17-01-2013, 12:34 PM
Cellular 4G/LTE/WiMAX Channel / Software/EDA Channel
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INTRODUCTION
Jacek Pierzchlewski and Torben Larsen, Aalborg UniversityLong Term Evolution (LTE) is a state-of-the-art standard for wireless communication, currently in technical implementation.1-5 The standard has been defined by the 3GPP organization and is publicly available – every engineer, researcher or student can download the official specification from www.3gpp.org. The 3GPP organization manages an international project called Evolved Packet System (EPS), which is widely known as “the 4th generation of mobile telecommunication systems (4G).” The Evolved Packet System includes the entire architecture of the 4G mobile systems, both packet network and radio interface. LTE is a part of the EPS project, which refers to a 4G air interface standard. Currently many companies in the world, as well as many universities, conduct research and development on this technology.
he authors of this article are involved in research on signal processing for LTE systems and they found that there is a lack of free software able to generate LTE signals. Although open source advanced LTE system simulators exist, no easy-to-use public domain signal generators exist to be used in signal processing research and development.
This article presents a MATLAB toolbox to fill this gap. Functions able to generate the downlink LTE signals are the main part of the toolbox. Together with the functions, a module named “LTE Professor” is presented. LTE Professor is a Graphical User Interface (GUI), which is able to generate LTE signals, analyze these signals and visualize LTE time/frequency resources utilization. The whole source code is GPL licensed and is publicly available at the authors’ website.6
The present article is divided into two main parts. The first part is an introduction to the LTE downlink Physical Layer. Here the basics of the LTE downlink time/frequency resources and signal generation are discussed. The second part of the article presents usage and architecture of the software, together with some examples of generated LTE signals.
LTE Downlink Introduction
The 4th generation of mobile telecommunication systems has, at least in theory, very good performance parameters in comparison to the previous generations.3 Unfortunately, this gain came at a price of significant complication of the whole system. The LTE protocol stack is divided into several layers. Additionally, there is a distinction between the downlink and uplink protocol stacks, since there are significant asymmetries between the different directions of data transmission. Description of the entire LTE system would exceed the limitations of a single article. Therefore, this work is focused on a MATLAB toolbox which emulates the LTE downlink transmitter. This transmitter translates code words, which are the input to the transmitter, into the LTE radio signal. The software is dedicated to engineers and scientists who are involved in research on modern communication signals and systems. In particular, this toolbox is useful in simulation of the LTE base station (BTS) transmission circuits, antenna systems and User Equipment (UE) receiver front ends. It can also be practical in the investigation of the LTE and Orthogonal Frequency Division Modulation (OFDM) channel models. In addition, this software can cooperate with models of higher LTE downlink layers.
LTE Downlink Transmitter
Figure 2 shows the position of the LTE downlink transmitter in the LTE protocol stack. There are two main parts of the LTE Physical Layer responsible for processing data from the higher layers. The upper part is responsible for multiplexing and channel coding.8 The bottom part is responsible for physical channels modulation and mapping to the resource elements.7 The MAC layer controls the entire physical layer.1,3,7,8 The presented MATLAB model emulates the bottom part of the Physical Layer.
The resource planes, in which signals and channels are mapped, are given to the OFDM modulator. The modulator generates the baseband signal. The baseband signal is then up-converted to the LTE radio signal. The presented software emulates both the baseband signal generator and the radio frequency generator. The baseband in-phase and quadrature signals (I and Q signals), as well as the radio frequency signal are the output from the presented model. Additionally, users have access to the resource planes and modulation symbols mapped to all physical signals and channels.
The Software Internals
Figure 7 shows the architecture of the implemented MATLAB models. The main ‘LTE_DL1a’ script controls the whole process. The LTE Resource Parameters Calculation (RPC) unit is run as the first sub module. This unit generates three structures: ‘sP,’ ‘sF’ and ‘sT,’ which contain LTE system parameters, LTE bandwidth parameters and LTE time parameters, respectively. These three structures are used in all later steps of the LTE signal generation. After running the RPC unit, three identical matrices are allocated in the Resources Allocation (RA) unit. These matrices reflect the time/frequency resources. The number of rows in the matrices is equal to the number of subcarriers and the number of columns is equal to the number of symbols in the entire LTE transmission. The reference and synchronization signals are added in the Signals Mapping (SM) unit. The channels are mapped to the time/frequency resources in the Channel Mapping (CM) unit.
Conclusion
The MATLAB toolbox, which is able to generate LTE downlink signals, has been presented. This program is published under the GPL open source license. The authors have prepared a website where the code is available for users. The website also contains a blog about the MATLAB LTE signal generator and a message board for information and comments exchange. The signals generated by the software are also included.
[attachment=47310]
INTRODUCTION
Jacek Pierzchlewski and Torben Larsen, Aalborg UniversityLong Term Evolution (LTE) is a state-of-the-art standard for wireless communication, currently in technical implementation.1-5 The standard has been defined by the 3GPP organization and is publicly available – every engineer, researcher or student can download the official specification from www.3gpp.org. The 3GPP organization manages an international project called Evolved Packet System (EPS), which is widely known as “the 4th generation of mobile telecommunication systems (4G).” The Evolved Packet System includes the entire architecture of the 4G mobile systems, both packet network and radio interface. LTE is a part of the EPS project, which refers to a 4G air interface standard. Currently many companies in the world, as well as many universities, conduct research and development on this technology.
he authors of this article are involved in research on signal processing for LTE systems and they found that there is a lack of free software able to generate LTE signals. Although open source advanced LTE system simulators exist, no easy-to-use public domain signal generators exist to be used in signal processing research and development.
This article presents a MATLAB toolbox to fill this gap. Functions able to generate the downlink LTE signals are the main part of the toolbox. Together with the functions, a module named “LTE Professor” is presented. LTE Professor is a Graphical User Interface (GUI), which is able to generate LTE signals, analyze these signals and visualize LTE time/frequency resources utilization. The whole source code is GPL licensed and is publicly available at the authors’ website.6
The present article is divided into two main parts. The first part is an introduction to the LTE downlink Physical Layer. Here the basics of the LTE downlink time/frequency resources and signal generation are discussed. The second part of the article presents usage and architecture of the software, together with some examples of generated LTE signals.
LTE Downlink Introduction
The 4th generation of mobile telecommunication systems has, at least in theory, very good performance parameters in comparison to the previous generations.3 Unfortunately, this gain came at a price of significant complication of the whole system. The LTE protocol stack is divided into several layers. Additionally, there is a distinction between the downlink and uplink protocol stacks, since there are significant asymmetries between the different directions of data transmission. Description of the entire LTE system would exceed the limitations of a single article. Therefore, this work is focused on a MATLAB toolbox which emulates the LTE downlink transmitter. This transmitter translates code words, which are the input to the transmitter, into the LTE radio signal. The software is dedicated to engineers and scientists who are involved in research on modern communication signals and systems. In particular, this toolbox is useful in simulation of the LTE base station (BTS) transmission circuits, antenna systems and User Equipment (UE) receiver front ends. It can also be practical in the investigation of the LTE and Orthogonal Frequency Division Modulation (OFDM) channel models. In addition, this software can cooperate with models of higher LTE downlink layers.
LTE Downlink Transmitter
Figure 2 shows the position of the LTE downlink transmitter in the LTE protocol stack. There are two main parts of the LTE Physical Layer responsible for processing data from the higher layers. The upper part is responsible for multiplexing and channel coding.8 The bottom part is responsible for physical channels modulation and mapping to the resource elements.7 The MAC layer controls the entire physical layer.1,3,7,8 The presented MATLAB model emulates the bottom part of the Physical Layer.
The resource planes, in which signals and channels are mapped, are given to the OFDM modulator. The modulator generates the baseband signal. The baseband signal is then up-converted to the LTE radio signal. The presented software emulates both the baseband signal generator and the radio frequency generator. The baseband in-phase and quadrature signals (I and Q signals), as well as the radio frequency signal are the output from the presented model. Additionally, users have access to the resource planes and modulation symbols mapped to all physical signals and channels.
The Software Internals
Figure 7 shows the architecture of the implemented MATLAB models. The main ‘LTE_DL1a’ script controls the whole process. The LTE Resource Parameters Calculation (RPC) unit is run as the first sub module. This unit generates three structures: ‘sP,’ ‘sF’ and ‘sT,’ which contain LTE system parameters, LTE bandwidth parameters and LTE time parameters, respectively. These three structures are used in all later steps of the LTE signal generation. After running the RPC unit, three identical matrices are allocated in the Resources Allocation (RA) unit. These matrices reflect the time/frequency resources. The number of rows in the matrices is equal to the number of subcarriers and the number of columns is equal to the number of symbols in the entire LTE transmission. The reference and synchronization signals are added in the Signals Mapping (SM) unit. The channels are mapped to the time/frequency resources in the Channel Mapping (CM) unit.
Conclusion
The MATLAB toolbox, which is able to generate LTE downlink signals, has been presented. This program is published under the GPL open source license. The authors have prepared a website where the code is available for users. The website also contains a blog about the MATLAB LTE signal generator and a message board for information and comments exchange. The signals generated by the software are also included.