Mobile surface terminal communication system

#The invention relates to the field of mobile communication systems. More particularly, the present invention relates to a communication system including a central terminal and a plurality of identical mobile surface terminals for communicating command and telemetry data.

#There have been several proposed Mars missions that require a networked communication system for communicating unpacketized command and control data between an orbiting spacecraft and a plurality of multiple mobile landers. The communication system can be used to support an investigation of Mars. The networked communication system may include several, for example, ten, small mobile landing vehicles, that is, landers, distributed over the Martian surface to form a global network of communicating mobile landers. The multiple mobile surface terminals are needed for surveying vast surface areas of Mars while communicating command and telemetry data with the orbiting spacecraft. For these Mars missions, more than one lander may be within the beamwidth of a single spacecraft antenna. Each of the mobile surface terminals, or landers, will each need communication transceivers and antennas. The commanding and tracking of the moving landers, as well as the reception of telemetry data is required during surveying operations.

#A conventional deepspace networked communications system includes multiple deepspace spacecraft communicating with an earth ground station. Each of the multiple deepspace spacecraft has a respective communication transceiver and antenna for communicating with the single earth ground station. The ground station tracks each of the spacecraft. The communication channel can be characterized as an additive white Gaussian noise channel communicating encoded data using conventional communication encoding, modulation, and channelization techniques. Such systems do not address fading and multiple path problems as the communication is primarily through empty space between the deepspace spacecraft and the ground station. A deepspace networked communications system includes a command uplink and a telemetry downlink. The deepspace networked communications system does not provide for command and control of multiple surface landers using command downlinks and telemetry uplinks.

#FIG. 1 is a diagram of a multiple mobile surface terminal system.

#FIG. 2 is block diagram of an uplink communication subsystem.

#FIG. 3 is block diagram of a downlink communication subsystem.

#An embodiment of the invention is described with reference to the figures using reference designations as shown in the figures. Referring to FIG. 1, a communication system is a communication network for communicating command and control data between a single spacecraft and multiple landers. A spacecraft 10 communicates with a plurality of N mobile surface terminals on the martial surface 11, such as terminals 12a through 12n, that may be moved over the surface 11 and near Martian hills 13. The landers are shown with wheels for movement and a top solar panel for power collection. As the mobile surface terminals 12a and 12n communicate with the spacecraft, direct, specular and diffuse components of the communication signals are created due to the Martian surface that creates fading and multipaths. For reliable communications, the spacecraft 10 and landers 12a and 12n use reliable simultaneous uplink and downlink communications in the presence of multipaths, fading and channel interference. The communication system includes the uplink communication subsystem is shown in FIG. 2 and the downlink communication subsystem is shown in FIG. 3.

#Referring to FIG. 1 and FIG. 2, the downlink communication subsystem enables communications from the spacecraft 10 down to N mobile surface terminals 12a through 12n, also referred to herein as landers A through N. The downlink communication subsystem includes a spacecraft downlink transmitter 20 having a spacecraft downlink antenna 22 communicating to the landers A through N, such as mobile surface terminals 12a through 12n. Each of the mobile surface terminal terminals, such as terminal 12n includes a mobile surface mobile surface terminal, or lander, downlink antenna 24, and a mobile surface terminal, or lander, receiver 26 for communicating command data over the downlink. The downlink extends between the spacecraft downlink antenna 22 and the lander downlink antenna 24. Preferably, the downlink communication subsystem further includes a spacecraft command antenna 28 for receiving command signals from an earth command transmitter 30.

#Using the downlink, direct sequence spread spectrum (DSSS) communications is applied using code division multiplexing (CDM) with quadrature signaling and with Walsh-Hadamard (WH) codes WA through WN, a pseudorandom noise (PN) code, and a pilot PNo code for communicating from the spacecraft to the landers. The downlink uses amplitude modulation with conventional high power amplifiers, not shown, operating at saturation within bit error rates as a function of the number of landers. The downlink subsystem uses CDM where the WH codes are used to separate the downlink command signals with reduced cochannel interference. The WH codes are well known for having zero cross-correlation at zero time delays. Thus, when synchronization of all landers can be maintained, the WH codes provide orthogonal sequences for isolating respective downlink command signals to the landers. The WH codes are used for downlink communications because the transmitted command data for each lander can be synchronized to start at the same time for one-to-many multiple access.