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What is Interleaving

  If the voice signal is modulated and transmitted directly after channel coding, due to the condition changes in mobile communication channel, a deep of the fading will influence a successive string of bits and cause high bit error rate. If the bits of a successive string are interfered or lost, the other end of … Read more

Frequency Hopping

When the voice signal is transmitted after being processed and modulated, the frequency hopping technique will be used too, i.e. the transmission carrier varies constantly at different timeslots (of course, the variation should comply with the frequency planning principles). The frequency hopping spread spectrum (FHSS) is a method for quickly switching the transmission of radio … Read more

Burst in GSM

The LogicalĀ  Channel is used in time multiplex in a physical channel, which is categorized according to the types of messages transmitted in the physical channel. Different logical channels are used in transmission of different types of information between BS and MS, such as the signaling or traffic data. In GSM system, five different types … Read more

Downlink Logical Channel in GSM

In 2G GSM Technology in forward direction Downlink (GSM BTS to GSM Mobile). There are mainly five Downlink Logical Channel in GSM. Frequency correction channel (FCCH) Synchronous channel (SCH) Broadcast control channel (BCCH) Paging channel (PCH) Access granted channel (AGCH) Frequency correction channel (FCCH) First start with FCCH which full form is frequency correction channel … Read more

Definition of Logical Channel in GSM

The physical channel is the medium over which the information is carried. The logical channel consists of the information carried over the physical channels. A Physical Channel (a TS, defined by a fixed position (0-7) on a given TDMA frame) may be used to broadcast messages containing different kinds of information: traffic messages for speech … Read more

What is Frame and Channel in GSM

The major basic concept concerned with the radio path transmission of the GSM system is the burst sequence (simplified as Burst). It is a string of transmission units including more than 100 modulation bits. The burst sequence has a restricted duration and seizes a restricted radio frequency spectrum. They can be described as output from … Read more

DTX: Discontinuous Transmission

Actually, during the communication process, the mobile subscriber talks only 40% of the time and there is not much useful information transmitted during rest of the time. If all the information is transmitted to the network, it will not only be a waste of the system resources but also add more interference to the system. … Read more

What is Channel Coding

To check and correct errors during the transmission, redundancy data and the information calculated from the source data are added to the stream so as to increase the bit rate. For the voice, the length of these codes is 456 bits every 20ms. The bit rate of code stream output from the voice coder is … Read more

What is Speech Coding

The coding mode is called Regular Pulse Excited-Long Term Prediction (RPE-LTP). It works as follow: 8KHZ of sampling is performed first, then divided into frames with 20ms; every frame has 4 sub-frames; the duration of every sub-frame is 5ms; and the pure bit rate is 13kbit/s. The voice compression coding technique is widely used in … Read more