256,621 research outputs found
Multiband CSMA/CA with RTS-CTS strategy
We present in this paper a new medium access control (MAC) scheme devoted to
orthogonal frequency division multiple access (OFDMA) systems which aims at
reducing collision probabilities during the channel request period. The
proposed MAC relies on the classical carrier sense multiple access/collision
avoidance (CSMA/CA) protocol with RTS / CTS ("Request To Send" / "Clear To
Send") mechanism. The proposed method focus on the collision probability of RTS
messages exploiting a multi-channel configuration for these messages while
using the whole band for data transmissions. The protocol may be interpreted as
an asynchronous frequency multiplexing of RTS messages. This method achieves
strong performance gains in terms of throughput and latency especially in
crowded networks. Index Terms-Carrier sense multiple access/collision avoidance
(CSMA/CA), multiband, throughput, MAC protocol
When Channel Bonding is Beneficial for Opportunistic Spectrum Access Networks
Transmission over multiple frequency bands combined into one logical channel
speeds up data transfer for wireless networks. On the other hand, the
allocation of multiple channels to a single user decreases the probability of
finding a free logical channel for new connections, which may result in a
network-wide throughput loss. While this relationship has been studied
experimentally, especially in the WLAN configuration, little is known on how to
analytically model such phenomena. With the advent of Opportunistic Spectrum
Access (OSA) networks, it is even more important to understand the
circumstances in which it is beneficial to bond channels occupied by primary
users with dynamic duty cycle patterns. In this paper we propose an analytical
framework which allows the investigation of the average channel throughput at
the medium access control layer for OSA networks with channel bonding enabled.
We show that channel bonding is generally beneficial, though the extent of the
benefits depend on the features of the OSA network, including OSA network size
and the total number of channels available for bonding. In addition, we show
that performance benefits can be realized by adaptively changing the number of
bonded channels depending on network conditions. Finally, we evaluate channel
bonding considering physical layer constraints, i.e. throughput reduction
compared to the theoretical throughput of a single virtual channel due to a
transmission power limit for any bonding size.Comment: accepted to IEEE Transactions on Wireless Communication
On the Stability of Contention Resolution Diversity Slotted ALOHA
In this paper a Time Division Multiple Access (TDMA) based Random Access (RA)
channel with Successive Interference Cancellation (SIC) is considered for a
finite user population and reliable retransmission mechanism on the basis of
Contention Resolution Diversity Slotted ALOHA (CRDSA). A general mathematical
model based on Markov Chains is derived which makes it possible to predict the
stability regions of SIC-RA channels, the expected delays in equilibrium and
the selection of parameters for a stable channel configuration. Furthermore the
model enables the estimation of the average time before reaching instability.
The presented model is verified against simulations and numerical results are
provided for comparison of the stability of CRDSA versus the stability of
traditional Slotted ALOHA (SA). The presented results show that CRDSA has not
only a high gain over SA in terms of throughput but also in its stability.Comment: 10 pages, 12 figures This paper is submitted to the IEEE Transactions
on Communications for possible publication. The IEEE copyright notice applie
A study and experiment plan for digital mobile communication via satellite
The viability of mobile communications is examined within the context of a frequency division multiple access, single channel per carrier satellite system emphasizing digital techniques to serve a large population of users. The intent is to provide the mobile users with a grade of service consistant with the requirements for remote, rural (perhaps emergency) voice communications, but which approaches toll quality speech. A traffic model is derived on which to base the determination of the required maximum number of satellite channels to provide the anticipated level of service. Various voice digitalization and digital modulation schemes are reviewed along with a general link analysis of the mobile system. Demand assignment multiple access considerations and analysis tradeoffs are presented. Finally, a completed configuration is described
RISnet: A Scalable Approach for Reconfigurable Intelligent Surface Optimization with Partial CSI
The reconfigurable intelligent surface (RIS) is a promising technology that
enables wireless communication systems to achieve improved performance by
intelligently manipulating wireless channels. In this paper, we consider the
sum-rate maximization problem in a downlink multi-user
multi-input-single-output (MISO) channel via space-division multiple access
(SDMA). Two major challenges of this problem are the high dimensionality due to
the large number of RIS elements and the difficulty to obtain the full channel
state information (CSI), which is assumed known in many algorithms proposed in
the literature. Instead, we propose a hybrid machine learning approach using
the weighted minimum mean squared error (WMMSE) precoder at the base station
(BS) and a dedicated neural network (NN) architecture, RISnet, for RIS
configuration. The RISnet has a good scalability to optimize 1296 RIS elements
and requires partial CSI of only 16 RIS elements as input. We show it achieves
a high performance with low requirement for channel estimation for geometric
channel models obtained with ray-tracing simulation. The unsupervised learning
lets the RISnet find an optimized RIS configuration by itself. Numerical
results show that a trained model configures the RIS with low computational
effort, considerably outperforms the baselines, and can work with discrete
phase shifts
Performance analysis of 2D-OCDMA system in long-reach passive optical network
International audienceIn this paper, a performance analysis is reported for optical code division multiplexing (OCDM) system for long-reach passive optical network (LR-PON) systems by taking into account multiple access interference (MAI), single-mode fiber (SMF) channel effects and receiver noise. The mathematical model representing the 2-D optical code parameters for different receiver structures used in optical code division multiplexing access (OCDMA) are developed, optimized and implemented using Matlab simulations, where channel imperfections, such as attenuation losses and chromatic dispersion have been considered. In the proposed system configuration, we have investigated the probability of error for Back-to-Back (B2B) with conventional correlation receiver (CCR), SMF with CCR receiver and SMF channel with successive interference cancelation (SIC) receiver. Additionally, SMF channel with SIC receiver system performance has been addressed by taking into account two key metrics, such as BER and Q-factor as function of simultaneous users, and fiber length, respectively. We have managed to substantially improve simultaneous multiuser data transmission over significant fiber lengths without use of amplification, where Q-factor of 6 at fiber length of 190 and 120 km, while a SIC receiver using 5 stages cancelation is employed for 2D prime hop system (2D-PHS) and for 2D hybrid codes (2D-HC), respectively
Modeling Noisy Feedback in Decentralized Self-Configuring Networks
This paper introduces a generalization of the notion of Nash equilibrium (NE), namely quantal response equilibrium (QRE). In the QRE, radio devices choose their transmit/receive configuration taking into account that the estimation of their own performance contains a noise component. Here, it is shown that the notion of QRE neatly models decentralized self-configuring networks (DCSN) where feedback messages are impaired by quantization noise or decoding errors. The main contribution of the paper is twofold. First, we show that under the presence of noise in the estimation expected utility, the notion of NE no longer holds, as players cannot be considered rational. Second, we introduce a learning technique that converges to a QRE in a fully decentralized fashion. We present numerical results in the context of a channel selection problem in a parallel multiple access channel in order to illustrate our theoretical results
- …