Presented by: Sohaib Malik

A radio whose functionality can be changed by changes in only the software

Key feature: ◦ Reprogramability ◦ Reusability of hardware.

Orthogonal Frequency Division Multiplexing (OFDM) Multiple Input Multiple Output (MIMO) Modern Channel Coding Receiver Synchronization

◦ Symbol Timing◦ Carrier Frequency Offset (CFO)◦ Sampling Frequency Offset (SFO)◦ MIMO Channel Estimation

N-Point OFDM System in Time Domain with Cyclic Prefix

256-Point OFDM System for WiMax

• Data-carriers 192 & Pilot-carrier 8 • Null Carriers 56: one at Centre, 28 lower freq, 27 high frequency guard carriers

Two types of Space-Time codes: Space-Time Block Codes (STBC) and Space-Time Trellis Codes (STTC). STTCs provide both coding and diversity gain but are computationally complex to decode hence are not used in commercial standards till now. STBCs are much more manageable but do not provide coding gain.

Alamouti suggested a simple Transmit diversity scheme for two antennas

This is a linear STBC (that can be decoded by linear processing) of rate 1. Linear STBCs of full rate for more than two Tx antennae are known not to exist. Higher order linear block codes are suggested by Tarokh at el in Space-Time Block Codes from Orthogonal Design.

Time 1 Time 2

Antenna 0 S0 -S1*

Antenna 1 S1 S0*

Auto-correlation or cross-correlation based◦ Plateau problem◦ Low complexity low performance

Maximum likelihood◦ Additional knowledge of SNR required◦ Good performance but high complexity

Chin-Liang Wang; Hung-Chin Wang, "On joint fine time adjustment and channel estimation for OFDM systems," Wireless Communications, IEEE Transactions on , vol.8, no.10, pp.4940-

4944, October 2009

Generated by mismatch between frequency of local oscillator of transmitter and receiver

Causes the time-domain signal to be multiplied by a complex exponential

Causes the frequency domain constellation to rotate. Also adds some ICI

In OFDM, frequency selective fading channel becomes a frequency non-selective fading channel for each sub-carrier

The channel is multiplicative in nature◦ Rj(k) = H(k) . Xc(k) + W(k)