Excavating
Patent
1986-06-30
1988-07-19
Smith, Jerry
Excavating
371 67, 371 53, G06F 1108
Patent
active
047590220
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The invention relates to a method and a receiver for receiving messages sent by radio.
BACKGROUND
The state of the art with regard to radio reception and receivers, particularly with regrad to receivers for personnel location, is described inter alia in Patent Application GB No. 2101779A, published in January 1983. Therein is discussed a personnel locator adapted for receiving calls sent by radio and for receiving and storing a plurality of messages and for displaying one message at a time in a display window. The received message is compared with each of the already stored messages and is stored in the memory of the receiver only if it differs from all of the messages already stored. With the intention that the probability should be increased that the message is properly received, it is sent repeatedly, but the mentioned comparison prevents it being stored more than once.
A weakness in the thus described personnel locator is that if a character in one of the received messages has been received in a distorted state, the comparison cannot shown that the same message has been received, and different versions of the same message will be stored twice and possibly several times.
In addition to the above-mentioned application, an example of the method of sending and receiving personnel locator calls is described in: "Final Report of the British Post Office Code Standardisation Advisory Group (POCSAG)", London 1978.
SUMMARY OF INVENTION
It is an object of the invention to provide an improved method for receiving messages sent by radio and an improved receiver relating to this method. The invention is also preferably, but not solely, intended for application to receivers for personnel location.
It is characteristic of the invention that instead of comparing a message in its entirety with previously received messages, parts of messages or so-called blocks are put together, these being received error-free as far as possible. There are control bits in each block, with the aid of which it is possible to determine whether the received and temporarily stored block is error-free or erroneous. When the message is received for the second time, it is once again determined for each of the blocks whether it is error-free or erroneous. A final version of the message is put together from one block in each pair of blocks which is error-free. If neither of the blocks in a pair is error-free, this is accomplished from the block containing the least number of errors.
Added control bits may be alternatively used for correcting errors in the received blocks. Methods and apparatus for discovering and correcting errors with the aid of added control bits are known in the prior art and thus need not be described in detail.
As mentioned above, it is known in the prior art to increase the probability of a message being transmitted error-free, by repeating a message. In the message provided in accordance with the invention, the increase in probability for an error-free message that a repetition gives is also utilized, and this probability is further increased by the message being divided into a plurality of blocks, each of which is thus considerably shorter than the entire message. Messages to be received in the receiver begin with the receiver's address code; the receiver is adapted solely to receive messages containing its own address code.
The method described so far is already applicable when the final version of a message is to be put together from a single stored message and the same message has been received a second time. In a development of the invention, a plurality of messages is stored in the receiver, and when one of these is received for the second time there is the problem of finding out with which of the stored messages the latter shall be put together. In accordance with the invention, this is solved such that an introductory block is inserted in each message after the address code, there being included in this block a special identity code for each message, to be stored together with the messages,
REFERENCES:
patent: 3732541 (1973-05-01), Neubauer
patent: 3781794 (1973-12-01), Morris
Beausoliel Robert W.
Smith Jerry
Telefonaktiebolaget LM Ericsson
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