Frequently, it is necessary to compare the performance of digital radios from several vendors. This can be accomplished through over-the-air testing on specific radio links. There are many limitations to this approach, however. These limitations include the difficulty of testing different radios under identical test conditions and the inability to control the propagation conditions at the time the test is run. Because of the latter limitation, tests typically do not cover the full range of propagation conditions that may be encountered by the radio on an operational circuit. Over-the-air testing, therefore, tends to be incomplete and to be very expensive to conduct.An alternative approach is to test the radios in the laboratory using a channel simulator. Channel simulators can easily emulate the full range of propagation conditions which may be encountered on a wide variety of links -- not just one specific link. The tests can be conducted in the laboratory under controlled, easily repeated test conditions. Radio testing using channel simulators, therefore, tends to be more comprehensive and less expensive to conduct.
The Institute has completed development of a general purpose channel simulation system that can be utilized for simulating a variety of different types of radio environments. The architectural design of this simulation system provides the flexibility needed to simulate many different types of propagation channels and noise and interference environments. For example, it can be utilized for simulating either wideband or narrowband high frequency (HF) propagation conditions and the crowded HF portion of the radio spectrum. It can also be used to simulate typical ultra-high frequency (UHF) or very-high frequency (VHF) channels and accompanying noise/interference environments. The system has been successfully used by industry in testing the performance of advanced HF radio system designs.
The significance of the general purpose simulation system described above is that is can be utilized for testing advanced digital radio systems that could be used in a variety of applications. One potentially new area for digital radio application is in Personal Communication Services (PCS) implementation. PCS is an advanced mobile communications technology that is being planned by equipment manufacturers and telecommunication service providers worldwide. PCS will provide a wide variety of new capabilities and services for both business and personal communications. The general purpose simulator being developed at the Institute can potentially be used for testing radios which are candidates for inclusion in PCS networks.
The Institute previously developed a line-of-sight (LOS) channel simulator that is useful in testing modern digital microwave radios. It has a number of unique features, including the ability to test microwave radios at their radio frequency (rf) rather than at some intermediate frequency (IF). This improves the reliability of the test results.
