Some multi-band or other tactical radios operate in the high frequency (HF), very high frequency (VHF) (for satellite communications), and ultra high frequency (UHF) bands. The frequency range of these multi-band tactical radios is from about 2 MHz to about 512 MHz. Next generation radios will probably cover about 2.0 to about 2,000 MHz (or higher) to accommodate wider bandwidths, higher data rate and less crowded frequency bands. Several standards have been developed for the different frequency bands. For HF, US MIL-STD-188-110B and US MIL-STD-188-141B specify waveform and minimum performance requirements of waveforms and radio equipment, the disclosures which are incorporated by reference in their entirety.
UHF standards, on the other hand, provide different challenges over the 225 to about 512 MHz frequency range, including short-haul line-of-sight (LOS) communication and satellite communications (SATCOM) and cable. This type of propagation can be obtained through different weather conditions, foliage and other obstacles making UHF SATCOM an indispensable communications medium for many agencies. Different directional antennas can be used to improve antenna gain and improve data rates on the transmit and receive links. This type of communication is typically governed in one example by MIL-STD-188-181B, the disclosure which is incorporated by reference in its entirety. This standard specifies a family of constant and non-constant amplitude waveforms for use over satellite links.
The joint tactical radio system (JTRS) implements some of these standards and has different designs that use oscillators, mixers, switchers, splitters, combiners and power amplifier devices to cover different frequency ranges. The modulation schemes used for these types of systems can occupy a fixed bandwidth channel at a fixed carrier frequency or can be frequency-hopped. These systems usually utilize memoryless modulations, such as a phase shift keying (PSK), amplitude shift keying (ASK), frequency shift keying (FSK), quadrature amplitude modulation (QAM), or modulations with memory such as continuous phase modulation (CPM) and combine them with a convolutional or other type of forward error correction code. Standard waveforms are often used.
Some defined standard waveforms use a fixed preamble for modem time and frequency synchronization before the transmission of data. Some defined standards, such as MIL-STD-188-110B and STANAG 4539, use a fixed and data bearing preamble, where data is encoded at a robust low bit rate to convey transmission parameters such as a data rate and/or interleaver setting. These preambles are not extensible or flexible. Additional data fields identifying additional or alternate transmission parameters or modes of operation cannot easily be added to these existing waveforms.
Typically, a modem operating in accordance with the MIL-STD-188-110B standard will acquire a signal while looking for a pattern. The modem will look at the different parameters in the preamble to determine what waveform it is receiving. This preamble usually has known symbols to obtain a reliable acquisition. Typically, there is a portion of the preamble having predetermined numbers that the modem uses to determine what waveform modulation follows and what interleaver setting is being used.
The preambles are not extensible because the preambles in these standard waveforms have a predetermined number of bits. Often two slots or values are left free with identifiers. It would be advantageous if additional information could be presented in the preamble to convey additional set-up or transmission parameters to more fully automate a radio system.