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 a mobile device “drain” much faster than when using voice services?

    To answer this question we need to remember how the subscriber accesses the packet network of the operator. 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 go through authorization and authentication on the operator’s network - these procedures are described in more detail in the article: GPRS from the inside. Part 2. Moreover, if the subscriber does not start activating PDP Contexts, then he is in the so-called. Idle condition. In this state, the subscriber still cannot 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 access after completing the GPRS Attach procedure is the transmission of short messages through the operator’s packet network - SMS over GPRS. You can read more about this service in the article Alternate path for SMS .

    Based on the foregoing, in order to determine the levels of use of the battery of a subscriber’s device, we need to consider two situations:
    • when the subscriber is in the GPRS Attach, but has not activated a single PDP Context
    • when the subscriber is in the GPRS Attach, and activated at least one PDP Context

    GPRS Attach, no PDP Context activated

    Consider the first case ... in this situation, because the subscriber does not transmit and does not receive any packet data, but only can update its location in the operator’s packet network, which means that the subscriber’s device can transmit only service data to the network, i.e. we can compare the battery consumption of a mobile terminal in addition to using voice services. That is here (en) is a description of a small experiment in which figured out how to grow the mobile device battery consumption, if to be constantly connected to the packet network of the operator, ie be in GPRS / EDGE Attach'e, but do not activate PDP Contexts.

    From this experiment, we see that the battery consumption practically does not change when the subscriber is constantly in the GPRS Attach, because the mobile terminal practically does not use a 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 significantly 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, while 1 TS is quite “enough” for voice services.

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


    Naturally, the more TS is allocated to one subscriber on one TRX, the higher the speed will be provided to him + the data flow encoding scheme will also influence the speed (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 main coding schemes for GPRS technology.

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

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

    PS: naturally, during the consideration we adopted several simplifications and assumptions, for example, we did not consider the TRX operating modes on the side of the base station - EFR [Enhanced Full Rate], HFR [Half Rate], which can “split” the time slot itself into 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 distribution mechanisms 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.

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