Principle of Power control in LTE

Power control – already being applied in 2nd and 3rd generation networks – has high potential for improvement of the performance of mobile networks.

Main benefits are:

1. It can bring down the interference in up- and downlink and hence enhances the capacity of the networks.

2. Additionally it helps to keep down the uplink-power consumption, thereby increasing the stand-by time for the UE.

3. Furthermore, from the EMC (Electro Magnetic Compatibility) point of view it can improve the situation considerably.

Principle : The transmission power is adapted in order to achieve the desired QoS (BLER/BER). This adaptation is necessary since the propagation channel is subject to several conditions, which generally vary in space and/or time,e.g.
• path loss
• log normal fading
• short term fading
• UE speed
• location (outdoor, indoor, in-car) etc.

Downlink power control determines the energy per resource element (EPRE). The term resource element energy denotes the energy prior to CP insertion. The term resource element energy also denotes the average energy taken over all constellation points for the modulation scheme applied.

Uplink power control determines the average power over a DFT-SOFDM symbol in which the physical channel is transmitted. In contrast to UTRAN based on WCDMA however the requirements for UL power control are more relaxed as a similar near-far problem of UTRAN does not exist. Compared with UTRAN the UL power control is slower. The PUSCH and the PUCCH are subject to a combined open and closed loop power control algorithm, i.e. to control the transmission power for UL channels a combination of an open (input: pathless, sysinfo and signaling) and a closed loop (TPC) method is used.

A cell wide overload indicator (OI) and a High Interference Indicator (HII) to control UL interference are exchanged over X2. An indication is given which PRBs an eNodeB scheduler allocates to cell edge UEs and hence will be most sensitive to inter-cell interference.

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