003 wimax key technologies

7/30/2019 003 WiMAX Key Technologies

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WiMAX Key Technologies

Petal Young

2010-May-13


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Contents

Advance Antenna Technologies

Hybrid Automatic Repeat Request (HARQ)

Adaptive Modulation and Coding (AMC)Scheduling Algorithms

Handoff

Power Control

Power Saving Modes

Quality of Service (QoS)


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n AAS Adaptive Antenna System

Beamforming (Smart Antenna)

n MIMO Multiple Input Multiple Output Space Time Coding (STC), Spatial Multiplexing (SM)

n Advantages:

Increased range/coverage

Increased capacity

Improved link quality/reliability

Increase spectrum efficiency

Lower power requirements


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Beamforming

n Beamforming is a technique to

control the directionality/sensitivity

of an array antenna s radiation

pattern based on the interference.

n Each user s signal is multiplied

with complex weights that adjust

the magnitude and phase of the

signal to and from each antenna. It

causes the output from the array of

antennas to form a

transmit/receive beam in the

desired direction and minimizes

the output in other directions.


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Space Time Coding (STC)

n Space Time Coding transmit

multiple, redundant copies of a data

stream to the receiver in the hope

that at least some of them may

survive the physical path between

transmission and reception in agood enough state to allow reliable

decoding.


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Spatial Multiplexing (SM)

n In SM-MIMO, multiple streams are

transmitted over multiple antennas.

n If the receiver also has multiple antennas,

it can separate the different streams to

achieve higher throughput.


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Contents




Handoff

Power Control

Power Saving Modes



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HARQ

n HARQ (Hybrid ARQ) is a combination of ARQ (Automatic Repeat

Request) and FEC (Forward Error Correcti on) coding.

n An HARQ scheme uses an error control code in conjunction with the

retransmission scheme to ensure reliable transmission of data packets.

n Every sent packet includes parity bits for error correction and detection.

Within the FEC capability, the errors will be corrected.

Beyond the FEC capability, ARQ is used.

n

HARQ types: Chase Combining

Incremental Redundancy

Base

Station


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Forward Error Correction

n The transmit end sends correctable codes and the receiver

uses a code correction decoder to automatically detect errors

and perform error correction.

n Coding schemes:

Convolutional Coding (CC)

Block Turbo Coding (BTC)

Convolutional Turbo Coding (CTC)

Low Parity Density Check (LDPC)

n CC is a mandatory scheme, while the others are optional

schemes. However, most manufacturers implement CTC


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Contents




Handoff

Power Control

Power Saving Modes



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AMC

n AMC stands for Adaptive

Modulation and Coding

Dynamically varies the size of

the raw channel.

Channel capacity can vary

depending on link conditions

n Key Features:

Increases the effective

coverage range.

Allows the system to adapt to

the actual fading conditions,

and use higher modulation

schemes when possible.


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AMC

n Mobile WiMAX supports AMC in both downlink and uplink with

variable packet size.

CC, CTC:

1/2, 2/3, 5/6

Repetition:

x2, x4, x6

16QAM

QPSK

64QAM (optional)

CC, CTC:

1/2, 2/3, 3/4, 5/6

Repetition:

x2, x4, x6

64QAM

16QAM

QPSK

Mobile WiMAX

UL

Code Rate

UL

Modulation

DL

Code Rate

DL

Modulation

Technology


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Contents




Handoff

Power Control

Power Saving Modes



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Resource allocation

n Resource allocation uses scheduling

algorithms to determine which users to

schedule, how to allocate sub-carriers

to them, and which power level is

appropriate.

n Aim of resource allocation:

Take advantage ofmultiuser

diversity and adaptive modulation to

provide high throughput while

considering fairness among users inthe system.

Multiuser diversit y describes the gains available by selectinga user or sub-set of users having good conditions

CSI Channel State Information


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Algorithm Comparison

Algorithm Sum Capacity Fairness Complexity

Maximum Sum Rate (MSR) Best Poor and Inflexible Low

Maximum Fairness (MF) Poor Best but Inflexible Medium

Proportional Rate Constraint (PRC) Good Most Flexible High

Proportional Fairness (PF) Good Flexible Low


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Contents




Handoff

Power Control

Power Saving ModesQuality of Service (QoS)


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Handoff

n Mobility management, enables the MS to retain its connectivity to the network

while moving from the coverage area of one BS to the next thru the handoff

process.

n Handover Schemes

Optimized Hard Handover (OHHO)

Fast Base Station Switching (FBSS)

Macro Diversity Handover (MDHO)

n Handover Control

Mobile initiated

BS initiated

Network initiated

n Cell Selection

Neighbor advertisements from Serving BS

Periodic intervals for scanning Neighbor BS


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Contents




Handoff

Power Control



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Power Control

n Purpose of power control

Remove the influence of slow fading in the wireless channel

Prevent power increase to decrease the overall interference level of the

system

Reduce the Tx power to the minimum level that meets the communication

quality requirement.

n Principles of power control

Power balance

Ensure approximately equal power of the wanted signals at the receive end

SNR balance

Ensure approximately equal C/I at the receive end

BER/FER balance

Ensure approximately equal BER/FER at the receive end


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Power Control

n Power Control Methods:

Open loop MS vary their own transmit power according to

received signal quality.

Closed loop - power is varied according to the base station

decision from comparison of the received signal quality to a set

point.

Mobile BTS

Signal Strength

Measurement

Setpoint

or

Reverse Closed Loop

Power Control

Reverse Open Loop

Power Control


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Contents




Handoff

Power Control



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Power Saving Modes

n Power management allows an MS to conserve battery

resources, a critical feature for handheld devices.

n Power saving modes:

Sleep Mode

Idle Mode (optional)


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Sleep Mode

n In sleep mode, an MS with active connections negotiates with the BS

to temporarily disrupt its connection over the air interface for a

predetermined amount of time, called the sleep window.

n Each sleep window is followed by a listen window, during which the

MS restores its connection.


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Idle Mode

n In Idle mode, MS can receive broadcast/multicast service

without registering to the network.

n Cell selection may occur but no handoff happens thus saving

power on the MS and saving resources on the BS.

n Paging is used to alert MS of incoming message.

n MS associates to a broadcast region formed by a paging group.


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Contents




Handoff

Power Control



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Qos Service Types


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