Asymmetrical digital subscriber line (ADSL) an in-depth study

Asymmetrical Digital Subscriber Line (ADSL) is one member of a group of broadband access technologies that uses the existing copper-based local loop of the analog PSTN for high-speed digital data transmission. One feature of ADSL is that it permits analog voice POTS transmissions to continue uninterrupted over the same wiring. Specifically, POTS continues to use the 0 to 4 KHz frequency range of the copper wiring, while ADSL uses bandwidth starting at 25 KHz and extending up to approximately 1.1 MHz for data transmission. The term asymmetrical refers to the fact that data rates downstream (to the user) and upstream (from the user) are not the same. Typical ADSL data rates range from 1.536 to 6.144 Mbps downstream and from 16 to 640 Kbps upstream. Local loop length, wire size, and the presence of devices to improve voice communication such as bridged taps and loading coils all affect ADSL data rates. Digital data is coded by one of two methods: Discrete Multitone Modulation (DMT) or Carrierless Amplitude and Phase Modulation (CAP). Echo control is also accomplished by one of two methods: Frequency Division Multiplexing (FDM) or echo cancellation. This paper consists of four sections: 1) A technical review and comparison of the CAP and DMT line encoding technologies. 2) A market review of the presence of CAP and DMT technologies in customer premise equipment (CPE) such as modems and routers. 3) A review of the POTS physical layer that exists between the ADSL subscriber and the Telco CO, and its impact on ADSL availability and quality of service (QOS). 4) A technical review of the newer, splitterless, G.Lite technolog

Multidimensional Optimized Optical Modulation Formats

This chapter overviews the relatively large body of work (experimental and theoretical) on modulation formats for optical coherent links. It first gives basic definitions and performance metrics for modulation formats that are common in the literature. Then, the chapter discusses optimization of modulation formats in coded systems. It distinguishes between three cases, depending on the type of decoder employed, which pose quite different requirements on the choice of modulation format. The three cases are soft-decision decoding, hard-decision decoding, and iterative decoding, which loosely correspond to weak, medium, and strong coding, respectively. The chapter also discusses the realizations of the transmitter and transmission link properties and the receiver algorithms, including DSP and decoding. It further explains how to simply determine the transmitted symbol from the received 4D vector, without resorting to a full search of the Euclidean distances to all points in the whole constellation

Proceedings of the Mobile Satellite Conference

A satellite-based mobile communications system provides voice and data communications to mobile users over a vast geographic area. The technical and service characteristics of mobile satellite systems (MSSs) are presented and form an in-depth view of the current MSS status at the system and subsystem levels. Major emphasis is placed on developments, current and future, in the following critical MSS technology areas: vehicle antennas, networking, modulation and coding, speech compression, channel characterization, space segment technology and MSS experiments. Also, the mobile satellite communications needs of government agencies are addressed, as is the MSS potential to fulfill them

Proceedings of the Fifth International Mobile Satellite Conference 1997

Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial communications services. While previous International Mobile Satellite Conferences have concentrated on technical advances and the increasing worldwide commercial activities, this conference focuses on the next generation of mobile satellite services. The approximately 80 papers included here cover sessions in the following areas: networking and protocols; code division multiple access technologies; demand, economics and technology issues; current and planned systems; propagation; terminal technology; modulation and coding advances; spacecraft technology; advanced systems; and applications and experiments

Solutions to Mitigate Cross-Phase Modulation Impairment in Coherent Fiber-Optic Communications

In this thesis, methods of exploiting and consequently, mitigating the nonlinearities in Cross-Phase Modulation (XPM) dominated ber-optic communication is suggested using the model provided by Ciena Corporation. An enhanced Bit Error Rate (BER) per Signal to Noise Ratio (SNR) is obtained using the solutions provided in this work compared to the state of the art methods used in Ciena Corporation. Solutions include exploiting the properties of XPM in order to devise methods to detect the received data with less probability of error in optical communication and also to come up with new constellation designs, suitable for XPM-dominated optical channels. Coherent optical communication and specifically, phase-modulated optical communication has received much attention due to its higher spectral efficiency and also better receiver sensitivity. However, due to the optical Kerr effect, two major phase nonlinearities are added to the phase of the received signal at the end of an optical ber link called Self-Phase Modulation (SPM) and XPM. This thesis is focused on XPM dominated ber-optic links and tries to exploit the properties of XPM in order to obtain a better performance compared to the methods in which the cancellation of XPM noise is the main objective. Finally, a constellation design is discussed, considering the model we use in this thesis. Constellation design suitable for optical communication and in particular, XPM-dominated fiber-optic channels, has already been a topic of vast research, but the outcome of such efforts is highly dependant on the model used to produce XPM values. Thus, our work is unique in its own way

The Telecommunications and Data Acquisition Report

Deep Space Network (DSN) progress in flight project support, tracking and data acquisition research and technology, network engineering, hardware and software implementation, and operation is discussed. In addition, developments in Earth-based radio technology as applied to geodynamics, astrophysics and the radio search for extraterrestrial intelligence are reported

Feasibility of a dynamic data rate satellite link for Inmarsat

Inmarsat is a predominantly commercial satellite system fitted on most United States Navy surface vessels including: frigates, cruisers, destroyers, amphibious ships and mine sweepers. It is primarily used for telephone, fax, email, web browsing, and the Global Command and Control System (GCCS). Inmarsat, however, has a very limited data rate. For ships fitted with the latest modem upgrade, Inmarsat provides a meager 128 kbps for support of its numerous functions. To improve upon Inmarsat's limited data rate, this thesis suggests a potential improvement to Inmarsat communications by integrating a dynamic data rate link that maintains the required probability of bit error without exceeding the allocated bandwidth. The results from this thesis show that link margin provisions from the static data rate design are able to support much greater data rates using advanced modulation and forward error correction techniques. The proposed adaptive dynamic link improves the link by measuring channel conditions to determine the fastest data rate for successful communications. When channel conditions are good, the adaptive dynamic link will communicate at a high data rate, and when channel conditions are poor, the dynamic link will communicate at a lower data rate to maintain a target probability of bit error ceiling.http://archive.org/details/feasibilityofdyn109453487US Navy (USN) author.Approved for public release; distribution is unlimited