2PAD’s Beamforming Software

Aziz AhmedSaid 12PAD’s Beamforming Software4th SKADS Workshop, Lisbon, 2-3 October 2008

2PAD’s Beamforming Software2PAD’s Beamforming Software

Design and Implementation

Aziz AhmedSaid (UoM)

Other Contributors

Stef Salvini, Fred Dulwich, Ben Mort (OERC), Chris Shenton (UoM)

Presented by Chris Shenton (UoM)


ObjectivesObjectives

• To design and implement a real-time 2 polarisation beamformer on 2PAD’s processing engine;

• To design and implement the data transfer, storage and display software to run on the back end host computer;

• To test, verify and evaluate 2PAD’s performance.


System OverviewSystem Overview

MultiChannelADC

DigitalSignal

Processor

LNA&

SignalCondition


Our task:Our task:

DigitalSignal

Processor

MultiChannelADC

LNA&

SignalCondition


2PAD’s Processing Engine2PAD’s Processing Engine


Software Design FlowSoftware Design Flow

- We designed and implemented a highly optimised kernel for the Cyclops suitable for realtime operations;- We have created a software library of the functions required to implement realtime applications on the Cyclops;- The host computer software will be impelemented in the near future.


Software Kernel and LibrariesSoftware Kernel and Libraries

• More efficient: Simple design, less latency, optimised for speed;

• Better usage of resources: Memory, thread units;

• Full control of the chip;

• Full access to all the software which enables further customisation/tuning for every application;


Typical Beamforming SchemeTypical Beamforming Scheme

BEAMFORMING SCHEME:a - Ususal way:•Poly-phase filtering;•Data reorganisation;•Narrow band Beamforming of one frequency band but all antenna signals at once;


Our Beamforming SchemeOur Beamforming Scheme

BEAMFORMING SCHEME:b - Our Scheme:•Poly-phase filtering;•Narrow band Beamforming of all frequency bands but for 2 antennas at a time.Reason for that:Data reorganisation in (a) requires a bandwidth proportional to the number of antennas and the signals bandwidth. Therefore it constitutes a bottleneck that reduces the maximum signal bandwidth that can be processed and the system's scalability.


Logical Mapping on the Logical Mapping on the Cyclops SystemCyclops System

- Outer Nodes perform the beamforming of two antennas;- Inner nodes add two partially formed beams;- The centre node performs the final addition and sends the data stream of fully formed beams to the host computer.


PhysicalPhysicalMappingMapping

- The Cyclops systems is organised in 8X3X2 racks; - 15 nodes are neede to beamform 16 antennas;- The array can be mapped as illustrated in the figure.


Data PathData Path

-Data is received into an input buffer then passes through a processing stage and the result is stored in an output buffer.- The difference between the three node types is the source and destination of the data:• For an Outer node, data is read from the Off-chip memory and transmitted via an ASwitch port;• For an Inner node, the data is received and transmitted via an ASwitch port;• For a Centre node, the data is received via an ASwitch port but it is stored in the Off-chip memory from where it is sent to a host computer.


Data FlowData Flow

This Figure shows the chronological progression of data through the pipeline stages inside a node.


Data Streams StructureData Streams Structure

- Data streams are constructed by the Outer nodes and are then used as they are by the Inner nodes.- Each node processes two input buffers and produces one outputs buffer.- Each buffer contains Nf frames (typically 32 frames of 1Kbytes).- A frame is the output data from the FFT-Poly-phase filter bank.- Each frame is divided into P sub-frames to hold data for P beams (P=1..8). For the input buffers of the Outer nodes, P=1 because the buffers receive raw data, no beams have been computed yet.- Each sub-frame, holds N/P complex samples (where N is the number of samples in a frame).


The BeamformerThe Beamformer

We have a fully working beamformer:

• 2 Polarisations;

• 1,2,4 or 8 beams (more is possible);

• NumberOfBeams X NumberOfFreqBands = K

(K represents the total bandwidth per polarisation)

• K ~= 300 for 1 beam and goes up to 800 for 8 beams (these are just initial estimations, based on simulations);

• For example for 8 beams: 100MHz per beam.


Simulation SetupSimulation Setup

- A MATLAB broadband beamforming simulation program is used to simulate and test the beamformer.- The program generates antennas signals for a given array geometry and sources configuration.- It also calculates the beamforming coefficients for the chosen directions.- The data is stored in files.- Using system calls, the Cyclops simulator is launched.- The Cyclops program, running in the simulator, reads the input files, performs the beamforming and stores the resulting data in an output file;- The MATLAB program then reads the output file and compares the Cyclops data with the data from the beams that it has computed.


Simulation ResultsSimulation Results

2 Polarisations, 2 Frames, 8 Beams per frame, 64 Frequency bands per beam.

- This figure shows the beamforming of two polarisations.- The data represents two frames, 8 beams per frame and 64 frequency bands per beam.- The dashed vertical lines separate beams, the solid vertical line seprates frames.


Simulation Results (Zoom)Simulation Results (Zoom)


SummarySummary

• We have designed and implemented a customised and highly optimised software kernel and libraries for the Cyclops.

• We have designed, implemented and fully tested a multi-beam, 2 polarisation beamformer for the Cyclops system.

• We have shown good correlation between theoretical simulation and simulated hardware.


Future workFuture work

• Create the Host computer software;

• Port the beamformer to the real hardware;

• Perform real test, verification and evaluation of the beamformer.

• Perform code and datapath profiling to fully understand the power vs performance characteristics of the system.

2PAD’s Beamforming Software

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