Evaluation of Long Term Evolution (LTE) for Network Speeds

Contents

Abstract

Introduction

LTE core network

LTE eNodeB

LTE Air interface

Logical Channels and their mapping with Physical Channels

Physical Channels and Transport Channel

Conclusions

References

Abstract

Every 10 years and so, there is the major change that occurs in the wireless communication promising more speed, flawless browsing, full network, greater connectivity and many more. Today, LTE, LTE-Advanced and LTE-A pro has been playing in the wireless network which is going to change in to 5G system in coming half-decade. The race of having 5G network in the world proves to have high speed and will create the chances if IoT based business. This paper has provided the brief introduction to the LTE, 5G network and their evolving technologies. How the LTE work and their physical layer with channel mapping is also been described in detail in this paper.

Introduction

Initial communication started with analog phones in early 90s which drifted to the digital communication known as GSM (Global System for Mobile Communications). However, this experiment wasn’t fruitful enough and then came LTE which began in 2005 by Japanese operator NTT DoCoMo which is assumed to be the fourth generation mobile communication network. As shown in Figure-1, First Generation (1G) communication system was based on voice services that came in 1981 and Second Generation (2G) cellular network arrived in 1991 works on digitization example GSM. Then come the third generation network that provided high speed of internet and was able to connect many users came into market in 2001.  Finally came Fourth generation mobile network that had mobile management, security, mobility and QoS where 10^th version of 4G became LTE- Long Term Evolution. LTE rel-8 was on 2009 while LTE Advanced came into 2011 that was based on IMT advanced requirements and finally came LTE Advanced Pro in Oct 2015which was the improved version of LTE advanced [1].

Figure 1: LTE History and Evolution [2]

There are several requirements that has to be satisfied to say the network as 5G. 5G should have data rate in Gbps ranging from 1-10Gbps. It also should have low latency, theoretically less than 10m/s. Connection should be almost 10 times stronger than present network and usage of energy should be less by almost 90%. 5G is the mixture of several technologies which has improved the spectral efficiency making the good use of different frequencies. For advancement of 5G, massive MIMO and beam forming are some of the technologies that are supporting for improving spectral efficiency [1].

LTE core network

LTE uses Flat network architecture which is very simple to understand as shown in Figure 2 which includes Mobile Management Entity, Serving-GW and PDN-GW as the core element.

LTE BUILDING BLOCKS

LTE architecture consists of four basic building blocks described below in details:

1. The User Equipment (UE): This devices is smart phone or the smart tablet of the user which allows the user to upload or download anything from internet.
2. The Evolved UMTS Terrestrial Radio Access Network (E-UTRAN):  This are the antennas or the network of antennas that provides the connectivity or the radio access to the UE [1].
3. The Evolved Packet Core (EPC): This is the core of the network which approves the request sent by UE and sent to PDN.
4. The Public Data Network (PDN): This is the commonly shared network that is used by many service providers to provide data in public.

LTE CORE NETWORK BLOCKS

1. PDN Gateway (P-GW): It allocated IP addresses to the UE.
2. Serving Gateway (S-GW): It works as internetworking where all IP packets are transferred through S-GW to eNodeB.
3. Mobility Management Entity (MME): It processes signal between UE and the CN as control node [1].

     Figure 2: LTE Architecture [3]

LTE INTERFACE

LTE interfaces are discussed as shown in figure 3 [1]:

Figure 3: LTE Interfaces [2]

COMPARISON BETWEEN 2G/3G AND 4G NETWORK

The difference between all this technologies are their limitation to provide the speed, connectivity and the network. 2G was based on the digital technology whose average speed was 56Kbps while 1G was based on analog technology. Both 1G and 2G worked on PSTN technology. Popular services like MMS, conference call and call holding came into light during this 2G generation of mobile technology. When the smart phones came in the market, good internet speed became necessary to browse internet, stream audio and videos, etc. UMTS standard came into existence while 3G was running where speed goes upto 2-3Mbps with the network technology of packet and working on internet protocol. While comparing the speed, 4G provides almost 4-6Mbps speed which was deployed using standard LTE [4].

LTE eNodeB

The access network of E-UTRAN consists of eNodeB networks as shown in Figure-4. ENodeB are usually connected to each other by the LT interface named X2. ENodeB when connected to EPC, they have the interface named S1. AS protocols is used when eNodeB communicates with the user equipment’s. While taking about the functionality of the ENodeB, it does the job managing the resources from radio admission to radio commission, scheduling, etc [4]. It also compresses the IP packet headers to transfer the data efficiently. Every data sent through radio is encrypted which means it provides security as well. All this functionalities are performed by several ENodeB managing many cells at a time. ENodeB works on several protocols that works on RAN protocol which helps in reducing the latency and improving the efficiency of the network [3].

Figure 4: Architecture of E-UTRAN [2]

LTE Air interface

In wireless cellular system, there are various medium of transmission which includes: FDMA (Frequency Division Multiple Access), CDMA (Code Division Multiple Access), TDMA (Time Division Multiple Access) and OFDMA (Orthogonal Frequency Division Multiple Access). The popular technology that is been used widely in LTE is OFDMA. The devices used in LTE works on all modulation schemes such as QPSK, 64QAM and 16QAM [4].

OFDMA/SC-FDMA

OFDMA is used as the digital carrier modulation technique where it satisfies the requirements needed by the LTE system such as spectral efficiency and cheap solutions. Also it possess high peak rates. In order to neutralize the effect caused by multipath fading, OFDMA is preferred. SC-FDMA creates the signal in the time domain and then using DFT transform [3], they are being spaced by some distance and then IDFT takes place where cyclic prefix is added.

Figure 5: OFDM Carrier Signal

SC-FDMA was specifically used in the uplink signals, the reason of which lies in their power of amplifying the signal. It operates in the range of 2-3dB as of Peak-to-Average Power Ratio [2]. This characteristics of SC-FDMA makes it more reliable for the system which eventually increase the power of the battery of the user equipments. It is been observed that with the increase in the order of modulation technique such as 16QAM and 64 QAM, in the bit error rate also increases.

FRAMING AND RESOURCE BLOCKS

OFDM uses resource blocks which are the OFDM symbols grouped together. It is the smallest unit of the frame. Many resource blocks come together to form one frame. This blocks are approximately in a size of 180 KHz in frequency domain. While in time domain, they are 0.5ms in size as shown in Figure-6.

Figure 6: Resource Blocking [3]

There are two types of frames: Frame type-1 & type-2. Type-1 frame is been used in FDM (Frequency Division Duplexing) and Type-2 frame is used in TDD (Time Division Duplexing). In frame type-1, uplink and downlink frames are not send at the same time. While at the same time, in frame type-2, there exist a special subframe that are created in between that helps in switching from downlink to uplink.

Logical Channels and their mapping with Physical Channels

Logical Channels are those channels which shows the type of data it is carrying which is termed as control channel. Other type of logical channel works on data of the user. Both channels have to perform their job in uplinks as well as downlink direction.

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Physical Channels and Transport Channel

Physical channel defines the place where to send the information while transport channel provides the path to send that information. In total, there are 3 uplink physical channels and 5 downlink channels as shown below.

For logical channels, the data transfer path are done through the MAC layer whose uplink and downlink channels are mentioned as below:

Figure 7: LTE Uplink-Downlink Channel Mapping [2]

As shown in the Figure-7, the mapping of all three channels are linked together. As seen for downlink channel, it can be seen that logical channels CCCH, DCCH, DTCH and MCCH are liked to transport channel DL-SCH. It carries the information and send to the physical channel PDSCH. Similarly, MTCH of logical channel is connected to MCH of transport channel which is used for multicasting transmissions and mapped to physical channel PMCH. Also, PCCH and BCCH which are used for broadcasting and paging purpose is mapped to PCH and BCH of logical channel which is again mapped with PDSCH and PBCH respectively of physical layer [2].

Similarly, for Uplink Channels, PUSCH which is used for uplink data transmission by the user devices is connected to UL-SCH of Logical Channel which is considered to be the main channel in transport channel is mapped to CCCH, DCCH, DTCH of the logical channel which is used for multi[le user equipment, or single user equipment or for multicasting [3].

Conclusions

Indeed, it is true that better network is required for many of the tasks in day to day life. From this paper, I have learned about the OFDM and their modulation techniques. From the basic building block, it is concluded that LTE has been used for the downlink and SC-FDMA is used for the uplink transmission of the data. With the installation of the 5G network, we will be able to quantify as well as able to optimize the network in energy efficient way while on the other hand, it is the big challenge to convert the LTE network into 5G.LTE network has the feature that will allow the operators to carry the experiments in achieving high speed while 5G is still under water.

References

[1] S. R. Biyabani, R. Khan, M. M. Alam, A. A. Biyabani, and E. McCune, “Energy Efficiency Evaluation of Linear Transmitters for 5G NR Wireless Waveforms,” IEEE Transactions on Green Communications and Networking, Article vol. 3, no. 2, pp. 446-454, 2019, Art. no. 8654701.

[2] B. J. Chang, S. T. Feng, and K. P. Jhuang, “Adaptive Carrier Aggregation with Differentiating Cloud Services for Maximizing Radio Resource Efficiency and Reward Toward 5G Cellular Network,” Wireless Personal Communications, Article vol. 105, no. 4, pp. 1401-1433, 2019.

[3] H. S. Ben Abdelmula, M. N. Mohd Warip, O. B. Lynn, and N. Yaakob, “An efficient scheduling scheme for heterogeneous services in OFDMA based 5G LTE-Advanced network with carrier aggregation,” in ISCAIE 2018 – 2018 IEEE Symposium on Computer Applications and Industrial Electronics, 2018, pp. 275-280.

[4] A. S. Konstantinov and A. V. Pestryakov, “Analysis of the Transmission Modes and Downlink Control Information in the LTE-Advanced / 5G Network,” in 2019 Systems of Signals Generating and Processing in the Field of on Board Communications, SOSG 2019, 2019.