digital network lecturer7

DIT

Dar es Salaam institute of Technology (DIT)

ETU 08102

Digital Networks

Ally, J

[email protected]

LTE Network

DIT

Peak data rate of 50/100 Mbps (uplink / downlink) Reduced latency enabling RTT (round trip time) <10 ms Packet-optimized Improved spectrum efficiency between 2- 4 times higher than

Release 6 HSPA Bandwidth scalability with allocations of 1.4, 3, 5, 10, 15 and 20

MHz Operation in FDD and TDD modes Support for inter-working with WCDMA and non-3GPP systems

(i.e. WiMAX) Good level of mobility: optimized for low mobile speeds (up to

15km/h) but support also high mobile speeds (up to 350km/h) Improved terminal power efficiency

DIT

LTE Requirements

Drivers for LTE There are at least three major key drivers for LTE mobile

broadband networks:

Demand for higher data-rates increasing device capabilities, growing mobile data

consumption

New spectrum allocation

Maintaining operator profitability while continued cost reduction and competitiveness.

DIT

LTE and LTE Advanced Comparison

DIT

LTE Overview The multiple access schemes in LTE:

Orthogonal Frequency Division Multiple Access (OFDMA) in downlink

Single Carrier Frequency Division Multiple Access (SC-FDMA) in uplink

LTE user transmissions can be divided in frequency and time Better orthogonality between users Interference is less or can be cancelled more easily Better network capacity can be achieved

The resource allocation in the frequency domain takes place with a resolution of 180 kHz resource blocks both in uplink and in downlink.

DIT

Basic LTE system architectureArchitecture is divided into four main domains:User Equipment (UE),Evolved UTRAN (E-UTRAN),Evolved Packet Core Network (EPC),Services domain.

DIT

LTE Networks Elements

DIT

Domains Three domains: UE, E-UTRAN and EPC form the so-

called Internet Protocol (IP) Connectivity Layer. This part of the system is also called as Evolved Packet System (EPS). The main function of EPS is to provide IP based connectivity All services will be offered on top of IP

The biggest architectural change is that EPC does not contain a circuit switched domain.

Main functionalities of the EPC are equivalent to the packet switched domain of the existing 3GPP networks.

As a logical element the SAE GW is a combination of the two gateways, Serving Gateway (S-GW) and Packet Data Network Gateway (P-GW)

DIT

Domains Since interfaces between S-GW and P-GW are defined in

standards, it is possible that S-GW and P-GW are implemented either separately or together.

E-UTRAN contains only one element type: Evolved Node B (eNodeB).

All radio functionalities are controlled by eNodeB. All radio related protocols are terminated in eNodeB.

E-UTRAN network is just a mesh of eNodeBs connected to neighbouring eNodeBs through the X2 interface.

Functionally eNodeB acts as a layer 2 bridge between UE and the EPC, by being the termination point of all the radio protocols towards the UE.

From functionality point of view the UE is similar like in 3G.

DIT

UE and eNodeB UE

Access device for user. Provides measurements that indicate channel conditions to the

network. eNode B performs

Ciphering/deciphering of the User Plane data Radio Resource Management (resource allocation, prioritizing,

scheduling, resource usage monitoring eNodeB is also involved with Mobility Management (MM) The eNodeB controls and analyses radio signal measurements

carried out by the UE. eNodeB makes signal measurements itself Based on measurement information eNodeB makes decisions to

handover UEs between cells.

DIT

Mobility Management Entity (MME) MME is the main control element in the EPC. It is

typically a server in a secure location in the operator’s premises.

MME operates only in the control plane and is not involved with the user plane data.

MME also has a direct logical control plane connection to the UE. Connection is a primary control channel between the UE and the network.

Main functions of MME: Authentication and Security Mobility Management Managing Subscription Profile and Service Connectivity

DIT

Serving Gateway (S-GW) S-GW takes care of user plane tunnel

management and switching, and relays data between eNodeB and P-GW.

The S-GW has a small role in control functions.

When bearers for UEs are set up, cleared or modified the S-GW allocates its resources based on requests from MME, P-GW or PCRF.

DIT

Packet Data Network Gateway (P-GW) P-GW is the edge router between the EPS and external packet

data networks. P-GW is the highest level mobility anchor in the system, and

usually it acts as the IP point of attachment for the UE. Thus, typically the P-GW allocates the IP address to the UE,

and the UE uses that to communicate with other IP hosts in external networks, e.g. the internet.

During mobility between eNodeBs, the S-GW acts as the local mobility anchor. The MME commands the S-GW to switch the tunnel from one eNodeB to another.

P-GW performs traffic gating and filtering functions as required by the service in question.

Both S-GW and P-GW are part of the network infrastructure maintained centrally in operator premises.

DIT

Policy and Charging Resource Function (PCRF), Home Subscription Server (HSS)

PCRF is the network element that is responsible for Policy and Charging Control (PCC).

HSS is the data repository for all permanent subscription data. Hence, HSS has the master copy of the subscriber profile

Main interfaces X2 interface: This interface is used in mobility between the

eNodeBs, and it includes functions for handover preparation, and overall maintenance of the relation between neighbouring eNodeBs.

S1-MME interface: Reference point for the control plane protocol between E-UTRAN and MME.

S1-U interface: Reference point between E-UTRAN and Serving GW for the user plane tunnelling and inter eNodeB path switching during handover.

DIT

FDD IMT Frequency Bands

DIT

TDD IMT Frequency Bands

DIT

Existing and Future 3GPP Bands

DIT

UE Categories and Capabilities

DIT

UE category

Maximum Throughput Support for 64QAM in Uplink

Downlink Uplink

1 10.3 Mbit/s 5.2 Mbit/s No




5 300.0 Mbit/s 75.4 Mbit/s Yes



8 300.0 Mbit/s 149.8 Mbit/s Yes


10 452.3 Mbit/s 102.2 Mbit/s No

OFDMA OFDMA is an extension of the OFDM transmission scheme by

allowing multiple users. That is, allowing for simultaneous frequency-separated

transmissions to / from multiple mobile terminals. In OFDM the user data is transmitted in parallel across

multiple orthogonal narrowband subcarriers. Each subcarrier only transports a part of the whole

transmission. The orthogonal subcarriers are generated with IFFT (Inverse

Fast Fourier Transform) processing. The number of subcarriers depends on the available

bandwidth. In LTE, they range from less than one hundred to more than

one thousand.

DIT

OFDM Operation

DIT

Cyclic Prefix (CP) Principle

Cyclic prefixes are used by OFDM systems to fight against the Inter Symbol Interference (ISI) due to multipath environments.

CP consists of a copy of the last part of a symbol shape for the duration of a guard time and adding it to the beginning of the symbol.

This guard time needs to be long enough to capture all the delayed multipath signals and avoid ISI at the receiver.

LTE’s typical symbol duration including the CP is around 71.64 µsec.

DIT

Types of Cyclic Prefix for LTEThere are two cyclic prefix options for LTE:

Normal cyclic prefix: For use in small cells or cells with short multipath delay spread. Its length depends on the symbol position within the slot being 5.21 µsec for the CP in symbol 0 and 4.6 µsec for the rest of symbols. The reason for these two different lengths is so that the slot duration is 0.5ms, facilitating at the same time, that the terminal finds the starting point of the slot.Extended cyclic prefix: For user with large cells or those with long delay profiles. Its length is 16.67µs and it is constant for all symbols in the slot.

DIT

OFDMA Benefits and DrawbacksBenefits

High spectral efficiency for wideband channels

OFDM is almost completely resistant to multi-path interference due to its very long symbol duration

Flexible spectrum utilization Relative simple implementation

using FFT/IFFT Easy MIMO techniques

implementation

Drawbacks Some OFDM Systems can

suffer from high PAPR (Peak Average Power Ratio)

Loss of orthogonality due to frequency errors

Doppler shifts impacts subcarrier orthogonaliy due to ISI

Accurate frequency and time synchronization

DIT

OFDMA Parameters

DIT

Comparison of OFDMA and SC-FDMA

LTE Frame Structures Ts is the basic time unit for LTE. Ts = 1/(15000 x 2048) seconds or about 32.6 ns. Downlink and uplink transmissions are organized into frames of

duration Tf = 307200 Ts. The 10 ms frames divide into 10 subframes. Each subframe divides into 2 slots of 0.5 ms. Two frame types are defined for LTE: Type 1, used in Frequency

Division Duplexing (FDD) and Type 2, used in Time Division Duplexing (TDD).

Type 1 frames consist of 20 slots with slot duration of 0.5 ms. Type 2 frames contain two half frames. Depending on the switch

period, at least one of the half frames contains a special subframe carrying three fields of switch information: Downlink Pilot Time Slot (DwPTS), Guard Period (GP) and Uplink Pilot Time Slot (UpPTS).

DIT

Frame Type 1 (FDD)

DIT

Frame Type 2 (TDD)

DIT

Uplink-downlink Configurations for the LTE

TDD Mode

DIT

D is Downlink subframe, U is Uplink subframe, and S is special subframe

The Resource Block Mapping of channels takes place in the time and

frequency domains in LTE. The primary element that support the mapping

process is the Resource Block (RB). The RB has a fixed size and is common to all channel

bandwidths/FFT sizes. In the time domain the RB is one slot ( 7 x 66.67µS

symbols). In the frequency domain there are 12 x 15KHz sub-

carriers. 1 symbol and 1 sub-carrier is known as a resource

element.

DIT

Defining a Resource Block

DIT

Channel Bandwidth

DIT

Theoretical Data Rates LTE does not officially meet the 4G requirements issued by

ITU in the definition for IMT-Advanced. The data rates available in LTE (up to 300 Mbps) are

substantially higher than previous generations of cellular standards.

It is worth noting that the maximum theoretical data rates of LTE Advanced (up to 3.08 Gbps) are compliant with the ‘4G’ definition of the IMT-Advanced requirements.

Throughput of digital wireless communications channels is defined by several factors, including:

symbol period utilization, symbol rate, modulation scheme, code rate, number of resource blocks, and number of spatial streams.

DIT

Throughput calculation for LTE SISO Link

Throughput = Data Subcarriers X Slots per second X Symbols per Slot X Bits per Symbol X Code Rate X Spatial StreamsWith LTE, the maximum throughput in a 1x1 SISO channel occurs when the eNodeB allocates all resource blocks (1200 subcarriers) for a 20 MHz signal bandwidth using the 64-QAM modulation scheme. In this case, the estimated theoretical throughput is 76.9 Mbps.

Throughput = 1200 data subcarriers X 2000 slots X 7 symbols X 6 bits X (4/5) code rate x 1 spatial stream = 76.9 Mbps

DIT

Throughput calculation for LTE Advanced 8x8 MIMO Link

For MIMO schemes, the addition of carrier aggregation increases the theoretical data rates of LTE Advanced further.

20 MHz channel bandwidth allows for 1,200 data subcarriers, the use of five aggregated carriers would increase the number of data subcarriers to 6,000. the maximum data rate can be calculated as follows:

Throughput = 6000 data subcarriers X 2000 slots X 7 symbols X 6 bits X (4/5) code rate x 8 spatial streams = 3.08 Gbps

LTE Advanced is the first commercial wireless standard that exceeds the IMT-Advanced requirements for 4G cellular

systems.

DIT

Maximum Downlink Capacity per Radio Channel

DIT

Maximum Uplink Capacity per Radio Channel

DIT

LTE Logical Channels Logical Control Channels

Broadcast Control Channel (BCCH) Paging Control Channel (PCCH) Common Control Channel (CCCH) Multicast Control Channel (MCCH) Dedicated Control Channel (DCCH)

Logical Traffic Channels Dedicated Traffic Channel (DTCH) Multicast Traffic Channel (MTCH)

DIT

LTE Transport Channel Downlink Transport Channel

Broadcast Channel (BCH) Downlink Shared Channel (DL-SCH) Paging Channel (PCH) Multicast Channel (MCH)

Uplink Transport Channels Uplink Shared Channel (UL-SCH) Random Access Channel (RACH)

DIT

LTE Physical Channel Downlink Physical Channel

Physical Broadcast Channel (PBCH) Physical Control Format Indicator Channel (PCFICH) Physical Downlink Control Channel (PDCCH) Physical Hybrid ARQ Indicator Channel (PHICH) Physical Downlink Shared Channel (PDSCH) Physical Multicast Channel (PMCH) Multicast Channel (MCH)

Uplink Physical Channel Physical Uplink Control Channel (PUCCH) Physical Uplink Shared Channel (PUSCH) Physical Random Access Channel (PRACH)

DIT

Channel Mapping

DIT

3GPP Evolution: From LTE to LTE-A/B/C

DIT

Release Roadmap

DIT

digital network lecturer7

Education