Bell labs layered space time (BLAST)

BLAST (Bell Labs Layered Space Time) is a transmission method developed by Bell Laboratories for mobile communications networks and WLANs that uses the available transmission bandwidths much more efficiently than other methods. BLAST is designed to achieve transmission values of up to 40 bit/ Hz, compared with the values currently possible of between 1 bit/Hz and 12 bit/Hz.

The BLAST method is based on an unwanted, but in RF transmission also unavoidable problem of wave propagation. The propagation time of individual carrier waves is different because the waves take different paths and are reflected by objects. This means that the same wave arrives at the receiver several times in succession with different field strengths at extremely short intervals. BLAST takes advantage of this effect by using antenna arrays or smart antennas at the transmitting and receiving ends. The carrier frequency is encoded with different signals and then radiated via the multi-antenna system. From the reflected signals arriving at the receiving end, which are different for each transmitted signal, the receiver determines characteristic features for each transmitter. With the characterization of each transmitter, the receiver is able to select the different signals from each other.

Theoretically, the throughput should increase proportionally to the number of antennas; i.e., approximately double with two antennas and quadruple with four. With this development, UMTS was able to transmit 19.2 Mbit/s in a 5 MHz channel. In comparison, it should be mentioned that current transmission methods such as Wideband Code Division Multiple Access(WCDMA) require a bandwidth of 20 MHz for 22 Mbit/s.