CDMA2000 1X ev-do Technical Features

Although the CDMA2000 1X has been deployed and operated by many wireless carriers to provide 153.6Kbps of data transmission links, it does not fully meet the requirements of high-speed access to the computer Internet. As a result, the industry has developed a CDMA2000 1X ev-do solution. In this article, we will comprehensively introduce the main technical features of 1X ev-do.

Features a

Forward Link Time Division multiplexing

The 1X ev-do takes full advantage of the asymmetry of data communication service and the low requirement of real time, and the forward link design of the last division Multiplexing (TDM) CDMA channel. For a forward link, at a given moment, a user will get the full power of the 1X ev-do carrier. In addition, whether it is Transmission control information or transmission business information, 1X ev-do carrier is always launched in full power.

Feature Two

Rate control

In the 1X ev-do network, the transmitting power of the forward link is invariable, that is, there is no power control mechanism. However, it adopts the rate control mechanism, and the rate changes with the quality of the forward RF link. The base station does not determine the rate of the forward link, but the mobile terminal requests the best data rate according to the measured c/i value. (Computer science)

Features three

Adaptive Modulation Coding Technology

According to the transmission quality of the forward RF link, the mobile terminal can request 9 kinds of data rate, the lowest is 38.4Kbps, the highest is 2457.6Kbps. The high speed data can be transmitted on the 1.25MHZ carrier, which is due to the use of High-order modulation and demodulation and the combination of error-correcting coding technology.

Features four

The scheduler maximizes the efficiency of RF resources

There is a scheduler in the base station that determines which user to use the next time slot. For 1xev-do, when the mobile terminal is in a fading state, the scheduler of the base station does not assign the transmission time or allocate the transmission time less. The scheduler allocates a time slot to a user based on the principle that the rate of the mobile terminal request is higher than its average throughput. This is the 1X ev-do multiuser diversity gain, which increases the capacity of the network.

Features five

Reverse Link Data Rate control

In the 1X ev-do system, there is no direct control over the data rate used by the reverse link mobile terminal, and the data rate information is carried in the packet transmitted by the mobile terminal.

The base station broadcasts the reverse link occupancy bit (RAB) to the mobile terminal to indicate to the mobile terminal whether the reverse link is full. If the reverse link is full, the RAB is "busy". At this point, the mobile terminal will reduce the data rate or retention rate of the reverse link transmission according to the random number of the basic test. If the random number is higher than the threshold of a particular data rate, the data rate is reduced, so the higher the data rate, the greater the likelihood that the rate will decrease.

Features six

The establishment of r-p conversation

In 1X ev-do Network, the route does not need international Mobile user identifier and mobile identification number (imsi/min), so 1X ev-do access terminal does not need to allocate imsi/min in advance. Additional solutions are required for R-P sessions to switch between the RNC and the PDSN. In order to successfully transmit conversations between the RNC/BSC (PDSN Internal, RNC) of the same pdsn, the IMSI of the mobile terminals should be the same.

Since the mobile terminal is not IMSI, when the RNC begins a session between the mobile terminal and the PDSN, it assigns a IMSI to the mobile terminal. In the standard of 1X ev-do, a new interface A12 is introduced. It is the interface between the RNC and the AN-AAA server. AN-AAA has two functions: First, completes the authentication to the mobile terminal; Secondly, in its authentication acceptance message, a IMSI value is returned to the RNC, which is used to establish the R-P session between the RNC and the PDSN.

If the AN-AAA server is not deployed in the 1X ev-do network, the RNC must assign IMSI to the mobile terminal in other proprietary ways, but it must be guaranteed that IMSI is unique across the network. When there is no AN-AAA server, the r-p session switch between the 1X ev-do RNC and the CDMA2000 1X BSc cannot be completed, and the mobile terminal can only rely on mobile IP to keep its IP address unchanged across the edge of the network. Deploying AN-AAA facilitates fast switching and improves the performance of mobile terminals as they pass through the network edge.