The symmetric-key cryptography, also called secret key cryptography, is a cryptographic method using the same key to encrypt and decrypt, ie, that the security of the algorithm is based on the key and not in algorithm. Examples of this type of cryptographic algorithms are: AES, DES, 3DES and RC5.

The spectrum

Regarding the spectrum, LTE becomes quite flexible, allowing bandwidths of 1.25MHz, 1.6MHz, 2.5MHz, 5MHz, 10MHz, 15MHz and 20MHz in the downlink and uplink [4]. Furthermore, it supports broadcast transmission in downlink and uplink-downlink modes, on the other hand, radio resources for broadcast transmissions can be modified according to the operator needs.

The various scenarios which may present between the interaction of different service providers and other networks that they have, are not largely affected because manufacturers have planned coexistence, within the same geographic area, of the EUTRAN with other networks such as 3G and coexistence between adjacent operators, so too, is the case of the overlapping in countries boundaries [4].

The LTE spectral efficiency exceeds largely to HSPA +, these are the results of Telefónica [9], the study provides a scenario of urban centers with high density of buildings, 2x2 MIMO antenna configuration for both cases and using 64QAM as modulation scheme, with this, the study says that LTE spectral efficiency exceeds to HSPA + by 20% at full load. It is apparent from Figure # 1 than for rural or suburban centers LTE benefits will outweigh, furthermore along the chart, the LTE superiority is denoted.

Figure # 1: Spectral efficiency in terms of resource use [9].

Macro-cells are not very efficient [1] in the residential area due to penetration problems that have been mentioned in a previous article, also in the macro-cells there are many users and is more difficult to provide QoS to all of them. For these reasons Internet Service Providers (ISP) have opted for femto-cell implementation at residential level, in order to increase the quality of services provided.

Femto-cells are low-power base stations that provide low cost and high quality wireless services to residential, in this area offer a coverage of approximately 10 m [2], which are designed to integrate automatically with macro-cell networks. Femto-cells integrate with mobile operator through a broadband connection, typically DSL [2] and [3], as can be seen in Figure # 1. However it can also be performed by a wireless link as mentioned in [4]. In General, the femto-cell redirects the traffic from the home cellular system, through the broadband connection, releasing the resource consumption of the macro-cell.

Figure # 1. Typical Femto-cell [3].