Chip TDM-A new orthogonal downlink transmission technique for CDMA cellular mobile radio

This paper presents and evaluates a novel modulation scheme for the downlink of a CDMA cellular mobile radio system known as Chip TDM. This scheme involves time division multiplexing the spread spectrum chips of the different users onto a single stream of chips, rather than adding them together as would be normal for a CDMA base station transmission. It is shown that time scrambling of the chips leads to an averaging of the multiple access interference. Simulations indicate that Chip TDM provides performance essentially identical to that provided by orthogonal Walsh functions. However, the new approach leads to lower transmitter peak to mean power ratio and lower receiver complexity