Wireless Broadband Transmission Overview

 

Wireless transmissions are used in many applications, ranging from military operations to satellite commercial transmissions or TV distribution. Commercial wireless transmissions can be segmented into different services and systems. The three main services which use wireless spectrum are:

 Telecommunications (including military, professional and personal communications)

 Networking (Wide Area Networks(WAN) and Local Area Networks (LAN)

 TV broadcasting

RF spectrum is a scarce resource which needs to be used efficiently. The three services above share different portions of the bandwidth and different transmission means:

 Terrestrial transmissions

  • Less than 2 GHz : UHF/VHF band, TV, military, mobile communications, cells between a few km and 50 km.
  • Between 2 and 4 GHz : LAN, Media Distribution Networks (MMDS), cells between few 100 m and 20 km
  • Above 20 GHz : Wireless Local Loop, cells of few 100 m to few km

 Satellite transmissions

  • L band : less than 10 GHz, used mostly for professional applications
  • Ku band : between 10 and 12 GHz, used mostly for broadcasting, continent wide coverage
  • Ka band : above 30 GHz, used for new broadband services, continent wide coverage for geostationary positions, 100 km cells for Low Earth Orbit

With analog transmission, each portion of the spectrum is used for very specific services and it is difficult to mix services between transmission systems. This led to a separation between telecommunication operators and TV broadcasters. With digital communications systems, it is possible to transmit a binary content on a portion of the spectrum. Depending on the bitrate, it is possible to transmit different types of information 'Services' that can share the transmission medium, such as:

 Voice : In the order of 10 kb/s

 Standard Internet Access In the order of 100 kb/s v Low quality video, fixed images In the order of 1 Mb/s

 High quality video (VHS like) In the order of 5 Mb/s

 Computer networking, multiplex of informations and TV programs (more than 10 Mb/s)

In recent years, fixed access traffic in the range of more than 30 Mb/s (fixed satellite reception, cable TV reception, professional networking, etc.) and mobile access to bitrates in the order of 10 kb/s (GSM) have been developed. The new trend is to develop mobile access to allow for higher traffic in order to provide the same information presently from fixed systems. Companies and households will immensely benefit from mobile receivers deployed in cars, trains, buses, …

Among the different types of communications, it is possible to distinguish two types of communications for different applications and different costs:

 Bi-directional communication : used for voice communication, computer networking, internet access

 Broadcasting : used for TV distribution, data broadcasting, internet multicasting/streaming Bi-directional communication : used for voice communication, computer networking, internet access
   Broadcasting : used for TV distribution, data broadcasting, internet multicasting/streaming

Dibcom believes that these two systems will continue to use different portions of bandwidth for cost and technological reasons. The first type of communication requires the allocation of a specific portion of the time/frequency spectrum to a user that will pay for the entire cost of reserving this bandwidth. On the other hand, the second type of communication can be used by a large number of users at the same time, thus sharing the cost of the bandwidth and also providing an excellent way to send advertisements and other sources of revenues which make the cost of the bandwidth lower for the end consumer.


In conclusion, we are envisioning future portable/mobile applications that will have access to both resources with a price differentiation. Looking at the different standards that exist in wireless consumer applications today represented in the picture below, it is interesting to observe that two standards seem to emerge for bi-directional and broadcast mobile communications, that is UMTS and DVB-T; UMTS being the straight forwards extension of GSM.



Digital wireless broadcast transmission uses the most recent transmission technology called Coded Orthogonal Frequency Division Multiplexing (COFDM), standardized in Europe by DVB-T, and adopted in Asia and Brazil for Digital TV broadcast. The robustness of COFDM in mobile environments makes it perfectly suitable for future mobile handsets capable of receiving broadband TV and data. However, the reception of TV implies a 99.99% availability of a received binary stream with a probability error of less than 10-12, which requires a probability error of less than 10-3 before error correction. While this reception quality is relatively easy to achieve in a fixed environment, the mobility creates strong distortion of the received signal which must be compensated for by the receiver in order to achieve acceptabel image quality. If at any time, the probability of error goes beyond this limit, the effects on the video image and sound are catastrophic.
DIBCOM aim is to concentrate its effort on the adaptation of COFDM technology for mobile environments, which will give access to several markets: TV Set Top Boxes with a better performance and coverage, Mobile Appliances capable to remain connected at speeds exceeding 300 km/h (cars and fast trains), and Personal Assistants enabling the reception of data and TV anywhere at any time.