Archive for November, 2010


This paper describes the characteristics of a new CubeSat transceiver for increased data throughput. Here, the authors utilize a commercial transceiver chip from 900 – 928 MHz ISM band. This new transceiver can adjust its data rate, its bandwidth and RF frequency throughout a given LEO (Low Earth Orbit) pass by measuring its receiving signal power. An algorithm controls and optimizes all these features.

We know that all of the components of the CubeSat should consume very low power and be small in size, so we have these limitations when it comes to the design area. The antennas used on most CubeSats are microstrip patch antennas because of their small size and flexibility. In this paper they used  this kind of antenna, which provides a worst case loss of 10dB over an isotropic (spherical) coverage.

Specifications of the single chip transceiver:

  • Texas Instruments cc1101
  • It transmit up to 500kbps
  • Provides 10mW RF output power while using 100mW of DC power
  • Adjustable channel filter bandwidth between 58-812KHz (receiver)
  • Consumes 50mW DC power (receiver)
  • Designed to be interfaced with a PIC (programmable intelligent computer) for control and data flow purposes
  • Can measure received signal strength and frequency offset

With just the features of the transceiver chip a person may know the capabilities of the communications system of the CubeSat. Another important element is the algorithm that controls this chip. It has to describe the operating mode in any condition that the CubeSat may experience. To confirm this paper, the authors ran a simulation of a 45-degree elevation pass and it increased data throughput performance by as much as 300%. They also recommend using a higher speed and more powerful PIC to optimize this system.

References: CubeSat-Communication Transceiver Paper

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Adaptive Radio Technologies (ART) offers a new platform that could significantly improve the CubeSat’s downlink bandwidth, but is not without its limitations.

In this paper, the traditional methods of downlink are compared to the new method proposed by ART.

The Low Earth Orbit to ground radio link is highly dynamic. The traditional approach by which radios are designed assume the worst-case scenarios, which gives reliability but is inefficient because is not utilizing the full capacity of a given channel. Los Alamos National Laboratory has developed advanced technologies that can fully exploit the dynamic channels that are used, thus improving the efficiency of small satellite radios. By adaptively changing the data transmission rate during a LEO satellite pass the adaptive radio is capable of bit rates as low as 117 kbps and as high as 18.6 Mbps.

This is achieved by measuring the signal strength and then using a conventional bit rate uplink to command the satellite to change the downlink’s bit rate. It is not practical to adapt this bit rate continuously; instead it can be adjusted at discrete steps to optimize the results. Given identical power, weight, and volume using the adaptive radio method provides 10 times more improvement than using conventional methods. To obtain these results a 2.4 GHz downlink frequency was used.

While this new concept provided by Adaptive Radio Technologies gives the best results in the downlink bandwidth, it is by using the 2.4 GHz frequencies. This creates a limitation because past CubeSats have used the amateur frequencies, which are also used by the ground station and are the frequencies that we should focus on as stated on the previous post.

Reference: www.adaptiveradiotech.com/presentations/jmp_smallsat_2009.pdf