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
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
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
Eb/No corresponds to energy per bit over interference plus noise density for a given target FER (typical FER target is 1%). In digital communications, it is customary to designate one-sided noise density with No. In CDMA, interference is dominated by the noise generated due to other users in the system. Here No, is refers to … Read more
Time diversity is a technique common to most digital transmission systems. The Rake Receiver is used to find and demodulate multipath signals that are time delayed from the main signal. Rake Receiver to Find and Demodulate Multipath Signals. Data is Interleaved : Spreads Adjacent Data in time to Improve Error Correction Efficiency Convolutional Encoding : … Read more
This graphically demonstrates why interleaving data improves error correction performance of data transmission systems. In the top Image, data is sequentially read out of a buffer than goes by rows. No interleaving is employed. The data is read and transmitted in numerical order. During transmission, data blocks 5 through 8 are corrupted by some interference. … Read more
CDMA extends the idea of diversity reception with the concept of soft handoff. In the slide, a mobile CDMA phone has established a call with base station one. As the mobile moves away from base station one and approaches base station two, a device in the phone known as the searcher identifies base station one … Read more
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
Voice data at 9600 bps or 14400 bps (full rate) is first passed through a convolutional encoder, which doubles the data rate for the 9600 bps case or increases it by 1.33 times for the 14400 bps case. It is then interleaved, a process that has no effect on the rate, but does introduce time … Read more
Pilot Channel Physical Layer The Pilot channel is essentially the short codes operating on their assigned PN offset. This is accomplished by selecting Walsh code 0 which is 64 zeroes (remember, the first code in any Walsh code set is always composed of all zeroes) as the Walsh code modulation data. In addition, the channel … Read more