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

Spectrum of normal time domain sequence Spectrum of classical frequency division multiplexing Spectrum of orthogonal frequency division multiplexing

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 1Time 2 Antenna 0S0S0 -S 1 * Antenna 1S1S1 S0*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 , 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 ◦ R j (k) = H(k). X c (k) + W(k)