4 ms·

There’s LTE-U and LAA but they are more about extending normal LTE at the cost of public bands. The basic problem is that LTE base stations assign time slots t

There’s LTE-U and LAA but they are more about extending normal LTE at the cost of public bands. The basic problem is that LTE base stations assign time slots to devices when to access the spectrum - that doesn’t work well when by regulation you need to play nice with other technology on the same band.

zokier 3y ago
> The basic problem is that LTE base stations assign time slots to devices when to access the spectrum - that doesn’t work well when by regulation you need to play nice with other technology on the same band Is there good source to read more on this? Based on quick Wikipedia reading, Wifi traditionally (and including this 802.11ah) uses OFDM in sort of TDMA arrangement, which also includes AP assigning time-slots to stations if I understand it correctly (which I very much might not). LTE is based on OFDMA/SCFDMA which (again afaik) are just further refinements on the concept, but similarly rely on allocating resources (time-slots on sub-carriers). And later Wifi standards have also started to use OFDMA. So on surface-level its not super clear what here makes Wifi more suitable for unlicensed use... something maybe on how those time-slots are allocated, but its difficult to compare the two especially when they use somewhat confusingly (for an outsider) different terminology.
- stefan_ 3y ago
  Sorry, I have been imprecise and my knowledge somewhat outdated. The basic issue is above TDMA/OFDMA; unlicensed bands require that you have some mechanism to detect if the channel is in use before you begin transmission, to ensure you do not hog the entire spectrum and can coexist with incompatible/foreign technologies. This is the best summary I could find: „Supporting LTE over unlicensed bands is not trivial. The key challenge is how to achieve har- monious coexistence between LTE and other sys- tems that are already operating in these bands. Conventional LTE cannot operate in unlicensed spectrum as it has no concern for cross-technol- ogy coexistence. For example, transmissions in an LTE radio access network (RAN) are continuous in time, and subject to centralized scheduling at the eNodeB (eNB). Even in the absence of data traffic, control and reference signals are transmit- ted over the air (at the OFDM symbol level) and are ubiquitous over time and its channel band- width.“ From Huang, Yan, et al. "Recent advances of LTE/WiFi coexistence in unlicensed spectrum.", use https://doi.org/10.1109/MNET.2017.1700124 https://doi.org/10.1109/MNET.2017.1700124 in sci-hub.

zokier 3y ago

> The basic problem is that LTE base stations assign time slots to devices when to access the spectrum - that doesn’t work well when by regulation you need to play nice with other technology on the same band Is there good source to read more on this? Based on quick Wikipedia reading, Wifi traditionally (and including this 802.11ah) uses OFDM in sort of TDMA arrangement, which also includes AP assigning time-slots to stations if I understand it correctly (which I very much might not). LTE is based on OFDMA/SCFDMA which (again afaik) are just further refinements on the concept, but similarly rely on allocating resources (time-slots on sub-carriers). And later Wifi standards have also started to use OFDMA. So on surface-level its not super clear what here makes Wifi more suitable for unlicensed use... something maybe on how those time-slots are allocated, but its difficult to compare the two especially when they use somewhat confusingly (for an outsider) different terminology.

stefan_ 3y ago
Sorry, I have been imprecise and my knowledge somewhat outdated. The basic issue is above TDMA/OFDMA; unlicensed bands require that you have some mechanism to detect if the channel is in use before you begin transmission, to ensure you do not hog the entire spectrum and can coexist with incompatible/foreign technologies. This is the best summary I could find: „Supporting LTE over unlicensed bands is not trivial. The key challenge is how to achieve har- monious coexistence between LTE and other sys- tems that are already operating in these bands. Conventional LTE cannot operate in unlicensed spectrum as it has no concern for cross-technol- ogy coexistence. For example, transmissions in an LTE radio access network (RAN) are continuous in time, and subject to centralized scheduling at the eNodeB (eNB). Even in the absence of data traffic, control and reference signals are transmit- ted over the air (at the OFDM symbol level) and are ubiquitous over time and its channel band- width.“ From Huang, Yan, et al. "Recent advances of LTE/WiFi coexistence in unlicensed spectrum.", use https://doi.org/10.1109/MNET.2017.1700124 https://doi.org/10.1109/MNET.2017.1700124 in sci-hub.