# Unit of spectral efficiency

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• #8985
Tom Aird
Participant

The unit of spectral efficiency quote in all the figures is bit/cu, however this is no the standard unit of spectral efficiency (bit/s/Hz) and there is no mention of this in the documentation.

Are these units the same thing, or is bit/cu something different?

Many thanks

#8986

Hi Tom,

the unit [bit/cu] stands for bit per channel use – thus you can also convert it to [bit/s/Hz].

Best regards,
Martin

#9073
Sherif
Participant

Hi Martin,

Can you please give the formula to convert from bits/cu to bits/s/Hz?

According to ueTrace.m,

channel_uses_total = sum(double(obj.assigned_RBs(TTIs_to_account_for)))*12*14;
obj.average_spectral_efficiency_bit_per_cu = sum_total_bits ./ channel_uses_total;

In the above, both data and control symbols (i.e., (.)*12*14) were taken into account in calculating bits/cu.
For the spectral efficiency (SE) in bits/s/Hz, will the channel use be a function of data symbols only? i.e.,

channel_uses_total = sum(double(obj.assigned_RBs(TTIs_to_account_for)))*((12*14)-(nRef_sym+nSync_sym));

If so, bits/s/Hz will always be greater than bits/cu.

Thank you.

Sherif

#9170

Hi Sherif,

as you see in “channel_uses_total”, it is defined as transmitted LTE symbols (one RB is 12 subcarriers * 7 symbol intervals, 2 consecutive RBs in time in one subframe are always scheduled for the same UE). Therefore, 1 bit/cu means that you transmit 1 bit over one LTE symbol –> 1 bit/cu = 1 bit/(15KHz*1/14ms)

Best regards,
Martin

#9275
Sherif
Participant

Hi Martin,

Thank you for the clarification. Therefore, the spectral efficiency conversion for LTE (with 14 OFDM symbols per (1 ms) frame and 15 KHz per subcarrier spacing) is:

y (bps/Hz) = x (bit/cu) / 1.0714.

Best regards,
Sherif

• This reply was modified 3 years, 4 months ago by Sherif.
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