A System View on SKA Bandwidth Usage

G.W. (Dion) Kant

AAVP Dwingeloo, 14 December 2011

Outline

• Introduction• Overview of main envelope requirements• The concept of a base element• Bandwidth requirements

Introduction

• Details in Document “AA-MID CONCEPT DESCRIPTION”

• Presentation to initiate some discussion• A technology independent approach!

Introduction

• Where are we now?

Design Requirements

• Analysis of /, and Bandwidth.• A technology independent approach!• Select technology after understanding the

repercussions of the requirements

SKA2 / envelope

𝑇 𝑠𝑦𝑠=𝑇 𝑠𝑘𝑦+𝑇 𝑟𝑒𝑐

Consequence for

SKA2 Survey Speed envelope

SKA2 Resulting HPBW

Minimum required bandwidth

• Utilize concept of a base element:• Base element is an antenna element

which provides just the required FOV:– Main-Beam solid angle: – is effective area of base element– #(base) elements required to implement

Minimum required bandwidth

• Total aggregated bandwidth from base elements:

Survey spaced in terms of base elements

Bandwidth from base elements

SKA band (MHz)

Remark (m^2)

(degrees^2)

(MHz)

(THz)

70 < f < 450 1 band AA-low 6 380 102460

38.9

70 < f < 177 2 band AA-low 1 1 107 2650 0.284 177<f<450 2 band AA-low 2 6 272 11603 3.16 400<f<1450 AA-mid, because of

overlap based on .at f=500 MHz.

100 500 464198 232

400<f<1450 AA-mid alternative 100 @ 500 MHz

500 62500 29.2

1000<f<20000 Based on 15 m dishes and an efficiency of 0.7. FOV may be expanded by PAF technology. This does not meet the SKA2 requirements!

1000 4365 4.4

Physical element behavior

• Assume constant (aperture antenna)

• Inherent physical element behavior does not provide flat FOV!

• Current requirements demand spending processing to create flat FOV

FOV processing

• Described by using a concept of an artificial element with effective area not constant as function of subband channels

Station Bandwidth

• #signals to be transported per subband

Aggregated signal transport bandwidth

Bandwidth

• AA-mid aggregated signal transport bandwidth from (base) receptors & from stations

AA-mid band (MHz)

from receptors (THz)

from stations (THz)

Lowest: 400<f<900 232 48.96 Highest: 950<f<1450 232 161.3 Lowest: 400<f<900 (Alt.) 29.1 29.1 Highest: 950<f<1450 (Alt.) 29.1 29.1

Station processing mechanisms

• Two station processing mechanisms are identified:1. A lossless source coding retaining all

available information denoted as station beam forming reducing correlator load:

2. A lossy source coding which is reducing the available information denoted as FOV processing

An integral survey speed

• Current SS requirement is a spot frequency property. Bandwidth is not involved.

• A practical way to include bandwidth is defined (Integral Survey Speed)

• Provides a means to define spectral efficiency

Spectral efficiency

• Average survey speed encoded in one Hertz bandwidth (ISS/Btot)

AA-mid band (MHz)

(m4K-2sr Hz)

(m4K-2sr Hz)

(m4K-2sr)

(m4K-2sr)

Lowest: 400<f<900

Highest: 950<f<1450

Conclusion

• An analysis is presented of three key science requirements

• Analysis not based on specific technology• Current science requirements dictate huge

differences in resource requirements over the different SKA bands.

• Tailor science requirements for better usage of physical antenna properties

Conclusion (continued)

• Introduced the concept of a base receptor element to analyse bandwidth requirements

• Aggregated bandwidth is a measure for required processing

Conclusion (continued)

• Two different station processing mechanisms are identified:– Signal processing required for limiting

information in the spatial domain;– Signal processing required for reducing the

processing load of a correlator subsystem. This one can be considered as a lossless recoding of information in the form of station beam forming providing the station beams.

From the archives

From the archives

15 Years of SKA AA Concepts