[asac][almanews] ALMA Memos 420 and 433 Released

[Stacy Oliver]

ALMA MEMO #4203

Digital Transmission System Signaling Protocol

Robert W. Freund (National Radio Astronomy Observatory)

2002/09/06

Keywords: signaling protocol, digital protocol, digital transmission, parallel data transmittion, optical fiber communication, data
scrambling, virtual parallel bus, OC-192, VPB

The ALMA Digital Transmission System (DTS) transmits digitized IF signals from an antenna to the correlator at the central location.
The digitized data is divided equally across four identical transmission elements. Each element formats the parallel data for serial
transmission over three 10 Gb/s optical fiber channels and converts it back into parallel data at the receiver. This Virtual
Parallel Bus (VPB) system is defined by the channel signaling protocol. The protocol is based upon a 160-bit frame structure using
line coding employing scrambling techniques. The frame consists of a  nchronization word, a sequence word, payload, and a checksum.
Modulo-2 addition of the frame with a pseudo random pattern scrambles the data to provide adequate recovery timing information and a
reduction of low frequency content.

View a pdf version of ALMA Memo #420.
http://alma.aoc.nrao.edu/memos/html-memos/alma420/memo420.pdf

Download a postscript version of ALMA Memo #420.
http://alma.aoc.nrao.edu/memos/html-memos/alma420/memo420.ps

________________________________________________________________________________________________

ALMA MEMO #433

2002: The Driest and Coldest Summer

R. Bustos (CBI Project)

2002/09/06

This memo reports NCEP/NCAR Reanalysis results for the southern hemisphere summer of 2002 (December 2001 - March 2002). The data
shows a very low amount of PWV as well as low temperatures, indicating that it has been the driest and coldest summer for the last
50 years. The results confirm the previous conclusions about interannual variability of PWV during the austral summer and that there
is no climatological trend of increasing PWV for the Chajnantor area. The Reanalysis data of the surface temperature shows a
decrease in average temperatures during the last three years. A direct relationship between the fraction of time when winds from the
east are present and the average amount of PWV is also obtained. As we have previously shown there are two different seasons with
different origins at the site: the summer (mid-December to mid-March) is related to a change in the region's circulation and
presents a high amount of PWV with the presence of easterly winds, and the winter (April to November) is more related to ENSO and
the Pacific Ocean activities.


View a pdf version of ALMA Memo #433.
http://alma.aoc.nrao.edu/memos/html-memos/alma433/memo433.pdf

Download a postscript version of ALMA Memo #433.
http://alma.aoc.nrao.edu/memos/html-memos/alma433/memo433.ps


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