On-line algorithm for optimizing throughput performance of wireless LANs

In this paper the bit error probability of the SFH/MFSK system in presence of wideband and tone interference in a fading environment is evaluated. Simultaneous license-free operation of tone-like applications, Frequency Hopping (FH), and Direct Sequence (DS) based LAN clusters is assumed to be the prime interference facing the subject FH wireless LAN (of the IEEE 802.11 standard). The wideband DS interference is considered to have a sinc2() shape Power Spectral Density (PSD) centered at the middle of FH signal band and tone interferers are assumed to be spread over the whole FH band of the intended signal. Assumptions of slow non-selective fading along with slow hopping justify a quasi-static treatment. Results shows that the FH system is more sensitive to tone interference and fading and less sensitive to wideband interference variations. The paper sheds light on the performance of wireless LAN operation in the unlicensed free band where many other LANs may exist.

In this paper, we propose a novel scheme to improve the performance of wireless local area networks (WLANs) in error-prone environment. The key idea of the scheme is to partition a frame into several blocks, and then to retransmit only the blocks that encountered errors in the previous transmission. To evaluate the performance of the scheme, we also develop an analytical model to analyze the saturated throughput performance. Extensive simulation and analysis results show that, 1) the proposed scheme can significantly improve the throughput performance of WLANs in error-prone conditions; 2) an optimum block size can lead to the maximum saturated throughput; 3) with an appropriate block size, the throughput can increase with the increase of the size of a frame, even in error-prone environment; and 4) the analytical results are highly accurate.

WLANs based on 802.11 standards are rapidly becoming popular in computer networks. Despite the advantages that have been obtained from this technology, its performance in terms of throughput, response time and security affected by many environmental factors such as distance, blockage, authentication mechanism and type of encryption used during the authentication and the data transmission. There are other security issues such as vulnerability to attack by the man-in-the-middle (MiM) attack which becomes a great concern for users and owners. However, the focus of this paper is for testing the WLAN performance under different conditions. The test results and recommendation can be used by designer and networks users to understand the limitation and how to improve the use of WLAN to optimize its capability. It is clear from the results obtained during the test, that WLAN response time is more affected by network load and very little effect by the size of encryption of WEP used in WLAN. The signal strength is very well affected by distance and blockage, which also affects the throughput. However, the throughput would be affected more with network load

Extended EDCA for delay guarantees in wireless local area networks

In wireless local area networks (WLANs), link-layer multicast is a promising technology for many multimedia applications, e.g., video conference, as multicast frames can reach multiple clients simultaneously. However, the efficiency of multicast in WLANs is unsatisfactory since multicast frames are transmitted at low data rates to reach clients with poor channel quality. Moreover, the reliability of multicast cannot be guaranteed either, as multicast transmissions are not acknowledged. Some recent works have utilized smart antennas to improve multicast performance. But most of them require customized hardware and are not designed for the latest IEEE 802.11 standard, 802.11n WLANs. In this paper, we consider link-layer multicast in 802.11n WLANs with smart antennas. We partition clients into several groups, then select an antenna pattern from smart antennas and a multicast rate for each group, and transmit the same frame to each group. We first examine the gain of smart antennas and reliability of various 802.11n data rates for multicast in indoor WLANs via experiments. We then present the system model for multicast over smart antennas and formulate the problem into a mixed integer program. After that, we propose an optimal algorithm for the mixed integer program, under the condition that the packet reception ratio (PRR) of all antenna patterns and data rates is known for every client. As clients join and leave the network frequently and the wireless channel is time varying, we also propose an on-line algorithm that is able to adapt the partition of clients, antenna pattern and multicast rate for each group dynamically, based on PRR reports from clients. We have implemented the on-line algorithm on off-the-shelf WLAN products and conducted extensive experiments to evaluate the performance. The results show that the proposed algorithm can significantly improve multicast throughput compared to other strategies, and at the same time guarantee high PRR for all clients.

In the present paper, we propose a broadcast ARQ protocol based on the concept of index coding. In the proposed scenario, a server wishes to transmit a finite sequence of packets to multiple receivers via a broadcast channel with packet erasures until all of the receivers successfully receive all of the packets. In the retransmission phase, the server produces a coded packet as a retransmitted packet based on the side-information sent from the receivers via feedback channels. A notable feature of the proposed protocol is that the decoding process at the receiver side has low decoding complexity because only a small number of addition operations are needed in order to recover an intended packet. This feature may be preferable for reducing the power consumption of receivers. The throughput performance of the proposed protocol is close to that of the ideal FEC throughput performance when the erasure probability is less than 0.1. This implies that the proposed protocol provides almost optimal throughput performance in such a regime.

A performance analysis of block ACK scheme for IEEE 802.11e networks

With the rapid proliferation of broadband wireless services, it is of paramount importance to understand how fast data can be sent through a wireless local area network (WLAN). Thanks to a large body of research following the seminal work of Bianchi, WLAN throughput under saturated traffic condition has been well understood. By contrast, prior investigations on throughput performance under unsaturated traffic condition was largely based on phenomenological observations, which lead to a common misconception that WLAN can support a traffic load as high as saturation throughput, if not higher, under nonsaturation condition. In this paper, we show through rigorous analysis that this misconception may result in unacceptable quality of service: mean packet delay and delay jitter may approach infinity even when the traffic load is far below the saturation throughput. Hence, saturation throughput is not a sound measure of WLAN capacity under nonsaturation condition. To bridge the gap, we define safe-bounded-mean-delay (SBMD) throughput and safe-bounded-delay-jitter (SBDJ) throughput that reflect the actual network capacity users can enjoy when they require finite mean delay and delay jitter, respectively. Our earlier work proved that in a WLAN with multi-packet reception (MPR) capability, saturation throughput scales superlinearly with the MPR capability of the network. This paper extends the investigation to the nonsaturation case and shows that superlinear scaling also holds for SBMD and SBDJ throughputs. Our results here complete the demonstration of MPR as a powerful capacity-enhancement technique for WLAN under both saturation and nonsaturation conditions.

Over the past few years, mobile networks have emerged as a promising approach for future mobile IP applications. With limited frequency resources, designing an effective MAC (Medium Access Control) protocol is a hot challenge. IEEE 802.11b/g/a/n networks are currently the most popular wireless LAN products on the market [1]. The conventional IEEE 802.11b and 802.11g/a specification provide up to 11 and 54 Mbps data rates, respectively. However, the MAC protocol that they are based upon is the same and employs a CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) protocol with binary exponential back-off. IEEE 802.11 DCF (Distributed Coordination Function) is the de facto MAC protocol for wireless LAN because of its simplicity and robustness [2,3]. Therefore, considerable research efforts have been put on the investigation of the DCF performance over wireless LAN [2]. With the successful deployment of IEEE 802.11a/b/g wireless LAN and the increasing demand for real-time applications over wireless, the IEEE 802.11n Working Group standardized a new MAC and PHY (Physical) layer specification to increase the bit rate to be up to 600 Mbps [3]. The throughput performance at the MAC layer can be improved by aggregating several frames before transmission [3]. Frame aggregation not only reduces the transmission time for preamble and frame headers, but also reduces the waiting time during CSMA/CA random backoff period for successive frame transmissions. The frame aggregation can be performed within different sub-layers. In 802.11n, frame aggregation can be performed either by A-MPDU (MAC Protocol Data Unit Aggregation) or A-MSDU (MAC Service Data Unit Aggregation). Although frame aggregation can increase the throughput at the MAC layer under ideal channel conditions, a larger aggregated frame will cause each station to wait longer before its next chance for channel access. Under errorprone channels, corrupting a large aggregated frame may waste a long period of channel time and lead to a lower MAC efficiency [4]. On the other hand, wireless LAN mobile stations that are defined as the stations that access the LAN while in motion are considered in this chapter. The previous paper analyzed the IEEE 802.11b/g/n MAC performance for wireless LAN with fixed stations, not for wireless LAN with mobile stations [5, 6, 7, 8, 9, 10]. On the contrary, Xi Yong [11] and Ha Cheol Lee [12] analyzed the MAC performance for IEEE 802.11 wireless LAN with mobile stations, but considered only IEEE 802.11 and 802.11g/a wireless LAN specification. So, this chapter summarizes all the reference papers and analyzes the IEEE 802.11b/g/a/n MAC performance for wireless LAN with fixed and mobile stations. In other words, we will present the analytical evaluation of saturation

This paper presents a study of mobile wireless LAN (WLAN) hotspots which are used to provide cellular-WiFi tethering service to personal devices. A dense deployment scenario for fixed and mobile WLAN is described and potential performance problems due to interference are identified. An analytical model for coexisting fixed and mobile WLAN hotspots with heterogeneous traffic is presented. The model is used to evaluate the performance of a mobile WLAN as it transits through a set of densely deployed fixed access points (APs), and performance problems due to lack of frequency coordination are identified. An adaptive channel assignment (ACA) scheme for improving mobile AP performance is proposed and evaluated. It is shown that significant performance gains can be achieved with ACA with maximum absolute and percentage throughput gains up to 1.24 Mbps and 42.8% respectively. We also show that setting the scanning interval in ACA requires consideration of the speed at which the mobile WLAN is moving in order to compensate for the throughput losses during channel scanning.

This paper explores the feasibility of leveraging concepts from deep reinforcement learning (DRL) to enable dynamic resource management in Wi-Fi networks implementing distributed multi-user MIMO (D-MIMO). D-MIMO is a technique by which a set of wireless access points are synchronized and grouped together to jointly serve multiple users simultaneously. This paper addresses two dynamic resource management problems pertaining to D-MIMO Wi-Fi networks: (i) channel assignment of D-MIMO groups, and (ii) deciding how to cluster access points to form D-MIMO groups, in order to maximize user throughput performance. These problems are known to be NP-Hard and only heuristic solutions exist in literature. We construct a DRL framework through which a learning agent interacts with a D-MIMO Wi-Fi network, learns about the network environment, and is successful in converging to policies which address the aforementioned problems. Through extensive simulations and on-line training based on D-MIMO Wi-Fi networks, this paper demonstrates the efficacy of DRL in achieving an improvement of 20% in user throughput performance compared to heuristic solutions, particularly when network conditions are dynamic. This work also showcases the effectiveness of DRL in meeting multiple network objectives simultaneously, for instance, maximizing throughput of users as well as fairness of throughput among them.

Currently, the IEEE 802.11n wireless local-area network (WLAN) has been broadly deployed world-wide for flexible and high-speed Internet access communications. Since it uses the limited number of partially overlapping channels (POCs) at 2.4 GHz band, the throughput performance is often degraded by interferences from signals of other WLANs. Thus, we have studied throughput drop estimation models for concurrently communicating multiple links under interferences, where the 40 MHz channel bonding (CB) and 20 MHz non-CB are considered separately. We have observed that the simultaneous use of CB and non-CB can improve the performance by enhancing the channel capacity while reducing the interference. In this paper, we study the throughput drop estimation model for concurrently communicating links under coexistence of CB and non-CB in IEEE 802.11n WLAN. The model accuracy is verified by comparing the estimated throughput with the measured one under various network topologies.

Providing quality of service (QoS) for converging traffic in wireless local area network (WLAN) is still a major issue for the researchers and industries. Due to the limited bandwidth and exposure to unpredictable interferences in a wireless environment, efficient management and optimization of the access protocols are essential to provide acceptable QoS for real-time traffic and fairness to best-effort traffic. In this paper, we investigate the throughput and delay performance of the legacy IEEE 802.11 and the 802.11e when carrying converging data in WLAN. We evaluate our recently proposed protocol known as wireless token network protocol (WTN) and show that WTN successfully increases performance of converging traffic in WLAN by, first, decreasing the size of the frames and subframes of the MAC header, and second, by implementing centralized polling to reduce collisions of packets.

In this paper, the performance of carrier sense multiple access with collision avoidance (CSMA/CA) based multi-user MIMO (MU-MIMO) uplink wireless local area networks (WLANs) is analysed. Analytical models are provided to compute the throughput of each user and the total energy consumption in a WLAN with a single user MIMO (SU-MIMO) technique as well as a MU-MIMO technique. By means of the analytical models, the throughput, fairness and energy consumption performances are studied for several WLAN scenarios. The numerical results show that the MU-MIMO technique provides higher throughput than the SU-MIMO technique only when the number of MIMO communication antennas is high and the medium access parameters of the users are configured properly. Further, the SU-MIMO technique is found to be more energy efficient than the MU-MIMO technique. However, the MU-MIMO technique provides better fairness over the SU-MIMO technique.

Wireless Local Area Networks (WLANs) and Wireless Metropolitan Area Networks (WMANs) are two of the main technologies in wireless data networks. WLANs have a short range and aim at providing connectivity to end users. On the other hand, WMANs have a long range and aim at serving as a backbone network and also at serving end users. In this dissertation, we consider the problem of Medium Access Control (MAC) in WLANs and the placement of Relay Stations (RSs) in WMANs. We propose a MAC scheme for WLANs in which stations contend by using jams on the channel. We present analytic and simulation results to find the optimal parameters of the scheme and measure its performance. Our scheme has a low collision rate and delay and a high throughput and fairness performance. Secondly, we present a MAC scheme for the latest generation of WLANs which have very high data rates. In this scheme, we divide the stations into groups and only one station from each group contends to the channel. We also use frame aggregation to reduce the overhead. We present analytic and simulation results which show that our scheme provides a small collision rate and, hence, achieves a high throughput. The results also show that our scheme provides a delay performance that is suitable for real-time applications and also has a high level of fairness. Finally, we consider the problem of placing Relay Stations (RSs) in WMANs. We consider the Worldwide Interoperability for Microwave Access (WIMAX) technology. The RSs are used to increase the capacity of the network and to extend its range. We present an optimization formulation that places RSs in the WiMAX network to serve a number of customers with a pre-defined bit rate. Our solution also provides fault-tolerance by allowing one RS to fail at a given time so that the performance to the users remains at a predictable level. The goal of our solution is to meet the demands of the users, provide fault-tolerance and minimize the number of RSs used.