Search results for "Telecommunications link"
showing 10 items of 71 documents
Analysis of duplexing modes in the IEEE 802.16 wireless system
2010
The IEEE 802.16 standard defines two main duplexing modes: Time Division Duplexing (TDD) and Frequency Division Duplexing (FDD). The FDD can be divided further into Full-FDD (F-FDD) and Half-FDD (H-FDD). F-FDD requires full duplexing support from subscriber stations and works with two frequency bands. TDD operates a single frequency band, but it does not need full-duplexing support. H-FDD is a combination of these: it works with two frequency bands and does not require full-duplexing support. The cost of this is a more complicated scheduling and added overhead. Still, H-FDD might be the only possible duplexing mode in some occasions. In this paper, these duplexing modes are compared and the…
Increasing the VoIP Capacity through MAP Overhead Reduction in the IEEE 802.16 OFDMa Systems
2010
One of the main issues with supporting VoIP service over 802.16 networks is the signalling overhead caused by the downlink MAP messages due to frequent transmissions and small packets. To decrease the MAP overhead, the 802.16 standard proposes some mechanisms, such as the compressed MAP and sub-MAPs. In this paper, we show by means of extensive dynamic simulations that sub-MAPs can reduce dramatically the signalling overhead associated with VoIP traffic and significantly improve overall VoIP capacity. At the same time, since sub-MAPs are more sensitive to packet drops, they tend to increase the number of HARQ retransmissions in downlink and transmission delays in the uplink direction.
Adaptive contention resolution parameters for the IEEE 802.16 networks
2007
In the IEEE 802.16 networks, the base station allocates resources to subscriber stations based on their QoS requirements and bandwidth request sizes. A subscriber station can send a bandwidth request when it has an uplink grant allocated by the base station or by taking part in the contention resolution mechanism. This paper presents analytical calculations for parameters that control the contention resolution process in the IEEE 802.16 networks. In particular, the backoff start/end values and the number of request transmission opportunities are considered. The simulation results confirm the correctness of theoretical calculations. They also reveal that the adaptive parameter tuning results…
Low‐complexity detection for uplink massive MIMO SCMA systems
2020
Paid Open Access UNIT agreement
Personal exposure to radio-frequency electromagnetic fields in Europe: Is there a generation gap?
2018
Background: Exposure to radiofrequency electromagnetic fields (RF-EMF) from mobile communication technologies is changing rapidly. To characterize sources and associated variability, we studied the differences and correlations in exposure patterns between children aged 8 to 18 and their parents, over the course of the day, by age, by activity pattern, and for different metrics of exposure. Methods: Using portable RF-EMF measurement devices, we collected simultaneous real-time personal measurements of RF-EMF over 24 to 72 h in 294 parent-child pairs from Denmark, the Netherlands, Slovenia, Switzerland, and Spain. The devices measured the power flux density (mW/m(2)) in 16 different frequency…
Resource allocation for OFDMA systems with multi-cell joint transmission
2012
This paper considers the downlink resource allocation of a coordinated multi-cell cluster in OFDMA systems with universal frequency reuse. Multi-cell joint transmission is considered via zero-forcing precoding. Furthermore, joint optimization of the user selection and power allocation across multiple subchannels and multiple cells is studied. The objective is to maximize the weighted sum rate under per-base-station power constraints. Based on general duality theory, two iterative resource allocation algorithms are proposed and compared with the optimal solution, which requires an exhaustive search of all possible combinations of users over all subchannels. Simulation results show that the t…
Joint Optimization of Detection Threshold and Resource Allocation in Infrastructure-based Multi-band Cognitive Radio Networks
2012
[EN] Consider an infrastructure-based multi-band cognitive radio network (CRN) where secondary users (SUs) opportunistically access a set of sub-carriers when sensed as idle. The carrier sensing threshold which affects the access opportunities of SUs is conventionally regarded as static and treated independently from the resource allocation in the model. In this article, we study jointly the optimization of detection threshold and resource allocation with the goal of maximizing the total downlink capacity of SUs in such CRNs. The optimization problem is formulated considering three sets of variables, i.e., detection threshold, sub-carrier assignment and power allocation, with constraints on…
Joint LMMSE equalizer for HSDPA in full-rate space time transmit diversity schemes
2005
This contribution presents a joint linear minimum mean square error (LMMSE) equalizer for full-rate space-time transmit diversity multi-code schemes based on W-CDMA, featuring two and four transmit antennas. Specifically, high-rate, high load systems are targeted, in order to analyze the high speed downlink packet access (HSDPA) of 3GPP Release 6. We derive an equivalent transmission scheme to equalize the received sufficient statistic in a single stage. To reduce the effects of multipath and multiuser interference, and to provide spatial and frequency diversity at the receiver, an LMMSE equalizer is employed. Computer simulations confirm that the proposed schemes achieve robust performance…
Multicast delivery of file download services in 3G mobile networks with MBMS
2008
This article investigates the efficient transmission of file download services to several users simultaneously in 3G mobile networks with HSDPA (High-Speed Downlink Packet Access) and MBMS (Multimedia Broadcast Multicast Services). HSDPA supports high speed point-to-point (p-t-p) transmissions (up to several Mb/s), whereas with MBMS the same content can be transmitted with a point-to-multipoint (p-t-m) connection to multiple users in a unidirectional fashion. Multicast delivery can be implemented through only p-t-p transmissions with HSDPA, a single p-t-m transmission with MBMS, or using both jointly in a hybrid approach by employing HSDPA for error repair of the MBMS p-t-m transmission. We…
Adapting Downlink Power in Fronthaul-Constrained Hierarchical Software-Defined RANs
2017
Abstract The proof-of-concept software-defined radio access network (RAN) is not flexible enough due to the inherent delay and the necessity of high-capacity fronthaul links. We are hence motivated to propose a hierarchical software-defined RAN architecture, over which the base stations (BSs) are abstracted into multiple virtual local controllers while these local controllers are administered by a high-level controller. Under such a hierarchical network architecture, we particularly investigate in this paper how to adapt the BS transmit power over a long term according to the network dynamics under the constraints of mobile user queue stability and limited fronthaul capacity. We first formu…