DECT NR+ TDMA in the Physical Layer

[Amr Moussa]

Hello,

I am evaluating the DECT NR+ PHY capabilities on the nrf9151 development kit, and I would like to understand how multiple access is implemented on the 9151 modem.

In the DECT-2020 specification: ETSI TS 103 636-3 Section 4.2 "Multiple Access" it states:

> The multiple access scheme for the DECT-2020 physical layer is based on Time Division Duplex (TDD) combined
with Frequency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA). The physical layer
operates with non-overlapping channels in frequency domain and non-overlapping transmission slots in time domain.

However it is unclear to me how devices negotiate which time slot they will broadcast on. Is this done through the synchronization training field, or the physical control channel, or some other mechanism? Furthermore is TDMA implemented in Nordic's current modem firmware?

Thanks in advance

[dejans]

Hi,

it is unclear to me how devices negotiate which time slot they will broadcast on. Is this done through the synchronization training field, or the physical control channel, or some other mechanism? Furthermore is TDMA implemented in Nordic's current modem firmware?

I will check this internally and get back to you by the end of next week.

Best regards,
Dejan

[dejans]

Hi,

Nordic implements physical layer of the DECT protocol stack as shown in the documentation and provides accompanying physical layer API to use services of the physical API. It is the responsibility of the user's software to use the primitives for channel and timeslot selection and schedule transmissions and reception. You can look at dect_shell and DECT NR+ Shell sample. 

it is unclear to me how devices negotiate which time slot they will broadcast on. Is this done through the synchronization training field, or the physical control channel, or some other mechanism?

Device operating in FT role transmits a periodic beacon. Among other things, it broadcasts random access resource allocation. A node operating in PT mode transmits a random access request to the random access resource allocation. Everything can be either fully random access based, or FT can schedule a semipersistent (periodic 1-N slots occurring at T interval) allocation for the PT. PHY API does not differentiate FT or PT operation. It is the responsibility of the layers above to implement these MAC roles.

is TDMA implemented in Nordic's current modem firmware?

TDMA operation is supported from the physical layer perspective, that is the user of the PHY API can schedule measurements, transmissions and receptions at 1/69.12MHz resolution. It is the responsibility of the layers above PHY API to synchronize to beacon transmissions of another node, get the cluster operating data from the parent node, and then schedule the transmissions and receptions to timeslots.

Best regards,
Dejan