Background

In some situations, there will be a high rate of bit error when sending digital information over a radio channel. One way of reducing the bit error rate is to increase the transmission power at the sender (i.e., sending with a stronger signal). However, it may not be possible or desirable to increase the transmission power so that the bit error rate stays on acceptable level. Another way of reducing the effective bit error rate is to use forward error correction codes (FEC codes). One FEC code is the well-known Reed-Soloman error correction code. The basic idea with FEC codes is to introduce extra bits/bytes (error correction bits/bytes) so that the original message can be recovered even if some bits were received incorrectly due to bit errors during the transmission. In the NASA Voyager program, transmission between the space craft and Earth used Reed-Solomon coding with 223 bytes of data packaged together with 32 bytes of error correction into a block of 255 bytes. Due to the error correction code, the original message (consisting of 223 bytes) could be recovered as long as at most 16 bytes had errors during the transmission. In this case the effective transmission rate is reduced with a factor 223/255, i.e., we only transmit 223 bytes of user information for every block consisting of 255 bytes. The rest (32 bytes) is used for error correction.

Sending long blocks with 255 bytes is not a good solution in fast real-time communication. There are several reasons for this, e.g., coding and decoding becomes computationally challenging for large blocks and no part of the message can be interpreted until all of the 255 bytes have been received and decoded. Luckily, Reed-Solomon and other FEC codes can also be used for shorter blocks than 255 bytes. However, in these cases the reduction of the effective transmission rate often becomes larger. This means that when selecting a suitable FEC code there are at least three different parameters that are potentially conflicting: (i) the number of transmission errors that can be corrected, (ii) the reduction of the effective transmission rate, and (iii) the time and computational resources needed to code and decode the messages.

Assignment

In this master thesis project different FEC codes should be evaluated based on their ability to correct transmission errors, the reduction of the effective transmission rate and the time and computational resources needed to code and decode the messages. The thesis project should suggest FEC codes suitable for real-time radio communication between fighter jets.

Who are we looking for

We are looking for 1-2 students on a master (or civilingenjör) program. This position requires that you pass a security vetting based on the current regulations around/of security protection. While, a possible future employment at SAAB will require security clearance, additional obligations on citizenship may apply.

Recommended skills

In order to do this thesis project, we believe that you need to have knowledge, or have an interest to acquire knowledge, in the following areas:

• Coding in general and FEC codes in particular
• Basics of radio communication
• Programming
• MATLAB

Contact

Interested students should contact:
Professor Lars Lundberg, BTH, lars.lundberg@bth.se
Dr. Alexander Westerhagen, SAAB, alexander.westerhagen@saabgroup.com

SAAB will potentially be interested in employing a successful candidate as an industrial PhD student as a continuation of the master thesis project.