Hi Marcus, Thank you for the explanation. I really appreciate it. I did not look at it that way. V/r LoyCurtis Smith From: Marcus Müller Hi LoyCurtis, there's no general resource; this is just time synchronization for wireless networks; you'd need to implement it within the bounds of the wireless system you're building. GPS does it differently than GSM than LTE than distributed radar systems than… I don't know whether and if so, how, OAI implements such things. This is a question for the OAI documentation, I guess. Typically, cellular base stations tend to have a shared clock and time – either via GPS-disciplined oscillators (such as the GPSDOs for the USRPs!) or via explicit distribution (via coax) or implicit distribution (recovered from the clock of the networking link). So, in larger networks, this is something that's solved with hardware making a shared clock available. However, there's in principle no mathematical obstacle that a base station that's able to receive other base stations could not derive its own version of time – just as a handset/UE does in a cellular network. It is, though, a bit dangerous, since of course everything you recover from a noisy, variable-group-delay channel, has its own variance, and so would the recovered clock and time (i.e., you get offset, jitter); and seeing that this is then used by many UEs to coordinate access, again incurring additional error, this can seriously limit performance. Also, a hardware solution comes as no additional computational cost to the signal calculation; doing a resampling by 1.00001 and a delay by 0.3376 sample periods is relatively expensive in terms of CPU cycles. Best regards, Marcus DISCLAIMER: Any attached Code is provided As Is. It has not been tested or validated as a product, for use in a deployed application or system, or for use in hazardous environments. 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On 26.01.22 09:30, LoyCurtis Smith via USRP-users wrote: > > Is there a resource for synchronizing multiple USRP x310s without an external reference > clock? > > Also, would SBX-120 daughterboards perform better when using multiple USRPs because of > its phase sync feature? > > V/r > > LoyCurtis Smith > > *From: *Marcus D. Leech <mailto:[email protected]> > *Sent: *Tuesday, January 25, 2022 11:14 > *To: *LoyCurtis Smith <mailto:[email protected]> > *Cc: *[email protected] > *Subject: *Re: [USRP-users] Re: Synchronization of two USRP x310s > > On 2022-01-25 11:12, LoyCurtis Smith wrote: > > Would their mechanism included UHD based code? > > Since UHD is the way ANY application talks to the radios, yes. But I have no idea if > OAI, as one of dozens and dozens of different appilcations > "out there" has any way to support that functionality. > > > Also, I assume that the only other option would be to purchase an Octoclock or some > other clock distribution module? > > Yes, you'd need some kind of shared 10MHz reference clock and 1PPS source, AND your > application needs to be able to configure the radios to > use it. > > > > On Tue, Jan 25, 2022 at 10:40 Marcus D. Leech <[email protected]> wrote: > > On 2022-01-24 20:53, LoyCurtis Smith via USRP-users wrote: > > My system setup is as follows: > > ·2 x USRP x310 with CBX-120 daughterboard > > ·2 x Ubuntu 18.04 workstation > > ·2 x Taoglas 45.8113 antenna > > ·2 x Internal Reference Clock (Master Clock set at 184.32 MHz) > > ·2 x Internal Time source > > ·2 x Connected via 1 Gig-E interfaces > > ·2 x Using UHD 4.1 > > The devices have been in two setups: stacked and a few inches apart. > > I am attempting to deploy a 5G network using the openairinterface (OAI) > software system. Both devices synchronize initially, then they fail. With > openairinterface, I am using frequency offset compensation at the UE. Its a > useful parameter when running over the air and/or without an external > clock/time source > (https://gitlab.eurecom.fr/oai/openairinterface5g/blob/develop/doc/RUNMODEM.md) > > Is there a way to synchronize the reference clock/timing of both USRP x310s > over the air? In the future, I will be attempting to connect a third USRP > x310. My setup will include one base station and two user devices. > > V/r > > LoyCurtis Smith > > Unless OAI provides some mechanism for that, the answer would be no. You need a > shared reference clock. > > > _______________________________________________ > USRP-users mailing list -- [email protected] > To unsubscribe send an email to [email protected] > > -- > > V/r > > LoyCurtis Smith > > > _______________________________________________ > USRP-users mailing list -- [email protected] > To unsubscribe send an email to [email protected] |
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