Chip (CDMA)

In <a href="/facts/Digital_communications/1yAhaANd">digital communications</a>, a chip is a pulse of a <a href="/facts/Direct-sequence_spread_spectrum/l3u1HVTd">direct-sequence spread spectrum</a> (DSSS) code, such as a pseudo-random noise (PN) code sequence used in direct-sequence <a href="/facts/Code-division_multiple_access/o2RLKE4M">code-division multiple access</a> (CDMA) <a href="/facts/Channel_access/CdCGxpcu">channel access</a> techniques.
In a binary direct-sequence system, each chip is typically a rectangular pulse of +1 or −1 amplitude, which is multiplied by a data sequence (similarly +1 or −1 representing the message <a href="/facts/Bit/S972NSaD">bits</a>) and by a carrier waveform to make the transmitted signal. The chips are therefore just the bit sequence out of the code generator; they are called chips to avoid confusing them with message bits.
The chip rate of a code is the number of pulses per second (chips per second) at which the code is transmitted (or received). The chip rate is larger than the <a href="/facts/Symbol_rate/YlQ3JHVr">symbol rate</a>, meaning that one <a href="/facts/Symbol_(data)/YlQ3JHVr">symbol</a> is represented by multiple chips. The ratio is known as the spreading factor (SF) or processing gain:

SF
          
        
        =
        
          
            
              chip rate
            
            
              symbol rate
            
          
        
      
    
    {\displaystyle {\mbox{SF}}={\frac {\mbox{chip rate}}{\mbox{symbol rate}}}}

Chip (CDMA) open-in-new

Chip (CDMA)