The fourth generation broadband concept

Fixed-broadband access technology is evolving from exclusively copper-based solutions to hybrid fiber-copper architectures. This article presents the expected next step in the evolution of broadband systems, which we call the fourth-generation broadband concept. It identifies a technical, infrastructural, and economical niche and describes how the fiber-access network is extended and forked to feed a last and ultimate generation of DSL systems, shown to have gigabit potential. The underlying infrastructural concept is presented, economic aspects are described and discussed, and achievable data rates are calculated.     

1260 nm InGaAs vertical-cavity lasers

The fabrication and performance of highly strained double-quantum well InGaAs/GaAs vertical-cavity lasers with record-long emission wavelength of 1260 nm at room temperature is reported. Depending on device diameter, the minimum threshold current is in the low mA-regime while the maximum output power exceeds 1 mW. The devices work continuous-wave over a wide temperature range of at least 10-120°C     

In-situ resource utilisation manufacturing of optically transparent glass from lunar regolith simulant

Journal of Materials Science - International space agencies are aiming to establish permanent outposts on the lunar surface. For that purpose, new technologies and equipment are being developed...     

An approach to analog mitigation of RFI

Among all noise sources present in wireline transmission systems we focus on one special type: narrowband radio frequency interference generated by radio amateurs (RAM) and broadcast radio stations. This disturbance, characterized by high power and narrow bandwidth, has the potential of overloading the receiver's analog-to-digital converter (ADC). Once the ADC is in saturation, any countermeasure taken in digital domain will fail. A viable way to face this problem is cancellation using the common-mode signal as a reference. This paper describes in detail an adaptive, mixed-signal, narrowband interference canceller employing a modified recursive least-squares algorithm, which is split into an analog and a digital part. The mixed-signal approach enables the circuit to generate an interference-cancelling signal of several MHz while operating the adaptive algorithm at some kilohertz. Simulation as well as measurement results show a steady-state disturbance suppression of about 35 dB. The convergence speed is high enough to protect the ADC from overloading due to time-variant HAM interference     

A time and frequency synchronization scheme for multiuser OFDM

We present a multiuser synchronization scheme for tracking the mobile's uplink time and frequency offsets. It uses the redundancy introduced by the cyclic prefix and does not need additional pilots. We show performance results of an orthogonal frequency division multiplexing (OFDM)-based radio interface based on the universal mobile telecommunication system (UMTS) parameters. For a UMTS-typical mobile channel environment, the performance of a coherent system employing the scheme is virtually indistinguishable from the performance of a perfectly synchronized system. In a differentially modulated system, synchronization errors decrease the system performance by about 0.7 dB compared to a perfectly synchronized system     

Zipper: a duplex method for VDSL based on DMT

We present a new duplex scheme, called Zipper, for discrete multitone (DMT)-based very high bit-rate digital subscriber line (VDSL) systems on copper wires. This scheme divides the available bandwidth by assigning different subcarriers for the upstream and downstream directions. It has high flexibility to divide the capacity between the up and downstream, as well as good coexistence possibilities with other systems such as ADSL. Simulation results show the high bit-rate performance in different environments such as mixed ADSL and VDSL traffic under radio frequency interference and with different background noise sources     

Zipper VDSL: a solution for robust duplex communication overtelephone lines

We overview a digital duplex scheme called Zipper, intended for DMT-based VDSL systems. The Zipper multicarrier duplex scheme represents a breakthrough toward digital implementation of frequency-division duplexing. A duplex scheme is a method to divide the capacity of a line between the upstream and downstream directions. Zipper divides the available bandwidth by assigning different subcarriers for the different directions. As a prerequisite, DMT symbols are extended with an additional cyclic suffix, and are shaped at both the transmitter and receiver. Zipper is characterized by high flexibility and high spectral compatibility with programmable spectrum usage, robustness against frequency-selective impairments such as radio frequency interference and bridge taps, interoperability with ADSL, and high spectral efficiency since no guard bands are needed     

A robust correlation receiver for distance estimation

Many methods for distance estimation, such as the ultrasonic pulse-echo method, involve the estimation of a time-of-flight (TOF). In this paper, a signal model is developed that, apart from the TOF, accounts for an unknown, linear frequency dependent distortion as well as for additive noise. We derive a TOF estimator for this model based on the criteria of maximum likelihood. The resulting receiver can be seen as an extension or generalization of the well known cross-correlation, or “matched filter”, estimator described, e.g., by Nilsson. The novel receiver is found to be more robust against unknown pulse shape distortion than the cross-correlation estimator, giving less biased TOF estimates. Also, bias versus noise sensitivity can be controlled by proper model order selection     

Making MLSD decisions by thresholding the matched filter output

This paper presents an iterative detector that, by thresholding the output of the matched filter, gives maximum-likelihood sequence detector (MLSD) decisions on binary, antipodally modulated symbols that have been corrupted by intersymbol interference and additive Gaussian noise. The detector will make decisions on some, but often not all, of the symbols in a transmitted sequence, and those decisions will be the same decisions as the MLSD would have made. The number of symbols that are detected is stochastic, varying from sequence to sequence. The basis of the detector is a bound on a crossterm of the quadratic form in the log-likelihood function for the transmitted sequence. The detector is simple in structure, consisting of a matched filter and two variable threshold values for each symbol     

MOVPE-grown GaInNAs VCSELs at 1.3 /spl mu/m with conventional mirror design approach

1.3 /spl mu/m oxide confined GaInNAs VCSELs designed using the same design philosophy used for standard 850 nm VCSELs is presented. The VCSELs have doped mirrors, with graded and highly doped interfaces, and are fabricated using production-friendly procedures. Multimode VCSELs (11 /spl mu/m oxide aperture) with an emission wavelength of 1287 nm have a threshold current of 3 mA and produce 1 mW of output power at 20/spl deg/C. The maximum operating temperature is 95/spl deg/C. Emission at 1303 nm with 1 mW of output power and a threshold current of 7 mA has been observed from VCSELs with a larger detuning between the gain peak and the cavity resonance.