OFDMA in-depth

3 days

Download brochureOrthogonal Frequency Division Multiple Access (OFDMA) is the key technique of leading contemporary and future wireless systems, including 3GPP-LTE and WiMAX. This course provides an in-depth explanation of the OFDMA, starting from its basics and going to such advanced aspects like combination with MIMO or operation under co-channel interference. The major part of the course consists of presentation of every single functionality belonging to the OFDM/OFDMA transmitter and receiver. This includes consideration of such important topics as synchronization, as well as channel estimation and correction.

The course utilizes a number of hands-on practical exercises using the state-of-the art LTE PHY Lab and WiMAX PHY Lab – Link Level Simulators applied to observe OFDM/OFDMA signals and waveforms generated by either LTE or WiMAX base stations and mobiles.

Fundamentals of Digital Communications

• Requirements imposed on broadband wireless access systems
• Classical schemes for radio transmission: single carrier modulation / mapping schemes (BPSK, QPSK, QAM)
• Review of classical schemes for multiple access (TDMA, FDMA)
• Spread spectrum transmission and CDMA
• General model of a digital communications system; sources of degradation

Large-scale and Small-scale Propagation

• Multipath effect and its influence on communications over radio
• Time spread, Doppler spread and angular spread
• Time selectivity, frequency selectivity and spatial selectivity
• Pathloss and shadowing
• Rician and Rayleigh fading, K-factor

OFDM Fundamentals

• Serial vs. Parallel transmission, multicarrier transmission
• Determination of the key OFDM modem parameters
• Continuous and discrete model of OFDM system
• OFDM signal in the time and frequency domains
• OFDM subcarriers and subcarrier separation
• Cyclic Prefix (CP) role, linear and circular convolution, impact on equalization
• IDFT/DFT, IFFT/FFT
• Block structure of the OFDM transceiver
• Equivalent OFDM model of parallel AWGN channels
• High Peak-to-average Power Ratio (PAPR) problem and possible countermeasures
• Advantages and disadvantages of OFDM

OFDMA Fundamentals

• OFDMA as an extension of OFDM
• Exploitation of the multiuser diversity phenomenon
• Creation of the time-frequency resource grid; single time-frequency resource granularity
• Adaptive assignment of time-frequency resources
• Combination with Adaptive Modulation and Coding
• Water-filling concept
• Scheduling and QoS support; example scheduler resource allocation problems
• Scalable OFDMA
• SC-FDMA
• Advantages and disadvantages of OFDMA

SynchronizationProblems in OFDMA

• Synchronization mismatches: carrier frequency, phase, symbol timing and sampling clock offsets
• Estimation of synchronization offsets
• Correction of synchronization offsets
• Synchronization methods working in time and frequency domain
• Pilot-based synchronization

OFDM/OFDMA Channel Estimation and Correction

• Pilot types (block, comb, mixed, grid), preambles
• Minimal requirements for pilot separation
• Architecture of OFDM channel estimator and corrector
• Zero-forcing and MMSE equalizer

Combination of MIMO with OFDM/OFDMA

• Introduction to multiple-antennas
• Transmit diversity, spatial multiplexing, single-user and multi-user MIMO, beamforming
• Open-loop and closed-loop MIMO
• Advantages of combining MIMO with OFDM/OFDMA
• 3-dimensional resource (time, frequency and space) allocation problem
• Pilots for MIMO/OFDM/OFDMA
• Combination of STBC and OFDM
• Combination of SFBC and OFDM
• Combination of Spatial Multiplexing and Beamforming with OFDM

OFDMA Under Co-channel Interference

• Overview of co-channel interference control methods
• Interference randomization, avoidance, cancellation and coordination
• Considerations of Single Frequency Network (SFN)
• Integer and fractional frequency reuse concepts
• Comparison of FDD and TDD co-channel interference scenarios

OFDM/OFDMA Applied in Standard Systems

• 3GPP LTE Rel. 8 and 9
• 3GPP LTE Rel. 10 and beyond (LTE Advanced)
• WiMAX (IEEE 802.16d and 802.16e)
• Other systems (WiFI, DAB, DVB)