TCI6630K2L: IQNet BCN Offset configuration for LTE UERx Frame Synch

Hi Anoop,

I've forwarded this to the experts. Their feedback should be posted here.

BR
Tsvetolin Shulev

IQN2 was not specifically designed to handle the drifting timing requirements of a UE.  BCN in particular is a free running counter that is meant to be sync'd to an outside source, then that offset is used as the basis for all other timing.  IQN2 also requires the frame to be subdivided into slots, symbols and samples which have a set number of clocks. These clocks are required for symbol data to be buffered to the pktDMA for output.  A timing drift will require constant monitoring and update, which may result in some packet/symbol drop.

>- IQNet PktDMA will be initially configured to receive un-aligned LTE DL samples

I don't have any experience/knowledge of how to receive unaligned samples.  IQN2 will necessarily fill symbols as programmed in each AxC.

 -dave

The UE/eNB time alignment is achieved through DL sync channels.

UE monitors and locks its frames to the eNB DL sync signals

eNB takes PRACH and reference signals time advance (TA) measurements at the eNB

The TA values are communicated by eNB to the UE, so the UE will adjust its UL transmission, so the frames are aligned at the eNB.

eNB is the master clock of the system. The eNB clock is locked to a GPS or a network time server (IEEE1588)

Best regards,

Constantin

 

Thanks for your respective responses, Woodall & Constantin.

We are aware that IQN2 wasn't designed for addressing UE timing drift correction.

Quoting Woodall: "BCN in particular is a free running counter that is meant to be sync'd to an outside source, then that offset is used as the basis for all other timing." --> This is exactly what we want, but for UE. We would like to configure this BCN Offset with the DL frame offset and align the received IQN2 samples to frame boundary.

We want to know how to configure the BCN Offset so that we can get Frame aligned samples to the PktDMA. We have already managed to configure a value to BCN Offset which resulted in an equivalent change in the BCN Frame Event, but, this did not have any effect on the RADT Symbol/Slot events through which IQ samples were reveived from PktDMA.

We would be really grateful if you could point us to the set of instructions that can achieve this or provide us some example code for this.

Thanks & Regards,
Anoop

Hi Anoop,

I am sorry to say that we do not have example code for configuring IQN2 as a UE.  In normal configurations, the master AT is locked to the frame boundary using the BCN offset as mentioned above and in the IQN2 user guide.  It then never requires updating.  The RadT and AxC timing offsets are offsets from the frame boundary, and will be set based on your configuration of channels - these are known offsets for basestation applications.  For a UE scenario these may be zero, or perhaps plus/minus a sample or two.

Note that if you update the IQN2 configuration while it is running, keep in mind that at some point during the frame it will read the registers for the next frame.  If IQN2 detects a disconnect it may stop processing entirely.  One example of this is when the symbol/clock LUTs do not agree with the total clocks in a frame (and BTW, a frame does not have to be 10ms, but rather clocks/sample, samples/symbol, symbols/slot, slots/frame).  It is also possible that an update in timing may cause the channel to drop a symbol, or drop all symbols until it reaches the next frame boundary.  For these reasons we always recommend shutting the channel down, reconfigure, wait a frame, then re-enable.  This may not be possible to do in a UE configuration.

Here is a similar thread where the user is trying to vary the frame time in real time. 

https://e2e.ti.com/support/dsp/c6000_multi-core_dsps/f/639/p/538296/1962947#1962947