automation, agriculture monitoring, and smart cities scenarios require fast and reliable alert delivery. In many systems, multiple sensors are entrusted to react to the same emergency event. Thus it is enough to receive an alert message from any of these sensors. However, such a message shall be reliably delivered as soon as possible. Recently published Wi-Fi HaLow standard defines the Restricted Access Window (RAW) mechanism that coordinates transmissions of numerous devices and thus can improve reliability and reduce delay. The paper proposes an approach for alert delivery with RAW and investigates how to select optimal RAW parameters, i.e. those parameters that minimize channel time consumption while providing satisfactory reliability and delay for the alert delivery.

The volume of traffic transmitted over cellular networks is growing significantly every year. To improve LTE network throughput, 3GPP has proposed License-Assisted Access (LTE-LAA), which allows utilizing the unlicensed 5GHz spectrum already used by Wi-Fi and other technologies. To enable fair resource sharing, LTE-LAA adopts CSMA/CA-based channel access with binary exponential backoff similar to Wi-Fi, However, because of the LTE-LAA technology constraints, the LTE-LAA base station may start data transmission only at rather rare licensed carrier slot boundaries. The essential question, what the base station should do between the end of the backoff procedure and the closest licensed slot boundary, is left implementation dependent. In the paper, we have developed analytical models to study the performance of different LTE-LAA implementations and analyze channel sharing fairness between LTE-LAA and Wi-Fi networks in the coexistence scenario. Moreover, we investigate how the performance of LTE-LAA channel access can be improved using New Radio flexible numerology, which is one of the main features of currently developed 5G systems.

Next generation Wi-Fi networks are expected to support real-time applications that impose strict requirements on the packet transmission delay and packet loss ratio. Such applications form an essential target for the future Wi-Fi standard, namely IEEE 802.11be, the development process of which started in 2019. A promising way to provide efficient real-time communications in 802.11be networks requires some modification of the uplink OFDMA feature originally introduced in the IEEE 802.11ax amendment to the Wi-Fi standard. This feature allows the access point to reserve channel resources for upcoming urgent transmissions. The paper explains why uplink OFDMA random access of 802.11ax does not perfectly fit the requirements of real-time applications and proposes an easy-to-implement modification of the channel access rules for future 802.11be networks. With extensive simulation, it is shown that this modification together with a new resource allocation algorithm outperforms the existing ways to support real-time applications, especially for a heavy load and a high number of users. In particular, they provide extremely low delays for real-time traffic, while the throughput for non-real-time traffic is reduced insignificantly.

Growing requirements for cellular network capacity made 3GPP consortium introduce License-Assisted Access (LAA), which implies unlicensed spectrum exploitation. Since these frequencies are already occupied by other technologies, such as Wi-Fi, it is vital to assure fair and efficient sharing of the unlicensed bands by LAA and Wi-Fi devices. Hence, LAA uses Listen Before Talk, the principle of which is similar to CSMA/CA implemented in Wi-Fi. Specifically, similar to Wi-Fi, an LAA base station performs the backoff procedure before every transmission attempt. However, the base station can only start LAA data transmission at licensed spectrum slot boundaries, which results in an extremely long vulnerable period from the end of backoff procedure till the slot boundary. During such a vulnerable period other devices, e.g., Wi-Fi stations, can occupy the channel, canceling the LAA transmission. To protect LAA transmissions, many developers propose sending a reservation signal during the whole vulnerable period, which in turn blocks Wi-Fi stations, occupying the channel with the useless signal and resulting in the channel resource sharing unfairness. To solve this problem, this paper designs a novel mechanism, which allows the LAA base station to detect collisions of Wi-Fi transmissions with the reservation signal. An analytical model for various LAA implementations is developed. Using the model, it is shown how LAA performance can be improved with the proposed mechanism without Wi-Fi performance degradation.

In the modern world, a high-speed wireless Internet connection is a necessity rather than a luxury. To improve the efficiency of Wi-Fi networks in dense deployment, a novel amendment to the Wi-Fi standard, namely IEEE 802.11ax introduces Orthogonal frequency-division multiple access (OFDMA). In contrast to legacy Wi-Fi, where performance of a station to a considerable degree depends on rate control, aggregation and other decision-making algorithms implemented at the station, in 11ax networks it is the access point that schedules channel time and specifies transmission parameters for both uplink and downlink. Although OFDMA scheduling in 11ax has much in common with that in cellular networks, e.g. LTE, 11ax has some peculiarities, especially for uplink transmission. Focusing on such peculiarities, in this paper, we investigate the scheduling problem in 11ax, propose a set of schedulers for 11ax, compare their performance and determine the gain achievable by the usage of OFDMA.

Inter-and intra-cell interferences significantly degrade the quality of service (QoS) in dense Wi-Fi networks. A promising way to cope with the interference is the use of centralized coordination of various stations in a Wi-Fi infrastructure network. Specifically, to avoid interference from the neighbors, the interfering stations need to execute orthogonal channel access and transmit data in non-overlapping channel times. The paper studies how to use the the features of IEEE 802.11aa/ax in order to guarantee reliable real-time video communication in dense Wi-Fi networks. In particular, IEEE 802.11aa allows an access point to reserve in advance a periodic sequence of channel times during which the data can be transmitted only between two devices, while the neighboring devices should keep silent. IEEE 802.11ax introduces trigger-based multi-user access, which can be done in a periodic way. To optimize and synchronize schedules of various access points a cloud controller can be used. Because of the random nature of the wireless channel and dynamic bit rate of a video stream, the amount of needed channel time varies. The paper proposes an approach on how to jointly use the reserved channel times and the idle channel times in order to satisfy QoS requirements of real-time video transmissions. A mathematical model is developed which can be used at the cloud controller to optimize the performance of the designed approach in terms of satisfying QoS requirements with the minimal channel time consumption. The high efficiency of the designed approach is evaluated with the real video traces.

Ultra Reliable Low Latency Communications (URLLC) is an important challenge for the next generation wireless networks, which poses very strict requirements to the delay and packet loss ratio. Satisfaction is hardly possible without introducing additional functionality to the existing communication technologies. In the paper, we propose and study an approach to enable URLLC in Wi-Fi networks by exploiting an additional radio similar to that of IEEE 802.11ba. With extensive simulation, we show that our approach allows decreasing the delay by orders of magnitude, while the throughput of non-URLLC devices is reduced insignificantly.

Nowadays multi-hop wireless networks have become a popular topic with various applications, including smart grids and sensor networks aimed at monitoring and quality control of industrial systems. In such networks, the amount of generated data is not high, but this data should be delivered with low delay. However, random access methods commonly used in multi-hop networks usually adopt a backoff procedure aimed at collision avoidance, which significantly increases packet delivery time in case of multi-hop transmission. In this paper, to reduce delays in multi-hop networks, we propose an extension to the well-known slotted ALOHA channel access method, which allows performing the first forwarding attempt instantly, without any backoff procedure. We have developed an analytical model to find the stability region of the proposed channel access method, as well as to find its optimal parameter values. In addition, we prove the high efficiency of the proposed method with simulation.

In modern versions of Wi-Fi, multicast transmission can be performed with a palette of methods defined in the IEEE 802.11aa amendment. Additionally, this amendment recommends to protect multicast transmission by transmitting in preliminarily reserved time intervals. Such an approach reduces interference with neighboring stations and increases the delivery probability. In the paper, we develop a general mathematical model of multicast transmission of a delay-sensitive flow. We use the model to evaluate the efficiency of the available multicast transmission methods and to choose such transmission parameters that minimize channel resource consumption while providing required Quality of Service.

Recently appeared the IEEE 802.11ah standard has introduced a new channel access mechanism, so-called Restricted Access Window (RAW). This mechanism allows an access point (AP) to reduce contention for the channel in overloaded Wi-Fi networks by limiting the number of stations simultaneously accessing the channel. The 802.11ah AP divides all associated stations into groups and allocates for each group an interval of time, which is called a RAW slot. This paper considers the RAW mechanism with enabled transmissions crossing slot boundaries, which means that a station is allowed to end the current transmission attempt even after a completion of the allocated RAW slot. We present a new mathematical model, which allows estimating throughput and energy consumption with this mechanism, and optimizing performance of RAW.

In early 2016 Wi-Fi Alliance announced a new technology - Wi-Fi HaLow - which aims to master the raising Internet of Things market with its tremendous number of devices. This technology brings revolutionary changes to Wi-Fi, improving transmission reliability and power efficiency in scenarios with thousands of sensor stations being connected to a single access point. However neither novel channel access methods, nor advanced power management schemes can be used until the stations are connected to the access point, because the access point may not know that the stations exist, to say nothing about their capabilities. Nevertheless, it may happen that a large group of sensor stations are simultaneously trying to connect to the access point, which inevitably leads to continuous collisions and finally to extremely long connection process. This problem has been addressed by the technology developers which designed the Centralized Authentication Control protocol. The protocol provides the access point with an opportunity to hasten the process by managing the ratio of stations which are allowed to start establishing a connection. In this paper, we study how the number of successes depends on this ratio and develop two algorithms, which hasten connection process close to the theoretical limit.

In order to meet the continuously increasing demands for high throughput in wireless networks, IEEE 802 LAN/MAN Standard Committee is developing IEEE 802.11ax: a new amendment for the Wi-Fi standard. This amendment provides various ways to improve the efficiency of Wi-Fi. The most revolutionary one is OFDMA. Apart from obvious advantages, such as decreasing overhead for short packet transmission at high rates and improving robustness to frequency selective interference, being used for uplink transmission, OFDMA can increase power spectral density and, consequently, user data rates. However, the gain of OFDMA mainly depends on the resource scheduling between users. The peculiarities of OFDMA implementation in Wi-Fi completely change properties of classic schedulers used in other OFDMA systems, e.g. LTE. In the paper, we consider the usage of OFDMA in Wi-Fi for uplink transmission. We study peculiarities of OFDMA in Wi-Fi, adapt classic schedulers to Wi-Fi, explaining why they do not perform well. Finally we develop a novel scheduler, MUTAX, and evaluate its performance with simulation.

LoRaWAN is a promising low power long range wireless communications technology for the Internet of Things. An important feature of LoRaWAN gateways is related to so-called capture effect: under some conditions the gateway may correctly receive a frame even if it overlaps with other ones. In this paper, we develop a pioneering mathematical model of a LoRaWAN network which allows finding network capacity and transmission reliability taking into account the capture effect.

In order to meet the rising demands for the Internet of Things technologies, Wi-Fi community has developed Wi-Fi HaLow. It extends Wi-Fi with new functionality supporting high number of autonomous devices with various power capabilities and traffic patterns. In the paper, we study the cooperation of such new mechanisms as TIM Segmentation and Restricted Access Window. TIM Segmentation reduces energy consumption for low-power devices retrieving data from the Access Point, while Restricted Access Window reduces contention and allows the Access Point to protect stations with different capabilities from interfering each other. We consider joint usage of these mechanisms in a heterogeneous network with a high number of low-power stations with rare traffic and several powered stations with saturated traffic. Specifically, for TIM Segmentation and Restricted Access Window we develop a simple and fairly accurate mathematical method to set up the parameters of the mechanisms in order to improve performance for both types of stations, i.e. to reduce power consumption for low-power stations and to increase throughput for the other ones.

While 3GPP has been developing NB-IoT, the market of Low Power Wide Area Networks has been mastered by cheap and simple Sigfox and LoRa/LoRaWAN technologies. Being positioned as having an open standard, LoRaWAN has attracted also much interest from the research community. Specifically, many papers address the efficiency of its PHY layer. However MAC is still underinvestigated. Existing studies of LoRaWAN do not take into account the acknowledgement and retransmission policy, which may lead to incorrect results. In this paper, we carefully take into account the peculiarities of LoRaWAN transmission retries and show that it is the weakest issue of this technology, which significantly increases failure probability for retries. The main contribution of the paper is a mathematical model which accurately estimates how packet error rate depends on the offered load. In contrast to other papers, which evaluate LoRaWAN capacity just as the maximal throughput, our model can be used to find the maximal load, which allows reliable packet delivery.

The ability to provide Quality of Service in Wi-Fi networks to a considerable degree depends on a used channel access method. A number of access methods allow a Wi-Fi station to preliminarily reserve a set of time intervals inside which transmissions are protected from interference. However, fixed parameters assigned to such reservations make them not so flexible as needed for serving Variable Bit Rate (VBR) traffic. On the contrary, random channel access mandatory for Wi-Fi provides such flexibility though at cost of reliability because of collisions and interference. In order to achieve both the reliability and flexibility, we propose a joint access method based on both reservations and random access. In this pioneering work, we study a VBR flow transmission process with the joint method and build its mathematical model. The model can be used to find appropriate parameters of the method which guarantee that QoS requirements of the flow are satisfied while the amount of used channel time is kept as low as possible.

Various networking protocols currently used in wireless networks disseminate much control information. In particular, the deterministic channel access protocol (called MCCA) specified in the IEEE 802.11 standard sends information about channel reservations. The standard proposes a novel approach to reduce this overhead, which is based on dividing various pieces of control information into several groups. When the content of some group changes, the station sends a differential update related to this group. However, a group management algorithm (GMA) - which directly affects the performance of such an approach - is not specified in the standard. Previous studies propose a simple GMA which is based on the idea to use as low number of groups as possible. However, when the content of groups changes very fast, the overhead is high. In this paper, we propose and study an enhanced GMA which manyfold reduces the overhead. We develop an analytical model to evaluate the proposed GMA performance and to find its optimal parameters. We also obtain an explicit formula for the optimal parameters in the asymptotic case. We show that such asymptotically optimal parameters, which do not depend on traffic parameters, provide low overhead in non-asymptotic case as well. Thus, the proposed GMA can be easily implemented without any complex method for parameters adjustment.1

The increasing amount of audio and video data transmitted over Wi-Fi networks raises a problem of parametrized Quality of Service (QoS) provisioning, which is challenging even for point-to-point transmission. QoS provisioning is much more complicated when a wireless access point (AP) streams IPTV or another multimedia flow to a group of receiving stations. This scenario is a typical use case for IEEE 802.11aa, a recently approved amendment to the Wi-Fi standard. To improve performance of multicast transmission, the amendment defines several approaches. In the paper, we study their efficiency in the case, when deterministic channel access with periodic reservations is used to improve reliability of multicast transmission. For that we develop a mathematical model and use the model both to compare efficiency of the approaches and to select the best parameters for channel reservation1.

To address 5G challenges, IEEE 802.11 is currently developing new amendments to the Wi-Fi standard, the most promising of which is 802.11ax. A key scenario considered by the developers of this amendment is dense and overlapped networks typically present in residential buildings, offices, airports, stadiums, and other places of a modern city. Being crucial for Wi-Fi hotspots, the hidden station problem becomes even more challenging for dense and overlapped networks, where even access points (APs) can be hidden. In this case, user stations can experience continuous collisions of beacons sent by different APs, which can cause disassociation and break Internet access. In this paper, we show that beacon collisions are rather typical for residential networks and may lead to unexpected and irreproducible malfunction. We investigate how often beacon collisions occur, and describe a number of mechanisms which can be used to avoid beacon collisions in dense deployment. Specifically, we pay much attention to those mechanisms which are currently under consideration of the IEEE 802.11ax group.

In the paper, we address the influence of Head-of-line (HOL) blocking on real-time video streaming in wireless networks. We consider short channel failures when the probability of successful packet transmission to a station abruptly drops to a near zero value. In wireless networks, the duration of such channel failure intervals may reach some hundred milliseconds, making packets staying in the same queue and destined for other stations be blocked and experience large delays. Because of delay sensitivity of real-time traffic, the quality of the received videos degrades. In the paper, we propose a feasible for implementation queue management algorithm to avoid video quality degradation. We prove by simulation that our algorithm outperforms existing solutions significantly, minimizing video quality degradation for the streams destined for stations with channel failures while avoiding blocking streams destined for other stations.

One of the today challenges for the mesh networks researches is reliable transmission of multimedia traffic. This traffic demands high quality of service (QoS), to provide which it is suitable to use Mesh Coordinated Channel Access (MCCA) - the novel medium access method described in IEEE 802.11s. According to MCCA, mesh stations (STAs) set up periodic reservations; if all STAs in the network support MCCA, every STA gets access to the medium with no contention during the reservations it has scheduled. Most papers devoted to MCCA are written under the assumption of ideal channel conditions. However, in order to satisfy QoS demands, it is necessary to take random noise into account. In this paper we propose an analytical model of the multihop MCCA-based streaming process in the presence of noise. The model predicts the Packet Loss Ratio (PLR) over the transmission route and can be efficiently utilized to analyze and optimize the process of traffic transmission.

The fundamental challenges in wireless multihop networks design are the problems of routing and hidden stations. Defining mesh networking, IEEE 802.11s amendment addresses both issues. It includes a routing protocol and novel deterministic channel access method, called MCCA, complementing random access traditional in IEEE 802.11 networks. The routing framework architecture allows extending or even replacing the default routing protocol for specific niche application, but it is not flexible enough to take advantage of using both traditional random access and novel deterministic access, as we show in this paper. Proposed flexibility enhancements are illustrated to bring benefits for the network performance.

IEEE 802.11s draft defining mesh networking includes two channel access methods: mandatory EDCA and optional MCCA. It is known that random access with EDCA, designed for ad hoc and infrastructure modes, is weak in multihop case because of the hidden stations effect. In contrast, by means of channel reservation and advertisement of set up reservations MCCA combats against the effect, provides more coordinated channel access and comes as a solution when better QoS is desired. In this paper, we draw readers attention to the hidden stations effect again and show that the interference caused by transmissions of ACK frames by hidden stations is not combated with MCCA. We evaluate the effect with a simulation model and propose a solution which is compatible with IEEE 802.11 and may be implemented in the framework of MCCA. Also, we discuss the issue of the interference coming out of MCCA advertisement horizon and propose a solution which appear to require more flexibility than provided by the current IEEE 802.11s draft.

Initially, IEEE 802.11 standard was not designed for multihop networks, but its market success gave it a powerful incentive, and nowadays IEEE 802.11 Working Group is preparing various amendments and looking for new application scenarios to ensure future success in the market. In this paper, we analyze the performance of an IEEE 802.11s mesh network and show that the effect of starvation caused by hidden terminals interference makes the distribution of channel capacity between links very much disproportional and unpredictable. Some links may be suppressed completely by other links and their throughput is close to zero. The effect of starvation was discovered by simulations in many papers. We investigate the roots of this phenomenon in a mesh network with an analytical model. Also, this paper reports the results of an outdoor testbed which was deployed to find out the scale of the starvation problem in a real network with Voice-over-IP, Video-over-IP and FTP traffic. While the results for VoIP may be considered as satisfactory, FTP traffic suffers dramatically from interference. So, at the end of the paper, we outline possible solutions to address starvation problem in mesh networks.

We investigate the delay of the bandwidth request under the truncated binary exponential backoff (TBEB) mechanism in the IEEE 802.16e, considering error-free/error- prone wireless channels. We derive the distribution of delay of bandwidth request packets in the TBEB by an analytic method on the assumption of Bernoulli request arrival process and error-free channel conditions, and extend the analytic results to the error-prone channel condition where the request transmissions have error with i.i.d. By numerical analysis we can find the optimal number of transmission opportunities for transmitting bandwidth requests of the TBEB satisfying QoS on delay bound and loss bound.

In this paper, we discuss some problems related to direct transmissions between QSTAs in an infrastructure 802.11 WLAN with a legacy access point (AP). In the infrastructure mode, collisions of data frames caused by hidden terminals interference can be avoided by the RTS/CTS exchange anticipating the data frames, if and only if all data communications between stations are performed via the AP. The interference problem is solved because all terminals are within the transmission range (TX range) of the AP. However, the RTS/CTS exchange is not enough to protect direct transmissions between QSTAs. In this paper, we analyze the state-of-the-art direct transmissions protection approaches, show their limitations, propose and simulate our own protection schemes.

Beaconing is crucial to ensure many services in networks, especially with distributed MAC. Being the first standardized distributed MAC for WPANs, ECMA-368 utilizes beacons for device discovery, channel reservation, mobility support, etc. In this paper, we develop an analytical method to find the distribution of the time which devices need for channel switching caused by environment changes such as open/close door effect. Verified by simulation results, the analytical model gives optimistic or conservative estimations, depending on the used assumption. The proposed method may be used to find the best beaconing parameters, which minimize the pause in network operation caused by channel switch or other network re-arrangements, which is very important for delay-sensitive applications.

Distributed media access control (MAC) architecture has many merits to make it a favorable candidate for high-data-rate wireless personal area networks (WPANs) with physical layer (PHY) based on ultrawideband (UWB) technology. This paper focuses on the WiMedia MAC, which is the first distributed MAC for WPANs, approved as a standard. In such a MAC, all devices transmit their beacons to provide timing reference and to broadcast control and reservation information, that is, to maintain device synchronization. We investigate problems related to beacon collisions, which occur when multiple devices join a piconet almost at the same time. To join a piconet or to resolve a collision, a device chooses a slot for its beacon randomly within some window. We show that an improper slot choice scheme leads to repeated collisions, increasing the time overhead to achieve device synchronization. It also leads devices into trouble in joining and collision resolution, even into deadlocks, when devices have no chance to escape repeated collisions. We develop an analytical model to evaluate the performance of various slot choice schemes for multihop WPANs. The model is employed to compare the efficiency of these choice schemes and to optimize their parameters to achieve the best performance.

In the paper we propose and study a novel packet transmission scheme aimed to overcome a fundamental overhead of WPAN MAC/PHY protocols and to improve ARQ performance. Specifically, we propose to combine two well- known techniques: fragmentation and aggregation by adding multiple Frame Control Sums (FCS) to each fragment. We show analytically and by simulation that the proposed scheme increases WiMedia MAC efficiency greatly. Although the WiMedia MAC has been used as a design base, this novel packet transmission scheme can be extended to other high rate wireless communication systems to cover mmWave.

In the legacy IEEE 802.11 ad hoc networks, beacons are commonly used to exchange timing information between stations, to maintain clock synchronization. To serve this purpose, the only beacon is enough, while multiple beacons are prohibited, during a beacon transmission window. With the appearance of 11s Amendment specifying mesh networking, beacons take the responsibility to support a novel Mesh Deterministic Access (MDA) method improving QoS for multimedia delay-sensitive traffic. Beacons of different stations become more individual now, and the current 11s beaconing scheme inherited from that in IEEE 802.11 ad hoc networks doesn't meet MDA requirements. This paper investigates more efficient beaconing scheme permitting multiple beacons in a beacon period. We develop a simple analytical model which estimates the beaconing scheme efficiency and allows tuning the scheme to improve the MDA support.

Existing IEEE 802.11 spec. provides no error recovery mechanism (ARQ) for multicast traffic. ARQ absence in wireless networks unreliable by their nature leads to frequent packet losses, which is inappropriate for most of multimedia applications. In the paper, we propose new reliable multicast mechanism supporting multimedia QoS (packet loss ratio, delay and throughput), in IEEE 802.11 Wireless Local Area Networks (WLANs). This mechanism is based on the concept of multiple ACK-leaders, i.e. multicast recipients responsible for data packets acknowledging. We develop an analytical model of the mechanism and use the model to study and to optimize the mechanism.

Internet access via Wi-Fi hot spots representing infrastructure Wireless Local Area Networks (WLANs) controlled by the IEEE 802.11 protocol [1] is very popular over the world. In the paper, we develop an analytical model to estimate Wi-Fi hot spot throughput, focussing on the problem of unfair access. The problem is caused by the signal capture and propagation loss phenomena, owing to which mobile terminals located near the Access Point (AP) can succeed in transmitting their packets in spite of possible collisions with terminals near hot spot borders. Consequently, the further a terminal is from the AP, the less portion of the network throughput it can use. The method developed in our paper allows finding optimal values of the protocol parameters to provide equal access opportunities for all terminals of the hot spot.

The main purpose of beaconing in the legacy IEEE 802.11 networks is maintaining stations clock synchronization. Recently appeared 11s Amendment specifying mesh networking makes beacons responsible for supporting the mesh deterministic access method (MDA) designed for delay-sensitive multimedia applications. In this paper, we study the legacy beaconing scheme and show its inability to support the MDA in a typical mesh network use case. We propose a P-persistent beaconing approach to improve the MDA support and analyze its efficiency. The simulation results show that applying the P-persistent approach successfully maintains and protects the channel reservations obtained via MDA.

In this paper, we investigate beaconing problems in Wireless Personal Area Networks (WPANs) with distributed control, which is being developed by Multi-Band OFDM Alliance. The problems are related to collision that is caused by multiple access to a piconet; and the collision resolution that is used in the MBOA MAC, i.e. random slot allocation for devices’ beacons. The collision problem and the current resolution may cause deadlock and prevent other devices from joining a piconet. We propose new solutions to resolve the collision without causing potential deadlock. We develop an analytical model to evaluate performance of the new schemes. The model can also be employed to determine parameters to achieve optimized performance.

IEEE 802.16 protocols for metropolitan broadband wireless access systems have been standardized recently. According to the standard, a subscriber station can deliver bandwidth request messages to a base station by numerous methods. This paper provides both the simulation and analytical models for the investigation of specified random access method, which is compared with centralized polling and station- grouping mechanisms. Based on the assumptions of Bernoulli request arrival process and ideal channel conditions, the mean delay of a request transmission is evaluated for varying number of transmission opportunities and different arrival rates.

We present an analytical method for estimating the saturation throughput of an 802.11 ad hoc LAN called also the Wi-Fi (wireless fidelity) LAN in the presence of noise distorting transmitted frames. This is the first method that allows analytical study of the Wi-Fi network performance with consideration of correlated channel failures usually inherent to wireless channels. Within the study, we consider the possible packet fragmentation that can be adopted to reduce the performance waste caused by noise-induced distortions. In addition to the throughput, our method allows estimation of the probability of a packet rejection occurring when the number of packet transmission retries attains its limit. The obtained numerical results of investigating Wi-Fi LANs by the developed method are validated by simulation and show high estimation accuracy as well as the method efficiency in determining the optimal fragmentation threshold.