Despite the digital communications revolution, a significant number of LMR operators continue to specify modern analog radio networks to serve their communities. Many others are successfully operating legacy analog LMR systems that continue to be optimized and fully supported. Beyond their support role, some manufacturers are developing solutions that upgrade the performance of these analog networks, giving existing and new analog operators ongoing value for the life of the network investment. When considering radio network design, acquisition costs, crowding or other restrictions on the spectrum, it may be necessary to overlap a single frequency’s coverage to guarantee seamless operation across the entire area. Obviously, multiple radio transmissions in the overlap zone on that frequency will experience interference.
One solution is to deploy a trunked system. Alternatively, a simulcast system, which utilizes equalization techniques to carefully time these transmissions, minimizes any interference by moving the affected regions of ‘interfered’ signal to ‘less desirable’ areas. This can create a system architecture that is ultra-reliable, spectrally-efficient and robust enough for mission-critical comms. Installing analog simulcast base stations provides these benefits, without the need to replace existing analog portable and mobile fleets. This results in additional savings, removing the inevitable admin overhead associated with new equipment rollout, and dramatically reducing the need for radio user training.
Tait analog quasi-synchronous (QS2 ) systems simultaneously broadcast the same information from all sites in a network using Digital Signal Processing (DSP) techniques to automatically equalize the received audio in terms of bulk delay, phase delay, and signal amplitude. Any differences in site linking characteristics are automatically corrected, ensuring that users receive distortion-free audio or data in the coverage overlap areas.
Linking QS2 systems requires a very stable and minimal delay, and the delicate time balance must be constantly maintained across the radio network. This stability is non-negotiable for simulcast systems, as whenever the propagation time between sites changes, the system needs to retrain, allowing for the new time by adding the necessary delay. That results in short periods of unavailability, which is simply unacceptable in business or mission-critical environments.
High-performance MiMOMax radio links with 4-wire audio interface between base stations provide low latency, low jitter, throughput capacity, and reliability, so that an analog simulcast system, such as Tait QS2 can efficiently and reliably cover a wide area with a single FM radio network channel. Combining this technology with a MiMOMax NDL linking system ensures the highest possible analog simulcast performance, with ultra-high throughput capabilities, and low latency and jitter rates. At 64QAM, the MiMOMax NDL linking provides 5ms latency with less than 10nsec jitter to support up to four QS2 channels.
|Modulation Mode||Latency||Channels Supported||Jitter|
|64QAM||5ms||Up to 4 Channels||<10nsec|
|16QAM||6ms||1 to 2 Channels||<10nsec|
This article is taken from Connection Magazine, Issue 6. Connection is a collection of educational and thought-leading articles focusing on critical communications, wireless and radio technology.
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