15EC81 - Wireless Module 1 PDF

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MAHARAJA INSTITUTE OF TECHNOLOGY Thandavapura, Nanjangud Taluk-571 302 Mysore district, Karnataka, India

Department of E Electronics lectronics and C Communication ommunication Engineer Engineering ing

semester r NOTES 8th semeste Wireless C Cellular ellular and LTE 4G Broadband 15 15EC EC EC81 81 MODULE – 1 CHAPTER 1: Key Enablers for LTE fea features tures •

OFDM

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Single carrier FDMA (SC-FDMA)

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Single carrier FDE (SC-FDE)

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Channel Dependent Multiuser Resource Scheduling

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Multi antenna Techniques

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IP based Flat network Architecture

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LTE Network Architecture (Sec 1.4- 1.5 of Text)

CHAPTER 2: Wireless Fundamentals •

Cellular concept

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Broadband wireless channel (BWC)

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Fading in BWC

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Modeling BWC – Empirical and Statistical models

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Mitigation of Narrow band and Broadband Fading (Sec 2.2 – 2.7of Text)

MEGHANA M N ASSISTANT PROFESSOR DEPT. OF ECE

MITT

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MODULE 1 CHAPTER 1 – KEY ENABLERS FOR LTE FEATURES

1. EVOLUTION OF MOBILE BROADBAND There are 5 cellular system technologies: 1G, 2G, 3G, 4G and 5G technology.

1.1 FIRST GENERATION (1G) TECHNOLOGY •

1G refers to the first-generation.

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It uses analog signal to transmit data.

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It was introduced in early 1980’s and designed exclusively for voice communication.

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AMPS (Advanced Mobile Phone system) standards were the popular 1G cellular system.

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1G data speed is up to 2.4kbps.

Example: cordless mobile system Drawbacks ➢ Poor Voice Quality and Poor Battery Life ➢ Large Phone Size and no Security ➢ no data services and no roaming ➢ Cannot transmit for long distance

1.2 SECOND GENERATION (2G) TECHNOLOGY •

2G refers to the second-generation.

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2G technology uses digital signals for first time.

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It was launched in 1991 and used GSM (Global System for Mobile communication) standards.

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2G data speed is up to 64kbps.

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Text(SMS) and multimedia transmission were introduced.

2.5G TECHNOLOGY •

2G technology along with GPRS (General Packet Radio Service) standard give rise to 2.5G technology.

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2.5G enabled roaming, web browsing, e-mail services and fast upload/download speed.

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2G data speed is up to 160kbps.

2.75 G TECHNOLOGIES •

2.75 G launched enhanced GSM standard called EDGE (Enhanced Data for Global Evolution).

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Its supports high data rate of upto 170kbps and it enables multimedia access.

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Example of 2G: Keypad mobiles Drawback of 2G: ➢ Limited data rates ➢ Basically circuit switched system ➢ Not supported for true mobility and less security.

1.3 THIRD GENERATION (3G) TECHNOLOGY •

3G refers to third generation.

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3G technology was introduced in year 2000s.

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Data transmission speed increased from170Kbps to 2Mbps.

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3G Technology uses CDMA( Code Division Multiple Access) – 2000 and UMTS (Universal Mobile Telecommunication System) standards.

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3G facilitates increased bandwidth and data transfer rates.

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Compatible with smart phones and Provides Web-based applications.

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Main characteristics of 3G network is it uses Digital broadband and with more speed.

3.5G TECHNOLOGY •

3.5 G technology was introduced in around 2000s where the evolution of network took next phase from 3G.

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3.5G is capable of using high bit rate than 3G and the new idea of mobility bit rate was introduced.

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The 3 main standards in 3.5G technology are HSDPA (High Speed Datalink Packet Access), HSUPA (High Speed Uplink Packet Access) and HSPA+ (High Speed Packet Access).

Example of 3G: smart phones Drawback of 3G: ➢ Expensive fees for 3G Licenses Services. ➢ It was challenge to build the infrastructure for 3G. ➢ High Bandwidth Requirement. ➢ Expensive 3G Phones. ➢ Large Cell Phones.

1.4 FOURTH GENERATION (4G) TECHNOLOGY •

4G refers to fourth generation.

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4G technology was introduced in year 2004.

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Data transmission speed/ bit rate of 5Mbps to 1000Mbps.

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4G Technology uses LTE (Long Term Evolution) standards.

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It supports mobile web access, cloud computing, global mobility support and high definition mobile TV.

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4G also enable a VOLTE (Voice Over Long Term Evolution) standard for high speed wireless communication for mobile phones and data terminals including IoT devices and wearable.

1.5 FIFTH GENERATION (5G) TECHNOLOGY •

5G refers to fifth generation.

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5G was started from late 2010s.

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Complete wireless communication with almost no limitations.

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It is highly supportable to WWWW (Wireless World Wide Web).

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Aims at higher capacity than current 4G, allowing a higher density of mobile broadband users.

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Supports interactive multimedia, voice streaming and enhanced security.

2. KEY ENABLING TECHNOLOGIES AND FEATURES OF LTE ***** Key Enabling Technologies and Features of LTE are

1. Orthogonal Frequency Division Multiplexing (OFDM) 2. SC-FDE and SC-FDMA 3. Channel Dependent Multi-user Resource Scheduling 4. Multi-antenna Techniques 5. IP-Based Flat Network Architecture

2.1 ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING (OFDM) ***** Q.: Explain the advantages of OFDM for LTE. [8M] June/July 2019 •

3G systems are based on CDMA technology. Advantage: CDMA Performs remarkably well for low data rate communications, where a large number of users can be multiplexed to achieve high system capacity. Limitation: CDMA cannot able to handle the large bandwidth required for high-speed applications and hence design becomes complex.

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OFDM has emerged as a technology for achieving high data rates and is widely used in Wi-Fi.

➢ The following advantages of OFDM led to its selection for LTE:***** 1. Elegant solution to multipath interference: •

The main aim is to achieve high Bit-rate transmissions in a wireless channel the critical challenge is Inter Symbol Interference (ISI) caused by multi path.

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At high data rates the symbol time is shorter; hence it only takes a small delay to cause ISI.

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OFDM is a multicarrier modulation technique which can be used to eliminate the ISI effect.

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In OFDM, the subcarriers are orthogonal to one another over the symbol duration.

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Thereby instead of using non-over lapping subcarrier, subcarrier can be overlapped over a channel which eliminates ISI.

2. Reduced computational complexity: •

OFDM can be easily implemented using Fast Fourier Transforms (FFT) at the sender side and Inverse Fast Fourier Transforms (IFFT) at the receiving end.

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The computational complexity of OFDM = (B log B Tm), where B is the bandwidth and Tm is the delay spread.

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Reduced complexity is mainly used the downlink as it simplifies receiver processing and thus reduces mobile device cost and power consumption.

3. Graceful degradation of performance under excess delay: •

The performance of an OFDM system degrades gracefully as the delay spread exceeds the designed value.

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OFDM is well suited for adaptive modulation and coding, which allows the system to make the best use of the available channel conditions.

4. Exploitation of frequency diversity: •

OFDM provides the range of frequencies to subcarriers in the frequency domain, which can provide robustness against errors.

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OFDM also allows scaling of channel bandwidth without affecting the hardware design of the base station and the mobile station.

5. Enables efficient multi-access scheme: •

OFDM can be used as a multi-access scheme by partitioning different subcarriers among multiple users.

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This scheme is referred as OFDMA and is used in LTE standard.

6. Robust against narrowband interference: •

OFDM is relatively robust against narrowband interference, since such interference affects only a fraction of the subcarriers.

7. Suitable for coherent demodulation: •

It is relatively easy to do pilot-based channel estimation in OFDM systems, which renders them suitable for coherent demodulation schemes that are more power efficient.

8. Facilitates use of MIMO: •

MIMO refers to a collection of signal processing techniques that use multiple antennas at both the transmitter and receiver to improve system performance.

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For MIMO techniques to be effective, it is required that the channel conditions are such that the multipath

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delays do not cause ISI interference. •

OFDM converts a frequency selective broad band channel into several narrowband flat fading channels where the MIMO models and techniques work well.

9. Efficient support of broadcast services: •

It is possible to operate an OFDM network as a Single Frequency Network (SFN).

• This allows broadcast signals from different cells to combine over the air and which enhances the received signal power, thereby enabling higher data rate broadcast transmissions.

➢ Disadvantages of OFDM: •

Peak-to-Average Ratio (PAR): OFDM has high PAR, which causes non-linearity and clipping distortion when passed through an RF amplifier.

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High PAR increases the cost of the transmitter.

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OFDM is tolerated in the downlink as part of the design, for the uplink LTE selected a variation of OFDM that has a lower peak-to- average ratio.

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The modulation used for the uplink is called Single Carrier Frequency Division Multiple Access. (SCFDMA).

2.2 SC-FDE and SC-FDMA ➢ Single-Carrier Frequency Domain Equalization (SC-FDE) •

It is a single-carrier (SC) modulation combined with frequency-domain equalization (FDE).

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It is an alternative approach to inter symbol interference (ISI) mitigation.

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It uses QAM (Quadrature Amplitude Modulation) rather than FFT/IFFT used in OFDM to send data.

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SC-FDE retains all the advantages of OFDM such as multipath resistance and low complexity, while having a low peak-to-average ratio of 4-5dB.

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It keeps the mobile station cost down and the battery life up.

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LTE incorporated a SC-FDE as a power efficient transmission scheme for the uplink.

➢ Single-Carrier Frequency Division Multiple Access( SC-FDMA) •

A multi-user version of SC-FDE, called SC-FDMA.

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The uplink of LTE implements uses to SC-FDMA, which allows multiple users to use parts of the frequency spectrum.

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SC-FDMA closely resembles OFDMA and also preserves the PAR properties.

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The drawback of SC-FDE is increases the complexity of the transmitter and the receiver.

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2.3 CHANNEL DEPENDENT MULTI-USER RESOURCE SCHEDULING •

Resource scheduling is mainly used in OFDM - Orthogonal Frequency Division Multiplexing and OFDMA - Orthogonal Frequency Division Multiple Access.

Figure 1: Resource mapping in OFDMA

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The OFDMA scheme used in LTE provides more flexibility with respect to channel resources allocation.

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OFDMA allows allocation in both time and frequency and it is possible to design algorithms to allocate resources in a flexible and dynamic manner to meet arbitrary throughput, delay and other requirements.

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The standard supports dynamic, channel-dependent scheduling to enhance overall system capacity.

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In OFDM, It is possible to allocate subcarriers among users in such a way that the overall capacity is increased.

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Allocation of subcarriers among users is called as frequency selective multiuser scheduling, which focuses on transmitting power in each user’s best channel portion.

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In OFDMA, frequency selective scheduling can be combined with multi-user time domain scheduling.

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Capacity gains are also obtained by adapting the modulation and coding to the instantaneous signal-tonoise ratio conditions for each user subcarrier.

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For high-mobility users, OFDMA can be used to achieve frequency diversity by coding and interleaving across subcarriers.

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Frequency diverse scheduling is best suited for control signalling and delay sensitive services.

2.4 MULTI-ANTENNA TECHNIQUES •

The LTE standard provides multi-antenna solutions to improve link robustness, system capacity, and spectral efficiency.

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Multi-antenna techniques supported in LTE include: 1.

Transmit diversity

2. Beam forming

3.

Spatial multiplexing

4. Multi user MIMO

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1. TRANSMIT DIVERSITY •

Diversity means send copies of the same signal by using two or more communication channels with different characteristics. This is a technique to prevent multipath fading in the wireless channel. f D(1) Data Symbols D(1)

Transmit Antenna 1

D(0) t

f

D(0)

D(0)*

Transmit Antenna 2

D(1)* t

Figure 2: Transmit diversity (SFBC)

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LTE transmit diversity is based on space-frequency block coding (SFBC) techniques.

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Transmit diversity is used in common downlink channels that cannot make use of channel-dependent scheduling.

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It increases system capacity and cell range.

2. BEAMFORMING •

Multiple antennas in LTE may also be used beamforming technique to transmit the beam in the direction of the receiver and away from interference, thereby improving the received signal-to-interference ratio.

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It can provide significant improvements in coverage range, capacity, reliability, and battery life.

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It can also be useful in providing angular information for user tracking.

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LTE supports beamforming in the downlink.

3. SPATIAL MULTIPLEXING •

In spatial multiplexing, multiple independent streams can be transmitted in parallel over multiple antennas and can be separated at the receiver using multiple receive chains through appropriate signal processing.

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Spatial multiplexing provides data rate and capacity gains proportional to the number of antennas used.

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It works well under good SNR and light load conditions. LTE standard supports spatial multiplexing with up to four transmits antennas and four receiver antennas.

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MIMO with Transmit diversity

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MIMO with Spatial Multiplexing

Figure 3: Comparison of MIMO with Diversity and spatial multiplexing

4. MULTI-USER MIMO •

Since spatial multiplexing requires multiple transmit antennas, it is currently not supported in the uplink due to complexity and high cost.

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Multi-User MIMO (MU-MIMO) allows multiple users in the uplink, each with a single antenna, to transmit using the same frequency and time.

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The signals from the different MU-MIMO users are separated at the base station receiver using accurate channel state information of each user obtained through uplink reference signals that are orthogonal between users.

Figure 4: Comparison between Single and multiuser MIMO

2.5 IP-BASED FLAT LTE SAE NETWORK ARCHITECTURE**** Q.: Explain flat LTE SAE architecture. [8M] June/July 2019 •

Apart from air interface the other aspects of LTE is Flat Network Architecture. Flat implies fewer nodes and less hierarchical structure for the network which reduces the infrastructure cost.

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It also means fewer interfaces and protocol-related processing and reduced inter-operability testing, which lowers the development cost.

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Fewer nodes also allow better optimization of radio interface, merging of some control plane protocols, and short session start-up time.

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Figure 5 shows how the 3GPP network architecture evolution.

Figure 5: 3GPP evolution toward a flat LTE SAE architecture

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Flat LTE architecture description

• 3GPP Release 6 architecture has four network elements in the data path: Base Station (BS), Radio Network Controller (RNC), Serving GPRS Service Node (SGSN), and Gateway GRPS Service Node (GGSN). •

Release 7 introduced a direct tunnel option from the RNC to GGSN, which eliminated SGSN from the data path.

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LTE on the other hand, will have only two network elements in the data path: the enhanced Node-Bore (eNode-B) and a System Architecture Evolution Gateway (SAE-GW).

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LTE merges the BS and RNC functionality into a single unit.

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The control path includes a functional entity called the Mobility Management Entity (MME), which provides control plane functions related to subscriber, mobility, and session management.

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The MME and SAE-GW collocated in a single entity called the Access Gateway (A-GW).

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A key aspect of the LTE flat architecture is that all services, including voice, are supported on the IP packet network using IP protocols.

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Whereas previous 2G and 3G systems had a separate circuit-switched sub-network for supporting voice with their own Mobile Switching Centers (MSC) and transport networks.

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LTE focuses on a single Evolved Packet Core (EPC) over which all services are supported, which could provide huge operational and infrastructure cost savings.

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However, LTE has been designed for IP services with a flat architecture, due to backwards compatibility reasons certain legacy, non-IP aspects of the 3GPP architecture such as the GPRS tunnelling protocol and PDCP (Pa...