The speech coding algorithm produces a speech block of 260 bits every 20 ms (i.e. bit rate 13 kbit/s). In the decoder, these speech blocks are decoded and converted to 13 bit uniformly coded speech samples. The 260 bits of the speech block are classified into two groups. The 78 Class II bits are considered of less importance and are unprotected. The 182 Class I bits are split into 50 Class Ia bits and 132 Class Ib bits.
Class Ia bits are first protected by 3 parity bits for error detection. Class Ib bits are then added together with 4 tail bits before applying the convolutional code with rate and constraint length K=5. The resulting 378 bits are then added to the 78 unprotected Class II bits resulting in a complete coded speech frame of 456 bits.
GSM Band 890 to 915= 25 MHz One GSM Channel BW= 200 KHz Total GSM channels=25MHz/200KHz=125
The purpose of channel coding is to maintain the frequency components in the data stream inside the bandwidth determined by the TX loop filter and RX filter.
Source Coding : this is done to reduce the size of the information (data compression) being transmitted and conserve the available bandwidth. This process reduces redundancy. e.g. zipping files, video coding (H.264, AVS-China, Dirac) etc. Channel Coding : this is done to reduce errors during transmission of data along the channel from the source to the destination. This process adds to the redundancy of data. e.g. Turbo codes, convolutional codes etc.
Color coding is used to identify the channel.
270.83 kbps
Any time-slot on any GSM radio channel assigned to GPRS usage is defined as a Packet. Data CHannel(PDCH).
actually the channel coding is used for the security of transmission of any digital data. and it also determines the appropriate channel for the tranmission of your message on internet
link acess protocol for the D channel is used in the radio link between bts and ms
For coding
GSM 900 operates at a frequency of 900 MHz, providing better coverage in rural areas due to its longer wavelength. GSM 1800 operates at a frequency of 1800 MHz, offering higher capacity and faster data speeds in urban areas. The choice between GSM 900 and GSM 1800 depends on the population density and geographic area where the service will be provided.
In antenna hopping the transmit antenna is changed during the interleaving period resulting in an increased channel diversity which can be converted into a performance gain through the channel coding.
Simply because of the band-width required to transmit and receive calls. If the channel spacing was narrower - they'd need to reduce the band-width - which would reduce the amount of data they could transmit.