Method and system for mobile station positioning in cellular communication networks

DETAILED DESCRIPTION OF THE INVENTION In IS-95 CDMA cellular network, each base station BS is synchronized to CDMA system time, which is derived from a precise time reference supplied by GPS satellites.
All base stations in CDMA network use the same frequency channel, or carrier.
Spreading codes are used to separate all signals in order to assure smooth channelization of both access and traffic communication channels, provide a level of privacy and preventing simple signal despreading.
Active BS transmits pilot signal to MS on the downlink using the same Pseudo-Noise (PN) sequence; however, each pilot is offset in time from the others, allowing the subscriber to differentiate the signals.
Each pilot PN sequence repeats every 26.
67 ms (at chip rate 1.
2288 Mchips/sec).
Each BS pilot is transmitted with offset of 64×n-chips (52.
08 μs), from other sequences.
Every subscriber communicating with the BS uses the same spreading code and offset (except for propagation delays as will be described later) so that the long code is used to identify both access and traffic channels.
A subscriber unit's (MS) time reference is offset from CDMA system time by the propagation time delays between base station BS and the mobile subscriber's phone MS.
These propagation delays create time and phase shifts in the system both in BS-transmitter and MS-receiver oscillators.
The Cellular Network Operator-Initiated Functions The Mobile Switching Center MSC is the heart of the wireless infrastructure network.
Every circuit from a mobile handset MS is served by BS, which then homes into MSC via the Base Station Controller BSC.
The MSC routes the calls to the PSTN, another MSC, an Internet Service Provider (ISP) or a private network such as Location Service LS, for connection to the appropriate destination.
To ensure service communications such as LS via traffic management, the wireless network uses BSC controllers to segment the network and control congestion.
The result is that MSCs route their circuits to BSCs, which in turn are responsible for connectivity and routing of calls for 50 to 100 wireless base stations BSs