The impedance (Z) is a measure of opposition that a circuit to a current when a voltage is applied. The impedance extends the concept of resistance circuits alternating current (AC), and has both magnitude and phase, unlike resistance, which has only magnitude. When a circuit is powered with direct current (DC), there is no distinction between the impedance and resistance; the latter can be thought csa impedance with zero phase angle.

One hertz is one cycle per second, meaning repeating cycle as an event. For example, hertz is applied physics measuring the number of times for a second wave (either acoustic or electromagnetic) is repeated or can be applied, among other uses, to ocean waves that reach the Beach vibrations per second or a solid. The quantity that measures the frequency hertz is called,in this regard, the inverse of the period. One hertz is an oscillation frequency of suffering a particle over a period of one second.

The dBi isotropic or decibel is a unit for measuring the gain of an antenna in reference to a theoretical isotropic antenna. The value dBi corresponds to the gain of an ideal antenna (theoretical) radiating the received power of a device to which it is connected, and which also transmits the signals received from space without regard either external or additional gains or losses powers.

General Packet Radio Service (GPRS) or general packet radio service created in the 80s is an extension of the Global System for Mobile Communications (Global System for Mobile Communications or GSM) for the transmission of data by packet switching. A similar service for mobile phones, the IS-136 system. It allows transfer rates of 56-114 kbps. These Class A devicesThey can simultaneously use GPRS and GSM services. Only Class B may be connected to one of the two services at all times. While GSM service (voice or SMS) is used, the GPRS service, which automatically restarts when the GSM service ends is suspended. Most mobile phones are of this type. Class C are alternately connected to one or another service. Switching between GSM and GPRS shouldperformed manually.

Universal mobile telecommunications system (Universal Mobile Telecommunications System or UMTS) is one of the technologies used by mobile third-generation successor to GSM, because the GSM technology itself could not follow an evolutionary path to get to providing services considered third generation. Although initially is designed for use in mobile phones, the UMTS network is not LIMITADaa these devices and it can be used by others. What are the differences between GSM and UMTS? The GSM system operates by TDMA, ie, time is divided into slots and each user is assigned a slot, ie, a period for which data can be transmitted. Therefore each channel is shared by a number of users. The system is a UMTS (WCDMA) code division multiple access dand broadband. In this system there are no time slots and GPRS. All users transmit simultaneously on the channel, but each user signals are encoded with a unique code so that even though we think that an "indecipherable signal" is formed by using the same frequencies simultaneously, It is not, because the base station is capable of decoding and re perfectly separate each of the communicationsreceived from different users. This obviously implies a much higher channel utilization, to not share in time.