The Technology And Technical Description

Published Date: 02 Nov 2017

1. Abstract

Today, the mobile communication trend is moving toward Long Term Evolution (LTE). LTE-Advanced is aim to reach the requirement of IMT-Advanced which is improving cover range, spectral efficiency, throughput, latency, and peak data rate over 3G quality. Multiple Input Multiple Output (MIMO) is the main key to reach the requirement. MIMO is using multiple antenna in both receiver side and transmitter sites with applying spacial multiplexing, diversity and beam forming in order to improve the quality and reach IMT-Advance. For LTE-Advance, the require downlink peak spectrum efficiency is 30bps/Hz and uplink peak spectrum efficiency is 15bps/Hz with 8*8 antennas for downlink and 4*4 antennas for uplink.

We will discuss about some technology mechanism of MIMO including how spacial multiplexing, diversity and beam forming function at MIMO system, how the structure of MIMO system and benefits of MIMO system.

2. Introduction

Long Term Evolution – Advanced (LTE-A) is introduced in order to meet the growth of high speed mobile and data networking. The first publicly conference was launched in 14 December 2009 in Oslo and Stockholm by TeliaSonera.[1]

LTE Advanced is then under various research and study conducted by 3GPP in order to meet the fundamental ITU-R requirement for 4G. Finally, the result of the study has shown that the 3GPP Release 8 LTE has met the 4G requirement apart from uplink spectral efficiency and the peak data rates.

LTE-A is built on the LTE OFDM/MIMO architecture to improve user experience in terms of throughput and network capacity. It evolved version of LTE is being developed by 3GPP which release 10 and 11. There are five major features: carrier aggregation, advanced MIMO, coordinated multipoint transmission, heterogeneous network (HetNet) support, and relays.

There are few highlighted features of LTE-Advanced which are very attractive. LTE-Advanced has wider bandwidth which enabled by carrier aggregation and higher efficiency which enabled by advanced MIMO techniques. Therefore, the peak data rate and the QoS can be guaranteed with a satisfy performance. In Malaysia, Telco Company Maxis Sdn. Bhd claims that their LTE–Advanced service has the peak download rates up to 75Mbit/s and typical average downlink rates range from 10 up to 30 Mbit/s.[2]

Besides of faster downlink and uplink speed, LTE-Advanced has lower data tarsnfer latencies. This can definitely decrease the delay and shorten the data transmission time required in those previous technologies. Furthermore, it improved support for mobility and greater coverage by guarantee the quality of service in moving user equipment. The users will no longer suffer data loss or transmission failed while they are on high speed train. [3]

LTE-Advanced is a very promising technology that could bring a greater life experience for us. Moreover, LTE-Advanced support backward compatibility with previous R8 and R9 version. This means the old 4G devices will not be abandoned.

3. Technology and Technical Description

3.1 Architecture

This is simple network architecture of a LTE-advanced network. As we go on, each of the above will have its own network architecture. Firstly let us talked about what is the EU. The EU stands for user equipment such as mobile phone, Ipad and etc which connect to the LTE network or wifi. The E-UTRAN is the UMTS Terrestrial Radio Access Network (E-UTRAN) while the EPC is the evolved packed core. The E-UTRAN is called an access network because it helps the EU to communicate with the EPC. This network consists of huge base station named eNB and below is network architecture for the E-UTRAN.

As you can see in the figure, each eNB is a base station and what it does is all low level operation of all it mobiles. Now let us talked about the evolved packed core or also known in short as the EPC. This is the main core in this network and below is the architecture of the EPC network.

HSS is the Home Subscriber Server(HSS) , it contains all the necessary information of all the network operator’s subscriber. P-GW is the Packet Data Network (PDN) Gateway(P-GW) which has access to the outside world. MME is the mobility management entity which controls the high level operation of the mobile. This is accomplished thru signalling messages and with the help of the Home Subscriber Services (HSS).

The Home Subscriber Server (HSS) component has been carried forward from UMTS and GSM and is a central database that contains information about all the network operator's subscriber. The S5/S8 is the interface between the serving and PDN gateway. Basically the S5 will be implemented if both the device are from the same network and S8 if they are from different networks.

Moving on let us see the architecture of MIMO which stands for multiple input and multiple output. In a MIMO system, a signal of the same frequency is send using multiple transmitter antennas (input) to a multiple receiver antennas (output). When MIMO techniques is used in LTE advanced, it increase data transfer rates and improve the overall capacity of the system significantly.

3.2 Features

3.2.1 Diversity

Diversity leads to improvement of link reliability by adding more redundancy to information through the channel. In this technique, several copies of the same signal are transmitted using multiple antennas into the air interface where they may experience fading independent of each other. In such scenarios there will be high probability that only some signals will undergo deep fades while others may not. This can be used to obtain diversity gain.

Transmit and receive diversity are the common schemes in a MIMO system and both of these do not require channel knowledge at the transmitter.

Transmit diversity refers to the use of techniques such as space time coding where each antenna transmits a differently encoded, fully redundant version of the same signal leading to redundancy in space and time.

http://ricardogiesta.com/wp-content/uploads/mimo.png

One such code that was designed for a two transmit antenna system is the Alamouti code. These codes are orthogonal in nature and hence it is used to provide full diversity gain.

It is described with the coding matrix

A2 =

Where ‘^’ denotes complex conjugate hence A1 and A2 within the matrix represent the two complex modulation symbols that are transmitted in two timeslots. There are also higher order space time codes that provide a better error rate performance. At the receiver maximum likelihood decoding is performed with only linear processing. Space time coding assumes perfect CSI at the receiver.

In the receive diversity the independently faded signals received at the antennas are used to provide diversity gain using techniques such as selection diversity, switching and Equal Gain Combining (EGC).

3.2.2 Spacial Multiplexing

Spatial multiplexing is a very useful transmission technique in MIMO systems to increase the overall capacity of the channel at high SNR values. Here a high data rate stream is split into several low data rate streams where each of them is transmitted by a different transmit antenna in the same frequency channel. If these signals arrive at the receiver antenna array with sufficiently different spatial signatures, the receiver can perform processing to separate these streams.

http://opticalengineering.spiedigitallibrary.org/data/Journals/OPTICE/23435/102001_1_1.png

If we consider a system with M transmit antennas and N receive antennas then the maximum spatial multiplexing order is given by:

NS= min (N, M))

Where MS is the number of streams which can be transmitted in parallel. At the receiver the data streams can be separated by the equalizer provided each of the data stream has undergone fading independent of each other. In spatial multiplexing there is no necessity for additional bandwidth and power.

3.2.3 Beam Forming

Beamforming is a signal processing technique that takes advantage of the fading channels. It primarily improves the received signal gain and coverage of the communication system. In this technique the transmission radiation pattern from an array of antennas is focused in the direction of specific user by constructively interfering in that specific direction. In order to achieve this, it is required to have reliable knowledge of the channel.

Based on the amount of channel knowledge gained various types of beamforming can be implemented:

Full CSI: Statistical Eigen vector beamforming is a reliable technique

Limited CSI: Grassmannian beamforming is used

No CSI: Blind beamforming technique is used where the CSI is blindly estimated from the received signal statistics.

C:\Users\XOPHY\Pictures\fig3b.jpg

3.3 Advantages and Disadvantages

MIMO has more benefits that its disadvantages. MIMO which based on wireless network can increase the coverage range, throughput and robustness of the data link. Besides that, it also increased throughput due to parallel data channelling at the same time. For example MIMO has the ability to provide high data rate compared to range and secondly by using 40 MHz channels to increase the available bandwidth for high data rate.

Furthermore, MIMO also has a better spectral efficiency at low cost. It drives greater bandwidth, reach and spectral efficiency at lower cost than alternative antenna technology. MIMO’s capacity scales are linearly with number of antennas. The MIMO systems capacity grows linearly with the number of antennas.

Moreover, MIMO has better interference suppression which guarantees a better quality of service (QoS) and lower bit error rate.

The disadvantages of MIMO are lesser than the advantages. The most significant drawback of MIMO is the need for multiple antennas which initial cost of the equipment installations is higher compared to existing equipment available. Besides that, the computational complexity for hardware and software should be concerned as well. However, those drawbacks will be eliminated when the LTE-Advanced technology become more mature as the cost of equipment will be decreased linearly to time. Moreover, a better hardware and software evolution will definitely reduce the complexity as time increases.

3.4 Comparison between four classes of multiple antennas system

There are 4 classes of multiple antennas system which are

Single Input-Single Output (SISO)

This is the most normal wireless communication way with only one transmitter and one receiver. For this kind of system, it don’t have beam forming technology applied. The transmitter is simply transmit the signal in all direction. For the receiver, it also just detect signal from all direction. Due to the signal will meet other objects while transmitting and being affected, the receiver might receive more than one signal which is some of them are distorted. Besides, the signal that meet other object and reflected to receiver might not be reach receiver at the same time with the signal that directly reach the receiver. So in this kind of case, receiver received an interference signal.

Single Input-Multiple Output (SIMO)

For the system of SIMO, it use a transmitter and more than one receiver. So, the system like this can use diversity to choose a more accurate signal or detect error by comparing 2 signal received from each receiver. It can be done by connect a computer to all receiver. However, it is not very common way to design a mobile communication network. Because, with the system like this, there are some possibility that integrate one antenna in a single user equipment.

Multiple Input-Single Output(MISO)

In this system, there is more than one transmitter and only one receiver is used. In this kind of system, beam forming technology can be applied in both transmitter and receiver side. By doing this, the receiver can detect only one direction and combined all the signal received from that direction and ignore the signal from other direction. So, signal to noise ration can be increase and error can be decrease. Besides, switched beam technology can be apply too. Switched beam technology is that antenna make some fixed bean with heightened sensitivity in specific direction. So, antenna choose those signal that are predetermined and fixed beam then switch to the other bean just as mobile device moves throughout the beam pattern.

Multiple Input Multiple Output (MIMO)

This system is using more than one transmitter and more than one receiver. Therefore we can use Antennas Diversity to differentiate which signal should be taken. Because receiver will have very big different in characteristics even we put them only a few inches different places from transmitter, so we can easily compare the signals from all receivers by connecting one computer to all receivers then decide which signal to be taken. MIMO using beam forming technology for both transmitters and receivers. Bean forming technology transmit signal with focus the transmit signal in only one direction. It use DMRS based pre coding to control the beam forming vector. Beam forming enable the signal to be amplify then improve the range of data rates. Besides, it also lower to interference to other signal and improve receive interference tolerance. For the receiver, it combine received signal from different directions.

Discussion

Recommendation

Conclusion