Several emerging wireline and wireless access network technologies exhibit asymmetry in their network characteristics. For instance, cable modem networks exhibit significant bandwidth asymmetry while packet radio networks exhibit media access asymmetry. A high degree of asymmetry can have an adverse effect on the performance of feedbackbased transport protocols. In this article, we study the ef...

In this paper, introduced below are the concepts of digital modulation used in many communication systems today. Techniques described include quadrature phase shift keying (QPSK) and quadrature amplitude modulation (QAM) and how these techniques can be used to increase the capacity and speed of a wireless network. These modulation techniques are the basis of communications for systems like cabl...

We propose and investigate an energy-saving algorithm for DOCSIS-3.0 cable access networks. Numerical simulations indicate a possible 17.4% energy-saving for 8000 cable modems, but also reveal a fundamental trade-off between energy and delay. OCIS codes: (060.4250) Networks; (060.4256) Network optimization

This article reviews space-time modem technology for mobile radio applications. We begin with motivations for the use of space-time modems and then brieey discuss the challenges posed by wireless propagation. Next, we develop a signal model for the wireless environment. Channel estimation, equalization , and ltering techniques for space-time modems in the forward and reverse links are then disc...

In this paper we focus on the Round Trip Delay (RTD) time measurement technique which is an easy way to obtain the operating condition information in wireless network (WN). RTD measurement is affected by various parameters of wireless network. We illustrate how these RTD parameters vary (in a telemanagement application) versus distance, baud rates, number of hops, between nodes, using radio mod...

The requirements for the analogue front-end for an ADSL modem are discussed, based upon the modem performance and the signal, noise and distortion-signal flows in the system. The relation between the various blocks and the asymmetric nature of the transmission are highlighted and their impact on the different blocks of the analog front end is indicated. The SNR specification of the A/D converte...

Higher Performance A DMT modem has shown in theory and practice that it can provide higher performance than a modem based on traditional SCM. Fig. 1 and 2 compare the throughput analysis of DMT and SCM in the presence of FEXT (far end crosstalk, the most common form of noise in VDSL.) This analysis was done using the assumptions in Table 1. Margin and throughput enhancements of DMT over SCM are...

Autonomous underwater vehicles (AUVs) are increasingly being considered for remotely supervised missions, primarily for routine subsea inspection tasks currently performed by tethered remotely operated vehicles (ROVs). This project is a step in the development of a high speed, networked wireless communication capability for AUVs using MIT Sea Grant's softwaredefined Reconfigurable Modem (R-Mode...

In this paper, we present a new approach to the digitization and compression of a class of voiceband modem signals. Our approach, which we call baseband residual vector quantization (BRVQ), relies heavily upon the simple structure present in a modem signal. After the signal is converted to baseband, the magnitude sequence and the sequence of residuals obtained when the phase within each baud of...