Let’s focus our discussion on Power Control in LTE for now. In this case data rate is variable, while transmitted power remains fixed as shown in the picture below. Modulation and coding schemes are varied to compensate for channel variations. However, in order to cope with variation in channel quality. In Rate Control: Transmitted power remains fixed. channel quality to provide a fixed data rate. In Power Control: Transmitted power is varied in accordance with channel quality as shown in the diagram. In order to provide data services, there can be two approaches to overcome channel variations. Let’s keep our focus on to Data Services alone for a moment. When it comes to Packet switched technologies such as LTE, we are mainly concerned with Data rate, unless if you are supporting Voice Services or other supplementary services i.e., VoLTE etc. Power control (Today, we will be talking about this alone.However, some specific ways to overcome these variations include. We are not going to list all of the ways and protection mechanisms done at these layers to protect the signal. In order to adapt signal from the variations of the wireless channel, predefined procedures exist at Layer 2, and Layer 1 to prepare and massage the signal from getting corrupted from these variations. How to adapt the signal to these channel variations? In order to overcome the variations and channel response between the transmitter (BS) and the receiver (user). Wireless channel can have varying channel response under different conditions.įor a signal to be transmitted successfully from the transmitter to the receiver, it should adapt to the variations of the wireless channel. However, in the uplink, the maximum transmission power is constrained by the maximum UE transmission power.In wireless communications, one of the main challenge is to adapt the transmitting signal to overcome the variations of the wireless channel. This way, the cell range in the downlink can be extended because the Node-B can always allocate more power to the coverage-limited UE. Most modern cellular systems also support power control, which allows, for example, allocating more power to the cell-edge users than the cell-center users. In order for the total uplink power to be the same as the downlink, approximately 100 UEs should be simultaneously transmitting on the uplink. This means that the total transmit power available in the downlink is approximately 100 times more than the transmission power from a single UE in the uplink. Typically, the maximum allowed downlink transmission power in cellular systems is 43 dBm, while the uplink transmission power is limited to around 24 dBm. In contrast, in the uplink a single UE has all its transmission power available for its uplink transmissions to the Node-B. This requires that the Node-B has very high transmission power capability because the transmission power is shared for transmissions to multiple UEs. A one-to-many service means that a Node-B transmits simultaneous signals to multiple UEs in its coverage area. The downlink transmissions in cellular systems are one-to-many, while the uplink transmissions are many-to-one. In cellular systems, the wireless communication service in a given geographical area is provided by multiple Node-Bs or base stations.
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