ja sorry maar het is in het Engels...
belofte maakt schuld...
White Paper: DroIP Diversity Repeating over IP
Abstract:
The author has been developing repeater systems for the last 25 years. In the quest of getting the largest coverage area everything is explored to get system improvements. With the design described in this paper he would like to open possibilities improving the current analog repeater systems by adding transmit and receive diversity as a valid counterpart to full digital solutions as D-star.
System description:
Receive coverage of a repeater can be improved by using two or more receivers at the same site, to deal with location fading. This technique is commonly used in wireless microphones and GSM. This is NOT what we are using. In order to improve the range of our test development system we are using 4 different RX sites, in triangular position with one receiver in the middle. We believe this system is superior to a single site using multiple receivers.
Transmit coverage of a repeater can be improved by adding additional transmitters. In our test development system the transmitters are co-housed at the three receive sites in triangular position.
Microwave links can be used to link the different receive sites and transmitters. It is more and more difficult obtaining frequencies as microwaves are more used by WiFi and Wimax applications. The world is turning into IP and networks are everywhere, so we use this new technology for interlinks.
Problems to solve:
1. a time standard is needed at each site
2. the received analog audio has to be encoded into IP at each site using minimum delay algorithms
3. the received signal strength (RSSI) has to be encoded with the received audio
4. The 4 incoming signals have to be voted possibly without decoding and have to be routed to the transmitters
5. The audio packets need time information for single frequency network (SFN) transmission
Test setup:
As we do not want to use standard PC’s due to the huge current consumption, we first have to build an encoder for each RX site. The encoder has to produce known length packets containing sampled audio (at 16 bit), receive signal strength level and relative time code.
The reference signal is a GPS receiver providing 1PPM signals. We are using a microchip solution that performs A/D for audio, A/D for RSSI as well as absolute time generation in between 1PPM pulses. The output are standard IP packets.
At the central point we will build a PC based concentrator that decodes the RSSI content of the packets in order to create a voted stream of best received audiopackets that are to be relayed to the transmitter sites with a delay as low as possible.
The packets are buffered at the transmitter site and synchronously broadcast at the requested time frame.
Simular systems in the actual world:
The transmit part of this system resembles DAB and DVB-T transmissions where a multiplex originating from one location is broadcast using multiple synchronous transmitters. The receive part of this proposed system is believed to be unique at the moment.
Call for input:
As we believe this system is ready to be developed, we are no specialist in all fields involved. So we are looking for any input in order to solve the different aspects of this design.
Hallaar January 12th 2008
Pedro M.J. Wyns B.E.(T)
ON7WP – AA9HX