# Resource Allocation
### Question: how many users share the limited radio resources?
Four major limited resources:
- Power
- [Bandwidth](Bandwidth.md)
- Time
- Space
Separate antennas by $\lambda/2$ since they are [dipole antennas](dipole%20antenna.md)
### Tradeoffs
Non-trivial tradeoff
Cell capacity in bps
Cell coverage - distance, how many users so each user can maintain [SNR](signal%20to%20noise%20ratio.md)
[QoS](Quality%20of%20Service.md)
Maximise the system energy efficiency - bit/Joule
There's no free lunch!
### Maximising Cell Coverage
Possible solution:
- radiate with max power all the time.
- This isn't good because the multicell interference increases
- Can lead to very low energy efficiency (in some cases)
$ SIR = \frac{\alpha P_i}{\alpha \hat{z_{j \neq i}} P_j+\delta^2}\approxeq \frac{P_i}{\hat{z_{j \neq i}} P_j}$
We also have [Signal to Interference plus Noise Ratio](Signal%20to%20Interference%20plus%20Noise%20Ratio.md)
## QoS
Minimum [data rate](data%20rate.md) requirement of a user
Some users may need a minimum [data rate](data%20rate.md) - user may be in a basement!
All transmit power may go to a single user.
- Low spectral efficiency if user is located at cell edge
- Some starving users
- System resources are under utilised - unfair on service provider
### How to maximise system energy efficiency (bit/joule)
Reduce transmit power?
- Loss in coverage
- Cannot guarantee [Quality of Service](Quality%20of%20Service.md)
## Power Control
Guarantee a certain link quality and for interference management
[CDMA](Code%20division%20multiple%20access.md) - 800 HZ changes (everyone is transmitting at the same time)
[GSM](Global%20System%20for%20Mobile.md) - [TDMA](Time%20division%20multiple%20access.md) - do power control at 2Hz
A power control algorithm - set of procedures to adjust the transmitted power
[SINR](Signal%20to%20Interference%20plus%20Noise%20Ratio.md) may not increase by boosting the transmit power of all users [^1]
### What if we don't do power control?
2 issues for interfering systems:
[Near-far problem](Near-far%20problem.md)
[Cell breathing](Cell%20breathing.md)
### Solution
Adjust the transmit power by:
1. Desired link quality ([receiver](receiver.md) power level or [SINR](Signal%20to%20Interference%20plus%20Noise%20Ratio.md))
1. This is fair!
2. Similar [data rate](data%20rate.md)
3. Hard to achieve practically but gives a direction.
2. Minimise interference
3. Battery saving (less important than interference management)
#### Strategy
Equalise as much as possible the received power per bit of all users at all times.
# References
1. [TELE4652-lecture-02](../../Spaces/University/TELE4652/Lectures/TELE4652-lecture-02-cellular-concepts-and-cellular-network-capacity.pdf)
# Footnotes
[^1]: Details in chapter 6 - [IS-95](Interim%20Standard%2095.md)/[CDMA](Code%20division%20multiple%20access.md)