Re:<<Xiaolingtong's technical flaws>>
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PHS/PAS Technology
Bo Zi, 05/2003
PAS (Personal Access System) is a dominant quasi cellphone service in China by UTStarcom and ZTE. PAS is essentially derived from PHS technology (Personal Handyphone System) invented in Japan in the early 1990s for densely populated urban areas with restricted mobility.
While they are both digital technology, PAS technology is very different from GSM in network configuration. For example, most PAS base stations have transmit power of 500 mW or less, much lower than GSM base stations (3000 mW). Because of low power level, PAS needs base stations with high density which, from technological and operational point of view, is not very efficient.
On every PAS handset, there is a data port which is used to write (burn) PSID called IMEI, a 15-digit code to allow the handset to be used in the public network and identify if the handset is unauthorized product. IMEI is similar to the SIM card in every GSM handset. The difference is a GSM handset can swap SIM cards, but IMEI is permanently burned into a PAS handset. While it is difficult to share or "steal" someone's handset, new IMEI code can be written on a "bare" PAS handset.
Since PAS handsets are readily available (including smuggled products), many retail shops allow customers to bring a bare handset to open a new account (only for a new IMEI). Because of this, it is possible to use the same IMEI code in two or more PAS handsets (some models do not work with duplicate code).
Switch-Over
A typical PAS base station can handle seven voice channels, which means some calls may experience blockage during busy hours. In other cases, even though calls are through, users cannot move in order to occupy the same voice channel. Once the user's position changes, his PAS handset will immediately begin switch-over from current base station to the nearest one. If all adjacent base stations are busy, the handset will keep searching until an available channel is found. The drawback is the ongoing call may drop some experience some delay if glitches occur during the switch-over. Handsets with seamless switch-over technology should render faster search time and minimal delay in communication.
Signal Strength
With UTStarcom's 702U handset, users can test signal strength in the current position. Specifically, with handset turned off, press the "#" key and "on/off" key, the LCD should display local signal strength and the version of software installed. Other PAS handsets may use different keystrokes to test signal strength. In general, the higher the strength, the better quality of the voice and less chance the call will be dropped. This method can be used to determine if a call should be made or wait until signal becomes better.
Even though PAS is still inferior to GSM and CDMA in voice quality and call success ratio, its low pricing (per-minute charge and one-way billing) has attracted many new customers who do not need roaming and significant mobility. After all, entry by PAS has created healthy competition with cellphone service, from which customers benefit in cost and service.
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