A preamble based diversity scheme for DECT using a new signal quality measure

PCS and RLL (radio in the local loop) are applications which set new demands on the DECT receiver, due to the fact that the RMS delay spread often exceeds 200 ns for outdoor environments. For comparison a typical low-cost DECT receiver based on a limiter-discriminator detector is not able to cope with more than 100 ns delay spread. A well-known solution which increases the receiver resistance to time dispersion is antenna diversity. The optimum realizable selection diversity scheme is based on the status of the R-CRC (cyclic redundancy check) check and it requires two parallel receiver chains. The simpler switching diversity scheme, normally used in commercial equipment, requires only one receiver chain, but it suffers from a strong velocity dependency. In this paper a diversity scheme using a new signal quality measure is presented. The signal quality is extracted successively in the two antenna branches during the DECT preamble which makes the scheme velocity independent as no significant delay is introduced. With the new quality measure it is possible to closely emulate genuine R-CRC selection diversity by use of only one receiver chain. For an E_b /N₀ of 25 dB, the maximum allowable RMS delay spread is increased from 180 ns for RSSI driven diversity to 220 ns with the new scheme. This is only 10 ns less than R-CRC selection diversity. For realistic hardware conditions, the performance is only degraded 10 ns which makes the new diversity scheme applicable for a practical implementation