Investigation of different technical solutions for a tactical airborne data link

This work is performed in the project Bredbandiga taktiska datalänkar, which is a Vinnova funded project within the NFFP5 programme. The project is a collaboration project between FOI and Saab Aeronautics and aims to develop recommendations for technical communication system parameters and choice of technical solutions for a tactical airborne data link system for data transmission between aircrafts and aircraft and ground. The assumed scenarios will greatly affect the radio performance. Also the used frequency band will have a major impact on the possibilities to achieve a high data capacity. A radio channel description has been developed for evaluation of the resulting performance for different technical solutions. The channel description is based on the adopted scenarios derived in a previous work package which treats operations over sea and land. The report shows typical maximum values of the delay and Doppler spread for the adopted flight scenarios. The delay and Doppler spread together with the jamming threat then determines appropriate symbol time, interleaving depth, whether equalizer is necessary, if Orthogonal Frequency-Division Multiplexing (OFDM) is a suitable choice, suitable frequency hopping rate and more. A communication system based on Time Division Multiple Access (TDMA) with a part that can be dynamically allocated is recommended in combination with spread spectrum to achieve a well trade-off between capacity and robustness against jamming. The evaluation is performed for four different frequency bands: 300 MHz, 1.8 GHz, 4.7 GHz and 15 GHz. The evaluation shows how different radio communication parameters affect the possibilities to achieve a net user data rate of 50 kbit/s, which is one of the user requirements. We can conclude that it is important to have a good antenna gain and a relatively high transmission power. High antenna gain, however, requires many antenna elements, which is possible to achieve at least for the highest frequency band. Error correction coding and interleaving is also important and will imply a reduced fading margin. Calculation examples for the investigated frequency bands show that it is possible to achieve about 50 kbit/s/user. In general, the two highest frequency bands show greatest opportunities to provide high data rates. However, the antenna systems will be complex with an increased cost as a consequence.