There are two main protocol standards in the world as a digital cordless phone system for private and business, WLL(FWA) and sort-range public portable phone system. The one is DECT and the other is PHS.

     DECT is a European standard developed by the ETSI (European Telecommunications Standards Institute). Originally it was planed to be ultimate cordless standard for European cordless telephony. It is designed to operate in the 1.9 GHz frequency band and is based on TDMA (time division multiple access) /TDD (time division duplex). The spectrum is segmented into 10 carriers with a separation of 1726 kHz and the number of TDMA channels for each carrier is 12 duplex time slots. It means the total number of voice channels is 120 (10 carriers x 12 time slots/carrier). The transmission rate is 1152 kbps per carrier. Speech coding is 32 kbps ADPCM (Adaptive Differential Pulse Code Modulation), and the modulation method is GFSK (Gaussian frequency shift keying). Channel assignment is dynamic. Maximum transmission power of the base and portable station is 250 mW witch is peak power used during the transmission of a time slot. Average power is 10 mW, resulting in long battery usage before recharge. For each voice connection two time slots are used for two-way transmission. In the other 22 time slots the portable station scans and evaluates other channels to hand over to a better channel when available.

     PHS is the Japanese-developed standard operating in the 1.9 GHz band. PHS was envisioned as an efficient low-cost cordless and portable phone system. The Research and Development Center for Radio Systems (RCR), currently known as the Association of Radio Industries and Businesses (ARIB), approved the RCR STD-28 standard in 1993. The first commercial service was provided in mid-1995 in Japan. Since then in many countries mainly in Asia PHS has been deployed.

     Time distribution is performed by adopting TDMA/TDD, with each carrier time division multiplexed into 4 duplex time slots operating in TDD mode with 5 ms for a total of 8 time slots. The transmission rate is 384 kbps, and modulation is pai/4-QPSK(Quadrature Phase Shift Keying). It is almost double more efficient than DECT. Speech coding is 32 kbps ADPCM, and channel assignment is dynamic. The maximum transmission power of the portable station is 80mw which is more safer to medical equipment and human body than DECT. The average power is 10mW same as DECT. The average power of base station is 10-500mW which means PHS can offer a wide selection of output power depending on the environment.

     PHS has greater tolerance to time dispersion than DECT, therefore PHS can provide better speech quality and faster traveling speed. The control carriers are fixed in PHS system different from DECT. It contributes to make the technology less complex, more cost efficient handsets and lower power consumption.


Refer to comparison table for details.