L15_Telemetry_Comms. - Swedish Institute of Space Physics


L15_Telemetry_Comms. - Swedish Institute of Space Physics

L15 Telemetry & Communications

Henrik Lindén, March 9, 2010

Swedish Institute of Space Physics, Uppsala, Sweden


Telemetry, Tracking & Command


• Function

• Requirements and Design

Communications Architecture

• Link Design

• Modulation and Coding

TT&C subsystem functions


• Wireless transfer of measurement data.


• Tracking the s/c position through Doppler shift,

and locking on to ground station carrier signal.


• Send commands to instruments and

components on the s/c.

• Critical commands can be stored, verified and


Requirements & Design

Signal Type; audio, video, data

Capacity; bandwidth, channels

Coverage Area; local, national, mobile

Signal Strength

Requirements & Design

Connectivity; direct link, relay, crosslinks

Availability; times per day

Mission Lifetime

Requirements & Design

Data rates

• Commands

• Health & Status

• Mission

2-8 kbps

40 bps -10 kbps

> 1Gbps

Data Volume & Storage

• Compression, transmission duration


• Assigned or existing

Requirements & Design


• Data rate, modulation


• Ground coverage, multibeam


Mass & Power

• Larger antennas or more power consuming


TT&C Block Diagram

8-12 GHz

2-4 GHz

12-18 GHz

Communications Architecture

The arrangement, or configuration, of

satellites and ground stations, and the

communication links between them.

• Uplink: Ground station to satellite

• Downlink: Satellite to ground station

• Crosslink/Intersatellite: satellite to satellite

• If the signal is relayed:

• Forward link: Ground station to satellite

• Return link: Satellite to ground station

Examples of Architectures

Link Design

Links are digital as standard.

• Less distortion and interference.

• Have low error rates, Bit Error Rate (BER) of

10^10 is possible.

• Easy to relay without loss.

TT&C must digitize data.

Link Bit rate examples

Link Design

Link-size equation

Mesurement of how strong the signal is.

Used to compute the signal to noise

ratio of the system.

5–10 is enough for a digital signal.

Link Design

E b

/N o

: ratio of received energy per bit to noise density

P: transmitter power

L l

: transmitter to antenna line loss

G t : transmit antenna gain

L s : space loss

L a : transmission path loss

G r : receive antenna gain

k: boltzmann´s constant

T s : system noise temperature

R: data rate

Modulation and Coding

Modulation varies the carrier wave.

Mostly frequency and phase modulation,

amplitude modulation is large and


Modulation give different BER and E b /N o .

Only transmit changes to reduce data.

Common Modulation Types

Link Budget

Power and

antenna gain

values, key items

in a space

system design.

More magazines by this user
Similar magazines