In 2009, Time Magazine called the Iridium global satellite program a tech failure. Motorola backed it for global satellite phone usage and filed for bankruptcy in 1999 after spending $5B to build and launch the infrastructure of satellites.
Now, along comes Iridium NEXT which will fully replace the current constellation as well as upgrade the ground system (See Figure 1). They will keep the 66 satellite Low Earth Orbit (LEO) + 6 in-orbit spares and 9 ground spares architecture and starting this year until 2017 will deploy using eight Falcon 9 launches. The new system will have expanded capacity and operational flexibility for M2M, higher data speeds and ability to host payloads. Voice quality will be improved as well.
The US government has plans for missions regarding communications and other customers will make use of the system like NSF, NASA, USAF STP and ESA. A global air traffic monitoring system as well as NOAA weather monitoring missions will be launched. Space debris will be monitored, magnetosphere will be monitored and Ka band communications will be deployed. And finally, Iridium satellites are crucial to remote science camps, especially the Amundsen-Scott South Pole Station. The first launch of Iridium NEXT was successful.
To support this effort, S3 Group, a supplier of RF and mixed-signal IP and tailored silicon solutions announced the availability of the world’s first fully integrated, single-conversion radio transceiver, to be used in satellite communications devices, handsets, transceivers and modems that will operate off the current Iridium® network and the Iridium NEXT system. Previously S3 also delivered a working chipset for the Iridium 9602 SBD Modem.
The following is an excerpt from a Microwave Journal article On the Direct Conversion Receiver—A Tutorial:
Low IF Single Conversion Receiver
Low IF single conversion, shown in Figure 2, is an offspring of the Direct Conversion Receiver (DCR). Its main purpose is to protect the receiver from all the DC-related problems that pertain to DCR, while retaining the DCR's benefit of elimination of high Q IF filters. As its name indicates, instead of directly converting the signal to baseband, the LO is slightly offset from the RF carrier, typically one to two channels. The low IF means that the fractional bandwidth of the IF bandpass filtering is large, making it possible to implement it with low Q components. The IF SAW or crystal filter needed in the high IF case can be replaced with an active RC filter or other filter suitable for low frequency operation, that is also conducive to silicon integration—that’s where S3’s solution comes in. The low IF signal may be translated to baseband through another mixer, or preferably, in the digital domain following analog-to-digital (A/D) conversion. Of course, this comes at the expense of faster and higher resolution A/D converters—this is S3’s expertise! If the IF frequency is equal to only one or two channel widths, then it is not possible to provide image rejection at RF, as the RF filter must be wide enough to pass all channels of the system. In this case, all image rejection must come from the quadrature down-conversion to the low IF, which itself resembles the Hartley architecture, once the baseband conversion is added.
This radio transceiver is a radical innovation from the current dual conversion architectures, common in the Mobile Satellite Services space. This single-conversion architecture enables the lowest form factor and lightest Satellite Transmit and Receive modem in the world. This solution further enables Iridium to substantially reduce form factor, power consumption and cost of products to market. It enables Iridium’s value added manufacturers (VAMs) and resellers (VARs) greater flexibility in embedding the Iridium data modems into their products.
The radio frequency integrated circuit (RFIC) is designed to be used in Iridium’s current L band satellite system, as well as Iridium NEXT, the forthcoming higher data-rate system, and includes a digital pre-distortion (DPD) algorithm which allows for greater flexibility in the choice of external critical components in the system.