Buffer Control Using Adaptive MQAM for Wireless Channels

We consider the problem of buffer control in wireless communication using adaptive transmission techniques. In our model, a transmitter at the physical layer has a buffer with fixed length and bits arrive into the buffer according to a Poisson distribution. A server takes bits out of the buffer, maps them into M-ary quadrature amplitude modulation (MQAM) symbols for transmission through a wireless link. We assume that the server can vary the data rate by changing the constellation size of its MQAM modulator. Our objective is to maintain the reliability of transmission, with respect to the required bit error rate (BER) at the receiver and the required buffer overflow probability (BOP), while minimizing average transmit power. We obtain the solution to this problem using dynamic programming and use simulation to show that the obtained solution provides a considerable gain in terms of average transmit power relative to less-adaptive transmission schemes.