High Transmission Power : BPSK or QPSK?
That's right. When we compare BPSK and QPSK at equal energy per bit, we find that QPSK requires twice the power of BPSK. From wikipedia:


  Although QPSK can be viewed as a quaternary modulation, it is easier
  to see it as two independently modulated quadrature carriers. With
  this interpretation, the even (or odd) bits are used to modulate the
  in-phase component of the carrier, while the odd (or even) bits are
  used to modulate the quadrature-phase component of the carrier. BPSK
  is used on both carriers and they can be independently demodulated.
  
  As a result, the probability of bit-error for QPSK is the same as for
  BPSK:
  
  $P_b = Q\left(\sqrt{\frac{2E_b}{N_0}}\right).$ 
  
  However, in order to achieve the same bit-error probability as BPSK, QPSK uses twice the
  power (since two bits are transmitted simultaneously).