The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
A number of rate adaptation protocols have proposed using instantaneous channel quality to select the physical layer data rate. However, due to fast channel variations, even aggressive probing of the channel before each data packet is often unable to offer an up-to-date notion of channel quality. In this paper, we propose a coherence-aware channel indication and prediction algorithm for rate adaptation...
Cognitive Radio Network (CRN) technology allows secondary users (SUs) to transmit data exploiting the wireless resources not utilized by licensed primary users (PUs). Channel exploration by SUs for finding transmission opportunities incurs non-negligible costs and is a key challenge in successful operation of CRN. In this paper, we investigate the joint effect of channel exploration order and stopping...
Cognitive Radio Networks (CRNs) aim to maximize the utilization of existing wireless channels by allowing secondary users (SUs) to transmit when licensed primary users (PUs) are not using the same channels. An SU monitors the CRN channels, sensing PU presence to avoid interference and estimating the link quality before transmitting. It stops when one or more available channels with satisfactory link...
In the last years we are seeing the increasing presence of multimedia applications together with a wide variety of terminals, from the PCs to the notebooks, from the smartphones to the tablets. In order to exploit such advanced services, ubiquitous and broadband connections are required. While urban or suburban areas can be covered by using terrestrial wireless broadband networks, there are several...
In this paper, we study ARQ feedback in the context of two-way wireless communications. In particular, we consider two nodes which wish to exchange data over a frequency division duplex, time-varying wireless additive white Gaussian noise with Rayleigh fading, channel. In two-way scenarios, unlike the more well studied one-way data scenarios, the data and resources allocated to feedback and channel...
Adaptive pilot patterns offer high throughput gains. However, their application requires additional feedback. In this paper, we investigate the feedback requirements for adaptive pilot patterns applied in Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing systems. The main goal is to support a wide range of Doppler spreads and Root Mean Square (RMS) delay spreads while keeping...
A cognitive user (CU) operates as a secondary user of a cognitive channel. Before transmission CU samples the channel until it estimates that the channel can be accessed successfully. When CU transmits a packet, it may nevertheless be unsuccessful because its estimate was wrong; CU knows about its failure and stops the ongoing transmission sometime before the transmission ends. Then CU restarts sensing...
OFDM based wireless communication systems split the available frequency band into so-called sub-carriers, and data is transmitted on each of these sub-carriers in parallel. With frequency selective fading, sub-carriers may experience different channel qualities. Thus, choosing a different modulation and coding scheme (MCS) per sub-carrier improves performance. However, this comes at an increase in...
To reduce the feedback load of OFDM-based wireless multicast systems, an opportunistic feedback scheme (OFS) is proposed. OFS aims to only feed the key channel gains that can significantly affect the system throughput back to the base station (BS). By mathematical derivation, the key channel gains are proved to belong to a channel gain interval, which can be estimated by a proposed statistical method...
In Cognitive Radio Networks (CRNs) secondary users (SUs) are allowed to transmit data exploiting the wireless resources (i.e., channels) not utilized by licensed primary users (PUs). Efficient resource discovery for finding available channels is a key aspect for successful SUs' operation. In this paper we investigate and propose different algorithms to discover the best CRN channels that, exploited...
Flexible channels enable Access Points (AP) and clients to determine channel widths and their center frequencies. The key challenge in flexible channels is how to determine proper channel width and center frequency for each link demands such that the overall system throughput could be improved. In this work, we introduce a distributed flexible channel assignment algorithm, DFCA. Different from prior...
In this paper, resource allocation problem with imperfect channel information in cognitive radio networks (CRNs) is studied concerning the multiple description coding (MDC) multicast transmission. The traditional unicast model is extended to MDC multicast in CRNs, which aims to maximize the total received rate of all cognitive radio (CR) users. Primarily, a new auxiliary variable, named as normalized...
This paper presents MIMO/CON, a PHY/MAC cross-layer design for multiuser MIMO wireless networks that delivers throughput scalable to many users. MIMO/CON supports concurrent channel access from uncoordinated and loosely synchronized users. This new capability allows a multi-antenna MIMO access point (AP) to fully realize its MIMO capacity gain. MIMO/CON draws insight from compressive sensing to carry...
Cognitive Radio Networks (CRNs) are designed to increase spectrum utilization by allowing unlicensed secondary users (SUs) to operate over existing wireless channels where primary users (PUs) have license to transmit. An SU searches for channels not currently occupied by PUs, it estimates their link quality and it aggregates the resources found available for transmission, by means of multi-channel...
This work addresses the radio resource allocation (RRA) problem for cooperative relay assisted OFDMA wireless networks. The relays adopt the decode-and-forward protocol and can cooperatively assist the transmission from source to destination. The RRA scheme addresses practical implementation issues of resource allocation in OFDMA networks: the inaccuracy of channel-state information (CSI) available...
This paper introduces a method of modulation and coding scheme (MCS) selection, which is based on channel quality indicator (CQI) feedback. Effective CQI feedback schemes by mapping signal-to-interference plus noise ratio (SINR) to CQI type based on effective SINR mapping (ESM). This paper improves system reliability by optimizing some parameters. The simulation shows optimized effective MCS selection...
Node mobility, signal fading and interference introduce dynamics in wireless channels. In 802.11 wireless networks, there are several transmission rates that can be adaptively selected by the MAC-layer rate control mechanisms to cater for various channel conditions. Accurately estimating the current channel conditions and successfully selecting the appropriate rates at the right time is critical to...
This paper investigates the sensing order problem for multi-user and multi-channel cognitive radio networks. While most of the literature studies focus on the sensing order for a single user, we consider the scenario in which multiple secondary users sequentially sense and access the channel according to their individual sensing orders. In multi-user case, channel access collisions among secondary...
The interference rejection combining (IRC) receiver, which can suppress inter-cell interference, is effective in improving the cell edge user throughput, and is required to function effectively in various development scenarios, e.g., in both closed-loop and open-loop multiple input multiple output (MIMO) multiplexing. The IRC receiver is typically based on the minimum mean square error (MMSE) criteria,...
Demands for high throughput and stable service quality are increasing. Frame aggregation mechanisms in IEEE 802.11n wireless local area networks (WLANs) can provide improved throughput, but the effect of A-MSDU decreases significantly in error-prone channels. Therefore, adaptive frame size estimation (FSE) depending on the channel condition is required to maintain the improved throughput. In this...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.