Member Login

E-mail:    Password:  




 TitleDate AddedCompany
whitepaper Protecting the Robustness of ADSL and VDSL DMT Modems When Applying DSM0000-00-00 Katholieke Universiteit Leuven
  When transmitting data over an ADSL or VDSL link, performance is very important. In order to improve the bit rate that can be achieved over the copper link, a lot of techniques like power backoff (PBO) and dynamic spectrum management (DSM) focus on the crosstalk and try to operate with lower noise margin. Today's ADSL and VDSL modems are very robust. Both in ADSL and VDSL there exist reconfiguration protocols that take care of changing noise environments. The intent of the paper is to know what the impact is of DSM on the robustness of these systems.

Tags: Components		   
whitepaper The Principles of OFDM2001-01-01 PRIMEDIA
  The principles of orthogonal frequency division multiplexing (OFDM) modulation have been in existence for several decades. However, in recent years these techniques have quickly moved out of textbooks and research laboratories and into practice in modern communications systems. The techniques are employed in data delivery systems over the phone line, digital radio and television, and wireless networking systems. This paper will review the fundamentals behind OFDM techniques, and also discuss common impairments and how, in some cases, OFDM mitigates their effect.   
whitepaper Broadband MIMO-OFDM Wireless Communications2004-02-04 Georgia Institute of Technology
  Orthogonal frequency division multiplexing (OFDM) is a popular method for high data rate wireless transmission. OFDM may be combined with antenna arrays at the transmitter and receiver to increase the diversity gain and/or to enhance the system capacity on time-variant and frequency-selective channels, resulting in a multiple-input multiple-output (MIMO) configuration. This paper explores various physical layer research challenges in MIMO-OFDM system design, including physical channel measurements and modeling, analog beam forming techniques using adaptive antenna arrays, space-time techniques for MIMO-OFDM, error control coding techniques, OFDM preamble and packet design, and signal processing algorithms used for performing time and frequency synchronization, channel estimation, and channel tracking in MIMO-OFDM systems.

Tags: Components, Mobile and Wireless		   
whitepaper On the Optimality of the OFDMA Network2004-07-15 University of Washington
  This paper studies the optimality of the OFDMA network. It is proved that in the multiuser multicarrier downlink system with independent decoding, OFDMA is the optimal multiple access scheme. It is also shown that the optimality of OFDMA holds for any adaptive modulation scheme whose Rate-SNR/SINR function can be approximated as a convex function.

Tags: Network Management		   
whitepaper Capacity Analysis on Downlink MIMO OFDMA Systems2004-08-24 University of Washington
  Motivated by the increasing popularity of OFDMA and MIMO, this paper studies the capacity of MIMO enabled OFDMA system under a generic multiuser multicarrier framework. This paper shows that in terms of total system capacity, OFDMA is the optimal downlink scheme for independent decoding receivers. To achieve the capacity bound however, one must solve a multiuser subcarrier allocation and the optimal power allocation jointly. The computational cost for finding the optimal solution is exponential with respect to the number subcarriers and polynomial with respect to the number of users. To alleviate the complexity, we propose two suboptimal subcarrier allocation criteria, namely, the Product-criterion and the Sum-criterion, for OFDMA MIMO systems.   
whitepaper Downlink Radio Resource Allocation for Multi-Cell OFDMA System2003-12-21 University of Washington
  Orthogonal frequency division multiple access (OFDMA) provides a feasible broadband platform where different forms of multiuser diversities (e.g., mutual interference, selective fading channels and bursty traffics) can be efficiently exploited. This paper presents a radio resource control (RRC) scheme for OFDMA systems where dynamic resource allocation is realized at both a radio network controller (RNC) and base stations (BTSs).   
whitepaper Performance of Joint Detection Techniques for Coded MIMO-OFDM and MIMO-MC-CDM2003-05-21 Universität Ulm
  This paper considers a coded transmission over a time-invariant MIMO channel where channel state information is present at the receiver but not at the transmitter. As basic modulation technique OFDM is applied. This paper investigates the performance of the system when spreading in frequency direction is included additionally (MC-CDM). In the case of MIMO-OFDM crosstalk only occurs because of the use of multiple transmit antennas, whereas MIMO-MC-CDM systems are additionally affected by interference among subcarriers.   
whitepaper On the Capacity of the Broadband Relay Networks2004-06-09 University of Washington
  The paper studies the capacity of the OFDM and the OFDMA relay networks. Two relay schemes, amplify-and-forward (AF) relay and decode-and-forward (DF) relay are analyzed and compared for both OFDM and OFDMA relay networks. A relay node selection algorithm is proposed for OFDMA relay network. Numerical results show that under small relay power transmission, AF outperforms DF while the opposite is true when the relay transmission power is high. It is also shown that OFDM relay always outperforms OFDMA relay network, however as the number of relay nodes increases, the gap between the two decreases.

Tags: Components		   
whitepaper PAPR Reduction in OFDM Systems Using Constellation Shaping0000-00-00 University of Waterloo
  Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier transmission technique, which is widely adopted in different communication applications. OFDM prevents Inter Symbol Interference (ISI) by inserting a guard interval and mitigates the frequency selectivity of a multi-path channel by using a simple equalizer. This simplifies the design of the receiver and leads to inexpensive hardware implementations. In systems with a high-speed transmission of data, large delay spreads can seriously limit the system performance due to ISI. Moreover, OFDM offers some advantages in higher order modulations and in the networking operation that position OFDM as the technique of choice for the next generation of wireless networks.   
whitepaper Cross-Layer Optimization of OFDM Systems for 4G Wireless Communications2004-08-16 Aalborg University
  This paper advocates cross-layer optimization over the whole ISO/OSI protocol stack. As an example this paper refers to a system using multiple description coding at application layer combined with orthogonal frequency division multiplexing at the link level to provide robustness against hostile wireless channels. In the proposed optimization design negotiation between application, data link control and physical layer is exploited to increase user quality of service in terms of picture signal to noise ratio and bandwidth efficiency. By means of channel simulation and coding measurements it is shown that this kind of cross layer optimization lead to the best results.

Tags: Components,