1,721,219 research outputs found
Performance of UMTS packet service over dedicated channels (DCH)
No full textThe provision of high speed packet data services in an efficient way is probably the most important challenge for UNITS since this can give an advantage with respect to second generation systems. The efficiency mainly depends on the radio interface and since it is characterized by a great flexibility it is of utmost importance to investigate the effect of different configurations on the system performance. In this paper we evaluate the performance of packet data services over downlink dedicated channels (DCH) by means of detailed simulations. Due to the traffic variability, ARQ mechanism and dosed loop power control the system behavior is quite complex and not so easily predictable as with constant rate services such as voice. We study the effect of several parameters (spreading factor, code rate, channel setup delay, etc.) on the system capacity by means of the delay-throughput curves. We show that the setting of parameters may be critical for system capacity and stability. For this reason we propose a flow control mechanism which is able to guarantee stability and to make the system capacity almost independent of channel rates
Performance of UMTS Packet Data Services over dedicated Channels (DCH)
No full textThe provision of high speed packet data services in an efficient way is probably
the most important challenge for the UniversalMobile Telecommunications System
(UMTS) since this can give an advantage over second generation systems.
The efficiency depends mainly on the radio interface due to its great flexibility.
It is of utmost importance to investigate the effect of different configurations on
the system performance. In this paper we evaluate the performance of packet
data services over downlink dedicated channels (DCH) by means of detailed
simulations. Due to the traffic variability, Automatic Repeat reQuest (ARQ)
mechanism and closed loop power control the system behavior is quite complex
and not so easily predictable as with constant rate services such as voice. We
study the effect of several parameters (spreading factor, code rate, channel setup
delay, etc.) on the system capacity by means of the delay-throughput curves.
We show that the setting of parameters may be critical for system capacity and
stability. For this reason we propose a flow control mechanism which is able to
guarantee stability and enable the system capacity to be almost independent of
channel rates
Topology optimization for hybrid optical/wireless access networks
No full textHybrid Wireless–Optical Broadband Access Networks (WOBANs) are gauging momentum as flexible, bandwidth-effective, and cost-effective solutions for providing connectivity to residential users in metropolitan areas. In this work, we address the issue of designing the topology of deployed WOBANs. Namely, we consider the case where the coverage of a Ethernet-based Passive Optical Network (EPON) is extended by an additional wireless segment which features multi-hop wireless links operated either according to the IEEE 802.11 standard, or to the IEEE 802.16 one. We propose a mathematical programming model which optimizes the overall WOBAN topology in terms of deployment cost, while accounting for the specific traffic requirements of the residential users, and the specific fea- tures of the technological components. The potentials of the proposed model are show- cased by deriving and commenting numerical results obtained when planning realistic WOBAN scenarios
Performance of W-CDMA UMTS radio access interface with mixed traffic
No full textThe provision of multimedia services to mobile users is one of the main goals of Third Generation (3G) systems. The traffic being transferred within 3G mobile networks will be composed by different information flows with various constraints on the required QoS (bit rate, delays, etc...). In order to reach such a goal, 3G standardization bodies have designed highly-flexible radio interfaces, characterized by a great number of physical parameters to be set by the operators. UMTS (Universal Mobile Telecommunication System) offers both circuit switched and packet switched transfer mode, and within each transfer mode, different QoS can be achieved by properly setting physical parameters such as the speed of physical channels, the power control scheme, the rate of the FEC protecting code, etc. In this paper we give an evaluation of the performance of W-CDMA UMTS radio access network (UTRA) when providing access to multimedia services. In particular, we analyze through detailed simulations a typical scenario where voice calls and web-browsing sessions share the same frequency carrier, the former using the dedicated channels (DCH), the latter being transferred on the downlink shared channel (DSCH)
Impact of mixed voice and data traffic on the UMTS-FDD performance
No full textThe provision of multimedia services to mobile users is one of the main goals of third generation (3G) systems. The traffic being transferred within 3G mobile networks will be composed by different information flows with various constraints on the required QoS (bit rate, delays, etc...). In order to reach such a goal, 3G standardization bodies have designed highly-flexible radio interfaces, characterized by a great number of physical parameters to be set by the operators. UMTS (Universal Mobile Telecommunication System) offers both circuit switched and packet switched transfer mode, and within each transfer mode, different QoS can be achieved by properly setting physical parameters such as the speed of physical channels, the power control scheme, the rate of the FEC protecting code, etc. We give an evaluation of the performance of W-CDMA UMTS radio access network (UTRA) when providing access to multimedia services. In particular, we analyze through detailed simulations a typical scenario where voice calls and Web-browsing sessions share the same frequency carrier, the former using the dedicated channels (DCH), the latter being transferred on the downlink shared channel (DSCH)
A New Outlook on Routing in Cognitive Radio Networks: Minimum Maintenance Cost Routing
No full textCognitive Radio Networks (CRNs) are composed of frequency-agile radio devices that allow licensed (primary) and unlicensed (secondary) users to coexist, where secondary users opportunistically access channels without interfering with the operation of primary ones. From the perspective of secondary users, spectrum availability is a time varying network resource over
which multi-hop end-to-end connections must be maintained.
In this work, a theoretical outlook on the problem of routing
secondary user flows in a CRN is provided. The investigation
aims to characterize optimal sequences of routes over which a
secondary flow is maintained. The optimality is defined according
to a novel metric that considers the maintenance cost of a route as
channels and/or links must be switched due to the primary user
activity. Different from the traditional notion of route stability,
the proposed approach considers subsequent path selections, as
well.
The problem is formulated as an integer programming optimization model. Properties of the problem are also formally introduced and leveraged to design a heuristic algorithm when information on primary user activity is not complete. Numerical results are presented to assess the optimality gap of the heuristic routing algorithm in realistic CRN scenarios
Radio planning of wireless local area networks
No full textIn this paper we propose mathematical models to tackle the WLAN planning problem. Our approach aims at maximizing the network efficiency by taking into account the inter APs domain interference and the access mechanism. Both the single channel and the multiple channels WLAN planning problems are considered. We give different formulations which capture at different levels of detail the effect of interference on the network efficiency. In order to evaluate the quality of the proposed models, we obtain the optimal solutions for synthetic network instances, and propose heuristics to get suboptimal solutions in a reasonable computation time. We show that the networks planned according to our approach feature higher efficiency than the one planned using classical models, like the minimum cardinality Set Covering Problem (SCP), by privileging network solutions with low power APs installed. The achieved gain reaches 167% in particular network scenarios. Moreover, we test the obtained solutions through simulation and real life testbed implementation; both analyses show that the networks planned with the proposed approaches are the ones with the highest saturation throughput with respect to those configurations obtained with SCP
Link Layer Support for Straming MPEG Video over Wireless Links
No full textStreaming video as a form of media is becoming increasingly popular on the Internet. Real-time media such as video requires delay constraints from the network to ensure good quality at the receiver. While watching a video stream on his portable device connected to the Internet through the last-hop wireless link, the mobile user of tomorrow will expect a good experience. But, the time-varying nature of the wireless link can cause video frames to be dropped/delayed, affecting the quality of video at the receiver. In this paper, we propose a link layer approach to improve the quality of MPEG video streaming over a wireless link. We use Bluetooth as the wireless technology on which to test our scheme. Our results show that the quality of streaming video can be substantially improved with our scheme, particularly in bad channel conditions
Efficiency of Physical Carrier Sensing in Wireless Access Networks
No full textWe propose an analytical approach for evaluating the impact of physical carrier sensing in simple wireless access networks. We describe the system through a time-continuous Markov Chain, and we gather from its solution performance measures in terms of throughput and collision probability. We derive qualitative dimensioning criteria for the carrier sensing itself under different network conditions
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