Agilent Technologies N1911A User Manual download pdf (Page 3)

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WiMAX Overview

WiMAX (worldwide interoperability for

microwave access) is based on wire-

less transmission methods deﬁ ned

by the IEEE 802.16 standard. WiMAX

was developed to replace broadband

cable networks and to enable mobile

broadband wireless access.

WiMAX offers a high-speed data ac-

cess to large geographical areas

covering distance up to 20 miles of

distance (deﬁ ned by IEEE 802.16).

Orignal IEEE 802.16 standard offers

10 GHz – 66 GHz point-to-point system

using tradisional single carrier modula-

tion with QAM. However, it has very

little industry adoption.

Since then, IEEE 802.16-2004 [1]

standard, often referred to as WiMAX,

deﬁ nes the Physical layer (PHY), and

Medium Access Control (MAC)

protocol for products that extend

Broadband Wireless Access (BWA)

from Local Area Network (LAN). The

standard contains speciﬁ cations for

licensed and unlicensed BWA

operation between 2 GHz and 11 GHz.

The IEEE 802.16-2004 standard

speciﬁ es Orthogonal Frequency Divi-

sion Multiplexing (OFDM) as the

transmission method for Non-Line-

Of-Sight (NLOS) connections to attain

high data rate. OFDM modulation uti-

lizes up to 256 subcarriers with band-

width 1.25 MHz to 28 MHz. Subcarriers

are spaced such that they are orthogo-

nal to each other, thus reducing signal

interference. The signal bandwidth in

the Base Station (BS) can be changed

based on transmission distance and

signal environment. The network

provider may also determine the band-

width available for users based on

various pricing plans. Signal condition

and bandwidth requirement will

determine which modulation is

selected for the individual data burst.

Figure 1 OFDM (ﬁ xed) and OFDMA (mobile) frame structure.

Fixed WiMAX Mobile WiMAX

Standard 802.16 802.16/802.16-

2004

802.16e/802.16-2005

Multiple access FDD, TDD FDD, TDD FDD, TDD, OFDMA

Modulation single carrier

with QAM

OFDM with BPSK,

QPSK, 16QAM,

64QAM

OFDMA with BPSK,

QPSK, 16QAM,

64QAM

Channel spacing 1.25MHz - 28MHz

FFT size 256 2048 1024, 512, 128

User carriers 200 various

Pilot carriers 8 various

Frequency range * 10-66GHz

Licensed

2-11GHz Licensed

& Unlicensed

< 6GHz Licensed

Application NLOS LOS

Table 1 OFDM and OFDMA standard.

See Table 1 summary of OFDM and

OFDMA standard. 802.16e is the

amendment to the 802.16-2004

standard focusing on the OFDMA

layer. OFDMA allows 128, 512, 1024 or

2048 subcarriers in 1.25, 5, 10, 20 or 28

MHz bandwidth respectively.

Figure 1 shows OFDM and Orthogonal

Frequency Division Multiple Access

(OFDMA) frame concepts. In OFDM,

the downlink consists of the Preamble

(P) followed by an Frame Control

Header (FCH) and the subsequent

bursts for the respecitve different

subscribers. In OFDMA, the bursts are

allocated according to downlink map.

The data bursts overlapping on the

same speciﬁ c will maximize the data

ﬂ ow in a complex enviroment.

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