NEC and JAXA co-develop a spread spectrum command receiver for commercial communication satellites

Tokyo, April 6, 2018 - NEC Corporation (NEC; TSE: 6701) and JAXA today announced the co-development of a command receiver that employs a spread spectrum modulation method (*1) for commercial satellites.

Compared with the Frequency Modulation and Phase Modulation methods conventionally used for commercial geosynchronous communication satellites, this new receiver has much higher immunity to electromagnetic interference and jamming, while maintaining the same levels of signal acquisition performance.

To monitor and control a satellite, uplink commands are generally transmitted from a ground station to the satellite.

Recently, an increase of satellite launches is making orbits crowded and generating electromagnetic interference with nearby satellites using the adjacent channel. This causes communication failures between satellites and ground stations.

Solving this problem requires manually switching to other frequency channels, which results in more operational costs.

Application of the spread spectrum modulation helps to overcome all these disadvantages. Compared with conventional methods, spread spectrum modulation is an effective method and raises tolerance to interference and jamming.

However, spread spectrum modulation requires a longer latency time to detect a carrier frequency. Especially during the transfer phase of a satellite to the Geostationary Orbit, the frequency shift and its rate due to the Doppler effect require more time to acquire signals (*2).

This technical issue made spread spectrum a less popular alternative to conventional methods.

Based on the design of the multimode integrated transponder (*3) that JAXA developed, NEC and JAXA devised algorithms for the spread spectrum modulation to detect a carrier frequency more promptly.

The optimal algorithm was derived though computer simulation, trial production and verification, and eventually its design parameters were optimized.

The new system can resist over 50 times (17dB) more intense interference or jamming than the conventional system, while keeping the acquisition time of the carrier signal under 5 seconds on average.

This command receiver will be able to reduce communication failures and satellite operators' workloads.

The new command receiver, named C40, has been added to the NEC product series of satellite bus subsystems. This receiver is adapted to the frequency band and operation of commercial communication satellites.

JAXA took up this joint research and development to fortify Japanese aerospace infrastructure and raise the country's international competitiveness.

To attract global interest, NEC and JAXA will exhibit C40 at the Japanese stall sponsored by JAXA and JETRO at the 34th Space Symposium, one of the world's biggest space exhibition, to be held from April 16 through 19 in the United States.

C40 Command Receiver

About the C40 Command Receiver (NEC Space Technologies website) https://www.necspace.co.jp/en/products/bus/pdf/cmdrx/CMDRX_C40.pdf

Notes:

• *1) Spread spectrum modulation: A communication method by which a transmission data spreads in the frequency domain, multiplying it with the periodic spreading code. A receiver can detect the desired transmission data by multiplying the received data with the same spreading code. This operation is referred to as de-spreading. After de-spreading, interference or jamming included in the receiving radio waves spread in the frequency domain. With its power density reduced, it becomes easier to distinguish the transmission data from the de-spreading data. Therefore, the spread spectrum modulation has resilience against interference and jammers.
• *2) Time that a satellite receiver needs to detect the signal from a ground station, and to synchronize the input with a carrier frequency.
• *3) Multimode integrated Transponder (MTP): A transponder of satellites, which has four modulation/demodulation modes, able to accommodate varying customer's needs. MTP is registered as a certified component by JAXA.