Today, Wi-Fi is over 25 years old. Yet, despite sharing the same branding name, today’s Wi-Fi boasts entirely new capabilities that were not even on the roadmap 25 years ago. This article aims to provide a holistic and comprehensive technical and historical tutorial on Wi-Fi, beginning with Institute of Electrical and Electronics Engineers 802.11b (Wi-Fi 1) and looking forward to IEEE 802.11bn (Wi-Fi 8). This is the first tutorial article to span these eight generations. Rather than a generation-by-generation exposition, we describe the key mechanisms that have advanced Wi-Fi. We begin by discussing spectrum allocation and coexistence, and detailing the IEEE 802.11 standardization cycle. Second, we provide an overview of the physical layer (PHY) and describe key elements that have enabled data rates to increase by over 1000×. Third, we describe how Wi-Fi medium access control (MAC) has been enhanced from the original distributed coordination function (DCF) to now include capabilities spanning from frame aggregation to wideband spectrum access. Fourth, we describe how Wi-Fi 5 first broke the one-user-at-a-time paradigm and introduced multi-user (MU) access. Fifth, given the increasing use of mobile, battery-powered devices, we describe Wi-Fi’s energy-saving mechanisms over the generations. Sixth, we discuss how Wi-Fi was enhanced to seamlessly aggregate spectrum across 2.4-, 5-, and 6-GHz bands to improve throughput, reliability, and latency. Finally, we describe how Wi-Fi enables nearby access points (APs) to coordinate in order to improve performance and efficiency. In the Appendix, we further discuss Wi-Fi developments beyond 802.11bn, including integrated millimeter-wave (IMMW) operations, sensing, security and privacy extensions, and the adoption of artificial intelligence (AI)/machine learning (ML).

This paper proposes a novel multi-agent deep reinforcement learning (MADRL)-based positioning algorithm for multiple unmanned aerial vehicles (UAVs) collaboration in mobile access applications where the UAVs work as mobile base stations. The primary objective of the proposed algorithm is to establish reliable mobile access networks for vehicle-to-everything (V2X) communications. This paper jointly considers energy-efficient UAV operation and reliable wireless communication services for realizing robust mobile access services. For the energy-efficient UAV operation, the reward function formulation of our proposed MADRL algorithm contains the features for UAV energy consumption models in order to realize efficient operations. Furthermore, for the reliable wireless communication services, the quality of service (QoS) requirements of individual users are considered as a part of reward function. Furthermore, this paper considers 60, GHz millimeter-wave (mmWave) mobile access for utilizing the benefits of i) ultra-wide-bandwidth for multi-Gbps high-speed communications and ii) high-directional communications for spatial reuse that is obviously good for avoiding interference among densely deployed users. Lastly, the comprehensive and data-intensive performance evaluation of the proposed MADRL-based algorithm for multi-UAV positioning is conducted. The results of these evaluations demonstrate that the proposed algorithm outperforms other existing algorithms.

Multi-stream 60 GHz communication can potentially achieve data rates up to 100 Gbps via multiplexing multiple data streams. Unfortunately, establishing multi-stream directional links is a high overhead procedure as the search space increases with the number of spatial streams and the product of AP-client beam resolution. In this paper, we present MUlti-stream beam-Training for mm-wavE networks (MUTE) a novel system that leverages channel sparsity, GHz-scale sampling rate, and the knowledge of mm-Wave RF codebook beam patterns to construct a set of candidate beams for efficient multi-stream beam steering. MUTE repurposes the mandatory periodic beam sweeps in 60 GHz WLANs to discover the dominant paths of the mmWave channel between the AP and any client with zero additional overhead. Coupling path estimates with beam pattern knowledge, MUTE selects a set of candidate beams that capture diverse or ideally orthogonal paths to obtain maximum stream separability. Our over-the-air experiments demonstrate that MUTE achieves 90% of the maximum achievable aggregate PHY rate while incurring only 1.2% of exhaustive search's training overhead.

IEEE 802.11ay is an amendment that enables enhanced throughput for IEEE 802.11 systems operating in the license-exempt 60 GHz band. By specifying advanced physical layer (PHY) features such as channel bonding and aggregation, multiple input multiple output (MIMO) transmission, and non-uniform modulation constellation, IEEE 802.11ay supports a maximum data rate of 100 Gb/s, making it an amendment of great interest for applications as diverse as wireless virtual reality (VR) and backhauling. In this paper, we provide a description and analysis of certain fundamental elements of the single-carrier (SC) PHY defined by IEEE 802.11ay. Among the topics that are discussed are the new frame format, modulation and coding schemes (MCSs), and beamforming training field defined in the amendment. Simulation results of key aspects for the topics covered are presented.

Multi-stream 60 GHz communication has the potential to achieve data rates up to $100$ Gbps via multiplexing multiple data streams. Unfortunately, establishing multi-stream directional links can be a high overhead procedure as the search space increases with the number of spatial streams and the product of AP-client beam resolution. In this paper, we present MUlti-stream beam-Training for mm-wavE networks (MUTE) a novel system that leverages channel sparsity, GHz-scale sampling rate, and the knowledge of mm-Wave RF codebook beam patterns to construct a set of candidate beams for multi-stream beam steering. In 60 GHz WLANs, the AP establishes and maintains a directional link with every client through periodic beam training. MUTE repurposes these beam acquisition sweeps to estimate the Power Delay Profile (PDP) of each beam with zero additional overhead. Coupling PDP estimates with beam pattern knowledge, MUTE selects a set of candidate beams that capture diverse or ideally orthogonal paths to obtain maximum stream separability. Our experiments demonstrate that MUTE achieves 90% of the maximum achievable aggregate rate while incurring only 0.04% of exhaustive search's training overhead.

IEEE 802.Had will take advantage of the large swath of available spectrum in the 60 GHz band to develop a protocol to enable throughput intensive applications such as wireless display and high speed sync-and-go file transfer. Functional requirements, evaluation methodology, and channel models are currently being developed by the task group in preparation for a call for proposals. Likely enhancements to 802.11 beyond a new 60 GHz PHY include personal basic service set, MAC modifications for directional antennas, fast session transfer between PHYs, beamforming, and spatial reuse. Therefore in this paper we give an overview of IEEE 802.Had, which is poised to define the next generation multi-Gbps Wi-Fi.

The unlicensed 60 GHz band brings the promise of multi-gigabit data rates to support new applications such as high definition video over wireless links. Signal propagation in the 60 GHz band significantly differs from that in the traditionally used 2.4 and 5 GHz bands. The propagation and penetration losses in the 60 GHz band are much higher. Furthermore, the signals are often reflected in indoor settings. Previous physical layer studies show that the use of directional antennas can significantly help in coping with these effects. In this paper, we address the problem of neighbor discovery in the 60 GHz band. We account for not only discovery via direct line-of-sight paths, but also via reflected beams. To the best of our knowledge, none of the previous efforts on higher layer protocols for use with directional antennas account for reflections. We consider two approaches for neighbor discovery (a) direct discovery where each node explicitly discovers its neighbors and, (b) gossip-based discovery where nodes exchange information with regards to their already discovered neighbors. We develop analytical models to capture the performance of the two approaches and validate the models via simulations in indoor settings with obstacles that reflect the transmitted signals. As one might expect, the gossip based discovery incurs a lower neighbor-discovery latency than direct discovery. We examine the impact of system parameters such as varying beamwidth and node density. Our study provides insights on the right choice of system parameters for efficient neighbor discovery in the 60 GHz regime.

The six articles in this special issue focus on the technology and applications of body area networking.

The wide harmonized spectrum in the unlicensed 60 GHz band has been considered for WPAN standardizations. Recently there is also growing interest in the industry to use the same band for multi-Gigabit WLAN usages and standardization. In this paper, we describe the unique challenges and analyze the feasibility of realizing a multi-Gigabit WLAN in this band. We present analysis and simulation findings on the transmission range and spatial reuse opportunity with beamforming. We also explore options for range extension and multi-band integration.

Spectrum sensing is essential to the realization of spectrum agility in cognitive radio (CR) networks. Although fundamental tradeoffs and theoretical limits associated with spectrum sensing have been studied extensively, there have been very few experimental studies focused on building a spectrum "sensor" with commercial off-the-shelf devices. We have therefore built a prototype of CR-based sensor implementation with off-the-shelf IEEE 802.11 devices. 1 In particular, we have explored issues in implementing a spectrum sensor, mostly at the MAC layer, as well as the difficulty in implanting sensing functions into industrial network interfaces. Our experimental results demonstrate the feasibility of building a spectrum sensor and the construction of an incumbent-detection mechanism with off-the-shelf devices. We have also identified technical difficulties, such as device-dependency in determining the detection threshold, in-band signal jamming between secondary devices, and adjacent channel interference due to out-of-band signal emission. This experimental experience has led us to suggest a sensor design guideline for commercial wireless interfaces which can also facilitate other CR-related research.

The 11 papers in this special issue focus on adaptive, spectrum agile and cognitive wireless networks. Some of the topics covered include: fundamental performance aspects of spectrum sharing; spectrum sensing capabilities in cognitive radios; detection and estimation approaches to spectrum sharing; MAC design in opportunistic spectrum access; and competitive spectrum sharing and resource allocation using concepts from game theory and pricing.

We explore the price dynamics in a competitive market consisting of spectrum agile network service providers and users. Here, multiple self interested spectrum providers operating with different technologies and costs compete for potential customers. Different buyers or consumers may evaluate the same seller differently depending on their applications, operating technologies and locations. Two different buyer populations, the quality-sensitive and the price-sensitive are investigated, and the resulting collective price dynamics are studied using a combination of analysis and simulations. Various scenarios are considered regarding the nature and accuracy of information available to the sellers. A myopically optimal strategy is studied when full information is available, while a stochastic learning based strategy is considered when the information is limited. Cooperating groups may be formed among the sellers which will in-turn influence the group profit for those participants. Free riding phenomenon is observed under certain circumstances

Abstract A growing need to have ubiquitous connectivity has motivated our research to provide continuous connection between various wireless platforms such as cellular networks, wireless local area networks (WLANs), and mobile ad hoc networks (MANETs). In this paper, we consider integration at the routing layer and propose two adaptable routing protocols (IRP‐RD and IRP‐PD) that exploit topology information stored at the fixed network components (cellular base stations and WLAN access points) for the route discovery and maintenance processes. Our proposed protocols can provide connectivity to the cellular network and/or WLAN hotspots through multihop routing, while differ in the gateway discovery approach used. In IRP‐RD, multihop routes to gateways to the cellular network or WLAN hot spots are discovered on demand, while in IRP‐PD out of coverage users proactively maintain routes to the gateways. Furthermore, proposed protocols can be used in any heterogeneous scenario, combining a cellular network and WLANs operating in infrastructure or ad hoc (MANET) mode. We provide simulation results that demonstrate the effectiveness of the proposed integrated routing protocols and show the advantages and drawbacks of each gateway discovery approach in different heterogeneous scenarios. Copyright © 2006 John Wiley & Sons, Ltd.

Bluetooth is a radio technology for wireless personal area networks in the 2.4 GHz ISM frequency band and allows short-range devices to be connected in the form of ad hoc networks. The Bluetooth medium access control protocol is based on a strict master/slave concept wherein any communication between slave devices has to go through the master. While this model is simple, the use of such a nonoptimal packet forwarding scheme incurs much longer delays between any two slave-devices as double the bandwidth is used by the master. In addition, if two or more devices want to communicate as a group, this can only be achieved by either multiple unicast transmissions or a piconet-wide broadcast from the master. To handle these issues efficiently, we propose a novel combination of dynamic slot assignment (DSA) and piconet partitioning. With DSA, the piconet master dynamically assigns slots to slaves so as to allow them to communicate directly with each other without any intervention from the master. Our proposed communication architecture provides for enhanced quality of service (QoS), better admission control, and multidevice conversation, which make a multicast-like communication feasible within the piconet. To widen the scope of DSA, we propose a QoS-aware enhanced DSA (EDSA) version where dynamic piconet partitioning and scatternet support are exploited by grouping devices into piconets as per their connection endpoints, enabling it to be employed over a scatternet. We have performed extensive simulations and observe that these schemes drastically enhance Bluetooth performance in terms of the delay and the throughput, while significantly reducing the network power consumption

This paper addresses the issue of routing in mobile ad hoc networks (MANETs) using directional antennas. Existing directional routing schemes either assume a complete network topology beforehand or simply use omni-directional routing schemes to forward packets in underlying directional environment. In this paper, we propose a Directional Routing Protocol (DRP) for MANETs. DRP is an on-demand directional routing protocol which assumes a cross layer interaction between routing and MAC layer and is inspired by Dynamic Source Routing (DSR) protocol. The main features of DRP include an efficient route discovery mechanism, establishment and maintenance of directional routing and directional neighbor tables (DRT and DNT, respectively), and novel directional route recovery mechanisms. We have implemented DRP on top of MDA; a MAC protocol for directional antennas and have compared its performance with the DSR protocol over both omni-directional and directional antenna models. Our results show that DRP considerably improves the packet delivery ratio, decreases the end to end packet latency, has lesser routing overhead, and is robust to link failures.

Abstract In this work we address the issue of deafness and hidden terminal problem in mobile ad hoc networks (MANETs) using directional antennas. To minimize these effects, we propose a MAC protocol for directional Antennas (MDA) which employs a novel enhanced directional network allocation vector (EDNAV) scheme and an efficient technique of diametrically opposite directions (DOD) transmission of RTS and CTS packets. We compare MDA with IEEE 802.11 and two recently proposed directional MAC (DMAC) schemes and results show that MDA outperforms these protocols in the majority of scenarios investigated. We also point out that the performance does depend on the network topology and the traffic pattern. A shorter version of this has appeared in Globecom 2005. Copyright © 2006 John Wiley & Sons, Ltd.

Abstract In this paper, we propose a directional antenna medium access (DAMA) protocol and its enhanced version called enhanced DAMA (EDAMA), which takes advantage of the benefits offered by directional antennas. Both of these schemes have been inspired by the IEEE 802.11 MAC, with major enhancements including a new neighbor discovery scheme, an optimized circular directional transmission of RTS and CTS to prevent the hidden node problem, reduce collisions and decrease node deafness, and also a multi‐buffer management scheme. A pair of communicating nodes using these schemes simultaneously transmits the circular directional RTS and CTS only to those sectors with neighbors, hence reducing overall communication delay and enhancing throughput. The main difference between DAMA and EDAMA lies in the way buffering is provided in the MAC layer. Unlike DAMA, which uses a single MAC buffer for all antenna beams as in IEEE 802.11, EDAMA employs separate buffers for each of the antenna sectors and introduces an integrated network and MAC cross‐layer design. This helps in eliminating the ‘self‐induced blocking’ problem prominent in existing directional MAC protocols. We have compared DAMA, EDAMA, IEEE 802.11, and two recently proposed directional MAC protocols, and results show that DAMA and EDAMA perform better than existing MAC protocols in the majority of the scenarios investigated, while EDAMA is observed to perform best. We also point out that the performance usually depends on the network topology and traffic pattern. Copyright © 2006 John Wiley & Sons, Ltd.

This paper addresses the issue of deafness and hidden terminal problem in a Mobile Ad Hoc Networks (MANETs) using directional antennas. To minimize these effects, we propose a MAC protocol for directional Antennas (MDA) which employs an enhanced directional network allocation vector (NAV) scheme and, a novel technique of Diametrically Opposite Directions (DOD) transmission of RTS and CTS. We compare MDA with IEEE 802.11 and two recently proposed directional MAC protocols and results show that MDA outperforms these protocols in the majority of scenarios investigated. We also point out that the performance does depend on the network topology and the traffic pattern.

A growing need for ubiquitous connectivity has motivated the integration of various wireless technologies such as cellular systems, WLANs and MANETs. In this paper we introduce the integrated routing protocol (IRP) that exploits topology information obtained by cellular base stations and WLAN access points in the route discovery and maintenance in a heterogeneous wireless access network. IRP also provides connectivity to the cellular network and/or WLAN hotspots through the multi-hop routing by allowing out of coverage users to maintain routes to Gateway Nodes (GN). We provide a simulation study of IRP with two different link quality metrics, number of hops and a new integrated metric based on the expected transmission time (ETT). Our results show that IRP improves the network coverage and capacity and allows connectivity alternatives that are not supported by other integrated solutions.

Abstract: In this paper we propose a Directional Routing Protocol (DRP) for MANETs. DRP is an on-demand directional routing protocol which assumes a cross layer interaction between routing and MAC layer. The main features of DRP include an efficient route discovery mechanism, establishment and maintenance of directional routing and directional neighbor tables (DRT and DNT respectively), and novel directional route recovery mechanisms. We have implemented DRP on top of an existing MAC protocol for directional antennas and have compared its performance with the popular dynamic source routing (DSR) protocol over both omni-directional and directional antenna models. Preliminary simulation results are found to be very promising.

The paper presents the ALCA (asymmetric link collision avoidance) protocol, which was designed to deal with a known deficiency of basic schemes for power control in IEEE 802.11 ad hoc networks. The performance of ALCA is investigated and results indicate that ALCA outperforms a known solution to the problem while being a considerably less complex solution.

In this paper, we propose a new scheme for small group multicast in mobile ad hoc networks (MANETs) named extended explicit multicast (E/sup 2/M), which is built on top of Xcast and introduces mechanisms to make it scalable with number of group members for a given multicast session. E/sup 2/M is based on the novel concept of dynamic selection of Xcast forwarder (XF) between a source and its potential destinations. The XF selection is carried out based on group membership and the processing overhead involved in supporting the Xcast procedure at a given node. If the number of members in a given session is small, E/sup 2/M works just like the basic Xcast scheme with no intermediate XFs. As group membership increases, the overhead involved in supporting an Xcast session also increases. Therefore, to reduce the overhead and provide scalability, in E/sup 2/M nodes may dynamically decide to become a XF. This scheme, which can work with few E/sup 2/M aware nodes in the network, provides the transparency of stateless multicast, reduces header processing overhead and makes Xcast scalable with the number of group members.

Bluetooth is a promising wireless technology aiming at supporting electronic devices to be instantly interconnected into short-range ad hoc networks. The Bluetooth medium access control protocol is based on the master/slave concept wherein any communication between slave devices has to go through the master. While this model is simple, it incurs longer delay between any two slave devices due to the use of non-optimal packet forwarding scheme and the use of double the bandwidth at the master. Moreover, if more than two devices want to communicate as a group, this can only be achieved by either multiple unicast transmissions or a piconet-wide broadcast from the master. To handle these issues efficiently, we propose a novel combination of dynamic slot assignment (DSA) and piconet partitioning. With DSA, the piconet master dynamically assigns slots to slaves so as to allow them to communicate directly with each other without any intervention from the master. Such proposed communication architecture provides for quality of service (QoS) requests, admission control, and multi-device conversation by which a multicast-like communication is feasible within a piconet. To widen the scope of DSA, we propose QoS-driven enhanced DSA (EDSA) where dynamic piconet partitioning and scatternet support comes into picture. Devices are grouped in piconets according to their connection endpoints in EDSA, enabling it to be employed over a scatternet. We have performed extensive simulations and observe that these schemes drastically enhance Bluetooth performance in terms of delay and throughput, while significantly reducing network power consumption.

Bluetooth is a radio technology for wireless personal area networking (WPAN) operating in the 2.4 GHz ISM frequency band. The Bluetooth MAC protocol is based on the master/slave concept wherein any communication between slave devices has to go through the master. While this model provides for simplicity, it incurs longer delay between any two slave devices due to far from optimal packet forwarding, the use of double the bandwidth, and also it wastes additional energy at the master. Moreover, if more than two devices want to communicate as a group, this can only be achieved by either multiple unicast transmissions or a piconet-wide broadcast, clearly resulting in inefficiency. We propose a novel dynamic slot assignment (DSA) scheme whereby the master device dynamically assigns slots to slaves so as to allow them to communicate directly with each other without master intervention. This proposed mechanism also provides for quality of service (QoS) requests, and multi-device conversation by which a multicast-like communication is implemented within a piconet. Through extensive simulation, we observe that this mechanism greatly enhances Bluetooth performance in terms of delay and throughput while incurring extremely low overhead.

Bluetooth is a radio technology for wireless personal area networking (WPAN) operating in the 2.4 GHz ISM frequency band. We introduce a novel Bluetooth architecture (BlueStar) whereby selected Bluetooth devices, called Bluetooth wireless gateways (BWGs), are also IEEE 802.11 enabled so that these BWGs could serve as ingress/egress points to/from the IEEE 802.11 wireless network and thus provide access to WANs such as the Internet. We propose mitigating interference between Bluetooth and IEEE 802.11 by employing a hybrid approach of adaptive frequency hopping (AFH) and Bluetooth carrier sense (BCS) of the channels. AFH labels channels as "bad" or "good", and Bluetooth devices only access those channels in the "good" state, whereas BCS is used to avoid collision by sensing the channel prior to any transmission. By combining AFH and BCS, we minimize the effect of the worst-case interference scenario wherein both a Bluetooth and an IEEE 802.11 interface are colocated in a single device. BlueStar enables Bluetooth devices, in either a piconet or a scatternet, to access the WAN through the BWG without the need for any fixed Bluetooth access points, while utilizing the widely deployed base of IEEE 802.11 networks. We define the protocol stack employed by BlueStar as well as indicate how BWGs efficiently manage their capacity allocation through different systems. We also mathematically derive an upper bound on the number of BWGs needed in a scatternet so that uninterrupted access to all Bluetooth devices could be provided.

The seamless communication of data and voice over short-range, point-to-multipoint wireless links between mobile and/or stationary devices is becoming a reality by newly introduced Bluetooth radio technology for Wireless Personal Area Networking, which can support only up to 1 Mbps of nominal bandwidth. It is based on a master-slave model where double the resources are allocated for any slave-to-slave communication via the master. In addition, it does not have any mechanism to serve demands exceeding this capacity. In this paper, we employ the concepts of Internet Traffic Engineering to maximize the channel utilization and optimize the performance of QoS-sensitive applications, with minimum possible interference. We introduce two novel techniques of Pseudo Role Switching (PRS) and Pseudo PaRtitioning (PPR) to alleviate bottlenecks in the existing schemes in a proactive manner. We propose a two-layered approach wherein we first achieve the maximum possible throughput in existing network using PRS technique, and then dynamically partition piconets using the PPR to satisfy the increased demands. It has been observed that combining both PRS and PPR drastically enhances the aggregate network throughput while minimizing the interference. Through extensive performance evaluations, we show that our proposed schemes reduce up to 50 % of the network overhead and increase the overall throughput by 200%.

The emergence of Bluetooth as a default radio interface has allowed handheld electronic devices to be instantly interconnected as ad hoc networks. These short-range ad hoc wireless networks, called piconets, operate in the unlicensed 2.4-GHz ISM (Industrial-Scientific-Medical) band where devices may be used to configure single or overlapping piconets, known as scatternet. As all piconets operate in the same frequency band, the presence of multiple piconets in the vicinity may create interference on signal reception. This paper employs a signal capture model to study the piconet MAC performance, taking inter-piconet interference into consideration. This model leads to several important mathematical relationships for Bluetooth networks, including successful packet transmission probability. Furthermore, our model and anticipated throughput are validated using extensive simulation. These results indicate that Bluetooth throughput is affected by multiple piconet interference. Definitely, our model can be considered to provide a solid foundation for future interference aware Bluetooth protocols.

The emergence of Bluetooth as a defacto radio interface has allowed handheld electronic devices to be instantly interconnected as ad hoc networks. Recent studies show that since Bluetooth operates in the unlicensed 2.45 GHz frequency band, the presence of multiple piconets in the vicinity creates intermittent interference on signal reception which, in turn, degrades the overall throughput of the network. Another kind of interference, called as persistent interference, is the one generated by IEEE 802.11 enabled devices as they use the same frequency band as Bluetooth, and thus may lead to significant performance degradation. In order to cope up with both of these interference sources, this paper proposes an interference aware Bluetooth segmentation algorithm (IBLUES), where Bluetooth packet types are selected depending on the packet success probability, which is calculated based on the interference generated both by multiple piconets, as well as by IEEE 802.11 devices. Among other things, we show that when the number of bridge nodes are larger than five the propagation delay between piconets increases rapidly. We have also observed a drastic overhead in the current Bluetooth piconet switching procedure and conclude that future enhancements to this procedure are crucial to efficiency of Bluetooth-based ad hoc networking.

Most studies on TCP over multi-hop wireless ad hoc networks have only addressed the issue of performance degradation due to temporarily broken routes, which results in TCP inability to distinguish between losses due to link failures or congestion. This problem tends to become more serious as network mobility increases. We tackle the equally important capture problem to which there has been little or no solution, and is present mostly in static and low mobility multihop wireless networks. This is a result of the interplay between the MAC layer and TCP backoff policies, which causes nodes to unfairly capture the wireless shared medium, hence preventing neighboring nodes to access the channel. This has been shown to have major negative effects on TCP performance comparable to the impact of mobility. We propose a novel algorithm, called COPAS (COntention-based PAth Selection), which incorporates two mechanisms to enhance TCP performance by avoiding capture conditions. First, it uses disjoint forward (sender to receiver for TCP data) and reverse (receiver to sender for TCP ACKs) paths in order to minimize the conflicts of TCP data and ACK packets. Second, COPAS employs a dynamic contention-balancing scheme where it continuously monitors and changes forward and reverse paths according to the level of MAC layer contention, hence minimizing the likelihood of capture. Through extensive simulation, COPAS is shown to improve TCP throughput by up to 90% while keeping routing overhead low.

Bluetooth is a promising wireless technology aiming at supporting electronic devices to be instantly interconnected into short-range ad hoc networks. Previous studies show that since Bluetooth operates in the unlicensed 2.45 GHz frequency band, the presence of multiple piconets in the vicinity creates intermittent interference on signal reception which, in turn, degrades the overall throughput of the network. In order to cope up with this interference source, this paper proposes a sophisticated interference aware Bluetooth segmentation algorithm (IBLUES), where Bluetooth packet types are selected depending on the packet success probability, which is calculated based on the interference generated by multiple piconets. Among other things, we show that when the number of bridge nodes are larger than five the propagation delay between piconets increases rapidly. We have also observed a drastic overhead in the current Bluetooth piconet switching procedure and conclude that future enhancements to this procedure are crucial to efficiency of Bluetooth-based ad hoc networking.

The emergence of Bluetooth as a default radio interface has allowed handheld electronic devices to be instantly interconnected as ad-hoc networks. These short range ad-hoc wireless networks, called piconets, operate in the unlicensed 2.45 GHz ISM (industrial-scientific-medical) band where up to eight devices may be used to configure single or overlapping piconets. As all piconets operating in the same frequency band, the presence of multiple piconets creates interference on signal reception. This paper employs a signal capture model to study the piconet MAC performance, taking inter-piconet interference into consideration. Furthermore, extensive simulation is performed to validate the throughput obtained from our model. These results indicate that Bluetooth throughput is sensibly affected by multiple piconet interference.

The emergence of Bluetooth as a default radio interface allows handheld electronic devices to be instantly interconnected into ad hoc networks. These short range ad-hoc wireless networks, called piconets, operate in the unlicensed 2.45 GHz ISM (Industrial-Scientific-Medical) band where up to eight devices may be used to configure single or overlapping piconets. This creates interference on the device from other devices operating in the same frequency band including microwaves and devices enabling various wireless LAN standards. This paper uses a signal capture model to study piconet MAC performance. Furthermore, simulations are used to validate the throughput obtained from this model. These results reveal important performance implications of the effect of inter-piconet interference on throughput.

The conventional approach to reliable multicast in computer networks relies on the retransmission on demand of lost packets. Existing multicast protocols adopt a static packet retransmission scheme (unicast or multicast) to retransmit these packets often leading to performance loss due to wasting bandwidth resources. This is worse if we consider the limited bandwidth resources wireless interfaces currently offer. Therefore, careful continuous monitoring and control is fundamental in these wireless mobile environments. This paper looks at solutions to the retransmission problem while taking into consideration network topology and the number of fixed and mobile users. Precise conditions and rules for packet retransmission are set taking into account the dynamics of the network state. Finally, this algorithm has been incorporated into a reliable multicast protocol with support to mobile users, known as the reliable mobile multicast protocol (RM2), for performance analysis.