Define the following terms and state their usage.

• Near-far effect
• Orthogonal code and its usage in mobile communication  
• FCC
• RVC
• TMSI

Near-far effect: The near-far problem is a condition in which a receiver captures a strong signal and thereby makes it impossible for the receiver to detect a weaker signal. The near-far problem is particularly difficult in CDMA systems, where transmitters share transmission frequencies and transmission time. Suppose a situation in which a receiver and two transmitters, one close to the receiver, the other far away are placed. If both transmitters transmit simultaneously at equal powers, then the receiver will receive more power from the nearer transmitter. Since one transmission's signal is the other's noise, the signal-to-noise ratio (SNR) for the farther transmitter is much lower. This makes the farther transmitter more difficult to understand. If the nearer transmitter transmits a signal that is orders of magnitude higher than the farther transmitter then the SNR for the farther transmitter may be below detectability and the farther transmitter may just as well not transmit. This effectively jams the communication channel. In short, the near-far problem is one of detecting or filtering out a weaker signal amongst stronger signals. For eg: if any two person want to communicate in an empty room then they can speak quietly, but to speak in a crowd both of them have to speak louder.

Orthogonal code and its usage in mobile communication:  CDMA is a multiplexing access method in which multiple users are allocated different codes to access the same channel. CDMA codes allow unique identification of signals from different sources and transmit these signals through the same time, space and frequency slots without interference. Thus it is necessary that CDMA codes should not correlate with each other. Two codes used for coding are referred as orthogonal when there is no effect of interference between two sets of signals on the received output. Orthogonal code do not show the strong autocorrelation property and thus requires the synchronization between the transmitter and the receiver. it gives zero cross-correlation. Walsh code is an example of orthogonal code.

FCC: Federal communication commission (FCC) is a government agency in the US that regulates the usage and licensing of frequency bands. Every country has its own regulatory agencies like FCC. In 1968, in the US the FCC reconsidered it as position on the cellular network concept. FCC agreed to allocate a larger frequency band for more number of mobile phones provided the technology to build a better mobile service be demonstrated. the FCC is responsible for rating personal computers and other equipment as either Class A or Class B. The ratings indicate how much radiation a personal computer emits. Almost all personal computers satisfy Class A requirements, which means they are suitable for office use. Class B machines, which are suitable for use anywhere (including the home), must pass more stringent tests. Class B indicates that the machine's radio frequency (RF) emissions are so low that they do not interfere with other devices such as radios and TVs. FCC in US is charged with regulating interstate and international communication by radio, television, wire satellite and cable.

RVC: RVC are the reverse voice channels. cell phones and base stations transmit or communicate with each other on dedicated paired frequencies called channels. Base stations use one frequency of that channel and mobiles use the other. Certain channels carry only cellular system data. We call these control channels. This control channel is usually the first channel in each cell. It's responsible for call setup. Voice channels, by comparison, are those paired frequencies which handle a call's traffic, be it voice or data, as well as signalling information about the call itself. A cell or sector's first channel is always the control or setup channel for each cell. The voice channel then handles the conversation as well as further signalling between the mobile and the base station. we call a base station's transmitting frequency the forward path. The cell phone's transmitting frequency, by comparison, is called the reverse path.  RVC are the voice channels that transmit frequency from mobile to base station.

TMSI: The Temporary Mobile Subscriber Identity (TMSI) is the identity that is most commonly sent between the mobile and the network. TMSI is randomly assigned by the VLR to every mobile in the area, the moment it is switched on. The number is local to a location area, and so it has to be updated each time the mobile moves to a new geographical area.

• The network can also change the TMSI of the mobile at any time. And it normally does so, in order to avoid the subscriber from being identified, and tracked by eavesdroppers on the radio interface. This makes it difficult to trace which mobile is which, except briefly, when the mobile is just switched on, or when the data in the mobile becomes invalid for one reason or another. At that point, the global "international mobile subscriber identity" (IMSI) must be sent to the network. The IMSI is sent as rarely as possible, to avoid it being identified and tracked.

• A key use of the TMSI is in paging a mobile. "Paging" is the one-to-one communication between the mobile and the base station. The most important use of broadcast information is to set up channels for "paging". Every cellular system has a broadcast mechanism to distribute such information to a plurality of mobiles.

• Size of TMSI is 4 octets with full hex digits and can't be all 1 because the SIM uses 4 octets with all bits equal to 1 to indicate that no valid TMSI is available.