Brief Summary of the project

Definition:

Simulation of a Multiple Input Multiple Output (MIMO) system using various Space Time Coding (STC) techniques in LabVIEW

MIMO-STC technique is one of the salient features of the WiMAX Mobile standarad, which along with Multiple Access scheme for multiple users, also marks it different from the WiMAX Fixed standard. The above simulation will be done specifically keeping in mind the WiMAX standard.

The success of the simulation will be done after comparing the published results (e.g. BER vs. Eb/N0 curves) for the various schemes with the results of my implementation

MIMO:

MIMO basically refers to using more than one transmitter antenna and more than one receiver antenna. The use of multiple antennas allows independent channels to be created in space and is one of the most interesting and promising areas of recent innovation in wireless communications. WiMAX systems are able to achieve frequency diversity through the use of multicarrier modulation. The focus of this technique is spatial diversity, which can be created without using the additional bandwidth that time and frequency diversity both require. In addition to providing spatial diversity, antenna arrays can be used to focus energy (beamforming) or create multiple parallel channels for carrying unique data streams (spatial multiplexing). When multiple antennas are used at both the transmitter and the receiver, these three approaches are often collectively referred to as multiple/input multiple output (MIMO) communication and can be used to

  • ·         Increase the system reliability (decrease the bit or packet error rate)
  • ·         Increase the achievable data rate and hence system capacity
  • ·         Increase the coverage area
  • ·         Decrease the required transmit power

Here, only the spatial diversity concept has been discussed and is aimed to be simulated.

STC:

STC or Space Time Coding is coding technique used for exchanging data in a MIMO system. The codes are designed to maintain an optimal balance between the diversity and code rate. The entire MIMO system and so the project has been divided into three main parts:

Part I : Transmit Diversity (Multiple Transmiter antennas)

This part will involve the simulation of possible STC techniques and their respective codes. Following a thorough study of the techniques, simulation in LabVIEW is envisioned, which might require complex manipulation of matrices involving real as well as complex constellation points obtained from various modulation schemes such as BPSK, QAM, QPSK, etc. The complexity will again increase as the number of transmitter antenna increases.

  1. Alamouti
  2. Space Time Block Codes
  3. Quasi Orthogonal Space Time Block Codes 
  4. Space Time Trellis (STT) 
  5. Super Orthogonal STT 
  6. Spatial Time Turbo Codes 
  7. Frequency Hopping Diversity Code 


Part II: Receive Diversity (Multiple Receiver antennas)
Each antenna will receive signals from each transmitter antenna. Thus to separate the different signals following three techniques are used. Only the first two are of substantial importance. The third is a special case of the second technique.

  1. Maximum Ratio Combining using Maximum Likelihood Receiver
  2. Selective Combining
  3. Equal Gain Combining 

After the various signals are separated out the original constellation symbols can obtained back by using corresponding decoders.

Part III: Closed Loops

WiMAX also has feedback facility for MIMO system which helps the transmitter and the receiver to get a better idea about channel characterization.

There are basically five feedback systems:

  1. Codebook based feedback 
  2. Quantized channel feedback 
  3. Channel Sounding 
  4. Antenna Selection 
  5. Antenna Grouping