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GPRS battery usage

Let's think together about the issue of battery consumption when using packet services using GPRS \ EDGE technologies.

Why, with the active use of GPRS / EDGE services, does the battery of the mobile device "sit down" much faster than when using voice services?

To answer this question we need to remember how the subscriber accesses the operator’s packet network. First of all, the subscriber must perform the GPRS Attach procedure (or Combined Attach - simultaneous connection to both voice and packet services), i.e. The subscriber must undergo authorization and authentication on the operator’s network - these procedures are described in more detail in the article: Inside GPRS. Part 2 . Moreover, if the subscriber does not start activating PDP Context, then he is in the so-called. Idle condition. In this state, the subscriber cannot yet receive, or send data through the packet network *, in order to start sending / receiving data, he needs to activate at least one PDP Context .
* - in fact, the only available service that a subscriber can get access to after completing the GPRS Attach procedure is the transfer of short messages via the operator's packet network - SMS over GPRS. More information about this service can be found in the article “ Backup for SMS” .

Based on the foregoing, in order to determine the subscriber's device battery usage levels, we need to consider two situations:

GPRS Attach, no PDP Context activated

Consider the first case ... in this situation because the subscriber does not transmit or receive any packet data, but can only update its location in the packet network of the operator, which means the subscriber’s machine can only send service data to the network, i.e. we can compare the battery consumption of a mobile terminal in addition to using voice services. Here (en) there is a description of a small experiment in which we figured out how much the battery consumption of a mobile device would increase if we were constantly connected to the operator’s packet network, i.e. be in GPRS / EDGE Attach'e, but do not activate PDP Context'y.
From this experiment we see that the battery consumption practically does not change while the subscriber is constantly in the GPRS Attach, since The mobile terminal practically does not use the radio network and does not transmit active data to the operator.

GPRS Attach, at least one PDP Context activated

On the other hand, we know that when using packet data, the battery consumption of the device increases quite a lot compared to using voice services. This is primarily due to the fact that several time slots (TS) can be allocated for packet services at the base station, and 1 TS is enough for voice services.

Let's take a look at the radio resource allocation scheme on the base station side for packet data. As you know, there is a maximum of 8 time slots on a single TRX cell, but at the same time they are dynamically divided between packet and voice services with a priority towards voice services (emergency calls, etc.)


Naturally, the more TS is allocated to one subscriber on one TRX, the higher the speed it will be given + the speed will also be affected by the coding scheme of the data stream (see table * below).
Channel codingCS1CS2CS3CS4
Single TS date rate, kbit / s9.0513.4015.6021.40
8 TS date rate, kbit / s72.00107.20124.80171.20

* - the table shows the basic coding schemes for GPRS technology.

Thus, we found that using the packet data, the subscriber can be allocated more TS on the base station side, which in turn will lead to an increase in the energy required to receive data on the subscriber’s mobile terminal and, as a result, this fact increases the battery consumption.

That is why the use of packet services based on GPRS / EDGE technologies significantly increases the battery consumption of the mobile terminal.

PS : Naturally, when considering we adopted several simplifications and assumptions, for example, we did not consider the TRX operating modes on the base station side - EFR [Enhanced Full Rate], HFR [Half Rate], which can “split up” the time slot itself by 8 or 16-kilobit "segments", providing a certain quality of voice transmission; We also did not consider the types of TS allocated for packet transmission and the mechanisms of distribution of these radio resources, but I think the general idea and explanation of the differences in the use of packet and voice services is obvious.

Source: https://habr.com/ru/post/101254/

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