IMPROVEMENT METHOD FOR QUALITY AND RELIABILITY VOICE AND DATA DISTRIBUTION USING DUAL WATCH SUBSCRIBER UNITS AND REDUNDANT DOWNLINK TRANSMISSION
Original Publication Date: 2015-Jul-10
Included in the Prior Art Database: 2015-Jul-10
Kuzio, Piotr: INVENTOR [+3]
The proposal is to use dual watch subscribers and transmission of the voice/data using main and secondary base radio (redundancy).
Improvement Method For Quality And Reliability Voice And Data Distribution Using Dual Watch Subscriber Units And Redundant Downlink Transmission
By Piotr Kuzio, Grzegorz Szyszka, Michal Szychowski
Motorola Solutions, Inc.
Narrowband communication systems (TETRA, P25, DMR or older ones) have multiple operational modes such as: simplex or duplex, where consecutively single frequency (talk-around) or single pair (TX/RX) of frequencies is used. However, there is no mode for redundant transmission over-the-air which seems to be missing part of public safety system, especially for life-threatening situations (priority or emergency calls). In contrast, on the infrastructure level redundancy is heavily employed to eliminate single point of failure.
Presented innovation proposes methods of activation and usage of redundant transmission from base radios and employing multiple receiver subscriber units (e.g. dual watch).
Subscriber radio, dispatcher or another Fixed Network Equipment (FNE) element can activate redundant downlink transmission based on multiple factors (subscriber capability, call priority, channel availability etc.) which are presented in detail in this paper.
There are multiple sources of the radio signal degradation which impacts on the quality of audio or data delivery:
- Distance to the base radio: weak signal as a result,
- Enclosed space (tunnel, indoor, underground): weak signal and reflections as a result,
- Outdoor urban area: reflections (multipath fading and wave cancellation) - Figure 1,
- Industrial noise: interference,
- Jamming: interference,
- Overload of control channel requests: slow responses from system as a result,
- Base radio failure (antenna / power amplifier / cable): no signal from the base radio.
Another problem is that any significant change in the existing design such as: relocation of base radios to improve coverage or signal reliability, replacement of the communication standards (broadband vs. narrowband) is expensive – see items below:
- Cost of infrastructure changes,
- Cost of user radios replacement,
- System migration outages, coordination, planning cost.
Base radio transmission redundancy on multiple channels (frequencies, time slots or orthogonal codes) and usage of user radio with multiple receivers (e.g. dual watch subscriber), antennas or decoders can improve problem described in the previous section. The list shown below presents improvement methods addressing particular problems:
- In case of weak or interfered signal combination of 2 signals can result up to 3 dB signal/noise ratio improvement,
- In case of multipath wave cancellation, if channel space between primary and secondary signal is relatively significant, secondary signal is not cancelled,
- In case of control channel overload, requests and responses can be delivered over one of multiple redundant control channels,
- In case of base radio transmission path outage (antenna, cable, power amplifier) ...