LTE Curs 1 _v2012

LTE for 4G Mobile Broadband
by Ren ANDREESCU

Curs 1

by Ren ANDREESCU

by Ren ANDREESCU

A set of several frequencies are used in one cell and other mutually exclusive

sets are used in other cells in the cluster. This arrangement forces one to examine the

criteria as to when a frequency can be reused again.

The figure provides an example of the popular 7-cell cluster arrangement, with six clusters surrounding a cluster in

the middle. In the middle of each cluster is a base station that must have the same

frequency set if the network is being built with the 7-cell cluster as the basis.

It can be shown that if the cluster size is N and the cell radius is R, the reuse

distance D is given by D = R (3N)1/2.

The cluster sizes need not be the same throughout the network. Cells can be split

to provide increased capacity (number of subscribers per square area) towards city

centers.

by Ren ANDREESCU

by Ren ANDREESCU

Flat Architecture of LTE and SAE ( System Architecture Evolution )

by Ren ANDREESCU

LTE Network Architecture

by Ren ANDREESCU

LTE Specifications

by Ren ANDREESCU

Multiple access scheme

DL: OFDMA with CP.

UL: Single Carrier FDMA (SC-FDMA) with CP.

Adaptive modulation and coding

DL modulations: QPSK, 16QAM, and 64QAM

UL modulations: QPSK and 16QAM

Rel-6 Turbo code: Coding rate of 1/3, two 8-state constituent encoders, and a contention-free internal interleaver.

Advanced MIMO spatial multiplexing techniques

(2 or 4)x(2 or 4) downlink and uplink supported.

Multi-layer transmission with up to four streams.

Multi-user MIMO also supported.

ARQ within RLC sublayer and Hybrid ARQ within MAC sublayer.

by Ren ANDREESCU

LTE Frame Structure

Two radio frame structures defined.

Generic frame structure: FDD and TDD.

Alternative frame structure: TDD only.

Generic radio frame has duration of 10 ms. It consists of 20 slots.

A slot has a duration of 0.5 ms. 2 slots comprise a subframe.

A resource block (RB) spans 12 subcarriers over a slot duration

of 0.5 ms. One subcarrier has bandwidth of 15 kHz.

by Ren ANDREESCU

Peak data rate

100 Mbps DL/ 50 Mbps UL within 20 MHz bandwidth.

Up to 200 active users in a cell (5 MHz)

Less than 5 ms user-plane latency

Mobility

Optimized for 0 ~ 15 km/h.

15 ~ 120 km/h supported with high performance.

Supported up to 350 km/h or even up to 500 km/h.

Enhanced multimedia broadcast multicast service (E-MBMS)

Spectrum flexibility: 1.25 ~ 20 MHz

Enhanced support for end-to-end QoS

Requirements of LTE

by Ren ANDREESCU

Subcarrier Mapping

by Ren ANDREESCU

LTE Frequency Bands

by Ren ANDREESCU

LTE Downlink - OFDM

by Ren ANDREESCU

Single Carrier with Frequency Domain Equalization

SC/FDE delivers performance similar to OFDM with essentially

the same overall complexity, even for long channel delay.

SC/FDE has advantage over OFDM in terms of:

Low PAPR.

Robustness to spectral null.

Less sensitivity to carrier frequency offset.

Disadvantage to OFDM is that channel-adaptive subcarrier bit

and power loading is not possible.

Single Carrier FDMA (SC-FDMA) is an extension of SC/FDE to accommodate multiple-user access.

by Ren ANDREESCU

Bandwidth Configuration

The transmission bandwidth configuration in MHz is given as:

where = 15 kHz is the subcarrier spacing.

by Ren ANDREESCU

SC-FDMA and OFDMA

by Ren ANDREESCU

LTE Bandwidth / Resource COnfiuration

by Ren ANDREESCU

LTE Frame Structure Type 1

by Ren ANDREESCU

System Capacity

The SINR in an OFDM system is approximatted , so the capacity is:

by Ren ANDREESCU

Capacity gains

by Ren ANDREESCU

The Basic assumption is: for less then 10% ISI there is no

need for equalization, and a simple detection can be done.

For the 2-3GHz band, a 10sec delay spread can be assumed,

the basic carrier spacing should be approximately 4KHz

(adding on top of that the Guard Interval).

by Ren ANDREESCU

Frequency Division Duplexing (FDD) Principles

One Frequency is Used for the DownLink, Using OFDM/TDM .

A Second Frequency is Used for the UpLink , Using OFDMA/TDMA .

by Ren ANDREESCU

OFDMA/TDMA Principles

Using OFDMA/TDMA, Sub Channels are allocated in the Frequency Domain, and OFDM Symbols allocated in the Time Domain.

by Ren ANDREESCU

UpLink OFDMA Symbol

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Using Special Permutations for Carrier Allocation

All usable carriers are divided into 23 carrier groups named basic group, each main group contains 23 basic groups.

There are 3 main groups.

by Ren ANDREESCU

Using Special Permutations for Carrier Allocation

Carriers are allocated by a basic series and its cyclic permutations

Basic Series:

0,5,2,10,4,20,8,17,16,11,9,22,18,21,13,19,3,15,6,7,12,14,1

After two cyclic permutations we get:

2,10,4,20,8,17,16,11,9,22,18,21,13,19,3,15,6,7,12,14,1,0,5

by Ren ANDREESCU

The effect of multipath channel on each of the subcarriers can be viewed in frequency domain

For the th subcarrier the received and demultiplexed sample value, Y(k), is given by Y(k) = X(k)* H(k), where H(k) is the frequency response of the th subchannel

by Ren ANDREESCU

We begin by grouping L data symbols into a block known as an OFDM symbol. An OFDM symbol lasts for a duration of T seconds,

where T = LTs.

In order to keep each OFDM symbol independent of the others after going through a wireless channel, it is necessary to introduce a guard

time between OFDM symbols:

by Ren ANDREESCU

This way, after receiving a series of OFDM symbols, as long as the guard time Tg is larger

than the delay spread of the channel, each OFDM symbol will interfere only with itself:

by Ren ANDREESCU

OFDM synchronization in (a) time and (b) frequency. Here, two subcarriers in the time domain and eight subcarriers in the frequency domain are shown, where fc = 10 MHz, and the subcarrier spacing f = 1 Hz

LTE Curs 1 _v2012

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