Codeword based power loading in MU-MIMO

Precoding is a common technique used in wireless transmissions where multiple data streams are spatially multiplexed by an access point or base station to a number of receiving stations by using multiple transmit antennas. The design of the precoder can be divided into two separate functional blocks: 1) the transmit filters, for example zero-forcing or minimum mean-square error, with unit norm columns and 2) the power loading. In a conventional system the transmit filters and power loading strategy are applied on individual OFDM subcarriers or groups of subcarriers. In this paper we study a codeword based power loading strategy combined with precoding. In this new technique the power allocation is done jointly across the subcarriers spanned by the encoded transmissions to optimise some codeword-related performance requirement. Simulations show that this strategy offers performance gain in terms of both packet error rate and throughput over conventional per-subcarrier power loading. The saving in computational complexity can also be significant, particularly for the MMSE precoder design.