Abstract: Most of the recent wireless LANs, broadband access networks, and digital broadcasting use Orthogonal Frequency Division Multiplexing techniques. In addition, the increasing demand of Data and Internet makes fiber optics an important technology, as fiber optics has many characteristics that make it the best solution for transferring huge frames of Data from a point to another. Radio over fiber is the place where high quality RF is converted to optical signals over single mode fiber. Optimum values for the bias level and the switching voltage for Mach-Zehnder modulator are important for the performance of radio over fiber links. In this paper, we propose a method to optimize the two parameters simultaneously; the bias and the switching voltage point of the external modulator of a radio over fiber system considering RF gain. Simulation results show the optimum gain value under these two parameters.
Abstract: In IEEE 802.11 networks, it is well known that the
traditional time-domain contention often leads to low channel
utilization. The first frequency-domain contention scheme, the time to
frequency (T2F), has recently been proposed to improve the channel
utilization and has attracted a great deal of attention. In this paper, we
present the latest research progress on the weighed frequency-domain
contention. We compare the basic ideas, work principles of these
related schemes and point out their differences. This paper is very
useful for further study on frequency-domain contention.
Abstract: This paper proposes an APPLE scheme that aims at providing absolute and proportional throughput guarantees, and maximizing system throughput simultaneously for wireless LANs with homogeneous and heterogenous traffic. We formulate our objectives as an optimization problem, present its exact and approximate solutions, and prove the existence and uniqueness of the approximate solution. Simulations validate that APPLE scheme is accurate, and the approximate solution can well achieve the desired objectives already.
Abstract: IEEE 802.11a/b/g standards provide multiple
transmission rates, which can be changed dynamically according to the
channel condition. Cooperative communications were introduced to
improve the overall performance of wireless LANs with the help of
relay nodes with higher transmission rates. The cooperative
communications are based on the fact that the transmission is much
faster when sending data packets to a destination node through a relay
node with higher transmission rate, rather than sending data directly to
the destination node at low transmission rate. To apply the cooperative
communications in wireless LAN, several MAC protocols have been
proposed. Some of them can result in collisions among relay nodes in a
dense network. In order to solve this problem, we propose a new
protocol. Relay nodes are grouped based on their transmission rates.
And then, relay nodes only in the highest group try to get channel
access. Performance evaluation is conducted using simulation, and
shows that the proposed protocol significantly outperforms the
previous protocol in terms of throughput and collision probability.
Abstract: It is well-known that in wireless local area networks,
authenticating nodes by their MAC addresses is not secure since it is
very easy for an attacker to learn one of the authorized addresses and
change his MAC address accordingly. In this paper, in order to
prevent MAC address spoofing attacks, we propose to use
dynamically changing MAC addresses and make each address usable
for only one session. The scheme we propose does not require any
change in 802.11 protocols and incurs only a small performance
overhead. One of the nice features of our new scheme is that no third
party can link different communication sessions of the same user by
monitoring MAC addresses therefore our scheme is preferable also
with respect to user privacy.
Abstract: This paper represents an investigation on how exploiting multiple transmit antennas by OFDM based wireless LAN subscribers can mitigate physical layer error rate. Then by comparing the Wireless LANs that utilize spatial diversity techniques with the conventional ones it will reveal how PHY and TCP throughputs behaviors are ameliorated. In the next step it will assess the same issues based on a cellular context operation which is mainly introduced as an innovated solution that beside a multi cell operation scenario benefits spatio-temporal signaling schemes as well. Presented simulations will shed light on the improved performance of the wide range and high quality wireless LAN services provided by the proposed approach.
Abstract: Voice over Internet Protocol (VoIP) is a form of voice
communication that uses audio data to transmit voice signals to the
end user. VoIP is one of the most important technologies in the
World of communication. Around, 20 years of research on VoIP,
some problems of VoIP are still remaining. During the past decade
and with growing of wireless technologies, we have seen that many
papers turn their concentration from Wired-LAN to Wireless-LAN.
VoIP over Wireless LAN (WLAN) faces many challenges due to the
loose nature of wireless network. Issues like providing Quality of
Service (QoS) at a good level, dedicating capacity for calls and
having secure calls is more difficult rather than wired LAN.
Therefore VoIP over WLAN (VoWLAN) remains a challenging
research topic. In this paper we consolidate and address major
VoWLAN issues. This research is helpful for those researchers wants
to do research in Voice over IP technology over WLAN network.
Abstract: In Public Wireless LANs(PWLANs), user anonymity
is an essential issue. Recently, Juang et al. proposed an anonymous
authentication and key exchange protocol using smart cards in
PWLANs. They claimed that their proposed scheme provided identity
privacy, mutual authentication, and half-forward secrecy. In this paper,
we point out that Juang et al.'s protocol is vulnerable to the
stolen-verifier attack and does not satisfy user anonymity.
Abstract: This paper presents a hybrid association control
scheme that can maintain load balancing among access points in the
wireless LANs and can satisfy the quality of service requirements of
the multimedia traffic applications. The proposed model is
mathematically described as a linear programming model. Simulation
study and analysis were conducted in order to demonstrate the
performance of the proposed hybrid load balancing and association
control scheme. Simulation results shows that the proposed scheme
outperforms the other schemes in term of the percentage of blocking
and the quality of the data transfer rate providing to the multimedia
and real-time applications.
Abstract: Partitions can play a significant role in minimising cochannel
interference of Wireless LANs by attenuating signals across
room boundaries. This could pave the way towards higher density
deployments in home and office environments through spatial
channel reuse. Yet, due to protocol limitations, the latest incantation
of IEEE 802.11 standard is still unable to take advantage of this fact:
Despite having clearly adequate Signal to Interference Ratio (SIR)
over co-channel neighbouring networks in other rooms, its goodput
falls significantly lower than its maximum in the absence of cochannel
interferers. In this paper, we describe how this situation can
be remedied via modest modifications to the standard.
Abstract: IEEE has recently incorporated CCMP protocol to provide robust security to IEEE 802.11 wireless LANs. It is found that CCMP has been designed with a weak nonce construction and transmission mechanism, which leads to the exposure of initial counter value. This weak construction of nonce renders the protocol vulnerable to attacks by intruders. This paper presents how the initial counter can be pre-computed by the intruder. This vulnerability of counter block value leads to pre-computation attack on the counter mode encryption of CCMP. The failure of the counter mode will result in the collapse of the whole security mechanism of 802.11 WLAN.