QoS managing

An important point with regard to providing QoS is to reduce signaling and interference. With this, operators can properly manage resources without such problems, in order to improve the services provided to users.

In this new scenario, the traffic generated from the UE to the eNodeB is deflected by an IP network before reaching the mobile network. The transmission of a information packet over an IP network is susceptible to delays, so the femto-cell may experience problems for obtaining an immune base time to jitter. Operators should ensure the concept of QoS in femto-cells, the parameters of these scenarios should be comparable to those offered by the macro-cells.

Some studies show that over 50% of voice calls and 70% of the data traffic comes from inside [1], voice calls do not require high bandwidth, but certain quality parameters are require to ensure the voice recognition of users at the other end of the communication, on the contrary, the data traffic requires high transmission rates to send information with a lot of megabytes, such as multimedia applications require, to name one example. One way to ensure high transmission rates on radio systems, is to maintain high signal quality at both ends of the communication, and hence, mitigate the effects of loss and interference in the communication channel.

In this context, operators have deployed femto-cells systems in order to decrease the distance to the EU and to maintain good signal quality. However, femto-cells must operate in the designated band frequency for such communication and match to the assigned frequencies to the operator, from this perspective, femto-cell generates interference and it can be given in the following ways [2]:

• Femto-cell to femto-cell.

• Femto-cell to macro-cell

• Macro-cell to femto-cell.

The interference problems between femto-cell is due the coverage that they have, this type of interference will occur primarily within the coverage limits where the femto-cells interact each other, the Figure # 1 shows this phenomenon, in which the FAP 1 and FAP 2 coverage have overlaps producing signal degradation for users of both femto-cells in that area.

Figure # 1. Interference problems between macro/femto cells.

The telecommunications network of an ISP (Internet Service Provider) is actually an interaction of various networks types, within LTE (4G) can be highlighted as an access network to the end user. The information flow reaches to the user through several infrastructures, on which the ISP carries data traffic, from this perspective, some necessary points will be discussed in order to ensure the Quality of Service (QoS) in such environments.

From the point of view of LTE management, it is permitted to define profiles and classes of services, which are key points when negotiating QoS mobile requirements during the communication establishment, the transit of packets, even in handovers. However, it is necessary to consider the access and transport network if we want to ensure end-to-end QoS.

Transport Network

A typical scenario of an Internet service provider could be described as shown in Figure # 1, it can be seen that LTE is only a part of the provider's access network. The ISP has different types of access networks depending on the provided services. All the necessary infrastructure to transport information from the access networks, must transit through the core network. The core is also connected with other different network types, where the end service is usually located (Internet, PSTN, ftp services, video streaming, voice or other), which the user wants to access.

Figure # 1. ISP's simplified topology [2].

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].