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WiCOMM-T FAQ

Frequently Asked Question
1. What is WiCOMM-T?

Benchmark WiCOMM-T – Wireless Digital Communication System is the actual implementation of modern digital communication system that we use today. It is a SDR platform with direct interface to MATLAB through Hi-Speed USB port of PC. WiCOMM-T platform provides maximum flexibility in learning a complete digital communication system concepts which includes:

  • Digital modulation techniques such as PSK schemes, QAM etc
  • Pulse shaping techniques, & Filtering concepts
  • Equalization techniques such as Linear Feedback, Decision Feedback equalizers, viterbi (GMSK)
  • Timing recovery, Channel estimation & frequency synchronisation
  • Basics of OFDM, CDMA, GSM etc.
  • Implementation of RAKE receiver

Since this platform makes use of Matlab as its interface, it is very flexible to the user to try out digital communication topics without any complicated steps or writing lengthy algorithms in C. MATLAB codes of all suggested experiment topics are available to user as reference.

2. How WiCOMM-T is better to use than the other communication training systems available?

WiCOMM-T is a SDR platform. It has ADC/DAC blocks, IF/RF modulation blocks and the interface to the PC. Rest of the systems is the software written in Matlab. All this put together forms the WiCOMM-T platform that is easy enough to use it. Modern digital communiation systems, say a cell phone, today uses only the above said blocks. Instead of PC and Matlab, they employ DSPs or ASICs to do the specific actions.

Other forms of kits includes DSP based systems where algorithms may have to be downloaded to the DSPs or FPGAs built in the hadrware. This means that code optimisation factors will get added to the work. Since users need to be focused to the concept and algorithms, WiCOMM-T ensures that all codes are handled at the PC level under Matlab. This helps to stay in focus with the concepts and not to worry about code optimisation, code conversion, requirement of other development platforms etc. So WiCOMM-T is a practical setup to understand modern digital communication platform.

3. What is the power level of the RF Antenna?

The power level for RF transmitter is +5dBm (3mW) typical.

4. CDMA – Apart from GOLD, can Walsh Code be used?

Yes. Both orthogonal and non-orthogonal codes can be used.

5. CDMA - Is Frequency hopping possible?

Yes. One can do this at the base-band level.

6. Can Simulink blocks be used with the system?

Yes. The Matlab codes that comes with the systems do not have simulink blocks but uses the direct Matlab codes. Users can convert the suggested experiments to Simulink blocks and use it with the WiCOMM-T. Codes required to interface the simulink block with the system are given with the experiment codes that comes with system.

7. Can external signal be fed from Vector Signal Generator? What are I/P levels?

Is it possible to feed I & Q signals at base band level, if so what is signal level? Yes. The signal should be 900mVp-p with a DC of 1.2V. Excess DC or high signal amplitude may damage the system. Feed as I-Q signal at IF input at Transmitter or Base band input at Receiver

8. Can the signals be monitored on Oscilloscopes, Spectrum Analyzers & Vector scopes.

BNC (for base band) and SMA (for IF) connectors are there and if input specs and output specs to the WiCOMM-T system are met, instruments can be connected. The input and output specs are given in the manual and user can try using the instruments based on this.

9. Is Channel Coding possible?

Yes. Since Matlab is used, it is possible to do channel coding.

10. Can noise be added externally, e.g. Adding 50ohm terminators, etc between SMA connectors, etc?

Noise may be introduced by attenuating the signal and then amplifying it again. User may try this as project. Care has to be taken while attenuating, amplifying and interfacing with the IF block. Improper impedance and power levels may damage the IF block permanently.

11. What is maximum data rate/symbol rate in WiCOMM T?

The system supports, various ADC and DAC sampling rates. The maximum sampling rate of DAC at transmitter is 5.5MBps complex (I&Q together) and of ADC at receiver is 5.5MBps complex. Therefore instead of specifying in symbol rate, sampling rate can be given from which the symbol rate can be derived depending on the symbols sampling rate at the TX and Rx. In addition to this, the transmitter has a Low Pass filter with 1.2MHz cutoff after DAC and receiver has a Low pass filter with 800 KHz cutoff before ADC. This also limits the maximum symbol rate possible.

12. What is the resolution of ADC and DAC?

8bits.

13. How multi-path effect is introduced in CDMA experiment? Can multi-path effect be realized using more than one kit?

Since the kits are usually placed nearby to each other, multi-path realization may be difficult in reality. So delayed and amplitude varied signals can be added in the transmission side before DAC. This creates multi path effect.

14. Is PED – B channel introduced in the transmitter code of OFDM experiment?

Yes

15. What is the modulation scheme used in base band experiment?

No modulation used. Since this experiment focuses on base-band only, no carrier is required and so no modulation used.

16. What type of Modulation is implemented in DFE method in Equalizer experiment?

QAM

17. What is the data rate of the signal that has been generated in Matlab irrespective of any specific experiment?

Different data rates are used for experiments. Refer the maximum possible data rate explanation.

18. What is the use of network feature that is being developed?

It is to collect the received data from another PC which is connected in the LAN. For Ex: Assume a setup in which 2 PCs having 2 WiCOMM-T kits connected such that one is transmitter and the other is receiver. Now from the first PC, say transmitter, user can collect the received data from the 2nd PC without going for any FTP requirement. This feature may help to have several other setup than the one said above. For example, there could be several receivers listening to one transmitter (using RF module) and so user can collect the data from all the receivers and do further study. Experiments using this have not been defined yet. Its specs will follow once the feature is implemented.