Personal Handy-phone System
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The Personal Handy-phone System (PHS), also marketed as the Personal Access System (PAS) and commercially branded as Xiaolingtong (小灵通) in China, is a mobile network system operating in the 1880–1930 MHz frequency band, used mainly in Japan, China, Taiwan and some other Asian countries.
Contents |
[edit] Outline
[edit] Technology
PHS is, essentially, a cordless telephone like DECT, with the capability to handover from one cell to another. PHS cells are small, with transmission power of base station a maximum of 500 mW and range typically measures in tens or at most hundreds of meters (some can range up to about 2 kilometres in line-of-sight), as opposed to the multi-kilometer ranges of GSM. This makes PHS suitable for dense urban areas, but impractical for rural areas, and the small cell size also makes it difficult if not impossible to make calls from rapidly moving vehicles.
PHS uses TDMA/TDD for its radio channel access method, and 32 kbit/s ADPCM for its voice codec. Modern PHS phone can also support many value-added services such as high speed wireless data / Internet connection (64 kbit/s and higher), WWW access, e-mailing, text messaging and even color image transfer.
PHS technology is also a popular option for providing a wireless local loop, where it is used to bridge the "last mile" gap between the POTS network and the subscriber's home. Actually, it was developed under the concept that it makes up a wireless front-end of an ISDN network. So a base station of PHS has a compatibility with, and is often connected directly to ISDN telephone exchange equipment (A.K.A. a digital switch).
As for its low-price base station, micro-cellular system and "Dynamic Cell Assign" system, PHS can afford more number-of-digits frequency use efficiency with lower cost (throughput per area basis), compared with typical 3G cellular telephone systems. It makes possible the flat-rate wireless service such as AIR-EDGE all over Japan.
The speed of AIR-EDGE data connection is accelerated by combining lines, each of which basically is 32 kbit/s. AIR-EDGE 1x or first version introduced in 2001 provide only 32 kbit/s service. In 2002, 128 kbit/s service (AIR-EDGE 4x) started. In 2005, 256 kbit/s (AIR-EDGE 8x) service started.
In 2006, the speed of each line was also up-graded to 1.6 times with the introduction of "W-OAM" technology. The speed of AIR-EDGE 8x is up to 402 kbit/s with the latest "W-OAM" capable instrument.
In April 2007, "W-OAM typeG" was introduced allowing data speeds of 512 kbit/s for AIR-EDGE 8x users. Furthermore, the "W-OAM typeG" AIR-EDGE 8x service is planned to be upgraded to a maximum throughput of 800 kbit/s, when the upgrading for access points (mainly switching lines from ISDN to fibre optic) in its system are completed. And it may exceeds the speeds of popular W-CDMA 3G service like NTT DoCoMo's FOMA in Japan.
[edit] Implementation
Originally developed by NTT Laboratory in Japan in 1989 and far simpler to implement and deploy than competing systems like PDC or GSM, the commercial services has been started by three PHS operators (NTT-Personal, DDI-Pocket and ASTEL) in Japan in 1995. However, the service has been pejoratively dubbed as the "poor man's cellular", due to its limited range and roaming abilities. Market share in Japan has been declining and NTT DoCoMo, which has absorbed NTT Personal, and ASTEL is going to terminate the PHS service. Some of other countries have already terminated offering PHS services and migrated to GSM.
But PHS has seen a resurgence in markets like China, Taiwan, Vietnam, Bangladesh, Nigeria, Mali, Tanzania and Honduras where its low deployment costs (estimated to be as low as 20% of a GSM network) make it attractive to operators. Wireless local loop (WLL) systems based on PHS technology are in use in some of the above-mentioned countries. In recent years, WILLCOM, formerly DDI-Pocket, is introducing flat-rate wireless network and flat-rate calling in Japan, which has reversed the local fate of PHS up to an extent. In China, there was seen an explosive expansion of subscribers until around 2005, but it has been calming down in 2006. In Chile, Telefónica del Sur on March 2006 launched a PHS based telephony service in some cities of the southern part of the country. In Brazil, Suporte Tecnologia has a PHS based telephony service in Betim, state of Minas Gerais, and Transit Telecom has announced a rollout of a PHS network in 2007.
China Telecom operates a PAS system in China, even though technically it was not regarded as allowed to provide mobile services, because of some particularities of the Chinese governance. China Netcom, the other fixed-line operator in China, also provides Xiaolingtong service. The system has been a runaway hit, with over 90 million subscribers signed up as of 2007. The largest vendors of the system are UTStarcom and ZTE.
A PHS global roaming service is available between Japan (WILLCOM), Taiwan and Thailand.
[edit] International development
- PHS's subscribers and major operators
[edit] References
[edit] External links
- PHS MoU Group
- Article on Xiaolingtong
- PHS in Taiwan
