s3.kth.se MUMS Lecture ACE course Agenda C-Programming language Global and local variables

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1 Agenda s3.kth.se MUMS Lecture ACE course 7 September, 005 C programming language. What is MUMS. Purpose. MUMS overview, hardware and frame-structure. MUMS_skeleton and MUMS_host. User interface, feedback, structure. A single-stream application in MUMS_offline. Computer exercise. Realization of a Spatially Multiplexed MIMO System C-Programming language Global and local variables C-programs consists of global variables and functions. Global variables are declared outside of functions. Local variables are declared inside functions. The data-types we will use are float (floating point 3bin numbers e.g e+003), int (integers between -^3 and ^3-), unsigned char (integers between 0 and 55). Example: float w_r, w_i, w_r, w_i; // Receiver weights real and imaginary parts. int frame_traffic_rx_ix; unsigned char feedback_value; void calculate_weights_and_feedback(hr,hi,hr,hi) { unsigned char local_feedback_value; } if (frame_traffic_rx_ix>=6) local_feedback_value= feedback_value; else local_feedback_value=0; // Default. w_r=hr-local_feedback_value*hi; w_i=hi; Local variable declaration Declaration of global variables

2 Pointers Using pointers to store data Examples of pointers: // Declaration float *IQ_symbols_buffer_pointer; unsigned char *feedback_buffer_pointer; // Example of use adress=(int) IQ_symbols_buffer_pointer; value=*iq_symbols_buffer_pointer; // Assume feedback_buffer_pointer =8. *feedback_buffer_pointer ++=59; *feedback_buffer_pointer ++=55; *feedback_buffer_pointer ++=4; Address Value Characters occupies one byte each. Complex valued calculations (how we do it) Conditional Inclusion // z=x*y in complex form float zr,zi,xr,xi,yr,yi zr=xr*yr-xi*yi; zi=xi*yr+xr*yi; A two dimensional complex array: Floats occupy four bytes. Adress Value Re{X[,0]} Im{X[,0]} Re{X[,0]} Im{X[,0]} Re{X[,]} Im{X[,]} Re{X[,]} Im{X[,]} //#define SISO #define RECEIVE_SELECTION //#define TRANSMIT_SELECTION #ifdef SISO // Code here for the SISO case #endif #ifdef RECEIVE_SELECTION // Code here for receiver selection #endif

3 Multi-User MIMO Test System MUMS Purpose: Demonstrate algorithms and procedures e.g. spatial multiplexing with feed-back. Insight into implementation issues, e.g. calibration, program efficiency. Find missing pieces in system design. Force our researchers to think about implementation issues. Give our students programming and hardware experience. Simplicity implies self contained implementations feasible as in project courses. Two nodes and two RX nodes (in all). A node consist of A PC computer. A DSP board inside the computer (EVM 670 PCI) Two receiver or transmitter modules (RX and, respectively) Two antennas. MUMS nodes Receiver Schematic Transmitter Schematic Carrier frequency Fc=766.6MHz LO MHz 7dBm G=0dB Narrow Crystall Filter OP amplifier and filter Carrier frequency 70MHz LO. Fc-70MHz 7dBm G=0dB Wide filter Center freq 70MHz To TTL TTL Digital step attenuator 0,0,0,30 db G=0dBm Narrow Crystall Filter Carrier frequency Fc=766.6MHz LO MHz 7dBm G=0dB Narrow Crystall Filter Resistive matching LO. Fc-70MHz 7dBm TTL TTL Digital step attenuator 0,0,0,30dB Carrier frequency 70MHz Wide filter Center freq 70MHz From G=0dB G=0dBm Narrow Crystall Filter Carrier frequency 0kHz Carrier frequency 0kHz 3

4 Narrow-Band Receiver/Transmitter ( 4kHz) Filters and Spectrum Transmitter spectrum Typical Impulse response A narrow filter eliminates adjacent channel interference. Reduces sampling rate and dynamic range requirements in singlecarrier applications e.g. EDGE., but introduces ISI, i.e. the transmitted symbols passes through a long filter. Single-cell setup Two-cell setup Host PC. Software: MUMS_host.exe Created using Microsoft P Visual C++ C I Opens matlab engine. EVM (DSP) Software: MUMS_skeleton.out ====>>> MyAlgorithm.out module module RX module RX module RX EVM (DSP) Software: MUMS_skeleton.out ====>>> P MyRXAlgorithm.out C I Host PC. Software: MUMS_host.exe Created using Microsoft Visual C++ Opens matlab engine. module module module module Internet RX module RX module RX module RX module RX + RX 4

5 Superframe (=round) Buffer and frame structure MUMS internal 67 traffic frames Feedback delay = 5 frames Buffer Buffer Buffer 3 Buffer 4 Buffer 5 Buffer 6 Buffer 7 Stream ½- frame offset Frame transmited Buffer Buffer Buffer 3 Feedback based on Transmission frame is aided with processed feedback based on frame Buffer 4 Buffer 5 Buffer 6 Buffer 7 Stream RX Buffer RX Buffer RX Buffer 3 Frame processed in RX RX Buffer 4 Feedback based on frame RX Buffer 5 RX Buffer 6 RX Buffer 7 Feedback: 3bits per frame 3 Symbols, rate 9600Hz RX Buffer RX Buffer RX Buffer 3 RX Buffer 4 RX Buffer 5 RX Buffer 6 RX Buffer 7 time MUMS_skeleton (DSP program) MUMS_host (PC program) Does buffer-handling to/from / Does up- and down-conversion to/from base-band and 0kHz. Does rough frequency and time synchronization/correction and a channel estimate. Provides feedback from receivers to transmitter (3bits per frame). Receives information from MUMS_host. Provides interface for students/developers algorithms through _Algorithm and RX_Algorithm. Performance evaluation parameters Matlab-script for presentation of results. Define algorithms to run in sequence. Custom parameters Location of files where to store results 5

6 Information transmitted over internet (by MUMS_host) (Master node = the node from which the system is controlled and viewed by the operator) Master to slave nodes. What algorithms to run/where to find them. Where to save results. Custom parameters. Frame length and number of correctable bits per frame (hypothetical code) Slave nodes to master nodes. Channel impulse response estimated by MUMS. Performance in terms of throughput and frame error rate. Files stored on hard-disc by MUMS_host A=R=_RawBuffer.dat A and R are the algorithm and round (super-frame) index it is omitted in the following). BasicParamDSPtoPC.dat BasicParamPCtoDSPdat RawBuffer.dat: DebugBuffer.dat DetectedBitsBuffer.dat IdleBuffer.dat StatisticsLog.dat ToMatlab Different versions of all files for the different nodes. Interfaces for _Algorithm Inputs DataToTransmit (for node ) DataToTransmit (for node ) frame_traffic_ix (Traffic frame counter) feedback_buffer (transmitted from node RX when in frame frame_traffic_ix-5) feedback_buffer (from node RX) custom,custom,custom3 Outputs Accessible through the host interface. IQ_symbols_buffer (3** floats representing x3 complex matrix) debug_buffer Accessible through the DebugBuffer file. Interfaces for RX_Algorithm Inputs IQTransmitReceive_buffer **3*5 floats representing the complex received signal in two consecutive frames with five times oversampling frame_traffic_ix (traffic frame counter) custom,custom,custom3 Outputs detected_bits_buffer no_detected_bits_with_feedback no_detected_bits_without_feedback feedback_buffer (for RX) feedback_buffer (for RX) debug_buffer 6

7 MUMS_offline Emulates a MUMS (single-cell) using only a PC. Uses code composer studio (with a simulated DSP ) and matlab. Provides interfaces for _Algorithm and RX_Algorithm that are identical to the ones in MUMS_skeleton except Different frame counters are used in transmitter and receiver namely frame_traffic_rx_ix and frame_traffic_tx_ix. Different debug buffers are used in transmitter and receiver namely debug_data_buffer_pointer_rx and debug_data_buffer_pointer_tx. Matlab is used for simulation of the channel, including frequency and timing jitter. Two propagation models Static Jakes. Information transfer between transmitter and receiver possible with global variables BUT NOT ALLOWED. Algorithms that work in MUMS_offline should work in MUMS_skeleton (except If rule above is violated) MUMS_example An example algorithm. Single-stream with selection/beamforming. Frequency correction, synchronization, and Your beamforming MUMS_example channel estimation is done. The MUMS_host MUMS_skeleton Hardware MUMS_offline selection/beamforming is to be implemented by you! z = MUMS_example Approach ( k) h p ( k 5n) x ( n) + h p ( k n) x ( n) + n ( k) 5 n z ( k ) h p ( k 5n) x ( n) + h p ( k n) x ( n) + n ( k ) = 5, n Philosophy in beam-forming and detection:, regard n 0terms as noise. h = h () 0, h = h () 0, h = h p() 0, h = h p ( 0) p z z p ( k) ( k) h = h h x h x ( k) ( k) ( k) = Hx( k) e( k) z + + e e ( k ) ( ) k Beamforming/selection Combining at the receiver: r RX RX RX ( k ) = [ w w ] z( k ) = w z( k ) Distribution at the transmitter: w x = = w ( k) s( k) w s( k) Resulting scalar channel model for beamforming design: ( k ) = ( w RX Hw ) s( k) e( k ) r + Effective SISO channel 7

8 Power Constraints Maximum ratio combing Total power constraint (typically used in papers): w + w Makes sense under interference limitation! For given beamformer weights: w * and assuming spatially white noise: E e( k ) e ( k ) = σ { } I Per element power constraint w, w (actual limitation in MUMS): Makes sense under power (=range) limitation! maximum SNR is obtained as: RX w = ( Hw ) * Receiver: Estimates frequency offset. Sequence of frames/actions used in MUMS_example frame_traffic_ix Transmits data using As -5 but with Transmitter: Sends orthogonal beamfoming without beamfoming white training. feedback available. Three aided by Sends all ones. training symbols included feedback. for channel estimation of effective SISO channel. Estimates timing offset and channel hr, hi,.,calculates weights/selection and sends feedback Combines incoming data knowing that transmitter has no feedback. Does channel estimation of effective SISO channel. No update of feedback. As -5 but knows that transmitter has feedback. No update of feedback. void _Algorithm(int tx_node_index){ switch (frame_traffic_tx_ix) { _Algorithm case 0: TransmitOnes(); // Transmit only ones to aid frequency. case : TransmitTrain(); // Transmit training sequence for channel estimation // and synchronization. default: TransmitData(); // Transmit data with modulation scheme // selected with parameter custom. } 8

9 RX_Algorithm void RX_Algorithm(int rx_node_index){ switch (frame_traffic_rx_ix) { case 0: FrequencyEst(); // case : EstimateChan(); // Estimate channel default: ReceiveData(); } Some Results from MUMS_example on Real Test-Bed 9