If you have been watching at the 4G ads surrounding us lately, medicine the number 150 Mbps must sound familiar to you. This is the download speed we are supposed to reach from now on if we jump into 4G.
However, as it usually happens with these matters, that is the system maximum theoretical speed, only reachable if the maximum bandwidth (20 MHz) is available, we are alone at the network and our mobile phone belongs to a specific category.
Unfortunately, it is quite difficult to accomplish these conditions simultaneously, and that’s why we will try to approach a more realistic speed depending on these features. There are a lot of features indeed that influence the download and upload speed we experiment. Of course, the network load will make it change significantly, but we leave this analysis, a lot more complex, for future posts.
For a start, we will suppose that the device has all the radio resources for itself for the following speed values shown. In this situation there are two things that affect in a direct way to the speed decrease: the LTE device category and the bandwidth that our 4G provider has available. Let’s have a brief look at them:

• LTE device categories

There are five different LTE UE categories (UE stands for User Equipment). They are needed to ensure that the base station, or eNodeB, can communicate correctly with the user equipment. By relaying the LTE UE category information to the base station, it is able to determine the performance of the UE and communicate with it accordingly. The following tables show the supported features for the five categories and the maximum speeds reachable for each of them:

The modulation that provides the highest speed is 64 QAM, as it sends more information per symbol; but the fact that it can or cannot be used depends on the radio channel instant state. We suppose this modulation is been used for the given speed values (if the device category supports it).

The more TX and RX antennas (MIMO) are used, the bigger speed. However it is quite probable that the device only supports a 2×2 MIMO squeme.
According to the antenna configuration, the maximum download speed in shown in the next table:

It is not until Category 4 when we can reach the famous 150 Mbps, and we could get even twice that speed with Category 5, though this speed is not advertised because on the standard LTE deployments being made in Spain, 2×2 MIMO is used.
It is also worth noting that UE class 1 does not offer the performance offered by that of the highest performance HSDPA category.
(All categories for a 20 MHz bandwidth).

The category our LTE device belongs to is something that could easily not be taken into account, and however will condition significantly its performance. High range devices available nowadays such as Iphone 5 or Samsung Galaxy S4 are Category 3 devices. Huawei has presented on march 2013 the Pocket Wi Fi LTE GL04P that has among its features been the world’s first 4G LTE Category 4 User Equipment.
LTE UE categories are defined in the 3GPP specification “3GPP TS 36.306 Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) radio access capabilities (Release 8)”.

• LTE Bandwidth

The configured bandwidth defines and limits the amount of physical resources that carry the information scheduled to the phone. The maximum configurable bandwidth in LTE is 20 MHz, but network providers may not use all of it, but 5, 10 or 15 MHz. So if we want to know the speed we can reach when we choose a provider, we should also know the bandwidth it is been using.
At the present moment, the spectrum distribution in Spain for the four LTE operators is as follows (the 800 MHz band is not yet available for LTE):

Even though they bought the license for 20 MHz, it is possible that it is not fully used at the beginning and so be extended in the future as the number of users increases. So this could be another possible reason for our speed falling.
Anyway if we supposed the 20 MHz are used, and also the best channel quality (that is 64 QAM), the maximum download and upload speeds for each category are as follows:

In order to have a reference, the 100 Mbps we get for a category 3 device and 20 MHz, fall to 79 Mbps with 10 MHz and to 39 Mbps with 5 MHz.
Therefore, we see that in the best situation, the 150 Mbps have fallen to 100 Mbps if we have a category 3 device. Starting with these 100 Mbps we will then have to take into account that we are not alone at the network and we have to share the resources with others users. Measurements taken in slightly loaded scenarios show peak rates between 50 and 70 Mbps as best performances at places where the coverage was maximum.
Even though the facts we have been discussing , with LTE we will experience better rates and much lower delays than with the previous HSDPA technology, but we have to take into account that those 150 Mbps are, at the moment at least, an utopia.

Published originally in http://intotally.com/tot4blog/ by Leticia Almansa López (contact)

Let’s go with a new post about LTE! Today, we’ll give you a brief description about LTE network architecture. Are you ready?

LTE network architecture keeps the same structure as in previous 3GPP technologies, it comprises three subsystems: the User Equipment (UE), the Access Network (AN) and the Core Network (CN).

E-UTRAN is the Access Network for LTE; it uses OFDMA in the radio interface to communicate with the User Equipment. Evolved Packet Core (EPC) is used in the Core Network to provide a all-IP architecture to give access to various services such as the ones provided in IMS and Internet.

The Quality of Service (QoS) of IP services can be adjusted according to the requirements of each service (e.g. bitrate, lags, Bit Error Rate…). Its signaling is communicated through external services platforms (e.g. IMS) transparently to the EPC Core Network.

In LTE the IP packet transfer service between the UEs and an external network is called EPS Bearer Service. Likewise the packet transfer service provided by the Access Network is called E-UTRAN Radio Access Bearer (ERAB).

The interconnection between the physical equipments in both the EPC and E-UTRAN is done through IP network-based technologies, so that the transport network is a conventional IP network. This way, any LTE network infrastructure contains IP elements such as routers, DHCP servers and DNS servers.

E-UTRAN architecture

The E-UTRAN Access Network comprises only one network element called evolved NodeB (eNodeB), which is the E-UTRAN base station. It includes the UMTS base stations (BTS, Node B) and their controllers (BSC, RNC). Its architecture description is detailed in the 3GPP specifications TS 36.300 and TS 36.401.

As the next figure depicts, a E-UTRAN Access Network only contains ENodeBs that allow connectivity between the UEs and the EPC Core Network. A ENodeB communicates with the other elements of the system through 3 interfaces: E-UTRAN Uu, S1 and X2.

The interface E-UTRAN Uu, also known as LTE Uu or simply LTE radio interface, allows data transfer between the ENodeB and the UEs. All the functions and protocols needed for this transfer and the control operations of the E-UTRAN Uu interface are implemented in the eNodeB.

The eNodeB connects with the EPC Core Network through the S1 interface, which is divided into two other interfaces: S1-MME for the control plane and S1-U for user plane support. On one hand, the user plane of an interface refers to the protocol stack used for the user data transfer through that interface (e.g. IP packets sent by the user to the E-UTRAN and EPC through the S1-U). On the other hand, the control plane refers to the protocol stack used to support the functions and procedures needed to manage the interface operations (e.g. configuring the eNodeB operations from the EPC through the S1-MME).

The division of the S1 interface into control plane and user plane allows the eNodeB to connect with two different nodes from the Core Network. This way the eNodeB communicates with an EPC entity responsible for plane control operations through the S1-MME interface (this entity is the Mobility Management Entity or MME), whereas it communicates with another EPC entity in charge of processing the user plane through the S1-U interface (this entity is the Serving Gateway or S-GW). This division is an important feature of the LTE interfaces protocol stack that allows an independent dimensioning of the signaling and traffic resources.

Optionally, the eNodeBs can connect between them using the X2 interface. These connections can be used to exchange signaling messages to handle the radio resources (e.g. to reduce interference) and also to manage traffic when users move from one eNodeB to another during a handover procedure.

Published originally in http://intotally.com/tot4blog/ by Leticia Almansa López (contact)

Today, we start, as we told you in previous posts a new and interesting section: Technology for beginners.

We’ll begin with LTE. Why? Because LTE is the present, and the future of mobile phone technologies. Maybe you’ve never heard about LTE, but I’m sure that 4G is familiar to you… Did you know that they are almost the same, with the difference that 4G is the commercial name of the LTE technology? Is that totally true?

LTE (Long Term Evolution) is a mobile communication standard developed by the 3GPP (http://www.3gpp.org/) with the aims to improve downlink and uplink data speeds and save vendor and operator costs since the the standard is less complex.

However, the ITU (International Telecommunication Unit) doesn’t consider as 4G the present LTE that is being deployed. Why?

The LTE standard was developed by the 3GPP from HSPA (High Speed Packet Access, or as maybe you know, 3.5G). The standard began in 2005 and resulted in Evolved Packet Core (EPC)  and a new access network called Evolved Universal Terrestrial Radio Access Network (E-UTRAN) specifications. All that was known as “3GPP Release 8″, and for example, that is what is being deployed at the moment in Spain.

LTE Release 8 was developed inside IMT-2000 (ITU naming), as a 3G Evolution, so many people called it 3.9G. In September of 2009, 3GPP presented its LTE-Advanced proposal for IMT-Advanced, officially called “3GPP Release 10”, what is the real 4G.

LTE Release 8 doesn’t reach the 4G standardized peak speed. This is (one of) the reason why is not correct to use this term, although in practice is easier to use this word and we’ll heard it everywhere. But there is a question… How will launch the operators the real 4G when it arrives?

Published originally in http://intotally.com/tot4blog/ by Leticia Almansa López (contact)