RACH is one of the most important steps in LTE protocol (actually in any Cellular protocol) and there are a lot of details to be covered as below. You would see a lot of issues and spend many many stressful days when you are testing the device at its early stage of the implementation, but once the device / modem is mature you would even forget about the fact that there is such a step called 'RACH' because this wouldn't cause any trouble.Īnyway. Even if the UE log provides the detailed information, there are not many people who can properly interpret those information and find out the root cause of the problem.
some provides pretty detailed information but others does not provide much detailed information. Even though you have access to the UE side If there are some problems in precondion stage, you have to completely rely on UE side log only, Network side log does not help anything. Why ?īefore UE decided to send RACH signal (RACH preamble), there are many preconditions to be met as described in From Power-On to PRACH. If you have any experience of testing UE or UE modem chipset at the very early stage of the development, you would have noticed that RACH is the most challenging point in terms of troubleshooting. Even in terms of protocol design, RACH design can be one of the most important / critical portions. In terms of Radio Access Network implementation, handling RACH wouldīe one of the most challenging job. Of view, it would seem that it is getting this initial UE signal in almost random fashion (e.g, in Random timing, Random Frequency and in Random Identification) because it has no idea when a user turn on the UE (Actually it is not completely random, there are a certain range of agreement between UE and Network about the timing, frequency location and possible indentification, but in large scale it would look like working in random fashion).
In CDMA, they call it 'Access Probe' as far as I know (but I don't have much knowledge on CDMA), in GSM they call it 'Channel Request', and in WCDMA / LTE they call it 'RACH'. Even though they use a little bit different name, in all cellular technology (CDMA, GSM, WCDMA, LTE) there is a specific signal that perform the same function. This is the first message from UE to eNB when you power it on. RACH stands for R andom A ccess Ch annel.
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