The architecture of the CDMA mobile sys tem (CMS) is developed based on three func tion groups service resource, service control, and service management. Compiled by AIGETOA Chennai (smeltitherabpigs.cf) E1- E1-E2 CM TECHNICAL Overview of CDMA 1X & EVDO For internal circulation of BSNL only. Lecture CDMA Network and System Architecture. CDMA Network and System Architecture. There is increasing demand for data traffic over mobile radio .
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students to understand the concept of CDMA technology. Contents .. In  it was claimed that the probability density function (pdf) of the received power Wireless ATM-Based Multicode CDMA Transport Architecture. Items 1 - 12 sides: in Europe, frequency-hopping GSM architecture became almost network implementations, GSM and CDMA, have advanced to keep pace. Cdma network and technology overview. transports that use service oriented architecture, a secure environment for business process integration.
The frequency of the transmitted signal is then made to change according to the code. Thus, it can be intercepted only by a receiver whose frequency is programmed with the same code.
Advantages Efficient utilization of fixed frequency spectrum. Flexible allocation of resources Multipath fading may be substantially reduced due to large signal bandwidth. No limit on a number of users. Impossible to decipher the code sent and better signal quality.
CDMA (Code-Division Multiple Access)
No sense of hand-off when changing cells. Reverse channels follow Dynamic power control. Use of Rate control enables reverse link load adjustment.
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Center for Environmental Research and Technology
Enter the email address you signed up with and we'll email you a reset link. Need an account? Click here to sign up. In other words, unlike synchronous CDMA, the signals of other users will appear as noise to the signal of interest and interfere slightly with the desired signal in proportion to number of users.
All forms of CDMA use spread-spectrum process gain to allow receivers to partially discriminate against unwanted signals. Signals encoded with the specified PN sequence code are received, while signals with different codes or the same code but a different timing offset appear as wideband noise reduced by the process gain.
This is not true for asynchronous CDMA; rejection of unwanted signals is only partial. If any or all of the unwanted signals are much stronger than the desired signal, they will overwhelm it. This leads to a general requirement in any asynchronous CDMA system to approximately match the various signal power levels as seen at the receiver. In CDMA cellular, the base station uses a fast closed-loop power-control scheme to tightly control each mobile's transmit power.
TDMA systems must carefully synchronize the transmission times of all the users to ensure that they are received in the correct time slot and do not cause interference. Since this cannot be perfectly controlled in a mobile environment, each time slot must have a guard time, which reduces the probability that users will interfere, but decreases the spectral efficiency. Similarly, FDMA systems must use a guard band between adjacent channels, due to the unpredictable Doppler shift of the signal spectrum because of user mobility.
The guard bands will reduce the probability that adjacent channels will interfere, but decrease the utilization of the spectrum. Flexible allocation of resources[ edit ] Asynchronous CDMA offers a key advantage in the flexible allocation of resources i.
There are a fixed number of orthogonal codes, time slots or frequency bands that can be allocated for CDM, TDMA, and FDMA systems, which remain underutilized due to the bursty nature of telephony and packetized data transmissions. There is no strict limit to the number of users that can be supported in an asynchronous CDMA system, only a practical limit governed by the desired bit error probability since the SIR signal-to-interference ratio varies inversely with the number of users.
In a bursty traffic environment like mobile telephony, the advantage afforded by asynchronous CDMA is that the performance bit error rate is allowed to fluctuate randomly, with an average value determined by the number of users times the percentage of utilization. Suppose there are 2N users that only talk half of the time, then 2N users can be accommodated with the same average bit error probability as N users that talk all of the time.
The key difference here is that the bit error probability for N users talking all of the time is constant, whereas it is a random quantity with the same mean for 2N users talking half of the time. In other words, asynchronous CDMA is ideally suited to a mobile network where large numbers of transmitters each generate a relatively small amount of traffic at irregular intervals.
For instance, if there are N time slots in a TDMA system and 2N users that talk half of the time, then half of the time there will be more than N users needing to use more than N time slots.
Furthermore, it would require significant overhead to continually allocate and deallocate the orthogonal-code, time-slot or frequency-channel resources.Used for forward power control. By using our site, you consent to our Cookies Policy. This tutorial provides a basic overview of CDMA in a user-friendly way.
Used for reverse power control. Moreover, since the optical beam power is constant, the system has immunity against the self- and cross-phase modulations.
There is no strict limit to the number of users that can be supported in an asynchronous CDMA system, only a practical limit governed by the desired bit error probability since the SIR signal-to-interference ratio varies inversely with the number of users. Above all, the polarization-based scheme is more promising for very-long-haul high-speed transmissions over the OCDMA networks.
Need an account? The frequency of the transmitted signal is then made to change according to the code.
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