I hope someone can help me with this. In 5G NR OFDM system, Bandwidth part switching is helpful for power savings. You reduce the transmission bandwidth and then you save on transmit power. That is clear. So i was thinking why hasnt 3gpp defined adaptation in time domain? Wouldnt that provide gains as well. In this case transmit over the whole bandwidth but for shorter time. Any difference in power savings
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$\begingroup$ All else being equal, shorter time $\approx$ higher power consumption. $\endgroup$– AlexTPCommented Apr 20, 2022 at 9:36
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$\begingroup$ @AlexTP why Alex? Thank you for your reply $\endgroup$– TyroneCommented Apr 20, 2022 at 12:43
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1$\begingroup$ @Tyrone because you need to keep the same energy for the same error performance. $\endgroup$– Marcus MüllerCommented Apr 20, 2022 at 12:44
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$\begingroup$ In terms of energy consumption is the UE consuming more power transmitting over 10 mhz and 14 symbols compared to 20 mhz and 7 symbols... that is not clear to me $\endgroup$– TyroneCommented Apr 20, 2022 at 13:08
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1$\begingroup$ @Tyrone because power = energy/time and the duration of 7 symbols is shorter than that of 14 symbols. In ideal cases, the energy consumption should be identical but higher power requirement implies more expensive hardware. In pratical cases, (in general) higher power implies more energy loss mainly due to heat conversion. Therefore, low bandwidth is prefered. Note that NR does have short scheduling (mini slots) but only for latency purpose. $\endgroup$– AlexTPCommented Apr 20, 2022 at 13:48
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OFDM defines the duration of your symbol to be equal to the number of subcarriers. So, that's impossible to change given a bandwidth, unless you've got a different (less frequency-selective) channel. So, OFDM symbol length is fixed.
The number of resource blocks assigned to UE is adjusted according to data volume requirement of the UE, so that kind of time-domain adaptability always has been the case.
answered Apr 20, 2022 at 9:58
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$\begingroup$ Thank you Marcus. Perhaps my question wasn't clear. And I apologize for that. I meant to say that why not allocate smaller # of OFDM symbols while keeping same bw $\endgroup$– TyroneCommented Apr 20, 2022 at 12:42
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$\begingroup$ As I wrote, that's exactly what is done when your UE gets a lower number of resource blocks allocated. $\endgroup$ Commented Apr 20, 2022 at 12:43
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$\begingroup$ Btw the number of resources blocks may have fixed # of symbols. By allocating different # of RBs doesn't necessarily mean fewer symbols $\endgroup$– TyroneCommented Apr 20, 2022 at 12:54
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$\begingroup$ Ok. Say I allocate 20 mhz and 14 ofdm symbols to UE. Then I decided to allocate 10 mhz and 14 symbols for power saving. Is that same as allocating 20 mhz and 7 symbols in terms of power savings $\endgroup$– TyroneCommented Apr 20, 2022 at 12:56