Group 5 - Transmission and modulation

Multimedia is a hot topic. Furthermore, mobile telecommunications, like GSM and DECT, has been a booming system. It's not a surprise that there's a study going on of combining these two fields of interest: Mobile multimedia.

It was our task to propose the most promising transmission and modulation concept for in an mobile multimedia environment. Main target was to choose between CDMA and OFDM. To be able to suggest the most promising technique, we've considered some concepts like DECT, W-CDMA, OFDM en MC-CDMA. DECT and CDMA have become world standards now, techniques based OFDM haven't yet.

DECT and W-CDMA are based on single carrier transmission. Biggest drawback of this form of transmission is inefficient use of the available spectrum. Furthermore W-CDMA is suffering from very high chiprates, which causes Inter Symbol Interference (ISI) and will lead to a restricted bandwidth in practice.

OFDM is a special form of FDM (Frequency Division Multiplexing) which is based on the orthogonality of adjacent carriers. By utilizing these techniques 50% of the spectrum can be saved. Because the transmission-speed over the carriers is lower than with single carrier transmission, the symbol period is increased and the system isn't suffering from ISI.

Because mobile multimedia needs more bandwidth than today's voice-communication, bandwidth is becoming scarce. Therefore multi-carrier transmission is suggested, in the form of OFDM. OFDM provides the highest spectrum efficiency. One drawback is that OFDM doesn't support handover yet, therefore it can not be utilized in a full mobile communication scheme.

We've also chosen to use current standards, so no investments have to be made in research of new transmission techniques.

The system we propose is called Mobile Multi Carrier System and is based on the Hiperlan standard. The specifications of MMCS are:

  • Carrier frequency: 5,15-5,30 GHz and 17,1-17,3 GHz
  • Uplink: OFDM modulation, TDMA Multiple Access
  • Downlink: OFDM modulation, TDMA Multiple Access
  • Uplink and downlink both in TDD
  • Throughput: 25 Mbps at introduction, to be extended to 155 Mbps
  • Range: 50 m for 25 Mbps, 800 m for 1 Mbps
  • Mobility: 10 m/s in a 360 degrees radius

The system will be introduced in 2002 on the professional market, based on a wireless LAN. If succesful, the system will be extended to a full mobile communication system.