OFDMA In-depth

Subject: 4G LTE
Category: Key Techniques
Duration: 3 days

Course outline:

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
● 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
● Advantages and disadvantages of OFDMA

Synchronization Problems 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)

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