Applications
a. Wireless Local Loop for Fixed and Mobile telephony
One of the most important advantages of CDMA is that it supports not only mobile telephony, but also fixed telephony services using the same infrastructure.
Therefore, WLL helps increase, cost effectively, the number of subscribers on a PSTN without staying behind in modern telecommunications technology such as cellular based telephony.
Operators can therefore manage two different kinds of subscribers existing on the same network:
i. Wireless fixed subscribers.
ii. Mobile subscribers.
i. PSTN direct connect network architecture
The wireless fixed network is formed of the following elements:
· PSTN-to radio interconnect: Provides concentration interface between the WLL System Controller (WiSC) and the landline network.
· WiSC: Provides radio channel control functions and serves as a performing monitoring concentration point for all cell sites.
· Base Transceiver Station (BTS): Is the cell site equipment that performs the transmission and reception functions of the radio signals.
· Fixed Wireless Terminal (FWT): Is a fixed radio telephone unit that interfaces to standard telephone set acting as a transmitter and receiver between the telephone and the BTS.
· Operation and Maintenance Center (OMC): Keeps track of the daily performance and statistics for network management and planning.
ii. Mobile Telephone Switching Office/Mobile Switching Center (MTSO/MSC) network architecture
This network provides the possibility for cellular operators to add fixed subscribers to an already existing cellular mobile network or to offer both fixed and mobile services on that same network.
It performs the billing and database functions and provides a trunked interface to the PSTN.
This network is formed of the following elements:
· MTSO/MSC: Which performs the billing and database functions and provides a trunked interface to the PSTN.
· OMC.
· Cell site equipment including the Base Transceiver Station (BTS).
· Base Station Controller (BSC): Processes calls to and from wireless end users and passes subscriber location and billing information to the local switch.
· FWT.
b. Advantages of WLL using CDMA
i. Operator benefits
· Free up the wireline infrastructure for long holding-time applications such as internet applications.
· Increase the number of subscribers due to higher capacity system and hence revenue increases.
· Decrease capital investment in excssive cell sites due to large cell site radius.
· Operate a fixed and mobile telephony system using the same infrastructure.
· Reduce cost of maintenance due to the fact that less cables are needed.
· No frequency planning needed.
ii. Subscriber benefits
· Good voice quality (as good as wireline voice quality).
· Prolonged battery life-time due to the use of complex vocoders.
· High degree of security due to the use of the PN sequence.
· Increased talk time for portables.
· Faster service especially for internet and multimedia.
c. Other applications
· SS was widely used, for the past fifty years, in military communications since it provided the advantage of transmitting signals without being detected by unintended receivers.
· Police radars can employ SS technology to avoid detection by radar detectors employed by drivers.
· Increase the number of subscribers on a CDMA based network in commercial communications .
