LTE Unlicensed (LTE-U)

Introduction

Long-Term Evolution (LTE) is the latest high-speed data standard of wireless communication. It is usually known as 4G LTE in cellphone or mobile devices.

LTE in Unlicensed (LTE-U) operates in open/unlicensed spectrum, such as in the 5GHz band. It aggregates with the licensed LTE in order to increase the data rate of the Advanced LTE system (unlicensed and licensed LTE system).

With the massive growth in data traffic and mobile devices, it is necessary to expand the mobile network system. While the licensed spectrum is limited in amount, the possible solution should be using the available unlicensed spectrum, even it might be conflict with the exist network, such as Wi-Fi.

It is recently proposed by Qualcomm, Ericsson, and Verizon that LTE-U should be utilize in unlicensed spectrum on the 5725-5850 MHz band so that it could be a "nice neighbor" with Wi-Fi.

Objectives

• Research on wireless communications, LTE, LTE-U and Wi-Fi in advance
• Simulate the LTE-U base station in ORBIT Lab using OMF commands, WiMax, and OpenAirInterface
• Transmit and Receive LTE Signal
• Apply analyzing tools, such as spectrum analyzer, GNU Radio, SNR
• Modify OAI source code and report the result

Theory

OpenAirInterface (OAI) is open-source based experimental research. It allows to simulate the digital communication environments, such as LTE. ​OAI Documentation

Real-world testbed:

• OAI SW + OAI HW or USRP B210/X300
• OAI EPC + OAI eNB <–> COTS UE
• Commercial/3rd party EPC + OAI eNB <–>COTS UE
• OAI eNB <–>OAI UE
• OAI + Signal generator/spectrum analyzer

The source code ​OpenAir4G is organized into 6 main repositories for different use cases: OpenAir1, OpenAir2, OpenAir3, OpenAir0, OpenAirCN, Targets.

Each repository focuses on a different data communication layer or focus of 3GPP implementation.

Figure 1. OpenAir LTE Protocol

OpenAir1 ​Code

• Open-source real-time and offline Software
• Baseband DSP SIMD-x86 routines for implementing LTE UE’s and eNB’s
• Simulation TestBenches for all LTE PHY/transport channels
  • Sensing Localization Techniques
  • PHY modeling tools
  • Propagating Measurement and Modeling
  • Basic DSP Routines for implementing LTE specifications
• Sounding Software, Physical (PHY) Abstraction Software, and Channel Simulation
  • Eurecom’s Multi-Input Multi-Output (MIMO) OpenAir Sounder (EMOS - Sounding Software) allows multiuser MIMO channel measurements in real time and store measurements from both user equipment(UE) and evolved NodeB(eNB)
  • PHY Abstraction Software contains all real-time/simulation signal processing, unitary TestBenches for the different channel coders and decoders, and modulation/demodulation (includes FFT/SC-FDMA front-end processing)
  • Channel Simulation Software contains simulation routines to test PHY, and TestBenches for unitary simulation of physical channels, and full system simulation, such as PHY, MAC (medium access control), RLC (radio link control), RRC (radio resource control), PDCP (packet data convergence protocol)

OpenAir2 ​Code

• Open-source real-time and offline Software
• Contains LTE MAC (36-213), RLC (36-322), PDCP (36-323)
• S1 interfaces for user and control planes of the eNB

OpenAir3 ​Code

• Open-source Linux Software suite for cellular and MESH networks
• Provides scripts and adaptations for the Linux networking suite

OpenAir0 ​Code

• Open-source real-time Hardware & Software for different Xilinx targets

OpenAirCN ​Code

• 3GPP-EPC implementation
• Small-scale 3GPP-EPC implementation
• Includes MME, P and S-Gateway, and HSS components

Targets ​Code

• Top-level target designs for use with and without Hardware in emulated or real-time modes

Analyzing Tools

Spectrum Analyzer

Hardware Spectrum Analyzer – Tektronix SA2600:

• Wire measurement must be connect with 30dB attenuator in order to avoid saturation
• Wireless measurement requires much higher gain than using wire

  Figure 2. Tektronix SA2600

Software Spectrum Analyzer – RTLSDR Scanner:

• PROS: user-friendly, convenient, remote access, software-based spectrum analyzer
• CONS: Realtek 2832 EZCap can’t tune to frequencies higher than 1.8GHz

Figure 3. RTLSDR Scanner

GNU Radio

GNU Radio is an important tool to obtain the Waterfall Plot. ​How to use GNU Radio

Signal-to-Noise Ratio (SNR)

There are 2 methods to approximate the SNR:

• Method 1: Estimate the noise power by measure the received signal power when transmitter is turned off.
• Method 2: Estimate the noise power by calculate the received signal variance.

The relationship between signal, noise, SNR:

• noise = variance = mean ( signal – mean ( signal ) )
• noise [dB] = 10 log (noise power)
• signal [dB] = 10 log (signal power)
• SNR = signal power / noise power
• SNR [dB] = signal [dB] – noise [dB]

MATLAB code to measure SNR:

Experiments

Experiment 1: Transmit and Receive LTE Signal

The experiment is simulated in Sandbox 1 with USRP Hardware Driver (UHD) using OAI software.

Figure 4. Received LTE Signal

Figure 5. I/Q Samples

Experiment 2:

Experiment 3:

Experiment 4:

Experiment 5:

Members

*Led by Dola Saha and Prof. Ivan Seskar

Cat Le, Electrical and Computer Engineering, Rutgers University

Demetrios Lambropoulos, Electrical and Computer Engineering, Rutgers University

Steven Cheng, Rutgers University

Materials

​Presentation: Week 1

​Presentation: Week 2

​Presentation: Week 3

​Presentation: Week 4

​Presentation: Week 5

​Presentation: Week 6

​Presentation: Week 7 ​OpenAirInterface

​Presentation: Week 8

​Presentation: Week 9

​Presentation: Week 10

​Presentation: Week 11

​Presentation: Week 12

Resources

​LTE Unlicensed Augmenting Mobile Data Capacity But Coexistence Needs Consideration

​U-LTE: Unlicensed Spectrum Utilization of LTE

​Extending LTE Advanced to Unlicensed Spectrum

​The Prospect Of LTE And Wi-Fi Sharing Unlicensed Spectrum

​Coexistence of LTE and WiFi Heterogeneous Networks via Inter Network Coordination