he immense potential of a conventional telephone cannot be exploited to its maximum due to the limitation imposed by the connecting wires. But this restriction has been removed with the advent of the cellular radio. Frequency Scarcity Problem If we use a dedicated RF loop for every subscriber, we need larger bandwidth to serve even a limited number of subs in a single city. Example A single RF loop requires 50 kHz B/W; then for one lakh subscribers, we need 1,00,000 x 50 kHz = 5 GHz. To overcome this B/W problem, subscribers have to share the RF channels on the need basis, instead of dedicated RF loops. This can be achieved by using multiple access methods FDMA, TDMA, or CDMA. Even then the number of RF channels required to serve the subscribers works out to be impracticable. Example Consider a subs density of 30Sq.Km., Grade of service as 1%, Traffic offered per mobile sub as 30m E. Then a number of RF channels required are − Radius(km) Area in Sq.km Subs RF Channels...

i. The design process of selecting and allocating channel groups for all cellular base stations within a system is called as frequency reuse or frequency planning. ii. Cellular radio systems rely on an intelligent allocation and reuse of channels throughout a coverage region. Each cellular base station is allocated a group of radio channels to be used with the small geographic area called a cell. Base stations in adjacent cells are assigned channel group which contains completely different channels than neighboring cells. iii. By limiting the coverage area to boundaries of a cell, same group of channels may be used to cover different cells that are separated from each other by distances large enough to keep interference levels within tolerance limits. iv. If each cell is allotted K sets of channels and if S channels are divided among N cells in unique and disjoint groups which have the same number of channels, then a total number of available channels can be S=KN. If the c...

This article introduces a basic acoustic echo canceller based on the Least Mean Squares (LMS) algorithm. Acoustic echo cancellers are necessary for many modern communications products.  I’m sure you’ve come across a time when you could hear your voice while speaking on the phone, correct? Well, that's an example of an acoustic echo. Acoustic echoes are a common problem that arise from audio signals bouncing off nearby objects and coupling into the microphone when the mic should only be picking up your voice or when directly coupling from a speaker microphone pair (like your phone). Without cancelling these effects, the communication system is pretty annoying to use. fig. 1 Here, the speech signal from a loudspeaker is acoustically coupled into the microphone of a speaker phone or hands-free cell phone, which is heard at the remote signal source as a return echo. The echo is suppressed by an echo canceller at the echo source by the system modeled in the fig...