907 research outputs found
Multiuser Diversity Gain in Cognitive Networks
Dynamic allocation of resources to the \emph{best} link in large multiuser
networks offers considerable improvement in spectral efficiency. This gain,
often referred to as \emph{multiuser diversity gain}, can be cast as
double-logarithmic growth of the network throughput with the number of users.
In this paper we consider large cognitive networks granted concurrent spectrum
access with license-holding users. The primary network affords to share its
under-utilized spectrum bands with the secondary users. We assess the optimal
multiuser diversity gain in the cognitive networks by quantifying how the
sum-rate throughput of the network scales with the number of secondary users.
For this purpose we look at the optimal pairing of spectrum bands and secondary
users, which is supervised by a central entity fully aware of the instantaneous
channel conditions, and show that the throughput of the cognitive network
scales double-logarithmically with the number of secondary users () and
linearly with the number of available spectrum bands (), i.e., . We then propose a \emph{distributed} spectrum allocation scheme, which does
not necessitate a central controller or any information exchange between
different secondary users and still obeys the optimal throughput scaling law.
This scheme requires that \emph{some} secondary transmitter-receiver pairs
exchange information bits among themselves. We also show that the
aggregate amount of information exchange between secondary transmitter-receiver
pairs is {\em asymptotically} equal to . Finally, we show that our
distributed scheme guarantees fairness among the secondary users, meaning that
they are equally likely to get access to an available spectrum band.Comment: 32 pages, 3 figures, to appear in the IEEE/ACM Transactions on
Networkin
Medium access control protocol design for wireless communications and networks review
Medium access control (MAC) protocol design plays a crucial role to increase the performance of wireless communications and networks. The channel access mechanism is provided by MAC layer to share the medium by multiple stations. Different types of wireless networks have different design requirements such as throughput, delay, power consumption, fairness, reliability, and network density, therefore, MAC protocol for these networks must satisfy their requirements. In this work, we proposed two multiplexing methods for modern wireless networks: Massive multiple-input-multiple-output (MIMO) and power domain non-orthogonal multiple access (PD-NOMA). The first research method namely Massive MIMO uses a massive number of antenna elements to improve both spectral efficiency and energy efficiency. On the other hand, the second research method (PD-NOMA) allows multiple non-orthogonal signals to share the same orthogonal resources by allocating different power level for each station. PD-NOMA has a better spectral efficiency over the orthogonal multiple access methods. A review of previous works regarding the MAC design for different wireless networks is classified based on different categories. The main contribution of this research work is to show the importance of the MAC design with added optimal functionalities to improve the spectral and energy efficiencies of the wireless networks
Security-aware fair transmission scheme for 802.11 based cognitive IoT
Cognitive IoT is exponentially increased because of various real time and robust applications with sensor networks and big data analysis. Each IoT protocol of network layer can be RPL, COAP and so on based on IETF standards. But still collision problems and security-aware fair transmission on top of scalable IoT devices were not solved enough. In the open wireless LAN system based cognitive IoTs, IoT node that is continuously being stripped of its transmission opportunity will continue to accumulate packets to be sent in the butter and spoofing attacks will not allow the data transfer opportunities to be fair. Therefore, in this paper, we propose a method to reduce the average wait time of all packets in the system by dynamically controlling the contention window (CW) in a wireless LAN based cognitive IoT environment where there are nodes that do not have fair transmission opportunities due to spoofing attacks. Through the performance evaluation, we have proved that the proposed technique improves up to 80% in terms of various performance evaluation than the basic WLAN 802.11 based IoT
Optimization of the interoperability and dynamic spectrum management in mobile communications systems beyond 3G
The future wireless ecosystem will heterogeneously integrate a number of overlapped Radio
Access Technologies (RATs) through a common platform. A major challenge arising from the
heterogeneous network is the Radio Resource Management (RRM) strategy. A Common RRM
(CRRM) module is needed in order to provide a step toward network convergence. This work
aims at implementing HSDPA and IEEE 802.11e CRRM evaluation tools.
Innovative enhancements to IEEE 802.11e have been pursued on the application of cross-layer
signaling to improve Quality of Service (QoS) delivery, and provide more efficient usage of
radio resources by adapting such parameters as arbitrary interframe spacing, a differentiated
backoff procedure and transmission opportunities, as well as acknowledgment policies (where
the most advised block size was found to be 12). Besides, the proposed cross-layer algorithm
dynamically changes the size of the Arbitration Interframe Space (AIFS) and the Contention
Window (CW) duration according to a periodically obtained fairness measure based on the Signal
to Interference-plus-Noise Ratio (SINR) and transmission time, a delay constraint and the
collision rate of a given machine. The throughput was increased in 2 Mb/s for all the values of
the load that have been tested whilst satisfying more users than with the original standard. For
the ad hoc mode an analytical model was proposed that allows for investigating collision free
communications in a distributed environment.
The addition of extra frequency spectrum bands and an integrated CRRM that enables spectrum
aggregation was also addressed. RAT selection algorithms allow for determining the gains obtained
by using WiFi as a backup network for HSDPA. The proposed RAT selection algorithm
is based on the load of each system, without the need for a complex management system. Simulation
results show that, in such scenario, for high system loads, exploiting localization while
applying load suitability optimization based algorithm, can provide a marginal gain of up to
450 kb/s in the goodput. HSDPA was also studied in the context of cognitive radio, by considering
two co-located BSs operating at different frequencies (in the 2 and 5 GHz bands) in the
same cell. The system automatically chooses the frequency to serve each user with an optimal
General Multi-Band Scheduling (GMBS) algorithm. It was shown that enabling the access to
a secondary band, by using the proposed Integrated CRRM (iCRRM), an almost constant gain
near 30 % was obtained in the throughput with the proposed optimal solution, compared to a
system where users are first allocated in one of the two bands and later not able to handover
between the bands. In this context, future cognitive radio scenarios where IEEE 802.11e ad hoc
modes will be essential for giving access to the mobile users have been proposed
Cooperative and fair MAC protocols for cognitive radio ad-hoc networks
A secondary user (SU) in multichannel cognitive
radio ad hoc network (CRAHN) has a limited transmission
range, which may raise a hidden multichannel sensing
problem. In addition, CRAHNs can be deployed ubiquitously,
and SUs from any CRAHNs could co-exist utilizing
the spectrum. This situation leads to the fairness issue of
spectrum resource sharing between the SUs. Both cooperative
and fairness issues are important to CRAHN performance.
In this paper, a cooperative and a non-cooperative
multichannel (MC)-MAC protocol is proposed. In order to
address the fairness issue, a fair multichannel (FMC)-MAC
protocol for CRAHN is proposed, which orientates to the
fairness in resource sharing. In this FMC-MAC, the SU
keeps the current backoff (CB) counter when a PU appears
to claim the intended channel. These proposed MAC protocols
are simulated using NS2 and compared with other
protocols. In addition, a mathematical model using Markov
chain is constructed for FMC-MAC and the performance
measures are derived. From results, the MC-MAC protocol
has enhanced the network utilization and the cooperative
scheme has significantly enhanced the packet delivery ratio
and decreased the end-to-end delay of SUs in high traffic.
The cooperative protocol enhances packet delivery ratio up
to 15 % and decreases end-to-end delay down to 32 %,
compared to the non-cooperative one. The FMC-MAC
protocol with other two existing protocols. From the
comparison results, a higher fairness has been shown by
FMC-MAC CB while still maintaining a high throughput
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