RACH Power Control (GSM)

Sep 08, 2005 4 Replies
J

Four questions about the RACH in GSM:


1) How is the RACH power controlled? I would assume that it starts off at some nominal power and then ramps up if unsuccessful. I would like to know some more details.


2) What would be the typical number of retrys before it gives up?


3) I gather that collision detection is not used. So I am guessing that failure to get a RACH message through is determined by there being no reply on the AGCH. Is that right?


4) Does the MS know what time slot to send the RACH on? How is this assigned? When is this assigned (in what process)?



I appreciate any help. I hope I'm in the right news group. Pleas elet me know if there is a more appropriate one.



Thanks,



Jim


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E

That is correct. The mobile times out for the AGCH response and retries again.

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J

Thanks,

I'd like to know more. Is there a particular specification that might answer these questions?

I am now trying to understand what information the RACH carries. I know it is only an 8-bit value that has CRC and block coding added. But what is the 8-bit value?

Jim

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E

I think you need to refer to GSM 04.08. It will give you information about the RACH format and will give you references to other specifications related to the topic.

You can find it at the 3gpp website.

The 8 bit CRC is calculated and added to the message. The receiving end would again compute the CRC to determine if it matches.

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J

That begins to answer my questions. A lot to wade through, though.

Thanks, Jim

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