System on Chip Design and Test

1Orthogonal Sub-carriers

Conditions for OrthogonalityEach subcarrier has exactly an integer number of cycles in the FFT interval.

2. The number of cycles between adjacent subcarriers differs by exactly one.2

3Single Carrier vs Multi Carrier

4Contd.

OFDM is resilience to frequency selective fading.5Multipath nature

ICIISIOFDM systems are usually designed to cope with multipath channelsISI 6Guard Interval (no signals)

Cause ICI 7. ICI and ISI Cyclic Prefix

8Contd.

OFDM is resilience to frequency selective channel and multipath nature of channel . It is designed for this area.Attractive in overcoming these challenges.

9So we talk about OFDM in fast fading (Channel estimation in fast fading channels )

10Carrier frequency offset (CFO) caused by Doppler frequency

11CFO for various systemsVelocity (km/hr)Doppler frequency (Hz)CFO30 163.890.001120655.560.004140764.810.005

In IEEE 802.11pOFDM and OFDMAOFDMA is multiuser version of OFDMOFDMA has the ability to dynamically assign a subset of subcarriers to individual usersOFDM technologies typically occupy nomadic, fixed and one-way transmission standards, ranging from TV transmission toWi-Fi as well as fixedWiMAXand newermulticast wireless systemslike Qualcomms Forward Link Only (FLO). OFDMA, however, adds true mobility to the mix, forming the backbone of many of the emerging technologies including LTE and mobile WiMAX.

1213OFDM

14OFDMA

15