MATLAB for Wireless Communication
Task 1: Your task is to implement an OFDM system over the audio channel via speakers and mics. The system should be capable of transferring a file (text, picture etc.) from one computer to another. Most system parametes are optional, but the system must include the following components:
• Aminimum of 64 subcarriers, 75-80% of them being used for data or pilots, the outer 20-25% being inactive (modulated with zero).
• 4-QAM symbol constellation, or larger.
• A preamble with pilots only, then data together with 4 sub-channels with continous pilot symbols.
• Your system must at least operate at 0.5 kb/s.
• Minimum separation between speaker and microphone is 1 meter.
• Minimum length of file: 20000 bits.
A convolutional code is optional, and can be used if there is need for it.
As soon as you can, reliably, transmit and decode the signal, you have passed Task 1. If you have stereo speakers and microphones you could also consider to implement MIMO or Alamouti coding to enhace the data rate or improve reliability, especially if you are an ambitious student. Do not forget to look at (by plotting them) the signals that you are transmitting. If they have a large peak-to-average power ratio it might be good to consider the use of a scrambler.
Task 2: A full duplex system should be implemented. The system should be packet based, and each packet must consist of at most 1000 information bits. In addition, parity bits should be inserted at the transmitter for each packet via a CRC. All packets are next sent to the receiver, which decodes each packet, and verifies the parity bits. The system parameters are the same as for task 1. Note that the packet length is subject to optimization. If the packet length is long, there will be many re-transmissions. The receiver next acknowledges the correctly decoded packets, and asks for retransmission of the incorrectly decoded packets. The transmitter now re- transmits the requested packets. This process is repeated until all packets have been correctly received at the receiver. A particular nice way to present this task is to let the file represent a picture. Then the receiver can plot the correctly decoded packets to the screen, while the incorrect packets show up as noise.