Impact of Interference on Capacity
Interference is always a main contributor to capacity degradation in 1G to 3G cellular network and LTE is no difference. Besides external interference, there is a strong relationship also between the number of users and overall cell capacity.
Field trial results confirmed that although overall cell uplink throughput is stable, the per user throughput will decrease as the number of users in the cell increases due to resources sharing On the other hand, field trial results confirmed the overall cell downlink throughput continues to degrade as the number of users increase. At the same time, the per user throughput also decrease as the number of users in the cell increases due to resources sharing. This clearly identifies interference control (either through cell coverage control, Downlink ICIC or efficient power control) as the most important factor in cell capacity protection.
Signal Interference Noise Ratio and Adaptive Coding
These two factors are extremely correlated and are both critical factors influencing the overall capacity of the cell and the network. Trial data below confirm the need of high SINR in order to achieve a high throughput in the downlink level and adaptive modulation technology is perfect to meet such requirement.
Radio (Transmitter) Power Availability
The selection of radio power will have a significant impact on both the coverage and capacity of an LTE cell. The impact is especially obvious for users at the cell edge as the eNodeB is most likely need to change the coding allocating due to the radio power and quality received by the cell edge user. The likelihood of cell edge users overcoming neighbor cells interference will also be highly dependent on the radio transmitter power installed and available at the cell site. The most commonly used power in LTE eNodeB is 20W and 40W at this moment. Conversely, the availability of UE power will also determine the uplink coverage and throughput a user can achieved. Most users are expected to be using Class 3 mobile (23dBm +/- 2dB)
Spectrum Bandwidth Availability
Operators will need to determine how much spectrum bandwidth is available for the deployment of LTE services and there is a direct correlation between available spectrum and the cell capacity for both Uplink and downlink.
Base Band Channel Card Processing Capacity
Similar to other technologies, EUTRAN planning engineers must also be aware of the limit due to hardware specific capacity. Examples of such limit include maximum throughput, maximum number of active users and CPU loading. Although product offers superior capacity, the final values may vary between different eRan releases due to continuous improvement.
As the pipeline connecting eNodeBs to the packet network, the capacity of the S1 and X2 links will play a critical role to the overall throughput and capacity available to final users.