2,655 research outputs found
Uplink Channel Estimation in WiMAX
WiMAX is an emerging and powerful technology in broadband wireless communications in that it can provide high-speed broadband voice and data ser- vices over distances much greater than Wi-Fi. However, like in any wireless communication system, signal distortion due to channel fading, noise, and Doppler can limit the overall transmission data rate and coverage. To minimize this effect, the receiver must perform channel estimation to remove the effects of the channel. To aid the channel estimation process, known pilot subcarriers are embedded into each OFDM symbol. In this thesis, we will develop and evaluate pilot-assisted channel estimation algorithms for 3 WiMAX modes and features: PUSC (Partial Usage of Subcarriers), AMC (Adaptive Modulation and Coding), and Channel Sounding. Our results show that channel delay spread and signal-to-noise ratio influence the performance of each algorithm and that knowledge of these properties can enhance the system's overall performance
Quantifying Potential Energy Efficiency Gain in Green Cellular Wireless Networks
Conventional cellular wireless networks were designed with the purpose of
providing high throughput for the user and high capacity for the service
provider, without any provisions of energy efficiency. As a result, these
networks have an enormous Carbon footprint. In this paper, we describe the
sources of the inefficiencies in such networks. First we present results of the
studies on how much Carbon footprint such networks generate. We also discuss
how much more mobile traffic is expected to increase so that this Carbon
footprint will even increase tremendously more. We then discuss specific
sources of inefficiency and potential sources of improvement at the physical
layer as well as at higher layers of the communication protocol hierarchy. In
particular, considering that most of the energy inefficiency in cellular
wireless networks is at the base stations, we discuss multi-tier networks and
point to the potential of exploiting mobility patterns in order to use base
station energy judiciously. We then investigate potential methods to reduce
this inefficiency and quantify their individual contributions. By a
consideration of the combination of all potential gains, we conclude that an
improvement in energy consumption in cellular wireless networks by two orders
of magnitude, or even more, is possible.Comment: arXiv admin note: text overlap with arXiv:1210.843
Design and implementation of an OFDMA-TDD physical layer for WiMAX applications
[Abstract]: This work describes the design, implementation, and performance evaluation of an orthogonal frequency division multiple access (OFDMA) time-division duplexing (TDD) physical layer (PHY) compliant with the worldwide interoperability for microwave access (WiMAX) standard using a costeffective software-defined radio (SDR) platform containing field programmable gate array (FPGA) and digital signal processor (DSP) modules. We show that the proposed SDR architecture is capable of supporting the wide variety of configuration options described in the WiMAX standard while fulfilling the stringent requirements of WiMAX OFDMA TDD PHYs. The architecture allows for the implementation of all TDD functionalities in the downlink and the uplink at both the base station and the mobile station. The proposed design is shown to efficiently use the available FPGA and DSP resources. We also carried out specific experiments that take into account the frame and the downlink map messages detection over ITU-R wireless channel models to illustrate the performance of the proposed design. Finally, we discuss the utilization of the proposed hardware architecture to implement the wirelessMAN-advanced air interface.This work has been partially supported by Indra Sistemas S.A., the Spanish Ministry of Defence with the technical direction of PEC/ITM under grant DN8644-COINCIDENTE, MINECO of Spain under grant TEC2010-19545-C04-01 and Xunta de Galicia, Spain, under grant 2012/287. The authors wish to thank J. M. Camas-Albar from Indra Sistemas S.A. for his help.Xunta de Galicia; 2012/28
Capacity analysis of reservation-based random access for broadband wireless access networks
AbstractâIn this paper we propose a novel model for the capacity analysis on the reservation-based random multiple access system, which can be applied to the medium access control protocol of the emerging WiMAX technology. In such a wireless broadband access system, in order to support QoS, the channel time is divided into consecutive frames, where each frame consists of some consequent mini-slots for the transmission of requests, used for the bandwidth reservation, and consequent slots for the actual data packet transmission. Three main outcomes are obtained: first, the upper and lower bounds of the capacity are derived for the considered system. Second, we found through the mathematical analysis that the transmission rate of reservationbased multiple access protocol is maximized, when the ratio between the number of mini-slots and that of the slots per frame is equal to the reciprocal of the random multiple access algorithmâs transmission rate. Third, in the case of WiMAX networks with a large number of subscribers, our analysis takes into account both the capacity and the mean packet delay criteria and suggests to keep such a ratio constant and independent of application-level data traffic arrival rate
Mobile WiMAX system performance â simulated versus experimental results
This paper addresses the downlink performance of mobile WiMAX operating at 2.3GHz in an urban environment. The analysis includes a comparison of simulated and experimental results. Simulated packet error rate (PER) versus Signal to Noise Ratio (SNR) graphs are generated on a per link-speed basis using a fully compliant 512 carrier mobile WiMAX simulator. Experimental data is gathered using a carrier-class basestation, a mobile-WiMAX enabled laptop, and a suite of application layer logging software. An H264 AVC encoder and IP packetisation unit is used to transmit video to a mobile client. Results show strong agreement in terms of simulated and captured PER. Using this data, the downlink operating range is evaluated as a function of the Effective Isotropic Radiated Power (EIRP) and path loss exponent. Results indicate that at low EIRP (32 dBm) the expected outdoor operating range is around 200-400m. Applying the UK OFCOM regulations for licensed operation in the 2.5GHz band, downlink operation in excess of 2km can be achieved
Real-time validation of a SDR implementation of TDD WiMAX standard
[Abstract]: This paper focuses on the validation of an innovative software-
defined radio architecture for a WiMAX system based
on commercially available field-programmable gate array
and digital signal processor modules. We provide a realtime
implementation of a standard-compliant time-division
duplex physical layer including a mobile and a base station
as well as downlink and uplink communications, thus obtaining
a full-featured physical layer. Additionally, a set of
different configurations are supported as described in the
standard and in the WiMAX Forum. The main contribution
of the paper consists in a reproducible and repeatable validation
of the implementation in representative scenarios. At
the same time, a characterization of the performance exhibited
by the system is provided based on bit error rate measurements
carried out using a custom-made, real-time channel
emulator.This work has been partially supported by Indra Sistemas
S.A. and the Spanish Ministry of Defence with the technical
direction of PEC/ITM under grant DN8644-COINCIDENTE. The authors wish to thank J. M. Camas-
Albar from Indra Sistemas S.A. for his help.
This work has been additionally funded by Xunta de
Galicia, Ministerio de Ciencia e InnovaciĂłn of Spain, and
FEDER funds of the European Union under grants with
numbers 10TIC003CT, 09TIC008105PR, TEC2010-19545-
C04-01, and CSD2008-00010.Xunta de Galicia; 10TIC003CTXunta de Galicia; 09TIC008105P
- âŠ