Understanding LTE with MATLAB-8 Chapter-2: Downlink and Uplink Processing in Details Downlink Processing Steps - Transport-block CRC (Cyclic Redundancy Check) attachment. Code-block segmentation and code-block CRC attachment. Turbo coding based on a one-third rate. Rate matching to handle any requested coding rates. Code-block concatenation to generate codewords. Scrambling of coded bits in each of the codewords to be transmitted on a physical channel. Modulation of scrambled bits to generate complex-valued modulation symbols. Mapping of the complex-valued modulation symbols on to one or more transmission layers. Precoding of the complex-valued modulation symbols on each layer for transmission on the antenna ports Mapping of complex-valued modulation symbols for each antenna port to resource elements Generation of complex-valued time-domain OFDM signal for each antenna port. LTE Downlink Tx Model Uplink Processing Steps - Transport-block CRC attachment. Code-block segmentation and code-block CRC attachment. Turbo coding based on a one-third rate. Rate matching to handle any requested coding rates. Code-block concatenation to generate codewords. Scrambling. Modulation of scrambled bits to generate complex-valued symbols. Mapping of modulation symbols on to one or several transmission layers. DCT transform precoding to generate complex-valued symbols. Precoding of the complex-valued symbols. Mapping of precoded symbols to resource elements. Generation of a time-domain SC-FDM signal for each antenna port. LTE Uplink Tx Model Single Carrier-Frequency Division Multiplexing - - SC-FDM used in uplink is based on DFT-precoded OFDM. SC-FDM signal generation is the same as the OFDM, with an additional M-point DFT introduced. DFT is less computationally efficient than computing the FFT. But certain DFTs whose sizes are of prime lengths can be efficiently implemented. This is the reason why LTE specifies the M-point DFT sizes as multiples of two, three, or five (all prime numbers). In uplink, DFT-transformed symbols are mapped to frequency subcarriers prior to the IFFT operation and cyclic prefix insertion. The data symbols of any individual user transmitted as a SC-FDM symbol must be either contiguous or evenly spaced in the resource grid. MU-MIMO - - In mobile systems, # Rx antennas (N) at the UE is often smaller than # Tx antennas (M) at the BS. MIMO Capacity gain is scaled by (M, N), (normally limited by # of UE antennas. To improve this, Uplink MU-MIMO used where different users transmit their streams on the same resource blocks while each transmitting on a single antenna in their mobile units and the BS will pair them together. The base station schedules the uplink transmission for each UE within the MUMIMO pair in the same subframe and on the same resource blocks. The pairing can change in time based on such considerations as power control, individual channel quality, and interference profile. LTE-Advanced allows us to share up to eight mobile terminals in MU-MIMO that share the same resource blocks. Uplink MU-MIMO MATLAB for Communication Systems Design - - Elaborate specifications in a model as a blue-print for implementation. Introduce innovative proprietary algorithms. Assess system-level performance. Accelerate simulation for large data sets. Fill gaps from computer model to implementation. Where does MATLAB fit? - - - MATLAB and Communications System Toolbox for algorithm and system design. MATLAB and Simulink for dynamic & large scale simulations. Accelerate simulation with a variety of options in MATLAB. Connect system design to implementation with C and HDL code generation.
